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Modelling hydrological processes influenced by soil, rock and vegetation in a small karst basin of southwest China
Abstract
Hydrological processes in karst basins are controlled by permeable multimedia, consisting of soil pores, epikarst fractures, and underground conduits. Distributed modelling of hydrological dynamics in such heterogeneous hydrogeological conditions is a challenging task. Basing on the multilayer structure of the distributed hydrology-soil-vegetation model (DHSVM), a distributed hydrological model for a karst basin was developed by integrating mathematical routings of porous Darcy flow, fissure flow and underground channel flow. Specifically, infiltration and saturated flow movement within epikarst fractures are expressed by the ‘cubic law’ equation which is associated with fractural width, direction, and spacing. A small karst basin located in Guizhou province of southwest China was selected for this hydrological simulation. The model parameters were determined on the basis of field measurement and calibrated against the observed soil moisture contents, vegetation interception, surface runoff, and underground flow discharges from the basin outlet. The results show that due to high permeability of the epikarst zone, a significant amount of surface runoff is only generated after heavy rainfall events during the wet season. Rock exposure and the epikarst zone significantly increase flood discharge and decrease evapotranspiration (ET) loss; the peak flood discharge is directly proportional to the size of the aperture. Distribution of soil moisture content (SMC) primarily depends on topographic variations just after a heavy rainfall, while SMC and actual ET are dominated by land cover after a period of consecutive non-rainfall days. The new model was able to capture the sharp increase and decrease of the underground streamflow hydrograph, and as such can be used to investigate hydrological effects in such rock features and land covers. Copyright © 2011 John Wiley & Sons, Ltd.
... The porosity of epikarst ranges from 1 % to 10 %, exhibiting strong heterogeneity. In previous research, the porosity is generally set to 10 % (Xu et al., 2020;Zhang et al., 2011). The mean epikarst B d of 2.4 g⋅cm − 3 is close to that of 2.5 g⋅cm − 3 from field investigations in our study area (Wang et al., 2020b). ...
... The mean epikarst B d of 2.4 g⋅cm − 3 is close to that of 2.5 g⋅cm − 3 from field investigations in our study area (Wang et al., 2020b). Considering the plant rooting depth and the water that plant can utilize from underlying rock fissures, the epikarst thickness is set to 2 m (Cai et al., 2022;Xu et al., 2020;Zhang et al., 2011). ...
... In this study, the third layer of the VIC model was defined as an epikarst zone for karst areas, whereas all three layers were soil for the non-karst areas. Generally, D epi varies in space ranging from 2 to 20 m or more Wang et al., 2020a;Zhang et al., 2011). However, the upper epikarst where the fissure network was strongly developed, was usually modeled. ...
Evapotranspiration (ET) is a vital factor in terrestrial water and energy cycles. Exploring the spatiotemporal variations in ET and transpiration (T) can improve our understanding of the role of vegetation restoration in the context of climate change. Karst ecosystems are particularly sensitive and vulnerable to environmental change. In this study, we investigated the spatiotemporal changes of ET, T, and the transpiration fraction (T/ET) in the Longjiang River Basin (LRB) of southwest China from 1987 to 2018 using the variable infiltration capacity (VIC) model. In karst areas, the original third soil layer in the VIC model was modified to an epikarst zone and a reservoir module was integrated with the model. Model validation and evaluation showed that the modified VIC model performed well in fitting the observations of runoff and ET. During the 32-year study period, ET, T, and T/ET increased by 2.30 mm·yr⁻¹, 2.21 mm·yr⁻¹, and 0.0006, respectively, with the significant increase concentrated in areas with increased forestland. High positive correlations between NDVI and ET, T, and T/ET were observed in areas where forestland and grassland increased. Temperature and wind speed were positively correlated with ET, T, and T/ET in areas with low altitude and abundant precipitation, where large areas of cropland are present. There was a positive correlation between precipitation and ET in karst areas, whereas the negative correlation between precipitation and T was mainly occurred in non-karst areas. The scenario analysis based on different land use data revealed that ET and T/ET exhibited significant differences in karst areas, but not in non-karst areas, indicating that karst areas were more affected by ecological restoration. Moreover, T did not show a significant increase after vegetation restoration, suggesting that increased ET was mainly caused by evaporation. This study provides insights into the effects of vegetation restoration and climate change on ET, T, and T/ET under different geological conditions and can help implement appropriate afforestation strategies in different geological settings.
... More specifically in this study, we sought to address two questions: (a) How (Figure 1). Chenqi has characteristic cockpit karst terrain, with contrasting landscape units of elevated hillslopes and low-lying depressions (Zhang et al., 2011(Zhang et al., , 2013Chen et al., 2018). Chenqi is drained by a single underground conduit, which links to three sinkholes located in the depression area. ...
... On hillslopes, the Quaternary soil depth is less than 30 cm. The epikarst decreases with altitude on the hillslopes with the thickness less than 5 m (Zhang et al., 2011). By contrast, the soil and epikarst in depression are much thicker. ...
... An additional passive store is used for the assumption of partial mixing of isotopes in the hillslope, which does not affect the dynamics of water storage. This assumption follows previous measurements that the rock fracture/conduit density decreases exponentially in the vertical direction in the hillslope (Zhang et al., 2011). ...
Hydrological and biogeochemical processes in karst environments are strongly controlled by heterogenous fracture‐conduit networks. Quantifying the spatio‐temporal variability of water transit time and young water fractions in such heterogeneous hydrogeological systems is fundamental to linking discharge and water quality dynamics in the karst critical zone. We used a tracer‐aided conceptual hydrological model to track the fate of each hour of rain input individually. Using this approach, the variability of transit time distributions and young water fraction were estimated in the main landscape units in a karst catchment of Chenqi in Guizhou Province, Southwest China. The model predicted that the mean young water (i.e < ~2 months old) fraction of ground conduit flow is 0.31. Marked seasonal variabilities in water storage and hydrological connectivity between the conduit network and fractured matrix, as well as between hillslopes and topographic depression, drive the dynamics of young water fraction and travel time distributions in each landscape unit. Especially, the strong hydrological connectivity between the land surface and underground conduits caused by the direct infiltration through large fractures and sinkholes, leads the drastic increasement in young water fraction of runoff after heavy rain. Even though the contribution of young water to runoff is greater, the strong mixing and drainage of small fractures accelerate the old water release during high flows during the wet season. It is notable that the young water may sometimes be the most contaminated component contributing to the underground conduit network in karst catchments, because of the direct transfer of contaminants from the ground surface with rain water via large fractures and sinkholes.
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... Field investigations have shown a rich fractured zone (epikarst) on hillslopes which has a thickness of 7.5-12.6 m, generally becoming shallower in an upslope direction (Zhang, Chen, Ghadouani, & Shi, 2011). In the depression, soils are thick (>2 m deep). ...
... In the depression, soils are thick (>2 m deep). Dominant vegetation ranges from deciduous broad-leaved forest on the upper and middle parts of the steep hillslopes to corn and rice paddy in the lower gentle foot slopes and depressions (Zhang et al., 2011). ...
... For the hillslope unit, spring discharge (S5) is generated by a perched water table above the low permeability layer of marlite Zhang et al., 2011). The discharge at S5 represents the hillslope flow from a larger upslope area and exhibits larger perennial flows (Table 1). ...
In cockpit karst landscapes, fluxes from upland areas contribute large volumes of water to low‐lying depressions and stream flow. Hydrograph hysteresis and similarity between monitoring sites is important for understanding the space‐time variability of hydrologic responses across the “hillslope‐depression‐stream” continuum. In this study, the hysteretic feature of hydrographs was assessed by characterising the loop‐like relationships between responses at upstream sites relative to subsurface discharge at the outlet of a small karst catchment. A classification of hydrograph responses based on the Multi‐Scale Smoothing Kernel (MUSS)‐derived distance classifies the hydrograph responses on the basis of similarities between hillslope and depression sites, and those at the catchment outlet. Results demonstrate that the temporal and spatial variability of hydrograph hysteresis and similarity between hillslope flow and outlet stream flow can be explained by the local heterogeneity of depression aquifer. Large depression storage deficits emerging in the highly heterogeneous aquifer produce strong hysteresis and multiple relationships of upstream hydrographs relative to the outlet subsurface discharge. In contrast, when depression storage deficits are filled during consecutive rainfall events, depression hydrographs at the high permeability sites are almost synchronous or exhibit a monotonous function with the hydrographs at the outlet. This reduced hydrograph hysteresis enhances preferential flow paths in fractured rocks and conduits that can accelerate the hillslope flow to the outlet. Therefore, classification of hydrograph similarities between any upstream sites and the catchment outlet can help to identify the dominant hydrological functions in the heterogeneous karst catchment.
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... The world's karst regions cover~20% (or 2.22 × 10 7 km 2 ) of the ice-free continental area on Earth and supply food and water to~25% of the world's population. However, water shortages in karst regions have become a common problem (Ford & Williams, 2007;Hartmann, Goldscheider, et al., 2014;Zhang et al., 2011), even in humid karst regions where precipitation is abundant, for example, in southwestern China (Nie et al., 2011). The karstic hydrological properties, including topography, discontinuous soil distribution, and interlaced matrices (micropores, small fissures, and fractures) and conduits (large fractures from the karstification), result in rapid infiltration and percolation of precipitation to the underground systems in karst regions (Jeannin & Grasso, 1997;Peng & Wang, 2012;Wang et al., 2004). ...
... Distributed models define the study region as two-or three-dimensional grids and simulate the hydrological processes within each grid, and the lumped models (also called the reservoir/bucket models) conceptualize the study region as only one grid and simulate the physical processes based on the relationships between storage and discharge (Hartmann, Goldscheider, et al., 2014;Martínez-Santos & Andreu, 2010). The distributed model is applicable in karst regions if detailed information about the surface and the underground structure can be obtained (Martínez-Santos & Andreu, 2010;Zhang et al., 2011). However, the complex environment makes it difficult to collect observational data of the underground structures in karst regions. ...
... The undisturbed soil samples were collected using a cutting ring (100 cm 3 ) at the soil surface. The epikarst porosity was set as a uniform value (0.1) based on previous research (Perrin et al., 2003;Zhang et al., 2011). In addition, field investigation of seven line transects on hillslopes in the Chenqi catchment were conducted to examine the distribution of soil depth in May 2017 ( Figure 2). ...
Understanding hydrological processes is essential for management of water resources and for promoting catchment sustainability. In karst regions, landscapes are spatially heterogeneous and include discontinuous soil distribution, and complex networks of matrices and conduits in hillslopes and depressions, which result in variation in hydrological processes. However, most previous studies have mainly focused on the effects of the distribution of soil depth and the fast‐slow flow in the matrices and conduits on hydrological processes and ignored the different hydrological processes related to hillslopes and depressions. This study improved the VarKarst model by adding randomly distributed soil and epikarst depths (RSE), fast‐slow flow (FS), and hillslopes and depressions (HD). The improved model was calibrated and validated in six large catchments (1,213–5,454 km²) and one small catchment (1.25 km²). Results showed that the schemes by combining FS and HD (Scenario FS + HD) and combining RSE, FS, and HD (Scenario RSE + FS + HD) improved model performance (calibrated and validated KGE ranged from 0.54 to 0.89 and AIC ranged from −336.49 to 669.77) compared models that included other schemes (original VarKarst, Scenario RSE, Scenario FS, Scenario HD, and Scenario RSE + FS), especially when reproducing discharge of peaks and recessions. These results suggest that there is a need to separate the hillslopes and depressions when modeling karstic hydrological processes.
... The study catchment of Chenqi, with an area of 1.25 km 2 , is located in the Puding Karst Ecohydrological Observation Station in Guizhou Province of south-western China (Fig. 1). It is a typical cockpit karst landscape, with surrounding conical hills separated by star-shaped valleys (Zhang et al., 2011;Chen et al., 2018). The catchment, which is drained by a single underground channel/conduit, can be divided into two units: depression areas with low-elevation (< 1340 m) and steeper hillslopes with high elevation ranging from 1340 to 1500 m. ...
... where i is the δ 2 H signature of the storage components (‰); the subscript of p-d represents rainfall infiltration in depression unit. Hence, partial mixing was assumed for the hillslope (e.g. the upper active storage V h mixing with the lower passive storage V pas in Fig. 3 since the upper rock fractures/conduits reduce exponentially along the hillslope profile (Zhang et al., 2011) according to (7) for the lower passive storage in hillslope. ...
... The model structure dictates that the main variability in the runoff response to precipitation is driven by the storage dynamics, depending on hydrological connec- tivity between the hillslope (V h ) and slow (V s ) and fast (V f ) flow reservoirs (Fig. 3). The modelled storage results show that slow flow reservoir was the largest store in the catchment (> 100 mm with a mean of 245 mm), consistent with the wide distribution of small fractures and matrix pores in the karst critical zone (Zhang et al., 2011(Zhang et al., , 2017. The fast flow reservoir had the smallest storage (the mean value was only 0.2 mm) because the underground river/conduit volume represents only a very small proportion of the porosity of the entire aquifer. ...
We developed a new tracer-aided hydrological model that disaggregates cockpit karst terrain into the two dominant landscape units of hillslopes and depressions (with fast and slow flow systems). The new model was calibrated by using high temporal resolution hydrometric and isotope data in the outflow of Chenqi catchment in Guizhou Province of south-western China. The model could track hourly water and isotope fluxes through each landscape unit and estimate the associated storage and water age dynamics. From the model results we inferred that the fast flow reservoir in the depression had the smallest water storage and the slow flow reservoir the largest, with the hillslope intermediate. The estimated mean ages of water draining the hillslope unit, and the fast and slow flow reservoirs during the study period, were 137, 326 and 493 days, respectively. Distinct seasonal variability in hydroclimatic conditions and associated water storage dynamics (captured by the model) were the main drivers of non-stationary hydrological connectivity between the hillslope and depression. During the dry season, slow flow in the depression contributes the largest proportion (78.4 %) of flow to the underground stream draining the catchment, resulting in weak hydrological connectivity between the hillslope and depression. During the wet period, with the resulting rapid increase in storage, the hillslope unit contributes the largest proportion (57.5 %) of flow to the underground stream due to the strong hydrological connectivity between the hillslope and depression. Meanwhile, the tracer-aided model can be used to identify the sources of uncertainty in the model results. Our analysis showed that the model uncertainty of the hydrological variables in the different units relies on their connectivity with the outlet when the calibration target uses only the outlet information. The model uncertainty was much lower for the “newer” water from the fast flow system in the depression and flow from the hillslope unit during the wet season and higher for “older” water from the slow flow system in the depression. This suggests that to constrain model parameters further, increased high-resolution hydrometric and tracer data on the internal dynamics of systems (e.g. groundwater responses during low flow periods) could be used in calibration.
... For instance, a total of 1247 wells were drilled in Guizhou during the drought period of 2007-2011 to provide potable water of 0.21 km 3 /yr (1.2 mm/yr), enough for nearly 1.78-million people to drink (Luo et al., 2012). An improved distributed hydrology-soil-vegetation model was developed and applied to a small karst basin in Guizhou by integrating the routings of porous Darcy flow, fissure flow and underground channel flow (Zhang et al., 2011), providing valuable information for understanding groundwater storage dynamics and its interaction with surface water storage in the karst areas of Southwest China. However, these previous studies were mainly focused on the small scales. ...
... ~412,900 km 2 ) in contrast to 28% of the karst regions in the western Yunnan province (i.e. the low karstic region, LKR,~390,000 km 2 ) (Chinese Academy of Geological Sciences (CAGS), 1979; Wang et al., 2007). HKR has higher permeability than LKR owing to its more developed epi-karst zones (Legrand and Stringfield, 1973;Zhang et al., 2011;Han, 2015). According to Chen et al. (2012), the hydraulic conductivity of the high-permeability epikarst aquifer is of the order 10 -3 m/s, while that in the low-permeability aquifer is about 10 -5 m/s. ...
... Second, as discussed in Section 4.3 the karstic aquifers in HKR respond more rapidly to precipitation owing to its higher permeability than that in LKR. Consequently, the earlier and heavier precipitation combined with the more efficient infiltration lead to a significant recovery of GWS after the extreme drought (Legrand and Stringfield, 1973;Zhang et al., 2011). However, the larger GWS G-RACE recovery in HKR was not observed in 2012. ...
The 2003–2013 monthly groundwater storage (GWS) anomalies in the highly karstic region (HKR) and low karstic region (LKR) in the Southwest China are estimated from the Gravity Recovery and Climate Experiment (GRACE) terrestrial water storage (TWS) data by using the ancillary data of surface water storage (SWS) and soil moisture storage (SMS) from the WaterGAP model simulations. The leakage errors in the estimated GWS anomalies are corrected through using the iterative forward modelling approach. The estimated GWS anomalies compare well with in situ groundwater-level observations with the correlation coefficient r = 0.71 and the root-mean-square-error (RMSE) = 42 mm. For both HKR and LKR, ∼60% of temporal variability of TWS is contributed by GWS variability, while SMS contributes to 18% (HKR) and 28% (LKR), and SWS contributes to 22% (HKR) and 14% (LKR) of the TWS variability. Due to the higher permeability of the epi-karst zones and their better connection with the subsurface aquifers, GWS anomalies in HKR show larger correlations with SWS (r = 0.73, RMSE = 51 mm) and SMS (r = 0.68, RMSE = 47 mm) and a shorter lag to precipitation than that in LKR (SWS: r = 0.56, RMSE = 50 mm, and SMS: r = 0.48, RMSE = 49 mm). During the extreme drought in 2009, GWS loss in HKR (LKR) was 74.3 mm/yr (42.7 mm/yr), accounting for 66% (62%) of total TWS loss. The severe GWS loss was mainly due to larger discharges through the well-developed subsurface drainage system rather than human depletion, since groundwater resources are still under-exploited in Southwest China (∼4 km³/yr, 12% of the potentially exploitable amounts). A quicker recovery of GWS from 2009 drought can be observed in HKR than LKR due to the larger and earlier (approximately one month) precipitation and infiltration, and quicker response of groundwater to precipitation in HKR.
... On hillslopes, field investigations have shown a rich fracture zone (epikarst) that has a thickness of 7.5-12.6 m (Zhang et al., 2011). Quaternary soils consist of mostly sand (56 %-80 %), fine sand (20 %-40 %), and calcareous soil and silt (1 %-10 %). ...
... For example, the calibrated k s ranges from 0.13 to 0.24 in hillslope and depression units, suggesting that about 76 %-87 % of the net precipitation recharges the fast-flow reservoir through large fractures and sinkholes in terms of I f /R = (1 − α)P /R+(1 − k s )α. This high percentage is consistent with the numerical results of Zhang et al. (2011), which were independently derived using a distributed model that considered the role of sinkholes in facilitating fast-flow recharge into the aquifer in the studied catchment. Charlier et al. (2012) found that about 60 % of recharge water entered the conduit network (fast channelized flow paths) in a small karst system in the French Jura Mountains. ...
Conceptualizing passive storage in coupled flow–isotope models can improve the simulation of mixing and attenuation effects on tracer transport in many natural systems, such as catchments or rivers. However, the effectiveness of incorporating different conceptualizations of passive storage in models of complex karst flow systems remains poorly understood. In this study, we developed a coupled flow–isotope model that conceptualizes both “fast-flow” and “slow-flow” processes in heterogeneous aquifers as well as hydrological connections between steep hillslopes and low-lying depression units in cockpit karst landscapes. The model tested contrasting configurations of passive storage in the fast- and slow-flow systems and was optimized using a multi-objective optimization algorithm based on detailed observational data of discharge and isotope dynamics in the Chenqi Catchment in southwestern China. Results show that one to three passive-storage zones distributed in hillslope fast-/slow-flow reservoirs and/or depression slow-flow reservoirs provided optimal model structures in the study catchment. This optimization can effectively improve the simulation accuracy for outlet discharge and isotope signatures. Additionally, the optimal tracer-aided model reflects dominant flow paths and connections of the hillslope and depression units, yielding reasonable source area apportionment for dominant hydrological components (e.g., more than ∼ 80 % of fast flow in the total discharge) and solute transport in the steep hillslope unit of karst flow systems. Our coupled flow–isotope model for karst systems provides a novel, flexible tool for more realistic catchment conceptualizations that can easily be transferred to other cockpit karst catchments.
... The bedrock is the foundation of soil formation and its properties can significantly impact the soil's ability to store water. Zhong et al. [32] found that vegetation growth and soil water content strongly related to lithologies in the karst region of southwest China; by using meta-analysis, Zhu et al. [33] showed that bedrock has a significant relationship with regolith water capacity globally, which is crucial to vegetation growth. Moreover, in the karst area, the bedrock is composed of more permeable materials, such as limestone or sandstone; so, the water can easily pass through the bedrock [34]. ...
... One plausible reason for this phenomenon is the high permeability and thin soil layer. CRR commonly exhibits a low water storage capacity [31,32]. Another possible reason is that the soil developed from carbonate rock is rich in clay, which has a low water-holding capacity because it lacks porosity. ...
Global warming is expected to enhance the severity and frequency of drought in subtropical areas; thus, understanding how vegetation growth responds to precipitation is crucial to comprehending the impact of these changes on ecosystem services, such as carbon storage. However, vegetation activity in subtropical karst regions in Southwest China is hard to explain when we merely consider the influence of climate and soil factors. In this study, we extended traditional research by combining bedrock data we aim to investigate the role of bedrock and its interaction with precipitation on plant growth in the Guizhou Province of China. We analyzed the differences in the precipitation–vegetation growth relationship in noncarbonate and carbonate rock regions, assessing the sensitivity of vegetation from two lithological types to drought. The results reveal that although there are no significant differences in climate and soil parameters between carbonate and noncarbonate regions, the normalized difference vegetation index (NDVI) in carbonate regions is more strongly related to precipitation (carbonate region: R2 = 0.67; noncarbonate region: R2 = 0.37), while the spring greenness–precipitation relationship show is more stable in the carbonate region. Our results show that the vegetation activity in the carbonate region is more vulnerable during the drought period, highlighting that the vegetation dynamic was not only regulated by climatic factors, and bedrock-caused water stress should be taken into account.
... Globally, about 15% of the non-ice continental surface is karst areas, with 16.5% of the population living in these areas (Goldscheider et al. 2020). China has one of the largest continuous karst areas (located in the southwest of China) and its karst percentage is as high as 26.5% (Zhang et al. 2011;Goldscheider et al. 2020). Karst waters, which include carbonate aquifers, provide fresh water to around 25% of the population globally (Ford & Williams 2007). ...
... The distributed and semi-distributed models discretize the karst watershed into several basic units (e.g., grids or sub-basins) and assign certain governing equations, parameters, and state variables to each basic unit according to the internal karst landform (Hartmann et al. 2014). The advantage of distributed and semi-distributed models is that they offer a thorough insight into hydrological processes within a karst watershed while also considering temporal and spatial variability (Zhang et al. 2011;Xu et al. 2020;. However, the high dataset requirements and considerable computing expense restrict the application of distributed and semi-distributed models in practice (Fatichi et al. 2016;Simmons et al. 2020). ...
Hydrological simulation in karst areas is of great importance and challenge. It is a practical way to enhance the performance of existing hydrological models in karst areas by coupling karst modules that represent hydrological processes in these areas. The near-surface critical zone structure affects runoff generation in karst areas significantly and its complex hydrological processes could be simplified with threshold behaviors. This study proposed a three-thresholds-based karst runoff generation module (3T-KRGM), which used three reservoirs to represent water storage in the soil zone, soil–epikarst interface, and epikarst zone. The 3T-KRGM is coupled with the Xinanjiang (XAJ) model to extend the applicability of the model to karst areas. Both the improved XAJ model and the original XAJ model were used in the Shibantang watershed, which is a typical karst watershed located in southwest China. The results indicate that the performance of daily discharge simulations was obviously improved by introducing the 3T-KRGM. In addition, both the parameter sensitivity analysis and baseflow simulation demonstrate that the 3T-KRGM is rational in structure. The 3T-KRGM could also be easily coupled into other hydrological models, thus benefiting the hydrological simulation in karst areas.
HIGHLIGHTS
We proposed a three-thresholds-based karst runoff generation module to improve model performance in karst areas.;
The theoretical basis of the module is a modification of a three-thresholds mechanism revealed by hillslope experiments.;
We coupled the module into the Xinanjiang model to extend its applicability in karst areas.;
The advantages of the module for hydrological simulation were verified from various aspects.;
... Increased and accelerated infiltration is usually favoured during storm events. As a result, there may be differences in storage capacities of overlying layers, flow rates, variations in flow directions, and thus in the contribution of different parts of the aquifer to a given spring (Zhang et al., 2011;Ravbar, 2013). An increase in groundwater level can cause steeper gradients, reduce the thickness of Fig. 7. Schematic presentation of the triple porosity of karst aquifers (Ravbar and Pipan, 2022). ...
... The effects of land use change on evapotranspiration processes (Moore and Heilman, 2011;Ferlan et al., 2016;Reichert et al., 2017), soil processes (Guan and Fan, 2020) and recharge dynamics (Zhang et al., 2011;Van Beynen and Bialkowska-Jelinska, 2012;Yu et al., 2015;Berthelin et al., 2020) are examined. By comparing several case studies, the complex interaction of factors affecting transpiration was illustrated Fig. 9. Schematic representation of the characteristics of the karst aquifer and evaluation of the basic hydrological processes through the karst aquifer. ...
Large-scale forest disturbances (LSFD) are an essential component of forest ecosystem dynamics. The effects of rapid loss of forest cover and other changes in forest ecosystems are inextricably linked to hydrologic processes such as evapotranspiration, soil and recharge processes. Among all hydrogeological systems, karst aquifers are important because of their exceptionally rich and unique biodiversity, biomass, and groundwater resources. At the same time, they are characterized by specific hydrological processes that make them highly vulnerable to environmental changes. Therefore, this study paid special attention to the effects of LSFD on karst hydrology. Using the PRISMA checklist, a thorough literature review of studies published between 2001 and 2020 was compiled into a comprehensive matrix dataset. In addition, an initial assessment of the global and regional distribution of forests on carbonate rocks was made based on publicly available geodatabases of forests and karst aquifers. The compiled information provides the first global overview of hydrological processes affected by LSFD, and identifies important knowledge gaps and future research challenges. The matrix dataset contained 117 full-text articles with a total of 160 case studies. Most publications were from 2011 to 2017, with more than half of the studies at the plot level and more than one-third at the catchment level. Studies on the effects of fires and pest and diseases infestations predominated. However, no articles were found on the effects of ice storms on hydrology in general or on the effects of pest and disease infestations on hydrology in karst areas. Of the 45.6 M km² of forested land worldwide, 6.3 M km² or 13.9% of all forests are underlain by carbonate rocks. Carbonate rocks cover about 15% of the land surface, which means that 31.3% of the world's karst aquifers are covered by forest. 29% of all case studies were conducted in karst areas, which is a high proportion compared to the proportion of forests in karst areas. However, these studies are unevenly distributed geographically. Most studies were conducted at the plot level, and only 21% of studies focused on natural LSFD, so forest management and land use change studies predominated. Although studies on the effects of LSFD on evapotranspiration processes between vegetation, air and soil are fairly well represented, infiltration and recharge processes in karst areas remain poorly understood and knowledge is lacking, particularly on groundwater flow and related hydrological processes. Regional studies and impacts on groundwater resources are also insufficient. The results indicate an urgent need for an integrated holistic interdisciplinary approach and a comprehensive understanding of the individual influencing factors, which would allow more accurate modelling of hydrological processes in forested karst aquifers.
... Few distributed hydrological models have been modified to be utilised for hydrological modelling of surface streamflow. An improved DHSVM-distributed hydrological model was therefore developed and applied to a small karst catchment (1.5 km 2 ) in China by modifying the flow routing estimation methods for porous Darcy flow, fissure flow, and underground channel flow (Zhang et al., 2011), and the findings provided new insights into the dynamic interaction between stored groundwater and surface water in karst terrains. Li et al. (2021) modified the runoff generation algorithm and the underground river confluence module in the Liuxihe model and reported the development of an improved Karst-Liuxihe (IKL) model that could help simulate the annual runoff and flood events for a small karstic watershed (13.1 km 2 ); the methods used to discretise the karst system have been established and included in the MODFLOW-CFP model. ...
... During this flood event, the soil, matrix, and underground conduit system in the HKB are almost saturated and the hydraulic connection type of the stream was gaining-connected (Bailly Comte et al., 2009). Under this condition, karst terrains can promote streamflow amplification and the reaction to precipitation is accelerated (Knöll et al., 2020), resulting in the observation of a steep rise limb in the hydrographs of the streamflow in karst-dominated basins (see Fig. 14(a)), similar behaviour in the karst region of southwest China was reported by Chen et al. (2008) and Zhang et al. (2011). ...
Study region
Hekou karst basin, southwestern China.
Study focus
The duality and complexity of hydrological behavior of karst systems pose challenges in precipitation-streamflow modelling, reliable hydrological models with high temporal resolution are warranted for predicting floods in humid flood-prone karst-dominated basins. This study proposes a grid-based distributed karst Xin’anjiang hydrological model (DK-XAJ), the model structure of each grid was developed using the conceptual Xin’anjiang model. Water exchange among each grid and the spatial heterogeneities of land use types and the karstification in each grid were considered. Information on two new linear reservoirs was added to represent the rapid-conduit and slow-matrix underground flow to improve the karst dual-porosities, the range of the underground runoff partitioning parameter was estimated from the observed flood recessions.
New hydrological insights
The DK-XAJ model demonstrated good successive hourly streamflow modelling performance with mean values of 0.84, 0.83, 0.28, and 0.88 for NSE, KGE, RRE, and R², and results during validation of one nested interior grid without recalibration was also good. The results indicate that the DK-XAJ model can help obtain detailed results for successive streamflow processes, the peaks of floods under different magnitudes and the marked increase and recession of the flash floods can be accurately reproduced and depicted. The DK-XAJ model can therefore be considered a new tool for the prediction of sub-daily precipitation-streamflow and flood events in karst-dominated basins.
... Field investigations have shown a rich fracture zone (epikarst) on hillslopes ( Fig. 1d) which has a thickness of 7.5~12.6 m, generally becoming shallower in an upslope direction (Zhang et al., 2011). Deciduous broadleaved forests and shrubs are mostly grown on the upper and middle parts of hillslopes, and corn is grown at the low 160 of the gentle hillslopes . ...
... CC BY 4.0 License. micropore, fracture and conduit media with permeability ranging across several orders of magnitude and the conductivity of the rock fractures decreasing with depth ( Fig. 1d) (Zhang et al., 2011). In these circumstances, the spatial variations in advection speed 615 are a major mechanism underlying macro-dispersion at catchment scale (Kirchner et al., 2001). ...
Representing passive storage in coupled flow-isotope models can facilitate simulation of mixing and retardation effects on tracer transport in many natural systems, such as catchments or rivers. However, the effectiveness of incorporating passive storages in models of complex karst flow systems remains poorly understood. In this study, we developed a coupled flow-isotope model that conceptually represents both “fast” and “slow” flow processes in heterogeneous aquifers to represent hydrological connections between hillslopes and low-lying depression units in cockpit karst landscapes. As this model originally included a varying number of passive storages at different positions of the flow system (e.g. fast/slow flow reservoirs combined with different hillslope/depression units), the model structure and relevant parameters were optimized using a multi-objective optimization algorithm. This was used to match detailed observational data of hydrological processes and isotope concentration in the Chenqi catchment in southwest China. Results show that the optimal structure for a coupled flow-isotope model incorporated only two passive storages in fast flow and slow flow paths of the hillslope unit. Using fewer or greater numbers of passive stores in the model could lead to under- or over-mixing of isotope signatures. This optimized model structure could effectively improve simulation accuracies for outlet discharge and isotope signatures, with > 0.65 of the modified Kling-Gupta efficiency. Additionally, the optimal tracer-aided model yields reasonable parameter values and estimations of hydrological components (e.g. more than 80 % of fast flow in the total discharge). Furthermore, results imply that the solute transport is primarily controlled by advection and hydrodynamic dispersion in steep hillslope unit, which is a remarkable phenomenon in the karst flow system. The study resulted in new insights, more realistic catchment conceptualizations and improved model formulation.
... The Chenqi catchment with surface area of 1.25 km 2 , is a typical cockpit karst landscape located at the Puding Karst Ecohydrological Observation Station in Guizhou Province, Southwest China ( Fig. 1). This catchment is surrounded by conical hills separated by star-shaped valleys (Zhang et al., 2011;Chen et al., 2018). The elevation ranges from 1,340 to 1,500 m above sea level (Fig. 1a). ...
... The time lags of NO 3 -N concentration peak to discharge peak for some rainfall events are only several hours (Fig. S2), even in the dry season. From previous studies in this catchment, the soil thickness is ~ 2 m, and the hydrological conductivity of the soil is about 10 -5 m/s for the lower cultivated areas (Zhang et al., 2011). According to this, from first approximations, it will take more than ~ 56 h for rain water and NO 3 -N to enter into underground conduit through soil matrix. ...
Although numerous studies on nitrate transport and transformation in karst catchments have been reported, many challenges in understanding nitrate fluxes remain due to the unique architecture of karst critical zones and complex hydrological processes. Water age is an important descriptor of hydrological function providing insight to into flow paths and water sources at the catchment scale. This offers a potential opportunity to better understand the spatio-temporal variations in nitrate dynamics in karst catchments. We linked the nitrate dynamics of underground conduit flow to water age extracted from a robust tracer-aided model for a karst catchment in southwestern China. The results show that nitrate dynamics in underground conduit flow are controlled by the coupling of nitrate supply and of flow paths in the karst catchment. High contributions of drainage from small fractures water leads to low nitrate concentrations in underground conduit flow during the dry season. This reveals that the small fractures may be another important “hot spot” for denitrification leading to nitrate removal in the karst critical zone. The switching between transport limited and supply limited conditions cause the marked variations in nitrate concentration of underground conduit flow during wet season. Although rapid infiltration via large fractures and sinkholes have strong dilution effects on nitrate in underground conduit flow at beginning of rainfall, more nitrate was transported out of the catchment with drainage during rainfall events due to the mobilization of soil nitrate by rainfall. Meanwhile, the capacity to transport nitrate out of catchment can be potentially activated when the ‘old’ water is displaced by rainfall under high wetness condition.
... Since obtaining sufficient information about conduit geometries and roughness is difficult, these scholars have improved the run-off generation and routing modules to describe the hydrological characteristics of karst aquifer systems, without considering detailed knowledge about the spatial distribution of the fracture network. Based on the multilayer structure of the distributed hydrology-soilvegetation model, Zhang, Chen, Ghadouani, and Shi (2011) developed a model for a karst basin by integrating mathematical routings of different kinds of flow, using 'cubic law' which is associated with fractural width, direction, and spacing to express the flow movement within epikarst fractures (Zhang et al., 2011). ...
... Since obtaining sufficient information about conduit geometries and roughness is difficult, these scholars have improved the run-off generation and routing modules to describe the hydrological characteristics of karst aquifer systems, without considering detailed knowledge about the spatial distribution of the fracture network. Based on the multilayer structure of the distributed hydrology-soilvegetation model, Zhang, Chen, Ghadouani, and Shi (2011) developed a model for a karst basin by integrating mathematical routings of different kinds of flow, using 'cubic law' which is associated with fractural width, direction, and spacing to express the flow movement within epikarst fractures (Zhang et al., 2011). ...
Hydrological processes in karst aquifer systems are controlled by highly permeable media, so studying flood processes in karst‐dominated regions is very important; however, it is still a challenge to model the hydrological dynamics in such strongly heterogeneous conditions. This study proposed a distributed Xinanjiang karst hydrological model (DXAJKHM) for simulating the flood processes in karst catchments, which was based on topographical information extracted from a digital elevation model. Considering the dual‐porosity in karst aquifer systems, the DXAJKHM was coupled with a traditional Xinanjiang conceptual hydrological model and utilized two karst reservoirs that simulated both the rapid underground run‐off and the slow underground run‐off in each grid cell. The uncertainty in the model parameters is estimated by the generalized likelihood uncertainty estimation method, and the parameters are determined by the shuffled complex evolution approach optimization algorithm. The simulation results demonstrated that the proposed DXAJKHM satisfactorily simulated the flood processes, and the model has better simulation effects for floods with larger flood peaks. In order to analyse the flood recession error, one run‐off signature index was employed to improve the model runs. This study thus provides a new approach to simulating and predicting floods in karst areas.
... E1, E2, E3, E4, E5: Events 1,2, 3, 4, and 5 respectively. magnitude higher concentration, flux, and total export than Event 2. A threshold of 80 mm for activation of overland flow has been suggested in this karst area (Zhang et al., 2011), consistent with the magnitude of Event 4. Thus, activation of additional hydrological pathways, such as overland flow, could further contribute to the delivery of nearby FIO sources to receiving waters during high intensity rainfall (Lloyd et al., 2016). Antecedent catchment conditions can influence E. coli transfer to receiving waters by increasing or decreasing the activation of overland and subsurface flow mechanisms (Hathaway et al., 2010). ...
... Event 1) and after numerous events had occurred (e.g. Event 4), when soil moisture is likely to have increased (Zhang et al., 2011). Low soil moisture due to dry antecedent conditions has been found to result in higher surface runoff generation and suspended sediment transport due to infiltrationexcess overland flow (McDowell and Sharpley, 2002;Puntenney et al., 2016). ...
Karst aquifers have distinctive hydrology and supply 25% of the world's population with drinking water, making them a critical geological setting for understanding and managing microbial water pollution. Rainfall causes elevated concentrations and loading of faecal microorganisms, e.g. E. coli, in catchment surface and groundwater systems, increasing the risk of human exposure to faecally-contaminated water. However, effective management of microbial water quality in complex karst catchments is constrained by limited understanding of E. coli - discharge responses to rainfall. We analysed how rainfall events of varying magnitude (2.4-100 mm) control E. coli-discharge dynamics at increasing spatial scales in a mixed land-use karst catchment in southwest China. During the wet season, hourly water sampling was undertaken throughout five storm events to characterise in high detail E. coli emergence with resulting flow across multiple sites of varying catchment area, stream order, and land-use. E. coli concentration was found to increase by 1-3 orders of magnitude following rainfall events. Maximum E. coli concentration and speed of E. coli recession were influenced by rainfall (amount, intensity), timing of agricultural activities, and position in the hydrological system. For high intensity events ∼90% of the cumulative E. coli export occurred within 48 h. E. coli concentration increased with increasing discharge at all sites. E. coli concentration at low discharge was higher in the headwaters than at the catchment outlet, while the rate of increase in E. coli concentration with increasing discharge appears to follow the opposite trend, being higher at the catchment outlet than the headwaters. This was attributed to the decreasing flow path gradient and increasing degree of development of the fissure network, but further event monitoring at varying catchment scales is required to confirm this relationship. The results provide novel insight into how rainfall characteristics combine with land-use and catchment hydrology to control E. coli export in karst landscapes.
... More seriously, the difficult-to-form karst soils are highly erodible, and severe erosion can occur in karst areas even for soils formed by other parent rocks that are typically classified as "normal erosion" types (Peng et al., 2013). This is typical of the self-destructive nature of karst systems; however it can be attenuated by the formation of vegetation that increase the forest canopy and the humus layer, reducing the contact surface between precipitation and surface runoff and the soil, reducing rainfall velocity and infiltration, reducing total soil erosion, increasing water transpiration, and creating animal habitats (Ruiz-Jaén and Aide, 2005;Zhang et al., 2011;Batori et al., 2014). ...
Karst landforms are widely distributed around the world, and karst rocky desertification has occurred on a large scale in many countries and regions, causing significant adverse impacts on local natural environments and societies. The improvement and rational use of karst soil is a key aspect of rocky desertification governance. Karst soil science studies are of great value in karst regions and are essential for controlling karst rocky desertification and ecological restoration. In order to understand the research hotspots and the development directions in the field of vulnerable karst soil environment, we undertook bibliometrics citation analysis on 1913 contributions to the literature written in the range from 2001 to 2019 based on the “Web of Science” core collection citation index database. Hopefully, this work will help to set up a scientific foundation for further studies. Using CiteSpace visualization software, we analyzed the distribution of disciplinary categories, reference co-citation clusters, and keyword clusters in the literature. The results show the basic characteristics and evolution of the literature related to karst pedology. We then recognized the main intellectual bases in the domain of karst soil science. This study also revealed the research hotspots and trends in this field. Through a bibliometrics citation analysis of research on karst vulnerable soil environment, the present study provides a quantitative and objective understanding of development directions that have emerged in this field over the past 19 years, offering a reference for future research.
... Other than simulations for SU at depth 0-20 cm, predictions could not fully capture the variability found by sensor-based measurements as found by others (Zhao et al., 2023). The difficulty of obtaining accurate SM simulations is not unique to the studied catchments, as similar model skill can be found elsewhere in the literature (Thyer et al., 2004;Zhang et al., 2011). For instance, Cuartas et al. (2012) used DHSVM and found E values ranging from − 16.86 to 0.6 when validating SM predictions in the Amazon. ...
... Correlation analysis showed significant negative correlations between SBD and SWC, which is consistent with prior research [52,53]. An increase in SBD reduces the distance between soil particles, leading to a decrease in soil porosity [54]. ...
Natural soil and vegetation recovery following human disturbance is the primary means of restoring degraded ecosystems globally. However, it remains unclear how vegetation recovery in the tropical karst areas of China affects the soil physicochemical properties. Here, we investigated the impacts of natural vegetation recovery on soil physicochemical properties at different soil depths in tropical karst areas in southwestern China, using a space–time substitution method. We found that with the natural vegetation recovery, soil bulk density (SBD) decreased. Soil pH initially decreased and then increased, reaching its lowest value during the shrubland stage. There was a significant increase in other soil physicochemical factors. In the soil profiles, SBD tended to increase with depth. The pH, total potassium (TK), total phosphorus (TP), and exchangeable calcium remained relatively stable across the different soil layers. TK, TP, available phosphorus, SBD, total nitrogen, pH, exchangeable magnesium, and available potassium significantly contributed to the soil physicochemical properties. Soil physicochemical properties were predominantly directly affected by litter and biological factors, albeit indirectly influenced by topographic factors. Our study provides crucial insights into karst soils and their relationship with vegetation recovery, which are pivotal for steering vegetation restoration and soil amelioration in karst areas.
... The semi-distributed and fully-distributed models aim to discretize the entire karst-dominated basin into 2D or 3D grids and subsystems (i.e., sub-basins, hydrology response units and hydrotopes), the physical processes equations are used to solve the water movements between computational elements (i.e., grid and sub-systems; Coustau et al., 2012;Ladouche et al., 2014;Adinehvand et al., 2017;Martínez-Salvador and Conesa-García, 2020;Bittner et al., 2020;Chen et al., 2022). The fully-distributed models have the potential to provide a very detailed insight into the karst hydrological processes, and are widely used for investigating the flow dynamics of well explored karst systems with small areas (Doummar et al., 2012;Zhang et al., 2011;Chang et al., 2019;Liu et al., 2021;Al Aamery et al., 2021); however, for the largescale karst-dominated basin, the general data unavailability of characteristic hydraulic parameters and structures of underground karst systems prohibits the application of this type of model (Hartmann et al., 2014b). Semi-distributed models, the transitions to fully-distributed and lumped models, have been proved to be able to account for the spatial variabilities of underlying surface factors and hydrological variables with reduced input data requirements (Pardo-Iguzquiza et al., 2018;Jeannin et al., 2021;Ollivier et al., 2020). ...
... Black-box models consider the entire karst aquifer as a single unit, so they have been used for the simulation of karst spring discharge and chemical constituents of spring water (e.g., Dreiss, 1982;Labat et al., 2000;Pinault et al., 2001;Denić-Jukić and Jukić, 2003;Hu et al., 2008). The most demanding are the distributed or numerical models, which require excessive information and/or assumptions about the spatial characteristics of karst aquifer (e.g., Kiraly et al., 1995;Bauer et al., 2005;Birk et al., 2006;Reimann et al., 2011Reimann et al., , 2014Zhang et al, 2011;Gallegos et al., 2013;Chen and Goldscheider, 2014;Xu et al., 2015Xu et al., , 2018Borghi et al., 2016;Chang et al., 2019). However, the spatial simulation of hydraulic behavior of a karst aquifer stays a challenge due to the complexity of schematic presentation and mathematical formulation, local heterogeneity of parameter fields, complexity of initial and boundary conditions, and finally uncertainties of results (Kiraly, 1998;Liu et al., 2021). ...
... The karst area in the southwest of China is one of the largest, most concentrated, and most developed karst landforms in the world [8,9]. The karst ecological ecosystems are fragile and have been degraded with shallow soil and a wide range of exposed bedrock [10,11]. ...
Influenced by the topography, the spatial variation of soil thickness on karst slopes is very large, and accordingly the spatial variation of soil moisture is also large. Therefore, analyzing the spatial heterogeneity of soil moisture on hillslopes is important for maintaining ecosystem stability. Combining geostatistical methods and GIS technology, the spatial variability and distribution pattern of soil moisture and the influencing factors of spatial variation and surface soil moisture (0–7 cm) on a typical karst shrub–grass hillslope were analyzed. The results showed that the mean soil moisture and coefficient of variation (CV) ranged between 25.7–42.6% and 10.3–20.9%, respectively, showing a moderate variation. The soil moisture presented a moderate or strong spatial autocorrelation in the sampling scale. The occurrence of rainfall events can exert a great influence on reducing the spatial heterogeneity of soil moisture. The spatial distribution pattern of soil moisture showed roughly plaque or stripe distribution. When soil moisture was much lower, the patch space fragmentation of soil moisture was higher. The soil moisture was higher in the low and middle parts of the plot. We can conclude that factors such as topography, vegetation, and weather conditions will exert a significant effect on soil moisture spatial variability. Areas with lower slope and higher vegetation coverage were more conducive to the retention of soil moisture.
... Spatially, from Figure 1c, this low-value area also has a high concentration of karst landforms. Previous studies [37][38][39][40] have reported that karst landforms are susceptible to drought and shallow soils with sparse vegetation due to precipitation infiltration and low carbon sequestration capacity as compared to non-karst landforms [41]; thus, the ecosystem WUE is also low and fluctuates in a "W" shape with longitude. ...
Water use efficiency (WUE) has garnered considerable attention at global and regional levels. However, spatio-temporal variations of WUE and related influencing factors in the complex karst landforms of southwest China require further elucidation. Herein, the ratio of gross primary productivity (GPP) to evapotranspiration (ET) obtained through the PML-V2 product was used to characterize ecosystem WUE, the spatio-temporal variations to ecosystem WUE, and responses to temperature, precipitation, and the enhanced vegetation index (EVI) in southwest China. The results showed that: (1) The ecosystem WUE in southwest China decreased with increasing latitude and altitude. Spatially, the ecosystem WUE fluctuates in a “W” pattern with increasing longitude because of the karst landforms’ distribution patterns. (2) The non-significant trend in increased ecosystem WUE during 2003–2017 may be associated with significant increases in the ET offsetting part of the GPP contribution to ecosystem WUE. Spatial distribution of changes in WUE is similar to GPP owing to the dominant role of GPP in changes to ecosystem WUE. (3) The multi-year average ecosystem WUE was lower in karst than in non-karst landforms; however, vegetation restoration projects have contributed in significantly increasing variation rate of ecosystem WUE in karst than that in non-karst landforms. (4) Temperature, precipitation, and EVI were generally positively correlated with ecosystem WUE and were important factors for the increase in ecosystem WUE. EVI characterized vegetation restoration indicators showed that the ecological engineering construction in the study area was effective and was the dominant factor of ecosystem WUE change in 59.59% of the study area. The results of this study are important for further understanding carbon and water cycling processes in karst regions.
... However, the lumped models cannot cater to the spatial variability of hydrogeological factors including karst landform, topography, land use/cover, evapotranspiration and precipitation, which are especially critical for karst catchments (Dreiss, 1982;Labat et al., 2000;Morrissey et al., 2020). In contrast, semi-distributed and distributed models provide more insights into karst hydrological processes, especially distributed models, which can be better used to evaluate the impacts of karst landform, land use/cover and climatic change on water resources (Bittner et al., 2018;Dubois et al., 2020;Ladouche et al., 2014;Malard et al., 2016;Ollivier et al., 2020;Sarrazin et al., 2018;Zhang et al., 2011). At present, however, these distributed models can only be applied to well-explored karst catchments of commonly less than 100 km 2 in area, because of the extensive input data requirements regarding the geometry and structure of karst aquifers (Hartmann et al., 2013a;Chang et al., 2019). ...
Runoff movement in karst catchments is of great complexity. Although many models have been developed for the rainfall-runoff simulation in karst catchments, the distributed ones, capable of taking into consideration the impacts of the spatial variability of hydrogeological factors, are few and can only be applied to well-explored karst catchments of commonly less than 100 km² in area. In this study, the previously-published DEM (Digital Elevation Model) -based distributed rainfall-runoff model (DDRM) was applied and modified for distributed rainfall-runoff simulation in a large-scale karst catchment by assuming the main parameters of runoff generation and routing for each grid cell to be a function of karst landform and topographic index (i.e., the mathematical expression of topographic features) to represent the hydrological effects of epikarst and underground river system. For model structure investigation, three versions of the modified DDRMs, i.e., the DDRM considering only karst landform (DDRM_K), the DDRM considering only topographic index (DDRM_T), and the DDRM considering both karst landform and topographic index (DDRM_KT), were set up and compared with the original DDRM (i.e., the original DDRM, termed as DDRM_O). All four DDRMs were calibrated with a multi-objective optimization framework that uses the Kling-Gupta Efficiency of streamflow (KGEQ) and the autocorrelation function of streamflow (KGEACF) as objective functions to improve parameter identifiability. The investigation was conducted in the Xijiang Basin, which is a typical karst catchment in Southwest China with an area of 309300 km². The results show that, compared with DDRM_O, DDRM_T barely benefits the rainfall-runoff simulation, while both DDRM_K and DDRM_KT noticeably enhance the simulation accuracy in terms of KGEQ. Due to the better performance in high flow and autocorrelation function of streamflow, DDRM_KT outperforms DDRM_K in general and has the potential to be successfully applied to large-scale karst catchments.
... The black-box models treat an aquifer as a black-box system and focus on establishing an overall relationship between input (infiltration) and output (discharge), completely disregarding the structure and the physical mechanisms of the aquifer (Dreiss, 1983;Mangin, 1984). The distributed models solve flow equations with temporal and spatial discretization over the whole aquifer, hence requiring detailed information on the aquifer structure and hydrological properties for producing an acceptable simulation (Zhang et al., 2011;Saller et al., 2013;Zheng et al., 2020). The lumped models provide a compromised tool for karst groundwater simulation in which linear or nonlinear reservoirs/compartments are used to represent different physical elements of the aquifer structure and groundwater circulation (Fleury et al., 2007(Fleury et al., , 2009Jukić and Denić-Jukić, 2009). ...
Tunnelling activities may significantly alter the groundwater balance in a karst aquifer, but assessment of this effect remains challenging due to the complex flow geometries and strong hydrogeological heterogeneity. In this study, based on extensive site characterization of an independent hydrogeological unit (HU) in which a deep-buried tunnel is under construction, we present a modified lumped model to evaluate the impact of tunnel construction on the discharge from the aquifer system. The lumped model consists of four interacting flow compartments and the associated water balance equations. A series of simplified models is then developed, by merging or removing some of the flow components that represent different mechanisms and relationships between recharge and discharge. The dominant hydrological processes in the HU are identified by comparing the performance of the models of different structures and by screening analysis of parameter sensitivities. It is found that the tunnel excavation captured a mean portion of 19% discharge from the aquifer system into the tunnel, which is comparable to the result predicted by 3D numerical simulations. This study evidences that as a first and simple approximation, the lumped models provide a useful tool for characterizing the dominant factors that govern the groundwater response and for evaluating the groundwater budget changes induced by anthropogenic activities such as tunnelling and underground mining in karst regions.
... Compared with the other region, karst catchment is more vulnerable to drought because of natural and artificial factors. The particular feature of carbonate rocks makes the soils in the karst region very thin (30-50 cm in thickness) (Zhang et al. 2011), which cannot hold enough water. Artificial factors, such as deforestation and agriculture, accelerate soil erosion and loss of water and cause ecological environment deterioration. ...
Karst depressions play an important role in runoff generation and concentration processes of karst catchments. Storm water tends to be stored in karst depressions firstly before routing to the catchment outlet. However, simulating methods of runoff processes considering the impact of karst depressions are rarely reported. To fill this concept and technology gap, we propose a conceptual hydrological model considering the role of karst depressions in this study. A three serial tank model coupled with two soil tanks is established at each grid in each subcatchment, to simulate surface runoff, interflow, groundwater runoff, and soil moisture dynamics. During the process of flow concentration, surface runoff from each grid is reduced by karst depressions at its lower reach. The surface runoff loss is controlled by the area ratio of karst depression and corresponding subcatchment. River channel routing is carried out based on the Muskingum approach. The conceptual hydrological model is further calibrated and validated over the Hamajing catchment, a small karst catchment in Hubei Province, China. Results show that the proposed model can generally reproduce the runoff generation and concentration processes well. Nash-Sutcliffe efficiency (NSE) coefficient is 0.85 during the calibration period and 0.78 in the validation period. Root mean squared errors are 6.24 m3/s and 5.35 m3/s during calibration and validation periods respectively. Sensitivity analysis indicates that the parameters related to the first tank are most sensitive to the simulation results, whereas the change of parameters related to the second and third tanks cannot significantly influence the simulation results. Additionally, the area ratio of karst depression has great influence on the runoff processes in karst catchment. This proposed conceptual model provides a simple approach to simulate the hydrological processes in karst region.
... In many regions of the world, karst groundwater also plays a vital role in agricultural and economic development (Olarinoye et al., 2020). Karst groundwater flow constitutes an important component of the hydrological cycle (Zhang et al., 2010), and supports the ecosystem and the karst critical zone. However, karst groundwater systems become more and more vulnerable due to the ever-increasing anthropogenic activities (Hao et al., 2016), such as agricultural irrigation (Han et al., 2017), tunnel construction (Vincenzi et al., 2014;Y. ...
Anthropogenic disturbance of karst groundwater systems by large-scale underground engineering activities is an important topic but is difficult to address due to the compound influence of the heterogeneity and construction progression. In this study, we adopt the coupled discrete-continuum modeling approach where both the tunnels and karst conduits are treated as discrete channels. Based on extensive site characterization, groundwater observations, and tunnel discharge data, we establish a three-dimensional coupled model for a karst aquifer where deeply-buried, long tunnels are being constructed. We perform high-resolution simulations to quantitatively evaluate the spatial and temporal characteristics of the tunnel construction impact on a karst groundwater system. The simulation results satisfactorily reproduce the tunnel discharge time-series. We show that the excavation and lining schedule is an important factor to consider when evaluating the hydrogeological impact. During tunnel construction, the groundwater drainage through the tunnels (5.3 × 10⁷ m³) accounts for a significant part of the total groundwater discharge (~11%) in the studied area. The continuous water influx to the tunnels results in widespread drawdown with an area of impact (with drawdown >5 m) covering 64.0% of the entire study area after four years of construction. The total discharge through karst conduits decreases by about 30% in response to the tunnel construction. Our simulation results predict that after completion of lining the groundwater system will slowly approach a groundwater level 5–10 m below the undisturbed level. This work demonstrates the use of coupled discrete-continuum models to study regional groundwater flow in karst aquifers affected by tunnel engineering activities and also provides a guidance for the impact assessment of other underground engineering projects in mining and transportation industries. The simulation methodology may be exploited for optimization of the construction plans to minimize hydrogeological impact and to ensure construction safety.
... Although some previous studies have shown that the soil and vegetation mantle plays an important role in the infiltration and storage of water in karst systems [37], hydrological functions of soil and vegetation layers in the hydrological cycle have been only marginally considered or even underestimated in the investigation of future hydrological processes in karst. The main reasons for this should be sought in poorly studied and understood infiltration mechanisms of soil and vegetation layers and their hydrological relationships with the overall groundwater recharge [38,39]. ...
Karst aquifers hold important water resources such as regional water budgets and freshwater supply. Due to highly dynamic hydrological processes in comparison to other less permeable systems, they are particularly susceptible to environmental changes. However, little research directly characterizes the impacts of climate and vegetation cover changes on karst water sources. In this study, we aimed to evaluate individual long-term impacts and impacts of sudden large-scale forest disturbances on changes in groundwater recharge and in spring discharge. The work is based on temporal analysis of forest cover and a comparison of trend analysis of hydro-meteorological parameters. To investigate and evaluate vegetation cover change impacts on groundwater recharge, we used a soil water balance model and compared estimated actual daily values of effective precipitation to its fictional estimation disregarding the vegetation cover change. The applied methodology enabled quantification of the impacts of climate and vegetation cover change on selected karst water sources. The study suggests that the vegetation cover can have a significant impact on the spring recharge. Large-scale disturbances that occurred in a short-term mitigated the effects expected from the trend analysis of hydro-meteorological parameters. In the long-term, in addition to climate changes, the multi-decadal natural vegetation overgrowth significantly contributed to the reduction in the spring's discharge values, especially in the warm season when water demand is higher. Therefore, the results are of key importance for developing proper water management and environmental policies.
... The majority of the previous studies in KMRSC have focused on a small basin scale with an area of several square kilometers for modelling the regional hydrological processes and its impact on water resources. The fracture distribution, pipeline structure characteristics and groundwater confluence path in the typical basin are determined by laboratory experiments and field observations in these studies, and then a model with complex structural parameters is established [17][18][19]. However, the evolution law of hydrological cycle and water resources in KMRSC remains unclear from the perspective of sustainable water resources management. ...
Distributed hydrological simulation in karst regions has always been a challenging task because of their unique hydrogeological characteristics. The karst mountain region of southwest China (KMRSC), one of the largest continuous karst areas in the world, contributes to about 54 percent of water supply in the basins. In spite of its importance, we have a poor understanding of the evolution laws of hydrological cycle and water resources in KMRSC. We developed a physically-based, distributed hydrological model, called Water and Energy transfer Processes (WEP)-karst model, for KMRSC by introducing the equivalent porous medium approach to the WEP-L model, and dividing the modelling domain into 2021 sub-watersheds. The area of sub-watersheds ranges from 55 to 920 km2, with an average value of 170 km2. The model showed a good performance in simulating the monthly discharge at 18 representative hydrological stations, with the Nash–Sutcliffe efficiency (NSE) values ranging from 0.71 to 0.94, and the relative error (RE) values from −9.8% to 8.3% during the validation period (1980–2000). Then, we employed an in-depth analysis of the temporal and spatial variation of main water cycle fluxes, including precipitation, infiltration, evapotranspiration, blue water (i.e., river runoff), and green water (i.e., vegetation transpiration) over 1956–2015. In addition, the impact of climate change on these fluxes was evaluated under the median emission scenario (RCP4.5). The results showed that: (1) annual average precipitation of KMRSC reached 1506 mm, which is 2.4 times of the national average level, and about 47% (701 mm) of it contributed to river runoff. The infiltration and evapotranspiration were 862 and 870 mm, respectively. The transpiration from plants and trees accounted for 51% of the evapotranspiration. (2) Except for the green water, other fluxes experienced a significant decrease over the past 60 years. Blue water showed the largest interannual fluctuation and the strongest sensitivity to climate change. (3) Both precipitation and infiltration concentrated from May to August, and blue water increased notably from May to June and peaked in June. Blue water and precipitation were more likely to decrease in the future over 2021–2050 due to the climate change.
... The "cubic law" is used for estimation of infiltration and percolation of the rock fractures in epikarst (P e ). The spatial distributions of the rock fracturs are stochastically generated according to field investigations of fractural characteristics, such as density, length and direction (details in Zhang et al., 2011). The ...
Transport of nitrogen (N) in karst areas is more complex than in non-karst areas due to marked heterogeneity of hydrodynamic behaviour in the karst critical zone. Here, we present a novel, distributed, coupled hydrological-biogeochemical model that can simulate water and nitrogen transport in the critical zone of karst catchments. This new model was calibrated using integrated hydrometric, water stable isotope, and nitrogen-N concentration data at the outflow of Houzhai catchment in Guizhou province of Southwest China. Hydrological dynamics appears to control N load from the study catchment. Combining flow discharge and water stable isotopes significantly constrained model parameterisation and mitigate the equifinality effects of parameters on the simulated results. Karst geomorphology and land use have functional effects on spatiotemporal variations of hydrological processes and nitrogen transport. In the study catchment, agricultural fertilizer was the largest input source of N, accounting for 86% of the total. Plant uptake consumed about 45% of inputs, primarily in the low-lying valley bottom areas and the plain covered by relatively thick soils. Thus, a large amount of N released from soil reservoirs to the epikarst (via fractures or sinkholes) is then exported to the underground channel in the limestone area to the south. This N draining into groundwater could lead to extensive, potentially long-term contamination of the karst system. Therefore, improving the efficiency of fertilization and agricultural management in valleys/depressions is an urgent need to reduce N losses and contamination risk.
... The higher diffusion (suggested by higher dye coverage) indicated that infiltrated water could be stored in the soil matrix and that vertical movement would occur when the soil was saturated or close to saturation, providing evidence for saturation-excess runoff. Zhang et al. (2011) also reported that saturation-excess runoff was the main surface flow pattern in karst hillslopes. ...
Core Ideas
Macropores and cracks are preferential channels in karst depression and downslope locations
Heterogeneity of soil property results in finger flow in karst mid‐ and upslope locations
High K s and soil layering weaken preferential flow in mid‐ and upslope locations
Preferential flow degree and infiltration rate can be independent in karst regions
In karst regions, soil architecture varies along topographical locations, resulting in marked differences in infiltration rates. However, the relationship between soil architecture and preferential flow (PF) is still unclear. In this study, dye tracing was used to investigate PF and the dominant effects of five types of soil architecture in a small karst catchment. These soil architectures included deep clay soil in farmland (CSF) and deep clay soil in shrubland (CSS) in the depression; shallow clay soil with minimally weathered, slanted bedrock on downslope locations (CSWD); shallow sandy loam soil with highly weathered bedrock on midslope locations (SLSM); and sandy loam soil with rock fragments on upslope locations (SLSU). The results showed that macropores and cracks were the major channels that resulted in a high degree of PF in depressions and downslope locations. Preferential flow also continued along the rock–soil interface in the downslope locations. Finger flow mainly appeared in mid‐ and upslope locations, and cracks mainly appeared in the surface soil layer. However, down‐ and upslope locations showed lower PF. We observed that PF might not contribute to the different infiltration rates in different topographical locations. Tillage in depressions damages macropores, thereby minimizing vertical percolation. The high saturated hydraulic conductivity ( K s ) of the soil matrix covered the development of PF in the mid‐ and upslope locations, and the decrease in K s weakened the formation of PF as a result of heterogeneity of soil properties. These findings demonstrate that infiltration‐excess runoff may occur in depressions and downslope locations and that saturation‐excess runoff may occur in mid‐ and upslope locations.
... With respect to previous modelling studies of karst systems, to our knowledge, only four have used models that explicitly include land cover properties, all of which were applied at the local scale with detailed on-site information. Three of these studies (Canora et al., 2008;Doummar et al., 2012;and Zhang et al., 2011) used generic hydrological models that were not specifically developed for karst areas but included enough flexibility in their spatially distributed parameters to represent the variability in soil and bedrock properties. The large number of parameters in these models hampers their application at large scales and does not comply with criterion 3 (parsimony). ...
Karst aquifers are an important source of drinking water in many regions of the world. Karst areas are highly permeable and produce large amounts of groundwater recharge, while surface runoff is often negligible. As a result, recharge in these systems may have a different sensitivity to climate and land cover changes than in other less permeable systems. However, little is known about the combined impact of climate and land cover changes in karst areas at large scales. In particular, the representation of land cover, and its controls on evapotranspiration, has been very limited in previous karst hydrological models. In this study, we address this gap (1) by introducing the first large-scale hydrological model including an explicit representation of both karst and land cover properties, and (2) by providing an in-depth analysis of the model's recharge production behaviour. To achieve these aims, we replace the empirical approach to evapotranspiration estimation of a previous large-scale karst recharge model (VarKarst) with an explicit, mechanistic and parsimonious approach in the new model (V2Karst V1.1). We demonstrate the plausibility of V2Karst simulations at four carbonate rock FLUXNET sites by assessing the model's ability to reproduce observed evapotranspiration and soil moisture patterns and by showing that the controlling modelled processes are in line with expectations. Additional virtual experiments with synthetic input data systematically explore the sensitivities of recharge to precipitation characteristics (overall amount and temporal distribution) and land cover properties. This approach confirms that these sensitivities agree with expectations and provides first insights into the potential impacts of future change. V2Karst is the first model that enables the study of the joint impacts of large-scale land cover and climate changes on groundwater recharge in karst regions.
Karst landforms interfere with the runoff generation and confluence process, resulting in generally poor hydrological simulation accuracy in karst watersheds. We proposed a new karst hydrological module, which has two cores. One is the karst water storage capacity distribution curve that represents the distribution of runoff generation thresholds in karst areas, and the other is the underground nonclosure coefficient that represents the nonclosure phenomenon of underground watersheds in karst areas. The new module was further coupled with the Xinanjiang rainfall–runoff (XAJ) model to establish a complete hydrological model for karst areas (referred to as XAJ‐karst model). The sensitivity of the XAJ‐karst model parameters was analysed using the Sobol method, and applied to a typical karst watershed in Guizhou Province, China, to test the model performance on daily and hourly time scales. In addition, we also explored the impact of dynamic changes in the nonclosure coefficient of underground watershed area in karst watersheds on model results. Results showed that the average value of Kling–Gupta efficiency (KGE) of the XAJ‐karst model on the daily and hourly time scales was 0.85 and 0.77, respectively. In comparison with the XAJ model, the average KGE value of the XAJ‐karst model on both daily and hourly scales improved by 10.8% and 6.4%, respectively, demonstrating better simulation accuracy. In addition, there is a underground nonclosure phenomenon in the Xiangyang watershed, and the actual area of underground watershed expands abruptly as the antecedent‐precipitation increases to the critical value. Moreover, the water storage and hysteresis effects of the karst landform result in a certain hysteresis in water exchange between the underground watershed and adjacent watersheds.
Desertification in karst is an effect of climate change and not sustainable anthropogenic activities, the combination
of which, however, causes the gradual loss of karst natural resources, such as soil, vegetation, and
groundwater. A considerable percentage of global karst areas is found in drylands, characterized by negative
water balance and scarce presence of soils. High fragility of the karst environment, and its vulnerability to land
degradation and pollution because of the peculiar anisotropic setting, environmental dynamics, and of the direct
connection between the surface and the subsurface, are at the origin of the severe problems deriving from
desertification processes in karst. In addition to natural drivers, such as geology and topography, karst desertification
is generally due to four main factors, mostly or partly related to human activity: deforestation, improper
land use, groundwater overexploitation, and climate changes. Through the analysis of a collection of studies
conducted in several karst territories around the world, the present paper aims to provide an overview of the
processes leading to desertification risks in karst areas. Emphasizing the need to preserve these fragile environments,
characterized by peculiar features and precious freshwater resources, this review summarizes the main
situations at the global scale of rocky desertification in karst, at the same time providing indications for
developing innovative and multi-disciplinary approaches addressed toward mitigation of the risk related to
desertification in karst.
Karst desertification areas exhibit high spatial heterogeneity, extensive rock exposure and systems with a complex hydrological structure. Understanding runoff generation mechanisms is important for the interpretation of hydrological processes in karst critical zones. A typical karst desertification catchment in Southwest China was selected for a 2-year hydrological observation study of rainfall events, and rainfall–runoff characteristics and hydrological responses were studied. The results showed that very high rainfall infiltration occurs in the catchment, with an average runoff coefficient of 3.6%, and the runoff coefficient during most rainfall events ranges from 0.01 to 0.05%. The rainfall–runoff process is comprehensively affected by the landform characteristics, rocky desertification environment and epikarst infiltration system in the catchment. The rocky desertification hillslopes in the upper and middle reaches of the catchment are characterized by high permeability and low water-holding capacity because of the large areas of exposed rocks and fissures, which amplify the epikarst precipitation infiltration rate. Depressions in the lower reaches result in an increase in the retention time of water in the epikarst, which exhibits low permeability and high water-holding capacity. In this study, it was revealed that antecedent hydrological conditions significantly impact runoff generation processes in catchments. Runoff in the catchment mainly comprises old water (> 50%), and continuous rainfall events lead to a gradual increase in the proportion of new water.
Understanding the origins and processes of riverine dissolved inorganic carbon (DIC) is crucial for predicting the global carbon cycle with projected, more frequent climate extremes yet our knowledge has remained fragmented. Here we ask: How and how much do DIC production and export vary across space (shallow vs. deep, uphill vs. depression) and time (daily, seasonal, and annual)? How do the relative contributions of biogenic (soil respiration) and geogenic (carbonate weathering) sources differ under different temperature and hydrological conditions? We answer these questions using a catchment‐scale reactive transport model constrained by stream flow, stable water isotopes, stream DIC, and carbon isotope data from a headwater karstic catchment in southwest China in a subtropical monsoon climate. Results show climate seasonality regulates the timing of DIC production and export. In hot‐wet seasons, high temperature accelerates soil respiration and carbonate weathering (up to a factor of three) via elevating soil CO2 and carbonate solubility, whereas high discharge enhances export by two orders of magnitude compared to cold‐dry seasons. Carbonate weathering is driven more by soil CO2 than water flow. At the annual scale, 92.9% and 7.1% of DIC was produced in shallow and deep zone, respectively, whereas 64.5% and 35.5% of DIC was exported from shallow and deep zone, respectively. These results highlight the uniqueness of subtropical karst areas as synchronous reactors and transporters of DIC during the hot‐wet monsoon, contrasting the asynchronous production and export in other climate regions. A future hotter and wetter climate with more intensive storms in the region may further intensify DIC production and export, accentuating the potential of subtropical karst regions as global hot spots for carbon cycling.
Taking the 14,030 panel of Zhaogu No. 2 coal mine as its research object, this paper studies the evolution characteristics of the developing height, propagation track and caving arch shape of water-flowing fractures under the influence of thick alluvium by utilizing a physical experiment, theoretical analysis and field investigation. The results show that the height and limit span of the water-flowing fracture zone experience four stages, which include the initial stage, slow-increasing stage, sudden-increasing stage and stable-increasing stage. With the increase in the mining influence range, the shape of the water-flowing fracture in overburden under the influence of thick alluvium is gradually formed. The water in the thick alluvium and the water in the upper phreatic aquifer of the bedrock penetrate each other to form a concentrated danger zone, and the expansion track of the mining water-flowing fracture connects the hydraulic connection between the upper concentrated danger zone of overburden and the panel of No. 2’s first coal seam. A large amount of water mixed with sandstone flows into the fracture surface of the bedrock’s broken rock block through the water-flowing fracture, leading to the instability of the load-bearing structure composed of the thick alluvium caving arch and the towering roof beam, which illustrates the whole process of water–sand inrush accidents in thin bedrock stope with deep thick alluvium.
Soil preferential flow infiltrating rapidly through the rock–soil interface is an important hydrological process in karst rocky desertification area. However, how does the water leakage in the near-surface fissures, especially those filled with soil, proceed? The role of preferential flow at rock–soil interface of those fissures on water leakage process still puzzles us. The goal of this study was to reveal the role of soil preferential flow at the rock–soil interface in the process of water leaking of near-surface fissures. Five typical types of near-surface fissures were selected in an area experiencing severe rocky desertification in Guizhou Province, China. Dye tracer testing was applied, combined with digital image processing techniques. The results indicated that the rock–soil interface flow on both sides of the fissures is the most important preferential flow form in the fissures in karst area. The dyed area ratio of preferential flow varied from 0.12 to 0.48 in the rock + soil profiles, from 0.06 to 0.37 in the soil profiles, and between 0.02 and 0.16 in the rock–soil interface. The rock–soil interface is the smallest in terms of both their variation range of dyed area ratio and preferential flow patterns compared with soil and rock–soil profiles. The soil preferential flow in near-surface fissures mainly occurs in the soil depth range of 0–20 cm. The preferential flow path is mainly affected by the rock–soil interface on both sides and can pass through the clay layer with poor permeability. However, the soil depth of the dyed part was more than 50 cm. The soil preferential flow at the rock–soil interface is the main form of rapid downward leakage of water in near-surface fissures in the karst rocky desertification area, which can flow to the bottom of clay layer with poor permeability.
Exposed bedrock in karst areas considerably alters runoff paths causing partial runoff to converge into a concentrated flow, which is a potential source of soil erosion risk. However, research is lacking on how concentrated flow affects regional soil erosion. In this study, the surface and underground dual structure in karst areas was simulated in a steel tank. Combined with runoff plot monitoring, the runoff conversion process and erosion characteristics of gently sloping farmland in karst areas under different water discharge rates were examined through indoor concentrated flow discharge scouring tests, and the influence of concentrated flow changes on the runoff spatial distribution and sediment yield in gently sloping farmland was clarified. The results demonstrated the following: (i) there existed a significant positive correlation between surface runoff and the water discharge rate (p < 0.01); the partial correlation coefficient value reached 0.87. The higher the water discharge rate, the more surface runoff formation was facilitated. (ii) When the slope remained the same, the underground runoff was relatively high at 3 L/min. Given the same discharge, a significant negative correlation between underground runoff and slope was found (p < 0.05); the partial correlation coefficient value reached −0.71. (iii) In response to a water discharge rate of 5 L/min, surface soil erosion was serious, and the maximum sediment transport modulus was 174.088 g/min∙m². A significant cubic function relationship existed between the scouring time and surface sediment yield. Overall, a critical flow rate occurred between 3 and 5 L/min, which controlled changes in surface runoff, subsurface runoff and surface sediment yield. Under highly concentrated flow, drastic soil erosion could occur. These results can provide a scientific basis for the control and prevention of concentrated flow-induced erosion in karst areas.
Karst plant habitats are generally harsh and vulnerable to climate and human interferences. Restoration of karst vegetation and its effect on water resources are affected not only by climate and anthropological interferences but also by different bedrock lithologies. In this study, changes to climatic factors, vegetation indices of the normalized difference vegetation index (NDVI), the leaf area index (LAI) and runoff during 1982-2015 were statistically identified over the Yangchang river basin (YRB) with two contrasting bedrock lithologies (carbonate rock and detrital rock) in southwest China. The Budyko equation and the hydrological model in LPJ (the Lund-Potsdam-Jena Dynamic Global Vegetation Model) were calibrated and improved to separate runoff change that could be attributed to climate and vegetation changes during 1982-2015. LPJ was used to predict the potential vegetation for natural recovery without human interference and its effect on the hydrological budget in YRB. Results reveal that the execution of the major ecological restoration project (the Grain for Green Project) in YRB since the early 2000s has significantly increased NDVI and LAI even in the drier period of 2004-2015. However, the human effort of vegetation restoration only reaches about 25% of the potential capacity in the whole study area. The reforestation in YRB could decrease runoff by about 7.0 to 7.6% in the period from 2004 to 2015, and 11.2% in the future when vegetation shifts from artificial to natural vegetation recovery. Meanwhile, thick soil in the non-carbonate area can store more water to support a large proportion of forest, and raise drought resistance. However, the limited water holding capacity of weathered bedrock in the carbonate area restricts large tree growth, and thus reduces drought resistance. These results point a need for consideration of how bedrock geology influences available water limitations when designing suitable reforestation strategies in southwest China.
To meet the sustainable development goals in rocky desertified regions like Guizhou Province in China, we should maximize the crop yield with minimal environmental costs. In this study, we first calculated the yield gap for 6 main crop species in Guizhou Province and evaluated the quantitative relationships between crop yield and influencing variables utilizing ensembled artificial neural networks. We also tested the influence of adjusting the quantity of local fertilization and irrigation on crop production in Guizhou Province. Results showed that the total yield of the selected crops had, on average, reached over 72.5% of the theoretical maximum yield. Increasing irrigation tended to be more consistently effective at increasing crop yield than additional fertilization. Conversely, appropriate reduction of fertilization may even benefit crop yield in some regions, simultaneously resulting in significantly higher fertilization efficiency with lower residuals in the environment. The total positive impact of continuous intensification of irrigation and fertilization on most crop species was limited. Therefore, local stakeholders are advised to consider other agricultural management measures to improve crop yield in this region.
Rainfall-runoff processes in the karst dominated regions are of great importance. However, not all areas in a karst-dominated river basin are covered by typical limestone and both limestone and soil cover may exist. This study proposes a coupled conceptual hydrological model for simulating the rainfall-runoff processes in karst-dominated areas. The model, named as K-XAJ, couples the traditional Xinanjiang (XAJ) model and a two reservoir-based karst model for simulating runoff in both the karst area and the non-karst area in the Lijiang River basin. Simulated results demonstrated that the proposed K-XAJ model satisfactorily simulated the rainfall-runoff processes. Compared with the traditional XAJ model, the K-XAJ model produced better forecasts. The peak flow predicted by the K-XAJ model was larger than that by the XAJ model, but the interflow routed by the K-XAJ model was significantly smaller than that by the XAJ model. The magnitude of groundwater predicted by the K-XAJ model was greater. This study thus provides a new way to simulate rainfall-runoff processes in karst areas.
Expansion of a detailed hydrological modelling from catchment- to national- or continental-scale is of important theoretical and practical significance, yet faces many challenges. We developed a high-resolution, physically-based hydrological model named WEP-CN (Water and Energy transfer Processes in China) for China. Different climatic and hydrological conditions and geological structures as well as their impact on infiltration and runoff were examined and incorporated in WEP-CN. The study area (9.6 million km²) was divided into 19,406 sub-watersheds and 81,687 contour belts. The computation units, model input, and model structure and parameters in WEP-CN were improved to obtain a well-defined simulation area, a more reliable input as well as a detailed description of soil moisture movement in several special vadose zones such as karst development, swelling and frozen soil. Continuous simulations of various natural hydrological processes were conducted for 62 years from 1956 to 2017. We demonstrated the efficacy of our model by comparing simulated and statistical monthly streamflow at 203 hydrological stations across the country. For the validation period of 1981-2000, the Nash-Sutcliff Efficiency (NSE) was found to be larger than 0.7 at 80% of the stations, and the absolute value of relative error (RE) was less than 10% at 95% of the stations. Our result highlights the benefit of incorporating new mechanisms on the special vadose zone water movement and accounts for the impact of elevation change on meteorological and vegetation variables. This paper can serve as a reference for large-scale hydrological simulation with diverse climate, topography and underlying surface conditions.
Most semi-distributed and distributed hydrological models can potentially be applied for comprehensive catchment simulations, but these models may require modifications to capture dominant hydrological processes. The Soil and Water Assessment Tool (SWAT) ecohydrological model, an open source program, provides flexibility for modification to capture different components of hydrological processes in a given catchment. In this study, two new approaches were tested to simulate the hydrological processes of a karst system in the Zagros Mountains, Iran. The major modifications used in these two methods included adjusting the percolation rates in karst hydrologic response units (HRUs) using SWAT-Maharlu Lake (SWAT-ML), and modification of the crack flow module using SWAT-Crack Flow (SWAT-CF). Hydrological datasets from 1980 to 2013 were used for calibration and validation of surface runoff, baseflow, crop yields, and actual evapotranspiration. Both modified models outperformed the standard SWAT model in simulating runoff. The respective average Nash Sutcliffe Efficiencies of the original SWAT, SWAT-ML and SWAT-CF were 0.64, 0.68 and 0.66. Also, the results showed that higher deep aquifer infiltration values were estimated in the modified models versus the standard SWAT for a karst HRU, which reflects more accurate levels of recharge to the deep aquifer. However, the results showed that karst conditions and geometry of sinkholes in karst zones did not play a major role in creation of runoff.
It is essential to assess streamflow response to climate and land-use change in catchment basins that serve cities and their surrounding areas. This study used the Distributed Hydrology Soil Vegetation Model (DHSVM) to simulate streamflow under different climate and land-use change scenarios in the Dashi River catchment, China. The most sensitive soil parameters were maximum infiltration, porosity, field capacity, and wilting point, while the most sensitive vegetation parameters were leaf area index (LAI) and vegetation height. The suitability of the DHSVM model was aligned with Nash–Sutcliffe model efficiency coefficients (NSE) greater than 0.41 and 0.84 at daily and monthly scales, respectively. Streamflow increased/decreased with increasing/decreasing precipitation, while it decreased with increasing air temperature. Furthermore, streamflow decreased with the increase in forestland due to higher water consumption, especially during summer. Results from this study could help us to better understand streamflow response to changes in climate and land use.
Karst aquifers differ from other aquifers because of the spectacular and rapid change of their initial hydraulic properties, by solution enlargement of certain discontinuities. As a consequence, underground flow paths concentrate in a hierarchised network from surface to a unique spring, while groundwater storage develops in connection to drainage.
Because of its very active role in karst landform evolution, the infiltration zone shows typical characters and properties. The nature of flows (hydraulic behavior), the karstic void distribution (structure), and the processes obviously distinguish it from the unsaturated zone of porous and fissure aquifers. Among these properties, the fact that man is able to enter it through caves and can directly observe some infiltration seepage, has been essential in karst concepts and its approach.
Investigation methods are reviewed. They are related either to a global approach of karst system, by studying its hydraulic behavior, or to a local approach, devoted to a natural (cave) or artificial (borehole) observation site. The most common methods are based on hydrodynamics (recession analysis, discharge or water level time series analysis) and on water geochemistry. But dye tracing tests, slug tests and neutron probe logging in boreholes, and morphostructural analysis and geophysics are used in some specific works. Therefore the most original investigations certainly are those based on air, water, CO2 and heat flows in caves.
The peculiarities of karst infiltration induce some practical consequences. Some of them are related to groundwater resources (recharge conditions, travel time) and quality (high variability of chemical contents). Those peculiarities must be taken into account in land management projects. In short infiltration characters and related mechanisms are responsible in a large part for karst aquifer vulnerability.
The Barton Springs segment of the Edwards Aquifer is the sole source of water supply for about 45,000 people in and immediately south of Austin, Texas. For water management purposes, it is important to be able to predict the availability of groundwater in response to future development and potential droughts. The Edwards Aquifer comprises heterogeneous carbonate rock strata that have developed a well-connected network of karst conduits. This karstic geological structure makes aquifer characterization and groundwater modeling challenging. Previously, Scanlon et al. (2001) developed a two-dimensional groundwater model for the Barton Springs segment using MODFLOW. The karst conduits were not explicitly represented in the model. Instead, the study area was divided into 9 zones for which the transmissivities were obtained through calibration. We revisit Scanlon et al.'s work in this study by using MODFLOW-DCM, a MODFLOW module developed to represent flow through karstic aquifers. MODFLOW-DCM adopts a dual-conductivity approach in which the aquifer is conceptualized as being composed of two interacting flow systems, i.e., the background matrix and the karst conduits. This approach allows karst aquifers to be modeled as coupled systems, and thus allows aquifer dynamics related to karst conduit flows to be accurately simulated. Our preliminary results show improved matching of both water level measurements and spring discharges records.
Ground-water flow and solute-transport simulation modeling are major components of most exposure and risk assessments of contaminated aquifers. Model simulations provide information on the spatial and temporal distributions of contaminants in subsurface media but are difficult to apply to karst aquifers in which conduit flow is important. Ground-water flow and solute transport in karst conduits typically display rapid-flow velocities, turbulent-flow regimes, concentrated pollutant-mass discharge, and exhibit open-channel or closed-conduit flow. Conventional ground-water models, dependent on the applicability of Darcy`s law, are inappropriate when applied to karst aquifers because of the (1) nonapplicability of Darcian-flow parameters, (2) typically nonlaminar flow regime, and (3) inability to locate the karst conduits through which most flow and contaminant transport occurs. Surface-water flow and solute-transport models conditioned on a set of parameters determined empirically from quantitative ground-water tracing studies may be effectively used to render fate-and-transport values of contaminants in karst conduits. Hydraulic-flow and geometric parameters developed in a companion paper were used in the surface-water model, TOXI5, to simulate hypothetical slug and continuous-source releases of ethylbenzene in a karst conduit. TOXI5 simulation results showed considerable improvement for predicted ethylbenzene-transport rates and concentrations over qualitative tracing and analytical ground-water model results. Ethylbenzene concentrations predicted by TOXI5 simulations were evaluated in exposure and risk assessment models.
Quantitative ground-water tracing of conduit-dominated karst aquifers allows for reliable and practical interpretation of karst ground-water flow. Insights into the hydraulic geometry of the karst aquifer may be acquired that otherwise could not be obtained by such conventional methods as potentiometric-surface mapping and aquifer testing. Contamination of karst aquifers requires that a comprehensive tracer budget be performed so that karst conduit hydraulic-flow and geometric parameters be obtained. Acquisition of these parameters is necessary for estimating contaminant fate-and-transport. A FORTRAN computer program for estimating total tracer recovery from tracer-breakthrough curves is proposed as a standard method. Estimated hydraulic-flow parameters include mean residence time, mean flow velocity, longitudinal dispersivity, Peclet number, Reynolds number, and Froude number. Estimated geometric parameters include karst conduit sinuous distance, conduit volume, cross-sectional area, diameter, and hydraulic depth. These parameters may be used to (1) develop structural models of the aquifer, (2) improve aquifer resource management, (3) improve ground-water monitoring systems design, (4) improve aquifer remediation, and (5) assess contaminant fate-and-transport. A companion paper demonstrates the use of these hydraulic-flow and geometric parameters in a surface-water model for estimating contaminant fate-and-transport in a karst conduit. Two ground-water tracing studies demonstrate the utility of this program for reliable estimation of necessary karst conduit hydraulic-flow and geometric parameters.
This work deals with a rainfall-discharge model applied to a well known karst aquifer. A new approach is developed in order to minimize the fitting parameters: here, some of the model parameters do not result from a simple fitting, as it was the case with earlier models, i.e., some of them were assessed from the hydrograph analysis. The conceptual model of the functioning is based on a production function based on a simple calculation of effective rainfall and a transfer function consisting of two reservoirs. A slow discharge reservoir transfers the low flow and a rapid discharge reservoir feeds the high flow. The model has three fitted parameters plus one for its initialisation. Three parameters are deduced from the hydrograph analysis over the entire time series. For example, the recession coefficient of the slow discharge reservoir is determined from the hydrodynamic analysis of the recession [Mangin, A., 1975. Contribution à l’étude hydrodynamique des aquifères karstiques. 3ème partie. Constitution et fonctionnement des aquifères karstiques. Annales de Spéléologie, 30 (1), 210–124].This model was tested over a ten years period on the Fontaine de Vaucluse French karst system. The first hydrological year is used for fitting the model; the nine other cycles validate the modelling. The good quality of the model is proved by the Nash criterion of 92.3% on the validation period. Moreover, the simulation results were validated by a statistical analysis of measured and simulated time series.The model successfully simulates both the high and low flow at the same time. Also it estimates the water volumes available in the different parts of the aquifer and it proposes a management tool capable of predicting the evolution of the discharge in different climate conditions.
This thesis presents a method for characterizing flow systems in karst aquifers by acquiring quantitative information about the geometric and hydraulic parameters of a karst conduit network from spring hydrograph analysis. The investigation method applied consisted of constructing simple conceptual models of karst systems, and deducing analytical formulae describing the connection between aquifer parameters and hydrograph recession coefficient. The resulting formulae were then applied for evaluating input parameters for numerical models of the Bure aquifer (Jura, Switzerland). The comparison between model simulation results and real-world data permitted to test the applicability of the analytical formulae. The Bure test site also provided as a basis for evaluating some general characteristics of conduit networks by steady-state numerical models. Analytical formulae identified two, significantly different flow domains, depending on the overall configuration of aquifer parameters. During the baseflow recession of mature karst systems, the conductivity of karst conduits does not influence the drainage of the low-permeability matrix. In this case the drainage process is influenced by the size and hydraulic parameters of the low-permeability blocks alone. This flow condition has been defined as matrix-restrained flow regime (MRFR). During the baseflow recession of premature karst systems and the flood recession of mature systems, the recession process is dependent not only on the hydraulic parameters and the size of the low-permeability blocks, but also on conduit conduc
The epikarst (also known as the subcutaneous zone) comprises highly weathered carbonate bedrock immediately beneath the surface or beneath the soil (when present) or exposed at the surface. Porosity and permeability are higher near the surface than at depth, consequently after recharge percolating rainwater is detained near the base of the epikarst, the detention ponding producing an epikarstic aquifer. Such an aquifer is found only where the uppermost part of the vadose zone is very weathered compared to the bedrock at depth. Sometimes this contrast in porosity and permeability does not occur either because the epikarst has been scraped off by glacial scour or because high porosity exists throughout the bedrock. In some conditions porosity may even diminish near the surface because of case-hardening. The epikarst is best developed in pure, crystalline limestones or marble where it is typically about 10 m thick. It then contains a suspended aquifer that is under-drained and sustains the distal tributaries of cave streams and small perennial flows emerging on hillsides (epikarstic springs). Slow leakage paths from the epikarst maintain seepage to many stalactites throughout the year. A distinction should be recognized between the location (and form) of the epikarst and the function of the epikarst, because the near surface zone in carbonate rocks does not always contain a suspended aquifer.
This volume has its roots in the distant past of more than 20 years ago, the International Hydrologic Decade (IHD), 1964-1974. One of the stated goals of the IHD was to promote research into groundwater situations for which the state of knowledge was hopelessly inadequate. One of these problem areas was the hydrology of carbonate terrains. Position papers published early in the IHD emphasized the special problems of karst; carbonate terrains were supposed to receive a substantial amount of attention during the IHD. There were indeed many new contributions from European colleagues but, unfortunately, in the United States the good intentions were not backed up by much in the way of federal funding. Some good and interesting work was published, particularly by the U. S. Geological Survey (USGS), but in the academic community the subject languished. About this same time the Cave Research Foundation (CRF), organized in 1957 to promote the systematic exploration, survey, and scientific study of the great cave systems of Mammoth Cave National Park, was casting about for a broader scope for its research activities. Up until that time, CRF research had been largely restricted to detailed mineralogical and geological investigations within the caves, with the main part of the effort concentrated on exploration and survey. The decision to investigate the hydrology required a certain enlargement of vision because investigators then had to consider the entire karst drainage basin rather than isolated fragments of cave passage.
Karstic aquifers in Southwest China are largely located in mountainous areas and groundwater level observation data are usually absent. Therefore, numerical groundwater models are inappropriate for simulation of groundwater flow and rainfall-underground outflow responses. In this study, an artificial neural network (ANN) model was developed to simulate underground stream discharge. The ANN model was applied to the Houzhai subterranean drainage in Guizhou Province of Southwest China, which is representative of karstic geomorphology in the humid areas of China. Correlation analysis between daily rainfall and the outflow series was used to determine the model inputs and time lags. The ANN model was trained using an error backpropagation algorithm and validated at three hydrological stations with different karstic features. Study results show that the ANN model performs well in the modeling of highly non-linear karstic aquifers.
This text book has four introductory chapters describing karst landforms and landscapes, a chapter on carbonate geochemistry and another on karst hydrology. The core of the book consists of four chapters on the chemistry of karst waters, the processes of sedimentary in-filling, the origin of caves, and the evolution of karst systems through geological time. There are two chapters on karst forms in evaporite rocks, and in granites and quartzites, and the final two chapters are on environmental problems of karst regions (land use and water quality). -K.Clayton
This paper argues that there are fundamental problems in the application of physically-based models for practical prediction in hydrology. These problems result from limitations of the model equations relative to a heterogeneous reality; the lack of a theory of subgrid scale integration; practical constraints on solution methodologies; and problems of dimensionality in parameter calibration. It is suggested that most current applications of physically-based models use them as lumped conceptual models at the grid scale. Recent papers on physically-based models have misunderstood and misrepresented these limitations. There are practical hydrological problems requiring physically-based predictions, and there will continue to be a need for physically-based models but ideas about their capabilities must change so that future applications attempt to obtain realistic estimates of the uncertainty associated with their predictions, particularly in the case of evaluating future scenarios of the effects of management strategies.
There are two competing sets of factors that control the original solutional shapes of the natural drainpipes that make up the conduit system. One set comprises the spatial variations in the rates of solution of the bedrock caused by the distribution and geometry of joints and bedding planes, by the variations in solubility of the limestone, and by the distribution of such lithologic features as shale beds, dolomite beds, sandy layers, and chert nodules. The second set comprises the variations in rates of solution caused by the shifting flow regimes of moving water. If flow velocities are low, the passage tends to be etched into a complex shape controlled by structural and lithologic factors and we speak of an etching geometry or structure-controlled geometry. If the rate of solution varies with flow velocity, the shape of the passages will be modified to accommodate the flow pattern and we speak of a hydraulic geometry. Etching geometries tend to be irregular and angulate; hydraulic geometries tend to be smooth, curvilinear shapes. The forms of solution conduits are further modified by bedrock breakdown, by sediment in-filling, and by the deposition of secondary calcite deposits so that the shapes of cave passages might be quite different from the original solution shapes. Some deduction and interpretation is needed on the part of the karst hydrogeologist.
The key to understanding the development of most solution depressions in karst is concluded to lie in subcutaneous processes in the epikarstic aquifer at the top of the vadose zone but beneath the soil. The epikarstic water-table is drawn-down above highly permeable vertical leakage paths at the base of the subcutaneous zone. This focuses stream-lines and hence corrosion activity. The radius of the cone of depression initially determines doline size. Positive feed-back factors reinforce these processes. A distinction can be made between 'draw-down depressions' and 'point-recharge depressions'. -from Author
The aim of this study was to investigate various modelling approaches applicable to the simulation of groundwater flow and transport in the karstified limestone aquifer of the Swabian Alb in southern Germany. Results from two karst areas showing significantly different flow characteristics are presented. At the first site near Heidenheim, the hydrogeological data indicated homogeneous aquifer conditions. A three-dimensio nal numerical model with a minimum mesh size of 87 m was used to simulate the groundwater flow pattern over a period of six years. The good agreement between predicted and measured water levels demonstrates the ability of standard porous media models to simulate the regional flow pattern in moderately karstified terrains. At the second site near Reutlingen, the karstification of the Jurassic limestone aquifer is more advanced resulting in more heterogeneous hydraulic conditions. From tracer tests, groundwater flow velocities of up to and above 100 m/h are reported. However, stable isotope investigations show that usually less than a quarter of the total flow contributes to what is considered the fast flowing conduit type system. A double-porosity flow and transport groundwater model was therefore developed to simulate the spring discharge, the groundwater level fluctuations and some of the tracer breakthrough curves. One porosity represents the moderately karstified aquifer zones with low conductivities and high storativities. The other porosity represents the highly karstified areas yielding high flow velocities but hardly any water level fluctuations. The double-porosity model was able to adequately reproduce all observed characteristics of the highly karstified system at the Reutlingen site.
Karstic aquifers in Southwest China are largely located in mountainous areas and groundwater level observation data are usually absent. Therefore, numerical groundwater models are inappropriate for simulation of groundwater flow and rainfall-underground outflow responses. In this study, an artificial neural network (ANN) model was developed to simulate underground stream discharge. The ANN model was applied to the Houzhai subterranean drainage in Guizhou Province of Southwest China, which is representative of karstic geomorphology in the humid areas of China. Correlation analysis between daily rainfall and the outflow series was used to determine the model inputs and time lags. The ANN model was trained using an error backpropagation algorithm and validated at three hydrological stations with different karstic features. Study results show that the ANN model performs well in the modeling of highly non-linear karstic aquifers.
The mathematical equivalents of parallel plate openings are used to simulate real fractures dispersed in orientation, distributed in aperture, and of arbitrary spacing. With this idealization of jointed pervious rock, the discharge of each conductor is a second rank tensor proportional to the cube of aperture and to the projection of a hydraulic gradient generally parallel to no conductor. One may add components of discharge through each intersecting conductor and components of discharge through intervening pervious blocks. The reciprocal of specific surface of the fracture system like spacing serves as a weighting factor for the tensor sum, which is the anisotropic Darcy's law permeability of an equivalent continuous medium.
Special cases of one, two, and three joint sets are modeled by applying Monte Carlo methodsto pair orientations of individual planes sampled from Fisher dispersions with apertures sampledfrom skewed normal distributions. Statistics of the orientation of principal axes and ofprincipal permeabilities are developed to show the relationship between joint geometry andanisotropy and to assess its variations.
A distributed hydrology-vegetation model is described that includes canopy interception, evaporation, transpiration, and snow accumulation and melt, as well as runoff generation via the saturation excess mechanisms. Digital elevation data are used to model topographic controls on incoming solar radiation, air temperature, precipitation, and downslope water movement. Canopy evapotranspiration is represented via a two-layer Penman-Monteith formulation that incorporates local net solar radiation, surface meteorology, soil characteristics and moisture status, and species-dependent leaf area index and stomatal resistance. Snow accumulation and ablation are modeled using an energy balance approach that includes the effects of local topography and vegetation cover. Saturated subsurface flow is modeled using a quasi three-dimensional routing scheme. The model was applied at a 180-m scale to the Middle Fork Flathead River basin in northwestern Montana. This 2900-km2, snowmelt-dominated watershed ranges in elevation from 900 to over 3000 m. The model was calibrated using 2 years of recorded precipitation and streamflow. The model was verified against 2 additional years of runoff and against advanced very high resolution radiometer based spatial snow cover data at the 1-km2 scale. Simulated discharge showed acceptable agreement with observations. The simulated areal patterns of snow cover were in general agreement with the remote sensing observations, but were lagged slightly in time.
Concentration breakthrough curves obtained from a tracer test and time series of environmental tracers were analyzed to characterize slow and preferential water flow in a karst aquifer of the Franconian Alb, Germany. Tritium (3H) and chemical tracers (uranine, bromide, strontium) were measured during low flow conditions and a storm runoff event. The mean transit time of water along the conduits was determined using bromide. Environmental tracer data collected between 1969 and 2003 were modeled to estimate the mean transit time of 3H in the fissured-porous karst system (diffuse flow). The modelling approach was also used to estimate the water volume of the karst system and the conduits. The results suggest that the total water volume in the fissured-porous karst aquifer is in the range of 57×106 m3 and approximately 6% of the total water volume is stored in the soil zone and the epikarst. The water storage capacity of the conduits seems to be of minor importance. A mean transit time of bromide in the range of 14h was calculated for the conduit flow. The fissures and the porous rock matrix have a calculated water saturated porosity of 5.5% and a mean transit time of approximately 62 years was calculated. Thus the porous rock matrix represents the major dilution and storage zone for pollutants in the karst system.
A hydrological forecasting model is presented that attempts to combine the important distributed effects of channel network topology and dynamic contributing areas with the advantages of simple lumped parameter basin models. Quick response flow is predicted from a storage/contributing area relationship derived analytically from the topographic structure of a unit within a basin. Average soil water response is represented by a constant leakage infiltration store and an exponential subsurface water store. A simple non-linear routing procedure related to the link frequency distribution of the channel network completes the model and allows distinct basin sub-units, such as headwater and sideslope areas to be modelled separately. The model parameters are physically based in the sense that they may be determined directly by measurement and the model may be used at ungauged sites. Procedures for applying the model and tests with data from the Crimple Beck basin are described. Using only measured and estimated parameter values, without optimization, the model makes satisfactory predictions of basin response. The modular form of the model structure should allow application over a range of small and medium sized basins while retaining the possibility of including more complex model components when suitable data are available.
Gray system theory uses a black-gray-white color spectrum to describe a complex system whose characteristics are only partially known or known with uncertainty. In this study, we use gray system theory to investigate the relation between precipitation and spring flows in a karst region in China. The gray incidence analysis was applied to the Liulin Springs, Shanxi Province, China to analyze the time-lag between spring flow and precipitation. The results showed that the average groundwater residence time at Liulin Spings is about 4 years. The gray system GM(1,2) model was subsequently used as a predictive tool for spring discharge. It was found that model predictions are in agreement with observed data. This study also shows that the discharge of the Liulin Springs primarily responds to climate change; anthropogenic impacts are secondary. The continuous decline of water level in the karst aquifer and waning of spring discharges in semi-arid regions of China might be largely a response of the groundwater system to the decline in regional precipitation over the past two decades.
The aim of this work is to compare the different karst water features and related water resources in South and North China.
In Southern China there are over 3,358 karst ground river systems with a total discharge of about 420×108m3 in the dry season. In North China, there are about 100 larger karst spring systems, each with a catchment area from 500km2 to over 4,000km2, and an average discharge from 1 to 13m3/s. The basic geo-ecological features of water, soil and air quality are described for typical karst regions of China. The
total quality of geo-ecology is evaluated by five important factors.
The understanding of the temporal and spatial dynamics of soil moisture and hydraulic property is crucial to the study of
several hydrological and ecological processes. Karst environments are extremely fragile because of thin soil and small soil
water holding capacity. A marked intensification of agricultural land use and deforestation due to increase of population
and thus expansion of agricultural areas has made the karst environment even more delicate. In this study, the soil moisture
contents (SMC) and hydraulic conductivities (K) along four karst hillslopes were measured in situ by time domain reflectometry and the Guelph Permeameter, respectively,
at test plots, each of which has a different vegetative cover, landform, land surface slope, soil property and content of
rock fragment. The statistical results from the measurements show that land cover changes strongly affect the distribution
of soil moisture and hydraulic properties. Compared with SMC in the bare soil areas, SMC values are 30.5, 20.1 and 10.2% greater
in the forest, shrub and grass areas, respectively. Vegetation roots significantly increase permeability of low-layer silt
soils. Measured K values were 0.8, 0.6 and 0.01cm/min for the forest, agriculture and bare soil areas, respectively. When the forest was destroyed
by fire or cut to become an agricultural area or bare soils, SMC would be reduced by 13.1 and 32.1%, respectively. If deforestation
leads to strong rock desertification, SMC was reduced by 70%. Bedrock fractures significantly reduce the SMC in the overlying
layer, but increase K values. SMC values of 30–45% would be reduced to 17–30% for the soil layer embedding rocks with and without fractures, respectively.
K values could be increased from 1.0 to 8.5cm/min. SMC are sensitive to terrain. A slope angle increase of 1° would reduce
SMC about 0.82%. These changes resulting from land cover and land use alterations offer useful information to further investigate
the response of ecosystem evolution to hydrodynamic processes.
A monitoring of spring and rain waters in the South of France during two hydrological cycles is presented. Rain waters were sampled after each precipitation event at 3 rain-gauge stations. Four karstic springs located in the same area have also been daily (high discharge events) to monthly (low flow periods) sampled. This paper focuses on compositional changes in the Cl− and Br− ions and the oxygen-18 (δ18O) and hydrogen (δD) isotopes during the high discharge events.The responses of the different karstic systems are quite homogeneous and reflect the hydrological state of the system. The waters discharged during the major autumn and winter high discharge events originate from the epikarstic reservoir and show characteristics chemical variations related to residence in the unsaturated zone close to the surface. Their residence time in the order of 1–3 months. Correlations between the composition of the spring-water and the rainwater during three successive high discharge events during the summer of 1998 indicate that the water for high discharge event “n” is derived from water from precipitation event “n − 1” via a piston-type mechanism with residence time of 2 weeks.These results are interpreted as an indication of the major role of the epikarst reservoir in the karst recharge functioning. The similar behaviour of the four springs, although located in different geological contexts allows to think that the epikarst role could be more important than previously thought.
The Milandre test site is a karst aquifer characterized by diffuse infiltration, a well developed conduit network, and several tributaries feeding an underground river. Field data include discharge rate measurements, stable isotopes, weekly rainfall and spring-water isotope sampling, and detailed isotope sampling during three flood events. Flood sampling was carried out at several tributaries corresponding to conduit flow, vadose flow and seepage flow. Weekly sampling showed a strong buffering of the rainfall isotopic signal at the spring. This attenuation suggests an important mixing reservoir in the system. Flood events showed highly peaking hydraulic responses but buffered rain isotope responses. These results indicate that the soil and epikarst sub-systems have an important storage capacity. A conceptual model of flow and transport in the soil and epikarst zone is proposed: Soil plays an important role in mixing due to the presence of capillary water storage. Consequently dampened concentrations reach the epikarst despite a rapid hydraulic response. The epikarst acts as the storage element and distributes water as either a base flow component or a quick flow component. When recharge exceeds a given threshold, excess infiltrated water bypasses the soil and epikarst and reaches the saturated zone as fresh flow. Based on this model, the significance of phreatic storage is thought to be limited, at least in Milandre test site. Hence the saturated zone is seen mainly as a transmissive zone through its well developed conduit network.
Various approaches can be used to simulate groundwater flow in karst systems, including equivalent porous media distributed parameter, lumped parameter, and dual porosity approaches, as well as discrete fracture or conduit approaches. The purpose of this study was to evaluate two different equivalent porous media approaches: lumped and distributed parameter, for simulating regional groundwater flow in a karst aquifer and to evaluate the adequacy of these approaches. The models were applied to the Barton Springs Edwards aquifer, Texas. Unique aspects of this study include availability of detailed information on recharge from stream-loss studies and on synoptic water levels, long-term continuous water level monitoring in wells throughout the aquifer, and spring discharge data to compare with simulation results. The MODFLOW code was used for the distributed parameter model. Estimation of hydraulic conductivity distribution was optimized by using a combination of trial and error and automated inverse methods. The lumped parameter model consists of five cells representing each of the watersheds contributing recharge to the aquifer. Transient simulations were conducted using both distributed and lumped parameter models for a 10-yr period (1989–1998). Both distributed and lumped parameter models fairly accurately simulated the temporal variability in spring discharge; therefore, if the objective of the model is to simulate spring discharge, either distributed or lumped parameter approaches can be used. The distributed parameter model generally reproduced the potentiometric surface at different times. The impact of the amount of pumping on a regional scale on spring discharge can be evaluated using a lumped parameter model; however, more detailed evaluation of the effect of pumping on groundwater levels and spring discharge requires a distributed parameter modeling approach. Sensitivity analyses indicated that spring discharge was much more sensitive to variations in recharge than pumpage, indicating that aquifer management should consider enhanced recharge, in addition to conservation measures, to maintain spring flow. This study shows the ability of equivalent porous media models to simulate regional groundwater flow in a highly karstified aquifer, which is important for water resources and groundwater management.
A hydrological forecasting model is presented that combines the important distributed effects of channel network topology and dynamic contributing areas with the advantages of simple lumped parameter basin models. Quick response flow is predicted from a storage/contributing area relationship derived analytically from the topographic structure of a unit within a basin. Average soil water response is represented by a constant leakage infiltration store and an exponential subsurface water store. A simple non-linear routing procedure related to the link frequency distribution of the channel network completes the model and allows distinct basin sub-units, such as headwater and sideslope areas to be modeled separately. Procedures for applying the model and tests with data from the Crimple Beck basin in the United Kingdom are described.
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