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Runoff and sediment modeling in a peri-urban artificial landscape: Case study of Olympic Forest Park in Beijing
Abstract
Highlights
► Scale appropriate modeling is necessary in the peri-urban artificial landscape. ► Spatially-varied runoff and sediment potentials necessitate site-specific BMPs. ► Overland features, especially constructed channels, affect hydrological response.
... Research and practice in the last decades has shown that urbanization has an adverse impact on the urban hydrological processes, such as the expansion of impervious areas accelerating runoff flow velocity and enlarging peak flow and runoff volume, resulting in increased risk of urban flood and water-logging [20]. In order to mitigate urban water-logging and flood disasters and reduce the flood losses, a large number of researchers have explored the quantitative impacts of urbanization on urban hydrological processes under extreme precipitation using the combination of field observations and hydrodynamic and hydrological models [21][22][23][24][25][26][27]. In addition, urban flooding risk assessment methods were developed based on various risk assessment theories [28]; e.g., the risk matrix method [29]. ...
... Currently, the studies of urban flooding have mainly focused on the floods occurring in metropolitan regions. In these regions, it was demonstrated that the dominant cause of urban flood disasters is water-logging induced by impeded drainage systems and extreme rainfall [21][22][23][24][25][26][27][28]. However, flood disasters occurring in small mountainous cities are significantly different from those of large cities [30]. ...
River channel occupation has made cities in the mountainous areas more vulnerable to floodwater out of river channels during rapid global urbanization. A better understanding of the influence of river channel occupation on urban flood disasters can serve as a reference in planning effective urban flood control strategies. In this study, taking a flood event that occurred on July 26th, 2017 in a city on the Loess Plateau as an example, field surveys, dynamics detection of the river channel using remote sensing technology, and scenario simulations with a two-dimensional flow and sediment model were utilized to quantitatively analyze the impacts of river channel occupation on urban inundation and sedimentation. The results show that river channel dynamics reduced by construction can be successfully detected using the combination of high-resolution images and Landsat time-series images. The variation of the water level-discharge relationship caused by the narrowing of the river channel and the increase of the flood-water level caused by water-blocking bridges/houses result in a significant reduction of the flood discharge capacity. The contribution of the narrowing of the river channel was 72.3% for the total area inundated by floodwater, whereas 57.2% of urban sedimentation was caused by the construction of bridges/houses within the river channel. Sustainable flood mitigation measures were also recommended according to the investigations and research findings in this study in order to reduce the social, environmental and economic damages caused by floods.
... However, the rainfall-runoff relationship is highly nonlinear and complex, and is dependent on numerous factors such as antecedent soil moisture, evaporation, infiltration and rainfall duration (Guan et al., 2016;Isik et al., 2013;Sajjad et al., 2015;Zhang et al., 2012). Many studies have investigated the hydrological impact of urbanization based on field data (Choi et al., 2016;Zhang et al., 2013). Gallo et al. (2013) assessed the effect of urban land cover on hydrological responses using summer runoff data from five catchments dominated by distinct urban land uses and found it was tightly coupled to the magnitude of rainfall (Gallo et al., 2013). ...
... Additionally, most existing catchment models (e.g., DWSM: Dynamic Watershed Simulation Model, HEC-HMS: Hydrologic Engineering Center-Hydrologic Modeling System, and DTVGM: Distributed Time Variant Gain Model) have strong advantages in runoff yield estimation with consideration of detailed landuse information. However, these models do not consider flow routing in the urban drainage system, and land surface conditions are static as a model input, rather than dynamic (Du et al., 2012;Isik et al., 2013;Zhang et al., 2013;Zope et al., 2016). Therefore, the applicability of hydrological model for the urbanization impact assessment is still a challenge. ...
Urbanization-induced landuse changes alter runoff regimes in complex ways. In this study, a detailed investigation of the urbanization impacts on runoff regimes is provided by using multiple runoff metrics and with consideration of landuse dynamics. A catchment hydrological model is modified by coupling a simplified flow routing module of the urban drainage system and landuse dynamics to improve long-term urban runoff simulations. Moreover, multivariate statistical approach is adopted to mine the spatial variations of runoff metrics so as to further identify critical impact factors of landuse changes. The Qing River catchment as a peri-urban catchment in the Beijing metropolitan area is selected as our study region. Results show that: (1) the dryland agriculture is decreased from 13.9% to 1.5% of the total catchment area in the years 2000–2015, while the percentages of impervious surface, forest and grass are increased from 63.5% to 72.4%, 13.5% to 16.6% and 5.1% to 6.5%, respectively. The most dramatic landuse changes occur in the middle and downstream regions; (2) The combined landuse changes do not alter the average flow metrics obviously at the catchment outlet, but slightly increase the high flow metrics, particularly the extreme high flows; (3) The impacts on runoff metrics in the sub-catchments are more obvious than those at the catchment outlet. For the average flow metrics, the most impacted metric is the runoff depth in the dry season (October ∼ May) with a relative change from −10.9% to 11.6%, and the critical impact factors are the impervious surface and grass. For the high flow metrics, the extreme high flow depth is increased most significantly with a relative change from −0.6% to 10.5%, and the critical impact factors are the impervious surface and dryland agriculture; (4) The runoff depth metrics in the sub-catchments are increased because of the landuse changes from dryland agriculture to impervious surface, but are decreased because of the landuse changes from dryland agriculture or impervious surface to grass or forest. The results of this study provide useful information for urban planning such as Sponge City design.
... Because conversion of forest land to farmland and urban built-up often expose the soil to direct rainfall and runoff, therefore increase soil erosion. For instance, there has been an increased effort to understand the effects of environmental changes on sedi-ment yield [BORAH et al. 2001;DE VENTE et al. 2008;GUZMAN et al. 2017;KUMAR et al. 2014;PAK et al. 2015;ZEINIVAND, SMEDT 2009;ZHANG et al. 2013]. Some studies linked sediment yield with climate change [ZHANG et al. 2016], water quality [BAI, WU--SENG 2005;RUSSO et al. 2011], wildfire [CANFIELD et al. 2005], aquatic life [PAPANICOLAOU, ABACI 2005], soil condition [FOX, MARTIN 2014;ZHANG et al. 2016], and type of climate [MEKONNEN et al. 2016]. ...
Abundant rainfall areas promote sediment yield at both sub-watershed and watershed scale due to soil erosion and increase siltation of river channel, but it can be curtailed through planned urbanization. The urbanization of Skudai watershed is analysed from historical and future perspective. A GIS-based model (Hydrological Simulation Programme-FORTRAN-HSPF) is used to modelled sediment flow using basin-wide simulation, and the output result is utilized in evaluating sediment yield reduction due to increased urbanization by swapping multiple temporal land-use of decadent time-steps. The analysis indicates that sediment yield reduces with increase urban built-up and decrease forest and agricultural land. An estimated 12 400 tons of sediment will be reduced for every 27% increase in built-up areas under high rainfall condition and 1 490 tons at low rainfall. The sensitivity analysis of land-use classes shows that built-up, forest and barren are more sensitive to sediment yield reduction compared to wetland and agricultural land at both high and low rainfall. The result of the study suggests that increased urbanization reduced sediment yield in proportion to the rainfall condition and can be used as an alternative approach for soil conservation at watershed scale independent of climate condition.
... Irvine, Perrelli, Ngoen-Klan, & Droppo, 2009), the model assumes soil topography and land use to be uniform (Merritt, Letcher, & Jakeman, 2003), which clearly is not the case in urban contexts. Also well-established models, such as MIKE (Spencer, et al., 2011) and SWAT (Zhang, et al., 2013) are not able to cover all relevant aspects of urban soil erosion. However, they can be applied to specifi c scenarios. ...
Accelerated soil water erosion is one of the major global environmental problems that adversely affect both rural and urban areas. While many investigations have been initiated to efficiently understand and effectively manage water erosion problems in agricultural areas, specific knowledge on urban water erosion is less pronounced. This paper aims at providing an overview of the extent at which erosion dynamics processes have been explored in urban areas. Based on the last decade’s publications, the majority (64%) of studies were conducted in the developed world, mostly in humid subtropical and humid continental climate regions. Furthermore, researchers largely concentrated on offsite erosion, focusing on contaminated sediments and on stream erosion. The employed methods were mostly traditional approaches (81% of all articles) compared to modern methods of remote sensing and modelling. This review identifies limitations in methods employed, and gaps in focal research topics and urban-specific management strategies. In particular, the paper argues that approaches oriented towards minimising the risks from water erosion in urban areas are urgently needed. The review findings are expected to be of interest to researchers, urban planners and environmental related managers.
... Such changes lead to a complicated mixture of modifications to the hydrologic cycle across a range of spatial scales. Surface runoff in most watersheds is observed to increase with urbanization (Rose and Peters, 2001;Weng, 2001;Lee and Heaney, 2003;Haase, 2009;Boggs and Sun, 2011;Zhang et al., 2013;Wu, 2015), while changes to other water budget components have been reported to typically be reduced, such as precipitation (Rosenfeld, 2000;Shepherd, 2006;Kaufmann et al., 2007;Hand and Shepherd, 2009), groundwater recharge (Lerner, 1990(Lerner, , 2002Foster et al., 1994;Rose and Peters, 2001;Zhang and Kennedy, 2006;He et al., 2009;Jeppesen et al., 2011;He and Hogue, 2012;Hibbs and Sharp, 2012;Barron et al., 2013), baseflow (Brun and Band, 2000;White and Greer, 2006;Jacobson, 2011;Nie et al., 2011), and evapotranspiration (ET) (Oke, 1979;Grimmond and Oke, 1986;Balling and Brazel, 1987;Dow and DeWalle, 2000a;Rose and Peters, 2001;Dimoudi and Nikolopoulou, 2003;Gober et al., 2009;Haase, 2009;Jeppesen et al., 2011;Ramier et al., 2011;Shields and Tague, 2012;Wijesekara et al., 2012;Barron et al., 2013;Bijoor et al., 2014;Gwenzi and Nyamadzawo, 2014). However, the magnitude and direction of the water budget component modifications are difficult to predict given the complexities of the urban system (Burian and Pomeroy, 2010). ...
This paper presents a study of the potential for green infrastructure (GI) to restore the predevelopment hydrologic cycle in a semi-arid urban catchment. Simulations of stormwater runoff from a 0.11-km² urban catchment in Salt Lake City, Utah, USA for predeveloped (Natural Hydrology, NH), developed (Baseline, BL), and developed with GI (Green Infrastructure, GI) conditions were executed for a one-year period. The study was repeated for a relatively dry year, wet year, and an average year based on precipitation amounts in the year. Bioretention and green roofs were chosen for the GI plan. Results showed that the water budget of the catchment with the GI plan implemented more closely matches the NH water budget compared to the BL scenario, for all three years (dry, wet, average). The BL and GI scenarios showed more significant modifications to the water budget than what has been found by studies in humid climates. Compared to the BL condition, GI annually reduces surface runoff by 35%, 45%, and 43% and restores evapotranspiration by 18%, 19%, and 25% for the dry, average, wet years, respectively. Based on the introduced water budget restoration coefficient (WBRC), the water budget of the study catchment was restored by the GI plan to 90%, 90%, and 82% of the predevelopment state in the dry, average, and wet years, respectively. By comparing the WBRC estimated for other studies, it is further inferred that the water budget is more significantly affected by development and GI restoration in semi-arid than humid climates, but the differences lessen as the precipitation amount increases.
... Many modeling studies concerning fluvial sediment transport at the coarse scales have focused on spatial and temporal distributions of sediment yields or relating these loads to the relatively stable features of these units such as mean slopes and elevations over monthly, annual, decade, or even longer periods (Forzoni et al., 2013;Medeiros et al., 2010;Mills and Bathurst, 2015;Patil et al., 2012;Syvitski and Milliman, 2007;Zhou and Li, 2015). Very few have explored the processes of sediment transport during storm events for the entire watershed and/or isolated subwatersheds (Bisantino et al., 2015;Zhang et al., 2013). Yet, watershed models have not been used to explore spatial variations of sediment transport and their connections within a watershed during a rainfall event, in particular an extreme event that could cause flooding. ...
... Articles that mention operational ecosystem management practices mostly focused on flood protection. Connectivity was a recurrent theme, i.e., connecting ecological structures, together with disconnecting, storing and buffering runoff water along the flow path (Borris et al., 2013; Zhang et al., 2013). Several articles described the replacement of traditional urban stormwater drainage systems with green stormwater infrastructure featuring bioretention, swales, waterscapes and stormwater wetlands (Che et al., 2014; Hogan and Walbridge, 2007). ...
... Many modeling studies concerning fluvial sediment transport at the coarse scales have focused on spatial and temporal distributions of sediment yields or relating these loads to the relatively stable features of these units such as mean slopes and elevations over monthly, annual, decade, or even longer periods (Forzoni et al., 2013;Medeiros et al., 2010;Mills and Bathurst, 2015;Patil et al., 2012;Syvitski and Milliman, 2007;Zhou and Li, 2015). Very few have explored the processes of sediment transport during storm events for the entire watershed and/or isolated subwatersheds (Bisantino et al., 2015;Zhang et al., 2013). Yet, watershed models have not been used to explore spatial variations of sediment transport and their connections within a watershed during a rainfall event, in particular an extreme event that could cause flooding. ...
In this study, we tested the prediction ability of the Dynamic Watershed Simulation Model (DWSM), an event-based watershed model, on an agricultural watershed in central New York State and its ability for use as a management tool. Using five different storm events, we identified a set of key parameters that allowed DWSM to best predict hydrographs and sedigraphs of the events for both the curve number and interception-infiltration rainfall-runoff methods. Subsequent sensitivity analyses revealed that modeling outcomes (i.e., peak water and sediment discharges, total event runoff volume, and event sediment yield) were most sensitive for the first method to CNAF, a factor adjusting runoff CN values, and most sensitive for the second method to HYCND and VOG, parameters reflecting soil hydraulic conductivity and interception loss. These analyses led to benchmark values of the key parameters and empirical relationships between precipitation and the three most sensitive parameters, which were validated using two additional storm events. Based on these results, we propose a general modeling procedure that can best predict event hydrographs and sedigraphs for watershed management planning.
... Each catchment surface was initially subdivided along with the boundary of unique land cover type. The linear street network including asphalt roads and brick alleyways that function as artificial corridors to regulate runoff transportation, were also adopted as sub-catchment boundaries (Jones et al., 2000; Zhang et al., 2012). Finally, the boundaries of TIA and EIA patches obtained by the above identification were used for further delineation. ...
Imperviousness, considered as a critical indicator of the hydrologic impacts of urbanization, has gained increasing attention both in the research field and in practice. However, the effectiveness of imperviousness on rainfall-runoffdynamics has not been fully determined in a fine spatiotemporal scale. In this study, 69 drainage subareas <1ha of a typical residential catchment in Beijing were selected to evaluate the hydrologic impacts of imperviousness, under a typical storm event with a 3-year return period. Two metrics, total impervious area (TIA) and effective impervious area (EIA), were identified to represent the impervious characteristics of the selected subareas. Three runoffvariables, total runoffdepth (TR), peak runoffdepth (PR), and lag time (LT), were simulated by using a validated hydrologic model. Regression analyses were developed to explore the quantitative associations between imperviousness and runoffvariables. Then, three scenarios were established to test the applicability of the results in considering the different infiltration conditions. Our results showed that runoffvariables are significantly related to imperviousness. However, the hydrologic performances of TIA and EIA were scale dependent. Specifically, with finer spatial scale and the condition heavy rainfall, TIA rather than EIA was found to contribute more to TR and PR. EIA tended to have a greater impact on LT and showed a negative relationship. Moreover, the relative significance of TIA and EIA was maintained under the different infiltration conditions. These findings may provide potential implications for landscape and drainage design in urban areas, which help to mitigate the runoffrisk.
... The model results suggest a higher impact of runoff if imperviousness is increased from 15 to 25% of the catchments areas. Zhang et al.'s (2013) study deals with a completely artificial environment (an artificial park with natural, roads, drainage networks, etc.) in the surroundings of Beijing (China). They use a Dynamic Watershed Simulation Model (DWSM) to simulate the runoff and sediment transport processes from monitored and design storms and try to assess the impact of Best Management Practices (BMPs) on runoff and sediment yield. ...
Preface: Hydrology of peri-urban catchments: processes and modelling
The lack of discharge observations and reliable drainage information is a pervasive problem in urban catchments, resulting in difficulties in parameterizing urban hydrological models. Current parameterization methods for ungauged urban catchments mostly rely on subjective experiences or simplified models, resulting in inadequate accuracy for urban flood prediction. Parameter regionalization has been widely used to tackle model parameterization issues, but has rarely been employed for urban hydrological models. How to conduct effective parameter regionalization for urban hydrological models remains to be investigated. Here we propose a parameter regionalization framework (PRF) that integrates donor catchment clustering and the optimal regression‐based methods in each cluster. The PRF is applied to an urban hydrological model, the Time Variant Gain Model in urban areas (TVGM_Urban), in 37 urban catchments in Shenzhen City, China. We first show satisfactory flood simulation performance of TVGM_Urban for all urban catchments. Subsequently, we employ the PRF for parameter regionalization of TVGM_Urban. PRF classifies 37 urban catchments into three groups, and the partial least‐squares regression is identified as optimal regression‐based method for Groups 1 and 2, while the random forest model is found to be best for Group 3. To evaluate the simulation performance of PRF, we compare it with eight single regionalization methods. The results indicate better simulation performance and lower uncertainty of PRF, and donor catchment clustering can effectively enhance the simulation performance of linear regression‐based methods. Lastly, we identify curve number, land cover area ratios, and slope as critical factors for most TVGM_Urban parameters based on PRF results.
Studies reviewed in this paper show anomaly for temperature pertaining to streamflow and rainfall showing different trends, especially in Ethiopia to support the research findings and interpretation. There are many hydrological models, including 54 physically distributed, lumped, and conceptual hydrological models, of which 28 have been used in Ethiopian river basins. The models include the most adaptable and commonly used SWAT model applicable from small areas up to large basins. It is indeed a challenge to use a single hydrological model as the data rely on consistency, limitation-free, and exactly fitted output. The overall performance of individual physically-based, conceptual, and machine learning (ML) models varied at different watersheds. Reasonably, ML performs very well, up to 0.99 for R² and NSE and up to 0.001 for PBIAS. Inopportunely, using a single hydrological model has its limitations; ensemble multi-individual models, coupling or hybridization of physical or conceptual models with machine learning, combining evolutionary optimization algorithms with ML, and also comparisons of multi-single hydrological models, and selecting the best one are recommended options. No single hydrological model is indispensable and can be termed as better than the other for any watershed. Somewhat, ML outperforms SWAT but cannot be considered an absolute substitute. The size of the watershed, the number of data used, and the ratio between calibrations year to validation year do not have a clear correlation with the performance, particularly for the SWAT model accounted for in this review. Optimization algorithms explore multiple options and choosing the right one is a tedious task before a final decision is taken.
Green roofs have been treated as practical low impact development (LID) strategies to retain stormwater runoff and alleviate the rainfall-induced flooding risks in urban regions. The purpose of this study was to analyze the hydrological effects of the spatial location of green roofs in urbanized catchments. In the built-up region of Beijing, 12 urbanized catchments with various architectural patterns were chosen as the study areas. To distinguish the spatial characteristics of roof surfaces, we defined the effective roof surfaces to distinguish from other types of roofs, which have more convenient or direct hydrological connections to drainage systems. A hydrological model was then used to simulate the stormwater mitigation performance of green roofs for the study catchments, which were assigned to different rainfall conditions. The simulation results confirmed the benefits of implementing green roofs for urban stormwater regulation. However, the spatial variability of green roofs showed inherent influences on the runoff mitigation capacity in urbanized catchments. Greening on effective roof surfaces would provide more effective stormwater regulation benefits, for reductions in both runoff volume and peak flow. In addition, the spatial arrangement characteristics of roof surfaces also influenced the hydrological efficiency of green roofs. The effect of the spatial location of green roofs on runoff mitigation was rainfall-dependent. These findings provide insights into the hydrological role of green roofs, and suggest that proper siting of LID facilities should be a consideration for urban stormwater management in order to fulfill the hydrological efficiency and cost-effectiveness planning target.
The objective of this study is to propose an event-based calibration approach for selecting representative semi-distributed hydrologic model parameters and to enhance peak ow prediction at multiple sites of a semi-urban catchment. The performance of three multi-site calibration approaches (multi-site simultaneous (MS- S), multi-site average objective function (MS-A) and multi-event multi-site (ME-MS)) and a benchmark at-catchment outlet (OU) calibration method, are compared in this study. Additional insightful contributions include assessing the nature of the spatio-temporal parameter variability among calibration events and developing an advanced event-based calibration approach to identify skillful model parameter-sets. This study used a SWMM5 hydrologic model in the Humber River Watershed located in Southern Ontario, Canada. For MS-S and OU calibration methods, the multi-objective calibration formulation is solved with the Pareto Archived Dynamically Dimensioned Search (PA-DDS) algorithm. For the MS-A and ME-MS methods, the single objective calibration formulation is solved with the Dynamically Dimensioned Search (DDS) algorithm. The results indicate that the MS-A calibration approach achieved better performance than other considered methods. Comparison between optimized model parameter sets showed that the DDS optimization in MS-A approach improved the model performance at multiple sites. The spatial and temporal variability analysis indicates a presence of uncertainty on sensitive parameters and most importantly on peak ow responses in an event-based calibration process. This nding implied the need to evaluate potential model parameters sets with a series of calibration steps as proposed herein. The proposed calibration and optimization formulation successfully identied representative model parameter set, which is more skillful than what is attainable when using simultaneous multi-site (MS-S), multi-event multi-site (MS-ME) or at basin outlet (OU) approach.
Urbanization significantly increases the risk of urban flooding. Therefore, quantitative study of urban rainfall-runoff processes can provide a scientific basis for urban planning and management. In this paper, the built-up region within the Fifth Ring Road of Beijing was selected as the study area. The details of land cover and urban function zones (UFZs) were identified using GIS and RS methods. On this basis, the SCS-CN model was adopted to analyze the rainfall-runoff risk characteristics of the study area. The results showed that: (1) UFZs within different levels of runoff risk varied under different rainfall conditions. The area ratio of the UFZs with high runoff risk increased from 18.90% (for rainfall return period of 1a) to 54.74% (for period of 100a). Specifically, urban commercial areas tended to have the highest runoff risk, while urban greening spaces had the lowest. (2) The spatial characteristics of the runoff risks showed an obvious circular distribution. Spatial cluster areas with high runoff risk were mainly concentrated in the center of the study area, while those with low runoff risk were mainly distributed between the fourth and fifth ring roads. The results indicated that the spatial clustering characteristic of urban runoff risk and runoff heterogeneity among different UFZs should be fully considered during urban rainwater management.
Key messageThe home-field advantage (HFA) hypothesis states that leaf litter decomposes faster in the habitat from which it was derived (i.e., home) than beneath a different plant species (i.e., away from home). We conducted reciprocal translocation experiments to explore the HFA effect of urban leaf litter decomposition. HFA of litter decomposition varied with species and season, and interacted with nutrient and environmental dynamics. ContextAlthough forest litterfall and subsequent decay are acknowledged as a critical factor regulating nutrient cycling, soil fertility, and ecosystem carbon budgets in natural ecosystems, they remain less understood in urban ecosystems and the evidence for HFA has not been universal. AimsWe select Beijing Olympic Forest Park (BOFP), the largest urban forest park of Asia, as a case study to explore HFA of leaf litter decomposition in urban forest ecosystems. We investigated the litterfall production, mass loss, and nutrient dynamics of two species (Robinia pseudoacacia and Pinus armandii) commonly planted in Beijing urban forest ecosystems. Methods
Variations in litterfall production were measured in R. pseudoacacia stand and P. armandii stands over 12 months. HFA of litter decomposition was explored by reciprocal leaf litter translocation experiments, and leaves were analyzed for C, N, and P during decomposition of 297 days. ResultsTwo major peaks of total litterfall in R. pseudoacacia were observed, while litterfall in P. armandii followed a unimodal distribution pattern, which were similar to seasonal patterns of broadleaf and coniferous litter production in natural forest ecosystems. The loss of initial ash-free mass of R. pseudoacacia (19 %) was about twofold of P. armandii (11 %). The litter quality (e.g., initial C, N, and P) might have contributed to the differences between broadleaf and coniferous species. Leaf litter decomposition of R. pseudoacacia showed seasonal switch of HFA. In contrast, P. armandii showed a constant HFA during the whole study period. ConclusionHFA of litter decomposition in urban forests varied by species and season. We found the seasonal switch of the HFA effect for R. pseudoacacia, which has not been observed in nonurban ecosystems. More observations or experiments with multiple species or mixed species across various cities are needed to understand the processes and mechanisms of litter decomposition and nutrient dynamics in the urban ecosystems.
Morning exercise in the park is getting increasingly popular in Beijing, while Beijing's Particulate Matter (PM) is getting worse. Studies indicated that the growing density of PM2.5 is positively correlated with the number of patients with circulatory system, respiratory and cardiovascular problems. To make people reduce the chance of exposure to PM2.5 as far as possible in the exercise and determine the most appropriate time and place for exercise, PM10 and PM2.5 were monitored in four sampling sites (broad-leaved forests, coniferous woodland, flower meadow and impervious surface) in December 2012 and May 2013 in Beijing Olympic forest park. And we selected four precipitation-free sunny days every month and monitoring occurred at least 48 h after precipitation. The concentrations of PM2.5, PM10 at the four different monitoring sites were also comparatively analyzed. Results indicated that the concentrations of PM10 and PM2.5 were both higher in heating period (December) than those in non-heating period (May) (p<0.05). In addition, the mean hourly concentrations of PM10 and PM2.5 in early morning and after 5:00 am were significantly higher than those in daytime (9:00 am-15:00 pm) (p<0.05), with the four different sites exhibiting the same hourly variation. Combined the study result, we argue that the traditional view that park, especially in the woods, is the best place to exercise in the morning should be corrected. 9:00 am to 15:00 pm is the best time for exercise, for the reason of low concentration of PM. Coniferous woodland and flower meadow are the best choice to morning exercise in non-heating period, while only impervious surface is the best choice for winter morning exercises. The results will provide scientific support for correcting the current false understanding in the morning exercise.
Urbanization has increased the risk of urban flood. Quantitative research of urban rainfall-runoff process, can provide a scientific basis for the scientific planning and management of the city. In this paper, the land use/cover data and urban functional zones within Beijing five-ring areas were classified with the aid of GIS and RS technology. The SCS-CN method, as a traditional empirical model in the fields such as surface hydrology, was selected for simulating the surface runoff potentials within different urban functional zones in this study. Meanwhile, we analyzed the distribution of the surface runoff under different return periods of precipitation. Then the index of Moran's I was used to recognize the "hot spots" and "cool spots" of surface runoff in Beijing five-ring areas. The result showed that, the distribution configuration of surface runoff experienced a remarkable difference under different return periods of precipitation. The area of high runoff potential regions increased from 18.90% to 54.74% across the whole five-ring areas when seeing 1-year and 100-year return periods of precipitation respectively. Due to the difference and diversity of the impervious surface rate, runoff risks differed significantly from each other across different urban functional zones. For example, the highest risk of runoff generation was captured in the commercial zone by the hydrological model, with an average of 24.76 mm under 1-year return period of precipitation. The preserved zones, on the other hand, had the lowest risks of runoff generation (7.36 mm). Furthermore, the potential risk of runoff depth became similar to the increase in precipitation return-period. Finally, the spatial cluster of various runoff risk zones was captured by using spatial autocorrelation analysis method. In general, runoff risk zones experienced a circular pattern, which decreased from the central to the peripheral region. In most cases, the commercial and residential zones located in the core area of the city were prone to higher runoff generation and risks. Large parks and natural green areas, on the other hand, can help to minimize the flooding risk, and thus can be treated as the low-risk zones. These zones are mainly situated within the fourth to fifth-ring road areas of Beijing city. In order to remit the flooding hazard, city administrators should take account of the distribution of runoff risk area and rainfall-runoff characteristics of various urban functional zones before the relevant regulations were formulated. And also the ecological advantage within the city should be made full use of to solve the urban flooding hazard.
This literature review summarizes significant technical literature published in 2012 and 2013 in all primary areas of urban wet-weather flows. The review covers a range of topics including characterization, pollution sources, monitoring and sampling, surface and groundwater impacts, mathematical modeling tools and decision support systems, regulatory policies, and control and treatment technologies. Some gaps in the literature compilation have also been identified and presented to support future research efforts.
Surface water nitrate (NO3/-) pollution from agricultural production is well established, although few studies have linked field N budgets, NO3/- loss in tile drained watersheds, and surface water NO3/- loads. This study was conducted to determine field sources, transport, and fiver export of NO3/- from an agricultural watershed. The Embarras River watershed at Camargo (48 173 ha) in east-central Illinois was investigated. The watershed is a tile-drained area of fertile Mollisols (typical soil is Drummer silty clay loam, a fine-silty, mixed mesic Typic Haplaquoll) with primary cropping of maize (Zea mays L) and soybean (Glycine max L.). Agricultural field N sources and sinks, tile drainage NOn concentrations and fluxes, and fiver NO3/- export were estimated for the entire watershed. Large pools of inorganic N were present following each harvest of maize and soybean (average of 3670 Mg N yr-1 over a 6-yr period). The source of most of the inorganic N was divided between N fertilizer and soil mineralized N. High concentrations of NO3/- were found in four monitored drainage tiles (5-49 mg N L-1), and tile concentrations of NO3/- were synchronous with Embarras River NO3/- concentrations. High flow events contributed most of the yearly NO3/- loss (24.7 kg N ha-1 yr-1) from tile drained fields in the 1995 water year (1 Oct. 1994 through 30 Sept. 1995) where high rainfall events occurred in a low overall precipitation year (in one tile 21% of the annual load was exported in 1 d). During the 1996 water year, NO3/- export in tiles was much higher (44.2 kg N ha-1 yr-1) due to greater precipitation, and individual days were less important. On average, about 49% (average of 1688 Mg N yr-1 over a 6-yr period) of the field inorganic N pool was estimated to be leached through drain tiles and seepage and was exported by the Embarras River, although depending on weather and field N balances this ranged from 25 to 85% of the field N balance over the 6-yr period. It seems likely that agricultural disturbance (high mineralization inputs of N) and N fertilization combined with tile drainage contributed significantly to NO3/- export in the Embarras River.
Considering the spatial character of parameters and precipitation controlling hydrologic processes, it is not surprising that Geographic Information Systems (GIS) have become an integral part of hydrologic studies. The primary motivation for this book is to bring together the key ingredients necessary to use GIS to model hydrologic processes, i.e., the spatial and temporal distribution of the inputs and parameters controlling surface runoff. GIS maps describing topography, land use and cover, soils, rainfall, and meteorological variables may become model parameters or inputs in the simulation of hydrologic processes.
Input parameters are used in hydrologic/water quality models to describe specific situations. These input parameters are never known with certainty. The models, although largely physically based, are not capable of describing the exact hydrologic and chemical processes that take place under natural conditions. Evaluation of models by a comparison of observed and predicted results is fraught with ambiguities resulting from the large number of parameters that must be estimated and the inherent variability in natural systems. This article puts forth a model evaluation protocol based on a simulation procedure which transforms parameter uncertainty into prediction uncertainty using probability density functions. Confidence intervals are placed on model results and decisions regarding model acceptability are made based on the magnitude of measured data, confidence intervals, and performance criteria placed on the model.
In this paper we examine how the nature of spatial variability affects
hydrologic response over a range of scales using five field studies as
examples. The nature of variability was characterized as either
stochastic, when random, or deterministic, when due to known, nonrandom
sources. We have emphasized how that characterization may change with
the scale of hydrologic model. The five field examples, along with
corresponding sources of variability, were (1) infiltration and surface
runoff affected by shrub canopy, (2) groundwater recharge affected by
soil depth, (3) groundwater recharge and streamflow affected by
small-scale topography, (4) frozen soil runoff affected by elevation,
and (5) snowfall distribution affected by large-scale topography. In
each example there was a scale, the deterministic length scale, over
which the hydrologic response was strongly dependent upon the specific,
location-dependent ecosystem properties. Smaller-scale variability may
be represented as either stochastic or homogeneous with nonspatial data.
In addition, changes in scale or location sometimes resulted in the
introduction of larger-scale sources of variability that subsume
smaller-scale sources. Thus recognition of the nature and sources of
variability can reduce data requirements by focusing on important
sources of variability and using nonspatial data to characterize
variability at scales smaller than the deterministic length scale. All
the sources of variability described are present in the same watershed
and affect hydrologic response simultaneously. Physically based models
should therefore utilize both spatial and stochastic data where scale
appropriate. Other implications for physically based modeling are that
modeling algorithms should reflect larger-scale variability which
generally has greater impact and that model and measurement grids should
be consistent with the nature of variability.
Correlation and correlation-based measures (e.g., the coefficient of determination) have been widely used to evaluate the "goodness-of-fit" of hydrologic and hydroclimatic models. These measures are oversensitive to extreme values (outliers) and are insensitive to additive and proportional differences between model predictions and observations. Because of these limitations, correlation-based measures can indicate that a model is a good predictor, even when it is not. In this paper, useful alternative goodness-of-fit or relative error measures (including the coefficient of efficiency and the index of agreement) that overcome many of the limitations of correlation-based measures are discussed. Modifications to these statistics to aid in interpretation are presented. It is concluded that correlation and correlation-based measures should not be used to assess the goodness-of-fit of a hydrologic or hydroclimatic model and that additional evaluation measures (such as summary statistics and absolute error measures) should supplement model evaluation tools.
The event-based Agricultural Non-Point Source (AGNPS) pollution model is used extensively to simulate sud~ice runoff, sediment yield and nutrient transport in unmonitored watersheds. Investigation, that compare AGNPS predictions to measured data are rare. The objective of the present study was to compare surface runoff and sediment yield predictions from AGNPS water quality simulation model and modified versions to measured data. Shortcomings of the AGNPS model were examined. The study was carried out using 52 rainfall-runoff events, 22 for calibration and 30for validation, from two small watersheds (GI and G2) in Bavaria, Germany. Evaluation of model outputs was based on statistical comparisons between measured and predicted values fior each rainfall-runoff event. We compared three different surface runoff prediction methods: uncalibrated curve number (Q]), calibrated curve number (Q2), and Lutz (Q3). The modifications made to sediment yield calculations encompassed: (i) replacement of the Universal Soil Loss Equation LS fiactor algorithm (SI) by one based on stream power theory (S2), and (ii) linkage of channel erosion by individual categories of particle size to runoff velocity (S3). Measured median for surface runoff was under-predicted by 55.5% using Q1, overpredicted by 36.8% using Q2 and over-predicted by 13. 1 % using Q3 in G1. The largest coefficient of efficiency (E) was calculatedfor Q3 with 0.96 followed by 0.93 for Q2 and 0.25 for QJ in Gl. In G2, measured median for surface runoff was underpredicted by 80.0% using Q1, overpredicted by 45.0% using Q2, and overpredicted by 35.0% using Q3 in G2. Best performance in terms E was calculated by Q3 (0.83) followed by 0. 76 for Q2 and 0.24 for Q1 in G2. Median sediment yield measurement was underpredicted by 57.2% using S1, underpredicted by 47.6% using S2 and underpredicted by 4.8% using S3 in G1. The largest E was calculated with 0. 90 for S3 followed by 0.57for S2 and 0. 26 for S1 in G1. Measured median for sediment yield was underpredicted by 53.9% using S1, underpredicted by 38.5% using S2 and overpredicted by 3.3% using S3 in G2. E was largest with 0. 72 (S3) followed by 0.60 (S2) and 0.57 (SI) in G2. Results of this study illustrated that a calibration Qf CN and Lutz method for surface runoff calculations and the use of variant S3 for sediment yield calculations with AGNPS model showed the highest merit to match measurements with predictions at the drainage outlet. Sediment yield. The event-based Agricultural Non-Point Source The"AGNPS) pollution model (Young et al., 1987, 1994) was designed to predict runoff volume, peak flow rate, sediment, and nutrient yield from medium to large-sized watersheds. The philosophy in developing AGNPS was to balance model complexity and model parameterization. A major objective was to describe major transport processes related to non-point source pollution within a landscape while using empirical and quasi-physically based algorithms. Basic model components include hydrology, sediment, and nutrient transport.
1] In Earth and ecological sciences, an important, crosscutting issue is the relationship between scale and the processes of runoff and erosion. In drylands, understanding this relationship is critical for understanding ecosystem functionality and degradation processes. Recent work has suggested that the effects of scale may differ depending on the extent of degradation. To test this hypothesis, runoff and sediment yield were monitored during a hydrological year on 20 plots of various lengths (1–15 m). These plots were located on a series of five reclaimed mining slopes in a Mediterranean‐dry environment. The five slopes exhibited various degrees of vegetative cover and surface erosion. A general decrease of unit area runoff was observed with increasing plot scale for all slopes. Nevertheless, the amount of reinfiltrated runoff along each slope varied with the extent of degradation, being highest at the least degraded slope and vice versa. In other words, unit area runoff decreased the least on the most disturbed site as plot length increased. Unit area sediment yield declined with increasing plot length for the undisturbed and moderately disturbed sites, but it actually increased for the highly disturbed sites. The different scaling behavior of the most degraded slopes was especially clear under high‐intensity rainfall conditions, when flow concentration favored rill erosion. Our results confirm that in drylands, the effects of scale on runoff and erosion change with the extent of degradation, resulting in a substantial loss of soil and water from disturbed systems, which could reinforce the degradation process through feedback mechanisms with vegetation.
Modeling and monitoring vadose zone processes across multiple scales is a fundamental component of many environmental and natural resource issues including nonpoint source (NPS) pollution, watershed management, and nutrient management, to mention just a few. In this special section in Vadose Zone Journal we present a collection of papers reflecting current trends in modeling and monitoring vadose zone processes from field to landscape scales. The objectives of this introductory paper are to set the stage for the special issue by providing background information, by showing the interrelationship of the papers, and by identifying the significant contribution(s) of each paper. The spectrum of topics covered includes (i) issues of scale, (ii) spatial analysis of model error, (iii) modeling of NPS pollutants and hillslope stability, (iv) the use of estimation and conditioning tools such as upscaling, pedotransfer functions, and generalized likelihood uncertainty estimation, (v) data assimilation in conjunction with flow modeling and passive microwave remote sensing to estimate moisture distribution, (vi) effective hydraulic parameters across spatial scales, (vii) spatiotemporal stability of soil properties (e.g., Cl¿, B, and NO3¿N transport; salinity; and soil physical and hydraulic properties), and (viii) nested sampling to determine spatial patterns. A commonality among the papers, whether for modeling or monitoring vadose zone processes, is the question of how to address complex issues of spatial and/or temporal variability at the scale of interest. Future research will likely involve inverse modeling, the use of multiple sensors to monitor at various scales, and continued applications of pedotransfer functions, upscaling and downscaling, and hierarchy of scales
The sediment discharge component of a watershed simulation model called RUNOFF is presented. The model component uses a runoff simulation component and simulates space and time distributed soil erosion, sediment transport and sediment deposition and computes sediment discharges in a small watershed resulting from a single rainfall event. The model component has two parameters, raindrop detachment and flow detachment coefficients, which are calibrated based on observed sediment discharges. Model validation is demonstrated on the USDA experimental watershed W-5 in Mississippi and sensitivities of the model parameters are analyzed.
A dynamic hydrologic model, which simulates space and time distributed rainfall excess and runoff in a small watershed resulting from a single rainfall event, is presented. The model uses efficient algorithms and requires information on watershed topography, soil and land use characteristics and time varying rainfall records. Since the only model parameters are the SCS runoff curve number and the Manning's roughness coefficient, the model is simpler and easier to apply to watersheds where sufficient data are not available. Model validation is demonstrated on the USDA experimental watershed W-5, Mississippi and sensitivites of the model parameters are analyzed.
This study compared the simulated results from the models, CREAMS, SWRRB, EPIC, ANSWERS and AGNPS with measured data of runoff and sediment yield on an annual and storm rainfall event basis. Results were obtained from a parallel, tile outlet terrace, a flatland watershed, and a small watershed with 3 to 8% slopes - all located in Mississippi. The comparisons showed that no one model worked well in every situation of runoff and sediment yield on the watersheds. Overall, CREAMS and SWRRB produced results that were close to the measured values more often than the other models, even though SWRRB required simpler inputs. AGNPS also produced results that were close to the measured values in many situations. EPIC produced results that were similar to the measured runoff in most situations, but not as good as the other models in predicting sediment yield. Results obtained by ANSWERS were not close to the measured values in most situations.
Land degradation and soil erosion are perceived as important problems in the dryland zones of the Mediterranean. Three-year measurements of hydrological and soil erosion data from a series of nested experimental watersheds in a semi-arid area of SE Spain are discussed. The aim was to study the role and effects of thresholds on the spatial connections between different system compartments, such as response units and sub-catchments that act at different levels of scale (plot to watershed scale). It was also the aim to quantify runoff and erosion at these different scales. Several types of thresholds are described and these are related to vegetation type and pattern, soil surface roughness, distance to the main channel, land use and tillage effects (intrinsic properties of the landscape) as well as rainfall intensity, duration and depth (external influence). The expansion of runoff generating areas under Hortonian overland flow is discussed in relation to vegetation structure and rainfall. Results showed that runoff and sediment yield results highly depend on the vegetation structure. The relation between rainfall intensity and rainfall depth and the hydrological response were established at five levels of scale. Three spatio-temporal process domains were analysed: the spot- and plot-processes at the finest scale, the hillslope, micro- and sub-catchment processes at the intermediate scale and catchment scale and main channel network processes at the broadest scale. An event with a 5-year recurrence period is discussed to illustrate the importance of scale related thresholds, explaining the relative importance of high intensity rainfalls. Soil erosion was found to be a magnitude larger on terraced valley bottoms (2500–3000 gm−2) when compared to the semi-natural hillslopes, where erosion figures were less than 10 gm−2. This indicated that the contribution of sediment from terraced cultivated lands is important and are an underestimated part of the sediment budget of semi-arid catchments.
IGR J17497-2821 (ATel #885) was further observed by INTEGRAL and SWIFT. The source is detected up to 200 keV by INTEGRAL. The ISGRI & JEM-X combined spectrum can be well represented by a powerlaw (index= 1.96+/-0.05) with a low absorption column density (NH
An analytical solution to the kinematic wave approximation for unsteady flow routing is presented. The model allows time-dependent lateral inflow with piecewise spatial uniformity and can be applied to complex kinematic cascades. Kinematic shocks are considered as manifestations of higher-order effects such as rnonoclinal flood waves, bores, etc. Within the context of kinematic approximation therefore we retain their dynamic effects by routing the discontinuities as they appear. Certain simplifying assumptions are made which permit closed form solutions and an efficient numerical algorithm, based on the method of characteristics, is employed. The resulting model, called an approximate shock-fitting scheme, preserves the effect of the shocks without the usual computational complications and compares favorably with an implicit finite difference solution. The efficiency and accuracy of the new method are illustrated by computing a variety of unsteady flows, ranging from simple cascades to complex natural watersheds.
The classical equation for concentration distribution of suspended sediment in open channel flow is valid for both field and laboratory data, provided that the bed material is of uniform size. For heterogeneous bed material, prevailing integration methods do not take into account bed material sorting. In order to evaluate the role of this sorting in influencing relative concentration and mean size profiles of suspended sediment, an integration procedure is outlined which assumes that the sediment sizes (in ϕ units) are normally distributed. Numerical evaluation of the integration equation for selected input values of the relevant variables shows the importance of the sorting factor. The efficacy of this factor depends on the flow strength and mean size of the bed material. In general, the effect of sorting is most pronounced in the case of low flow strength and coarse bed material.
A clear understanding of a model is important for its appropriate use. In this article, eleven watershed scale hydrologic and nonpoint-source pollution models are reviewed: AGNPS, AnnAGNPS, ANSWERS, ANSWERS-Continuous, CASC2D, DWSM, HSPF, KINEROS, MIKE SHE, PRMS, and SWAT. AnnAGNPS, ANSWERS-Continuous, HSPF, and SWAT are continuous simulation models useful for analyzing long-term effects of hydrological changes and watershed management practices, especially agricultural practices. AGNPS, ANSWERS, DWSM, and KINEROS are single rainfall event models useful for analyzing severe actual or design single-event storms and evaluating watershed management practices, especially structural practices. CASC2D, MIKE SHE, and PRMS have both long-term and single-event simulation capabilities. Mathematical bases, the most important and critical elements of these mathematical models, were identified and compiled. In this article, a comprehensive summary of the compilation is presented in tabular form. The flow-governing equations and their solution methods used in each of the eleven models are discussed. The compilation of the mathematical bases of these models would be useful to determine the problems, situations, or conditions for which the models are most suitable, the accuracies and uncertainties expected, their full potential uses and limitations, and directions for their enhancements or new developments. AGNPS, AnnAGNPS, DWSM, HSPF, MIKE SHE, and SWAT were found to have all the three major components (hydrology, sediment, and chemical) applicable to watershed-scale catchments. SWAT is a promising model for continuous simulations in predominantly agricultural watersheds, and HSPF is promising for mixed agricultural and urban watersheds. Among the single-event models, DWSM provides a balance between the simple but approximate and the computationally intensive models and, therefore, is a promising storm event model for agricultural watersheds.
The U.S. Environmental Protection Agency (EPA) has initiated a research project to develop an evaluation framework for the optimal placement of best management practices (BMPs) options at strategic locations in mixed land use urban watersheds. The integrated watershed-based stormwater management decision-support framework (ISMDSF) is to be based on a geographical information system (GIS) watershed/BMP database, cost, and hydrologic, hydraulic, and water quality modeling to achieve desired water quality objectives. The initial phase of this research is expected to be completed in early 2005. While this work is ongoing and many tasks have yet to start, this paper presents the project background, rationale, approach, initial review findings of watershed and BMPs models, and the preliminary design recommendations of the framework.
Hortonian runoff was measured from plots with lengths of 1·25 and 12 m, and at watershed level for rainstorms during the 1996 rainy season in cental Côte d'Ivoire, Africa. A clear reduction in runoff coefficients was found with increasing slope lengths, giving order of magnitude differences between runoff measurements at point level (1 m2: 30–50% of total rain) and watershed level (130 ha: 4% of total rain). Runoff reduction from 1·25 and 12 m slopes was reproduced for each major runoff-producing rainstorm at two different sets of plots, but the reduction was erratic for rainfall events which produced little runoff. In addition, runoff reduction varied wildly from one rainstorm to the next. In the analysis, we show that the spatial variability of runoff parameters causes the erratic behaviour during rainstorms with little runoff. During the more important, larger runoff-producing events, which give 78% of total runoff, the temporal dynamics of the rainfall–runoff process determine the reduction of runoff coefficients from longer slopes. A simple infiltration/runoff model was used to simulate the field results, thereby confirming the importance of rainfall dynamics as an explanatory factor for measured reduction of runoff coefficients. Copyright © 2000 John Wiley & Sons, Ltd.
The performance of a hydrological model is usually assessed first by visual inspection of the measured and computed hydrographs. Numerous statistical criteria are available for numerical evaluations of model accuracy in each single year, in a particular season of the year, or in a sequence of years or seasons. In the last case, the problem of computing the overall result has to be considered. If too many criteria are used and the criteria are switched frequently, an assessment of a model's performance becomes difficult for a potential user. Therefore, this paper concentrates on just three criteria and their combined evaluation: The Nash-Sutcliffe coefficient, which compares the model computed discharge with the average measured discharge; the “coefficient of gain from daily means” in which a uniform average discharge is replaced by daily average discharges; and the volumetric difference between the total measured and computed runoff. The three criteria are combined in a three dimensional representation that allows intercomparisons of model performance in a single diagram.
A series of large rainfall simulator experiments was conducted in 2002 and 2003 on a small plot located in an experimental catchment in the North Island of New Zealand. These experiments measured both runoff and sediment transport under carefully controlled conditions. A physically based hydrological modelling system (SHETRAN) was then applied to reproduce the observed hydrographs and sedigraphs. SHETRAN uses physically based equations to represent flow and sediment transport, and two erodibility coefficients to model detachment of soil particles by raindrop erosion and overland flow erosion. The rate of raindrop erosion also depended on the amount of bare ground under the simulator; this was estimated before each experiment. These erodibility coefficients were calibrated systematically for summer and winter experiments separately, and lower values were obtained for the summer experiments. Earlier studies using small rainfall simulators in the vicinity of the plot also found the soil to be less erodible in summer and autumn. Limited validation of model parameters was carried out using results from a series of autumn experiments. The modelled suspended sediment load was also sensitive to parameters controlling the generation of runoff from the rainfall simulator plot; therefore, we found that accurate runoff predictions were important for the sediment predictions, especially from the experiments where the pasture cover was good and overland flow erosion was the dominant mechanism. The rainfall simulator experiments showed that the mass of suspended sediment increased post-grazing, and according to the model this was due to raindrop detachment. The results indicated that grazing cattle or sheep on steeply sloping hill-country paddocks should be carefully managed, especially in winter, to limit the transport of suspended sediment into watercourses. Copyright © 2006 John Wiley & Sons, Ltd.
Based on recent reviews of 11 physically based watershed models, the long-term continuous model soil and water assessment tool (SWAT) and the storm event dynamic watershed simulation model (DWSM) were selected to examine their hydrologic formulations, calibrate, and validate them on the 620 km(2) watershed of the upper Little Wabash River at Effingham, Ill., and examine their compatibility and benefits of combining them into a more comprehensive and efficient model. Calibration and validation of the SWAT by comparing monthly simulated and observed flows and adjusting the model-assigned resulted in coefficients of determination and Nash-Sutcliffe coefficients for individual years and cumulatively for the calibration period (1995-1999) and for the entire simulation period (1995-2002) mostly above or near 0.50 with an exception of 0.05 and -0.27, respectively, in 2001, relatively a dry year. Visual comparisons of the hydrographs showed SWAT's weakness in predicting monthly peak flows (mostly underpredictions.) Therefore, SWAT needs enhancements in storm event simulations for improving its high and peak flow predictions. Calibration of DWSM was not necessary; its three physically based parameters were taken from SWAT. Validation of DWSM on three intense storms in May 1995, March 1995, and May 2002 resulted 1, -29, and 16% errors in peak flows and 0, -11, and 0% errors in times to peak flows, respectively. Comparisons of DWSM's 15-min flow hydrographs with SWAT's daily flow hydrographs along with the 15-min and daily observed flow hydrographs during the above three storms confirmed that DWSM predicted more accurate high and peak flows and precise arrival times than SWAT. DWSM's robust routing scheme using analytical and approximate shock-fitting solutions of the kinematic wave equations was responsible for the better predictions, the addition of which along with its unique combination with the popular runoff curve number method for rainfall excess computation to SWAT would be a significant enhancement. Parameters and data of both the models are interchangeable and, therefore, are compatible and their combination will result in a more comprehensive and efficient model.
Infiltration through a small (3 × 9 × 1 m) experimental earthen liner, similar to those used for waste disposal was evaluated. The liner was constructed using full-size compaction equipment, and in-situ ponded infiltration rates were measured using two large (1·5-m diameter) sealed double-ring infiltrometers. An average apparent steady-flux density of 1·5 × 10−7 cm/s was achieved after two to three weeks. Wetting front depths of 7·3 cm and 9·6 cm after 46 days were calculated assuming a Green-Ampt piston flow infiltration system. One of the infiltrometers was ponded with water containing rhodamine dye and after the 46-day infiltration test, a uniform rhodamine dye front was observed at about the 4-cm depth. Sharpness of the dye front suggests that the piston flow assumption is a reasonable one. Apparent saturated hydraulic conductivity of the liner was estimated from the infiltration data to be no more than 3·6 × 10−8 cm/s, meeting the present EPA permeability requirement for earthen liners of no more than 1 × 10−7 cm/s. Transit time for the wetting front to reach the liner bottom at the 0·91-m depth was predicted to be about three years. Seepage flux after liner saturation was estimated at 4·8 × 10−8 cm/s for a liner ponded with 30 cm of water.
The analysis of water and element cycling plays a key role in understanding ecosystems. The definition of clearly outlined budget areas is necessary therefore and is usually approached by analysis of natural surface and subsurface watersheds. However, many of the elements of natural watersheds, e.g. structures in the underground section or at the catchment boundaries, are often largely unknown and are very demanding to explore fully. To overcome these disadvantages artificially created systems might be an appropriate alternative. Compared to a natural catchment, the boundaries and inner structures of an artificial watershed can be planned and defined in advance. This paper presents the initial development phase of just such an artificial catchment built for interdisciplinary ecological research. The site covers an area of 6 ha and is one of the largest artificial watersheds worldwide constructed for scientific purposes. It was completed in 2005 and then left to allow an ecosystem to develop without further restrictions. Its initial state allows the detailed investigation of the first steps of ecosystem development. The creation and properties of this site as well as the first results of an ongoing monitoring program are presented here. First analysis of soil conditions, hydrology, geomorphology, and vegetation illustrate the initial state of the site. The substrate can be regarded as almost unweathered material. Initial characteristics were found with respect to the hydrological behavior of the catchment such as only low infiltration rates probably due to still missing preferential flow paths into the substrate which result in a dominant role for surface run-off. Accordingly, a strong relationship exists between rainfall events and changes of the lake's water level. Also the vegetation cover demonstrates that the succession began very close to point zero of the development.
Morphological linkages and discontinuities have been defined in both natural and anthropogenic terms. Such terms are considered useful in understanding the spatial and temporal roles of erosion from source areas, as indicated by linkages, when they are in operation, and by discontinuities, which act as storages or buffers in stabilizing landscapes. The latter slow erosion and promote conservation particularly in Mediterranean areas, where human impacts are thought to be more important than natural processes. These concepts are illustrated by reference to three case studies in the Durance Valley: in a part of a Mediterranean landscape, on a floodplain segment and along of the main channel. While there are major concerns in more semiarid parts of these seasonally dry zones, present conditions in the more humid south of France, supplied also by exotic upper catchments, are under less threat of degradation. This is until such times when water shortages may occur, due to changed regimes, as anticipated in the predicted global warming climate changes, and by the continuing development in this area.
Laboratory and small-scale field observations have yielded fundamental insights into the causes of nitrate pollution. Detection of downstream, off-site impacts of nitrate pollution reveals its effects. However, there is a gulf in our knowledge and practice that prevents the expertise gained at the small-scale from contributing to a sound scientific basis for planning at the catchment scale. Many modellers may thus rely on simple empirical models when simulating nitrate pollution at the catchment scale as these models can reflect their judgments and uncertainties. Other modellers struggle to apply physically-based, distributed models within complex, three-dimensional heterogeneous landscapes, inducing equifinality and predictive uncertainty problems. One way for planners and scientists to advance is to create scale appropriate modelling techniques, which can call upon a range of model types [including complex physically-based, quasi-physical, semi-distributed models and lumped Minimum Information Requirement (MIR) models]. This paper argues that the modeller must use the appropriate model type, at the appropriate scale, in order to best understand nitrate losses observed at that scale. When simulating at the catchment scale, the modeller must accept that there are processes that are not fully understood and cannot be modelled with accuracy, yet the modeller must still produce decision support tools that are capable of solving real world problems, despite inherent model uncertainty. Thus, this paper will show, through a fully worked example, how hydrological flow paths and nitrate pollution sources can be simulated at the catchment scale by first, reflecting our understanding of the physical world and second paying full respect to catchment scale issues and uncertainty problems. The River Great Ouse (1400 km2) case study is a typical intense arable region of the UK, where the available data sources are by no means perfect, but where nitrate policy must still be implemented. Thus, physically-based model simulations, simple MIR models, GIS data sources and ‘expert’ knowledge are brought together to create a simple, applied modelling toolkit to simulate nitrate pollution and support catchment policies that reduce the loss of nitrate to rivers.
The effects of different vegetation types on runoff generation and soil erosion were investigated. The study was conducted at the Southern part of West Bank, about 10 Km north-west of Hebron city, during 2005, 2006 and 2007. Five treatments were implemented; forests planted with P. halepensis (F), natural vegetation dominated by S. spinosum (W.S), natural vegetation where S. spinosum was removed (W/o.S), cultivated land (C), and deforestation (Df). Three types of data were estimated in each plot: runoff after each rainfall event, sedimentation at the end of the rainy season, and chemical and physical soil properties. The obtained results indicate that there are significant and important differences in runoff generation and sediment production with respect to the different types of vegetative cover. Forest and natural vegetation dominated by S. spinosum treatments exhibited the lowest amounts of runoff, with averages of 2.02 and 1.08 mm, respectively, in comparison to other treatments. The removal of S. spinosum significantly increased the total amount of runoff and sedimentation compared to the forest and S. spinosum treatments. In addition, runoff significantly increased (4.03 mm) for the Df treatment compared to that of the forest site. The greatest amount of sedimentation was observed in cultivated land and with deforestation.The forest and S. spinosum treatments exhibited the highest percentages of organic matter of the five investigated treatments.The results indicate that forests and natural vegetation dominated by S. spinosum prevent or decrease the risk of runoff and soil erosion. In conclusion, the removal of S. spinosum and forest trees as a means to improve rangeland productivity increases runoff and sediment fluxes if not accompanied by careful grazing management. In addition, interchangeably using arid and semi-arid lands as rangeland and for cultivation may have significant negative impacts on the production potential of these lands.
Measurements of surface runoff from uniform slopes of different lengths in West Africa have shown that longer slopes tend to have less runoff per unit of length than short slopes. The main reason for this scale effect is that once the rain stops, water on long slopes has more opportunity time to infiltrate than water on short slopes. A validated simple model is put forward that quantifies the scale effects and predicts under which circumstances they can be expected to be most significant. An overview is given of management options that are available to farmers to reduce runoff at the field and slope level. The potential effects of these management options on the hydraulic conductivity, Ksat, and Manning's roughness coefficient, n, are qualified. The model is subsequently used to calculate the effect of changes in Ksat and n on the runoff from slopes under rainfall conditions found in West Africa. Finally, two design examples are given, namely maximum field lengths and dimensioning of interceptor drains.
The principles governing the application of the conceptual model
technique to river flow forecasting are discussed. The necessity for a
systematic approach to the development and testing of the model is
explained and some preliminary ideas suggested.
Mechanisms and Control of Agricultural Nonpoint Source Pollution under Infiltration Excess Runoff Pattern, North China. PhD Dissertation
- X H Wang
Wang, X.H., 2004. Mechanisms and Control of Agricultural Nonpoint Source Pollution under Infiltration Excess Runoff Pattern, North China. PhD Dissertation. Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Beijing, China.
Porous City: A Multiscale Modelling of Peri-urban Hydrology
- D Schertzer
- I Tchiguirinskaia
- E Ei-Tabach
Schertzer, D., Tchiguirinskaia, I., EI-Tabach, E., 2008. Porous City: A Multiscale Modelling of Peri-urban Hydrology. Geophysical Research Abstracts, vol. 10, EGU2008-A-11454.
Negotiating with Nature: The Evolution of Urban Parks in the Twin Cities. Honors Projects. Paper 2 Scale effects of Hortonian overland flow and rainfall–runoff dynamics in a West African catena landscape
- A A Trahan
Trahan, A.A., 2007. Negotiating with Nature: The Evolution of Urban Parks in the Twin Cities. Honors Projects. Paper 2. <http://digitalcommons.macalester.edu/ envi_honors/2>. van de Giessen, N.C., Stomph, T.J., de Ridder, N., 2000. Scale effects of Hortonian overland flow and rainfall–runoff dynamics in a West African catena landscape. Hydrol. Process. 14, 165–175.
Hydrologic and water quality model for tile drained watersheds in Illinois. Paper presented at
- D K Borah
- R Xia
- M Bera
Borah, D.K., Xia, R., Bera, M., 2000. Hydrologic and water quality model for tile drained watersheds in Illinois. Paper presented at 2000 ASAE Annual International Meeting, Milwaukee, Wisconsin, USA. Borah, D.K., Xia, R., Bera, M., 2002. DWSM-A dynamic watershed simulation model.
Computer Models of Watershed Hydrology Water Resources Publications, Highlands Ranch Mathematical Models of Large Watershed Hydrology Mathematical Models of Small Watershed Hydrology and Applications Urbanization in China: Critical Issue in an Era of Rapid Growth
- V P Singh
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Singh, V.P., 1995. Computer Models of Watershed Hydrology. Water Resources Publications, Highlands Ranch, Colo. Singh, V.P., Frevert, D.K., 2002a. Mathematical Models of Large Watershed Hydrology. Water Resources Publications, Highlands Ranch, Colo. Singh, V.P., Frevert, D.K., 2002b. Mathematical Models of Small Watershed Hydrology and Applications. Water Resources Publications, Highlands Ranch, Colo. Song, Yan, Ding, Chengri, 2007. Urbanization in China: Critical Issue in an Era of Rapid Growth. Lincoln institute of Land policy, USA.
A study on storm and rainfall pattern in Beijing city
- M Wang
- X C Tan
Wang, M., Tan, X.C., 1994. A study on storm and rainfall pattern in Beijing city. Hydrology 3, 1–6.
Municipal Storm Water Management
- T N Debo
- A J Reese
Debo, T.N., Reese, A.J., 2002. Municipal Storm Water Management, second ed. USA CRC Press, Washington, DC.
Hydrologic Modeling of the Court Creek Watershed Contract Report 2000–04, Illinois State Water Survey Watershed-scale hydrologic and nonpoint-source pollution models: review of mathematical bases
- D K Borah
- M Bera
Borah, D.K., Bera, M., 2000. Hydrologic Modeling of the Court Creek Watershed. Contract Report 2000–04, Illinois State Water Survey, Champaign, IL. Borah, D.K., Bera, M., 2003. Watershed-scale hydrologic and nonpoint-source pollution models: review of mathematical bases. Trans. ASAE 46 (6), 1553–1566.