[Show abstract][Hide abstract] ABSTRACT: Soil erosion is the root cause of environmental and ecological degradation in the Loess Plateau of the Yellow River. Watershed sediment dynamics was fully analyzed here, and a physically based, distributed, and continuous erosion model at the watershed scale, named the Digital Yellow River Integrated Model (DYRIM), was developed. The framework, the key supporting techniques, and the formulation for natural processes were described. The physical processes of sediment yield and transport in the Loess Plateau are divided into three subprocesses, including the water yield and soil erosion on hillslopes, gravitational erosion in gullies, and hyperconcentrated flow routing in channels. For each subprocess, a physically based simulation model was developed and embedded into the whole model system. The model system was applied to simulate the sediment yield and transport in several typical years in different watersheds of the Yellow River, and the simulation results indicated that this model system is capable of simulating the physical processes of sediment yield and transport in a large-scale watershed.
Advances in Water Resources Engineering, Edited by Chih Ted Yang, Lawrence K. Wang, 01/2015: pages 1-40; Springer International Publishing., ISBN: 978-3-319-11022-6
[Show abstract][Hide abstract] ABSTRACT: This paper develops an algorithm for computing spatially distributed monthly potential evaporation (PE) over a mountainous region, the Lhasa River basin in China. To develop the algorithm, first, correlation analysis of different meteorological variables was conducted. It is observed that PE is significantly correlated with vapor pressure and temperature differences between the land surface and the atmosphere. Second, Dalton model, which was developed based on mass transfer mechanism, was modified by including the influences of the related meteorological variables. Third, the influences of elevation on monthly temperature, vapor pressure and wind velocity were analyzed, and the functions for extending these meteorological variables to any given altitude were developed. Fourth, the inverse distance weighting method was applied to integrate the extended meteorological variables from five stations adjacent to and within the Lhasa River basin. Finally, using the modified Dalton model and the integrated meteorological variables, we computed the spatially distributed monthly PE. This study indicated that spatially distributed PE can be obtained using data from sparse meteorological stations, even if only one station is available; the result showed that in the Lhasa River basin PE decreases when elevation increases. The new algorithm, including the modified model and the method for spatially extending meteorological variables, developed in this paper can provide the basic inputs for distributed hydrological models.
[Show abstract][Hide abstract] ABSTRACT: Water use efficiency is a critical index for describing carbon-water coupling in terrestrial ecosystems. However, the nonlinear effect of vapor pressure deficit (VPD) on carbon-water coupling has not been fully considered. To improve the relationship between gross primary production (GPP) and evapotranspiration (ET) at the sub-daily time scale, we propose a new underlying water use efficiency (uWUE = GPP · VPD0.5/ET) and a hysteresis model to minimize time lags among GPP, ET, and VPD. Half-hourly data were used to validate uWUE for 7 vegetation types from 42 AmeriFlux sites. Correlation analysis shows that the GPP · VPD0.5 and ET relationship (r = 0.844) is better than that between GPP · VPD and ET (r = 0.802). The hysteresis model supports the GPP · VPD0.5 and ET relationship. As uWUE is related to CO2 concentration, its use can improve estimates of GPP and ET, and help understand the effect of CO2 fertilization on carbon storage and water loss.
[Show abstract][Hide abstract] ABSTRACT: With rapid socio-economic development over the past three decades in China, adverse effects of human activities on the natural ecosystem are particularly serious in arid regions where landscape ecology is fragile due to limited water resources and considerable interannual climate variability. Data on land use, surface and ground water, climate, gross domestic product (GDP) per capita from the middle Heihe River Basin were used to (i) examine changes in water consumption, land use composition, and vegetation cover; (ii) evaluate the effectiveness of short-term management strategies for environmental protection and improvement, and (iii) apply and extend the environmental Kuznets curve (EKC) framework to describe the relationship between economic development and environmental quality in terms of the normalized difference vegetation index (NDVI). The results showed that with rapid development of agriculture and economy, land use change for the period 1986–2000 was characterized by the expansion of constructed oases, considerable contraction of oasis-desert transitional zone and natural oases. This has led to a decrease in ecosystem stability. Since 2001, effective basin management has brought about improved environment conditions, with a more optimal hierarchical structure of vegetation cover. The original EKC model could not explain most of the observed variation in NDVI (R2 = 0.37). Including additional climate variables, the extended EKC model to explain the observed NDVI was much improved (R2 = 0.78), suggesting that inclusion of biophysical factors is a necessary additional dimension in the relationship between economic development and environmental quality for arid regions with great climate variability. The relationship between GDP per capita and NDVI, with the effect of precipitation and temperature taken into consideration, was adequately described by an N-shaped curve, suggesting that the relationship between society and the environment followed a process of promotion, contradiction, and coordination.
[Show abstract][Hide abstract] ABSTRACT: This paper develops a parallel dynamic programming algorithm to optimize the joint operation of a multi-reservoir system. First, a multi-dimensional dynamic programming (DP) model is formulated for a multi-reservoir system. Second, the DP algorithm is parallelized using a peer-to-peer parallel paradigm. The parallelization is based on the distributed memory architecture and the message passing interface (MPI) protocol. We consider both the distributed computing and distributed computer memory in the parallelization. The parallel paradigm aims at reducing the computation time as well as alleviating the computer memory requirement associated with running a multi-dimensional DP model. Next, we test the parallel DP algorithm on the classic, benchmark four-reservoir problem on a high-performance computing (HPC) system with up to 350 cores. Results indicate that the parallel DP algorithm exhibits good performance in parallel efficiency; the parallel DP algorithm is scalable and will not be restricted by the number of cores. Finally, the parallel DP algorithm is applied to a real-world, five-reservoir system in China. The results demonstrate the parallel efficiency and practical utility of the proposed methodology.
Advances in Water Resources 05/2014; 67:1-15. · 2.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper develops a methodology for optimizing the hydro unit commitment (HUC) for the Three Gorges Project (TGP) in China. The TGP is the world's largest and most complex hydropower system in operation. The objective is to minimize the total operational cost. The decision variables are the startup or shutdown of each of the available units in the system and the power releases from the online units. The mathematical formulation must take into account the head variation over the operation periods as the net head changes from hour to hour and affects power generation. Additionally, the formulation must consider the operation of 32 heterogeneous generating units and the nonlinear power generation function of each unit. A three-dimensional interpolation technique is used to accurately represent the nonlinear power generation function of each individual unit, taking into account the time-varying head as well as the non-smooth limitations for power output and power release. With the aid of integer variables that represent the on/off and operation partition statuses of a unit, the developed HUC model for the TGP conforms to a standard mixed integer linear programming (MILP) formulation. We demonstrate the performance and utility of the model by analyzing the results from several scenarios for the TGP.
IEEE Transactions on Power Systems 11/2013; PP(99):1-10. · 2.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The distributed basin model (DBM) has become one of the most effective tools in river basin studies. In order to overcome the efficiency bottleneck of DBM, an effective parallel-computing method, named temporal-spatial discretization method (TSDM), is proposed. In space, TSDM adopts the sub-basin partitioning manner to the river basin. Compared to the existing sub-basin-based parallel methods, more computable units can be supplied, organized and dispatched using TSDM. Through the characteristic of the temporal-spatial dual discretization, TSDM is capable of exploiting the river-basin parallelization degree to the maximum extent and obtaining higher computing performance. A mathematical formula assessing the maximum speedup ratio (MSR) of TSDM is provided as well. TSDM is independent of the implementation of any physical models and is preliminarily tested in the Lhasa River basin with 1-year rainfall-runoff process simulated. The MSR acquired in the existing traditional way is 7.98. Comparatively, the MSR using TSDM equals to 15.04 under the present limited computing resources, which appears to still have potential to keep increasing. The final results demonstrate the effectiveness and applicability of TSDM.
[Show abstract][Hide abstract] ABSTRACT: Static armored gravel surfaces composed of man-made and natural gravels have been analyzed using precise digital elevation models. The scaling behavior and spatial arrangement of the gravel surfaces were evaluated and discussed with respect to the successive formation of stable armor layers. The key results relate to structure functions and imbrication analysis of these surfaces: (1) man-made gravel surfaces show a similar scaling behavior and spatial correlation pattern to natural gravel surfaces; (2) man-made gravel surfaces have larger Hurst exponents than natural gravel surfaces; and (3) man-made gravels are poorly imbricated in comparison with natural gravels. Our results suggest that different morphological structures between man-made and natural gravels were attributed to shape features of individual grains.
[Show abstract][Hide abstract] ABSTRACT: River coding method for drainage networks plays an very important role in the physical simulation of river basins. In this study we developed a new river coding method named Multi-tree Coding Method (MCM), which has the following features: (1) it is established on a topological pattern reflecting the dendriform structure of drainage networks; (2) the multi-tree code can be effectively managed by the database to perform convenient topological search toward drainage networks using Structured Query Language (SQL); (3) the multi-tree code does not exhibit digital overflow problems in the computer, thus any resolution and scale drainage networks can easily be coded; and (4) it supports high-efficient search process. A river reach can be directly positioned in a drainage network under MCM, without the complex search process from all river reaches. This feature has great potential to improve the computational performance of basin models. We demonstrate here the efficiency and practicality of MCM by testing it in the Yalu Tsangpo river basin, Tibet. A drainage network with 140,745 digital reaches was extracted from the digital elevation model (DEM), and the multi-tree codes of all river reaches were obtained.
[Show abstract][Hide abstract] ABSTRACT: Imbrication of static armor surfaces is investigated based on laser-scanned DEMs collected from both flume experiments and the field. Two approaches are employed to study the imbrication including inclination index and aspect and slope (AS) method. The inclination index is found to be a sensitive and valid method for indicating the existence of imbrication. Application of this method, however, requires high-resolution surfaces. A positive relationship is obtained between the inclination index and effective grain size, which can be used to deduce the historical armoring shear stress. The AS method based on the statistics of local gradients describes the imbrication in a more straightforward way. However, this method is based on the statistics of orientations of grids rather than individual grains. An improved AS method is proposed in this study based on orientations of grains with the help of automated grain segmentation method. The improved AS method makes this method more reasonable and increases the applicable range.
Geomorphology 07/2012; s 159–160:116–124. · 2.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Roughness of successively developed gravel surfaces in flume experiments is investigated using laser scanned elevation fields. Scaling behavior of these surfaces is studied using structure functions. The results show that all surfaces exhibit good scaling behavior for two scaling regions. Multifractal analysis based on singular measures is then conducted for the two scaling regions, respectively. The relatively smaller scaling region characterizing subgrain scale roughness exhibits evident nonstationarity and intermittency. In contrary, the measures for the larger scaling region characterizing the spatial distribution of grains are more stationary and less intermittent than the measures for the subgrain scaling region.
[Show abstract][Hide abstract] ABSTRACT: Physically based modeling approach has been widely developed in recent years for simulation of dam failure process resulting
from overtopping flow. Due to the lack of field data, there exist few applications to natural quake dams with complex erosion
mechanisms. This paper presents a physically based simulation of the failure process of the Tangjiashan Quake Dam formed as
a result of the “May 12, 2008” Wenchuan earthquake in China. The one-dimensional model adopted features as cost saving but
enables capturing the main characteristics of the failure process, where selective sediment transport and gravitational slope
collapse are accounted for. The simulated flow hydrograph and breach progression process are generally in good agreement with
the observed data. Unsteadiness and non-uniformity are found to be substantial characteristics of breach progression during
the failure process of natural quake dams. Sensitivity analysis showed that the Manning resistance coefficient and the erodibility
coefficient in Osman and Thorne’s (J Hydraul Eng 114(2):134–150, 1988) model significantly influences the flow peak discharge but has less influence on its occurrence time, while the velocity
lag coefficient associated with bed-load transport may affect the two breaching parameters substantially.
[Show abstract][Hide abstract] ABSTRACT: Restricted computational capacity has become a key factor in limiting the development of a majority of distributed basin models. Parallel computing is one of the most effective methods for solving this problem. Although many parallel-computing methods have been employed in basin models, few studies have carried out theoretical research on parallel characteristics of river basins. In this paper, the drainage network of river basins is treated as a binary-tree structure. Using the binary-tree theory, we find that there exists a maximum speedup curve (MSC) for an arbitrary drainage network. The x-coordinate of the MSC represents the number of processors used during the computing, while the y-coordinate corresponds to the maximum speedup ratio (MSR) that can be obtained. Under several essential assumptions, the theoretical function of MSC is established. The function indicates that the MSC consists of an ascending section and a horizontal section. A parallel algorithm capable of acquiring the MSC is proposed as well. Using this algorithm, the MSC is tested at two different-resolution drainage networks of the Lhasa River Basin. A 2-year rainfall-runoff process is simulated. The results prove the existence of MSC. However, primarily influenced by the load imbalance of subbasins, the simulation values of MSR are usually smaller than the theoretical ones.
[Show abstract][Hide abstract] ABSTRACT: This paper introduces the development of a dynamic parallel algorithm for conducting hydrological
model simulations. This new algorithm consists of a river network decomposition method and an
enhanced mastereslave paradigm. The decomposition method is used to divide a basin river network
into a large number of subbasins, and the enhanced mastereslave paradigm is adopted to realize the
function of this new dynamic basin decomposition method through using the Message-Passing Interface
(MPI) and Cþþ language. This new algorithm aims to balance computation load and then to achieve
a higher speedup and efficiency of parallel computing in hydrological simulation for the river basins
which are delineated by high-resolution drainage networks. This paper uses a modified binary-tree
codification method developed by Li et al. (2010) to code drainage networks, and the basin width
function to estimate the possible maximum parallel speedup and the associated efficiency. As a case
study, with a hydrological model, the Digital Yellow River Model, this new dynamic parallel algorithm is
applied to the Chabagou basin in northern China. The application results reveal that the new algorithm is
efficient in the dynamic dispatching of simulation tasks to computing processes, and that the parallel
speedup and efficiency are comparable with the estimations made by using the basin width function.
Environmental Modelling and Software 12/2011; 26(12):1736-1746. · 3.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Many urban nonpoint source pollution models utilize pollutant buildup and washoff functions to simulate storm runoff quality of urban catchments. In this paper, two urban pollutant washoff load models are derived using pollutant buildup and washoff functions. The first model assumes that there is no residual pollutant after a storm event while the second one assumes that there is always residual pollutant after each storm event. The developed models are calibrated and verified with observed data from an urban catchment in the Los Angeles County. The application results show that the developed model with consideration of residual pollutant is more capable of simulating nonpoint source pollution from urban storm runoff than that without consideration of residual pollutant. For the study area, residual pollutant should be considered in pollutant buildup and washoff functions for simulating urban nonpoint source pollution when the total runoff volume is less than 30 mm.
[Show abstract][Hide abstract] ABSTRACT: Restricted computing power has become one of the primary factors obstructing advancement in basin simulations for majority of hydrological models. Parallel computing is one of the most available approaches to solve this problem. Using binary-tree theory, we present in this study a common parallel computing framework based on the message passing interface (MPI) protocol for modeling hydrological processes of river basins. A practical and dynamic spatial domain decomposition method, based on the binary-tree structure of the drainage network, is proposed. This framework is computationally efficient, and is independent of the type of physical models chosen. The framework is tested in the Chabagou river basin of China, where two years of runoff processes of the entire basin were simulated. Results demonstrate that the system may provide efficient computing performance. However, primarily because of the constraint of the binary-tree structure for drainage network, this study finds that unlimited enhancement of computing efficiency is impossible to realize.
[Show abstract][Hide abstract] ABSTRACT: The particular challenges of modeling control systems for the middle route of the south-to-north water transfer project are
illustrated. Open channel dynamics are approximated by well-known Saint-Venant nonlinear partial differential equations. For
better control purpose, the finite difference method is used to discretize the Saint-Venant equations to form the state space
model of channel system. To avoid calculation divergence and improve control stability, balanced model reduction together
with poles placement procedure is proposed to develop the control scheme. The entire process to obtain this scheme is described
in this paper, important application issue is considered as well. Experimental results show the adopted techniques are properly
used in the control scheme design, and the system is able to drive the discharge to the demanded set point or maintain it
around a reasonable range even if comes across big withdrawals.
Keywordsthe south-to-north water transfer project–control scheme–Saint-Venant equations–model reduction–pole placement
Science China Technological Sciences 01/2011; 54(4):781-792. · 1.19 Impact Factor