Watersheds In Semi-arid Regions Research Articles

Soil loss estimation using RUSLE model: Comparison of conventional and digital soil data at watershed scale in central Iran

Sustainable agriculture and eco-environment conservation face constant threats from soil erosion in mountainous regions. This study aimed to predict soil loss in the mountainous watershed by applying the Revise Universal Equation Soil Loss (RUSLE) and Sediment Delivery Ratio (SDR) models and to evaluate the efficacy of the RUSLE model through the observed data in a hydrometric station. Comparing a polygonal, and a digital soil map (prepared by the Kriging method) for deriving the K factor to estimate soil loss was another objective of the recent research. In this study, two scenarios were examined for the calculation of spatial variation of the K-factor; scenario I comprised soil data derived from a legacy soil map with eight soil units and the data from their representative soil profiles (i.e., traditional soil survey), and scenario II comprised K-factor derived from 100 studied sites using kriging technique (i.e., digital soil survey). The results of RUSLE modeling showed that there was no significant difference between scenario I (7.97 t/(ha. yr)) and scenario II (7.93 t/(ha. yr)) for predicting soil loss with the RUSLE model. This finding confirms that the RUSLE model with limited and legacy data can provide a reliable prediction of soil loss in the given watershed. Moreover, long and short-term periods were used to estimate soil loss, while in the long-term period, estimated soil loss had higher accordance with actual soil loss. Sediment delivery ratio was calculated using models of Vanoni, Boyce, USDA-SCS, and Slope-based models. The results indicated that the Slope-based model had the highest fitness (R2=0.946, ME=0.27, and RMSE=0.275 for scenario I and R2=0.9443, ME=0.26 and RMSE=0.40 for scenario II), with observed sedimentation rate at the hydrometric station at the outlet of the watershed. Overall, predicted soil loss severity map using the traditional soil map by RUSLE model could provide trustworthy information for decision makers and governors at the given and similar watersheds in semiarid regions.

Flood forecasting with a dam watershed event-based hydrological model in a semi-arid context: case study in Morocco

Abstract Event-based rainfall-runoff mechanism modeling is a very useful process for flood forecasting, in particular at the level of the dam watersheds in semi-arid regions. In this regard, this paper presents a flood modeling application in the Sidi Mohammed Ben Abdellah (SMBA) dam watershed in Morocco, using the HEC-HMS model. The Soil Conservation Service (SCS) Curve Number (CN), the SCS Unit hydrograph, and the Recession were chosen as loss, transform, and baseflow methods respectively. The various frequency floods entering the SMBA dam were simulated using the elaborated model. The results show that it is possible to estimate the volumes of water generated during floods satisfactorily with errors of 6–11%, while the error in peak flow is around 20%. The median NSE, during validation, is 0.58 and the R2 is about 0.67. Sensitivity analysis shows that the runoff volume, the peak flow, and the NSE were found to be more sensitive to lag time and CN parameters. The developed event-based model will make it possible to carry out several simulations allowing the assessment of the North to South Water Transfer Project operation, in particular, the SMBA dam reservoir management during the flood periods.

Impact of rainfall spatiotemporal variability and model structures on flood simulation in semi-arid regions

The spatiotemporal heterogeneity in precipitation and underlying surfaces and hybrid runoff generation mechanism make hydrological modelling and forecasting in semi-arid regions becoming a challenging work. Therefore, to provide a reference for the development of hydrological models in such regions, two nested hydrological experimental watersheds in semi-arid regions were selected for attribution analysis. Based on the concept of large-sample hydrology, large-scale numerical simulation experiments were performed by constructing different spatial and temporal scale rainfall schemes and combining three hydrological models with different runoff generation mechanisms. Finally, the influences of the time step, station density, and model structure on the flood simulations in semi-arid regions were evaluated. The spatial interpolation technique was used simultaneously to describe the high-dimensional complicated nonlinear relationships between the influencing factors and simulation results. The results show the following: (1) the flood simulation accuracy was more sensitive to the time step than the spatial station density of the rainfall schemes and was highly dependent on the time step of the original observation data, and (2) compared with the accuracy of the rainfall schemes, the model structure plays a dominant role in flood simulation accuracy. Thus, the hybrid model has significant potential for flood forecasting in semi-arid regions by combining different runoff generation mechanisms. (3) The spatial interpolation technique based on the k-nearest neighbour algorithm can construct a high-dimensional distribution between the influencing factors and model simulation accuracy, and describe the complicated relationships among the time step, station density, model structure, and flood simulations.

Institutional performance and participatory paradigms: Comparing two groups of watersheds in semi-arid region of India

Watershed development programmes carried out in different agroclimatic conditions in India resulted in beneficial impact in terms of productivity enhancement and natural resources conservation, but less attention paid to institutional and participatory aspects. This paper explored the performance of various institutions regarding execution of watershed development programmes in semi-arid region of India. Recorded observations from documents maintained at watershed level and information collected through primary survey as well as focus group discussion with different types of stakeholders were used for analysis. The results indicated lacunae in participatory aspects during programme implementation process like monitoring activities, management of common property resources and equity. Gap in linkages and differential level of performance of various watershed level functionaries indicates the necessity for corrections in the structures and linkages pattern for sustainability of the infrastructure and institutions. The study also showed unequal priorities by the implementing agencies towards institutions, land and water resources development, production enhancement activities and fodder resources development as well as rationalities of technical, economic, financial, political and social aspects among the watersheds.

Hyper-concentrated flow response to aeolian and fluvial interactions from a desert watershed upstream of the Yellow River

Aeolian and fluvial interactions (AFIs) are critical earth-surface processes in arid zones, especially in desert watersheds. The response of hyper-concentrated flows to seasonal alternate AFIs shows very high rates of sediment transport and has important environmental and ecological consequences from local to global scales. Here, we present the aeolian processes-induced hyper-concentrated (AHC) flows that occurred in the Sudalaer desert watershed upstream of the Yellow River, which primarily transport non-cohesive coarse aeolian sand (>0.08mm) and show a peak suspended sediment concentration (SSC) of 1.1 to 1.4×106mgl−3. Our field study and theoretical analysis indicate that non-cohesive coarse aeolian sand downstream in the channel can be entrained from the bed and can be suspended in the turbulent flow by the significant runoff generated upstream with a SSC γ0 value of 0.5×106mgl−3. Severe aeolian processes can provide an abundant coarse sediment supply in the channel, which, once entrained, can also trigger and promote the development of AHC flows. We define, for the first time, the ratio of the weight percentage of coarse sediment to fine sediment C>0.08mm/C<0.05mm as the optimal grain size indicator (OGI) in suspended sediment, indicating that, as the fraction of coarse sediment increases, the significant runoff gradually changes to hyper-concentrated flows and reaches the peak SSC when OGI=3.25. Due to the high frequency of sandstorms and the infrequency of rainstorms, most of the significant rainfall-induced runoff with a certain SSC γ0 can develop into AHC flows and can substantially contribute to the total sediment yield, even leading to deleterious effects on the downstream river system and ecology. Compared with other desert watersheds in semiarid regions, we propose that a SSC γ0 of 500kgm−3 is the threshold criteria for the occurrence of AHC flows in the arid desert watersheds. Comprehensive governing of soil erosion in the upstream gully-dissected slopes is an essential and effective measure for controlling AHC flows.

Comparison of deep soil moisture in two re-vegetation watersheds in semi-arid regions

Soil moisture stored below rainfall infiltration depth is a reliable water resource for plant growth in semi-arid ecosystems. Along with the large-scale ecological restoration in Chinese Loess Plateau, identifying the ecohydrological response to human-introduced vegetation restoration has become an important issue in current research. In this study, soil moisture data in depth of 0-5 m was obtained by field observation and geostatistical method in two neighboring re-vegetation watersheds. Profile characteristics and spatial pattern of soil moisture was compared between different land use types, transects, and watersheds. The results showed that: (1) Introduced vegetation drastically decreased deep soil moisture when compared with farmland and native grassland. No significant differences in deep soil moisture were found between different introduced vegetation types. (2) An analysis of differences in soil moisture for different land use patterns indicated that land use had significant influence on deep soil moisture spatial variability. Land use structure determined the soil moisture condition and its spatial variation. (3) Vegetation restoration with introduced plants diminished the spatial heterogeneity of deep soil moisture on watershed scale. The improvement of land use management was suggested to improve the water management and maintain the sustainability of vegetation restoration. (C) 2014 Elsevier B.V. All rights reserved.

Use of watershed factors to predict consumer surfactant risk, water quality, and habitat quality in the upper Trinity River, Texas

Surfactants are high production volume chemicals that are used in a wide assortment of “down-the-drain” consumer products. Wastewater treatment plants (WWTPs) generally remove 85 to more than 99% of all surfactants from influents, but residual concentrations are discharged into receiving waters via wastewater treatment plant effluents. The Trinity River that flows through the Dallas–Fort Worth metropolitan area, Texas, is an ideal study site for surfactants due to the high ratio of wastewater treatment plant effluent to river flow (> 95%) during late summer months, providing an interesting scenario for surfactant loading into the environment. The objective of this project was to determine whether surfactant concentrations, expressed as toxic units, in-stream water quality, and aquatic habitat in the upper Trinity River could be predicted based on easily accessible watershed characteristics. Surface water and pore water samples were collected in late summer 2005 at 11 sites on the Trinity River in and around the Dallas–Fort Worth metropolitan area. Effluents of 4 major waste water treatment plants that discharge effluents into the Trinity River were also sampled. General chemistries and individual surfactant concentrations were determined, and total surfactant toxic units were calculated. GIS models of geospatial, anthropogenic factors (e.g., population density) and natural factors (e.g., soil organic matter) were collected and analyzed according to subwatersheds. Multiple regression analyses using the stepwise maximum R 2 improvement method were performed to develop prediction models of surfactant risk, water quality, and aquatic habitat (dependent variables) using the geospatial parameters (independent variables) that characterized the upper Trinity River watershed. We show that GIS modeling has the potential to be a reliable and inexpensive method of predicting water and habitat quality in the upper Trinity River watershed and perhaps other highly urbanized watersheds in semi-arid regions.

Two-dimensional simulations of extreme floods on a large watershed

Summary We investigate the applicability of the Two-dimensional, Runoff, Erosion and Export (TREX) model to simulate extreme floods on large watersheds in semi-arid regions in the western United States. Spatially-distributed extreme storm and channel components are implemented so that the TREX model can be applied to this problem. TREX is demonstrated via calibration, validation and simulation of extreme storms and floods on the 12,000 km 2 Arkansas River watershed above Pueblo, Colorado. The model accurately simulates peak, volume and time to peak for the record June 1921 extreme flood calibration and a May 1894 flood validation. A Probable Maximum Precipitation design storm is used to apply the calibrated model. The distributed model TREX captures the effects of spatial and temporal variability of extreme storms for dam safety purposes on large watersheds, and is an alternative to unit-hydrograph rainfall-runoff models.

A daily runoff simulation in semi-arid watersheds based on soil water deficit calculations

Initial soil water content just before a rainfall event is an input required for the calculation of a basin's water balance including infiltration and runoff. However, for most watersheds such information is not available because its evaluation involves a large amount of labor. The objective of this study is to describe a practical model with which to estimate time-dependent changes of a basins soil water content. It is further used for predicting runoff water yield when rainfall depth is the only known component of the water balance equation (WBE). Two distinct cases of the WBE are discussed: (1) a runoff-producing storm; (2) a storm without runoff. Runoff events from four watersheds in southern Arizona were measured throughout 8 to 17 years and analyzed in this study. Rainfall-runoff relationships are described in this model by an empirical quadratic regression equation which includes four parameters. They were estimated by an optimization subroutine which was used to determine the minimum difference between measured and modeled results. The optimized parameters enable simulations of the continuous dynamic change of an index of the soil water content as well as predictions of runoff depths. It was found that the predicted runoff agrees reasonably well with the observed runoff. The minimum coefficient of determination ( r 2) between the computed and actual runoff for the multi-annual data sets was 0.62 and the maximum 0.86. Runoff threshold value was found to be a function of the basin average soil texture. The lowest threshold was 4.6 mm for clay soil and the largest was 9.0 mm for sandy soil. Since direct soil water measurements were not taken, we interpreted the acceptable agreement between measured and predicted runoff as an indirect validation of the soil water model. It is concluded that the model could be useful for extending short records of simulated runoff on nearby ungaged watersheds in semi-arid regions.

Distributed Model for Small Semiarid Watersheds

A distributed model for estimation of runoff volumes and peak rates of flow from small semiarid watersheds is shown to produce reasonable estimates for mean runoff and flood frequency distributions. The model is simplified and constructed to require a minimum of observed data for calibration. The model simulates runoff volume and peak discharge rates for individual storm events. It can also be used to estimate water yield and a surface water balance incorporating transmission losses in ephemeral stream channels. Experimental data are compared with the simulation model predictions. Individual components of the model could be improved with further research and data. However, based on available information contained in soils and topographic maps and published sources, the distributed model can be used to estimate runoff rates and amounts from ungaged watersheds in semiarid regions.