A Dissipative Hydrological Model for the Hotan Oasis (DHMHO)

Various hydrological models have been designed to simulate moisture transformation in the water-cycle system between atmospheric water, surface water, soil water and groundwater. But few have been designed specially for oases in arid desert areas where the ecology and the environment are vulnerable because of unwise water-land resources utilization. In order to analyze the moisture transformation in the Hotan Oasis in the Taklimakan Desert in China, and hence to provide scientific references for the rational exploitation and allocation of the limited water-land resources, for the purpose of ensuring that the vulnerable ecology and environment there can be gradually improved and the social economy there can develop sustainably, a dissipative hydrological model for the Hotan Oasis (DHMHO) was developed. It was an outcome of years of systematic study on the moisture transformation in arid areas and on the water–land conditions in the Hotan Oasis. Based on statistics, DHMHO introduces two empirical equations whereby we dynamically calibrated model parameters with monthly data from year 1971 to 1995. Then the calibrated parameters were used to model the moisture movement from 1996 to 2003 and thereafter rationality check and error analysis were conducted. The error analysis results show that the absolute relative errors between simulated and observed groundwater depth values are almost (11 of 12 points) within 20%, and those in annual watershed outflow simulation are mostly (six of eight points) within 20% with an average annual Nash–Sutcliffe Efficiency Coefficient (NSEC) of 0.80. With DHMHO and IPCC assessment, we also simulated the moisture transformation and dissipation in the Hotan Oasis from the year 2011 to 2020. Results show details of the water resources in the Hotan Oasis in the next decade and hence are expected to provide scientific references for establishing rational exploitation and allocation policies on the local water–land resources in the future.     

小流域产流产沙动力学模型

按自然水系划分单元,每一单元又被概化为“一本打开的书”概化后的单元又区分为几个微地貌区。各单元水沙过程演算至流域出口迭加得流域产流产沙过程。此法一方面解决了降雨,侵蚀和下垫面的不均匀性,另一方面又解决了水沙的演算问题。坡面和沟道水流用运动波方程描述并用四点隐式差分格式求其数值解。根据水流作功和能量平衡原理推导出各微地貌区上的土侵蚀量计算公式,建立起具有物理过程基础的小流域产流产沙模型。     

黄土丘陵沟壑区坡面水保措施及植被对流域尺度水沙关系的影响

根据黄土高原高含沙水流的特点,认为次暴雨的产沙模数和径流深可用线性正比关系式来表示,关系式中比例系数表示流域单位径流深的输沙能力、次暴雨过程中流量超过临界值后的稳定含沙量以及流域历次洪水的平均含沙量。在此模型基础上,以黄土丘陵沟壑区的王家沟的两个毗邻地貌相似的两条沟为研究区,其中一条沟为经治理而另一条则未治理。探讨各种坡面水土保持措施及植被对流域水沙关系的影响。结果表明,治理流域和非治理流域具有相同的水沙关系,被治理沟的植被等坡面措施在流域尺度上仅通过减水来减沙。这主要是因为植被等坡面措施不能显著改变沟道的输沙能力,且由于植被不能很好地控制沟谷侵蚀和重力侵蚀,使得水流进入沟道后又会获取充足的泥沙补充,达到和治理前相同的径流输沙能力。因此可以认为,在仅有植被和其它坡面治理措施的情况下,治理流域的减沙率可用减水率来估计。本文的实际计算表明,在多年平均尺度、年际尺度和次暴雨尺度这一方法都有较好的精度。     

Influence of Scale on SWAT Model Calibration for Streamflow in a River Basin in the Humid Tropics

The Soil Water Assessment Tool (SWAT) was applied to the 2,530 km² Chaliyar river basin in Kerala, India to investigate the influence of scale on the model parameters. The study was carried out in this river basin at two scales. Parameters such as land use, soil type, topography and management practices are similar at these scales. The model was initially calibrated for streamflow and then validated. Critical parameters were the curve number (CN2), soil evaporation compensation factor (ESCO), available water holding capacity (SOL_AWC), average slope length (SLSUBBSN), and base flow alpha factor (ALPHA_BF). Using the optimized value of various parameters, stream flow was estimated from parts of the basin at two different scales—an area of 2,361.58 km² and an area of 1,013.15 km². The streamflow estimates at both these scales were statistically analysed by computing the coefficient of determination (R ²) and the Nash–Sutcliffe efficiency (E_NS). Results indicate that the SWAT model could simulate streamflow at both scales reasonably well with very little difference between the observed and computed values. However, the results also indicate that there may be greater uncertainty in SWAT streamflow estimates as the size of the watershed increases.     

Simulation of Runoff and Suspended Sediment Transport Rate in a Basin with Multiple Watersheds

Accurate runoff and suspended sediment transport rate models are critical for watershed management. In this study, a physiographic soil erosion–deposition (PSED) model is used in conjunction with GIS, to simulate the runoff and sediment transport process during storm events in a multi-watershed basin. This PSED model is verified using three typhoon events and 33 storm events in Cho-Shui River Basin, located in central Taiwan. Cho-Shui River Basin has 11 sub-watersheds displaying a variety of hydrologic and physiographic conditions as well as high concentrations of suspended sediment in river flow and a steep average channel bed slope of 2%. The results show the capability, applicability, and accuracy of the PSED model for multi-watershed basins.     

A Distributed Kinematic Wave–Philip Infiltration Watershed Model Using FEM,GIS and Remotely Sensed Data

Distributed rainfall–runoff modeling is very important in the water resources planning of a watershed. In this study, a kinematic wave based distributed watershed model which simulates runoff on an event basis has been presented here. The finite element method (FEM) has been used to simulate the overland runoff and channel flow. Philip model has been used for the infiltration estimation. To find out runoff at the outlet of the watershed, both overland flow and channel flow models are coupled. The coupled model has been applied to a typical Indian watershed. Remotely sensed data has been used to obtain the land use (LU)/land cover (LC) for the watershed. Slope map of the watershed has been obtained using geographical information systems (GIS). The grid map of the watershed which contains overland flow elements connecting to channel flow elements has been prepared in GIS. The elemental input files such as slope and Manning’s roughness are prepared using the GIS and are directly used in the model. The model has been calibrated using some of the rainfall events and validated for some other events. The model results are compared with the observed data and found to be satisfactory. A sensitivity study of the infiltration parameters, overland and channel flow Manning’s roughness and time step has also been carried out. The developed model is useful for the simulation of event based rainfall–runoff for small watersheds.     

基于径流侵蚀功率的流域次暴雨输沙模型研究——以岔巴沟流域为例

流域次暴雨侵蚀产沙模型研究是国内外土壤侵蚀研究的重点领域之一。提出了基于径流深和洪峰流量模数两个流域次暴雨洪水特征参数的径流侵蚀功率的概念;利用岔巴沟曹坪水文站1959至1990年间历年实测的次暴雨洪水径流泥沙资料,系统研究了该流域次暴雨径流侵蚀功率与流域输沙模数之间的相关关系,建立和验证了基于径流侵蚀功率的岔巴沟流域次暴雨输沙模型。结果表明,岔巴沟流域次暴雨径流侵蚀功率与流域输沙模数之间具有极显著的幂函数相关关系;模型验证期的次暴雨输沙模数模拟值与实测值之间具有较好的一致性。     

三峡库区小流域降雨入渗和产流产沙特征试验研究

三峡库区暴雨集中,历时短,强度大,是造成土壤侵蚀的重要因素。为开展对三峡库区小流域降雨入渗和产流产沙特征研究,通过建立三峡库区小流域微缩模型,分别实施降雨强度为60,90,120 mm/h的3场人工模拟降雨,对小流域模型降雨入渗规律和径流侵蚀过程进行了分析。研究结果表明:径流量均随降雨强度的增加而增加,而降雨强度增加入渗的作用仅在一定范围内是有效的;随着降雨的进行,产流强度和入渗率都趋于稳定状态,入渗率服从对数函数规律,产流强度呈幂函数变化;3场降雨中累计产沙量和累计径流量的关系均满足幂函数形式,含沙量和侵蚀量之间呈较好的线性关系。该研究成果可为这一区域的水土流失防治提供重要的科学依据。     

Estimation of Soil Erosion and Sediment Yield During Individual Rainstorms at Catchment Scale

Lushi basin, named after the Lushi County, is one of the sub-basins of the Yellow River basin in China. The basin is suffering from severe soil erosion problems, especially during the “wet” season. In order to identify the proper soil management approaches for the basin, an erosion model is designed to estimate the soil erosion and sediment yield during single events. The hydrological model used for the estimations in the study is the BTOPMC model, which is developed based on the TOPMODEL. Under the model structure of BTOPMC, a modified form of the Universal Soil Loss Equation (USLE) was incorporated as a core module of the erosion component. In the modification, the runoff ratio, an important determinant of soil erosion, was brought into the USLE equation and consequent modifications were made to the soil erodibility and slope length factors. A concept of total sediment transport capacity for single events is applied in the model to route the surface erosion from each discrete cell to the basin outlet. The BTOPMC model was used in simulating the river discharges and sediment yields for 29 events in the Lushi basin. Its acceptable performance validates the model’s predictive ability in simulating the basin-scale erosions during individual rainstorms.     

WetSpa Model Application for Assessing Reforestation Impacts on Floods in Margecany–Hornad Watershed,Slovakia

The spatially distributed hydrologic model WetSpa working on a daily or hourly time scale combines elevation, soil and landuse data within GIS, to predict flood hydrographs and spatial distribution of hydrologic characteristics in a watershed. The model is applied to the Margecany–Hornad river basin (1,131 km²) located in Slovakia. Daily hydrometeorological data from 1991 to 2000, including precipitation data from nine stations, temperature data from four stations and evaporation data measured at one station are used as input to the model. Three base maps, i.e., DEM, landuse and soil types are prepared in GIS form, using 100×100 m cell size. Results of the simulations show good agreement between calculated and measured hydrographs at the outlet of the basin. The model predicts the daily/hourly hydrographs with good accuracy, between 75–80% according to the Nash–Sutcliff criteria. For assessing the impact of forests on floods, the calibrated model is applied for a reforestation scenario using the hourly data of the summer of 2001. The scenario considers a 50% increase of forest areas. The model results show that the reforestation scenario decreases the peak discharge by 12%. Investigation of peak discharges from the whole simulation period, shows that the scenario results are reduced by 18% on average. Also, the time to peak of the simulated hydrograph of the reforestation scenario is 14 h longer than for the present landuse. The results show that the effect of land cover on flood is strongly related to storm characteristics and antecedent soil moisture.     

Application of a Simple Raster-Based Hydrological Model for Streamflow Prediction in a Humid Catchment with Polder Systems

The hydrological processes are controlled by many factors such as topography, soil, climate and land management practices. These factors have been included in most hydrological models. This study develops a raster-based distributed hydrological model for catchment runoff simulation integrating flood polders regulation. The overland flow and channel flow are calculated by kinematic wave equations. A simple bucket method is used for outflow estimation of polders. The model was applied to Xitiaoxi catchment of Taihu Lake Basin. The accuracy of the model was satisfactory with Nash–Sutcliffe efficiencies of 0.82 during calibration period and 0.85 for validation at Hengtangcun station. The results at Fanjiacun station are slightly worse due to the tidal influence of Taihu Lake with high values of root mean square errors. A model sensitivity analysis has shown that the ratio of potential evapotranspiration to pan evaporation (K), the outflow coefficients of the freewater storage to groundwater (KG) and interflow (KSS) and the areal mean tension water capacity (WM) were the most sensitive parameters. The simulation results indicate that the polder systems could reduce the flood peaks. Additionally, it was confirmed that the proposed polders operation method improved the accuracy of discharge simulation slightly.     

Critical Area Identification of Potential Soil Loss in a Typical Watershed of the Three Gorges Reservoir Region

Identifying critical soil loss-prone areas is necessary to better control soil loss in the Xiangxi watershed, the river basin nearest the Three Gorges Dam. A crucial element of this scheme is the development of a risk assessment model that can identify critical potential soil loss areas for land use prioritization and soil conservation. An assessment model for the risk of potential soil loss based on the revised universal soil loss equation and sediment delivery ratio was developed in this work. The proposed model consists of five multiplied factors: the rain and runoff erosivity, soil erodibility, slope steepness and length, vegetation cover, and sediment delivery. The risk of potential soil loss in the Xiangxi watershed was assessed using the developed model integrated with the ArcGIS platform along with precipitation data, soil data, DEM, and MODIS NDVI images. The risk values ranged from 0 to 478.18, and were categorized into four classes. The classification showed that critical and sub-critical areas accounted for 4.48% and 6.05% respectively, of the entire Xiangxi watershed area. The results of the identification of critical and sub-critical areas were verified by analyzing the relationship between the variations of the agricultural land area and those of sediment discharge. Statistical relationship analysis between the distribution of critical/sub-critical areas and two parameters (the cell distance to the nearest river channel and the slope) showed that the critical and sub-critical areas for potential soil loss in the Xiangxi watershed assemble in the zone with a cell distance below 2,000 m, or in the zone with slopes above 25°.     

黄河流域水土保持减沙计算方法存在问题及改进途径探讨

水文法保法是分析计算汉域治理减水减沙效益常用的两种方法，但都存在一些问题。水文法计算的基础是帮雨沙资料建立的产沙模型，该模型很难准确地反映降雨产沙的自然规律；水保法计算的基础是制定的水土保持措施减沙定额，很难完全符合客观实际。本文从不同途径提出了三种经过改进的计算方法，即小流域天然产流量对比法、坡面综合措施减少沙系统数法和最大可能产沙量法。试算结果表明，在具有必要的前提下，应用这三咱方法分析计算流     

标准小区和大型坡面径流场径流泥沙监测方法分析

通过对子午岭林区地未开垦及开垦后分布设的标准小区与大型坡面径流场所测定的径流，泥沙资料进行对比分析，提出在非林地的坡面上有标准小区观测资料建立的坡面土壤流失方程有局限性；在林地上，无论是标准小区，还是大型坡面径流场所测定的径流，泥沙量，均可作为有林小流域径流量和混沙量的参考值。另根据对大型坡面径流场，标准小区和小流域把口站所测定的径流量，泥沙量资料进行分析，认为利用标准小区所测定的非林地泥沙量可以     

岷江镇江关流域分布式水文及泥沙侵蚀模型研究

基于空间地理信息系统的流域分布式水文泥沙模型为研究流域产流产沙及在河道中的汇流、输移过程提供了,科学有效的手段.针对岷江上游镇江关流域土壤易受降雨侵蚀的问题,采用水沙耦合的流域分布式水文综合模型,对该流域1990年后典型年的径流及泥沙侵蚀输移过程进了数值模拟,并结合镇江关水文站的实测资料对模型进行了验证,计算成果令人满意.分析表明,近年来岷江上游地区的年径流和输沙量均呈现出下降的趋势,且后者下降速率更快,说明泥沙侵蚀输移与径流相比对流域环境变化的反应更为敏感,今后水土保持工作应注重坡面治理.     

吕二沟小流域水土保持措施对径流和侵蚀产沙的影响

以甘肃天水吕二沟流域22年实测水文泥沙数据为基础,从降水～侵蚀产沙、径流～产沙关系入手,统计分析了小流域水土保持措施对径流和侵蚀产沙的影响。结果表明：小流域径流和侵蚀产沙在年内的分布与降水的季节分配和植被生长发育期有关;径流和侵蚀产沙的年际变化是随流域水土保持措施全面实施和小流域林草植被面积的增加,流域径流量和侵蚀产沙量逐渐减少。从单次降水～径流、降水～侵蚀产沙关系曲线来看,小流域水土保持措施发挥着明显的减水、减沙效益,为流域的综合治理、水土资源的合理开发利用提供科学依据。     

乌兰木伦河流域暴雨产沙分析研究

乌兰木伦河流域位于沙粗沙地区，其产流，产沙变化具有独特的规律。本文用考虑雨强时空分布的超渗产流模型及胜前期影响雨量为参数分别就涨水、落水段的含沙星 与流量关系的流域沙经验模型以计算产流量和产沙量，效果良好，基本满足实用要求，具有生价值，也可应用于同类流域。     

岔巴沟流域植被变化特征及其对水沙的影响

基于30 m×30 m分辨率陆地卫星(Landsat)遥感数据分析1987—2018年岔巴沟流域植被覆盖度的时空演变特征并生成流域土壤面蚀等级图,分析其对流域产流产沙的影响。结果表明:岔巴沟流域植被覆盖度整体呈现快速增长趋势,从1987年的24.7%增加至2018年的53.1%;流域植被覆盖度构成发生很大转变,2002年以后中、高覆盖度区域比例大幅上升,增长主要集中在丘陵沟壑地区;随着植被覆盖度的增长,流域产流产沙呈现减少趋势,地表面蚀有所减少,植被对产沙影响大于对产流影响。     

Effects of Urbanization Factors on Model Parameters

This study mainly explores effects of urbanization factors on hydrograph parameters. Urbanization impacts of the developing watershed are evaluated based on rainfall–runoff simulations. A total of 51 rainfall–runoff events occurred from 1966 to 2002. Forty of these were calibrated, and effects of urbanization factors on runoff hydrographs resulting from a simple hydrological model were assessed. The block Kriging method was used to estimate the mean rainfall of the Wu-Tu watershed, and its hourly excesses were calculated by using the non-linear programming method. The remaining 11 cases were used to test the established relationships. The calibration and verification results confirm that the integral methods used in this study effectively illustrate the hydrological and geomorphic conditions in complex urbanization processes. Parameter n responds more sensitively than parameter k to increasing impervious areas and population densities. Additionally, parameter n responds more strongly to imperviousness than to population. Therefore, an impervious area is an important reference for analyzing hydrological changes of urbanization in the Wu-Tu watershed.     

Prioritizing Structural Management by Quantifying the Effect of Land Use and Land Cover on Watershed Runoff and Sediment Yield

Hydrological processes in a mixed land use watershed are significantly influenced by land use (LU) and land cover (LC). In order to quantify the effect of LU/LC, topography, and morphology, runoff and sediment yield of a small multivegetated watershed in a sub-humid subtropical region in India were simulated by the Soil and Water Assessment Tool (SWAT) model and were compared with measured values. The mixed land use watershed displayed a synchronized runoff response to monsoon rains. Measured runoff and sediment yield varied one sub-watershed to another and ranged, respectively, from 256.33 to 367.83 mm and from 0.27 to 11.65 t/ha for 734.90 mm of rainfall in 2000 and from 310.36 to 393.49 mm and from 0.84 to 10.71 t/ha for 765.50 mm of rainfall in 2001. The correlation coefficient between rainfall and runoff was 0.86, that between runoff and sediment yield was 0.56, and that between rainfall and sediment yield was 0.55. The sub-watersheds with relatively high forest cover (SWS1 and SWS2) showed significantly less runoff and sediment yield (310.36 mm and 0.84 t/ha), whereas a sub-watershed with more area under cultivation produced higher runoff (393.5 mm) and higher sediment yield (11.65 t/ha). Measured and model simulated estimates of runoff and sediment yield from different sub-watersheds were employed to prioritize control measures in the watershed comprising areas under cultivation, waste, fallow and eroded land, and forest and bushes. The average estimates of sediment yield from different sub-watersheds were used to prioritize the checkdam construction as an effective measure to control sediment transport to downstream water resources.