Hypsometric Integral Estimation Methods and its Relevance on Erosion Status of North-Western Lesser Himalayan Watersheds

Assessment of erosion status of a watershed is an essential prerequisite of integrated watershed management. This not only assists in chalking out suitable soil and water conservation measures to arrest erosion and conserve water but also helps in devising best management practices to enhance biomass production in watersheds. The geologic stages of development and erosion proneness of the watersheds are quantified by hypsometric integral. The estimation of hypsometric integral is carried out from the graphical plot of the measured contour elevation and encompassed area and by using empirical formulae. In this study, efforts were made to estimate the hypsometric integral values of the Sainj and Tirthan watersheds and their sub watersheds in the Lesser Himalayas using four different techniques, and to compare the procedural techniques of its estimation and relevance on erosion status. It was revealed that the hypsometric integral calculated by elevation–relief ratio method was accurate, less cumbersome and easy to calculate within GIS environment. Also comparison of these hypsometric integral values revealed that the Sainj watershed (0.51) was more prone to erosion than the Tirthan watershed (0.41). Further, the validation of these results with the recorded sediment yield data of 24 years (1981–2004) corroborated that the average annual sediment yield during this period for Sainj watershed (0.53 Mt) was more than that of the Tirthan watershed (0.3 Mt). Thus, the hypsometric integral value can be used as an estimator of erosion status of watersheds leading to watershed prioritization for taking up soil and water conservation measures in watershed systems.     

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.     

Estimation of Sediment Yield and Areas of Soil Erosion and Deposition for Watershed Prioritization using GIS and Remote Sensing

A Geographical Information System (GIS) based method is proposed and demonstrated for the identification of sediment source and sink areas and the prediction of sediment yield from watersheds. Data from the Haharo sub-catchment having an area of 565 km² in the Upper Damodar Valley in Jharkhand State in India was taken up for the present study due to availability of gauged data at multiple locations within watershed area. The watershed was discretized into hydrologically homogeneous grid cells to capture the watershed heterogeneity. The cells thus formed were then differentiated into cells of overland flow regions and cells of channel flow regions based on the magnitude of their flow accumulation areas. The gross soil erosion in each cell was calculated using the Universal Soil Loss Equation (USLE). The parameters of the USLE were evaluated using digital elevation model, soil and landuse information on cell basis. The concept of transport limited sediment delivery (TLSD) was formulated and used in ArcGIS for generating the transport capacity maps. An empirical relation is proposed and demonstrated for its usefulness for computation of land vegetation dependent transport capacity factor used in TLSD approach by linking it with normalized difference vegetation index (NDVI) derived from satellite data. Using these maps, the gross soil erosion was routed to the watershed outlet using hydrological drainage paths, for derivation of transport capacity limited sediment outflow maps. These maps depict the amount of sediment rate from a particular grid in spatial domain and the pixel value of the outlet grid indicates the sediment yield at the outlet of the watershed. Up on testing, the proposed method simulated the annual sediment yield with less than ±40% error.     

Multi-Criteria Decision Making Approach for Watershed Prioritization Using Analytic Hierarchy Process Technique and GIS

Watershed prioritization based on the natural resources and physical processes involves locating critical areas of erosion, which produce maximum sediment yield to take up conservation activities on priority basis. The present study was taken up with a specific objective of prioritization of micro-watersheds using Multi-Criteria Decision Approach – Analytic Hierarchy Process (AHP) based SYI model (AHPSYI) under GIS environment for a case study area of Mayurakshi watershed in India. This method basically uses information of Potential Erosion Index (PEI) and Sediment Delivery Ratio (SDR), indicative of transport capacity. In the present study, sediment delivery factors viz., topography, vegetation cover, proximity to water courses and soil were translated into GIS layers and integrated using Boolean conditions to create a data layer of spatially distributed SDIs’ across the watershed. For assessment of PEI, important watershed parameters viz., land use/land cover, soil, slope, and drainage density maps were integrated in the GIS environment using Weighted Linear Combination method (WLC) by assigning weights to themes and ranks to features of individual theme using AHP technique. A comparison between AHPSYI based sub watershed prioritization map with that of prioritization map based on the observed sediment yield data revealed that about 78 % of the area showed concurrence. Thus, it can be inferred that the watershed prioritization based on only thematic layers can be dependable to maximum extent. Subsequently, proposed approach was adopted for prioritization of the study area at micro watershed scale, where area under high and very high categories together constitutes around 33 % of the study area. Around 100 micro-watersheds out of 276 watersheds are under moderate to very high category respectively, signifying the need for watershed management.     

Sediment TMDL Development for the Amite River

The Amite River is recognized as one of the 15 water bodies impaired by sediments in Louisiana, USA. Based on US EPA’s Protocol sediment TMDL (Total Maximum Daily Load) development is conducted for the Amite River and described in this paper. The TMDL development consists of four components: (1) development of a new model for cohesive sediment transport, (2) estimation of sediment loads (sources) due to watershed erosion, (3) river flow computation, and (4) determination of sediment TMDL for the Amite River. Using the mass conservation principle and Reynolds transport theorem a new 1-D model has been developed for computation of suspended cohesive sediment transport. Sediment erosion in the Amite River Basin is calculated by combining the USLE (Universal Soil Loss Equation) model with GIS and the digital elevation model of the Amite River Basin. Digital elevation data was imported into the GIS which generated inputs for USLE. The calculated average annual rate of soil erosion in the Amite River Basin is 13.368 tons per ha, producing a nonpoint sediment load of 103 mg/L to the Amite River. The flow computation is performed using the HEC-RAS software. The computed sediment concentration in the Amite River varies in the range of 3–114 mg/L and sediment TMDL is 281.219 tons/day. The reduction necessary to support beneficial uses of the river is 55% or 275.946 tons/day. Results indicate that the combined application of the new 1-D sediment transport model, GIS, USLE model, and HEC-RAS is an efficient and effective approach to sediment TMDL development.     

紫色土区小流域泥沙输出过程对雨型和空间尺度的响应

以紫色土区3个具有不同集水面积、物理特征和土地利用方式的小流域为研究对象，在1999～2000年间对流域野外自然降雨下泥沙输出过程进行了监测，旨在从小流域尺度阐明径流含沙量过程特征及其空间约束效应。结果表明：天然降雨侵蚀过程中流域径流含沙量时间曲线表现为波浪起伏形、幂函数递减形和抛物线复合形3种类型；峰值径流流量后，含沙量降低，表现为变化幅度小的低含沙量特征。泥沙输出过程对流域空间尺度的响应受降雨型式的强烈影响。均匀型降雨侵蚀下，径流含沙量时间曲线表现为低含沙量的波浪起伏形，并且，随流域面积的增加，次降雨平均含沙量增加；间歇型降雨侵蚀下，随流域面积的增加，径流含沙量曲线从抛物线复合形向幂函数递减形过渡；中大型降雨侵蚀下，径流含沙量时间曲线表现为幂函数递减形，泥沙输出过程对流域空间尺度的响应不敏感。     

昆明市松华坝水源区小流域土壤侵蚀分析

以1993-2009年松华坝水源区及昆明市的气象资料、2009年土地利用资料、第二次全国土壤普查资料、水源区牧羊河小流域的径流和泥沙观测资料为基础,用SWAT模型模拟分析了牧羊流域土壤侵蚀的空间差异。结果表明：牧羊河小流域输沙在年际上表现为与年降水量和输沙量峰谷变化具有较好的一致性,在年内表现出,输沙主要集中在6-9月;空间上牧羊河土壤侵蚀模数多年平均值介于21.4~4 586.5 t/(km²·a),且以中轻度为主,土壤侵蚀模数的空间变化与土地利用类型和地形坡度密切相关;土壤侵蚀模数与降水在年际变化上有较好的一致性。这一研究可为水源区土壤侵蚀空间分布的掌握和估算,以及制定有针对性的水土保持措施提供重要的理论依据。     

基于137Cs技术的侵蚀产沙对土地利用变化响应——以三峡库区斑竹林小流域为例

小流域是三峡库区入库泥沙的策源地,研究其侵蚀产沙状况对正确预测三峡水库来沙变化趋势非常重要。以三峡库区典型农业小流域--斑竹林小流域为研究对象,通过¹³⁷Cs示踪技术,研究了土地利用变化对流域侵蚀产沙空间分布的影响。结果表明：旱地退耕的其他林地和水田改的旱地的侵蚀堆积情况与土地利用变化前相差不大;在土地利用变化后的短期内,该流域侵蚀产沙变化较小,旱地是流域主要的侵蚀产沙源地,水田是淤积区。     

基于GIS黄土丘陵沟壑区分布式侵蚀产沙模型的构建——以蛇家沟小流域为例

分布式侵蚀产沙模型是土壤侵蚀模型的重要发展方向,本研究将蛇家沟流域下垫面划分为5 ×5m的栅格,每个栅格内赋予相应的高程、坡度、地貌、土地利用等属性信息.根据流域DEM,确定流域的汇流方向、流路与汇流累积面积.在蛇家沟流域内采用“穷举算法”对SCS-CN模型的参数值进行校正.基于DEM、地貌、土地利用以及降雨等资料,利用黄土丘陵沟壑区良好的水沙关系,运用VB.NET+ARC ENGINE9.2+ SQLSERVER2000构建分布式侵蚀产沙模型.模型结构简单,输入参数比较少,利用求产流来求产沙,考虑了土地利用、汇流等因素具有一定的物理意义,并能达到一定的预报精度.其中产沙模型是建立在黄土丘陵沟壑区普遍的水沙关系基础上,通过校正水沙关系式系数及产流模型中的CN、λ值可在其它相似的小流域内使用.该研究可为黄土丘陵沟壑区水土保持治理效果评价提供依据.     

Spatial Decision Support System for Watershed Management

A prototype spatial decision support system (SDSS) is presented for watershed management. The SDSS integrates landuse/landcover derived from the remote sensing data, real-time hydrological data, geographic information system, and a model-based subsystem for computing soil loss, land capability classification and engineering measures. A graphical user interface has been developed to allow effective use by decision makers. The model-based subsystem employs a process-based soil erosion model to compute soil loss in spatial environment. Computed pixel-based soil loss information is an input to the land capability classification and watershed management modules. The developed SDSS can help the end users in avoiding the laborious procedures of soil erosion calculations and analysing various thematic layers to get suitable watershed management practices. The SDSS for watershed management is applied to the Tones watershed in India to compute soil loss, to prioritise watersheds, and to suggest various watershed management practices.     

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。     

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。     

Modelling Watershed Scale Soil Loss Prediction and Sediment Yield Estimation

Computer simulation models are becoming increasingly popular in predicting soil loss for various land use and management practices. A GIS-based system, GeoUSLE, was developed in this study for soil loss prediction and sediment yield estimation in the watershed scale. The Universal Soil Loss Equation (USLE) and watershed analysis models are incorporated in the system. The required watershed information and USLE factors are derived from digital elevation models (DEMs) and remote sensing data. The GIS-based system can flexibly delineate drainage networks and watersheds and rapidly query the sediment yield at any point or watershed outlet via the point-and-click interface. The study presents an example application of the system to an agricultural reservoir watershed in central Taiwan. The estimated result shows that the developed system scales up USLE applications from the slope to the watershed, which can be used to assess the erosion hot spots in a watershed for the management decision making.     

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.     

Runoff and Sediment Yield Modelling for a Treated Hilly Watershed in Eastern Himalaya Using the Water Erosion Prediction Project Model

The Water Erosion Prediction Project (WEPP) watershed model was calibrated and validated for a hilly watershed treated with graded bunding and water-harvesting tank in high rainfall condition of eastern Himalayan range in India. The performance of the model for the treated watershed was unacceptable with percent deviation of −45.81 and −38.35 respectively for runoff and sediment yield simulations when calibrated parameter values for the nearby untreated watershed were used. This was possibly due to differences in soil properties and average land slope. When soil parameters were calibrated for the treated watershed, the model performance improved remarkably. During calibration, the model simulated surface runoff and sediment yield with percent deviations equal to +6.24 and +9.02, and Nash–Sutcliffe simulation coefficients equal to 0.85 and 0.81, respectively. During validation period, the model simulated runoff and sediment yield with percent deviations equal to +8.56 and +9.36, and Nash–Sutcliffe simulation coefficients equal to 0.81 and 0.80, respectively. The model tended to slightly under-predict runoff and sediment yield of higher magnitudes. The model performance was quite sensitive to soil parameters namely, rill erodibility, interrill erodibility, hydraulic conductivity, critical shear stress and Manning’s roughness coefficient with varying levels. The WEPP model picked up the hydrology associated with bund and water-harvesting tank, and simulated runoff and sediment yield well with overall deviations within ±10% and Nash–Sutcliffe simulation coefficients >0.80. Simulation results indicate that in high slope and high rainfall conditions of eastern Himalayan region of India where vegetative measures are not adequate to restrict soil loss within the permissible limit, the WEPP model can be applied to formulate structure-based management strategies to control soil loss and to develop water resources.     

侵蚀泥沙颗粒中137Cs的含量特征及其示踪意义

通过对黄土丘陵区典型小流域—燕沟的林地、坡耕地与沟口洪水泥沙的颗粒组成分析 ,发现其颗粒组成有明显的差异 ,表明该研究区在侵蚀过程中发生了一定程度的颗粒分选 ,而在泥沙输移过程中颗粒分选不明显 ,在应用1 37Cs示踪流域侵蚀速率或利用沟口泥沙推算流域侵蚀模数时应适当进行颗粒校正。通过对坝地沉积泥沙1 37Cs含量进行分析 ,结果表明 ,1 37Cs含量、沉积厚度与次降雨侵蚀强度、侵蚀类型之间存在密切关系 ,同时运用沉积样中核素含量特征可望解决流域尺度坡面侵蚀与沟谷侵蚀的比重关系这一研究难题。     

泥石流泥沙输移比的概念与计算方法探讨

通过泥石流SDR,可将泥石流流域侵蚀产沙、泥沙输移及泥石流沟道和入汇处主河河床演化有机地联系起来,用于推求流域的土壤侵蚀量,泥石流沟道的冲刷与淤积状况,泥石流所输送的泥沙进入主河的数量,以及对下游河道演变、水库使用年限的影响程度等方面。但目前泥石流SDR的研究还没有开始,在分析泥石流输沙特征的基础上,将SDR引入泥石流输沙的研究中,并将泥石流SDR分解为反映泥石流沟输沙能力的沟道泥石流SDR和反映主河输移泥石流泥沙能力的汇口泥石流SDR两个环节。给出了根据定义使用实际的监测数据计算两类泥石流SDR的具体方法,并在蒋家沟中实施,计算出蒋家沟2007年的一场泥石流过程中沟道SDR为0.14,入汇主河后的悬移质汇口泥石流SDR为0.36。泥石流SDR的模型计算法方面也根据定性分析列出了可能的影响因子,在总结河流SDR的研究成果和分析泥石流输沙特性的基础上进行了模型建立方法的初步探讨。     

鹤毛河小流域水土流失现状及综合治理措施分析

为防治水土流失,改善人居环境,推进经济社会发展,在分析鹤毛河小流域土地利用现状、水土流失情况等基础上,对流域水土流失分布区域采取拦沙坝、河道护岸、村庄人居环境改善等典型治理措施,并利用林草措施及封育治理有机结合的措施,有效防治了水土流失,改善了生态环境,实现流域内水土保持措施效益最大化。     

大暴雨作用下黄土高原典型流域水土保持措施减沙效益研究

正确评估大暴雨条件下流域水土保持措施的减沙作用,可为科学揭示流域侵蚀产沙变化的驱动机理提供理论支撑。综合采用改进的水土保持成因分析法、林草植被减沙模型和分布式土壤侵蚀模型,对近10年大暴雨作用下4个典型流域的水土保持措施减沙作用进行了系统分析和研究。结果表明:佳芦河流域水土保持措施在"2012.7.27"大暴雨中减沙效益为65.4%;杏子河流域在"2013.7.12""2013.7.25"和"2013.7.27"三场连续降雨中,水土保持措施减沙效益分别为56.5%、40.7%和36.5%;西柳沟流域上游在"2016.8.17"大暴雨中,林草植被措施减沙效益达84.2%;岔巴沟流域在"2017.7.26"大暴雨中,水土保持措施减沙效益为79%。大暴雨作用下水土保持措施减沙效益明显,但遭遇连续极端降雨情况,水土保持减沙效益会降低。     

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。