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。     

Estimation of Soil Erosion and Sediment Yield Using GIS at Catchment Scale

A GIS-based method has been applied for the determination of soil erosion and sediment yield in a small watershed in Mun River basin, Thailand. The method involves spatial disintegration of the catchment into homogenous grid cells to capture the catchment heterogeneity. The gross soil erosion in each cell was calculated using Universal Soil Loss Equation (USLE) by carefully determining its various parameters. The concept of sediment delivery ratio is used to route surface erosion from each of the discritized cells to the catchment outlet. The process of sediment delivery from grid cells to the catchment outlet is represented by the topographical characteristics of the cells. The effect of DEM resolution on sediment yield is analyzed using two different resolutions of DEM. The spatial discretization of the catchment and derivation of the physical parameters related to erosion in the cell are performed through GIS techniques.     

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.     

Assessment of Sediment Yields for a Mixed-landuse Great Lakes Watershed: Lessons from Field Measurements and Modeling

The Soil Water Assessment Tool (SWAT) was implemented to determine annual sediment yields and critical source areas of erosion for the Buffalo River Watershed. Model calibrations were performed by comparing simulated streamflow discharge and sediment concentrations against measured values. Monte-Carlo simulations were performed to identify the most sensitive parameters and the “best-fit” parameter ranges. This study especially highlighted the importance of snow parameters, which, previously had not been identified as sensitive for model simulations. The cover (C) and practice (P) values for croplands had to be reduced considerably from default model values to constrain simulated sediment yields within the observed data range. The model did not simulate an ice-scour event which generated a substantial amount of sediment. The average annual sediment yield simulated by SWAT for the Buffalo River watershed (108,593 ha) amounted to 0.8 tons/ha/yr. The Cazenovia Creek subwatershed contributed the largest portion (45%) of the total sediment yield from the Buffalo River watershed. We attribute the higher sediment yields from Cazenovia Creek to the greater proportion of steep slopes in this subwatershed. The accuracy and reliability of SWAT sediment predictions at the small watershed (second order or less) and storm-event scales will depend on the accuracy of input information, especially the resolution of the landuse-landcover (LULC) layer, the number of rainfall stations used in simulations, and the number of internal sites against which the model has been calibrated.     

Catchment Erosion and Sediment Delivery in a Limno-Reservoir Basin Using a Simple Methodology

Accelerated soil erosion is a threat for the societies due to the loss of ecosystems services. Soil erosion and sediment delivery have been assessed in a small catchment of Central Spain with a new water body, the Pareja Limno-reservoir, located in its outlet. This limno-reservoir was created in 2006 with environmental and recreational purposes in the riverine zone of a large reservoir. Sedimentation risk is an issue of concern regarding limno-reservoirs environmental feasibility. Thus, the study of the soil erosion in the Pareja Limno-reservoir catchment and its sediment delivery seemed of the utmost importance. In this paper we establish an affordable and simple methodology to address it. A soil erosion and deposition monitoring network was installed in the Ompólveda River basin (≈88 km²), which flows into the Pareja Limno-reservoir. Results obtained were related with those from a sedimentation study previously carried out in the limno-reservoir. Gross hillslope erosion in the catchment was 6.0 Mg ha^?1 year^?1, which is in agreement with values reported for Mediterranean areas. After subtraction of the deposition measured, a soil loss of 1.2 Mg ha^?1 year^?1 was found in the catchment. Sediment delivery ratio (SDR) was estimated to be 3.8 %. SDR is low as a result of the low connectivity between the stream network and the limno-reservoir. Some local characteristics may also have a secondary influence in the low SDR value. Results obtained support the environmental feasibility of the Pareja Limno-reservoir from the sedimentation risk perspective. They also demonstrate that the methodology followed allows the assessment of soil loss and sediment delivery at a catchment scale, and the identification of areas where the erosion problems are most severe.     

Simulation of Agricultural Management Alternatives for Watershed Protection

The Bosque River Watershed in Texas is facing a suite of water quality issues including excess sediment, nutrient, and bacteria. The sources of the pollutants are improperly managed cropland and grazing land, dairy manure application, and effluent discharge from wastewater treatment facilities. Several best management practices (BMPs) have been proposed for pollution reduction and watershed protection. The overall objectives of this study were to demonstrate a modeling approach using Soil and Water Assessment Tool (SWAT) model to simulate various BMPs and assess their long-term impacts on sediment and nutrient loads at different spatial levels. The SWAT model was calibrated and validated for long-term annual and monthly flows at Valley Mills and for monthly sediment, total nitrogen (TN) and total phosphorus (TP) at Hico and Valley Mills monitoring locations. The BMPs including streambank stabilization, gully plugs, recharge structures, conservation tillage, terraces, contour farming, manure incorporation, filter strips, and PL-566 reservoirs were simulated in the watershed areas that met the respective practice’s specific criteria for implementation. These BMPs were represented in the pre- and post-conditions by modifying one or more channel parameters (channel cover, erodibility, Manning’s n), curve number (CN), support practice factor (P-factor), filter strip width, and tillage parameters (mixing efficiency, mixing depth). The BMPs were simulated individually and the resulting Hydrologic Response Units (HRUs), subwatershed, and watershed level impacts were quantified for each BMP. Sensitivity of model output values to input parameters used to represent the BMPs was also evaluated. Implementing individual BMPs reduced sediment loads from 3% to 37% and TN loads from 1% to 24% at the watershed outlet; however, the changes in TP loads ranged from 3% increase to 30% decrease. Higher reductions were simulated at the subwatershed and HRU levels. Among the parameters analyzed for sensitivity, P-factor and CN were most sensitive followed by Manning’s n. The TN and TP outputs were not sensitive to channel cover. This study showed that the SWAT modeling approach could be used to simulate and assess the effectiveness of agricultural best management practices.     

黄土高原风水蚀交错带风力作用对流域产沙贡献的空间特征研究

利用黄土高原风水蚀交错带水文站水沙资料及有关气象资料,分析了风力作用对流域产沙贡献的空间特征。结果表明:风沙区并不是风蚀贡献最大的区域,风蚀贡献率约为1/4。风沙区和黄土丘陵沟壑区交界处的风蚀贡献急剧增大。靠近风沙区并有零星片沙分布的区域,风蚀贡献率约为1/3。风蚀贡献最大的区域为穿过风沙区和黄土丘陵沟壑区的流域,约为2/5。黄土丘陵沟壑区,风蚀贡献率约为1/10～1/4。河源梁涧区的风蚀贡献率小于1/10。风蚀贡献率的大小依次为河源梁涧区<黄土丘陵沟壑区<风沙区<风沙区和黄土丘陵沟壑区交界处<穿过风沙区和黄土丘陵沟壑区的流域。整个黄土高原风水蚀复合区风力作用产生的输沙量接近流域总输沙量的1/10～1/5,风沙入河量占d>0.05 mm粗泥沙年输沙量的1/4。     

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。     

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.     

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.     

紫色土丘陵区小流域地面侵蚀量预报

 针对长江上游紫色土丘陵区小流域面积侵蚀及泥沙输移特征以及现有资料的可利用性，用演绎法建立了小流域地面侵蚀的预报模型及相应的输沙预报模型。模型参数求取简便，经研究区的典型小流域实测资料检验，预报精度较高，可用于研究区资料短缺小流域的地面侵蚀量和输沙量的估算。     

长江上游泥沙输移比初探

首先阐述泥沙输移比界定的三个条件一是粒级 ,二是时间 ,三是空间 ,在此基础上讨论了长江上游泥沙输移比研究中存在的主要问题是缺少可靠的侵蚀产沙量 ,对悬移质和推移质的分界线不明确 ,对坡面侵蚀产沙和重力侵蚀产沙在总输沙量中的权重缺少量的概念 ;针对上述问题对河道及沟道泥沙输移比的推理分析 ,再根据反映泥沙输移比的形态指标的定性分析 ,认为长江上游除丘陵宽谷区泥沙输移比会小于 0 .5外 ,高中山区长时段的泥沙输移比都接近 1(不包括泥石流在内的重力侵蚀 )。     

Identification of critical erosion prone areas in the small agricultural watershed using USLE,GIS and remote sensing

In the present study, Karso watershed of Hazaribagh, Jharkhand State, India was divided into 200 × 200 grid cells and average annual sediment yields were estimated for each grid cell of the watershed to identify the critical erosion prone areas of watershed for prioritization purpose. Average annual sediment yield data on grid basis was estimated using Universal Soil Loss Equation (USLE). In general, a major limitation in the use of hydrological models has been their inability to handle the large amounts of input data that describe the heterogeneity of the natural system. Remote sensing (RS) technology provides the vital spatial and temporal information on some of these parameters. A recent and emerging technology represented by Geographic Information System (GIS) was used as the tool to generate, manipulate and spatially organize disparate data for sediment yield modeling. Thus, the Arc Info 7.2 GIS software and RS (ERDAS IMAGINE 8.4 image processing software) provided spatial input data to the erosion model, while the USLE was used to predict the spatial distribution of the sediment yield on grid basis. The deviation of estimated sediment yield from the observed values in the range of 1.37 to 13.85 percent indicates accurate estimation of sediment yield from the watershed.     

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。     

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。     

Optimizing Structural Best Management Practices Using SWAT and Genetic Algorithm to Improve Water Quality Goals

A genetic algorithm (GA), an evolutionary optimization technique, is coupled with a semi-distributed hydrologic model, Soil and Water Assessment Tool (SWAT) to find an optimum combination of structural Best Management Practices (BMPs) that meets the treatment goals at a watershed scale. The structural BMPs considered in the study are detention ponds, parallel terraces, filter strips, grassed waterways, and grade stabilization structures which are all applicable in agricultural watersheds. The decision variables in the optimization model are the type, size, and location of BMPs which minimize the construction cost and simultaneously reduce sediment and nutrients to target levels at the watershed outlet. The model is demonstrated on the Silver Creek, a sub-watershed of the Lower Kaskaskia watershed in Illinois. The model is used to compare three different sediment and nutrient reduction cases (i.e. 20%, 40%, and, 60%) at the watershed outlet.     

不同管理措施对密云水库流域水量水质变化的影响

在密云水库上游控制流域建立SWAT(Soil and Water Assessment Tool)水文模型,根据实测水量-水质数据对模型的参数进行优化。识别流域土壤侵蚀和污染物关键区域,并对不同管理措施对流域水量-水质的影响进行定量研究。研究结果表明:密云水库流域土壤侵蚀强度较大的集中在流域中下游临近河道的区域;潮河流域非点源污染状况较为严重,潮河和白河总氮流失超高风险区分别占总面积的62.62%和43.09%,白河流域总磷均为低流失风险区,潮河流域总磷高流失风险区占17.81%;等高耕作和梯田种植对于产沙量和污染物都有较好的去除效果,其中等高耕作对于产沙量和总氮、总磷负荷的削减率,潮河分别为25.16%、10.79%和32.89%,白河为47.60%、34.92%和53.49%;通过对比退耕还林和退耕还草措施得知,退耕还林的效果更优。研究结果可为密云水库流域水土保持和水环境治理提供决策依据。