基于MODCYCLE分布式水文模型的区域产流规律

为了分析区域产流时空变化规律以及不同下垫面的产流特征,采用了具有物理机制的分布式水文模型——MODCYCLE模型,并以天津市为例进行深入研究。该模型在综合考虑土壤、下垫面条件、降雨条件等多方面因素的基础上,采用修改后具有地表积水机制的Green-Ampt方程计算产流量。计算结果表明,1）1997－2004年天津市8 a平均总产流系数约为16%,其中陆面产流系数不足10%。2）陆面产流主要集中在北部山区、中心城区及东部沿海地区;水面产流主要集中在中部及东南部地区。3）陆面产流中城市区产流系数最大,8a平均为44.1%;农村居民地的产流系数也较大,为24.5%;天然林草和河滩地的产流系数不足10%,农田由于田埂的作用几乎不产流。     

Frequency–magnitude relationships for precipitation,stream flow and sediment load events in a small Mediterranean basin (Vallcebre basin,Eastern Pyrenees)

Precipitation, discharge and suspended sediment concentrations were continuously measured during 10 years (1995–2004), at the Ca l'Isard sub-basin (1.32 km²) of the Vallcebre experimental catchments. Daily precipitation record is 22 years long. When the ranks of the events obtained with the diverse variables considered (precipitation depth, peak discharge, runoff depth, suspended sediment concentration and sediment load) were compared, the results confirmed the complexity of the response of the catchment and demonstrated that precipitation is an irregular criterion for ranking the main sediment transporting events. When the partial duration series corresponding to the 10% major events were analysed, daily precipitation, peak discharge and sediment concentration series showed good fits with log-normal distributions, but event precipitation, runoff and sediment load series needed bi-modal log-normal distributions. This behaviour may be attributed to the fact that event mass magnitudes depend not only on event intensity but also on its duration.     

IMPACTS OF LAND COVER CHANGE SCENARIOS ON STORM RUNOFF GENERATION: A BASIS FOR MANAGEMENT OF THE NYANDO BASIN,KENYA

The effects of conceptual land cover change scenarios on the generation of storm runoffs were evaluated in the Nyando Basin. The spatial scenarios represented alternatives that vary between full deforestation and reforestation. Synthetic storm events of depths 40, 60 and 80 mm were formulated according to the rainfall patterns and assumed to have durations corresponding to the runoff times of concentration. The Natural Resource Conservation Service–Curve Number model was used to generate runoff volumes within the sub‐catchments, which were subsequently routed downstream to obtain effects in the whole basin. The simulated land cover change impacts were evaluated relative to values obtained from the actual land cover state of the basin in the year 2000. From the results, an agricultural land cover scenario constituting of about 86 per cent of agriculture indicated increased runoff volumes in the entire basin by about 12 per cent. An agricultural‐forested land cover scenario with 40 and 51 per cent of forest and agriculture respectively revealed reduced runoff volumes by about 12 per cent. Alternatively, a scenario depicting a largely forested land cover state with about 78 per cent of forests reduced the runoff volumes by about 25 per cent according to the model estimates. Runoff volumes in the basin were also likely to reduce by about 15 per cent if the appropriate land cover scenario for the respective sub‐catchments were to be assumed for runoff management purposes. Considering the prevalent data uncertainty, the study effectively highlights the potential hydrological vulnerability of the basin. The results obtained can form a basis for appropriate catchment management of the area. Copyright © 2012 John Wiley & Sons, Ltd.     

华北土石山区土地利用/土地覆被变化的水文响应研究——以张家口云州水库流域为例

以张家口云州水库流域为例研究华北土石山区土地利用/覆被变化的水文响应.收集研究区1968年、1980年和2000年遥感影像.采用MaptGIS解译得到不同时期的土地利用网,采用ArcView分析获得空间数据和属性数据.并利用研究区逐日降水量和径流量数据,分析不同土地利用时期的水文响应.结果表明:华北土石山区土地利用变化对流域年径流具有显著影响.1981-2000年间植被条件较好的土地利用较1968-1980年间产流有所减少,多年平均径流系数下降了22.22%.在相同的降水条件下,根据不同土地利用降水与径流的拟合曲线进行预测,发现1981-2000年间土地利用产流比1968-1980年间减少了15%～3O%.不同土地利用在相同降水条件下的产流仅在生长季节具有明显差异,也就是说土地利用变化对产流的影响具有季节性,在枯水季节无显著影响.植被条件好的时期产流能力明显下降.     

黄土丘陵沟壑区不同土地利用类型水土流失效应

为了探究黄土丘陵沟壑小流域不同类型植被措施的水土保持效益,以地处黄河中游内蒙古段的圪坨店小流域为研究区,建立6个投影面积为5 m×20 m的径流监测小区,基于野外径流小区定位监测和降雨监测数据,分析不同年份降水特征和坡面不同土地利用类型(油松、沙棘、人工草地、天然草地、农田)对产流产沙的影响,并设置裸地径流小区作为对照,采用不同土地利用类型径流系数和单位面积侵蚀量与裸地的比值表征减流减沙效益。结果表明:研究时段(2014—2017年)内,降水集中分布在6—9月。不同土地利用类型的径流量和泥沙量差异显著(p<0.05),径流量最小的是油松林地,为(4.55±3.25)L; 径流量最大的是裸地,为(412.73±97.09)L。不同土地利用类型径流量具体表现为:裸地>农田(玉米)>天然草地(针茅)>人工草地(苜蓿)>沙棘>油松林。泥沙量观测结果与径流量类似,最小的是油松林,为(0.8±0.38)g/L; 最大的是裸地,为(87.36±15.37)g/L。不同土地利用类型径流系数和侵蚀模数差异显著(p<0.05),其中,农田径流系数最高,为12.26%±1.27%,油松林径流系数最低,为0.09%±0.06%,不同土地利用类型径流系数具体表现为:农田>天然草地>人工草地>沙棘>油松林地。同样的,油松侵蚀模数最低,是(0.002±0.001)kg/(m²·a),农田侵蚀模数最高,为(1.49±0.71)kg/(m²·a)。观测时段内,不同土地利用类型侵蚀模数与径流系数表现一致。综上所述,植被恢复能有效控制水土流失,不同植被措施的减流减沙效益有显著差异,具体表现为:油松>沙棘>人工草地>天然草地>农田。研究结果可为黄河中游内蒙古段植被恢复流域综合治理提供依据。     

基于改进径流曲线数模型的北京密云坡地径流估算

密云区是北京重要的地表饮用水源地,准确模拟地表径流量,对于分析泥沙和污染物的运移十分重要。近年来,学者们运用径流曲线数(soil conservation service curve number,SCS-CN)模型计算本区地表径流量,但预报精度不理想;未考虑降雨过程和雨强对于产流过程的影响,可能是造成预报误差的重要原因。该文利用密云石匣小流域5个坡面径流小区共201场降雨产流资料,提出次产流径流曲线数计算方法,以改进SCS-CN模型并分析改进后模型模拟效果。结果表明,次产流径流曲线数与多年平均径流曲线数的比值和最大30 min降雨量与次雨量的比值之间呈显著幂函数递增关系,据此提出计算次产流径流曲线数的幂函数方程,以改进SCS-CN模型。当曲线数为0.02时,改进后模型模拟效果最好,效率系数为0.693,明显高于未改进的SCS-CN模型。改进后模型对裸地和耕地的产流模拟效果较好,但对林地的产流模拟效果不理想。今后需在深入分析产流机理的基础上,进一步提出与土壤特性有关的模型参数优化方法。     

嘉陵江流域下游地表径流对土地利用变化的响应

近年来,嘉陵江流域下游发展迅速,流域内的土地利用发生了较大变化,下垫面的变化影响了流域的地表径流。在遥感和地理信息系统的支持下,通过解译1993年、2004年、2014年嘉陵江流域下游的遥感影像,获得了该流域不同时期的土地利用情况,并在此基础上,运用分布式水文模型的SCS模型模拟地表径流,分析了嘉陵江流域下游地表径流对土地利用变化的响应。结果表明:（1）1993—2014年,嘉陵江流域下游土地利用以耕地转出为主,耕地是研究区唯一减少的土地利用类型,而且减少量较大,居民点及工矿用地和草地以转入为主,其他用地的空间转移较为复杂;（2）以汛期6月份的累年平均降水量190 mm作为嘉陵江流域下游的降水量,土地利用类型综合产流能力1993年 > 2004年 > 2014年,径流系数分别为0.699,0.671,0.668,在空间分布上南部地区 > 中部地区 > 北部地区;（3）研究区不同类型土地利用的产流情况与土地利用类型面积相关联,当土地利用—土壤组面积发生变化时,其对应的产流能力也会发生变化,进而影响地表径流。     

A simple approach to soil loss prediction: a revised Morgan–Morgan–Finney model

A revised version of the Morgan–Morgan–Finney model for prediction of annual soil loss by water is presented. Changes have been made to the way soil particle detachment by raindrop impact is simulated, which now takes account of plant canopy height and leaf drainage, and a component has been added for soil particle detachment by flow. When tested against the same data set used to validate the original version at the erosion plot scale, predictions made with the revised model gave slopes of a reduced major-axis regression line closer to 1.0 when compared with measured values. The coefficient of efficiency, for sites with measured runoff and soil loss, increased from 0.54 to 0.65. When applied to a new data set for erosion plots in Denmark, Spain, Greece and Nepal, very high coefficients of efficiency of 0.94 for runoff and 0.84 for soil loss were obtained. The revised version was applied to two small catchments by dividing them into land elements and routing annual runoff and sediment production over the land surface from one element to another. The results indicate that, when used in this way, the model provides useful information on the source areas of sediment, sediment delivery to streams and annual sediment yield.     

太湖上游地区面源污染氮素入湖量模拟研究

以太湖上游地区为研究对象,通过TM/ETM解译获取土地利用信息,应用IDRISI软件的水文分析模块,对太湖上游地区进行流域划分,选择代表性小流域进行野外监测,分析流域土地利用与河流水质的联系,估算林地、耕地产出径流的面源污染总氮浓度特征;在此基础上采用代表性流域实测参数与分布式水文模型相结合的思路,开发基于单元格网的面源污染模拟模型,应用1980~2000年水文站实测序列对模型进行率定和校验,模拟太湖上游地区面源污染总氮的空间分布及入湖量。研究结果显示,太湖上游地区林地产出径流的总氮浓度参数为0.778 mg L-1,耕地产出径流的总氮浓度参数为2.518 mg L-1。模型及参数在太湖上游地区具有较好的应用效果,验证区径流模拟的平均误差为13%,总氮输出量模拟的平均误差为11.6%。应用模型估算太湖上游面源污染总氮入湖量为7 632 t a-1,约占总入湖量的40.8%。研究区内不同土地利用类型的面源污染总氮输出差异较大,其中耕地面源污染总氮输出量为4 289 t a-1,占面源污染输出总量的56.20%;林地和城镇用地面源污染总氮输出量分别为1 849 t a-1和1 270 t a-1,占面源污染输出总量的24.22%和16.64%。     

密云水库上游流域次降雨坡面产流产沙特征

以北京市密云县石匣小流域为研究区,利用2006-2010年连续5 a的坡面径流试验小区观测资料,运用统计方法,分析了密云水库上游流域的降雨、产流产沙特征以及在不同土地利用和不同坡度条件下,降雨量、降雨强度与产流、产沙之间的关系。结果表明:1)该研究区域水土保持治理措施实施的关键时间为每年的7、8月份,当降雨量大于10 mm时,应注意采取水土保持措施;2)在裸地、耕地和林地条件下,高雨量、中雨强型降雨为导致产流、产沙的主要雨型,在草地条件下,中雨量、高雨强型降雨为导致产流、产沙的主要雨型;3)中雨量高雨强型降雨条件下,林地的减流效益最好,低雨量低雨强型降雨和高雨量中雨强型降雨条件下,耕地的减流效益相对较低,草地和林地的减流效益差异不大;在3种不同雨型条件下,耕地、草地和林地的减沙效益差别不大;4)裸地条件下,降雨量与产流量间的关系更为密切,尤其在14.4°坡面下相关性最高;耕地条件下,产流量与降雨量的相关性较好,产沙量则与降雨强度的相关性较好,11.4°的坡面产流量、产沙量与降雨因子间的相关系数最高;草地条件下,降雨强度与产流量间的关系较为密切;林地条件下,产流量、产沙量与降雨因子间的相关性均不显著。研究结果可为密云水库上游水土保持措施及农业面源污染管理措施的科学实施提供依据。     

华南湿热山地小流域径流对气候变化和人类活动的响应——以宁江为例

基于1953—2013年宁江流域5个气象站日气温、降水量及控制站河口水文站月径流量数据与1986年、1995年、2005年、2013年宁江流域土地覆被分类数据,运用Mann-Kendall趋势分析、小波分析及累计量斜率变化比较法探讨了1953—2013年宁江流域气候变化与人类活动对径流变化影响。结果表明:(1)1953—2013年宁江流域温度发生显著上升,变化率为0.139℃/10a,降水变化波动较小,而径流量出现显著下降。(2)1990年前流域内径流量与气温、降水存在较为明显的27a周期规律,1990年以来受人类活动影响加大,径流量变化周期受到破坏,未能体现全域性;但在小尺度周期11a上仍与降水量保持同步,表明宁江流域径流量主要受降水影响。(3)随着经济发展以及水土保持工作的进行,到2013年林地面积占整个流域的73.8%,草地面积下降41.6%,耕地面积减少61.2%,土地利用变化较大区域发生在兴宁市北部。(4)与1953—1958年比,1959—2008年宁江流域径流量增加气候变化和人类活动贡献率分别为62.2%和37.8%,2009—2013年降水和人类活动对径流减少贡献率为45.8%和54.2%。     

Evaluation of runoff,peak flow and sediment yield for events simulated by the AnnAGNPS model in a belgian agricultural watershed

The AnnAGNPS model, widely utilized as a practical tool for addressing erosion problems and land use planning, was implemented in a small agricultural watershed located in central Belgium, to assess its prediction capacity of runoff, peak flow and sediment yield in humid temperate conditions. Model performance was evaluated at the event scale by using a database reporting hydrological, geomorphologic and land use data collected during a 2‐year period. Seventeen events were modelled and compared with the corresponding observations at the watershed outlet. The model performed well in predicting the largest runoff volumes, as shown by the high values achieved for the coefficients of efficiency (E = 0·89) and determination (r² = 0·92). However, some events resulted in zero runoff simulation. The prediction capability for peak flow and sediment yield was poor (E = 0·35 and 0·16, respectively). This inaccuracy can have several causes: the internal model deficiencies may be due to the incomplete representation of watershed complex processes, while external problems may be related to the conditions within the modelled watershed and the quality of recorded data. On the whole the AnnAGNPS model may be considered as being suitable to simulate the significant runoff events in the experimental watershed. However, the model may be seen as better suited for comparative assessments of alternative management and policy scenarios and for gross estimation of nutrient loads rather than the precise prediction of a single event, consequently helping in the prediction of land degradation problems in the experimented conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

人工集水面降雨径流观测实验研究

野外降雨径流观测实验研究表明 :土质集水面 (自然黄土坡面、清除杂草自然黄土坡面和夯实集水面 )的降雨产流方式为超渗产流 ,受降雨强度的影响大 ,径流的产生主要是由几次高强度的暴雨引起。此类集水面的年平均集水效率在 7.4%～ 35 .5 %之间 ,因此 ,增大集水区面积是保证土质集水面收集到更多雨水的基本途径。油毡、沥青和混凝土处理集水面的产流过程受降雨量和降雨强度的影响小 ,年平均集水效率在 5 0 %～ 80 %之间 ,但投资成本较高 ,其雨水利用方向是和设施农业相结合 ,修建固定集水面 ,发展高投入高产出农业。塑料膜集水面一次性投入低且平均集水效率较高 ,但寿命较短 ,建议利用简单临时性的移动塑料集水面收集雨水以供大田作物缺水期补灌。     

漯河市规划区雨洪格局空间分布特征综合量化研究

[目的]探索城市雨洪格局空间分布规律,为海绵城市建设提供参考。[方法]建立GIS数据库,ArcGIS空间模拟与SCS-CN,SWMM模型相结合,定量分析20a重现期和2h,85.43mm降雨,漯河规划区产流和积水分布特征。[结果]研究区径流量和径流系数(相等)、径流体积、峰值流量、积水区域的自相关Moran's I系数分别为0.338(p0.001),0.142(p0.001),0.101(p0.001),0.918(p0.001),表明产流与积水分布均呈现显著集聚性,土地类型和管网分布对产流影响大于积水过程,而地形影响则相反;径流量和径流系数由中心向外递减趋势,径流体积与峰值流量受汇水区面积和城市管网分布影响;高产流风险区不透水面占该区域82.73%,径流系数0.7和不透水面70%的汇水区集中在城市中心;积水区用地类型以农业用地、城市绿地、道路用地为主,分别占总面积的36.56%,21.39%,21.82%,分布特征存在显著差异。[结论]城市地表结构变化与城市产流和积水分布关系密切,综合量化方法可以直观地反映城市雨洪格局特征与趋势。     

Potential Use of Newly Isolated Bacterial Strain Ochrobactrum anthropi in Bioremediation of Polychlorinated Biphenyls

The effects of urbanization on runoff pollutant concentrations and pollutant loading were studied in three urban catchments of varying imperviousness and land use type in the city of Lahti, Finland. Imperviousness of the catchments were 19 % (“Low”), 62 % (“Intermediate”) and 89 % (“High”). During the 2-year study period, runoff quantity was measured continuously and samples were taken for water quality analysis. Besides imperviousness, land use type strongly affected pollutant concentrations: differences in total phosphorus (tot-P), Al, Cr, Zn and Pb concentrations were observed especially between the city centre catchments (High and Intermediate) and the residential catchment (Low), while total suspended solids (TSS), total nitrogen (tot-N), Mn, Co, Ni and Cu concentrations increased with increasing imperviousness. As for pollutant loads, imperviousness was strongly related to TSS, tot-P, Al, Mn, Zn, Cr, Co, Ni and Cu export. The effects of urbanization on runoff quality were season dependent: urbanization increased runoff volumes and, hence, pollutant loads, especially during warm seasons. Still, highest pollutant export in the catchments occurred during spring. Nevertheless, the warm period produced comparable loads to spring at the city centre catchments. Pollutant concentrations, especially in the city centre catchments, exceeded thresholds set for surface waters, indicating a need for runoff treatment in water quality protection.     

东北黑土区融雪径流对流域产沙的贡献及因素分析

[目的]揭示流域融雪期径流产沙特征及对全年总产沙的贡献,阐明东北黑土区影响融雪期产沙贡献的主控因素,并进而为东北黑土区流域综合治理提供科技支撑。[方法]基于东北地区203个气象站点数据以及15个流域水文站点径流泥沙资料,通过提取流域降水、地形、气候、土壤和土地利用等因子,采用多因素相关分析的方法,开展融雪期产沙贡献影响因素研究。[结果]东北黑土区不同流域年均降雪量占年均降水量的比例为3.7%～23.9%,空间分布差异较大,呈东南多、西北少的分布特点。融雪期径流深占全年径流深比例为13.7%～32.5%,融雪期产沙量对全年产沙量的贡献3.8%～23.47%,融雪期产沙模数占全年产沙模数的3.1%～35.9%,且它们空间分布规律性差。年均降水量、降雪量占降水量比例、融雪期径流深占全年径流深比例3个因素与融雪期产沙贡献在0.05的水平上呈显著相关。降雪量占降水量比例对流域融雪期产沙量和产沙模数的贡献率分别为25.41%和30.22%。最大高程对流域融雪产沙量和产沙模数的贡献率分别为24.36%和20.38%。[结论]东北区融雪期产沙对流域全年产沙有较大贡献,且受多重因素影响,未来应加强融雪期的侵蚀产沙观测研究。     

岔巴沟流域汛期径流模拟及地表产流特征分析

气候变化是影响流域水文循环过程的重要驱动因素,近年来,气候变化导致极端降雨—径流事件的频繁发生对人类社会经济发展构成了严重的威胁。因此,迫切需要开展流域水文模拟和产流特征分析。土壤和水评估工具(SWAT)是一种具有物理机制的分布式水文模型,已被广泛用于评价变化环境下的水文过程。以黄土高原岔巴沟流域为研究区,通过利用与黄土高原地区产流模式更为接近的Green-Ampt下渗法驱动SWAT模型模拟了岔巴沟流域日尺度的水文过程,并以水文响应单元为分析对象,结合4个降雨—径流事件的地表产流量和地表径流系数分析了降雨强度和前期土壤含水量对不同土地覆被产流特征的影响。结果表明：(1)基于Green-Ampt下渗法驱动的SWAT模型率定期和验证期E_NS为0.76,0.74,R²为0.78,0.75,模型能够较好地模拟日尺度流域水文过程;(2)流域不同土地覆被下地表径流系数随最大雨强的增加呈显著上升趋势,且最大降雨强度大于16 mm/h后地表径流系数显著增加,当土地覆被为耕地时降雨转化为地表径流的比例最大,其次为草地和林地;(3)前期土壤含水量的大小可以揭示大...     

典型泥石流小流域降雨和土地利用对坡面侵蚀的影响

[目的]揭示泥石流小流域降雨和土地利用对流域内坡面侵蚀的影响和作用,为泥石流的生态治理提供科学依据。[方法]以白龙江流域一级支沟——甘家沟泥石流小流域为研究区,基于该流域已建的5个径流小区(裸地、坡耕地、草地、土坎梯田、经济林地)连续5年的观测资料,利用K-均值聚类法,选择降雨量(P)、降雨历时(D)和最大30 min降雨强度(I₃₀)3个降雨指标,将该流域46次侵蚀性降雨事件划分为3类雨型(Ⅰ型、Ⅱ型、Ⅲ型),以平均径流系数和平均土壤流失量为主要指标,定量化分析了不同降雨雨型和土地利用类型对坡面产流产沙的影响和作用。[结果]径流和土壤流失对降雨的响应存在差异,平均径流系数为Ⅰ型降雨最高,其次为Ⅲ型和Ⅱ型降雨;土壤流失量为Ⅱ型降雨>Ⅰ型降雨>Ⅲ型降雨。最大30 min降雨强度与5种土地利用类型的径流系数和土壤流失量的正相关性最高,其次为降雨量、降雨历时。5种土地利用类型的平均径流系数为裸地>经济林地>坡耕地>草地>土坎梯田,土壤流失量为裸地>坡耕地>经济林地>草地>土坎梯田。降雨和土地利用相互作用下,径流...     

Rural land use in England and Wales and the delivery to the adjacent seas of nitrogen, phosphorus and atrazine

Abstract. In an exploratory study land use in 27 catchments covering most of England and Wales was assessed (using the land use classification devised by the then Institute of Terrestrial Ecology, now a part of the Centre for Ecology and Hydrology) and related to loads and concentrations of total nitrogen, phosphorus (mainly as orthophosphate (Op)) and some pesticides in river flows reaching the surrounding seas in the years 1990–1993. There are good correlations between seven land use types and the concentrations of total nitrogen ( r =0.83) and Op ( r =0.73) entering the seas. The correlations for individual land use types are best for arable land: total nitrogen, r =0.77; Op, r =0.65; and are positive. However, except for the mixed arable and grassland, the relationships between the other five land use types (improved grassland, upland grassland, upland moorland, upland mixed, and afforested and upland) and contaminant concentrations are negative. If data from the Mersey catchment are discarded, on the grounds that contaminant concentrations in the river seem unduly high, correlations between land use and contaminant concentrations reaching the seas are improved for all land uses: total nitrogen, r =0.89; Op, r =0.83; and atrazine, r =0.78. Loads and concentrations of pollutants in rivers entering the sea could be used to validate models of losses from catchments. Models may need to take greater account of runoff and transport of soil particles than they do presently.     

Impact of afforestation on hydrological response and sediment production in a small Calabrian catchment

Extensive afforestation using Pinus and Eucalyptus has taken place in Calabria since the early 1960's to control expansion of calanchi and biancane. In 1978 three small catchments were established near Crotone to monitor the effect of afforestation on hydrological response and sediment yield. In 1992, rainfall simulation experiments were carried out on plots in these catchments to determine more precisely the effect of tree and ground vegetation on surface runoff and erosional response. Most experiments were carried out in a logged catchment with slopes ranging from 20 to 30° and aspects from SW to NE. Results showed complex runoff generation and sediment production, reflecting the effect of microclimate and subtle variations in vegetation on infiltration characteristics. On south-facing slopes with little ground vegetation runoff generation was rapid with runoff coefficients from 27 to 37% and peak sediment concentrations reaching 83.7 g · 1⁻¹. On north-facing slopes with good tree cover, little grass, but continuous leaf litter, runoff coefficients reached 21%, but peak sediment concentration was only 3.6 g · 1⁻¹, while on recently logged north-facing slopes with dense grass cover the highest runoff coefficient was only 5.5% runoff coefficient, and there was virtually no sediment production. Implications of results for forest management and soil conservation are discussed.