An Efficient Multiple-Dimensional Finite Element Solution for Water Flow in Variably Saturated Soils

Multiple-dimensional water flow in variably saturated soils plays an important role in ecological systems such as irrigation and water uptake by plant roots; its quantitative description is usually based on the Richards＇ equation. Because of the nonlinearity of the Richards＇ equation and the complexity of natural soils, most practical simulations rely on numerical solutions with the nonlinearity solved by iterations. The commonly used iterations for solving the nonlinearity are Picard and Newton methods with the former converging at first-order rate and the later at second-order rate. A recent theoretical analysis by the authors, however, revealed that for solving the diffusive flow, the classical Picard method is actually a chord-Newton method, converging at a rate faster than first order; its linear convergence rate is due to the treatment of the gravity term. To improve computational efficiency, a similar chord-Newton method as for solving the diffusive term was proposed to solve the gravity term. Testing examples for one-dimensional flow showed significant improvement. The core of this method is to produce a diagonally dominant matrix in the linear system so as to improve the iteration-toiteration stability and hence the convergence. In this paper, we develop a similar method for multiple-dimensional flow and compare its performance with the classical Picard and Newton methods for water flow in soils characterised by a wide range of van Genuchten parameters.

Relations among Sap Flow, Soil Moisture, Weather, and Soybean Plant Parameters in High Water Demand and Final Growth Stages

The dynamics of sap flow in relation to plant morphology and weather conditions during reproductive growth of soybean (Glycine max. L. Merr.) influence decisions pertaining to efficient irrigation management and other inputs for high yields. Field studies began in 2017 at Marianna, Arkansas to measure moisture dynamics of soybeans during seed fill (R5 to R7) using heat balance stem flow gauges. Sap flow was highly correlated to solar radiation with maximum rates observed during beginning seed fill (R5). A solar radiation efficiency (SRE) value, calculated as hourly sap flow rate per Watt-hour of solar radiation (g/Wh2), is proposed. The SRE relates to crop water demand and hydraulic resistance of the soil-root-stem-leaf-pod-seed pathway. SRE values ranged from 0 - 1.2 g/Wh2. Soil moisture, growth stage, time of day, and weather conditions influenced the SRE, with higher values observed in the morning, late afternoon, and during R5 growth. Peak sap flows of 39 g/h at R5, 25 g/h at R6, and 3 g/h at R7 occurred. The ratio of measured sap flow to estimated crop evapotranspiration was 0.9 to 1.3 during R5 to R6.9 (maximum dry matter), but dropped to 0.2 at R7. Further research is needed to better understand late season reproductive moisture dynamics in soybeans.

Soil and water loss in the Lancang River-Mekong River watershed (in Yunnan section, China) and its control measures

According to a lot of hydrological and environmental monitoring data, the condition of soil and water loss in the Lancang River Mekong River watershed (in Yunnan section, China) is described. The occurrence and development of soil and water loss is analyzed. The conclusion is that: (1) generally, the situation of soil and water loss in the Lancang River Mekong River watershed (in Yunnan section, China) is light, however, soil and water loss in some regions is serious, especially in the middle reach area of the river; (2) soil and water loss in the Lancang River Mekong River (in Yunnan section, China) watershed presents developing tendency and it is mainly caused by human beings. In accordance with these results, the control measures for soil and water loss are discussed.

排渗失效下尾矿库溃坝三维模型试验研究

针对尾矿库渗透破坏模式,为克服二维试验槽边壁效应对模型渗流走向及溃决位置的影响,本文以某尾矿库为原型,基于自主设计的三维尾矿库溃坝模型试验平台,进行了排渗设施失效诱发的尾矿库溃坝模型试验研究,揭示了该尾矿库的溃决模式及溃决机理。结果表明:(1)排渗失效导致的溃坝呈现局部流土破坏-坝体累计变形-深层滑动面发展贯通-整体突发失稳的渐进伴突发型溃决演化模式;(2)坝体孔隙水压力骤变是坝体发生滑动破坏的关键响应指标,预示着坝体将在短时间内由滑动体前后缘局部散浸软化、流土、塌陷转变为大范围溃决,可作为坝体溃决事故的前兆信息;(3)排渗失效导致的尾矿库溃坝过程具有渐进性和突发性的特点,发生散浸与流土破坏的过程时间较长,发生深层滑动和溃决的时间短暂,该特征可为尾矿库渗透破坏隐患治理及坝体溃决应急响应提供参考。研究结果对尾矿库溃坝的灾害预防具有重要的现实意义。

2023年甘肃积石山6.2级地震灾害特征

2023年12月18日,甘肃省临夏州积石山县发生6.2级地震,震源深度10km。此次地震造成了大量人员伤亡。地震强度较大,建筑结构、非结构构件震害严重;生命线系统多见破坏;场地灾害主要表现为土壤液化、山体崩塌、液化流滑,其中以金田村的液化流滑现象尤为突出。与2018年印尼帕鲁7.5级地震、1303年洪洞8.0级地震、1920年海原8.5级地震相比,此次地震液化流滑现象具有低角度、大范围、长距离的显著特征。现场调查分析发现,充分的水利补给、物源区的明显凹陷是导致本次地震液化流滑规模巨大的原因,且此次流滑与2018年帕鲁地震流滑现象有多处相似之处,但两者流滑机理上存在着本质的不同,值得后续深入研究。对于此次地震,美国地质调查局给出的人员伤亡及场地破坏预测偏向保守,急需发展匹配抗震设防能力的震害预测方法。

考虑非达西渗流的泥浆离心脱水分析

为深入探究离心脱水技术在处理主要由黏性土组成的建筑废弃泥浆时的内在机理及其影响因素,利用分段线性化方法,充分考虑黏性土中渗流的非达西特性以及土体变形的非线性特征,建立在离心作用下能够考虑其非达西渗流特性的泥浆脱水分析模型。通过与已有研究成果及室内试验结果的对比,证明了该模型的有效性。在此基础上,分析了模型参数对脱水过程的影响。研究结果表明:脱水速度和最终土水界面位移量随着电机转速的增大而增大;增加泥浆初始厚度会增大最终土水界面位移量,但会降低初期的土水界面移动速度;压缩指数在初期对土水界面位移的影响并不明显,但其增大会导致最终土水界面位移量的增加;非达西渗流参数的增大会导致土水界面位移的减少,但通过提升电机转速,可以有效地降低非达西渗流对脱水效果的不利影响。研究成果可为离心脱水技术在建筑废弃泥浆处理中的进一步优化与应用提供借鉴和参考。

Re-Examining Field-Surveyed Variations in Elevation and Soil Properties with a 1-m Resolution LiDAR-Generated DEM

This article presents a 2017 LiDAR-DEM guided 1-m resolution examination of field-surveyed elevation and soil property variations (5 × 5 m spacings) conducted in 1977 across a hummocky New Brunswick field used for potato production. This examination revealed that the field incurred minor elevation differences likely due to upslope erosion as revealed through increasing Sand % and CF % with increasing elevation, and increasing Silt % along low-lying areas. Soil moisture, field capacity, permanent wilting and nitrate nitrogen (NO3-N) also increased at downslope locations. Directly as well as indirectly, soil pH, ammonium nitrogen (NH4-N), Caesium137 (Cs137) and Mehlich-3 extracted Ca, Mg, K, Fe, Mn, Cu, and Zn were likewise affected by topographic location. Factor analyzing these variables led to: 1) a Soil Loss Factor that captured 24% of the textural variations;2) a Soil-Cropping Factor accounting for 16% of the N, P, K, Ca, Mg, Mn variations;3) a Soil Organic Matter (SOM) Factor relating 9% of the in-field variations for SOM, Fe, Zn, Cu to via organo-metal complexation and low NO3-N retention. Many of the topographic variations increased or decreased with the metric DEM-projected depth-to-water index (DTW) index. This index was set to 0 along DEM-derived flow channels with minimum upslope flow-accumulation areas of 0.1, 0.25, 0.5, 1 or 4 ha. Among these, the DTW > 4 ha threshold was useful for reproducing the textural variations, while the DTW > 0.25 ha threshold assisted in capturing trends pertaining to moisture retention and elemental concentrations.

土壤水蚀对荒漠草原针茅斑块分布格局形成的影响

[目的]探讨土壤水蚀对希拉穆仁草原克氏针茅斑块分布格局的影响机制,为该区域的水土流失治理提供理论依据。[方法]采用野外调查和方差均值比率法设定了3个分布格局(聚集分布、均匀分布和随机分布格局)2个对照(不放牧和裸坡),进行降雨强度为30,60,90,120 mm/h的室内模拟降雨试验,量化了不同分布格局坡面的产流产沙过程。[结果](1)重度放牧和不放牧为聚集分布格局,中度放牧为均匀分布格局,轻度放牧为随机分布格局。(2)30 mm/h雨强不产流,60 mm/h雨强产流率呈:裸坡>聚集分布>随机分布>均匀分布>不放牧;90 mm/h雨强呈:裸坡>聚集分布>均匀分布>随机分布>不放牧;120 mm/h雨强呈:裸坡>聚集分布>不放牧>均匀分布>随机分布;(3)30 mm/h雨强不产沙,60 mm/h雨强产沙率呈:裸坡>均匀分布>不放牧>随机分布>聚集分布;90 mm/h雨强呈:裸坡>聚集分布>均匀分布>随机分布>不放牧;120 mm/h雨强呈:裸坡>不放牧>聚集分布>均匀分布>随机分布;(4)120 mm/h雨强随机分布的减沙效益最好,可减少88.76%,90 mm/h雨强的不放牧减流效益最好,可减少45.78%。[结论]放牧促使克氏针茅出现斑块化的现象,土壤水蚀加剧了裸地斑块的形成,进而使克氏针茅斑块出现了不同的分布格局。

根-土复合体岸坡渗流及稳定数值模拟

植物护岸中根系力学效应可显著提高岸坡浅层稳定性,但对降雨和水位变化等条件下,根系水力效应与力学效应之间相对关系变化对岸坡浅层稳定性影响的研究较少。采用数值分析方法模拟了岸坡根-土复合体从非饱和到饱和(降雨工况和水位上升工况)、从饱和到非饱和(水位下降工况)过程中根-土复合体水力效应对岸坡渗流场的影响,进一步分析了不同水力特性条件下根-土复合体对岸坡浅层稳定性的影响。模拟计算结果表明:(1)在设定的3种降雨强度下,根-土复合体的优先流入渗作用与降雨强度和降雨时间均呈正相关,而排水作用与降雨强度和降雨时间均呈负相关。在长历时的小降雨或短历时的强降雨情况下,由于降雨影响深度增大,根-土复合体水力效应带来的消极影响占主导地位。(2)在水位下降工况下,根-土复合体排水作用有滞后性,力学效应仍占主导地位;在水位上升工况下,根-土复合体增渗作用随水位上升速率增加而增强,根-土复合体的力学效应逐渐被水力效应所掩盖。研究结果对植物护岸工程应用具有借鉴意义,即使采用植物生态护岸,也应加强坡面排水和坡体排水措施。

盐渍土地区路基边坡冲刷破坏影响因素

了解水流特征、边坡结构和土质条件对边坡冲刷的影响及其破坏形式,是为盐渍土地区工程设计和施工防护提供科学依据的前提。结合室内试验方法,对盐渍土路基边坡冲刷工程进行模拟。结果表明:水流的冲刷致使路基边坡发生明显的变化,边坡坡脚首先受到水流的影响,其动态过程表征为水流浸泡冲刷—形成淘空槽—边坡上部土体掉落—冲刷深度范围扩大;随着流速、水深增加,坡脚冲刷程度增大,而坡比的影响恰恰相反;此外冲刷角的变化改变了最大冲刷深度出现的位置;相比于NaCl盐渍土路基边坡,Na 2SO 4盐渍土盐量的增加,坡脚处冲刷范围和最大冲刷深度出现呈现相反的减少趋势。

外源秸秆对污染土壤氧化还原过程水分散性胶体态重金属的影响

土壤胶体尤其是水分散性胶体,作为一种重要的污染物载体,在重金属吸附、迁移以及生物吸收过程起着重要作用。通过土壤培养试验探讨了外源添加水稻秸秆在氧化还原波动条件下如何影响土壤液相中及水分散性胶体中重金属的分布。结果表明,外源秸秆增加厌氧过程液相中溶解性有机碳(DOC)、砷(As)、铁(Fe)、锰(Mn)、钙(Ca)、钾(K)、硅(Si)、铝(Al)、镁(Mg)等浓度,降低了厌氧过程氧化还原电位(Eh)及铜(Cu)、铅(Pb)等浓度,提高了好氧过程Pb浓度。利用非对称流场流分馏-紫外可见-电感耦合等离子体-质谱联用技术(AF4-UV-ICP-MS),测得水分散性胶体颗粒主要分布在0.3~3 kDa、3~40 kDa和130 kDa~450 nm三个粒径范围,各粒径颗粒的组成有所差异,主要含有机质、无机黏土矿物和铁矿物等。外源秸秆促进液相中Fe和As由胶体态向溶解态转化,促进镉(Cd)和Cu由溶解态向胶体态转化。本研究有助于揭示农业活动影响重金属迁移转化及有效性的界面机制。

膜下滴灌滴水流量对棉花根系分布的影响

为探明膜下滴灌条件下滴水流量对棉花根系分布的影响,采用田间定位试验,设置3组滴水流量,分别为1.69 L·h^(-1)(W169)、3.46 L·h^(-1)(W346)和6.33 L·h^(-1)(W633),分析膜下滴灌土壤水吸力对棉花根系空间分布特征的影响。结果表明:滴水流量越大,膜外裸地和膜内土壤的基质吸力越小,边行棉花根系吸水受到的胁迫程度也越小,W633处理膜下根区土壤水吸力分布均匀且适合棉花生长,棉花根长密度水平分布不论是初期还是后期均呈双峰抛物线分布;棉花根重密度呈现出相同的变化规律,内、边行棉花根重密度在花期、铃期、吐絮期的差值分别为42.26、-0.22、97.40 g·m^(-3)。当滴水流量越小时,膜外裸地的基质吸力大于膜内土壤的基质吸力,致使边行棉花的根系吸水受到较大胁迫,W169处理棉花根长密度水平分布由生育初期的双峰抛物线分布变为后期的单峰抛物线分布;内、边行棉花根重密度在花期、铃期、吐絮期的差值分别为299.70、304.86、369.84 g·m^(-3)。表明随着滴水流量的增加,膜下滴灌行间棉花根系生长更加均匀,研究结果可为棉花膜下滴灌系统设计提供技术参考。

模拟干旱下杨树树干液流特征及其对环境因子的响应

[目的]研究干旱对杨树人工林树干液流的影响,可以深入理解杨树人工林对全球降水格局改变的响应。[方法]于2018年9月—2020年11月以东台林场10年生杨树(Populus deltoides)人工林为对象,采用穿透雨移除法模拟干旱处理:CK(对照)、D_(1)(30%穿透雨移除)、D_(2)(50%穿透雨移除),利用热扩散探针技术连续测定杨树人工林的液流变化,结合同步监测的环境因子,揭示杨树人工林对环境因子的响应规律。[结果](1)3个处理下杨树人工林树干液流年变化曲线呈现单峰型,与饱和蒸汽压差、光合有效辐射的年际变化曲线相似。树干液流速率在夏季达到峰值,接着随着时间推移逐渐下降,到达林木休眠期时液流密度趋近于0;(2)模拟干旱下,随着截流程度增大,树干液流随之降低。D_(1)和D_(2)生长季液流密度平均值比对照组显著下降了24%~39%(p<0.05);(3)混合效应模型表明饱和蒸汽压差和土壤温度与液流变化极显著相关(p<0.01),大气温度,降雨量和土壤温度与液流变化显著相关(p<0.05)。[结论]移除30%的穿透雨提高了各环境因子对液流变化的解释程度,即干旱条件下会提高树干液流对环境变化的敏感性,其中土壤含水量对液流变化的解释率最高。未来仍需继续探讨树木自身性状对环境的响应。

甘肃省庆城县极端暴雨下水保措施抵御暴洪灾害的能力

[目的]最大洪峰流量是导致暴洪灾害的决定性因素。研究小流域降水频率、治理程度与洪峰流量、暴洪灾害损失的关联性,为水土保持减灾防灾工作提供科学依据。[方法]采用回归分析、对比分析等方法,对甘肃省庆阳市庆城县蔡家庙、野狐沟两条相邻流域1981—2022年水保措施的调水效益以及降水因子、水保措施对洪峰流量的影响进行分析。[结果](1)小流域水保措施调水效益随治理程度的提高而增加,随降水频率的提高而减少。(2)年最大日降水量对洪峰流量变化具有极显著的正向影响(p<0.01),贡献率系数为0.707;治理程度对洪峰流量呈负影响,贡献率系数为-0.237。(3)30 a一遇洪峰流量(频率为3%)与50 a一遇洪峰流量(频率为2%)灾害损失强度分别达到1.74×10^(5),3.13×10^(6)元/km^(2),后者比前者增长了16.95倍。[结论]影响洪峰流量变化的主要因素是年最大日降水量。水保措施对削减洪峰流量具有显著的影响。流域治理程度越高,削减洪峰流量的效果越明显,减少暴洪灾害经济损失的能力越大。

全吸力范围非饱和持水函数和渗透性函数的预测模型

非饱和土的持水函数和渗透性函数是刻画其持水能力和水分运移的基本参数。由于物理机制不同,持水函数及渗透性函数在毛细阶段和吸附阶段的特征有显著差异。多数传统的持水和渗透性函数仅考虑了毛细阶段内,毛细水的持水和渗透特性,不能表征吸附阶段内吸附水的特征。为使传统函数模型在吸附阶段也适用,以传统VG持水函数和VG-M渗透性函数为基础,用修正参数C(ψ)修正VG持水函数,并以此确定非饱和土的残余值ψr,区分毛细水的毛细流动和吸附水的薄膜流动。基于薄膜流动的特点,提出参数Γ(ψ),改进了传统VG-M渗透性函数在吸附阶段内低估非饱和渗透系数这一问题,从而建立了全吸力范围的渗透性函数模型。最后用3组持水及渗透性试验结果验证修正模型的合理性,结果表明修正持水函数模型和渗透性函数模型的预测结果在吸附阶段较传统模型更符合实测结果。

富水砂层土压平衡盾构渣土改良技术研究

富水砂层土体具有流塑性差、渗透性强的特点,土压平衡盾构施工时易造成排土困难和喷涌事故。针对西安地铁10号线穿越富水砂层的土压平衡盾构工程,采用膨润土泥浆和泡沫剂改良盾构渣土,提出了改良渣土流塑性的评价方法,基于其流塑性和渗透性确定最佳改良方案,为工程提供借鉴和参考。结果表明:(1)当改良渣土塌落后无开裂或坍塌、塌落形状为梨形、塌落度为180~210 mm、塌落渣土与地面接触角θ为0°~90°时,流塑性合适,此时改良渣土的渗透系数于90 min内稳定在10-5cm/s,满足工程要求;(2)最佳改良方案为:渣土、膨润土、水三者质量比保持在200∶1∶40~200∶1.5∶44之间,泡沫剂溶液体积比浓度为2%,泡沫注入比为6%。

Soil Moisture Response to Rainfall in Forestland and Vegetable Plot in Taihu Lake Basin,China

Soil moisture and its spatial pattern are important for understanding various hydrological,pedological,ecological and agricultural processes.In this study,data of rainfall and soil moisture contents at different depths(10 cm,20 cm,40 cm and 60 cm) in forestland and vegetable plot in the Taihu Lake Basin,China were monitored and analyzed for characteristics of soil moisture variation and its response to several typical rainfall events.The following results were observed.First,great temporal variation of soil moisture was observed in the surface layer than in deeper layer in vegetable plot.In contrast,in forestland,soil moisture had similar variation pattern at different depths.Second,initial soil moisture was an important factor influencing the vertical movement of soil water during rainfall events.In vegetable plot,simultaneous response of soil moisture to rainfall was observed at 10-and 20-cm depths due to fast infiltration when initial soil was relatively dry.However,traditional downward response order occurred when initial soil was relatively wet.Third,critical soil horizon interface was an active zone of soil water accumulation and lateral movement.A less permeable W-B soil horizon interface(40-cm depth) in vegetable plot can create perched water table above it and elevate the soil water content at the corresponding depth.Fourth,the land cover was an effective control factor of soil moisture during small and moderate rainfall events.In the forestland,moderate and small rainfall events had tiny influences on soil moisture due to canopy and surface O horizon interception.Fifth,preferential flow and lateral subsurface interflow were important paths of soil water movement.During large and long duration rainfall events,lateral subsurface flow and preferential flow through surface crack or soil pipe occurred,which recharged the deep soil.However,in more concentrated large storm,surface crack or soil pipe connected by soil macropores was the main contributor to the occurrence of preferential flow.Findings of this study provide a theoretical foundation for sustainable water and fertilizer management and land use planning in the Taihu Lake Basin.

Soil surface roughness change and its effect on runoff and erosion on the Loess Plateau of China

As an important parameter in the soil erosion model, soil surface roughness（SSR） is used to quantitatively describe the micro-relief on agricultural land. SSR has been extensively studied both experimentally and theoretically; however, no studies have focused on understanding SSR on the Loess Plateau of China. This study investigated changes in SSR for three different tillage practices on the Loess Plateau of China and the effects of SSR on runoff and erosion yield during simulated rainfall. The tillage practices used were zero tillage（ZT）, shallow hoeing（SH） and contour ploughing（CP）. Two rainfall intensities were applied, and three stages of water erosion processes（splash erosion（I）, sheet erosion（II） and rill erosion（III）） were analyzed for each rainfall intensity. The chain method was used to measure changes in SSR both initially and after each stage of rainfall. A splash board was used to measure the splash erosion at stage I. Runoff and sediment data were collected continuously at 2-min intervals during rainfall erosion stages II and III. We found that SSR of the tilled surfaces ranged from 1.0% to 21.9% under the three tillage practices, and the order of the initial SSR for the three treatments was ZT〈SH〈CP. For the ZT treatment, SSR increased slightly from stage I to III, whereas for the SH and CP treatments, SSR decreased by 44.5% and 61.5% after the three water erosion stages, respectively, and the greatest reduction in SSR occurred in stage I. Regression analysis showed that the changes in SSR with increasing cumulative rainfall could be described by a power function（R2〉0.49） for the ZT, SH and CP treatments. The runoff initiation time was longer in the SH and CP treatments than in the ZT treatment. There were no significant differences in the total runoff yields among the ZT, SH and CP treatments. Sediment loss was significantly smaller（P〈0.05） in the SH and CP treatments than in the ZT treatment.

Severe drought strongly reduces water use and its recovery ability of mature Mongolian Scots pine(Pinus sylvestris var. mongolica Litv.) in a semi-arid sandy environment of northern China

Trees growing in a semi-arid sandy environment are often exposed to drought conditions due to seasonal variations in precipitation, low soil water retention and deep groundwater level.However, adaptability and plasticity of individuals to the changing drought conditions greatly vary among tree species.In this study, we estimated water use(Ts) of Mongolian Scots pine(MSP;Pinus sylvestris var.mongolica Litv.) based on sap flux density measurements over four successive years(2013–2016) that exhibited significant fluctuations in precipitation in a semi-arid sandy environment of northern China.The results showed that fluctuations in daily Ts synchronously varied with dry-wet cycles of soil moisture over the study period.The daily ratio of water use to reference evapotranspiration(Ts/ET0) on sunny days in each year showed a negative linear relationship with the severity of drought in the upper soil layer(0–1 m;P<0.01).The decrease in Ts induced by erratic drought during the growing season recovered due to precipitation.However, this recovery ability failed under prolonged and severe droughts.The Ts/ET0 ratio significantly declined with the progressive reduction in the groundwater level(gw) over the study period(P<0.01).We concluded that the upper soil layer contributed the most to the Ts of MSP during the growing season.The severity and duration of droughts in this layer greatly reduced Ts.Nevertheless, gw determined whether the Ts could completely recover after the alleviation of long-term soil drought.These results provide practical information for optimizing MSP management to stop ongoing degradation in the semi-arid sandy environments.

Distribution Regularity of Debris Flow and Its Hazard in Upper Reaches of Yangtze River and Other Rivers of Southwestern China

In the upper reaches of Yangtze River and other rivers of southwestern China, the debris flows develop and lead to most serious disasters because of the various landforms, complex geological structures and abundant rainfall. The distribution of debris flows has regularity in the regions with different landform, geological structure, and precipitation. The regularities of distribution of debris flows are as following： （1） distributed in transition belts of different morphologic regions; （2） distributed in the area with strong stream trenching; （3） distributed along fracture zones and seismic belts： （4） distributed in the area with abundant precipitation; （5） distribution of debris flow is azonal. The activity of abundant debris flows not only brings harm to Towns, Villages and Farmlands, Main Lines of Communication, Water-Power Engineering, Stream Channels etc., but also induces strong water and soil loss. According to the present status of debris flow prevention, the problems in disasters mitigation and soil conservancy are found out, and the key works are brought up for the future disasters prevention and soil conservancy.