径流作用下泥石流固体物质冲刷速率试验研究

[目的] 探讨泥石流固体物质的冲刷深度随时间的变化规律,以及对应的冲刷速率与不同影响因素之间存在的关系,为泥石流规模预测及防治工程设计提供参考依据。[方法] 根据激光测距仪的历时测距原理,借助试验方法分析泥石流固体物质冲刷深度随时间的变化规律以及对应的冲刷速率与不同影响因素之间的关系,包括来流流量、水力半径、沟床纵坡以及细粒物质含量等。[结果] 冲刷速率与水力半径间呈指数关系,与来流流量间呈正相关关系,与能坡梯度间呈指数关系;若固体物质为均匀冲刷,冲刷速率与剩余切应力成线性正相关关系;对于初始含水率相对较低的固体物质,冲刷速率随着细粒物质含量的增大呈微小增大趋势。[结论] 在薄层径流条件下,能坡梯度对冲刷速率的影响高于水力半径。     

溯源冲刷实验观测分析

溯源冲刷在土壤冲刷过程常常扮演着重要的角色,为加强推估土壤冲蚀量之精确度,对于溯源速度与溯源冲刷量之估算即为主要课题。本研究对于均匀砂以固定流量下进行溯源冲刷实验分析,由溯源冲刷形态与演变的观测,进而分析溯源速度和溯源冲刷量。结果显示,溯源冲刷速度与冲刷量和时间呈 1/2指数关系,由此结果将可供水利工程规划设计参考用。     

大凌河自然冲刷深度分析

研究河道自然冲刷深度 ,可确定跨河建筑物设计的经济、安全性。影响河道自然冲刷的因素主要有水流、河床质、流域地形地貌等。大凌河下游区河道冲刷较普遍 ,河床演变较大 ,以大凌河中下游上窝堡、朝阳、锦县 3个水文站资料为基础研究资料 ,分析建立最大冲刷深度 (Hs)与相应流速 (v)、水深 (h)之间的相关关系 ,最大流速和水深的相关性较好 ,可供使用。     

黄土高原沟头侵蚀柔性防护措施研究

黄土高原沟壑纵横,塬面水流在入沟过程中,不断冲刷沟头,导致沟底下切,沟壁坍塌,形成溯源侵蚀。为防止从沟头跌落的水流对沟底冲刷,减缓沟头侵蚀发展,保护塬面,采用柔性防护措施消减水流动能。试验通过覆麦草和土工布模拟柔性防护措施,研究柔性防护措施的消能机理。试验以裸土为对照,测定在高水头冲刷下,不同防护措施的冲刷坑深度、坑径、坑面积及坑容积,定量分析了柔性防护措施的作用效果。结果表明:随着覆麦草量的增加,冲刷坑深度呈线性递减、容积呈指数递减;而加覆土工布,能显著提升防护效果;在4.93 m试验水头冲刷3 min的条件下,覆2 400 g/m²麦草和1层土工布能够完全保护土面不被冲刷。柔性防护措施具有良好的消减水流动能的作用,对防止沟床下切,有效保护塬面,防治沟头侵蚀效果显著。     

不同宽度冲刷槽对崩岗崩积体产流产沙的影响

为了解不同宽度冲刷槽对坡面冲刷侵蚀过程中产流产沙的影响,该研究以崩岗崩积体为对象,通过不同冲刷槽宽度(10、20、30、40、50 cm)和不同单宽流量(1.2×10-2、2.4×10-2、3.6×10-2、4.8×10-2 m2/min)相结合的室内模拟冲刷试验,研究不同宽度冲刷槽对崩积体产流产沙的影响。结果表明:1)单宽流量为1.2×10-2,2.4×10-2,3.6×10-2 m2/min时,不同冲刷槽宽度之间径流率、产沙率存在显著差异(P0.05);单宽流量为4.8×10-2 m2/min时,不同冲刷槽宽度之间径流率、产沙率差异不显著。2)单宽流量一定,不同冲刷槽宽度下径流率随时间变化趋势相同;单宽流量为1.2×10-2 m2/min时,不同冲刷槽宽度条件下产沙率和含沙量随时间变化趋势不同,其他单宽流量下产沙率和含沙量随时间变化趋势相同。3)单宽流量相同,不同冲刷槽宽度下累积径流量差异不显著;单宽流量为1.2×10-2,2.4×10-2,3.6×10-2 m2/min条件下,不同冲刷槽宽度下累积产沙量和平均含沙量差异显著(P0.05)。该研究揭示了冲刷槽宽度对崩积体产流产沙的影响,为今后试验冲刷槽宽度的选择提供参考。     

草地坡面径流调控放水试验研究

通过坡面放水模拟径流冲刷试验，研究了不同放水流量下草地减水减沙效应，并从起流历时、径流流速、径流深度等方面分析了草地调控水沙的机理。结果表明：（1）草地具有显著的减水减沙效应，平均径流系数较对照减少28．3％，输沙率较对照减少78．4％。（2）裸地与草地坡面产流规律一致，裸地土壤坡面的输沙率呈先增后减再增的变化趋势，而草地坡面的输沙率呈先增后减然后逐渐趋于稳定。（3）草地能将坡面径流起流历时推迟3倍以上，可将径流流速减小40％，从而使草地坡面的径流入渗率明显增加，使径流的冲刷能力和输沙能力迅速下降。（4）草地对径流深度的影响不明显，径流深度的变化难以反映草地对径流的调控作用，径流流速可能会更好地反映水土保持措施的径流调控效果和能力。     

晋西黄土丘陵沟壑区山区道路冲刷及防治研究

在晋西黄土丘陵沟壑区,山区道路产流产沙是流域产流产沙的重要组成部分,道路往往成为径流泥沙输移的通道之一.据观测,山区道路的冲刷量是随着路面水流流线长度的增加而增大的,故其防治应从缩短水流流线等方面入手.采取道路路边排水渠与早井相结合、道路设横隔,可有效地防治路面冲刷,达到保护山区道路之目的.     

路基边坡坡面冲刷发生条件探讨

探讨了坡面冲刷过程中土壤的受力情况、坡面流能量及其平衡。从土壤的冲刷起动拖曳力入手 ,得出了发生坡面冲刷的条件。最后给出了一个工程算例。     

草被覆盖对坡面细沟发育影响试验研究

利用试验土槽和放水冲刷试验方法，研究了3种流量（3L／min、5L／min和8L／min）、3种覆盖度（O、30％和80％）下坡面细沟发育变化过程及特征。结果表明，覆盖度越大，细沟的数量、深度、宽度越小。在3L／min流量下，30％和80％覆盖的坡面基本不产生细沟，而当流量增到8L／min时，空白坡面冲刷极为剧烈，坡面被冲塌。水流形态的变化间接反映了细沟的演变过程。     

冲刷时间对土壤分离速率定量影响的实验模拟

土壤分离过程为侵蚀产沙提供了物质准备 ,对它发生、发展的过程进行准确模拟 ,具有重要的实践和理论意义。利用变坡实验水槽 ,在较大流量 (0 .5～ 1 .5 L / s)和坡度 (5°～ 1 5°)范围内 ,系统研究了冲刷时间对土壤分离速率的定量影响。研究结果表明 :不同流量和坡度条件下 ,土壤分离速率均随着冲刷时间的延长而呈良好的幂函数形式下降 (Dr=At B) ,系数 A随着流量和坡度的增大而增大 ;土壤分离速率与坡度和流量间的关系随着冲刷时间的不同而不同 ,当冲刷时间在 1 0 s以内时 ,随着冲刷时间的增加土壤分离速率与流量和坡度间的相关性增大 ,当冲刷时间大于 1 0 s后 ,随着冲刷时间的增大其相关性反而减小 ;以土样下切 2 cm为条件 ,建立了最佳冲刷时间与流量和坡度间的幂函数关系 ,为相关实验径流冲刷时间的设计提供了思路     

黄河流域第三副区坝系拦沙输沙监测成果分析

黄河流域第三副区聂家河小流域坝系工程布局以现有骨干工程为骨架,各级沟道自上而下逐段布设小型淤地坝、中型淤地坝和骨干工程,分级拦蓄径流泥沙;在其示范坝系的典型淤地坝上布设了降雨、拦沙及输沙监测点.监测结果表明:坝系工程抬高了侵蚀基准,稳定了沟坡,控制了沟床下切和沟岸扩张,增强保土保水能力,尤其骨干坝在坝系拦沙中起关键作用,能够快速有效地拦蓄径流泥沙,控制水土流失,是水土保持生态建设的重要措施,为保护下游河流安全起到了重要作用.     

河道冲淤调整对窟野河产沙量影响初步分析

实测资料表明窟野河流域神木—温家川区间输沙模数异常偏大,通过对该区间泥沙冲淤调整特点的分析和洪水期河道冲刷增加沙量的计算,阐明了河道冲淤调整对窟野河产沙量的影响,并提出了水土保持综合治理建议,以期为预测黄河来沙量及流域水土保持提供支持。     

长江滨江城市环境保护工程之一——汉口边滩防洪及环境综合治理效益浅析

从定、动床试验及环境保护进行分析研究。定床试验:研究工程实施后,本河段的水位,流速、流态及天兴洲左右汊分流比的变化;动床试验:研究在不同典型水文年条件下的河势、河道冲淤变化及疏浚区的回淤问题,为治理方案的比选优化及工程决策提供科学依据。这是长江干流滨江城市河道整治的先声,是城市规划建设中环境保护工程实施的首例,意义重大。其环境、社会及经济等效益也将十分显著。     

裸露砒砂岩区坡面侵蚀过程中地表粗糙度与水力侵蚀特征参数的关系

坡面地形起伏状况是影响土壤侵蚀状况的重要因素,深入了解地表粗糙度和产流产沙以及水动力参数之间的关系是研究坡面土壤侵蚀过程的基础.采用野外原位模拟冲刷试验,使用三维激光扫描仪结合ArcGIS提取地形因子参数,研究了裸露砒砂岩区坡面侵蚀过程中地表粗糙度与侵蚀特征参数的关系.结果表明:(1)冲刷强度的增大使得阻力特征参数逐渐...     

Changes in bedload transport rate associated with episodic sediment supply in a Japanese headwater channel

We conducted field monitoring of bedload transport rate associated with experimental sediment release in a natural channel to clarify behavior of the supplied sediment on mixed size bed. Observation of bedload rate at two sites along the 30 m channel reach revealed that downstream migration of finer particles delay compared with coarser particles. Ratio of the bedload sediment that deposited during the migration was higher for finer sediments. These behaviors of the mixed size particles were clear during passage of the sediment wave without changes in water discharge. Flashing peak of discharge that caused artificially by opening of the dam gate did not destroy channel bed structure including steps and pools formed by coarser sediments, and only small amount of bedload was mobilized. Both reach scale channel features including steps, pools, and riffles as well as fine scale features (i.e., armour coat) likely increased critical shear stress of particles and decreased bedload rate during our experiment. Extreme sediment supply induced two types of sediment deposition; (1) filling the pools in reach sales and (2) the intrusion of fine particles into the coarser sediment that formed an armour layer. The all grain size fractions can deposit as type (1) when shear stress of stream water is not enough to entrain bedload particles, while deposition type (2) occurs when finer sediment pass over channel bed on which armour coat is well-developed. Deposition of finer sediment into coarser sediment that forms armour coat is affected by grain size distribution of bed surface sediment. Thus, impact of the sediment supply on downstream channel depends on both bedforms and grain size distribution of bed surface sediment over which the supplied sediment pass.     

Channel aggradation below Chew Valley Lake,Somerset, U.K.

Variations of channel substrate composition are described for a regulated river which has experienced channel change since dam completion. Sediment samples were obtained using bulk (grab) sampling and freeze-coring. Data derived from the two methods are shown to differ. Bulk-sample data describe the bed surface layer; its grain-size variations are related to bedform. Freeze-core data describe the sub-surface structure and the fine size-grades.The gravel framework-supported substrate of the control reaches constrasts with the sand-dominated substrate of the aggraded reach, although in both cases the substrate coarsens upwards. In the former this relates to the development of a sand matrix within the gravel-framework substrate, and in the latter, sand-bed channel, to the progressive addition of a gravel component towards the surface which is related to the process of channel change. At the local-scale, bedform is shown to exert an important control on the character of substrate change induced by flow regulation.     

Bed scouring downstream of hydraulic structures under steady flow conditions: Experimental analysis of space and time scales and implications for mathematical modeling

Sediment transport and bed deformation in alluvial rivers are space and time dependent. The knowledge of the space and time scales can be helpful for the definition of predictive procedures of an alluvial reach response to changing boundary conditions. In this work, attention is paid to scouring process occurring downstream of the rigid basement of a hydraulic structure. The analysis is focused on transient bed profiles which are determined, under steady flow conditions, by a decrease of the upstream sediment transport rate. In particular, the paper is aimed at improving understanding of the space and time scales required by the alluvial system to reach the equilibrium conditions. For this purpose, movable-bed runs are carried out in a straight laboratory channel, for two values of the water discharge. During each run, the longitudinal bed profiles are measured at different times. Based on experimental data, spatial scale factors of the bed scouring and of the bed load transport to reach the equilibrium conditions are defined. Particularly, it is found that the scour length varies especially during the first evolution phase and then it oscillates around of a mean value that is about 40% of the channel reach interested by the phenomenon under consideration; an expression is found for the adaptation coefficient which allows the estimation of the spatial delay of the bed load transport rate. Using both the collected data and literature data an expression defining the time scale of scouring is deducted. According to this expression the non-dimensional time scale is related to Shields parameter through an exponential law. Then, by the help of a 1-D numerical model previously developed by the writer, the implications for choosing the spatial and temporal resolutions, on which numerical results depend significantly, are shortly discussed. The results show that the time and space scales, which represent physical constraints of the spatial and temporal resolutions, need to be properly defined in order to simulate the scouring process evolution.     

Effectiveness and geomorphological impacts of check dams for soil erosion control in a semiarid Mediterranean catchment: El Cárcavo (Murcia, Spain)

The construction of transverse structures (check dams) is a widely used method in Spanish Mediterranean areas to stabilise gullies and ephemeral streams, to reduce channel incision and to prevent sediment deposition downstream. The effectiveness of check dams and their effects on the morphology of ephemeral channels (ramblas) were investigated in a semiarid, highly degraded catchment. In the study area, 36 dams were surveyed, of which 29 were filled up with sediments, 2 had been destroyed and only 5 had still not completely filled with sediments. The streams above the dams held sediments, which resulted in a decrease in the longitudinal gradient. Field observations of changes in the cross-sectional shape of the stream channel, the composition of channel bed material, and bankfull stage measurements indicated that the dams cause erosion downstream. The amount of sediments stored by the dams was found to be higher than the amount of eroded material in the downstream reaches of the dam.     

基于力矩法的元谋干热河谷冲沟沟头土体稳定性模拟与验证

元谋干热河谷冲沟活跃沟头具有"跌坎陡立、内凹洞发育、溯源侵蚀剧烈"等特征,土体崩塌是沟头溯源侵蚀的主要过程之一。该文综合考虑沟头形态特征和裂缝发育等因素,基于力矩分析方法,模拟研究了干热河谷冲沟沟头土体稳定性。结果表明,沟头土体稳定性受土壤含水量、内凹洞发育高度、裂缝发育深度及其距沟壁的距离等多个因素影响。沟头土体稳定性系数,随土壤含水量和裂缝发育深度的增大呈显著指数函数降低,随内凹洞发育高度的增大呈显著线性函数降低,随裂缝发育距沟壁距离的增大呈二次多项式增大。以土壤含水量作为标准对模拟结果进行了检验,发现沟头土体失稳崩塌时,崩塌体和崩塌面实测的土壤含水量分别为模拟值的69.8%~87.6%和82.0%~95.5%,评价结果较为可靠。崩塌面土壤含水量与模拟值更为接近,说明裂缝发育对沟头土体稳定性非常重要。研究结果可为元谋干热河谷沟头土体崩塌预测及沟头治理措施制定提供重要的理论参考。     

MIKE耦合模型模拟淤地坝对小流域暴雨洪水过程的影响

为科学认识淤地坝建设对黄土高原小流域暴雨洪水过程的影响,该文通过分布式水文模型MIKE SHE和一维水动力模型MIKE 11耦合模拟了不同坝型组合和坝系级联方式下的小流域暴雨洪水过程,研究表明:1)淤地坝系建成后会使小流域洪水的洪峰和洪水总量明显减少,其中骨干坝减幅最小,中型坝次之,小型坝减幅最大;串联、并联、混联3种坝系级联方式均使洪峰流量和洪水总量明显减小,其中混联坝系减幅最大,并联坝系次之,串联坝系最小。2)淤地坝建设改变了洪水历时,其中骨干坝和中型坝增加了洪水历时,而小型坝缩短洪水历时。3)沟道连通性指数与洪峰流量、洪水总量均有很好的相关关系,淤地坝建设明显降低了沟道连通性,通过改变沟道连通性调控了小流域的暴雨洪水过程。可为黄土高原淤地坝安全运行提供科学依据。