Fast clogging problem of open check dams and a new type suggestion:curved footed type open check dam

Driftwood is one of the important physical components in mountainous rivers which causes severe hazards due to the clogging of bridges,culverts,and narrow sections during floods.Therefore,the understanding of driftwood dynamics and mitigation measures are crucial for managing wood in rivers.Open check dams are the most commonly used engineering measure for preventing driftwood from reaching downstream areas.Nevertheless,these open check dams frequently lose their sediment transport function when they are blocked by sediment and driftwood,especially during major flood events.This paper proposes a new type of open check dam for preventing from clogging.Thus,flume experiments were conducted to examine the influence of different types of open check dams on the characteristics of driftwood deposition.For the model with wood length(LWD)=16.5 cm,wood diameter(D)=15 mm,and wood number(N)=172,the highest trapping efficiency was observed with 90.1%and 87.2%retention rates for the classical debris flow breaker and curved footed open check dams,respectively.Laboratory tests showed that through this proposed design,woody debris blockage in a very short time was prevented from the accumulation of woods beside the dam.In addition to this,most of the sediment passed through the check dam and most of the driftwood got trapped.It can be briefly stated that the geometrical design of the structure plays an important role and can be chosen carefully to optimize trapping efficiency.By designing this type of open check dams in mountain river basins,it may provide a better understanding of the driftwood accumulation and basis for the optimal design of these structures.Further development of the solution proposed in this work can pave the way for designing different types of open check dams for effective flood management.

Check dam extraction from remote sensing images using deep learning and geospatial analysis:A case study in the Yanhe River Basin of the Loess Plateau,China

Check dams are widely used on the Loess Plateau in China to control soil and water losses,develop agricultural land,and improve watershed ecology.Detailed information on the number and spatial distribution of check dams is critical for quantitatively evaluating hydrological and ecological effects and planning the construction of new dams.Thus,this study developed a check dam detection framework for broad areas from high-resolution remote sensing images using an ensemble approach of deep learning and geospatial analysis.First,we made a sample dataset of check dams using GaoFen-2(GF-2)and Google Earth images.Next,we evaluated five popular deep-learning-based object detectors,including Faster R-CNN,You Only Look Once(version 3)(YOLOv3),Cascade R-CNN,YOLOX,and VarifocalNet(VFNet),to identify the best one for check dam detection.Finally,we analyzed the location characteristics of the check dams and used geographical constraints to optimize the detection results.Precision,recall,average precision at intersection over union(IoU)threshold of 0.50(AP_(50)),IoU threshold of 0.75(AP_(75)),and average value for 10 IoU thresholds ranging from 0.50-0.95 with a 0.05 step(AP_(50-95)),and inference time were used to evaluate model performance.All the five deep learning networks could identify check dams quickly and accurately,with AP_(50-95),AP_(50),and AP_(75)values higher than 60.0%,90.0%,and 70.0%,respectively,except for YOLOv3.The VFNet had the best performance,followed by YOLOX.The proposed framework was tested in the Yanhe River Basin and yielded promising results,with a recall rate of 87.0%for 521 check dams.Furthermore,the geographic analysis deleted about 50%of the false detection boxes,increasing the identification accuracy of check dams from 78.6%to 87.6%.Simultaneously,this framework recognized 568 recently constructed check dams and small check dams not recorded in the known check dam survey datasets.The extraction results will support efficient watershed management and guide future studies on soil erosion in the Loess Plateau.

Flood risk assessment of check dams in the Wangmaogou watershed on the Loess Plateau of China

Check dams have been widely used in China’s Loess Plateau region due to their effectiveness in erosion and flood control.However,the safety and stability of the check dam decrease with the operation process,which increases the probability of dam failure during flood events and threatens local residents’ life and property.Thus,this study simulated flood process of the check dam failure in the Wangmaogou watershed in Yulin City,Shaanxi Province,China,calculated different types of inundation losses based on the flood inundation area within the watershed,and determined the number of key flood protection check dams by classifying the flood risk levels of the check dams.The results showed that 5 dams in the watershed were subject to overtopping during different rainfall return periods,which was related to their flood discharge capacity.Dam failure flood process showed a rapid growth trend followed by slow decrease,and the time of flood peak advanced with increase in the return period.After harmonization of evaluation scales,the magnitude of flood inundation losses can be ranked as:economic losses(212.409 million yuan) > life losses(10.368 million yuan) > ecological losses(6.433 million yuan).The risk value for both individual dams and the whole dam system decreases as the return period increases.The number of key flood protection check dams in the Wangmaogou watershed was 2,3,3,3,4,and 5 for floods with return periods of 10,20,30,50,100,and 200 years,respectively.The results provided a theoretical basis for the safe operation and risk evaluation of check dams in the Loess Plateau Hills watershed.

Sediment sources and their impacts on a check dam-controlled watershed, Loess Plateau, China

Soil erosion is a major issue in Loess Plateau,China,and quantitative analyses of sediment sources are crucial for soil erosion control.In this study,a combination of flood couplet analysis and composite fingerprint identification was used for historical reconstructions of soil erosion in sediment source areas in Loess Plateau.Each flood couplet was constructed based on sediment 137Cs activity,and past soil erosion was calculated using soil bulk density and storage capacity curves.The contribution rates of the sediment sources were calculated using the fingerprinting method,and the amount of erosion in the sediment source areas was estimated.The best fingerprint combination(Cr,Ni,V,and TOC)enabled a 97.2%recognition of sediment sources from 29 flood events(1956–1990)in the Loess Plateau.The contribution rates of gullies,farmland,grassland,and shrubland were 44.89%,26.38%,10.49%,and 18.24%,respectively.These four land use types contributed 1,227,751,512,and 279 tons of sediments,respectively.Re-vegetation decreased soil erosion(1966–1983),whereas deforestation increased soil erosion(1956–1965 and 1984–1990).Rational soil and water conservation measures on slopes and check dam construction in gullies are therefore suggested to mitigate erosion.

淤地坝与check dam的差异及其英文译法

淤地坝是黄土高原重要水土流失治理工程措施,对减少入黄泥沙、增加耕地面积发挥了重要作用。关于淤地坝英文翻译,普遍采用check dam,然而其并不能真实反映黄土高原水土保持工程建设实际情况,因此,笔者从目的、功能、尺寸等方面,系统对比黄土高原淤地坝与国外check dam的差异。在此基础上,建议采用淤地坝汉语拼音“Yudiba dam”表达这类大量分布在黄土高原可在拦截泥沙、减少沟道侵蚀、增加耕地面积的水土保持工程措施,从而明确其与国外check dam的区分。

Failure mechanisms and risk mitigation of check dams on the Chinese Loess Plateau: A case study at the Gutun Gully

Loess is long-term aeolian dust deposition, characterized by loose structure, concentrated participle distribution and unstable mineral composition, and thus easy to cause extensive collapsibility and have general water sensitivity. To reveal the difference in water sensitivity between naturally intact(NI) loess and mechanically compacted(MC) loess used for the check dam, the transient water release and imbibition method(TRIM) was used to acquire the suction stress–expanded hydraulic characteristic curves for the NI and MC loess and explore possible approaches for formulating the potential of loess water sensitivity. Based on the Local Field of Safety(LFS) associated with slope stability, we constructed a finite element model of a check dam to depict its failure processes under different rainfall scenarios. The results revealed the strong water sensitivity in NI loess, while the MC loess retained a certain water-sensitive potential. This capacity depends on the ‘water sensitivity coefficient’ obtained from the suction-stress characteristic curve,which better presented the deformation potential of the two loess samples at different water content levels. In the context of LFS, we identified two failure patterns in the dam body that were involved in loess water sensitivity under hydromechanical conditions: rainfall erosion-induced shallow mudflow failure, and preferential-infiltration progressive failure. These patterns may provide new insights into dam-breakage mechanisms and potential chain effects of check dams on the Chinese Loess Plateau from the perspective of soil–water interactions, which is vital for predicting the position and timing of check dam failure, and mitigating risks.

Using Hydraulic Engineering Model Experiment to Study the Sediment Trapping Efficiency of Adjustable Check Dam

The construction of fully closed check dam (CD) is a conventional flood prevention mechanism implemented on rivers. Fully closed CDs trap large amounts of sediments in rivers to stabilize the river slopes and control erosion. However, fully closed CDs cannot selectively trap sediment and may easily overflow, causing them to losing their ability to mediate and hold sediments. Previous studies proposed the concept of “breathable CDs”. The researcher introduced metal slit dam (SD) that could be assembled and disassembled quickly and conveniently. Once a CD reaches maximum capacity, operators must ensure that the water channels of the dam are free from blockage. Moreover, they must inspect the internal accumulation conditions of the dam periodically or immediately following heavy typhoon rains. When necessary, either the sediment buildup in the upriver blockage must be cleared, or the transverse structure of the dam must be removed to allow fine particles to be discharged along with a moderate amount of water. These actions can free up the sediment-storing capacity of the dam for the next heavy typhoon rains. In addition, operators should also inspect the damages inflicted on the dam, such as erosion, wear and tear, and deformation conditions. Damaged components should be disassembled and repaired if possible, or recycled and reused. The present study performed channel tests to simulate closed CDs, SDs, steel pipe dam (SPDs), and steel pipe plus slit dam (SPSDs) for 50-year and 100-year frequency floods. Results were then analyzed to determine the sediment trapping (ST) effects of various CDs, the effects of “adjustable CDs”, and the changes of moderated riverbeds.

The siltation of debris flow behind check dam in the midstream of Bailong River

Siltation gradient and siltation length are important parameters for designing gravity check dams for debris flows,which directly affect the accuracy of estimates of interception capacity.At present,siltation gradient calculations are based primarily on empirical values,and range from 0.4 to 0.95 times the channel slope coefficient.The middle reaches of the Bailong River are one of the four areas in China that are most severely affected by debris flow hazards.Gravity dams are widely employed in this mountainous area.However,field studies of their capacity are lacking.In this paper,the operations of check dams were investigated.Based on field investigation results and theoretical analysis,calculations for siltation gradient,siltation length,and dam storage capacity are established.The impact of debris flow density,channel slope,and particle size weight percentages are discussed.The calculations show that the theoretical values for siltation gradient are consistent with measured values with 83.6% accuracy;and theoretical values of siltation length are consistent with measured values with 91.6% accuracy.The results of this research are an important reference for optimal height and spacing of dams,estimation of dam storage capacity,and disaster prevention.

Check Dams in an Ephemeral Stream in a Tropical Deciduous Forest Extend Water Period with Minimal Effect on Reptile Assemblage

Although numerous check dams have been constructed in many countries, and its effect on physical factors were well documented, only a few reports were available on its effect on biotic component in adjacent area. This research aims to address effects of the check dam on reptile assemblage in an ephemeral stream based on an assumption that reptile live in the stream and adjacent area may be susceptible to prolonged hydroperiod after check dam construction. Ten stream transects and 40 terrestrial strip transects, including 5, 10, 25, and 50 m from the stream, were used to monitor reptile diversity and composition in a deciduous forest of northern Thailand during April 2009 to February 2011. Physical factors related to water pattern in the stream and the terrestrial habitats were also collected. Results on physical factors indicated that the water pattern and soil moisture in the stream, as well as leaf litter moisture in the terrestrial habitat were increased as a result of the check dam. However, rarefaction curve indicated that reptile diversity was not significantly different between pre- and post-check dam periods in every transect. Moreover, Morisita’s index of similarity indicated that reptile composition between pre- and post-check dam periods was approximately the same (86% - 100%). These results indicated that reptile assemblage was not affected by the check dam. It can be concluded based on data of one year after the check dam construction that check dam can effectively prolong water and moisture to the habitat with minimal effect on reptile assemblage in the area.

Dynamic Modeling Framework of Sediment Trapped by Check-Dam Networks:A Case Study of a Typical Watershed on the Chinese Loess Plateau

Check-dam construction is an effective and widely used method for sediment trapping in the Yellow River Basin and other places over the world that are prone to severe soil erosion.Quantitative estimations of the dynamic sediment trapped by check dams are necessary for evaluating the effects of check dams and planning the construction of new ones.In this study,we propose a new framework,named soil and water assessment tool(SWAT)–dynamic check dam(DCDam),for modeling the sediment trapped by check dams dynamically,by integrating the widely utilized SWAT model and a newly developed module called DCDam.We then applied this framework to a typical loess watershed,the Yan River Basin,to assess the time-varying effects of check-dam networks over the past 60 years(1957–2016).The DCDam module generated a specific check-dam network to conceptualize the complex connections at each time step(monthly).In addition,the streamflow and sediment load simulated by using the SWAT model were employed to force the sediment routing in the check-dam network.The evaluation results revealed that the SWAT-DCDam framework performed satisfactorily,with an overestimation of 11.50%,in simulating sediment trapped by check dams,when compared with a field survey of the accumulated sediment deposition.For the Yan River Basin,our results indicated that the designed structural parameters of check dams have evolved over the past 60 years,with higher dams(37.14%and 9.22%increase for large dams and medium dams,respectively)but smaller controlled areas(46.03%and 10.56%decrease for large dams and medium dams,respectively)in recent years.Sediment retained by check dams contributed to approximately 15.00%of the total sediment load reduction in the Yan River during 1970–2016.Thus,our developed framework can be a promising tool for evaluating check-dam effects,and this study can provide valuable information and support to decision-making for soil and water conservation and check-dam planning and management.

Effects of a check dam system on the runoff generation and concentration processes of a catchment on the Loess Plateau

As an important soil and water conservation engineering measure,more than 100,000 check dams are constructed across the Loess Plateau;these dams play a vital role in reducing floods and sediment in the region.However,the effects of check dams on hydrologic process are still unclear,particularly when they are deployed as a system for watershed soil and water management.This study examined the watershed hydrologic process modulated by the check dam system in a typical Loess Plateau catchment.By simulating scenarios with various numbers of check dams using a distributed physically-based hydro-logical model,the effects of the number of check dams on runoff generation and concentration were analyzed for the study catchment.The results showed that the presence of check dams reduced the peak discharge and the flood volume and extended the flood duration;the reduction effect on peak discharge was most significant among the three factors.The system of check dams substantially decreased the runoff coefficient,and the runoff coefficient reduction rate was greater for rainstorms with shorter return periods than for rainstorms with longer return periods.The check dams increased the capacity of the catchment regulating and storing floods and extended the average runoff concentration time in the catchment that flattened the instantaneous unit hydrograph.This study reveals the influencing mech-anism of check dam system on the watershed hydrological process under heavy rainstorm conditions and provides a theoretical basis for evaluating the effects of numerous check dams on regional hydrology and water resources on the Loess Plateau.

Quantitative assessment of the influence of terrace and check dam construction on watershed topography

Terrace and check dam construction has substantially changed land surface morphology,which in turn affects modern surface processes.Digital elevation models(DEMs)provide an effective way to quantitatively analyze surface morphology and processes.However,existing DEMs lack sufficient ability to express artificial terrain.Based on 1:10000 topographic maps of the Zhifanggou watershed,a series of artificial terrain DEMs for the study site were constructed by both field investigation and remote sensing images from 1938 to 2010.Digital terrain analysis was used to quantitatively assess the influence of terrace and check dam construction on the watershed terrain.The results showed that the artificial terrain DEM could capture the spatial distribution patterns of terraces and dam lands and improved the ability of DEM to express terrain.The construction of terraces and check dams clearly changed the surface elevation.The average elevation change of each terrace mainly ranged between–1.5 and 1.5 m,while the annual average deposition height of the dam lands was 9.16 cm.The average slope,slope length,and slope length and steepness factor of the watershed decreased with the effect of the artificial terrain on the surface,and their averages decreased by 0.65°,6.75 m,and 0.83,respectively,from 1938 to 2010.Although the construction of terraces reduced their surface slope to nearly 0°,the slope of terrace embankments rapidly increased,to more than 45°,which may lead to gravitational erosion and potential terrace damage.Terracing reduced the slope length in both the terrace distribution area and downslope of the terraces.Check dam deposition reduced the slope and slope length of the channel.This study contributes to a better understanding of the topographic change rules after terrace and check dam construction,and aids in elucidating the mechanisms of soil erosion process influenced by artificial topography.

Experiments on Channel Evolution Caused by Check-dam Failure

A 10 m long,0.2 m wide flume was employed to simulate the channel bed evolution of check-dam failure.The experiment longitudinal profiles,the gradient of channel bed,head-cutting propagation distance and deposition length were compared with the theoretical solution derived from a sediment transport diffusion equation.In contrast with the theoretical solution,two different gradients were obtained upstream and downstream of the check-dam.The theoretical solution provides a good description of the changes upstream of the check-dam. The ratio of clear water depth to sediment moving layer thickness in the experiment was analyzed and showed that high concentration sediment laden flow was taken in the incipient of check-dam failure,which may be the reason why the experiment result was slightly different from the theoretical solution in the downstream of check-dam.

黄土高原径流侵蚀功率输沙模型的改进

水土流失对流域生态危害严重,输沙量模拟和预测可以为流域水土流失防治提供依据,因此精确的输沙模型是流域水土流失治理的重要工具。为了精确模拟变化环境下黄土高原年输沙量,该研究基于黄土高原19个水文站的径流和输沙数据,通过随机森林变量重要性度量方法评估年径流侵蚀功率、淤地坝指数、淤地坝相对指数、归一化植被指数、不透水地面积等因子对流域年输沙量的影响,使用非线性最小二乘法估算年输沙模型参数,对比分析不同因子组合的年输沙模型精度,提出适用性较强的黄土高原年输沙模型,据此开展年输沙量变化贡献率分析。结果表明:1)以幂函数形式构建的仅含径流侵蚀功率单因子输沙模型精度与流域面积有显著的负相关关系,相关系数为-0.505(P<0.05),模型精度随着流域面积增大而下降,在面积大于7000 km^(2)的流域适用性较差;2)年径流侵蚀功率、淤地坝指数及不透水地面积因子组合建立的多因子年输沙模型在黄土高原适用性最佳,模型在率定期纳什效率系数平均值为0.84,均方根误差平均值为0.21亿t,在验证期纳什系数平均值为0.79,均方根误差平均值为0.27亿t。3)影响研究流域年输沙量变化的因素依次是:年径流侵蚀功率、不透水地面积和淤地坝指数。研究可以为黄土高原不同区域水土流失防治和生态治理工作提供理论支撑。

高海拔地区宽级配泥石流冲击拦砂坝试验研究

在高海拔地区,由于山高谷深,坡表物质受物理风化严重,物源级配宽度范围大,泥石流的发育频率高,冲击力大,导致拦砂坝损毁严重。为研究高海拔地区宽级配泥石流对拦砂坝的冲击规律,以西藏地区发育的泥石流为原型,建立宽级配泥石流冲击拦砂坝的物理试验模型,选取泥石流容重、水槽坡度与泥石流固相最大粒径为变量,进行27组水槽试验,研究冲击力特征。结果表明:(1)宽级配泥石流在冲击拦砂坝过程中经历“冲击爬高、旋滚回流、堆积回淤”3个接触演化阶段,泥石流容重越小,爬高越大,冲淤过程的阶段性表现越明显;(2)拦砂坝的坝前冲击力随宽级配泥石流容重的增大而减小,在相同坡度和级配的条件下,容重越大,水流携带固体物源运动越困难,泥石流流速降低,泥石流的冲击力减小;(3)拦砂坝的坝前冲击力随沟槽坡度增大而增大,沟槽坡度越大,宽级配泥石流的流速和流深越大,泥石流冲击力就越大,并且泥石流固相粒径越大,坡度对冲击力的影响效果越明显;(4)拦砂坝的坝前冲击力随宽级配泥石流固相最大粒径增大而增大,且变化趋势较泥石流容重及沟槽坡度条件改变时更加显著,最大粒径与泥石流流速、流深没有明显规律关系。研究成果将为宽级配泥石流防治和研究提供一定的数据参考。

淤地坝排洪渠—溢洪道组合式泄洪过流的物理试验和数值模拟

为探究排洪渠连接溢洪道的过流形式能否适用于满淤积状态下的淤地坝,采用物理模型试验与数值模拟相结合的方法,研究了排洪渠—溢洪道组合形式对淤地坝减蚀、泄洪能力的影响。结果表明,在该连通方式下,坝地及溢洪道内整体水流平稳,仅在溢洪道进口前出现紊乱流态;排洪渠的布设减小了坝地的径流流速,可有效抑制洪水对淤积土体的冲刷侵蚀破坏;在上游来流量较小时,溢洪道的流量系数小于设计值,但随着流量增大,淤地坝泄流能力增强并满足泄洪要求。研究结果可为后续淤地坝的除险加固工程提供参考依据。

黄土高原半干旱区淤地坝安全监测方法

[目的]监测黄土高原半干旱区淤地坝在汛期后形变程度,及时准确发现淤地坝的异常情况,为黄土高原半干旱区淤地坝安全监测提供更加科学可靠的技术方法。[方法]通过三维激光扫描仪对两座淤地坝进行扫描,由此得到高密度、高精度、连续完整的3D点云数据,然后将点云数据导入HD Scene软件进行点云预处理,最后通过Cloud Compare以及Geomagic Control软件进行建模对比分析。[结果]两期点云模型对比可以看出,东沟淤地坝模型大量点云的偏移量在0.05 cm以下,少量点云达到了最大偏移值0.2 cm。西沟淤地坝模型大量点云的偏移量在0.1 cm以下,极少量点云达到了最大偏移值0.4 cm。汛期降水量占全年的77.34%,汛期后两座淤地坝均会产生较小的坝体沉降和水平位移,但西沟淤地坝的形变受水压分量影响更为明显。[结论]将三维激光扫描技术应用于黄土高原半干旱区淤地坝安全监测,可以快速精准掌握淤地坝汛期后是否发生形变以及形变程度,使得淤地坝安全监测工作更加精准可靠。

小流域拦砂坝上下游冲淤特征调查分析

极端降水诱发的泥石流具有规模大、沿程侵蚀严重、淤埋范围大等特点,需要在小流域内修建梯级拦砂坝工程进行调控。在汶川地震影响区域内选取33条典型泥石流沟道进行调查,获取了105座拦砂坝特征参数以及梯级拦砂坝作用下的沟道冲淤形态变化,总结了拦砂坝的类型及判别方式,提出了实体坝与透过性坝的4种坝型组合模式、梯级坝的坝间距下2种回淤模式。进一步分析了梯级坝的特征模式(坝型组合模式、回淤模式)对沟道的冲淤形态(回淤坡降折减系数、冲刷深度相对系数)的影响。结果表明实体坝与透过性坝的组合模式(SO、OS模式)对沟道回淤形态影响明显,两种回淤模式中的互馈式运行模式对淤积形态影响显著,回淤相互不影响的独立运行模式下的冲刷作用更强烈。研究结果可为小流域内梯级坝的坝型选择、坝间距优化提供参考。

强震区抽蓄电站沥青混凝土面板堆石坝抗震稳定性分析

我国西北强震区某拟建抽水蓄能电站上水库采用沥青混凝土面板堆石坝,最大坝高161 m。为分析该坝抗震稳定性,在大坝非线性静力分析基础上,采用改进的等效粘弹性模型和有限元动力时程法等理论,对大坝开展三维有限元地震反应和坝坡抗震稳定性计算。结果表明,大坝在100年1%超越概率的校核地震(地震加速度为0.48g)作用下,坝体及面板的动力反应分布规律合理。其中,坝体顺河向、坝轴向、竖向加速度极值分别为13.93、13.91、13.80 m/s^(2)。考虑静动叠加后,在沥青混凝土面板反弧段的拉应变极值达0.95%,但小于改性沥青混凝土抗拉强度的一般允许值。因此,大坝即使遭遇0.48g的校核地震作用,亦能保持较好的整体安全性,不会出现重大抗震安全事故。