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.

基于漂木分离效果的鱼脊型水石分离结构参数优化

为了研究鱼脊型水石分离结构对泥石流（特别是携带漂木的泥石流）的减灾效果,通过模型实验,探讨水石分离格栅对漂木的分离效果及其主要结构参数对分离效果的影响,根据实验结果结合已有研究成果,进一步讨论主要结构参数的优化取值方法。实验证明,水石分离结构可对漂木产生良好的减灾效果,但各结构参数需合理设置,其中,引流坝引流口开口宽度b与漂木长度L之间应满足b（0.5-1.0）L以满足漂木的过流需求,水石分离格栅长度S需考虑漂木在流体中的运动速度而适当放大,肋梁间距a与漂木直径D之间应满足a〈3.85D以满足漂木分离率达80%以上的需求,肋梁倾角γ=90°时漂木分离效果和结构稳定性最佳。

泥石流中漂木的运动和拦截特征

泥石流中携带的漂木往往具有很大的冲击破坏力,并且在沟道突缩处容易堵塞形成临时堵塞体造成严重的次生灾害。考虑漂木尺寸、漂木量以及泥石流密度等因素对漂木的影响,通过理论分析和模型试验研究了漂木的输移和在沟道突缩处的堵塞规律。通过理论分析和试验结果分析发现:漂木在泥石流流体表面向下游运动过程中由于两端受力不均匀会发生旋转使其长轴方向趋于平行于上游泥石流流向,这一现象随泥石流容重变小越明显;漂木尺寸对漂木拦截率有一定的影响,在漂木相对长度比L/B≤0.75时,对漂木拦截率影响较小,漂木被拦截的类型均为盲区停积型,漂木相对长度比0.75<L/B<1时,漂木拦截率增大,但是在漂木相对长度比L/B=1时,由于发生堵溃现象拦截率下降,随后漂木堵溃现象减弱,拦截率又逐渐增高,此时拦截类型主要为横向拦截型,理论分析和试验数据较一致;漂木量对漂木拦截率也有较大影响,在总体上,漂木拦截率随着漂木数量的增加而增加,当漂木数量N<120时,被拦截数量较少,漂木的长度对其基本没有影响;漂木数量N>120时,随着漂木数量的增大,多根漂木同时到达沟道突缩处的几率增大,漂木拦截率增大。综上可知,泥石流容重、漂木数量和漂木相对长度对漂木的堵塞均有较大影响,探讨漂木在泥石流中的输移和堵塞规律以及了解漂木致灾特征以及工程防治具有重要的指导意义。

Experimental Studies on Debris Flow with Logs Focusing on Specific Weight Difference of Log Species

There are many experimental approaches,field investigations and numerical calculations for movements of woods in a clear water and debris flow.However,kinematic conditions for accumulated logs and the interactions between a main flow and logs have not been fully evaluated.Mitigations for woods need taking into account the characteristics of tree species such as conifer and broad-leaf trees and of shapes such as root swells and crown.In the present study,we focus on the differences in specific weight of conifer and broad-leaf trees with some moisture in a sediment-water mixture flow with narrow flow width,and consider that conifer and broad-leaf tree are floating and submerged solid phase,respectively.Flume tests are conducted in steady flow of clear and debris flow over a rigid bed in order to evaluate conifer and broad-leaf tree movement in clear water and debris flow.Experimental data indicates that dimensionless transverse diffusion coefficient can be 0.1 to 0.4 and 0.3 to 0.9 in flow direction.Those diffusive characteristics seem to be independent of Reynolds number and Froude number,but dependent of bed slope,i.e.,gravity,though detailed considerations are needed to discuss about flow characteristics such as spatial eddy structures,momentum transfer induced by interactions of logs and so on.

缝隙坝对携带漂木的泥石流减灾效果实验研究

山洪泥石流灾害中携带漂木的情形时有发生,漂木产生的灾害效应也越来越受到关注,但现有泥石流防治工程多未考虑漂木的影响。因此,有必要对漂木存在条件下拦砂坝的调控效果进行研究。以缝隙坝为例展开模拟实验,结果表明泥石流中携带漂木时,漂木多运动在流体表面,且先于泥沙到达坝前,是否在缝隙坝开口处形成漂木堵塞体对缝隙坝前泥沙堆积体形态、泥沙流出率、漂木拦截率均有重要影响。若未形成漂木堵塞体,坝前泥沙堆积体有明显侵蚀槽,泥沙流出率较无漂木时略低;一旦形成漂木堵塞体,坝前泥沙堆积体无明显侵蚀现象,泥沙流出率显著减小,漂木总拦截率显著增大。缝隙坝对不同漂木组分的拦截效果不同,漂木长度L与缝隙开口宽度b的比值L/b越大,越容易被拦截。漂木中L/b>1的组分含量越大,漂木总拦截率越大,且L/b>1的漂木存在是形成堵塞体的关键条件。

Wood-inhabiting marine fungi from the coast of Shandong, China Ⅲ

Five species of higher marine fungi were observed on the incubated drift and intertidal woods collected from the coasts of Yellow Sea and Bohai Sea. Among them, Halosphaeriopsis was a genus newly recorded for China. Taxonomy and morphology of these species were discussed in this paper. The specimens were deposited in Mycology Herbarium at Qingdao Agricultural University (MHQAU).

漂木对泥石流输移过程影响试验研究

泥石流搬运大量漂木造成严重危害。通过模型试验,模拟了水力型泥石流搬运漂木并经缝隙坝调控的整个输移过程,分析了漂木长度、漂木量对泥石流输移过程及缝隙坝调控性能的影响。研究结果表明,漂木长度对泥沙启动、缝隙坝过流模式和堵塞特征有重要影响。随着漂木长度增大,泥沙启动率逐渐减小,稳定的漂木对泥沙具有锚固作用。当漂木长度L_(w)与缝隙坝开口宽度b的比值L_(w)/b<1.0时,漂木对缝隙坝泥沙拦截率及坝后泥沙堆积体中影响不大。当1.0<L_(w)/b<1.5时,漂木在缝隙坝处产生轻微堵溃现象,不形成稳定堵塞体。泥沙拦截率随着L_(w)/b的增大而增大,L_(w)/b≥1.5时,易形成稳定的漂木堵塞体。缝隙坝泥沙拦截率可达90%以上,坝后堆积体回淤纵坡显著减小,靠近坝体的堆积体粗化现象明显,中值粒径随着L_(w)/b的增大而增大。漂木相对体积V_(w)/V_(s)>0.05时对上述过程有一定影响。本研究为深入理解漂木的影响及缝隙坝的优化设计提供了依据。

山东海岸木生海洋真菌的研究Ⅶ

从山东省渤海、黄海海域检查到4种海壳目真菌,分别为Aniptodera chesapeakensis、Ligninco lalaevis、Nais inornata、Natantispora retorquens,子囊孢子均为椭圆形、双胞、无色。本文对这4个种的形态学进行了描述和讨论。研究标本和菌种保存于青岛农业大学真菌学标本室(MHQAU)。