Study on hydro-environmental properties of rubble weir constructed of coarse rokcs

提出了一种“碎石丘堰”作为河流排放控制系统。该堰预计将成为一个自然友好型结构，以控制水流排放，使水生动物能够顺流运动。通过室内试验和理论分析，对该结构进行了水力学和水环境性能的研究，从而对结构进行了合理的设计。首先进行室内试验，找出流量对水深、堰孔率、碎石粒径等参数的函数依赖关系。在明渠中设置卵石堰模型，在明渠中设置不同尺寸和粒径的卵石堰。通过一维流动分析，得到了堰内水面剖面的解。根据紊流多孔介质流动的实验公式，对堰内的流动阻力进行了计算。求解得到了流量与上游流量之间的函数关系。通过对雷诺数、孔隙度、比粒径、堰宽比、无量纲水深等因素的分析，得到了理论流量曲线。在较宽的流动条件下，该解与实验数据具有较好的相关性。其次，应用粒子图像测速技术（PIV）对堰周局部流动结构进行了实验研究，该技术提供了流场的时间和空间尺度信息。由于水生生物的栖息地受水流结构的时变影响很大，从环境的角度考虑水流运动的时间和空间尺度在确定堰的尺寸是非常重要的。第三，采用多变量分析方法提取含能涡流的不同尺度；其中一些对堰的坍塌负有责任，一些在气-水界面之间的气体传递中起重要作用，另一些影响水生动物的活动，等等。第四，通过测量多孔体内部压力波动，研究了结构的动力稳定性。从堰顶面下游的局部水流力取最大值出发，给出了结构破坏或倒塌的临界条件。综合本课题的研究成果，可以从水动力和水环境两个角度对碎石丘堰进行结构设计。与传统的金属或混凝土堰相比，碎石丘堰有望成为保护生态系统更好的河流结构。少

A "rubble mound weir" was proposed as a river discharge control system. The weir is expected to be a nature-friendly structure for controlling flow discharge in a way that it allows streamwise movement of aquatic animals. In order to make a suitable design of the structure, its hydrodynamics and hydro environmental properties were examined by performing laboratory experiments and a theoretical analysis. First, a laboratory experiment was carried out in order to find functional dependency of discharge on parameters such as water depth, weir's porosity, rubbles size, etc.. The weir model constructed of pebbles was installed in an open channel, where weir's dimension and grain diameter were varied. A one-dimensional flow analysis was performed to obtain a solution for water surface profile inside the weir. Flow resistance in the weir was evaluated from an experimental formula for turbulent porous media flow. The solution leads to a functional relationship between discharge and upstream wa … More ter depth. A theoretical discharge-curve was obtained through the analysis as functions of Reynolds number, porosity, specific grain size, weir's aspect ratio, dimensionless water depth, etc.. The solution was well correlated with the experimental data under wide range of flow conditions. Second, local flow structure around the weir was experimentally examined by applying a particle image velocimetry, PIV, which provides information of time and space scales of the flow fields. Because habitats of aquatic lives are very much influenced by time-dependent flow structure, it is very important from an environmental point of view to take time- and space- scales of flow motions into consideration in determining the weir's dimension. Third, a multi-variables analysis was applied to pick up various scales of energy-contain eddies ; some of them are responsible in collapsing the weir, some play important roles in gas transfer between the air-water interface, the others affects activities of aquatic animals, and so on. Fourth, dynamic stability of the structure was investigated by measuring pressure fluctuation inside the weir's porous body. The critical condition for failure or collapse of the structure was given from local flow force that takes the maximum value at the downstream side of the weir top surface. Integrating results from the present research project, one can make structural design of the rubble mound weir from both of hydrodynamic and hydro-environmental points of view. The rubble mound weir is expected to be a river structure that better preserves ecological system than conventional metal or concrete weirs. Less