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

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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