遊水地の確実な調節効果を確保するための河道水位のコントロール−茨城県那珂川御前山遊水地の例−

抄録

A retarding basin was planned at Gozenyama 41km upstream of the Naka River at a design flood of 10-year return period. This retarding basin has severe conditions; large river bed variation, steep bed slope of 1/765 and small design overflow depth of 44cm. In order to ensure the planned regulating effect of flow, reliable control of the water level is required. We studied effective measures for control of water level using both a movable bed experiment with a scale of 1/50 and calculation of improved semi-two dimensional unsteady flow model. We also studied mitigation method for river improvement plan, ecosystem and landscape. It was found that the most effective control can be done at curved point located in downstream of overflow levee. The restriction of river bed variation is required at this point to fix the sand bar inside of curved reach. As a result, the effectiveness of a series of four bed girdles, the crests of which are designed to fit the present river bed is found.