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Flow Regime Transition of Rubble Mound Weir During a Flood

Author(s): Kohji Michioku

Linked Author(s): Kohji Michioku

Keywords: Rubble mound; Rockfill; Gabion; Weir; Porous media; Discharge rating curve; Flow transition

Abstract: Hydrodynamics of a rubble mound weir was investigated by performing an unsteady flow analysis under a single-peaked flood event. The weir was exposed to emerged, partially-submerged and completely-submerged conditions depending on the flood stage and the flow was accordingly shifted from a porous media flow to a two-layer flow consisting of an open channel flow overlying a porous layer. The flow experiences the six regimes during the flood depending on the relative height of water surface to the weir and on the backwater effects. Hysteresis of hydraulic variables was plotted in a "flow regime map" in which the six flow regimes were categorized in a plane consisting of the storage depth and the head difference along the weir. In order to examine performance of the rubble mound weir as a flood controller, time histories of stage and discharge were compared with those of an impermeable solid weir with the same geometrical dimensions. By analyzing energy and momentum balances, the rubble mound weir was proven to have better performance than the impermeable weir not only as a flood controller but also as an energy dissipater. In addition to its function as a hydraulic facility, a rubble mound weir may serve as a water purification system by physically and biochemically removing pollutants in the course of infiltration through the porous body. In order to discuss its ecohydraulic performance, pollutant removal rate was estimated by assuming pollutants to be removed by primary reaction.


Year: 2023

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