STUDY ON THE EFFECTIVENESS OF THE CONTINUOUS PILES METHOD TO CONTROL RIVER-MOUTH CLOSURE ON GRAVEL BEACHES

Abstract

 Several small and medium-sized rivers connecting to the Shichiri-Mihama coast are closed due to sand and gravel. The progression of river mouth closure increases the risk of flooding in the river basin, so countermeasures are necessary. In this study, piles were installed in a staggered pattern to prevent river mouth closure. The study focused on the effects of the countermeasures on lowering the height of the berm, advancing the location of the berm to the offshore side, and controlling the amount of sedimentation in the overland area. Hydraulic model experiments were conducted under various wave conditions to clarify the effects of different installation conditions of the countermeasure piles on topographic changes. It was confirmed that the installation of the countermeasure piles suppressed the accumulation of landward-rushing gravels, regardless of the spacing of the countermeasure piles. In particular, under wave conditions with large wave steepness, the effect of the countermeasure piles became more pronounced as the spacing of the countermeasure piles became closer together.