Observation of Sediment Discharge Rate Using a Hydrophone

Abstract

In order to elucidate how the riverbed elevation or the depositional gradient of sabo dams varies from moment to moment, it is necessary to observe the temporal variation of the sediment discharge rate. Due to technical difficulties, however, no means were available for measuring changes in sediment discharge rate. A hydrophone that can record the numbers of collisions between sand particles and special pipes or board installed along a riverbed is one of the promising methods for measuring how the sediment discharge rate varies from moment to moment. We actually installed a hydrophone made of steel pipe in the bed of a torrent in the Hachisu-dani Valley of Mount Rokko. Although no large-scale flood occurred during two years of observation after the hydrophone was installed, the records obtained from the hydrophone prove that the sediment discharge rate is qreater in the former half of a flood than in the later half of a flood. Since the occurrence of the Hanshin-Awaji earthquake in January, 1995, the observed sediment discharge rate has shown a better correspondence with the water discharge rate.