DEVELOPMENT OF A RIVERBED VARIATION MODULE TO PREDICT SAND COVER RATE FOR THE FORAGING HABITAT OF AYU FISH

Abstract

 Sand cover rate (SCR) is an important factor to explain the foraging habitats of ayu (Plecoglossus altivelis). Hence, a module of riverbed variation in a gravel-bed river with bimodal sediments was developed. The module calculated SCR, and the changes in SCR were defined as being driven by sand transport in the form of a suspended load that is deposited on stones (e.g., cobbles or pebbles) and in the interstices of stones. The prediction accuracy was examined by comparing the calculated SCR with the SCR measured in the field. The results showed that the spatial pattern of sand deposition/erosion predicted by the module was almost close to the measured one, though the predicted SCR tended to be higher/lower than the measured value. Chronological changes in the SCR calculated by the module suggested that sand deposits started forming along shorelines after the peak of a flood and then expanded toward the centers of the flow in channels in the end stage.