||Sand grain producing-transport processes estimated from gravel-sand grain roundness on dams-constructed Tenryu River, central Japan
Utsugawa, TakakoShirai, Masaaki
Geographical Reports of Tokyo Metropolitan University
108 , 2016 , Department of Geography, Tokyo Metropolitan University
Fluvial sand grain producing–transport processes were examined along the damsconstructed Tenryu River, central Japan. The authors focused on downstream changes in shale grain roundness on gravel-sand size fraction with 1 φintervals. Roundness is a suitable parameter for assessing grain producing-transport processes since it reflects the extent of detritus breaking and abrasion. The effects of such physical actions on each size fraction were studied by means of a field survey (pebble gravels) and laboratory analyses (granule-coarse sand grains). The results suggest that pristine grains were produced from pebbles in both upstream and downstream reaches of the Funagira Dam, the nearest dam from the mouth of Tenryu River. Additionally, collected evidence demonstrates that grains finer than 1 mm in diameter were transported through the Funagira Dam, as indicated by their roundness. Thus, further studies on operating breaking and abrasion mechanisms acting upon detritus could enable contriving the appropriate countermeasure based on a model of “sand grain production from gravels during fluvial transport”.