人為的撹乱による湖底微地形および底泥堆積構造の変化

Abstract

An experimental study was performed to test the disturbance of sediments by scratching for shellfish-gathering and run of boats at full speed. It has been noted by Geological Survey of Japan that paired and single lines appear on sonic side-scan records of the almost whole areas of the South Basin of Lake Bi wa. As a result of this experimental study the lines were assigned as tracks of scratching for shellfish-gathering. Bottom surface of the experimental area was observed by diving also before and after the experimental scratchings and runs. Comparative studies were made on X-ray CT scanning pictures and ordinary radiographic pictures of the cores obtained from the scratched places and the non-affected distant places in the experimental area. Depth of the scratched sediments was several centimeters from the surface. Full-speed runs of the fishing-boat did not affect the microtopography and structure of the bottom surface.