Sediment budget analysis for large areas in Japan

点击翻译按钮获取中文摘要

Severe erosion has been observed in many coastal area in Japan, partly due to reduction of sediment supply from river basin, and partly due to interruption of sediment movement due to coastal structures. Sediment budget analysis has been carried out for large areas in Japan, by organizing a research group covering whole of the country from Hokkaido to the western part of Japan. Furthermore, the research area has been extended to foreign country. Since it is important to introduce whole of the research results, some of the primary results will be described.1.Based on long-term shoreline survey data on Sendai Coat located in northeast of the main land in Japan, sediment budget analysis has been carried out successfully. Especially, longshore distribution of sediment transport rate has been well estimated by considering factors such as sediment loss into the offshore direction and interruption of longshore sediment movement caused by offshore breakwaters. Similar long-term accumulation of … More shoreline survey data is highly recommended foe precise sediment budget analysis.2.Long-term bathymetric data on Ishinomaki Coast has been analyzed for evaluating effect of headlands construction along the coast. It is found that the coastal morphology reached its equilibrium in the very recent years, except the down drift end of the study area where the mouth of the Naruse River is located. Due to the reduction of the sediment supply to the mouth, severe erosion of the sand spit can be observed.3.Similar problem of sand spit intrusion can be seen at several river mouths such as Sagami, Ohyodo and Watari Rivers. In order to clarify such a complicated processes, equilibrium condition for cross sectional area at a river entrance. According to the process-based modeling developed herein, it is shown that the equilibrium condition can be described by two dimensionless parameters indicating relative importance of river and coastal sedimentations. The model results are applied to river mouths in Japan, and its applicability has been confirmed. Similar modeling will be useful for estimating sedimentary environment at a river mouth under combined influence of waves, river discharge and tides. Less