島根県大橋川における水位上昇の事例について

Several periods of water level rise in the Ohashi River, Shimane Prefecture were studied. Either fl ood in the Hii River or high water levels in Lake Nakaumi have caused water level rise in Lake Shinji and the Ohashi River. Current velocity in the Ohashi River can be estimated from differences in water level between the Matsue and Yahata observatory stations under normal flow conditions, but this technique is difficult to apply during flood events. During fl ood events, the slope from Yada to Yahata was much larger than that from Matsue to Yada, indicating that the downstream section of the Ohashi River was restricting river fl ow under fl ood conditions. Comparison of different fl ood events in the past showed that the relationship between rainfall amount and fl ow rate in the Hii River is highly variable. Future investigation is needed to elucidate the hydrographic relationship between fl ow in the Ohashi River, and upstream phenomena, water level rise in Lake Shinji, fl ood in the Hii River, and various patterns of precipitation.