Abstract
During April 2006-December 2006, an investigation was conducted on aquatic insects and river flow rate in mountainous areas upstream of the Ibi and Neo Rivers in Gifu Prefecture, Japan. These mountainous areas experience extremely high annual rainfalls, and many streams have been destroyed due to frequent debris flow disasters in the past. In July 2006, a high river flow rate with maximum velocity of 1.78 m/s (St.1) and 2.63 m/s (St. 2) was observed due to extremely heavy rainfall with total rainfall in a month of 976 mm (St. 1) and 482 mm (St. 2). Although prior to this, the number of aquatic insects was 452 (St. 1) and 124 (St. 2) respectively, the numbers significantly reduced to 42 (St. 1) and 28 individuals (St. 2) after the storm. During this period, the number of individuals dropped to 10% (St. 1) and 22% (St. 2). As a result of factor analysis, the Shannon-Weaver index (H') was high for low water temperature, and it tended to lower for high flow velocity and low flow velocity. In this study, it appears that certain aquatic insects were swept downstream due to the effects of the high river flow.
