2014 Volume 23 Issue 1 Pages 11-17
In general, the effect of forest conservation projects does not appear in the short term. Koyama and Okumura analyzed the changes in flow regime with the progress of conservation works in a small mountainous basin in Tottori Prefecture by three tank models: the 1981, 1983 and 2000 models, which reproduced the runoff for the year before the conservation projects were started, the year they were completed, and eighteen years after completion, respectively. In the present study, the long-term trends of the change of runoff characteristics due to forest conservation projects are discussed by focusing on the unit hydrograph method with a multiple regression model in the same basin as in Koyama and Okumura's study. Three unit hydrographs are made that match Koyama and Okumura's study and used to analyze the same rainfall data observed in 2001. Base on the analytical results, both the flood and scarce water control functions were temporarily lowered during the conservation project. But eighteen years after their completion, both have improved. These results greatly agree with Koyama and Okumura's results.
