COMPARISON OF SUBBASIN CHARACTERISTICS OF OGOUCHI RESERVOIR USING CLUSTER ANALYSIS

Abstract

 Management of water quality of reservoir is an important issue in water supply. Now water supply coverage ratio in Japan is more than 98%, and there is an increasing need of supply of drinking water with safe, and good taste. Watershed forest is expected to have a various functions such as water storage, flood mitigation, and purification through soil. Ogouchi reservoir, target area in this research, is one of the water resource of Tokyo Metropolitan Waterworks. There are both private and governmental forest within the watershed. Recently, there arises a problem that some privately owned forest are not properly managed because forest industry is depressed, and owners are being aged. Therefore, the waterworks is trying to purchase to manage forest under private ownership. However, as the total watershed area ranges upto 240km², priority should be put on each subbasin for its proper and efficient management. With above backgrounds, this research focused on prioritization of subbasins in watershed of Ogouchi reservoir, in view of forest management. Forest data is acquired from each prefectural government and also from Tokyo Metropolitan Waterworks. Those data are summarized into 51 subbasins and provided for cluster analysis. 51 subbasins were classified into 7 clusters, and its priority was discussed based on characteristics of each cluster. As a result, cluster 7, which exists around central part of the reservoir, is found to have the highest priority.