先行降雨指数による渓流取水の評価事例

The possible intake of water in an area with no large reservoir has been evaluated for planning-purposes. For example, this kind of study is effective for analysis of a run-of-river irrigation system. For supplementing past discharge data, estimating the discharge due to precipitation data using arun-off model is effective. After the discharge estimated, a stochastic evaluation for planning will betried. In this paper, an approximated analysis with no successive data of measured discharge for makinga run-off model is discussed. The stochastic relation between the API value given from precipitationdata and small discharge Q is introduced as the stochastic model for estimating the discharge. This relation was computed using the least square program. If the order of discharge is in the effective rangeof this API～Q relation, the stochastic evaluation for planning the drought damage will be possible. Inthis case, the measured discharge data are needless to be successive for getting the API～Q relation.The other merits are as follows. The error component of discharge given from the physical run-off model is as large as the range ofdays, because the longer the discharge estimated days are, the more difficult it is to estimate the watervolume in the catchment area. Different from the physical run-off model, the error component of discharge is free from the length of estimated days. When daily cumulative values (for example, dry days, cumulative insufficient water volume and soon) are used as an index for the possible intake of water, the errors of the index affected by variationof API～Q will be as small as the discharge estimated days being longer. Since the API at 0:00 a.m. is used in this paper, the estimated Q of a rainy day is not in goodagreement with measured one. So, this approximated analysis leads to a safer evaluation for droughtdamage.