Storage to be Provided Impounding Reservoirs for Municipal Water Supply

There is undoubtedly a definite relation between the storage provided in an impounding reservoir "on any stream and the quantity of water which can be supplied continuously by it. The relation, however, is a complex one; and our knowledge of its character is limited. The following study is made to see how far it may be possible to separate this complex relation into parts, some of them being of such a nature that they may be studied separately with definite results, and afterward to treat all the remaining variation on the basis of probabilities, using all data from a number of different streams; -and to study them in comparison with the normal law of error. Among the elements that can be studied separately are the following: 1. The size of the catchment area. 2. The mean annual run-off per square mile. 3. The portion of water area and the loss by evaporation' from it. This relation is a complex one, and data for determining it are less adequate than could be desired. Nevertheless, some approximations can be reached.