Versions of the drainage area ratio method for transfer of daily or monthly stream flows

Using the drainage area ratio (DAR) method, daily or monthly flows gauged at a nearby station are transferred to an ungauged section where a dam is to be built by multiplying them by a real number resulting from raising the ratio of the drainage areas of the dam section and of the station to an exponent n. Commonly, n is taken as 1. Using the daily flows of two stations nearby a dam section on the same stream or a neighbouring stream, having a common N-year-long gauging record, it is proposed that 365 linear regressions be fitted to N pairs of 365 daily flows and relate them to the DARs. The daily flows at the dam section can then be computed using 365 values of n' each belonging to 1 day. Next, using the same analytical model applied to monthly flows, 12 monthly flows are transferred to the dam section. Five versions of the DAR method – three of which have constant exponents – were investigated. The method with n = 1 was found to be the worst performer.