Monthly flow estimation of a catchment is a major task for the design of irrigation system in a required commanded area. We generally estimate runoff as annual or monthly flow, extreme low flow & flood flow. Annual or monthly flow are required for the design of irrigation water requirement where as extreme low flow & flood flow are determined for the design of hydraulic structures & river training works. Here, in this article we are mainly concerned to the estimation of monthly flow in catchment area of study. When long term flow data of study are available, we use frequency analysis method. In absence of such records, we can apply regional & empirical method to calculate monthly flows.
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