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