Magnitude–frequency analysis to assess effective discharge at daily and monthly timescales in South Indian River basins

Abstract

‘Effective discharge’ is defined as a discharge that carries maximum amount of sediments over a prolonged period of time. Magnitude–Frequency Analysis (MFA) provides a mathematical framework to determine effective discharge. MFA considers (1) the discharge at a location that follows a lognormal probability distribution and (2) sediment load which exhibits a power law relationship with the discharge. An important task for hydrologists is to determine reliable estimates of effective discharge at locations of interest within river basins. There is a dearth of attempts to assess effective discharge estimates within South Indian River basins. Present study demonstrates the utility of MFA to arrive at effective discharge estimates based on daily and monthly stream flow data at 30 gauges in four southern river (Mahanadi, Godavari, Krishna and Cauvery) basins flowing through Indian Peninsular region. Evaluation of effective discharge at daily and monthly timescales is carried out to understand the behavior of effective discharge estimates over different timescales. It was observed that the assumption of lognormality was invalid for daily discharge data at all gauges while it was valid at monthly scale for 12 gauges. Results from this study can find use in efficacious planning and management of reservoirs in South India.