Design Discharge Estimates from Frequency Analysis of Annual and Summer Maximum Flow Series

Anbreena Anjum* and Munir Nayak
National Institute of Technology Srinagar, India
*Corresponding Author: Anbreena Anjum, National Institute of Technology Srinagar, India.

Published: May 19, 2025

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Abstract  

Floods, one of the most common and destructive natural disasters, have always been a significant part of Earth's history. Extreme flood occurrences can sometimes have a long-lasting effect on hydrologic systems. Therefore, planning, designing, and managing a variety of facilities require a hydrologic and hydraulic understanding of floods. Hydrologic flood frequency analysis is a method of forecasting future frequencies of floods by utilizing statistics and probability. In this study, the discharge data of River Jehlum in Kashmir-India, was analysed for annual & summer maximum flood peaks and flood frequency analysis was performed on nine gauging stations, using probability distributions. These included gamma distribution, Log Pearson Type-III distribution & Extreme Value Distribution (EV-I). The corresponding PDF, CDF, shape, scale & location parameters were obtained, fitting distributions, calculating flood quantiles and subsequently results were plotted. Corresponding confidence intervals at 95% were also constructed for flood quantiles from the best fitted distribution. The frequency curves obtained were compared with empirical estimates. The 100-year return period flood discharge was obtained at all the gauging stations which is useful in design of hydraulic structures. The delineation of River Jhelum watershed and sub basins was done in ArcGIS software using 30m SRTM Digital Elevation Model-DEM. The seasonality of discharge peaks and the corresponding extreme magnitude variations were studied to relate the seasonality of flood peaks with magnitudes. Rainfall and snowmelt contribute to the flood discharge, and the relative contribution of each changes with the season. The study has completed flood frequency analysis at each gauging station on River Jhelum and obtained the design discharge both for annual and summer data for comparison.

Keywords: Flood; Frequency Analysis; quantiles

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