Development of Rainfall-Intensity-Duration-Frequency (IDF) curves for Ranikhola Watershed, Gangtok, India

Abstract

Sikkim is a mountainous state of India, receives heavy rainfall and frequent landslides and floods. Rainfall is one of the most important climatic parameters having great influence in Himalayan regions. Information on rainfall intensity and duration are correlated to landslide and it is important to understand the rainfall characteristics and variability as it has a significant impact on crop yield and production in agriculture sector. Rainfall Intensity-Duration-Frequency (IDF) curve is a relationship between rainfall intensity, duration and return period commonly used in hydrology for flood forecasting and provide better soil conservation and soil management strategies. The present study is conducted to develop the Rainfall-Intensity-Duration-Frequency (IDF) curves for various duration and recurrence periods for Ranikhola watershed, located in East Sikkim. It is one of the major tributaries of Teesta Basin. Analysis of change in rainfall pattern and intensity is a paramount important from engineering point of view for designing and planning of water resource structures. The daily rainfall data of 28 years from 1985 to 2012 were collected and disaggregated. Gumbel's Probability method found to be suitable for study area. It was observed that among 5 monsoon months viz. June, July, August, September and October, maximum rainfall intensity of 259.785 mm/h was in July month and minimum rainfall intensity of 168.265 mm/h was in August. It was also noticed that rainfall intensity increases with increased in recurrence period.