Development of Flood Forecasting Model for Chenab River Basin

Abstract

River Chenab experiences significant floods during the monsoon season. There are some major projects on the river, such as Salal dam, Baglihar, and Dulhasti. On the directions of the Governing Body of NIH, this study was taken up to develop a flood forecasting model for the Chenab Basin. The objectives of the study were to implement snow-melt and rainfallrunoff models for the Chenab basin up to Akhnoor. Different data layers of the Chenab basin (such as basin boundary, drainage network, DEM, elevation bands, hydro-meteorological network etc.) were generated in GIS. The drainage map of the basin was used to mark various sub-basins at Benzwar, Sirshi, Premnagar, Dhamkund, and Akhnoor. Around 30 years of rainfall data at more than 20 sites and 13 years of discharge data at 10 sites were entered in hydrological data entry system and plots of flood observations at different gauging sites were generated. Using the daily data of rainfall stations, average daily rainfall was worked out in different sub-basins for different flood events. Plots of daily rainfall and discharge data at different stations indicate that most of the flood events in the Chenab basin are generated from rainfall storms mostly concentrated in the middle and lower reaches of the basin below Benzwar/Sirshi. In view of the status of availability of data and the factors responsible for generation of flood, WINSRM model was applied considering daily rainfall and discharge for sub-basin downstream of Benzwar/Sirshi up to Akhnoor. Model parameters were calibrated and validated to get the best match of observed and simulated flows at Akhnoor. The travel time of flood wave from Benzwar to Akhnoor is less than one day and hourly hydrological data were crucial for this study. So, availability of short-term (hourly) rainfall, flow, and met data were investigated from different departments. 3-hourly rainfall data and hourly discharge data of Akhnoor and Salal dam site were available for the flood event of year 2006 (September 1 – 6, 2006) and the same were used to simulate flood using unit hydrograph for the sub-basin between Premnagar and Akhnoor (Area – 5043 sq. km). Synthetic unit hydrograph (UH) was developed for this subbasin. Using the 3-hourly rainfall of Salal station, the daily rainfall data of various stations (obtained from CWC) for the flood event (September 1 – 6, 2006) were disaggregated and 3-hourly average rainfall in the sub-basin was computed. This rainfall pattern was convoluted with the UH to get the simulated flood at Akhnoor. Simulated flood matches with the expected pattern of flow at Akhnoor to a considerable extent. If short-term ranfall and flow data of some additional flood events could be gathered, then the unit hydrograph can be fine-tuned so as to better match the observed flow pattern and peak discharge at Akhnoor. Based on the rainfall catch at different stations during various flood storms events, some important rainfall stations have been identified for automatic/ self-recording instrumentation for flood forecasting purpose.