Hydraulic Modelling of Flood Assessment in Chenab Basin Pakistan

Abstract

Floods are among the most frequent and destructive natural hazards in Pakistan, particularly along the Indus River and its major tributaries, where rapid population growth and unregulated development have substantially increased exposure to flood risk. This study presents a comprehensive flood-assessment framework that integrates Remote Sensing (RS), Geographic Information Systems (GIS) and hydraulic modelling to delineate and quantify flood inundation within the Chenab Basin one of the most flood-prone regions of Punjab. Multi-temporal Landsat imagery acquired before, during and after flood events was processed to compute the Normalized Difference Water Index (NDWI), Modified NDWI (MNDWI) and Water Ratio Index (WRI) for effective flood detection. Among theseindices, the MNDWI demonstrated the highest classification accuracy (>90%), as validated against field observations and high-resolution satellite imagery. Land-use and land-cover (LULC) maps were generated using supervised maximum-likelihood classification to assess the exposure of agricultural lands and settlements. A 30-m Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) was employed to derive a Digital Terrain Model (DTM) and to develop a one-dimensional hydraulic model using HEC-RASand HEC-GeoRAS for floodplain simulation. Flood discharges corresponding to return periods ranging from 2.5 to 100 years (455,000–1,665,000 cusecs) were simulated for the river reach between the Taunsa and Guddu barrages. The results indicate that approximately 68% of the study area was inundated during the 2010 flood, with prolonged flooding observed in low-lying areas around Muzaffargarh and Rajanpur. Overall, the integration of optical satellite-derived water indices with hydraulic modelling proved to be an effective approach for rapid and accurate flood assessment, facilitating the delineation of high-risk zones critical for flood-risk reduction and spatial planning in Pakistan.