Simulating Decadal Sedimentation in the Upper Indus Basin and Tarbela Reservoir Using SWAT Model

Abstract

Tarbela Reservoir, one of Pakistan's key irrigation and hydropower sources, has experienced diminishing live storage due to high sediment generation from the Upper Indus Basin (UIB), over the past three decades. This study monitors sedimentation trends from 1994 to 2023 using Satellite data from USGS STRM, ERA5-Land Climate Reanalysis, FAO's Digital Soil Map of the World, and Global Land Cover dataset. Ground data came from the Surface Water Hydrology Project and Tarbela Dam Project Library. Using ArcSWAT, a 30-year model was developed for a 102,028 km² area, with 64 HRUs and 26 subbasins to assess spatial heterogeneity. Sensitivity analysis, calibration, and validation were performed using SWAT-CUP and SUFI-2 algorithm showing excellent model performance with 22 parameters. The model achieved R² of 0.89, NSE of 0.84 during calibration, and R² of 0.81, NSE of 0.68 during validation. Model simulations for the Upper Indus Basin at Besham Qila show 78% of precipitation contributes to stream flow, with 61% as surface runoff. July presents peak rainfall, sediment yield, and water flow. Annual surface runoff averages 505.35 mm, with upland sediment yields from 5,772.90 to 2,086.09 Mg/ha. Significant in stream sediment deposition (-2,082.52 Mg/ha) heightens flood risks. Decadal sediment yield decreased from 5.9–385.3 tons/ha to 2.7–370.6 tons/ha. Reforestation, terracing, check dams, and sustainable land use practices are recommended to control sediment generation and deposition in Tarbela reservoir. Continuous monitoring and stakeholder engagement are essential to maintain reservoir storage capacity and hydropower efficiency.