Optimizing Manchar Lake Management: Integrated Strategies for Water Quality and Quantity Restoration

Abstract

Manchar Lake, Pakistan’s largest freshwater body, faces severe threats from climate extremes and human-induced pressures. This study identified critical thresholds for sustainable lake management by evaluating water quantity and quality under various scenarios. Using Landsat images, the modified Penman formula, and seepage rate analyses, the Water Loss Ratio (WLR), the ratio of total annual losses to average annual volumes, was calculated. The WLR consistently exceeded 1.0 due to the lake's shallow depth, indicating excessive losses. Hydrodynamic modeling revealed that maintaining a minimum area of 201.4 km² and an annual volume of 0.269 km³ is essential to minimize losses. For water quality, Total Dissolved Solids (TDS) simulations revealed that excluding inflows from the Main Nara Valley Drain (Scenario 2) reduced TDS levels from 4900 to 750 mg/L within two years. While freshwater diversion (Scenario 9) met water demands with increased TDS levels. A combined strategy of initially excluding polluted inflows, followed by controlled freshwater diversion after the construction of Gaj Dam construction kept TDS below 1500 mg/L, which is still acceptable for irrigation. These findings provide a practical, replicable framework for balancing water quantity and quality in lakes located in arid regions.