Flood Routing of Discharge Mangla Emergency Spillways using 1D and 2D Modeling in HEC-RAS

Abstract

Water storage and provision plays an important part in the progress of contemporary society. Dams are the most common reservoir to store the water which can be used to produce electricity and to irrigate the land. Mangla dam is Pakistan's largest and first ever dam which was built after the creation of Pakistan. The main purpose of this dam is to control flooding, generate electricity and to irrigate the crops in areas where less than 10mm rainfall occurs throughout the year. The dam height was raised to 1242 ft from 1202 ft during the Mangla dam raising project in 2009. The annual power generation capacity was increased to 1120 MW. To accommodate the discharge produced by the maximum probable flood in the region, the capacity of the emergency spillway needs to be increased to at least 20,000 cusecs after the raising project. WAPDA asked the Pakistan Army to increase the capacity of the emergency spillway called Barakas Nallah and remove the installations/buildings from the areas which are prone to the flood. HEC-RAS 6.0 is used for simulations of the flood to identify flood prone zones. 1D and 2D simulations are run to get the information about the flood risk areas. Simulations were carried out for 8000, 15000, 20000, 30000, 50000 and 100000 cusecs of discharge, all buildings which are vulnerable to flood at a chosen maximum design discharge should either be cleared, or diversionary measures employed for flow.