COMPUTER SIMULATION STUDY FOR RESTORATION AND DISASTER MITIGATION OF MOUNTAINOUS STREAMS

Abstract

The purpose of this study is to review the various techniques available for River Restoration issues and develop a computer-based framework for Restoration and disaster mitigation for actual Case Study. In this present document, the case study of Assi Ganga River which is a tributary of Bhagirathi River is taken, which falls in the category of mountainous streams. This river has experienced a high increase in discharge from135 m3/sec to 2665 m3/sec within one hour during August 2012 cloudburst event, resulting in heavy bed load boulder movement with huge volume of silt load in downstream areas due to steep slope of the river. Main aim of this dissertation is to analyze the natural disaster events of mountainous streams like cloud burst, concentrated rainfall and flash flood events and propose a new approach of using Cascade Grade control weir made of abrasion resistant material in series as cascade development combined with suitable Block Ramps on the stream bed for disaster mitigation of mountainous streams. The steep bed slope of these streams and the movement of large sized bed load boulders with significant suspended silt load poses very serious hazard in the downstream areas. Thus, a strategy to mitigate such disaster can be done by weakening the high stream power of the channel by breaking up the steep energy gradient line by positioning Grade control weir in series as cascade development and reducing channel flow velocity by increasing bed roughness with suitable Block Ramps provision. Mathematical model investigation for disaster mitigation and restoring mountainous stream is examined using notional representation of Grade Control Weir and Block Ramps using HEC-RAS software. Reduction in channel stream power, flow velocity, shear stress and energy gradient of the channel for various arrangements of weirs for different heights, positions and number combine with various Block Ramps arrangements and by using only Block Ramps were analyzed, and the optimal and acceptable arrangement was found as arrangement-7 with 10 weirs of 3m height. This arrangement results in ~52.8 %, ~68.3 %, ~63.1 %, reduction in velocity, shear stress and stream power respectively with respect to the original velocity, shear stress and stream power of the channel and values are within limiting value of non-destructive potential. Weir position, Shape along with Type-B Unstructured Block Ramps position, number and other detailing as arrangement-7 (detailing asTable 6.6) is suggested to mitigate the disaster and restore the River to natural functioning