MODELING OF RIVER RESTORATION ANALYSIS - A CASE STUDY

Abstract

The purpose of this study is to to review the techniques available for analyzing and assessing River Restoration issues and develop a framework for River Restoration for actual Case Study. In the present communication, the case study of Assi Ganga River which is a tributary of Bhagirathi River is adopted, which falls in the category of hilly streams. This river has experienced a high increase in discharge from135 m3/sec to 2665 m3/sec during August 2012 cloudburst event, resulting in heavy bed load boulder movement along 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 hilly streams like cloud burst and flash flood events and propose a new approach of using innovative Piano Key Weir (PKW) structures made of abrasion resistant material in series as cascade development on the stream, for hazard moderation of hilly streams. The steep bed slope of hilly streams and the movement of large sized bed load boulders along with significant suspended silt load poses very serious hazard in the downstream areas. Thus, a strategy to minimize such devastation can be to weaken the high stream power of the channel by breaking up the steep bed slope by positioning PKW in series as cascade development. Mathematical model investigation for moderating hazard and restoring hilly stream is examined using notional representation of Piano Key weir in cascades using HEC-RAS software. Percentage reduction in unit stream power, floe velocity, shear stress and energy gradient of the channel for various arrangements of weirs for different heights and positions were analyzed, and the optimal and acceptable arrangement was found to be the cascade system with weirs of 10 in height, distance between each weir being around 2 kilometers. In addition to this, the backwater of PKW will be able to create in-stream storage for drinking, agricultural or other domestic purposes and also for small hydro-power development. It increases the specific flow three to four times as compared to any other over-flow spiliway, making it hydraulically much more efficient. Thus, it enhances safety, storage and flood control efficiency by better handling cloud burst flood than any other conventional weirs.