Risk Assessments of Hydro-Power Projects along the Nagavali River, Odisha-Andhra Pradesh, India

Nagavali river has come into the limelight since 2005 because the Govt of India had announced for constructing ten hydro-powers projects in the river basin. Nagavali river is flood-prone. The river flows through a complex structural longitudinal valley between eastern and western ridges in Orissa and Andhra Pradesh before meeting with the Bay of Bengal. Out of those ten project sites, two sites, i.e., at Hathipahar region in Rayagada, Orissa and the Thotapalli village in Vizianagaram District, Andhra Pradesh, have been selected for the risk assessment.  The Hathipahar region is situated over a piedmont slope of the eastern ridge (formed of Khandelite-granite), and the Thotapalli site is located over a rolling plain. In July 2006, due to torrential rainfall and flash flood, the under constructed dam at Hathipahar collapsed. The valley experienced vast changes in channel shifting (about 550 meters), headword erosion, valley incision and soil loss. The Thotapalli site was not affected, and thus, the construction was completed in 2010. Consequent flood events of   2011 and 2015 caused massive erosion and enlargement of the reservoir from 2.1 sq. km. to 9.16 sq. km, and the upstream course of the river merged with the reservoir.

The present research aims at estimating damage and assessing socio-environmental risk along with these two sites. For assessing flood risk, the SCS-CN model has been used and validated with real-time discharge data, land use-land cover change, spatio-temporal variations in channel width-depth, and sedimentology. Google Earth and SRTM DEM have been used for detecting such changes. Field surveys have been carried out to prepare a micro-level elevation model, damage estimation and lithological formation of the area. The research also focuses on assessing the possibility of continuing the proposed hydro-power sites since the existing sample sites are already experiencing massive erosions and destructions.

Keywords: piedmont slope, flash flood; hydro-power project; SCS-CN model; risk assessment