Senior Manager (GIS)
Manager (GIS), RMSI
Project Lead (GIS), RMSI
A major landslide in Tibetan Himalayas on the banks of river Pareechu created an artificial dam, causing water to build up into a mammoth artificial lake spread across approximately 200 hectares of land and 60 metre deep. The steadily rising water levels threatened to breach the dam and cause flash floods down the river, devastating life and property
Fear of flash floods gripped the state of Himachal Pradesh ever since Chinese authorities warned their Indian counterparts, late July, about an imminent disaster brewing up, down the streams of river Sutlej. A major landslide in Tibetan Himalayas on the banks of river Pareechu, a tributary to river Spiti, which in turn is a tributary to Sutlej, created an artificial dam causing water to build up into a mammoth artificial lake spread across approximately 200 hectares of land and 60 m deep. The steadily rising water levels threatened to breach the dam and cause flash floods down the river.
As part of an independent Risk Analysis Study, carried out by RMSI, a team comprising Remote Sensing, GIS, Hydrology and Risk Management experts conducted a ‘Dam Break Analysis Study’ to quantify the potential risk in case a breach in the artificial lake formed on Pareechu river, had happened.
The team conducted a quick but comprehensive study using remote sensing images, digital elevation and housing data, 2001 census of the region and hydrological and spatial analyses to quantify the potential risk in terms of affected population size and estimated property losses. GIS techniques having the capability to process and display geo-spatial information were widely used. The team identified the artificial lake close to 32.30 N and 78.70 E using remote sensing images available from Aster. An area covering the lake and a 220 km stretch of the river Sutlej extending from the lake up to Rampur was taken to be the study region.
A high-resolution digital terrain model (DTM) was developed for the study region to determine longitudinal profiles and cross-sections of the river at 1 km interval through out the 220 Km stretch. RMSI formulated the problem of ‘Dam Break Analysis’ into three major components.
In the first component, the characteristics of the breach, i.e. the geometry of the breach and how long it takes to develop were formulated. Different types of dams are likely to fail in different ways and hence different breach characteristics have to be defined for each. For this study, the dam was assumed to be an earthen one and the breach was assumed to grow progressively from a relatively small to a large size over a finite time before reaching a steady state. The volume and total head of water in the lake was estimated based on the information available from various sources with regard to the physical features of the lake. Three breach scenarios differing from each other in terms of breach head, the worst case being 60m, were considered for the analysis. For each breach head, associated breach width and breach discharge were computed using the National Weather Service (NWS) procedure.