Geospatial technologies as an aid to decision support system for assessment of urban floods in GHMC areas of Hyderabad

Abstract

Urban flooding is a manmade disaster. Increased surface imperviousness due to urbanization along with encroachments of nalas and waterbodies and inadequate drainage infrastructure system are the chief culprits for urban flooding. Flooding in an urban area brings about severe economic, structural, and environmental damages, and can be associated with casualties too. The current paper illustrates the role of GIS technology in urban drainage mapping and analysis. It identify the pre-disposing factors that lead to urban floods and explains the effect of each factor on urban floods, the trend and relationship to each other. The flooding in some areas of GHMC during September 2016 came as a grim reminder of the unprecedented Musi floods of 1908 and the recent floods in August 2000. There are about 403 different waterbodies like tanks/lakes/reservoirs in GHMC areas as identified from the Survey of India toposheets on 1:25,000 scale. Alarmingly, only a minuscule 169 lakes have a water spread of over 10 ha, an indication of how intertwined political and real estate ambitions have dealt a death blow to many waterbodies. To address city’s problems, especially inundation of areas, remodelling of storm water drains (nalas) and identifying the obstructing structures on nalas and lake beds, Remote Sensing & GIS technologies are effective tools. The majority of GHMC area is drained by Musi river catchment. The Digital Elevation Model (DEM) of the entire drainage basin of GHMC is prepared using cartosat data and micro watersheds are also delineated. The daily surface runoff is calculated during the flood days using Automatic Weather Stations (AWS) rainfall data. The natural drainage course is identified from the Survey of India Toposheets on 1:25,000 scale and it is compared with Revenue and Urban parcels data to find out the encroachments and bottle necks in drainage course. The required nala widths are calculated by making use of hydrological parameters. Finally a model storm water plan is developed by making use of existing nala widths to overcome the flood menace in GHMC. Hence Geospatial technology is an effective tool in mapping and analyzing the spatio-temporal data and to inform the stakeholders and decision makers of the locations in controlling flooding and improve decision making.