Journal of Information and Computational Science ISSN: 1548-7741 An Assessment of Flood Vulnerability Zone in Greater Chennai Corporation, Tamil Nadu 1*Dhamodaran R and 2Madha Suresh V 1Research Scholar, CNHDS, University of Madras, Chennai – 600025 2Professor, Department of Geography, University of Madras, Chennai – 600025 * Corresponding Author Abstract An assessment of flood vulnerability region is the major research study which provides a precise account about the vulnerable regions. The vulnerable regions are further identified and implement the mitigation strategy for the community. It renders help in providing safe guidance of the people headed towards the camps, prior to the occurrence of the flood. The parameters that will allow the researchers to efficiently detect the flood vulnerable regions are the Geology, Geomorphology, Soil, Landuse / Land cover, Elevation, Slope, Drainage Density and Rainfall. The research study utilized geographical information system (GIS) for the delineation of flood zone in Greater Chennai Corporation. The authors examined the vulnerability region using weighted overlay techniques in which the individual parameters assigned to certain weights based on the influence of flood hazard. The authors also highlighted the vulnerable region based on five categories such as Very high, High, Medium, Low and Very low. The study resulted that the region along the coast line which covers 21.31 sq.km are very highly vulnerable and followed by high vulnerable region covered at the largest area 101.8 sq.km. The study enables the stake holders and administrative leaders to implement the mitigation strategy efficiently. Keywords: flood vulnerable region, geographical information system, drainage, LULC 1. Introduction In recent years there is an increase in frequency and intensity of flood disaster, due to climate change at a global level which is directly increasing the intensity of disasters. Due to the alteration in atmospheric circulation pattern, there is heavy rainfall in short span mixed with adverse topographical conditions combined with human-induced factors lead to loss of life and properties (Meera and Gupta, 2017). Greater Chennai Corporation is affected the most during the 2015 flood along the east coast of India. Its terrain characteristics are very flat and average coastal elevation is around two meters with reference mean sea level, thus making it hard to drain the floodwater. It is clearly understood that urban development without proper plan causes to increase in the severity of the flood disaster. Hence it is important to induce water resource Volume 10 Issue 5 - 2020 122 www.joics.org Journal of Information and Computational Science ISSN: 1548-7741 management in planning to properly manage the flood (Tas, 2016). These characteristics of the Greater Chennai Corporation is the natural and manmade factors causing flood. In this context the present paper seeks to assess the flood vulnerability through applying Geographical Information System (GIS) and weighted overlay method. 1.2 Study Area Figure 1: Study Area Greater Chennai Corporation is situated in the northerly part of Tamil Nadu along the east coast of India, is located in between latitudes of 12o59’ and 13o9’ north and longitude of 80o12’ and 80o19’ east (Fig. 1). It is bounded by Tiruvallur in North and West, Chengalpattu district in South, Bay of Bengal in East. Chennai is divided into fifteen administrative zones which are Tiruvottriyur, Ambattur, Manali, Perungudi, Anna Nagar, Teynampet, Royapuram, Kodambakkam, Sholinganallur, Thiru-vi-ka Nagar, Adyar, Tondiarpet, Valasaravakkam, Madhavaram and Alandur. Based 2011 census data, Chennai accounts for a population of 4,681,087 people and with a population of 26,903 per km2 (District Hand Book, 2016–17). The average rainfall of Chennai district is 1298 mm and receives maximum amount of precipitation from October to November during onset of Northeast monsoon (CCC&AR and TNSCCC ,2015). The region is drained by three river system which are Kosasthalaiyar (North), Coovum (Central) and Adyar (South). 2. Materials and Methodology The study was carried out based on the following parameters namely; Geology, Geomorphology, Soil, Landuse / Landcover, Elevation, Slope, Drainage Density and Rainfall Volume 10 Issue 5 - 2020 123 www.joics.org Journal of Information and Computational Science ISSN: 1548-7741 which are necessary to identify the flood vulnerable region in Greater Chennai Corporation. The datasets (Tab. 1) were acquired from the concerned sectors which consists of government and non – government agency which are Geology and Geomorphology from GSI, Soil from National Bureau of Soil Survey, Sentinel-2 and SRTM from USGS, Rainfall from IMD. The research methodology implemented for study is illustrated in Figure 2. Landuse / Landcover was processed from Sentinel -2 Imagery which involved in atmospheric correction in order to remove induced noise and classified using supervised image classification to acquire land based information. Elevation data assessed using Digital Elevation Model (STRM) through which low lying region was identified. Slope and Drainage Density was obtained through SRTM DEM data; the slope was calculated using the elevation value which provides the gradient to identify the plain region and water movement. Elevation data was corrected to fill in gaps with sink tool. Drainage density was calculated from DEM data which involved in finding of flow direction, flow accumulation and Strahler method was used derive stream order. Stream Order was used to generate drainage density using the formula “Stream length / Basin Area”. Rainfall was converted into spatial information through Inverse Distance Weighted (IDW) method. The flood vulnerable region was assessed using Weighted Overlay Method where each parameters was assigned weightage based on influence with overall weight of 100 and each parameters sub-class were ranked from 1(Low) to 5 (High) based on the characteristics. Finally, the parameters were overlaid and based on the weightage the output was classified into 5, consisting of vulnerability – Very High, High, Moderate, Low and Very Low. Volume 10 Issue 5 - 2020 124 www.joics.org Journal of Information and Computational Science ISSN: 1548-7741 Flood Vulnerability Data used Satellite Based Conventional Image Processing LULC Rainfall Elevation Soil Slope Geology Drainage Density Geomorphology Weighted Overlay FLOOD VULNERBALE ZONE Figure 2: Methodological Flowchart for present study Table 1: Datasets used for the study Sl. Data Used Source Resolution No. 1. LULC United States Geological Survey (USGS) – 10m Sentinel-2 2. Elevation United States Geological Survey (USGS) – 30m DEM (SRTM) 2. Slope United States Geological Survey (USGS) – 30m DEM (SRTM) 4. Drainage United States Geological Survey (USGS) – 30m DEM (SRTM) 5. Geology Geological Survey of India (GSI) 1:50,000 6. Geomorphology Geological Survey of India (GSI) 1:50,000 7. Soil National Bureau of Soil Survey 1:50,000 8. Rainfall Indian Meteorological Department (IMD) - Volume 10 Issue 5 - 2020 125 www.joics.org Journal of Information and Computational Science ISSN: 1548-7741 3. Result and Discussion Figure 3: Geology Figure 4: Geomorphological 3.1 Geology Greater Chennai Corporation (GCC) consists of diversified geological formation ranging from various time series starting from Archaean to present tertiary age. It can be distributed into four main groups based on the development like Archaean Crystalline, Consolidated Gondwana, Gondwana, Tertiary Sediments and Alluvium. Geology (Fig.3) is one of the vital parameters in flood vulnerability assessment, GCC has following geological formation which are Cuddalore Formation, Alluvium- Fluvial, Fluvio-Marine-Mangrove swamps, Peninsular Gneiss, Khondalite and Satyamanagalam Group. The spatial coverage was assessed for six features namely; Cuddalore Formation covers 2.27 sq.km (0.53%), Alluvium- Fluvial with 128.92 sq.km (30.28%), Fluvio-Marine-Mangrove swamps with 18.84 sq.km (4.42%), Peninsular Gneiss with 77 sq.km (18.22%), Khondalite with 3.29 sq.km (0.77%) and Satyamanagalam group with 9.91 sq.km (2.16%). 3.2 Geomorphology The geomorphological aspect is significant in determining the flood vulnerability of the study area undertaken, through analyzing the physical structures, chemical configuration, and landforms. The region consists of six geomorphological (Fig. 4) units which are Young Coastal plain, Old Coastal plain, Flood plain, Alluvial plain younger / lower, Pediplain weathered/buried, and Pediment – Inselberg Complex. Weightage was assigned based on the water-holding properties and assessment of spatial coverage revealed the extent of the features, Young Coastal plain covers 114.35 (26.83%), Old Coastal plain with 73.18 sq.km (17.18%), Flood plain with 2.82 (0.66%), Alluvial plain younger / lower with 116.41 sq.km (27.33%), Pediplain Volume 10 Issue 5 - 2020 126 www.joics.org Journal of Information and Computational Science ISSN: 1548-7741 weathered/buried with 118.63 (27.85%) and Pediment – Inselberg Complex with 0.53 sq.km (0.12%). Figure 5: Soil Figure 6: Landuse / Landcover 3.3 Soil It is an indispensable part of nature which helps to sustain life on earth, soil is available in various form-based texture, chemical composition, fertile rate, and built on solution effects. GCC soil composition also consists of a mixture of sandstone, sedimentary rock, and clay, for studying the flood vulnerability soil is analyzed based absorption, percolation rate, and maximum