FLOOD INUNDATION MAPPING AND 1-D HYDRODYNAMIC MODELING USING REMOTE SENSING AND GIS TECHNIQUE Mr. Praveen Kumar Thakur 1 , Mr. Accarapol Sumangala 2 1 Scientist/Engineer, Water Resources Division, Indian Institute of Remote Sensing-Dehradun, India; thakur.praveen@hotmail.com 2 Department of Public Works and Town & Country Planning Rama 9 Rd. Huaykuang, Bangkok Thailand; accarapol@yahoo.com ABSTRACT This study is an attempt to develop an integrated methodology for flood mapping using combination of RADARSAT, IRS LISS- III/LANDSAT satellites images and Geographic Information Systems (GIS), and Hydrodynamic modeling for September 2003 flood event of Puri District, Orissa, India. The main objective of this study is to generate flood inundation maps using DEMs (ASTER), flood modeling using hydrodynamic models and comparing with the flood extent maps derived from RADARSAT SAR satellite images (4, 11, 13 September 2003). The flood inundation areas were extracted from RADARSAT images by visual and digital interpretation. Digital Elevation Models from ASTER was used to derive cross sections in flood plain and six cross sections were collected during field visit to Puri district, which were further adjusted from cross sections as derived from DEMs. The stage- discharge relationships were established using the observed flood gauge and discharge data at available cross sections. Hydrodynamic model HEC-RAS (Hydraulic Engineering Center-River Analysis System) is used to find the longitudinal profile, water level and routed discharge along Bhargavi, Kushabhadra rivers and flood mitigation canal at upstream of Kushabhadra river. This information was further used in Hec-GeoRAS GIS to find out the flood inundation area. The results of this study show that integration of GIS and hydrodynamic modeling is an efficient way to predict and map the flood areas. KEYWORDS: Flood, RADARSAT-SAR, IRS LISS-III/LANDSAT, 1-D Hydrodynamic modeling, ASTER DEM, HEC-RAS. INTRODUCTION Floods are considered the most significant natural disaster affecting from the perspective of their frequency, financial cost and most importantly the impact on the population and the disruption to socio-economic activities. Flooding refers the inundation of an area by unexpected rise of water by both dam failure or extreme rainfall duration and intensity in which life and properties in the affected area are under risk. There is one problem with the use of conventional passive sensor satellite imagery for flood inundation mapping as floods occur during or immediately after periods of heavy rainfall. In India, generally flood occurs during monsoon period and at that time due to the cloud cover, optical remote sensing image has their limitation in mapping the flood extent, so radar image can be used for accurately mapping the extent of flood. The active Synthetic Aperture Radar (SAR) sensor allows acquisition of images independent of cloud cover, so in many studies, combination of Geographic Information System (GIS), SAR imagery, high resolution digital elevation model (DEM) gives the flood inundation map with flood depth. The advantage of 1-D hydrodynamic models is that they provide a very accurate description of the water levels and discharge along longitudinal river profile and at selected cross sections across the river. This study is an attempt to develop an integrated methodology for generate flood inundation map on using GIS and hydrodynamic modeling and to obtain flood risk map in flood area of Mahanadi delta Orissa. OBJECTIVES The broad objectives of this study are: 1. Analysis of the flood frequency to understand behavior of flood over study area from observed gauge and discharge data. 2. To generate the flood inundation maps using combination of 1-D hydrodynamic models and GIS environment. 3. To prepare flood risk map over study area. 4. To evaluate and compare the flood inundation area from microwave remote sensing data and that simulated from hydrodynamic models. STUDY AREA The study area is in Delta region of Puri District of Orissa state and is located at 85 o 45 ’ 22.32 ” E; 20 o 21 ’ 20.36 ” N to 86 o 04 ’ 01.65 ” E; 19 o 48 ’ 47.52 ” N. This District is closed to the Bay of Bengal. The District of Puri, the holy land of Lord Jagannath is located in the coastal track of Orissa. Its boundaries extend in the north to Jagatsinghpur District, in the south to the Bay of Bengal and Ganjam District, in the west to Khurda District and in the east to the Bay of Bengal. Figure 1 shows the 23 rd October 2000 Landsat image of study area. Fig. 1: 23 rd October 2000 Landsat image of study area.