III-2-Web GIS Application for Flood in Upper Assam

Abstract

Large tract of the Brahmaputra basin in Assam is prone to floods. The flooding is caused mainly due to breaches in the embankment of the Brahmaputra. In Upper Assam, Dhemaji district is one of the most frequently flooded area. The district lies north of the Brahmaputra River. Often the right bank embankment of the river is breached causing flooding in Dhemaji. In this study, the Brahmaputra, other tributaries and embankments in the vicinity of Dhemaji district are mapped. The flood inundation map prepared from satellite data is processed and converted into Vector map. Main river in the district is Gai (earlier known as Sisi). Various maps prepared are available in native GIS format requiring GIS software to handle them. A new technology viz Web GIS in which GIS is combined with Internet has since emerged. In Web GIS, spatial information is disseminated on Web and may be accessed through a web browser. Operations namely display, navigation, query etc. may be performed on the spatial data. However, a Web GIS application requires dedicated software. These are available in both open source and commercial domain. Open source Web GIS software has several advantages, like it is simple to use, it costs nothing except hardware, in it complex application may also be developed etc. In this work, an open source Web GIS software Mapserver is used for dissemination of information on floods in Upper Assam, particularly in Dhemaji and Lakhimpur districts. In the application, vector layers of flood inundation, river course and embankments are displayed. Flood inundation map was prepared from IRS LISS-III data of August 1998. The inundation occurred mostly in the floodplains of the rivers. Large area is inundated adjacent to the embankment breach site. For visible and near infrared satellite data, the cloud cover hinders the mapping of inundation area. Thus, the inundation map depicted in Web GIS application shows part of the inundated area only. Full application may contain inundation maps of several years and other layers e.g. administrative regions etc.