Geographic information system (GIS) provides a broad range of tools for determining area affected by floods and for forecasting areas that are likely to be flooded due to high water level in a river. When spatial data are used in an information system, one tends to speak of a spatial information system. Spatial data has a physical dimension and geographic location.
Spatial data stored in the digital data base of the GIS, such as a digital elevation model (DEM), can be used to predict the future flood events. The GIS data base may also contain agriculture, socio-economic, communication, population and infrastructural data. This can be used, in conjunction with the flooding data to adopt an evacuation strategy, rehabilitation planning and damage assessment in case of a critical flood situation.
Geographic information system have three important components - Computer hardware, set of application modules and a proper organisational network. These three components need to be in balance if the system is to function satisfactorily.
The advantage of using GIS are :
- Fast accessibility
- Data manipulation without disturbing original data.
- Quick retrieval of information
- Sharing/using of data by many users.
- Security and safety of data.
- Easy updating of information.
- Good and accurate representation of result.
Study area
General Description of the Area :
Dikrong river is one of the important north bank tributaries of Brahmaputra river in Assam. The catchment area of Dikrong is 1528 sq.km. which covers a part of the lower hills of Arunachal Pradesh and a part of Lakhimpur district of Assam between latitude 26
o55’ N and 27
o20’ N and longitude 93
o15’ E and 94
o00’ E. The river originates at an elevation of about 2580 metre near the border of Lower Subansiri district and East Kameng district of Arunachal Pradesh. Out of the total catchment area of 1528 sq.km., 270 sq.km. lies in Assam and remaining 1258 sq.km. lies in Lower Subansiri district of Arunachal Pradesh.
Flood in this sub basin, particularly in the plain areas which lies in Assam, is a regular annual phenomenon which causes inundation to vast areas on both banks and as a result cultivable lands and human dwellings of these areas are adversely affected. Since flood water from the river Dikrong generally inundates flood plains in the Lakhimpur district of Assam, we have selected this part of the basin in Assam as our study area which is of 270 sq.km. This portion of Dikrong basin lies between latitude 26
o55 N and 27
o11 N and longitude 93
o48 and 94
o00 E.
Population:
Population of this basin area in Assam as per 1991 census report was 83,172 nos with a population density 308 nos. per sq.km. People of this region depends mainly on agriculture. The cultivation is subjected to frequent floods which adversely affects economic condition of the people in this region.
Climate:
This area of the basin experiences a hot moist summer with cool dry winter. The cold season starts from mid November and ends in the beginning of March followed by pre monsoon rains. The monsoon set in early June and continues upto the end of September. The maximum temperature recorded was 36.4
o C in 1990 and the average monthly temperature varies from 17.9
o C to 29.7
o C. The average annual rainfall recorded at Sisathar (1982 - 1994) was 2588 mm and the relative humidity varies from 69 - 90 %.