Flood disaster prediction model using Remote Sensing data and geographic information system
Shiro Ochi, Shunji Murai
Institute of Industrial Science University of Tokyo
Suvit Vibulsresth
National Research Council of Thailand
Abstract
This paper describes about the new method to analyze the flood flow. The rainfall in the mountainous area flows partly on the surface and partly under the ground depending on the runoff ratio which is determined by the geology, the land cover, the slope gradient etc.. the water on the slope surface flows in the course of the slope aspect. The slope gradient and slope aspect are computed from DEM. The authors have developed the flood flow model using the hydrographic theory. Runoff ratio has a influence on the flow rate, so even if the precipitation is the same the quantity of the flow becomes different. In our study the runoff ratios are assumed with the slope gradient and NVI which comes from the satellite data. The flood flow model allows a simulation study for various cases of vegetation cover conditions including deforestation, which will provide prediction of flood disaster.
Introduction
In November 1989, there occurred a serious flood disaster over NAKHON-SI-TAMARAT in southern part of Thailand. The causes of this catastrophe are considered as the following points.
- An abnormal rainfall.
- The deforestation in the mountainous area.
- The surface geology of weathered granite.
In order to predict the flood disaster and to make flood-control, many hydrological methods have been proposed, but some of them are black-box type, or some of them need much investigation. In developing countries where deforestation is advancing and the drastic landuse changes take place almost every year; it is difficult to know the up-to-date characteristics of the basin. In this sense remote sensing data is very necessary to monitor the land cover change.
Methodology
- Slope Direction
The water on the slope should flow in the course of the slope aspect. The flow model can be made from DEM (digital Elevation Model) by the following procedure. On the 3x 3 grids of DEM the center pixel has the slope direction, which has the steepest to every pixel, which has the direction around the center (Fig.1a). One unit of rainfall is given toe very pixel which has the slope direction (Fig. 1b), and the water in the pixel flows tot eh direction (fig. 1c). After that, one unit of rainfall is given to every pixel again and then flows to the slope direction (Fig. 1d. e). By continuing this process unit steady state (Fig. 1i.j), we can get the quantity of the flow and pick up the stream. Fig. 2 shows the successive image during this process which generates the drainage pattern. The thickness of the line represents the quantity of the flow. The rainfall given to each pixel is changed according to the strength of the precipitation and the runoff ration.
Fig 1 Flow model on 3x3 grids
Fig.2 Drainage pattern generation
