The flood hazard maps are prepared in the raster format to generate the flood
depth for various return periods. The generated raster formats are converted into
vector format, and the extreme flood spread area polygons are clipped for the
different return periods for different LULC conditions. The clipped raster maps are
made uniform by using the slice tool in Arc GIS. From the allocated weights, the
flood hazard map is categorized into seven classes, namely, no flood hazard, very
very low, very low, low, moderate, high, and very high, by the standard deviation
method of classification. The class-wise susceptibility areas of flood hazard for
different LULC of the years 1986–2036 are shown in Table 3.10.
Fig. 3.13 Floodplain map of the Koraiyar basin for LULC of the predicted year 2036 with
100 years return period
Table 3.9 Floodplain area
for different LULC and return
periods
Return period in years
Floodplain area (in km
2
)
LULC 1986
LULC 2036
2
20.09
20.87
5
21.35
21.93
10
32.10
33.64
50
39.41
40.92
100
41.16
42.88
72
S. Natarajan and N. Radhakrishnan