Geography Reference
In-Depth Information
The substantive objective of this chapter is to examine the formida-
bility of using high resolution remote sensing data and GIS techniques to
assess and identify flood prone areas before occurrence in Lagos State-
large coastal city of Nigeria. The GIS-based flood risk methodology so-
developed for a littoral urban region proved to be helpful in extracting
flood prone areas based on elevation from SRTM digital elevation model
(DEM) and proximity to source of hazard. Such risk areas were then
classified into magnitudes of potential risk and five classes were
identified-very high, high, moderate, low and very low. This extracted
flood mask was further used to estimate the proportion of agricultural
land and urban land likely to be affected in the event of a flood episode.
To support grass root policy, the areal calculation was disaggregated into
local government area territory. Furthermore, land use/ land cover data of
the study region was extracted from Landsat image using a supervised
classification method based on maximum likelihood algorithm. The
extracted potential flood risk masks were overlaid on the land cover data
so as to assess the likely impact of flood on the various land uses-
agricultural land use and urban land use. In the same way, the identified
flood prone area masks were entered into Google earth engine for the
purpose of quick visual impression and mapping the flood vulnerable
areas by neighborhood and road infrastructures. The five-class vulnerabi-
lity feature was then overlaid on the local administrative map data loaded
with the projected population figure of the study region. From here the
vulnerable population was estimated by Local Government Area (LGA).
The results of the study show that GIS technique is a formidable tool for
flood risk analysis, mitigation and pre-hazard planning. This can be seen
from the series of thematic maps that were generated which were used to
develop a large GIS-assisted database. It is evident that the database so-
generated will facilitate flood risk management and provide an effective
framework that will support policy formulation.
1.
I
NTRODUCTION
Floods have become the most frequent and widespread natural disaster
which has claimed many lives, degraded natural ecology, disrupted social and
economic activities, destroyed properties and farmlands worth billions of
dollars (Nkeki et al., 2013; Taubenbock et al., 2011; Thieken, et al., 2014;
Ologunorisa, 2006). Some examples are the 1972 Rapid City, South Dakota
flood in the United States which claimed about 238 lives and caused millions
of dollars in damage, the 1975 Banqiao dam flood in China which drowned
about 26,000 people and caused another 140,000 death as a result of epidemic
outbreak, the 1983 Pacific flood, northwest of the United States destroyed pro-
