Nyarko, Benjamin Kofi 
beef 
FLOOD RISK ZONING OF GHANA: ACCRA EXPERIENCE 
tion. 
Benjamin kofi Nyarko 
rbon Department of Geography & Tourism 
University of Cape Coast, 
Cape Coast, Ghana 
o do 
csucc@ghana.com 
ntes IC-24 
S KEY WORDS: Flood, Hazard, Mapping, GIS, Integration. 
ing 
ABSTRACT 
le do Accra has been experiencing periodic flooding that affect properties and lives. The government 
seeing the dangers involved, commissioned institutions such as Ministry of Works and Housing, 
ral Town and Country Planning and City Engineers to identify such areas and adapt measures that 
e will help reduce the effect of the periodic event. These institutions identify flood risk zones using 
conventional methods such as watermarks on buildings and reported cases in the news media. 
Works carried out by these agencies were not able to give details about potential areas that are 
from likely to experience this extreme event. Hence there was the need to find a new method of 
identifying and mapping of potential flood risk zones. To determine flood risk zones in Accra 
and its environs a hydrological model (modified rational model) was integrated into the GIS 
platform, by the arithmetic overlay operation method, using operators such as addition and 
division. The results show that the delineated areas however experience same rainfall intensity of 
140.2 mm yet the flood intensities of these areas differ. For instance, the high flood risk zone 
covers 35.66 percent of the study area, whiles the low risk zone covers 26.85 percent. And the 
sion. potential areas likely to experience periodic floods with a given input of rainfall are mostly 
below the 350-meter contour. 
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a na 
— —H— 
1 INTRODUCTION 
1.1 Background 
Risk is a factor, element, or course involving danger or can be seen as the possibility of suffering 
harm or loss (Encarta 99). Risk has become an issue that is being discussed in various fields, in 
which varied definitions have been given and has developed without any discipline claiming 
authority (Stig, 1996). Studies of risk cover issues like identification and estimation of risk, risk 
assessment and evaluation, including monitoring and management of risk (Gerrard, 1995). 
I Ea 
Renn (1992) classified the concept of risk into seven units namely: 
The actuarial 
The epidemiological (toxicology) 
The engineering (including probabilistic risk assessment) 
The economic (including risk-benefit comparisons) 
The psychological (including psychometric analysis) 
Social theories of risk (sociological and anthropological studies) 
Cultural theories of risk (using grid groups analysis) 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 1039