Flood control and assessment of Accra using the weap hydrological model
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Date
January, 2018
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Abstract
The increase in the frequency and intensity of flood in some parts of Greater Accra Region
is becoming a matter of great concern to the entire nation due to its negative effects on the
development of the region. These floods have over the years been attributed to numerous
factors including; climate change, urbanization, poor drainage systems, sea level rise and
over population. The study used Water Evaluation and Planning (WEAP) hydrological
model to estimate the surface runoffs for the sub-basins and also to find the correlation
between Standardized Precipitation Index (SPI) and the historical flood events in Greater
Accra. The study also determined the surface runoffs generated within each sub-basin.
The WEAP model was used to generate surface runoff from 1990 to 2040 taking 1990 as
the base year. ArcGIS 10.3 was used to delineate eight sub-basins and thereafter deter mined the characteristics of the sub-basins. Rainfall normalization was performed using
the Standardized Precipitation Index and the results were verified against historical flood
events for the basin over the study period. The model output was compared to observed
stream flow measurement. In general a good correlation of 0.81 and 0.71 were obtained
for correlation coefficient and coefficient of determination respectively. The study re vealed that, a minimum rainfall of about 60 mm would cause flood across all the eight (8)
sub-basins. Also, extreme rainfall with SPI of 1.5 or more would cause flood in Greater
Accra. The month of June was found to produce the highest volumes of surface runoff
while December generated the least volumes of surface runoff with average runoffs of 2.4
ii× 106 m3
and 1.0 × 106 m3
respectively. It was confirmed from the research that, higher
volumes of rainfalls in the sub-basins generates higher surface runoffs and therefore there
are higher tendencies for floods to occur when rainfalls are high.
Description
A thesis submitted to the Department of Physics, Kwame Nkrumah University of Science and Technology, in partial fulfillment of the award of degree of Mphil( Geophysics)
Keywords
Flood control, Weap hydrological model, Accra