ABSTRACT
Floods are a serious global
issue attracting attention and research from academia, the media and other
international discourse. Consequently, they have become critical national
issues especially with African countries who lack the financial resources and
technical knowhow to mitigate its impacts. The Aboabo community (a suburb of
Kumasi), located in the transitional forest zone of Ghana has become vulnerable
to the devastating effects of flooding in recent times due to climate change,
exponential population growth, and rapid urbanization. In order to reverse this
trend and lessen the debilitating impacts of flooding on this community, there
is a need for the development of a flood risk map which will form the basis of
any future flood management and planning activities. This study presented a
holistic approach in the development of a flood risk map and discusses its
significance in Flood Risk Management.
In order to create a digital
representation of the study area, a Digital Elevation Model (DEM) was created.
Hydrological analysis necessary to determine flow direction and accumulated
flow (resulting from e.g. rainfall, surrounding streams) was performed on the
depressionless DEM of the study area. Reclassified slope angles (i.e. high
slope areas, medium slope areas, and low slope areas) and stream buffer zones
(within 50m of stream network) were added in ArcGIS environment to generate
flood risk maps. The flood risk maps showed three risk zones -High risk, medium
risk zone and low risk zone. To further demonstrate the potential of flooding
in these three risk zones, a simulation-based approach was adopted. A simple
vector-based method which only required the extents of flood levels in
simulating flood extent based on the derived drainage lines, their depth and
their capacity to hold rainfall run-off was used. With the aid of the elevation
measure, flood water levels were selected. The flood contours showed the extent
of flood at a given flood level. The flood model extents were further overlaid
on a geo-referenced Google Earth image of the study area which visibly
demonstrated areas at risk in the event of floods. Based on existing literature,
questionnaires and interviews were administered to respondents in the Community
and stakeholders to investigate the causes and effects of floods. With over 84%
response rates, majority of the residents attributed the cause and effect of
flooding to lack of drains/choked drains and gradual weakening of buildings
respectively.
The research clearly
demonstrated the application of GIS through hydrological analysis, carrying out
flood simulations and the administering of questionnaires and interviews with
stakeholders, is very essential in providing guidelines for Flood Risk Mapping.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background
The effects of climate change are
shown to have immensely affected the changing weather conditions in many parts
of the world. There is a global concern about global warming. Global warming is
leading to climate change as noted in the third assessment report of the
Intergovernmental Panel on Climate Change (IPCC, 2001). Global warming has
caused incidences of tsunamis, melting of iceberg, washing away of shorelines,
flooding and drowning of islands (IPCC, 2001).Consequently, flooding has become
of great interest to humanity (Oppong, 2011). Floods claim approximately 20,000
lives annually, leaving people homeless in the process and have negative
implications on at least 20 million people all over the world (Smith, 2011).
Floods have claimed over 10,000
lives in the United States of America since 1900 (Adeoye et al., 2009).
Statistics also show in 1998, floods affected approximately 30 million people
in 52 out of 64 districts in Bangladesh mainly as a result of climate change
and economic growth in low-lying regions (Khan et al, 2011).
In July and August, 2010, Pakistan
was hit by one of the worst floods in their history of disasters rendering 20
million people homeless (Straatsma et al, 2010).
Over 22,000 people in Nepal had to
relocate temporarily due to floods. It further stated 46,000 houses were left
totally damaged and more than 130,000 hectares of agricultural lands were
submerged by floods (Asian Development Bank, 2007).
In 2011, Thailand also experienced
heavy rains that lasted nearly 12 weeks claiming over 500 lives in the process.
All these reports and studies, illustrates the devastating effects of floods
(Orok, 2011).
Floods are crucial national issue
as a great number of African countries lack the resources, both financially and
technologically, to fight the effects and impacts of flooding (Satterthwaite et
al., 2007).
Between 1996 and 2005, floods have
posed several devastating and terrifying effects on the continent of Africa
(Satterthwaite et al., 2007).. Within that period, there were approximately 290 flood-disasters
reported. Over 8,183 people lost their lives, approximately 23 million people
were consequently affected in diverse ways. The results of the huge economic
losses were estimated at approximately $1.9 billion (Satterthwaite et al.,
2007).
Flooding is one of the leading
disasters in Ghana and has major impacts on people and their livelihoods. The
period between 1968 and 2011, incidences of flooding have killed approximately
three hundred people leaving over 3 million people affected (Okyere et al.,
2012). Flooding also comes with an increase in epidemics especially through the
spread of waste, flood water and the accumulation of water and consequent
blockage tends to be conducive breeding grounds for mosquitoes (Feng et al.,
2007; Messner et al., 2007).
Among the various types of land
use/cover, urban areas have the greatest tendency of modifying the hydrological
behaviour of a catchment. The construction industry (roads, buildings, etc)
accompanying urbanisation creates impermeable surfaces impeding infiltration of
water and lead to overland flow leaving urban areas highly susceptible to
floods (flash floods) especially when there are bad drainage network systems
(Okyere et al, 2012).
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