Environmental and Sustainability Indicators 19 (2023) 100286 Contents lists available at ScienceDirect Environmental and Sustainability Indicators journal homepage: www.sciencedirect.com/journal/environmental-and-sustainability-indicators Geophysical assessment of flood vulnerability of Accra Metropolitan Area, Ghana Georgette Baaba Atakorah a, Alex Barimah Owusu a, Kofi Adu-Boahen b,* a Department of Geography and Resource Development, University of Ghana, P. O. Box LG 25, Legon, Accra, Ghana b Department of Geography Education University of Education, Winneba, Box 25, Winneba, Ghana A R T I C L E I N F O A B S T R A C T Handling Editor: Meg Holden In light of Ghana’s exploding population, rapid urbanization, and the imminent threat of climate change, urban flooding is a severe and increasing developmental concern. This study was conducted against the proposition that Keywords: without anthropogenic factors, geophysical factors drive flooding within Accra Metropolitan Area. This study Flooding assessed spatial patterns of flood vulnerability using geophysical variables. The spatial analytical technique of Climate change weighted overlays was applied to ascertain the spatial variation of flood vulnerability. Based on geophysical Vulnerability Accra metropolitan area variables, the study finds that only 71% of the metropolis is highly susceptible to flooding. Overlay of Hazards geophysical flood vulnerability map with residential neighbourhoods, the results correlated with known vulnerable areas. Three hazard level categories—high, medium, and low—have been established for the flood risk areas. Suburbs with a high or moderate risk of flooding necessitate more sophisticated engineering safe- guards. The analysis also found that areas with medium and high incomes are becoming more vulnerable to flooding. The study proposes that efforts at flood control must focus on proper physical planning, stringent development control, elimination of drainage network flaws, and limiting the city’s lateral expansion. 1. Introduction impervious surfaces caused by the cities’ rapid growth and surface paving impede infiltration (Arnold et al., 1996; Addo, 2016). Amoako The regularity with which floods occur, their severity, scope, and the and Inkoom (2018) point to inadequate city-wide trash management cost of destruction are all increasing globally (Moubarak et al., 2021; techniques, lax structural expansion management, and substandard Omran et al., 2021). Floods are one of the most prevalent natural ca- housing development procedures as additional crucial explanations. tastrophes. Numerous lives have been lost due to this global phenome- In Ghana, especially in Accra, urban flooding has emerged as a sig- non, which has also severely harmed the economies of several nificant development challenge (Karley, 2009). Substantial flood ca- industrialized and developing countries. Urban flooding is a severe and tastrophes have been documented during the 1950s in the following growing development concern in developing countries against popula- years: 1955, 1960, 1963, 1973, 1986, 1995, 1999, 2001, 2002, 2010, tion growth, unchecked urbanization, and the dangers of climate change and 2011 (Rain et al., 2011) and 2015 (International Federation of Red (Arnous and Omar, 2018; Dube et al., 2022). Urban flooding is becoming Cross and Red Crescent Societies Ghana, 2016). Accra’s extensive more common in Africa, and its causes are changing. Cities have recently property devastation occurred throughout 1955, when the first signifi- seen urban flooding when there has been a lot of prolonged rain or rainy cant flood occurrence was recorded (Amoako and Frimpong-Boamah, periods. This has resulted in too much surface-flowing water for the 2015). According to Asumadu-Sarkodie et al. (2015), between 1955 drainage networks to manage (Parvin et al., 2016). Physical factors, and 1997, flooding caused assets worth over $30 million to be demol- such as prolonged, heavy rainfall, impermeable rocks, excessively ished, 100 people to die, and 10,000 to become homeless during or right saturated soils, steep slopes, compacted dry soils, etc., because of after the flooding. Flooding-related hazards, as well as vulnerabilities, flooding; these factors are made worse by human factors. These keep getting exacerbated. For instance, in 2015, 200 individuals peri- human-induced issues, which include inadequate physical planning and shed, 187 homes were demolished entirely or in part, and 46,370 people defects in the drainage system, are generally the result of rapid and were damaged by flooding (International Federation of Red Cross and unplanned development (Amoako and Inkoom, 2018). Increased Red Crescent Societies Ghana, 2016). Property lost in this tragedy is * Corresponding author. Department of Geography Education, University of Education, Winneba, P.O Box, 25, Winneba, Ghana. E-mail addresses: gbatakorah@gmail.com (G.B. Atakorah), owusuba@yahoo.com (A.B. Owusu), kadu-boahen@uew.edu.gh (K. Adu-Boahen). https://doi.org/10.1016/j.indic.2023.100286 Received 4 May 2023; Received in revised form 23 July 2023; Accepted 26 July 2023 Available online 27 July 2023 2665-9727/© 2023 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by- nc-nd/4.0/). G.B. Atakorah et al. E n v i r o n m e n t a l a n d S u s t a in a b i l it y I n d i c a t o r s 19 (2023) 100286 Fig. 1. Map of Accra Metropolitan area. Fig. 2. Workflow for mapping flood hazard. projected to have cost $55 million (Dogbevi, 2017). Flooding in Accra flooding events experienced in Accra. Amoako and Frimpong-Boamah has become a perennial occurrence. In the effort of the Government of (2015) recognized a potential contribution of climate change and Ghana to proactively manage it, GH¢197 million (approx. $38 million) unpredictability to Accra’s flooding. These have been connected to al- was allocated for control of perennial flooding in Accra in 2019, indi- terations in rainfall and temperature patterns, as well as coastal flooding cating the magnitude of the menace at hand (Appiah-Adjei, 2019). and erosion. Accra’s natural drainage is altered due to increasing and Many drivers have been identified to have contributed to the unregulated development, climate change, and excessive precipitation, 2 G.B. Atakorah et al. E n v i r o n m e n t a l a n d S u s t a in a b i l it y I n d i c a t o r s 19 (2023) 100286 Fig. 3. Schematic diagram of the interaction between the physical causative factors of flooding. Source: Authors construct adapted from Ozkan and Tarhan (2016). which increases the amount of peak runoff velocity and puts the city at Table 1 risk of flooding (Acodjoe and Afuduo, 2015). Mitigation of Accra’s Rates of physical causative factors. floods has primarily been a battle for succeeding administrations. Interactions between Rates Outcome Almost every administration has developed one plan or another to factors eliminate overflows from the city landscape permanently. However, Flow 1 major +1 minor (1x1) + (1x0.5) 1.5 strategies to address these floods have been criticized for being reactive Accumulation = and ad-hoc, often implemented after a severe flood. Examples of such Slope 3 major + 0 minor (3x1) + (0x0.5) 3.0 efforts include the GH¢197 million allocated for controlling perennial = floods in Accra, implemented in 2019 (Appiah-Adjei, 2019), the Na- Land cover 3 major +1 minor (3x1) + (1x0.5) 3.5 tional Flood Contingency Plan development, and the district flood = Rainfall Intensity 1 major + 1 minor (1x1) + (0x0.5) 1.5 disaster management plans by various Districts Assemblies. The main = activities involved in these projects include widening drainage channels, Soil 1 major + 1 minor (1x1) + (1x0.5) 1.5 demolishing buildings cited on waterways and drains and waste man- = agement. The recent attempt is the implementation of the Greater Accra Resilient and Integrated Development project (GARID), which is stated as the first among a series of projects designed to build the resilience of Table 2 Classification and weighting of factors. Factor Domain Descriptive Level Proposed weight (a) Rate (b) Weighted rate (a*b) Total weight % Flow Accumulation (m) 0 - 5123513725 Very Low 2 1.5 3 28.5 11 5123513726-1344922353 Low 3 4.5 1344922354-259377884 Moderate 6 9 2593778825-40828 High 8 12 Soil (%) Pinthosols Very High 10 1.5 15 22.5 9 Luvisols Low 4 6 Acrisols Very Low 1 1.5 Landcover Built up Moderate 6 3.5 21 42 16 Bareland Low 3 10.5 Water Very Low 2 7 Vegetation Very Low 1 3.5 Rainfall Intensity (mm) 150 – 187 Very Low 2 1.5 3 45 18 187- 207 Low 4 6 207 – 228 Moderate 6 9 228 – 248 High 8 12 248 - 274 Very High 10 15 Slope (%) 0-32.28448044 Low 10 3 30 33 13 32.28448045 - 66.3914718 Very High 1 3 DEM 0-33 Very HIgh 10 3.5 35 84 33 33-67 High 8 28 67-270 Moderate 6 21 Total 255 255 100 3 G.B. Atakorah et al. E n v i r o n m e n t a l a n d S u s t a in a b i l it y I n d i c a t o r s 19 (2023) 100286 Fig. 4. Landcover vulnerability map of Accra Metropolitan Area. Accra. The initial phase is five (5) years covering 2020 to 2025 (GARID the Accra Metropolitan Area based on geophysical variables using GIS Secretariet, 2020). After flood events, the government’s reactive spatial analytical techniques. This is one of the most critical and valu- response to flood involves compensating those whose homes were able steps for comprehensive and effective flood risk management. To impacted. The recent proactive action undertaken annually is the reduce flood-related damage and vulnerability, the city government and desilting of selected drains within the city, which unfortunately tend to the general population will be helped by creating a flood risk map. By be filled again by uncollected desilted silt and litter of solid waste on the enforcing measures like zoning restrictions and building requirements, streets by the onset of the next rains. etc., land usage within the most susceptible zones can be managed, ul- As such, there is a need for holistic planning and implementation of timately reducing the extent of flood damage. Additionally, this work comprehensive flood risk management plans to mitigate and prepare for will add up and extend previous research findings on anthropogenic flood disasters based on an accurate understanding of the geophysical causes of flooding and flood risk mapping in Ghana by (Karley, 2009; characteristics and the type of plans that suit that geophysical envi- Rain et al., 2011; Amoako and Frimpong-Boamah, 2015; Gyau-Boakye, ronment. Many research works on floods in AMA have focused on and 1997; Nyarko, 2002) and (Asumadu-Sarkodie et al., 2015) by critically concluded that anthropogenic factors are the primary determinants. assessing the flood vulnerability based on the geophysical setting of the They have cited indiscriminate littering, poor drainage system, narrow city. drains, building on waterways and poor flood management practices (Appiah-Adjei, 2019; Gyau-Boakye, 1997; Amoako and Boamah, 2015; 2. Materials and methods Rain et al., 2011; M Braimah et al., 2014). This study holds a counter view that without human presence, the geophysical characteristics 2.1. Study area would facilitate flooding in the study area and that inadequate attention has been paid to the geophysical characteristics of AMA and its catch- The survey was conducted in the Accra Metropolitan Area (AMA), ment area. The paper’s novelty is to adequately examine the impact of Ghana’s official and regional capitals (Ghana Statistical Service, 2012). each geophysical signal on the vulnerability in the research area. This According to the 2010 population and housing census, AMA had an study used a deductive approach. Indicator approaches are typically estimated 1,665,086 people, or 42% of the entire region’s population structured around a multi-criteria analysis structure that explicitly as- (Ghana Statistical Service, 2014) and with a 2021 population of 284, sesses numerous conflicting components in decision-making. The extent 124 with 134,045 males and 150,079 females. Ga West Municipal, Ga to which vulnerability assessments inform flood adaptation policies is South Municipal, the Gulf of Guinea, and La Dadekotopon Municipal are mainly unknown. The study uses an approximate indicator-based tech- Accra’s northern, western, southern, and eastern neighbours, respec- nique to build a flood vulnerability indicator map for AMA with relevant tively. Accra is sometimes referred to as the AMA. According to GSS and specific flood vulnerability indicators. The study therefore aimed to (Ghana Statistical Service, 2012), it has around 139.67 km2 (53.93 sq assess the spatial differences in flood vulnerability and susceptibility of mi) land area. The research area’s spatial dimension was calculated 4 G.B. Atakorah et al. E n v i r o n m e n t a l a n d S u s t a in a b i l it y I n d i c a t o r s 19 (2023) 100286 Fig. 5. Rainfall vulnerability map of Accra Metropolitan Area. using the borders in place before the 2018 reconfiguration. The land cover data was generated from the Landsat 8 OLI image The general terrain of the AMA is between 20 and 70 m above mean classification acquired on April 15, 2018, from the United States sea level, with infrequent isolated hills and plains (Nyarko, 2002; Kor- Geological Survey (USGS) website. The classification was made for four tatsi and Jørgensen, 2001). The city has a water table between 4.80 and classes; water, bare land, built-up, and vegetation. Bare land and vege- 70 m below the earth’s surface, with an average gradient of roughly 11% tation were further reclassified into areas of low flood possibility and (Nyarko, 2002). Three broad vegetation zones, comprising shrubs, built-up areas into high flood possibility and water. grassland and coastal lands, are found in AMA. However, Soil data covering AMA was sub-setted from global soil data acquired human-induced and climatic factors have altered the original vegetation from International Soil Reference and Information (2019). The data was cover (Owusu, 2018). Soil types in AMA include lateritic sandy clay soil, developed as vector data and then converted to raster using ArcMap’s residual clays and gravels, alluvial and marine mottled clay and drift "feature to raster" tool. The resulting layer of the soil data was reclas- materials from wind erosion. Alluvial, impervious black cotton soils are sified to group different soil types into high, moderate and low vulner- common in low-elevation, poor-drained locations (Ministry of Local ability to flooding based on their permeability levels. ArcGIS 10.7 Government and Rural Development, 2012). The map of the Accra software was used to model flow accumulation from the digital elevation Metropolitan Area is depicted in Fig. 1. model data ASTGTM2_N05W001 obtained from USGS. According to Tarboton et al. (1991) and Jenson and Domingue (1988), the flow accumulation tool calculates the cumulative flow as the total weight of 2.2. Methods all cells flowing into each downslope cell in the output raster. Additionally, a system is built to display the flow in each grid cell. A comprehensive literature review was conducted to ensure Filling sinks in the DEM data was the first step in creating a new dataset. adequate knowledge about the causes of flooding in AMA and how This method lessened the inaccuracies in the data that was obtained. The vulnerable urban people are to flooding. To accurately classify an area output was then reclassified as high flood vulnerability, medium flood within AMA as flood-prone, factors such as rainfall intensity, soil, flow vulnerability and low vulnerability. The slope tool in ArcGIS was used to accumulation, slope and land cover were identified as the geophysical generate the slope map from the DEM data. According to climateps.com, drivers of flooding in AMA. Using similar methodologies, Arnous et al. the average elevation of AMA is about 68 m. This was used as the (2022) and Arnous and Mansour (2022) investigated the impact of parameter for delineating the areas with high and low vulnerability topography, lithology, and geological structures on the coastal zone of during reclassification. Ras Ghareb City, Gulf of Suez, basin system in Egypt. The investigations Rainfall data was transformed into an uninterrupted surface overlay of Dekongmen et al. (2021) mainly concentrated on the drainage den- using a computation tool for the inverse distance weighting (IDW) sity, slope patterns, and elevation patterns of the Accra Metropolis. A technique. Results from the IDW analysis were then reclassified to flood susceptibility (vulnerability) map was made using GIS software change and group values into new values for straightforward after these factors’ relative contributions to flooding were weighted. 5 G.B. Atakorah et al. E n v i r o n m e n t a l a n d S u s t a in a b i l it y I n d i c a t o r s 19 (2023) 100286 Fig. 6. Slope map of Accra Metropolitan Area. interpretation. Rainfall values were reclassified to represent high, me- These scores were based on expert judgement, as indicated in Table 2. dium and low vulnerability to flooding. Fig. 2 illustrates the steps in Table 2 displays the weighted average percentage of each factor. The executing the geoprocessing function in the model builder tool. ratio of elements is calculated for rainfall intensity (18%), flow accu- mulation (11%), soil (9%), land cover (16%), and slope (13%), corre- sponding to their effects on the likelihood of flooding. Thematic maps 2.3. Weighted overlay showing the thematic modelling variables’ results are presented and discussed in the next section. Ozkan and Tarhan’s (2016) model was used to rate the flood risk among the various hazard metrics. The flood susceptibility map was 3. Results produced using five geophysical causal variables. The technique shown in Fig. 3, which depicts how all the elements communicate, was used to This section presents the investigation findings of the spatial differ- calculate the value. One causative component strongly impacts the entiation of the six (6) geophysical determinants of flood risk. The in- aspect the arrow points to, as seen by the solid lines connecting the two dicators are land cover, rainfall, slope, soil, flow accumulation and elements. The dashed line joining two causative factors shows a slight elevation (Digital Elevation Model). (secondary) impact on the component the arrow points at. For instance, flow build-up has a secondary effect on the slope, even though it i. Land cover essentially affects land usage. One (1) point was given to the consider- able influence, and one-half point (0.5) was given to the modest effect to Flood vulnerability based on land cover types shows high to low compare the two items. As shown in Table 1, a factor rate is determined exposure (Fig. 4). as the total effects on other parties. The places within the city that have been recognized as having a Since each element affects flood threats differently, the weighted greater risk of flooding are those that are more densely populated and approach was used, and weights were assigned to each factor. Factor have more extensive sections of impervious surfaces. As a result, rain- weights were calculated using the Ozkan and Tarhan (2016) water penetration is impeded, and runoff emerges. These include Accra methodology. Central, Dansoman and Darkuman, Circle and Avenor areas Areas with Table 1 above displays the ratios that were calculated for the various medium and low flood vulnerability have vegetation cover, and the soil elements. All data layers were integrated and categorized into the cho- has higher absorptive capacity than built-up areas. These include sen classes in ArcMap. By multiplying the estimated ratio and its esti- Achimota and Legon areas. mated weight to acquire the total weight of each element, the weight and proportions of each factor were combined to facilitate an in-depth ii. Rainfall pattern examination of prospective flood threats. Different descriptive levels and weights ranging between 0 (very low) and 10 (very high) were used. 6 G.B. Atakorah et al. E n v i r o n m e n t a l a n d S u s t a in a b i l it y I n d i c a t o r s 19 (2023) 100286 Fig. 7. Soil vulnerability map of Accra Metropolitan Area. Rainfall-induced flooding is high in built-up areas, particularly in iv. The soil in the area slums and low to middle-income communities with poor physical planning and drainage facilities. These areas include Alajo, Asylum Soil permeability is crucial when determining how well the soil will Down, Adabraka, Korle Gonno, Mamprobi and Labadi. Areas showing absorb water (Fig. 7). Higher penetration soils, like sandy soil, are less medium and low flood vulnerability are well-planned residential areas likely to flood since water can easily infiltrate them with little resistance. with adequate drainage facilities, though sometimes poorly drained or Soils in AMA are predominantly acrisols, clay-rich soils with low obstructed. Flooding generally happens when there is more rain than the permeability, thereby increasing the area’s vulnerability to flooding. drainage system can handle. The study areas within this category are Areas with Luvisol soils have high flood vulnerability because of their Tesano, Abeka, Akweteman, Abelenkpe, Dzorwulu, Roman Ridge, North higher clay content and high base saturation. Over 90% of the study area Kaneshie and Ringway Estate. Low-accumulation communities include has medium soil-based flood vulnerability except for some small areas of Legon, Achimota, Green Hill, East Legon, North Dzorwolu and Airport East Legon, which have high soil-based flood vulnerability as the site is Residential Area. Where drainage channels are absent or blocked, waterlogged. The vertical strip of the western boundary has plinthosols annual local flooding results from heavy rainfall that typically occurs soil that makes the area less vulnerable. during brief storms. Rainfall based flood vulnerability map is shown in Fig. 5. These conditions are common in the study area as it has always v. Flow accumulation been observed during the rainfall seasons. Water usually flows and accumulates at lower elevation areas. This iii. Slope in the area makes the metropolis a low flood-vulnerability area interspersed with medium to high flood-vulnerability areas (Fig. 8). Fig. 6 presents slope induced flood vulnerability map. The slope of The high-risk regions bordering water bodies like Densu, Sakumo the land is a principal variable that affects the movement of water. Lagoon, and the Odaw-Korle-Chemu watershed, which runs through the Running water travels swiftly on steep slopes, lowering the water city’s centre with multiple tributaries, are where the medium and high collected into the soil underneath. AMA is a gently sloping area (Nyarko, flood susceptibility areas are located. Poor drainage systems, such as 2002), and water does not flow quickly, thus making the area highly those with inadequate, disconnected, and improperly channelled susceptible to flooding, as indicated in Fig. 6. Few isolated knolls and sewers, also contribute to a high-flow build-up. hills like Legon Hills are less vulnerable. The low flood-prone areas (Fig. 6) were also observed within the contour ranges of 46–66 m. This vi. Elevation of the area shows that the surface runoffs from the steep slope areas flow toward the gentle slope zones, which serve as high convergence zones of the runoffs Lower flood vulnerability areas have higher elevations than the high leading to the occurring floods. flood risk areas associated with low hills (Fig. 9). Moreover, high-risk 7 G.B. Atakorah et al. E n v i r o n m e n t a l a n d S u s t a in a b i l it y I n d i c a t o r s 19 (2023) 100286 Fig. 8. Flow accumulation vulnerability map of Accra Metropolitan Area. zones in AMA are bordering lagoons and rivers, built-up areas with targeted for flood management and prevention interventions. Areas with impervious surfaces, and bare lands with clay soils. These locations in low flood vulnerability tended to be the first- and second-class resi- the CBD and old residential areas include Accra Central, Adabraka, Korle dential areas (medium-high class) in Accra: Airport Residential Area, Gonno, Mamprobi, Dansoman and Darkuman. Others include Accra Dzorwulu, Roman Ridge, Abelempke, East Legon and Greenhill. Newtown, Maamobi and Nima. These neighbourhoods have well-planned drainage systems, and Anthropogenic factors have contributed to low elevation levels in tarred roads and generally clean, but care must be taken to efficiently AMA, making the area highly susceptible to floods. manage their drainage networks to sustain their minimal vulnerability These six (6) characteristics that are specifically connected to the to flooding. Identifying the susceptibility to flooding is the first step to flood that might happen in AMA are combined to create a synthesis map developing an effective response strategy. of flood risk zones. The final flood hazard map illustrating flood sus- ceptibility zones is created and displayed in Fig. 10 due to integrating 4. Discussion annotated maps with the weighting technique thematically. Maps of flood susceptibility have been crucial for managing, The final map shows that close to 50% of AMA is a high flood communicating, and controlling floods. In the past few years, Accra’s vulnerability (susceptibility) area based on the weighted combined ef- frequent floods have emerged as one of Ghana’s issues during the rainy fect of six geophysical indicators. About 25% of the site is classified as season, particularly in June and July. The six (6) bio-physical markers moderate risk, and the remaining 25% is low. These six factors have lead us to conclude that it is impossible to avert floods in AMA, but it is their strengths and weaknesses in promoting or reducing floods, and possible to lessen their severity and related effects. With this flood sus- their combined effect could be seen as powerful real-life experiences. ceptibility map, it is possible to take preventative action to reduce the Although this study is based on modelling, all the identified high flood- likelihood of future flooding and its adverse consequences. The flood risk areas flood annually. AMA’s southern region lies near the ocean. In susceptibility map indicates that despite specific differences, practically their study of Accra Metropolis, Dekongmen et al. (2021) discovered every area of Accra is susceptible to flooding. About 71% (94841.3 km) comparable findings concerning the area’s height. It is not exceptionally of the entire surface of AMA lies among the high to medium flood pos- high, a coastal plain with poor soil drainage, inadequate land cover, and sibility classifications, which are divided into high, medium, and low. excessive water accumulation. In essence, these are what cause floods in The flood vulnerability map was overlaid with the AMA neighbourhoods the studied region. Due to swift reaction times and high peak discharges, (Community) layer, and all the towns where floods have occurred fell heavy rains can induce flash floods. Flooding happens when there is inside the areas with a high likelihood of flooding, as indicated in nowhere for surface water to flow due to low elevation. Accra is a Fig. 11. Mpoase, Chorkor, Korle Gono, Bukom, Ussher Town, Old low-lying metropolis with an average height of less than 70 m above sea Fadama, Abbosey Okai, Mataheko, New Russia, Opetekwe etc., fall level. Therefore, the city’s more notable areas are vulnerable to flooding within the high and medium flood vulnerability categories. These are anytime it rains without a sufficient drainage framework. slum areas, some of which are located along the Odaw River and must be This study considers anthropogenic modification of these 8 G.B. Atakorah et al. E n v i r o n m e n t a l a n d S u s t a in a b i l it y I n d i c a t o r s 19 (2023) 100286 Fig. 9. Elevation map of Accra Metropolitan Area. Fig. 10. Synthesis map of flood vulnerability of Accra Metropolitan Area. geophysical deficiencies as a possible positive input to reduce the flood widening existing storm drains and a sound waste management system, vulnerability of the area. For instance, introducing proper physical may help improve runoff and provide flood controls. However, the planning and city engineering, a sound drainage system, including anthropogenic modification of the geophysical environment 9 G.B. Atakorah et al. E n v i r o n m e n t a l a n d S u s t a in a b i l it y I n d i c a t o r s 19 (2023) 100286 Fig. 11. Flood possibility map overlaid with towns in Accra Metropolitan Area. Other drainage ditches frequently release significant quantities of silt into the Korle Lagoon, situated along the coast south of AMA. This worsens the lagoon’s dire situation (Asumadu-Sarkodie et al., 2015). Similarly, due to their positioning in the city and inadequate flow, Accra’s Odaw River and Korle Lagoon, intended to be essential outlets for runoff and stormwater overflow to the sea, are now considered sig- nificant flood risks. The Odaw River and its tributaries, Nima, Onyasia, Dakobi, and Ado, drain most of AMA’s built areas. The river basin has the most significant population density in AMA, with almost 60% of those who live in the Greater Accra Region nearby. Approximately 30% of the population is under threat due to continuing flooding, according to the Ministry of Works and Housing (2019). Avenor, Glefe, James Town, Kotobabi, and other neighbouring informal settlements such as Fig. 12. Dredging of the odaw river. Alajo, Kokomlemle, Mpoase, Kpehe, and others are also plagued by the Source: Graphic online perennial flooding. The annual flow of the Korle Lagoon and Odaw River has been decreased due to silt and solid waste build-up, and numerous implemented in AMA has somewhat exacerbated and escalated the governments have attempted in vain to dredge the two water bodies and already precarious situations created by the geophysical environment. return them to their prior condition. According to Arkorful (2008), For instance, inadequate infrastructure development, faults, and Accra will nonetheless flood when it rains unless the Korle Lagoon is drainage network flow have all triggered floods in the city (Aryee- constructed to allow the Odaw River to empty into it. Between February tey-Attoh, 2001; Rain et al., 2011). Several low-lying areas in Accra and May 2019, one million cubic meters of waste materials were experience major periodic flooding due to culverts that are too small for distilled from the Odaw River and Korle Lagoon (Myjoyonline.com, the job and significant drains that have become clogged with silt from 2019). Until this recent stride, management of the surface water bodies years of abandonment and poor upkeep. In Accra, gullies and erosion remained a challenge, thus exacerbating the already dire situation can be seen on the road surfaces and in the soil between buildings with (Fig. 12). untarred roadways. Flood water cannot enter accessible drains as a Again, poor municipal engineering, illiteracy, and flagrant contempt result. As a result of erosion, some urbanized areas near the catchment for building codes have led to numerous Accra houses being erected in provide a lot of sediments, which causes problems related to reduced the city’s green belt zones, depleting vegetation and increasing areas’ capacity. Additional drains lead to the Korle Lagoon due to erosion; susceptibility to erosion and floods (Waterworld, 2010; Acodjoe and several urbanized areas near the catchment deliver a lot of sediments. Afuduo, 2015). Inappropriate disposal and collection of solid waste in 10 G.B. Atakorah et al. E n v i r o n m e n t a l a n d S u s t a in a b i l it y I n d i c a t o r s 19 (2023) 100286 Accra negatively correlate with flooding within the city. Existing waste Arnous, M.O., Mansour, B.M., 2022. Utilizing multi-temporal thermal data to assess management systems cannot successfully collect the volume of solid environmental land degradation impacts: example from Suez Canal Region, Egypt. Environ. Sci. Pollut. 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Ghana Statistical Service, 2012. 2010 population and housing census report. Accra 2012. expense of little rainfall. Yet, modern technological innovations coupled Ghana Statistical Service, 2010 Population and Housing Census: District Analytical with anthropogenic modification of these geophysical conditions could Report, 2014. Accra Metropolitan, Accra. reduce floods. Unfortunately, over the years, AMA (City of Accra) has Gyau-Boakye, P., 1997. Flood control measures: Hazard mapping. Accra: Water Research not succeeded in this direction. Instead, anthropogenic modifications of Institute of Centre for Scientific and Industrial Research (CSIR). International Federation of Red Cross and Red Crescent Societies Ghana, 2016. Floods the geophysical conditions have worsened the flooding. There is, Emergency Plan of Action (EPoA) (MDRGH011. Retrieved from. https://reliefweb. therefore, the need for re-engineering of the city. 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