Physical Vulnerability of The Gambia’s Coastline in the Context of Climate Change

Abstract

The Gambia’s coastline, known for its unique ecosystems and vital role in the country’s economy through fisheries, tourism, and agriculture, is becoming increasingly vulnerable as a result of the combined effects of climate change and human activity. This coastline sustains an important portion of the population by providing livelihoods and contributing to food security, as well as housing critical infrastructure including ports, urban areas, and tourism hubs. However, as climate change intensifies pre-existing vulnerabilities, such as increased sea-level rise, coastal erosion, and extreme weather events, these socio-economic assets are becoming more and more vulnerable. As a result, this study focused on investigating the physical vulnerability of the coastline in the context of climate change. The vulnerability assessment was conducted using the coastal vulnerability index approach, utilising a combination of oceanographic data, remote sensing, and field observations. The research outcomes supported the identification of key areas at risk and examined the contributing factors such as tidal ranges, storm surges, and human activities. The findings highlight the immediate and long-term threats to coastal communities, infrastructure, and natural habitats. Due to the vulnerability provided by geological and geomorphological factors, the average Coastal Vulnerability Index (CVI) score of 29 indicates a high level of exposure to coastal hazards from Buniadu Point to Barra. From Banjul to Cape Point, the average coastline dynamic rate is positive at 0.21 m/year, indicating some accretion. Despite this, the CVI score of 22 indicates significant vulnerability to coastal hazards from Bald Cape to Salifor Point. The study also explored potential mitigation and adaptation strategies to enhance coastal resilience to sea-level rise, coastal erosion, and flooding. Integrated and sustainable strategies were outlined to support policy-making and community-based initiatives towards safeguarding coastal regions of The Gambia against the backdrop of climate change.

1. Introduction

Globally, coastlines are increasingly facing major challenges emanating from wave actions and human activities, partly influenced by climate change [1,2]. Over the past decades, West African Coastlines have experienced high levels of vulnerability due to the combined and dynamic impacts of sea-level rise and sand winning, leading to coastal erosion and shoreline displacement [3]. In the scientific world, different understandings and conceptualizations of vulnerability exist due to lack of a shared common language and the differences in scientific disciplinary backgrounds. As a result, there is no universal definition for vulnerability, given its dynamic nature and critical influences from climate change impacts at various spatial and temporal scales [4]. Arguably, vulnerability describes the likelihood that exposed elements, such as physical assets, capital, and human lives, will sustain harm and incur damage and loss when affected by single or multiple hazard events [5].

Similarly to the coastlines of most West African countries, the coastal regions of The Gambia are characterised by their low-lying landscapes, dynamic ecosystems, and significant economic activities, are increasingly susceptible to the adverse effects of climate change and human factors [6]. This vulnerability poses a multi-faceted challenge that encompasses environmental, socio-economic, and developmental challenges. Coastal erosion in The Gambia is primarily driven by increased wave activity and the inundation of low-lying areas as sea levels rise. Both factors contribute to a shrinking coastline and the physical loss of ecosystems and the services they provide. Uncontrolled construction activities along the coastline have already become a notable issue regarding coastal erosion. Additionally, climate change, particularly rising sea-level and more frequent storm surges, are expected to worsen this problem.

Research studies indicate that average sea-levels are rising globally at an alarming rate, contributing to increased coastal flooding and erosion, and the case of The Gambia is even more critical. Projections suggest that vulnerable countries such as The Gambia will witness significant changes in coastal dynamics over the coming decades. Furthermore, the significant reliance of local communities on fisheries and agricultural practises along the coast makes them particularly susceptible to displacements threatening their livelihoods and food security. The phenomena of rising sea levels, increased intensity and frequency of extreme weather events, and alterations in oceanic currents are contributing to severe coastal erosion, periodic flooding, and significant loss of critical habitats. These changes are not only threatening the natural environment but are also posing severe risks to human settlements, economic activities, and cultural sites along the coast [7].

Sea-level rise and coastline erosion pose serious threats to low-lying coastal regions in The Gambia. A one-metre rise could submerge over 50% of Banjul, Barra, and the Banjul Port, affecting essential infrastructure. The Gambia’s low-lying landscape means a one-metre increase might flood over 8% of the country, impacting 61% of mangroves, 33% of wetlands, and over 20% of lowland rice-growing areas. Key locations like Banjul and ferry terminals along the River Gambia could be significantly affected. Rising sea levels may also salinize shallow aquifers, threatening the drinking water supply for urban areas. Furthermore, coastal erosion along the country’s 80 km coastline could harm the vital tourism industry, leading to ongoing concerns about the future of coastal areas [8].

Even though the amount of research on coastal risk is increasing, most of it concentrates on larger, established countries, leaving smaller, and developing countries like The Gambia with important knowledge gaps. Understanding the distinct physical and socioeconomic vulnerabilities that these nations face is hampered by this asymmetry. Furthermore, a lot of research focuses on societal vulnerability or specific physical processes rather than thoroughly examining the combined effects of physical drivers and climate change [8,9,10,11].

Some studies have been conducted in some sections of the Gambian coastal zone, mostly focusing on the social vulnerability and exposure of coastal communities; however, comprehensive exploration on the physical dimensions and combined impacts of climate change and physical processes is still lacking in the online scientific database [3,8,12]. Unlike many other types of disasters such as floods and drought, coastal erosion and coastline displacements are irreversible, and the resulting adverse impacts on humans and coastal biodiversity are eternal.

Using a Coastal Vulnerability Index (CVI) framework to assess the interaction between physical processes and climate change, this study fills these gaps by offering a thorough examination of the physical vulnerability of The Gambia’s coastline. By concentrating on The Gambia, this study offers insightful information that can guide customised, situation-specific adaptation plans for developing countries.

To support the development of integrated and sustainable solutions to inform policy recommendations on engineering and coastline protection, there is the need for a comprehensive exploration of these dynamic physical vulnerability processes. Therefore, the main objective of this research is to explore and investigate the underlying drivers of the physical vulnerability of The Gambia’s coastline in the context of climate change, focusing on the combined interactions and impacts of the physical processes that exacerbate coastal landscape susceptibility stress.

2. Study Area

The sites for this study focused on The Gambia coastal zone (Figure 1). The Gambia’s coastline, characterised by its sandy beaches, mangroves, and unique biodiversity, is increasingly at risk due to the adverse effects of climate change. The Gambia’s coastline zone has a variety of geomorphological features that have been formed by both natural and human activities. The Gambia is characterised by three distinct and significant landscape types, each contributing to the country’s unique environment and ecological diversity. These include the floodplains, the colluvial slopes, and the highlands. The coastal region is covered by unconsolidated marine and aeolian sands, along with low-lying sand dunes. Beneath these layers, ferruginous sandstones create cliffs reaching up to 20 m above Cape St. Mary. The Gambia includes barren areas like intertidal mudflats and sandy beaches. The open ocean coast offers expansive sandy beaches, while sheltered regions are home to mangrove swamps and woodlands. Preserving these unique features is essential for the health and sustainability of the environment [13].

Larger portions of the beaches consist of medium to fine quartz sand, with some featuring notable densities of cockle (Acra senelis) shells that create yellow sand. These beaches are often bordered by rugged headlands of sandstone and laterite, with significant formations found at Sanyang and Cape Point, as well as offshore islands like the Bijol Islands. To better understand this coastal region, the study area is categorised based on geomorphic features and vulnerability to sea-level rise, referencing the UNEP/OCA PAC Report [14]. From Buniadu to Barra Point, the strand-plain coast includes sandy barriers and beach ridges, alongside extensive mangrove systems that provide habitat for birds, source of timber, and serve as fish spawning grounds. In the Banjul to Cape Point stretch, net longshore sediment transport occurs from Cape St. Mary toward the Gambia River, influenced by waves from the west and southwest. Key features in this area include barrier spits and island systems, enhancing the region’s ecological diversity and resilience.

Banjul, the capital of The Gambia, is situated on a low area of erodible sedimentary + rocks, with its highest point around 2 m above sea level. This strategic location on the largest recurved sand spit offers opportunities for effective coastal management. The coastline from Cape Point to Fajara features actively eroding cliffs, with some areas stabilised. Cape Point’s strong bedrock provides natural wave protection. Kololi Point extends from Fajara to Bald Cape, showcasing wave-cut cliffs that underline the need for monitoring erosion patterns. The sandy cliffs between Bijilo Forest Park and Brufut fish landing spots reach heights of about 30 m. North of Bald Cape, the beach’s instability, marked by shifting sand spits, presents opportunities for ecosystem restoration. Rocky outcrops offer additional protection at low tide.

Near the Tanji River entrance, a growing sand spit indicates ongoing sediment accumulation. From Solifor Point to Sanyangg Point, the coast rises to an ancient cliff, providing insights into the region’s geological history. South of Sanyang Point, the expanding strand-plain impedes the flow of River Kakima into the ocean, highlighting the importance of sediment management. Between Sanyang Point and Kartong Point, the Gunjur Fish Landing and Kafaya Beach Resort are vital economic features.

Facilities at Gunjur are positioned safely from the sea, while strategies at Kafaya can enhance storm resilience. The southern coastline, stretching from Kartong Point to the mouth of the Allahein River, features dynamic sand spits and beach ridges. This low-lying, 2.5 km wide strand-plain, mostly covered with mangroves and less than 1 m above sea level, presents opportunities for conservation and sustainable development, especially regarding potential sea-level rise.

Climate change has historically had a significant impact on The Gambia’s shoreline, showing itself in a variety of ways. Rising sea levels and more frequent storm surges have accelerated coastal erosion, which has harmed essential coastal infrastructure and resulted in a progressive loss of land [13]. Communities, agriculture, and infrastructure have all been severely disrupted by the increased frequency and severity of coastal flooding, with urban floods severely damaging houses and crops. Rising sea levels and altered precipitation patterns have also caused saltwater intrusion into freshwater sources, endangering drinking water supplies and agricultural output [15]. Because fish breeding habitats are disrupted by coastal erosion and changes in oceanic conditions, the already weak fisheries sector has also been impacted. In addition to posing serious socioeconomic issues for the country, the cumulative effects of these climate change impacts have endangered livelihoods, especially for people who depend on agriculture and fisheries [13].

3. Materials and Methods

The vulnerability assessment is based on the conceptualization of risks as a function of hazards, exposure, and adaptation choices and responses [16]. The approach has been widely adopted due to its wide robustness and reduced complexities in investigating social–ecological systems, according to the methodological guide for assessing vulnerability to climate change at the community level.

3.1. Calculation of Coastal Vulnerability Index

The coastal vulnerability index is a method used to assess the coast’s susceptibility to predicted future sea-level rise [17]. It refers to oceanographic circumstances, namely wave height, tidal range, and run-up, as well as geological variables such as coastal geomorphology, coastline position dynamics, and coastal slope. It combines the coastal system’s sensitivity to change with its inherent ability to adapt to changing environmental conditions, providing a relative estimate of the system’s vulnerability to the effects of increasing sea levels [18]. The seven variables widely used include a tidal range contributing to flooding hazards; wave height linked to flood hazards; coastal slope linked to flood shoreline dynamic; historic shoreline erosion rates; geomorphology linked to erodibility; and historical sea-level rise rates linked to eustatic and hydrostatic.

Studies have demonstrated various methodological approaches in investigating coastal erosion, including the classical social vulnerability and risk assessment; however, the Coastal Vulnerability Index (CVI) appeared as the most widely adopted approach [3,19]. The CVI aims to identify coastal areas at high risk by evaluating key factors such as low coastal relief, erodible substrates, current and historical evidence of subsidence, significant coastline retreat, and high wave and tide energy. By employing these criteria in its ranking methodology, the CVI provides valuable insights for managing and protecting vulnerable coastal zones. However, storm surge intensity and sediment movement were not taken into account. Previous investigations classified wide tidal coastlines as high-risk, while micro-tidal coasts (tide range < 2.0 m) are considered low-risk [20,21]. As a result, extensive tidal coasts are ranked as low risk. This adjustment is primarily motivated by storms’ possible influence on coastal evolution and their impact in relation to tide range.

In this study, CVI is used, and followed the approach outlined by Thieler and Hammar-Klose 1999 [22] (see Equation (1)). It includes eight variables that determine coastal vulnerability to erosion and flooding. The eight parameters include relief or topography, lithology or rock type, geomorphology, sea level, vertical land movements, changes in shoreline (horizontal), tidal variability, as well as the height of the wave. The study focuses on seven indicators such as geomorphology, slope, change in shoreline, geology, sea level, the average height of the waves, and the range of the tides. To compute CVI, the square root of the product of the indicators was considered. The indicators are also sorted from 1 through 5 and divided by the total number of indicators.

It is vital to note that these indicators are the fundamental causes of coastal vulnerability (physical), and are both quantitative and qualitative in nature, with unique units. ArcGIS, DSAS, and Google Earth Pro were used in data extraction, integration, and visualisation of results.

$$CVI=\sqrt{\frac{\left(a\ast b\ast c\ast d\ast e\ast f\ast g\right)}{7}},$$

(1)

where

a—slope, b—geomorphology, c—geology, d—relative sea level, e—shoreline displacement, f—tidal range, g—wave height.

3.1.1. Variables Used

The CVI approach in this study considers seven variables, including geology, geomorphology, relative sea level, slope, tidal range, wave height, and shoreline displacement. This allowed the exploration of the physical processes propelling the coastline vulnerability.

Slope

The relief of an area has marked influences on the level of vulnerability to flooding and the rate at which shorelines retreat [23]. To derive the slope data for The Gambia, the Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) was obtained from the NASA EarthData website. The DEM was further imported into ArcGIS environment, using spatial analysis to extract the slope shapefiles (Figure 2). The slope data are important for assessing physical exposure inundations through water flow and accumulation capacity.

Geomorphology

Various geomorphological characteristics that have been shaped by both natural and human activity may be found along The Gambia’s coastline (Figure 3). There are three main types of landscapes in The Gambia: highland, hydromorphic colluvial slopes, and floodplains. With a few low-lying sand dunes, the coastal region’s soils are mostly composed of unconsolidated marine and aeoline sand. Ferruginous sandstones form cliffs no more than 20 m above Cape St. Mary on top of these unconsolidated soils. Sand beaches and intertidal mudflats are examples of naturally occurring barren places in The Gambia. In this study, the coastal geomorphology of The Gambia was used for assessing the CVI [13].

Geology

The Gambia’s underlying geology is almost entirely made up of flat sedimentary strata that dip gently and thicken gradually to the west [24]. The entire area is covered by the Continental Terminal formations on the surface. Heterometric sand with argillaceous characteristics makes up these tertiary period deposits (Figure 4). These are linked to the maritime OLIGOMIOCENE’s sand, marno-limestone, and argillaceous sandstone [25].

Relative Sea Level

A datum known as mean sea level (MSL) denotes the average height of the water’s surface across all tidal phases. Typically, local hourly water level heights over a 19-year period are used to determine it. As the sea surface follows the Earth’s gravitational field, which varies with location, it fluctuates considerably from one part of the Earth to another. Satellite altimeters are used to measure and average variations in global mean sea level, enabling researchers to use global mean sea level as an indicator of climate change [26]. Coastal tide gauges are often used to record Mean Sea Level (MSL). It is influenced by both actual fluctuations in the water level and the vertical movements of the ground where the gauges are located [27]. Tidal gauges have been used to measure sea level variation in West Africa particularly in Dakar region. Over the years, a number of organisations have carried out the measurements, including the UNESCO Intergovernmental Oceanographic Commission and the Service Hydrographique et Océanographique de la Marine (SHOM). Since they have been taking place for more than a century, these observations have yielded important information about the region’s sea level fluctuation [28].

According to Jallow et al., 1996, it was projected that about 92 km² of land in the coastal zone of The Gambia is likely to be flooded and inundated as a result of only one (1) metre of sea-level rise (SLR) and The Gambia will likely lose its capital city, Banjul under this scenario [8]. These illustrations make it crucial to include sea-level data in the CVI. The sea-level rise time series data extend from 1992 until 2018 (Figure 5). These data was explored and presented descriptively to identify the trend over time.

To include sea level in the CVI mapping, data should be added to the layer’s attribute table. A new file is generated by selecting Table Option and Add Field, followed by the creation of the new field.

Shoreline Displacement

DSAS, an extension of ArcGIS software version 10.8, is being used to assess the dynamics of the Gambia’s coastline between 2014 and 2023 (Figure 6). It is based on various factors. The shoreline change envelope (SCE), the end point rate (EPR), the net shoreline movement (NSM) and the linear regression rate (LRR). By dividing the net shoreline movement (NSM) by the time elapsed between the oldest and youngest shorelines (see Equation (2)), the end point rate which is calculated using the DSAS tool, an ArcGIS software extension determines the shoreline displacement, an indicator of the susceptibility to coastal erosion. The NSM distance, expressed in metres (m), that separates each transect’s oldest and most recent shorelines [29].

EPR = NSM/(Time between oldest and recent coastline),

(2)

where

EPR is the end point rate.

NSM is the net shoreline movement.

Five Landsat images (1984, 1994, 2004, 2014, and 2023) were employed (

Table 1. Landsat images’ information (1984, 1994, 2004, 2014, and 2023) of The Gambia.

Satellite/Sensor	Path/Row	Number of Bands	Spatial Resolution (m)	Acquisition Date
Landsat 5/TM	205/051	7	30	17 December 1984
Landsat 5/TM	205/051	7	30	22 May 1994
Landsat 7/ETM	205/051	9	30	6 March 2004
Landsat 8/OLI_TIRS	205/051	9	30	22 February 2014
Landsat 9/OLI_TIRS	205/051	9	30	28 April 2023

Source: https://www.usgs.gov/ (accessed on 6 January 2024).

).

Range of the Tidal Waves

Tidal patterns significantly influence both temporary and recurrent flood events. The extent of the coastal zone and size is largely determined by its expansive tidal range. Sections with strong tidal forces are found in vast intertidal zones with low elevation, making them highly susceptible to permanent inundation due to sea-level rise. Additionally, these areas face an increased risk of occasional flooding due to storm surges, especially when these surges occur at high tide. These observations are drawn from existing oceanographic data.

Height of Waves

This indicator allows the assessment of the volume of beach material that can be moved out to sea, resulting in its permanent removal from the coastal system. To evaluate the risk associated with wave height, we consider the highest significant wave heights in various coastal regions. In this context, we aim to analyse significant wave values, which are directly linked to the intensity of marine erosion.

4. Results

4.1. Coastal Vulnerability Index at Regional Level

The CVI is a statistic that assesses coastal areas’ vulnerability to erosion and other disasters. It takes into account geomorphology, geology, sea-level rise, waves, tides, coastal slope, and the rate at which shorelines change. The physical CVI is usually calculated using a mix of physical characteristics.

The physical CVI assessment for all coastal regions in The Gambia reveals varying levels of exposure to coastal erosion (

Table 2. The physical coastal vulnerability of coastal regions in The Gambia.

Regions	Average CVI	Percentage (%)
Lower Niumi	29	25
Banjul	29	25
Kanifing	21	18.1
Kombo Saint Mary	18	15.5
Kombo South	19	16.4
Total	116	100

). The Gambia’s physical CVI was evaluated for several regions, with the results shown in the table below:

The Lower Niumi and Banjul regions have the highest CVI score of 29, indicating greater susceptibility than other coastal areas in The Gambia. These regions account for 50% of the total CVI. Kanifing has a CVI of 21, suggesting a high susceptibility to coastal disasters. It accounts for around 18% of the overall CVI. Kombo Saint Mary region has a CVI score of 18, indicating moderate vulnerability in comparison to others. It represents around 15.5% of the total CVI. Kombo South has a CVI of 19, indicating moderate susceptibility, like Kombo Saint Mary. It contributes around 16% of the overall CVI.

4.2. Coastal Vulnerability Index (CVI) at the Local Level

The physical coastal vulnerability of several areas along The Gambia’s coast, as well as the elements used to calculate the CVI are below mentioned (

Table 3. The physical coastal vulnerability of coastal localities in The Gambia.

Littoral Cells	Average Slope (%)	Geomorphology	Geology	Average Sea Level (mm/Year)	Average Tidal Range (m)	Average Mean Wave High (m)	Average Coastline Dynamic Rate (m/Year)	Average CVI
Buniadu Point to Barra	4	Barrier beaches	Poorly sorted unconsolidated sediments	1	1	2	−0.84	29
Banjul to Cape Point	6	Barrier beaches	Fine unconsolidated sediments, poorly sorted unconsolidated sediments	1	1	2	0.21	29
Cape Point to Fajara	0.78	Cliffs	Poorly sorted unconsolidated sediments	1	1	2	−0.82	15
Fajara to Bald Cape	186	Sandy cliffs	Poorly sorted unconsolidated sediments	1	1	2	−0.43	17
Bald Cape to Salifor Point	6	Sand beaches, Sandy cliffs, Cliffs	Poorly sorted unconsolidated sediments	1	1	2	0.23	22
Salifor Point to Sanyang Fishing Village	13	Cliffs	Poorly sorted unconsolidated sediments	1	1	2	2.4	10
Sanyang Fishing Village to Allahein River	12	Sand beaches, Cliffs	Fine unconsolidated sediments, poorly sorted unconsolidated sediments	1	1	2	−0.46	23

).

From Buniadu Point to Barra, the littoral cell has a mild average slope of 4%, indicating a gradual inclination. The primary geomorphological feature is barrier beaches, which are accompanied by poorly sorted unconsolidated sediments. Despite an average sea-level increase of 1 mm per year and a 1 metre tidal range, the negative average coastal dynamic rate (shoreline displacement) of −0.84 indicates severe erosion. As a result, the average Coastal Vulnerability Index (CVI) score of 29 indicates a high level of exposure to coastal hazards.

The stretch of coastline, which runs from Banjul to Cape Point, is made up of barrier beaches and a combination of fine and poorly sorted unconsolidated material. The average slope is significantly steeper (6%), with equivalent sea-level increase and tidal range.

Significant differences in physical traits and vulnerability levels are seen when coastal vulnerability is analysed across the littoral cells. With average CVI scores of 29, regions like Banjul to Cape Point and Buniadu Point to Barra show high vulnerability due to the presence of barrier beaches, poorly sorted unconsolidated sediments, and dynamic rates that show a small amount of accretion or erosion. On the other hand, with CVI values of 15 and 10, respectively, Cape Point to Fajara and Salifor Point to Sanyang Fishing Village show significantly less vulnerability. These locations are distinguished by cliffs and higher average slopes, which offer increased resilience against coastal hazards. Notably, the existence of sand beaches and a mixture of fine and poorly sorted sediments contribute to the moderate susceptibility of Sanyang Fishing Village to Allahein River, which has a CVI score of 23. These patterns demonstrate how geology, geomorphology, and coastline dynamics interact to shape a region’s susceptibility to coastal hazards brought on by climate change.

Despite a positive average coastline dynamic rate of 0.21, indicating some accretion, the CVI score is still high at 29 due to the vulnerability provided by geological and geomorphological factors.

From Cape Point to Fajara, the coastline is characterised by cliffs and poorly sorted unconsolidated sediments, with an average slope of 0.78%. Despite the modest slope, the negative average coastal dynamic rate of −0.82 suggests strong erosion processes. As a result, the CVI score is 15, indicating considerable susceptibility relative to other cells. In contrast to the previous cell, the littoral cell from Fajara to Bald Cape has sandy cliffs with a remarkable average slope of 186%. Despite the presence of poorly sorted unconsolidated sediments and similar environmental conditions, the CVI score is moderate (17). This could be attributed to local sediment dynamics and shoreline stabilisation initiatives.

From Bald Cape to Salifor Point, this littoral cell is made up of sand beaches, sandy cliffs, and cliffs, with an average slope of 6%. Despite a positive average coastline dynamic rate of 0.23, indicating some accretion, the CVI score of 22 nevertheless indicates considerable vulnerability to coastal hazards. From Salifor Point to Sanyang Fishing Village, this littoral cell is characterised by cliffs and a moderately steep average slope of 13%. The area has a significant positive average coastal dynamic rate of 2.4, indicating strong accretion. As a result, the CVI score is relatively low at 10, indicating decreased susceptibility compared to other cells.

From Sanyang Fishing Village to Allahein River, this area has sand beaches and cliffs with an average slope of 12%. Despite the presence of both fine and poorly sorted unconsolidated sediments, the negative average coastal dynamic rate of −0.46 suggests erosion activities, resulting in a high CVI score of 23.

These findings provide crucial information on the coastal risks in The Gambia. They also have a direct impact on achieving the SDGs. This study promotes global goals such as climate resilience (SDG 13), ecosystem conservation (SDG 14 and 15), and community well-being (SDG 1, 2, and 11) by addressing specific vulnerabilities using sustainable development strategies. These results demonstrate the importance of focused regulations and well-coordinated coastal zone management in reducing hazards while promoting sustainable development along The Gambia’s coastline.

5. Discussion

The majority of the coasts in The Gambia are vulnerable to the effects of climate change, including coastal erosion, flooding, and advanced sea due to increasing sea levels [30]. According to Koks et al. (2019), The Gambia is among the top twenty countries with the highest multi-hazard Expected Annual Damages (EAD) relative to GDP [31]. Furthermore, the frequency of storm surges and coastal temporal floods is increased when normal hydrodynamic factor functioning is disrupted [32]. Low-lying locations and coastal systems are particularly vulnerable to coastal flooding brought on by excessive water levels [33]. Increased wave activity and the flooding of low-lying areas due to sea-level rise are the main causes of coastal erosion in The Gambia [8].

Pollution, unnatural settlement, and sand mining are some of the ways that human activity along the coast exacerbates this predicament [3]. With population expansion and development pressures, people are developing in coastal areas, resulting in the proliferation of megacities in coastal countries around the world [34,35]. This condition, in addition to the impacts of climate change in coastal countries renders the population living along the coast vulnerable to coastal erosion. As a result, scientists are becoming increasingly interested in vulnerability assessments as a means of responding to risks in coastal zones. The majority of coastal erosion studies over the last few decades have mostly focused on assessing coastal vulnerability using the CVI [7,36,37,38,39,40,41,42,43,44,45,46,47,48].

The vulnerability of the coastline is driven by an interactive network of interconnected elements that influence the coastal region’s resilience. Geomorphology and landforms have a considerable impact on vulnerability. In addition, mangroves and wetlands help to stabilise coasts [1]. Sea-level rise, caused by rising global temperatures and glacial melt, exacerbates vulnerability by increasing coastal floods and erosion. High-energy waves and storm surges, especially during extreme weather events, exacerbate erosion and flooding. Tidal range accentuates the impact, especially in places with frequent water level swings. Urbanisation, deforestation, infrastructure development, sand mining, and pollution all affect natural coastal processes, reducing erosion defences [49].

The results show that the coastline of The Gambia is vulnerable due to a complex interaction of oceanic, geological, and geomorphological forces. A high degree of exposure to coastal risks is indicated by an average CVI score of 29 from Buniadu Point to Barra (Figure 7). This is owing to the littoral cell’s mild average slope of 4%, which indicates a gradual incline. Barrier beaches, which are accompanied by poorly sorted unconsolidated sediments, are the main geomorphological characteristic. A negative average coastal dynamic rate of −0.84 implies serious erosion, even with a one-metre tidal range and an average sea-level rise of 1 mm annually. Barrier beaches with a mixture of fine and badly sorted unconsolidated material make up this section of the coast, which stretches from Banjul to Cape Point. With an identical rise in sea level and tidal range, the average slope is much steeper (6%).

From Banjul to Cape Point, because of the vulnerability supplied by geological and geomorphological causes composed by barrier beach, fine unconsolidated sediments, poorly sorted unconsolidated sediments, the CVI score is still high at 29 even if the average coastline dynamic rate is positive at 0.21, suggesting some accretion. Furthermore, the coastline between Cape Point and the Fajara area has an average slope of 0.78% and is characterised by sea cliffs and poorly sorted unconsolidated sediments. Strong erosion processes are suggested by the negative average coastline dynamic rate of −0.82, despite the moderate slope. Consequently, the CVI score is 15, which indicates vulnerability in comparison to other cells. The coastal cell from Fajara to Bald Cape features sandy cliffs with an impressive average slope of 186%, which contrasts with the previous cell.

Despite the presence of poorly sorted unconsolidated sediments and similar environmental conditions, the CVI score is moderate (17). This could be attributed to local sediment dynamics and shoreline stabilisation initiatives. From Bald Cape to Salifor Point, this littoral cell is made up of sand beaches, sandy cliffs, and cliffs, with an average slope of 6%. Despite a positive average coastline dynamic rate of 0.23, indicating some accretion, the CVI score of 22 nevertheless indicates considerable vulnerability to coastal hazards. From Salifor Point to Sanyang Fishing Village, this littoral cell is characterised by cliffs and a moderately steep average slope of 13%. The area has a significant positive average coastal dynamic rate of 2.4, indicating strong accretion. As a result, the CVI score is relatively low at 10, indicating decreased susceptibility compared to other cells.

From Sanyang Fishing Village to Allahein River, this area has sand beaches and cliffs with an average slope of 12%. Despite the presence of both fine and poorly sorted unconsolidated sediments, the negative average coastal dynamic rate of −0.46 suggests erosion activities, resulting in a high CVI score of 23.

From Buniadu Point to Barra and Banjul to Cape Point have consistently high CVI scores, indicating crucial locations that need urgent attention to mitigate severe erosion and related hazards. Beyond just erosion or accretion rates, the difference between accretion-dominated regions (e.g., Cape Point to Fajara) and erosion-dominated regions (e.g., Banjul to Cape Point) shows that geomorphological features and geological susceptibility have a considerable impact on vulnerability [50]. These findings emphasise the significance of tailored coastal management strategies that incorporate site-specific geological and geomorphological features in order to successfully reduce vulnerabilities.

Choosing live shorelines over hard seawalls promotes habitat and adaptation to changing conditions. Managed retreat schemes identify high-risk locations for gradual relocation away from shorelines, which are supplemented by zoning rules that limit new construction in susceptible zones. Stormwater management strategies, such as enhanced drainage systems and green infrastructure, reduce flooding hazards. Coastal protection techniques, such as sea walls, breakwaters, and artificial reefs, can help reduce storm surge and SLR impacts while limiting erosion [51].

Communities dealing with the consequences of increasing sea levels must implement adaptation strategies to protect their residents, infrastructure, and natural surroundings. Elevated infrastructure and structures are critical, demanding construction at higher elevations to reduce flood hazards. Retrofitting existing structures to accommodate expected sea-level rise is critical. Governments can promote community participation and education by holding awareness campaigns and seminars that allow locals to participate in decision-making processes. Community awareness campaigns and education programmes educate communities on the impacts of the increasing rise in sea level and adaptation strategies, encouraging community involvement in planning processes. Sea-level rise is a community-wide multi-stakeholder problem at the local level, adaption methods can be more effective if the primary stakeholders, such as the government, people, and companies, work together to shape them [52].

Integrated Coastal Zone Management (ICZM) frameworks enhance comprehensive planning that takes into account ecological, social, and economic concerns while encouraging cross-sector coordination. The ICZM process must connect government and community, science and management, and sectoral and public interest in the preparation and implementation of each action. ICZM aims to maintain coastal resources, ecological functioning, and values through effective planning and coordination in a social, political, institutional, and economic framework to ensure sustainable development of the coastal zone [53].

Governments have great power in assisting vulnerable communities as they face the problems posed by increasing sea levels. They can provide support in a variety of ways by employing a multidimensional strategy. It is critical to put in place strong policy and regulatory frameworks, such as zoning regulations that limit development in high-risk coastal areas and construction codes that require flood-resistant structures [54].

Financial support methods such as grants, subsidies, and low-interest loans help homeowners and companies adapt, and insurance programmes give critical coverage against climate-related hazards [54]. Infrastructure investment, notably in flood protection and resilient utilities, improves community resilience. Long-term investment in research and monitoring initiatives to track sea-level rise, erosion rates, and coastal dynamics is critical for developing personalised, context-specific solutions to coastal vulnerability [55].

Investing in natural barriers and ecosystem restoration, including mangroves, coral reefs, and wetlands can help absorb wave energy and stabilise shorelines. Beach replenishment and dune restoration improve coastal resilience by restoring degraded beaches and preserving natural buffer zones. Ecosystem restoration programmes, such as wetland conservation and beach nourishment, help to strengthen natural erosion and flooding defences. According to Ottman (1994), mangroves serve as a natural defence against storm surges and coastal erosion [56]. Mangroves connect estuaries, seagrass meadows, coral reefs, and open ocean regions by acting as transitional zones between marine and terrestrial habitats [57].

International cooperation is critical for addressing trans boundary concerns, requiring engagement with neighbouring countries and international organisations to share information and best practises. West Africa Coastal Areas Management Program is an example of international cooperation in mitigating the effects of climate change in littoral zones and strengthening local populations’ adaptation capacities [55]. Collaboration at the regional and international levels promotes collective action to solve common concerns and advance global climate mitigation and adaptation agreements. Long-term planning solutions, which incorporate adaptive pathways and scenario planning, provide flexibility in responding to changing conditions. Finally, capacity-building and training programmes can provide local governments and community leaders with the updated knowledge and expertise required to implement effective adaptation strategies. In sum, the government is encouraged to take a proactive and inclusive strategy, involving multi-stakeholders with multidisciplinary expertise, to strengthen the resilience of vulnerable communities.

6. Conclusions

The expansion of megacities in coastal regions has increased vulnerability to coastal hazards, demanding extensive vulnerability assessments to guide adaptation and management methods. Coastal vulnerability assessments, which frequently use approaches like the CVI, offer an important overview of coastline susceptibility to erosion and inundation. The consequences of climate change on coastal landscape such as sea-level rise, land loss, and alterations in storm patterns, provide substantial concerns for coastal populations around the world. Low-lying coastal countries, such as The Gambia, face significant hazards, potentially affecting essential infrastructure and ecosystems. For example, the littoral cell from Buniadu Point to Barra is extremely vulnerable to coastal hazards, with a CVI score of 29 due to strong erosion processes despite a relatively gentle average slope of 4%. Similarly, the coastline from Banjul to Cape Point has barrier beaches and poorly sorted unconsolidated sediments, resulting in a high CVI score of 29 despite a slightly steeper average slope of 6%. In contrast, the littoral cell between Salifor Point to Sanyang fishing village has extensive accretion, resulting in a low CVI score of 10 despite a very high average slope of 13%.

Effective adaptation and management techniques are critical for increasing resilience and reducing the risks associated with coastal vulnerability. Moving forward, coordinated efforts are required to incorporate scientific assessments, community participation, and policy interventions into coastal management methods. Coastal communities can better adapt to climate change impacts through prioritisation of resilience-building strategies, sustainable coastal development, and ecosystem conservation. Finally, tackling coastal vulnerability necessitates a comprehensive approach that balances biophysical, economic, and social dimensions to promote long-term development and resilience in coastal communities. This study recognises certain limitations, as the CVI framework focuses primarily on physical factors and does not directly incorporate socio-economic aspects, such as population density, economic activities and cultural heritage. Future research could improve the CVI methodology by incorporating socio-economic variables and exploiting high-resolution datasets to provide a more holistic assessment of coastal vulnerability. By addressing these shortcomings, future work can better inform decision-making and support the development of integrated coastal zone management strategies.