Floods have been a major natural disaster, affecting the Gambia over the last decade. It effects has been a cause for concern, because the Gambia is situated in the low lying coast and it has a low capacity in resolving the problems on floods. As a result of the rising sea levels, along with excess rainfall and high tides, the Gambia’s river reaches its flood stage, causing flooding and inundation.
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According to UNFCCC (2007), the Gambia is part of the world’s most vulnerable countries, that are prone to the effects of sea level rise and the country’s has a few resources to reduce the risks, it poses for the future. The aim of this report is to understand the impacts of sea level rise on river flood and also, to understand its consequences for the flood risk management in Gambia.
Geography and Demography
The Gambia, being the smallest country in the African continent, has an area of 11,000 km (NEA, 2010). Studies from the UNEP(no date) claim that, about one third of its surface area is covered by the Gambia’s river with marsh lands along its banks. Its river originates from the Futa Djallon highlands in Guinea, bisecting the country into a narrow strip of land, approximately 400 km long and 30 km wide on both sides of Gambia (see Figure 1). Gambia is bordered on all sides, by the Republic of Senegal and on the west, by the Atlantic Ocean (GOTG, 2008).
Figure 1: Map of the Gambia ( Jaiteh and Saho, 2006)
Climate and population
The Gambia’s climate is known to be subtropical, with dry seasons from November to May, and wet seasons from June to October. Rainfalls and tides are known to be the key factors that influence the rivers flows, as the rainfall ranges from 850-1,200 mm per annum (NEA,2010). However, over the past decades, there has been massive outbreaks of drought due to low rainfall patterns. As a result, relatively little vegetation cover, has increased the vulnerability of severe floods, because of inadequate permeable surfaces. During the wet seasons, the excess rainfalls, is the period when the overflow of the river banks and into the floodplains, reaches its peak (GOTG, 2008).
The Gambia’s population is now estimated at 1.36 million (Jaiteh and Saho, 2006) with a density of over 130 persons/km2 (UNDP, 2000). A study by Columbia University(2007) claim that almost 62% of the population, residing outside the 10 meter elevation of the coastal areas, are at risk of coastal flooding, and they are susceptible to the effects from sea level rise(see Figure 2). Also 14% of the population, living in the upper river division and the 13% of the population living in the Central river division are those, under greatest threat of river flooding.
Figure 2: Population density map(Columbia Univeristy,2007)
The country’s geomorphology is made up of its river, which divides the country into two separate forms of a plateau. The lower valley is up to a total land area of 39 percent and its swamps are prone to floods, thus it is only 2 km away from the river ( Jaiteh, 2008).
Jaiteh (2008) states that, the country’s highest land heights are in the east of the country, although they are not above 60 meters. The areas shaded in green are those that are more prone to river floods, hence it is less than ten meters above mean sea level (see Figure 3). Correspondingly, the river flow is up to 30 percent below 10 meters above mean sea level and up to 20 percent during flood seasons (NEA, 2010)
Figure 3: Elevation Map of The Gambia (Jaiteh, 2003)
Flooding in The Gambia
Flooding has been the most common hazard, which affected people throughout the world. Annually, 75million people are affected by flood related disasters (Coppola,2011). In Gambia, the national disaster management agency (2008-2011) reported that between 2002 and 2006, there have been 65 flood events. Human activities add to the vulnerability of flood prone areas, especially in the north bank division, deforestation and poor farming tends to reduce the soils’ ability to hold the flood waters, and this causes more runoffs and erosion (NEA, 2010).
Floods can be considered as natural occurrence, rather than pinning it on the effects from climate change. Knuckman (2011) states that, as the catchment reaches its excess water levels, its loses its ability to restore this excess water and then flooding arises. In addition to that, Cooper and Pilkey (2004) believe that other factor listed below also contributes to the factors that trigger floods. There are three main factors that influence river floods are:
Sea level Forcing: Due to the high rations between the width and length of the river estuary, Jaiteh and Sarr (2011) have claimed that, sea level rise will increase towards the inner part of the river estuary and this applies to the river Gambia due to it land along the river is flat.
Wind forcing: The wind pressure has a huge impact on the water level. Reports from the Gambia’s meteorology office reveal that, during the last 10 years, there has been a 25cm difference in the water levels between the rainy and the dry season, due to shifts of wind speed. During the rainy season, the forces of the wind has a higher load over the rivers surface
Tributary forcing: The river’s mean discharge ranges from 460-90 m3 (Leseck et al, 1980)and the impacts of the severe stream flows affects the rivers tributaries, increasing pressure on the river’s pressure..
Surface evaporation is expected to increase, and this can place additional constraints on management rules of an upstream reservoir in the country. Also, integrated Water Resources Management (IWRM) institutions faces problems associated with the water floods from sea level rise, as drainage congestion increases the height of flood levels.
During wet seasons, when excess precipitation triggers the river to reach its flood stage, causing the flooded water to flow to the flood plains and unto the land (GOTG, 2008). In1999 and 2003, there was a serious flood event that occurred in Upper River and Central River Regions, affecting 13.1% of the country’s population (National disaster management agency2008-2011). The Gambia’s has developed a national disaster management agency in 1996, as a response strategy, to provide emergency assistance; rescue, relief and precautionary operations, for all the disasters in the country. Under this agency, there has been a framework called the strategic action plan, which provides a pathway on what actions and mechanisms to be undertaken for an effective disaster management for the Gambia.
For instance, in terms of precautionary strategies of floods, this management agency provides sand bags, as flood proofing against the flood water levels during the rainy seasons. Although this process has not been effective, because during the recent floods (1999 and 2003), the forces of the flood waters has exceeded the capacity of those existing sand bags over the recent years (GOTG, 2008).
A case study event: July 2010 floodings (Jaiteh and sarr 2011)
In September 2010, there was an extreme flood event from heavy rainfalls; affecting 1,000 and 790 people were displaced. The National Red Cross provided financial support on those affected, whilst Red Crescent societies, were responsible for the emergency rescue and rehabilitation aid (DREF, 2010)
Jallow et al(1996) carried out a research of a one meter sea level rise scenario on the coastal zone. He concluded that, 1m rise in sea level due to flooding would lead to a total land loss of 92 km² in Banjul, because its elevation , and Banjul is built on a low lying sand spit (see Figure 4). An estimated total cost of 217 million US Dollars, worth of land could be lost, including the mangroves on St. Mary’s Island, and along the river banks in the north bank divisions (National Climate Committee Banjul, 2003).
Figure 4: Areas susceptible of flooding with a 1 meter sea level rise (GOTG, 2007)
The Gambia government has also formulated a national adaptation program of action on (NAPA) on climate change, which is under the administration of the UNFCCC. This framework was signed by the Gambia in June 2001, as a means of developing adaptations to climate change and also, to attain preventive schemes for natural disasters such as floods (Jaiteh and Sarr, 2011).
Currently, there have been no existing engineering flood defenses in place, against the prevention of floods in the Gambia. According to executive director of the National disaster management agency, claimed that “inadequate resources and low funding has been the country’s main stumbling block, in generating effective flood protection structures such as embankments and dykes”. Mr Khan, further went on to say that, there has been ten contingency action plans, funded by the World Bank in 1998 to enhance sustainable actions for their flood risk management strategy.
Effects of sea level rising in Gambia
The sea level is rising due to an increased temperature from the atmosphere; which causes thermal expansions in the oceans and the melting of the ice caps( Gehrels and Long, 2008). This outcome increases the water level of the sea to rise.
Reports from IPCCC(2007) claimed, that global sea level is likely to increase by 18 cm to 59 cm by 2100. In Gambia, it is believed that the sea levels could rise by 15cm to 95 cm by 2100 (UNFCCC,2007). This means that, if global warming is not monitored , the challenges of coping with extreme flood will perpetuate, which will cause future constraints to the Gambia’s disaster management agency. This outcome of global warming, threatens the risk of potential rivers flooding at an alarming rate in the future if there is not reduction in greenhouse gases.
Rising sea levels, inundates the coastal zone, due to its low lying feature the Capital city Banjul is vulnerable to flooding it is less than one meter above mean sea level (see figure 3). It is believed that the relationship between the effects of sea level rise, is caused by the changing climate conditions and the natural occurrence of the river (Hunt,2000). For instance, at the rivers estuary, the rising water level from the sea, with heavy precipitation during the wet season increase the risks of flooding in the rivers floodplains (National Disaster Management Agency, 2008-2011). On the other hand, Jallow et al (1996) reveals that, high tides on the river estuaries, influenced by the westerly winds has also been a major factor why the river Gambia floods. Unfortunately, the tide record recorder has not been in function over the past years, for further analysis (see Table 1)
Table 1: Tidal recorder table: Water levels from tide records taken in Banjul, from 1979 to 1993(Jallow et al 1996)
The tide recorder above shows that, the water level has remained constant about two meters between 1979-1984, and towards the late 1980s due to low tides, there has been drastic shift between 1988 till 1993.
Evidence of the high water levels can be seen in 1980, when huge river floods occurred in the central river division, accompany with heavy storm surges (Jallow et al, 1996). Conversely the NEA (2000) claimed that the tidal currents mostly influences floods in the river estuary than the coastline, thus are weaker by the coastline; Banjul, and higher up to1m/s in the rivers estuary.
Figure 3: Current Elevation of Banjul (Jallow et al, 1999)
The Disaster agency mainly undertakes a disaster response and risk reduction system, than a disaster prevention scheme. In 2007, the agency formulated a risk reduction policy, called a ‘hazards Profile of the Gambia and its Vulnerability and Capacity Assessment Report’, to identify the hazards, and the potential threats it poses to the country to the country (National Disaster Management Agency 2008-2011).
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In 2008 the Gambia government developed a National Disaster Management Act which stressed, that the all adaptation and precautionary measures undertaken for flood preventions must be effective and capable to serve long-term purposes. Thus in the event of the 2003 flooding in Central River Division (CRD), the practical early warnings has not been efficient in alerting people before floods occurs.
In the 2003 event, it was unreliable because it did not reach the entire region. Therefore, a change in its the response strategy of the monitoring systems. Post 2003 the government proposes to produce a more resourceful flood risk management plan that consists of geospatial information’s to improve the monitoring services to produce positive effective warning systems. There has been a proposal to develop a mapping program to manage the rivers floodplains along central river division (NEA, 2010).
Currently the UNDP in the collaboration of a National disaster management program provides project guidelines on,
1. How to review of early warning systems,
2. How to analyze management systems, in precautionary measures and
3. The provision of regular feedbacks to those responsible stakeholders (NEA, 2010).
The United nations has recommended to the local government to develop artificial channels such as canals and build dams as mechanisms against flood. More over, the government has been has been reluctant, on these developments, especially dams, as they can cause the changes in the course of the river and its establishment, has not been financially viable.
The UNDP support to the Gambia on floods, encourages a capacity building approach, in which grassroots development, enhances the local community with skills on planting mangroves around there neighborhood, as preparation plans to deal with the flood waters before flood occurrence (UNDP,2000).
Recently, the UN International Strategy for Disaster Reduction (UNISDR) provided technical support to the Gambia’s assessment of the national institutional framework for the national program of Action. This was not been supportive because it has not clearly indicate areas prone to river flooding, induced sea level rise, to provide accurate analysis on research to cope with the risks from both sea level and flooding. Furthermore, the nonexistence of physical flood defenses against flood preventions, and this has been the why vulnerability increases of the country’s liability to floods (NEA, 2010).
LONG-TERM plans and Recommendations
Construction of physical defenses
It is significant to build a low cost seawall or a bulkhead to cope with the effects of sea level and floods along the coastline. The seawall has a 1:2 slope, a 2-metre beam and a height above water of 1.2 times sea level rise scenario. This would protect the coastline where there land is less than one meter above mean sea level, along Banjul area, by the mangrove systems. It is adequate to use dikes made up of about 1.5 to 2 meter to control the water levels (NEA, 2010)
Wetland preservation and mitigation
The estuary of the Gambia River contains economically important wetlands and mangrove systems. The mangrove systems on the Kombo St. Mary Island and Kombo Peninsular are regarded as vital breeding grounds for various aquatic species. Efforts should be made to protect these areas by declaring them as protected wetlands. This would discourage exploitation of the resources in these wetlands. This can examine the impacts of upstream dams on the Gambia River in terms of reduced sediment supply.
Effects of sea level rise on flood risk management
The constraints that the rising sea level has on flood risk management affects the Gambia’s land use planning and the water resource management. There is the need to increase the use of floodplains against floods, and also development the rivers basin.
Water resource management
In producing a better river basin, flood management need to identify the connection of the rivers flowing patters. The Gambia’s integrated water resource management ensures that the water quality is being preserved, and dams and wells are protected against contamination of the flood waters. When river flooding occurs, the major problems arises from drainage congestion and these are regarded as the significant effects of raising water levels on flood risk management
Land use planning
The Gambia needs to map out the most vulnerable locations of flood risks, to enable accurate impact assessments, between land-use planning and the protection of the infrastructures. Also, the contingency plan should include flood scenarios that are beyond the projected situation, in order to increase its management capacities.The lands office and physical planning should avoid the allocation of lands that are susceptible of flooding. For instance dried up streams in kombo peninsular, consists of new settlements, and has recently flooded during the rainy seasons. People residing at areas prone to flooding should be advice to raise their gate above the mean flood levels.
It can be concluded that, the impacts of rising sea levels will continue to increase the risk of flooding across the country, if the preventive systems are not enhanced productively in the future. This is because, the Gambia focus all their attention on the response systems, than prevention systems of floods and the effects of sea level rise, rather than tackling the root causes of the problems, and then finding means of preventing its occurrence. Lack of appropriate data has been a stumbling block in producing the accurate findings, for effective risk management systems. Although, Gambia has been classified as a net sink country, the amount of greenhouse gases eliminate from the atmosphere is more than those produced (NEA, 2010). Yet it is been severely affected by the global climate change effects over the last decade. Its management systems undertake an integrated approach, such as policy formulations and contingency plans, rather than establishing of physical defenses.
To sum it up, the most important method to manage the effects of sea level rise on floods is to reconstruct those groynes(trunks of rhun palm inserted into the sea) in Banjul to capture those sediments transported during erosion (see Figure 5). The construction dikes, can possible be, one of the most efficient form of flood defences. Also, catchment flood management strategy can be an essential tool in providing a sustainable protection on managing flood risks. The facilitation of a catchment flood management plan will enable the Gambia, to benefit from the understanding flood risks of the river Gambia, in order to tackle its consequences efficiently. In this way, the national disaster management and the rest of the stakeholders will undertake a more technical style towards their flood management plan.
In addition to that, there has been poor records to verify flood magnitudes and its frequency and if this was available, there will be allocation, there will be accurate analysis that can provide inappropriate technique to manage future flood risk managements’ for the Gambia.A corporation that brings together the efforts of the local government, UN agencies, NGOs, civil Society and local communities is the most effective form of a achieving a sustainable flood management strategy would create an inclusive disaster management framework in the country and to improve governments capacities to manage and counter to floods effectively.
Received feed back: supervisor wants me to provide a picture of a dikes, as I have written in my conclusion that, it cal be the most effective form of flood risk of management. Please run this thru your plagiarism website for me. I am in Uni working on my powerpoint slides
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