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.
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..