SPECIAL REPORT ON THE SIERRA LEONE MUDSLIDE – A CALL FOR REFLECTIONS
We mourn with the people of Sierra Leone and pass our condolences to each and every affected person; we hope the nation rises strongly at this moment to prevent such occurrence in the future.
The mountainous town of, Regent, Free Town, like most part of Sierra Leone, has a tropical climate, with an average temperature of 28°C. It experiences dry season and wet season, due to the African monsoon, which runs from May to November in the north, and from April to November in the south. The Food and Agricultural Organization (FAO) of the United Nations (UN), in its 2016 AQUASTAT database, estimated the West African nation experiences an annual quantity of rainfall of over 2500 mm (98 inches). In the database of countries on the basis of precipitation by rainfall, Sierra Leone stands at twelfth position globally. With these data in mind, a mudslide happening due to rainfall would have seemed somehow probable. Furthermore, the sad reality is that it occurred, and both climate change and man’s/woman’s neglect of his/her environment played key roles. The American Meteorological Society (AMS), in its released, State of the Climate in 2016 report, indicated that year 2016 was the hottest year in 137 years of record keeping. The global average sea level rose by 3.4 mm (0.13 inches), and the variability of precipitation around the world was extreme. Due to several climate change factors, the region experienced its heaviest torrential rainfall in about two decades. Heavy rains on extremely dry soils, without proper protection was a combination for disaster – How?
Let us do a little brain exercise on soil mechanics. When rain falls, and hits the ground, its ability to dislodge soil particles is dependent on, the rain, diameter, angle of impact, velocity (depending on wind velocity), and the soil properties such as, cohesiveness, permeability, and effective stress. Imagine, rain droplets with relevant diameter and velocity, striking a particular dry soil surface at an effective angle. Gradually, the soil particles will be dislodged from their position, the soil will continue to absorb water until it is fully saturated. With soil saturation and soil particles dislodged; if the rain continues, surface water (water logging) appears transporting soil particles from one location to another, as bed, bouncing, or floating material, depending on the soil mass. A mudslide tends to follow a river-like path. When dislodged soil give way, a mudslide can be induced, picking up other soil materials on its flow path, including rocks and boulders. To prevent this situation, there are two likely solutions; the first would be to reduce the rapid soil saturation or alter the river-like flow path of the mudslide. These solutions can be affordably and naturally met by the planting of trees. A town in the country with the highest annual rainfall in Africa, with its people living between the mountains and the sea, and with increasing sea levels, a mudslide was bound to make it home. Trees could have helped reduce the gravity induced mudslide. However, the increasing population of the town, has resulted in deforestation so as to build houses in the flood prone area. Construction of houses in the Peninsula Forest area increased soil destabilisation.
According to the BBC, the deputy director of Sierra Leone’s Environment Protection Agency (EPA), in 2015, warned “irresponsible actions taken on the hills will affect the city greatly”. He further stated, “Until we stop dumping waste into drainages, until we stop clearing the trees, we will always face severe consequences of climate change”. There is legislation against informal settlements in the area of the Peninsula Forest but it is not being enforced probably due to lack of political-will caused by the people’s prejudice towards the Government, and the authority’s relationship with wealthy home owners in the Peninsula. Abdulai Baraytay, the Sierra Leone’s President spokesperson stated that the EPA warned the residents about the dangers of the region but were chased away from the area by residents. The actions and inactions of both the Government and the citizens on the floodplain, has resulted in the loss of invaluable lives. To prevent future occurrence, the Government must enforce the relocation of people away from the floodplain, as stated in the legislations. However, the vulnerability of informal settlements cannot be eradicated with a magic wand. The availability of vacant lands in flood plain areas, will likely be a bias motivator for citizens to continue building on floodplain.
Floods can broadly be categorised into two, fluvial, when river overflow and burst their banks, or pluvial, when rainfall exceeds drainage systems capacity before it reaches the river. These two types of floods most times occur when the soil cannot absorb rain water due to saturation. With residential buildings floored with cement concrete, bricks, or blocks, the area of soil which can absorb rain water is further reduced. To comprehend how trees will help reduce flooding resulting into mudslide, we will go back to our soil mechanics with a bit of irrigation. Imagine vegetative cover of trees, when rain falls, depending on its angle of impact, most rain droplets are likely to first fall on leaves of trees, before going to the ground. The droplet impact will be intercepted by the leaves which will likely split it, reducing its diameter, and eliminating its velocity. The leaves will then transfer most of the split droplets directly to the ground at a reduced velocity, while few will go to the ground through the branches and trunk. This first action will reduce the rate at which soil is dislodged, inevitably reducing flood. Fallen tree leaves create a deeper, rich humus soil, which along with the surface root helps intercept rain water flow. The sub-surface roots, extends into the soil, absorbing the soil water, increasing soil friction, cohesion, permeability and effective stress. Increased infiltration into the soil will reduce surface water flow which may result in the mitigation against flood.
The benefits of trees to floodplain region must be continually communicated. Tree cutting is induced by, house construction, need of fire wood for cooking, road construction, etc. The Government of Sierra Leone, all Government, and concerned stakeholders on the African continent, must ensure they formulate and enforce policies which prohibit informal settlement in, forest areas, floodplains, and slide prone mountainous areas. Reforestation works should also be increased due to its benefits to the environment and man. We must remember that man/woman makes the environment, and the environment will make the man/woman.
By David Temitope
Research Fellow – Policy Analyst