Hydrological

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Sierra Leone Hydrology

Five main rivers flow from northeast to southwest across Sierra Leone: the Little Scarcies, Rokel, Jong, Sewa and Moa rivers. In addition, there are six smaller drainage basins: the Great Scarcies, Lokko, Rokel Estuary, Western, Robbi/Thauka and Sherbro Water Resources Areas. River runoff is highly seasonal, reflecting the seasonal distribution of rainfall. In the Rokel river, discharge increases from May, peaks in September and decreases to near-zero by March (Lapworth et al. 2015


Water Resources

Surface Water

There are 12 River Basins and Water Resources Areas in Sierra Leone. River Basin areas have recently been redrawn and recalculated using HydroSHEDS software. Three of the River Basins (Great Scarcies, Little Scarcies and Moa) originate in Guinea, while the Mano River Basin originates in Liberia. 


Ground Water

Groundwater is a vital element of the natural water cycle helping to sustain river levels and inland valley swamps in the dry season. Groundwater is the main source of drinking water for rural communities in Sierra Leone and the groundwater storage is limited. Nearly 80% of Sierra Leone sits on geological formations collectively referred to as Basement Complex or crystalline basement. Basement aquifers of significant extent occur across much of sub Saharan Africa and they are of particular importance because they are characterised typically as having low yield and limited storage. In Sierra Leone development of groundwater sources today is mostly from low yielding hand dug wells equipped with hand pumps.


Rainfall

The quantity of water available in Sierra Leone varies significantly from place to place and season to season. Average annual rainfall varies from less than 2000mm in the drier areas of the northeast of the country to about 2500mm in the southeast and more than 4000mm in the Freetown Peninsula. However a substantial amount of Sierra Leone’s rainfall (around half) is lost by evapotranspiration, and the numerous rivers discharge water directly to the sea in the absence of significant abstractions


Hydrological Monitoring Stations

The Ministry of Water Resources under the Sierra Leone Water Security Project 2015 in collaboration with the Bumbuna Watershed management Authority have installed about thirty three (33) hydrological monitoring stations in different locations across the country. These monitoring stations collect data in several parameters which include
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