The Lake Chad watershed
The Lake Chad watershed is a vast inland basin of about 2,388,700 km2 covering almost all of Chad (1,091,500 km2), part of Cameroon (46,800 km2), Nigeria (180,200 km2), Niger (674,000 km2), Sudan (82,800 km2), Central African Republic (218,600 km2), Libya (4,600 km2) and Algeria (90,000 km2).
Average surface water flow: the Chari-Logone sub basin
There are two main geological formations:
- The base consists of crystallophyllian and igneous rocks of the Precambrian age. It is the seat of discontinuous aquifers;
- Formation of sedimentary covers spanning the Quaternary to the Cambro-ordovician period. They are full of large continuous aquifers with substantial freshwater resources.
The Lake Chad Basin features vast areas consisting of sedimentary formations (sand, sandstone), serving as continuous aquifer seats in the following forms:
- unconfined aquifers (often referred to as the "water table");
- deep captive or semi-captive aquifers, which are artesian under certain hydraulic and topographical conditions;
- The discontinuous layers found in the base areas.
Continuous and transboundary aquifers account for almost three quarters of the basin’s total area;
From top to bottom, it features:
- The primary sandstone aquifer: it is shared between Chad, Sudan, Libya, Niger and Algeria;
- The Nubian sandstone aquifer: it is shared between Chad, Libya, Egypt, Sudan;
- The system of superimposed aquifers of the Lake Chad basin (Fig.) which is shared between Chad, Cameroon, CAR, Cameroon, Niger, Nigeria;
- The Cretaceous aquifer: It is little known nowadays. It sits unconformably on the Crystalline base;
- The CT aquifer (Lower aquifer in Nigeria) which is confined at the centre of the basin and around Lake Chad but is phreatic in the low lands and southern Chad;
- The lower Pliocene aquifer (middle aquifer in Nigeria). Located between 250 and 300 m. There is no clear boundary between the aquifer and the Continental Terminal. It is artesian around Lake Chad over a surface area of about 6,000 km2 and is exploited in Niger and Nigeria by several artesian boreholes. The Pliocene series begins with a sandy series (Lower Pliocene) and continues with 200m thick clay sedimentation which separates the Pliocene from the Quaternary aquifer.
- The water table.
Le mur l’aquifère de la nappe quaternaire se situe entre 50 et 180 m. Le mur est plus profond sous le lac Tchad. Les profondeurs/sol des niveaux statiques varient de 5 m en bordure du Chari à 80 m au centre du creux piézométrique. Les niveaux les moins profonds se localisent près des cours d’eau. Plusieurs creux piézométriques ont été identifiés au Tchad, Cameroun, Nigeria et Niger. Depuis quelques décennies, les travaux montrent que le niveau d’eau de la nappe s’abaisse dans ces zones de creux piézométriques. La nappe est d’extension régionale et constitue la principale ressource exploitable par la population. Les eaux sont douces (1 g/l) à très minéralisées (jusqu’a 7 g/l).
Quaternary layer wall is located at a depth of 50 to 180 m. The wall lies much deeper under Lake Chad. Static depths /ground levels vary from 5 m along the Chari to 80 m in the centre of the piezometric trough. The shallower levels are located near the river. Several piezometric troughs have been identified in Chad, Cameroon, Nigeria and Niger. In recent decades, research has shown that the water table has been dropping in these piezometric trough areas. The water table has a regional scope and is the main resource available for exploitation by the population. The water varies from fresh (1g/l) to highly mineralised (up to 7g/l).
The objective of the LCBC’s Environment and Water Resources Department is to manage water resources and the environment with a view to sustainable development. This document seeks to profile the huge freshwater resources contained in the Lake Chad Basin, which are shared among several member states of the Lake Chad Basin Commission.
- Study of the quaternary layer in Chad (BGR-CBLT project)
- Locating of water points (open wells, boreholes, and piezometres) to monitor groundwater in the Lake Chad basin.
- Installation of PCD to monitor surface waters
- Installation of piezometres to monitor groundwater
- Hydrogeological study of the Logone Basin (BGR-CBLT Project)