The Matar micro-dam was inaugurated on Thursday by the authorities and the German Embassy in Chad. This Matar recession dam, which has just been rehabilitated by the NGO Help-Tchad with the financial support of the German Government, was built by the NGO Africare during the great drought of the 1980s.
The structure is located in the lowlands of Ouadi-chock, in a section located about 5 km west of the town of Abougoudam. It is fed by a fairly large watershed whose origin is located about a hundred kilometers to the east.
The rehabilitated dam is 1490 meters long and has an average height of 2 meters compared to the major bed. The estimated harvested area is 208 hectares while the estimated exploitable area is 450 hectares. The width of the left spillway is 38.3 meters while the right one is 12 meters.
Activities interrupted for more than a decade
According to testimonies, the work has been a very important contribution to improving the food security of the population during its operation, especially during the period of great drought. Activities had been halted for more than a decade because of the dam failure.
State of degradation
Before its rehabilitation, the dike was in a rather remarkable state of degradation. It was noted the clear rupture of the dike over a distance of 94 meters, thus widening the width of the central minor bed, and the significant destruction of the profile of the earthen dike over its entire width, under the effect of water erosion. Concerning the spillways, the middle spillway was threatened by the rupture of the dike and scouring downstream.
Technical studies carried out between October 2017 and November 2018 made it possible to assess the work leading to the rehabilitation of the dam: earthworks for the dike and the strengthening of the spillways.
The implementation of this work took place between the months of February and October 2019. The masonry and riprap work were carried out by four groups with the high labor intensity method, thus allowing the creation of employment. The earthworks of the dyke were carried out under the supervision of the machinery rented from the companies ERCB, ATLA and other individuals.
Work on the central spillway
In place of the reinforcement of the central spillway initially planned, a new 38.3 m spillway was built on the left bank. During the work, it was observed that the existing masonry was defective in the foundation and the soil became more and more unstable in depth. The maintenance of this spillway was therefore not guaranteed because of its condition and the difficulties of the site. This site is abandoned and the spillway is located sideways on the left bank.
“The problem of water in eastern Chad remains a major concern, despite the potential of the area, as well as the implementation of several projects by partners operating in the area. The population cannot meet its needs normally and does not have sufficient access to basic social services (water, health, shelter, nutrition, etc.)”,
Work on the right-side spillway
The work focused only on the reinforcement of the upstream sidewalls to protect the dike. During the work, difficulties were encountered, the most notable of which were the displacement of the site of the central spillway, the rather early flows from the Ouadi in May and the distance from the lateritic gravel quarries.
Recommended downstream maintenance
At the end of the works, it is now recommended that the dam be reinforced by the construction of upstream spreading sills to extend the cultivable area, and the implementation of an adequate strategy for the maintenance of this dam in order to avoid returning to the initial state.
