The Remaining Storage and Rate of Siltation of Mairuwa Dam, Funtua, Katsina State, North-western Nigeria

Mairuwa impounded reservoir (Dam) which was constructed in 1970, had an initial installed capacity of 5.5 million cubic meters and it is the main source of piped water supply to Funtua and its environs for the purpose of irrigation farming and potable water supply. The volume of rainfall in the drainage basin is 102,259,006m3. Runoff coefficient of the area is 0.23. Volume of total runoff is 23,519,571m3. Total volume of material eroded from the drainage basin is 4,703m3/a. After 50 years of impoundment, continuous siltation caused by sediment being deposited annually is affecting its usefulness to the people. In order to determine the remaining storage of the reservoir, there is need to study the reservoir’s bathymetry using boat, satellite navigator and metric tape with a heavy stone attached to it. Results of this measurement show that as at 2020, the remaining storage of the reservoir is 1,944,000m3 representing 35% of the installed capacity. The rate of siltation is 349,920m3/y and loss in volume is 3,556,000m3 representing 65% of the total storage. The rate of erosion in the drainage basin of 102 km2 is calculated to be 0.45mm/a. This is far higher than the world average of 0.088mm/a. The reservoir will be completely silted up if preventive measures are not taken. This will result to inadequate supply of piped water to Funtua and Environs.