Sedimentation Assessment of a Small Reservoir at Afaka Forest Reserve, Kaduna, Nigeria

Abstract

The sedimentation assessment of a small reservoir constructed in 1987 at the Afaka Forest Reserve, Kaduna, Nigeria was carried out between 2004 and 2013. The procedure for the assessment involved the peripheral survey as well as bathymetric survey of the reservoir to determine its water surface area and mean water depths, by means of a hand-held Global Positioning System, GPS (Model: GPSmap76CSGARMIN) and a 4m leveling staff, respectively. The study showed that the reservoir storage capacity has decreased, due to sediment build-up, from its initial design capacity 16400m³ to 10665 m³, implying a storage loss of about 35%. A linear relationship was established between the reservoir storage capacity and the age of the reservoir and the result shows a rate of change (decrease) in the reservoir storage capacity of 221m³yr^-1. This implies that the reservoir storage capacity would eventually reduce to zero at reservoir age of 76.5, if desilting is not carried out. For economic justification, it is recommended that the reservoir be desilted, at least, every 15 years by a capacity of 3280m³ (which is equal to reservoir depth of 0.66m), equivalent to 20% of the design capacity, to ensure continuous life span of the reservoir. Results of reservoir sedimentation assessment are necessary tools that serve as guide for safe design of reservoirs for various catchments.

Key Words: Reservoir sedimentation, Storage capacity, Assessment, Catchment, Afaka Kaduna