ASSESSMENT OF THE MAGNITUDE OF SUSPENDED SEDIMENT PRODUCED BY THE GORUBA TRIBUTARY OF THE KUBANNI RIVER, ZARIA.

Y.O.Yusuf, E.O Iguisi., A.L. Bello, and O.F. Ati.

The Ahmadu Bello University (ABU) dam, constructed to provide water for the university community, receives water and sediments from the upstream catchment area of River Kubanni, which is made up of four tributaries. An earlier study attempted an assessment of the magnitude of sediment produced by the northernmost (Malmo) tributary of the river where a Channel Sediment Yield (CSY) of 482 tons/yr and Specific Sediment Yield (SSY) value of 92 tons/km2/yr were derived for the catchment area. Part of the recommendation was that future studies should look into the spatial spread of sediment contribution into the reservoir by all the in-flowing streams so as to determine which inflow is the most problematic in terms of reservoir sedimentation. An attempt is being made here, using similar method, to look at the southernmost tributary which is the Goruba tributary in order to make a comparison between the two. The study area was monitored for one year with data on sediment concentration and stream discharge collected from the gauging station. The discharge was derived using the Velocity-Cross sectional area method while suspended sediment samples, collected at the gauging station using the USDH 48 sampler with onward analysis in the laboratory were used to determine the suspended sediment concentration and the rating curve was used to allow a reasonable estimate of suspended sediment yield for the study area. Although the number of days of continuous flow differ significantly for the two sub-basins, with that of Goruba being much lesser, the statistics including the channel and specific suspended sediment yield of the Goruba stream (12880.547 tons/yr and 702.7 tons/km²/yr) is more than that of the Malmo stream in folds. The higher sediment yield value and the information thus provided portend the need for increasing catchment management and conservation measures to control sediment yield into the Ahmadu Bello University reservoir as it was observed that sand mining and intensive cultivation is still going on within the basin.

Key words: Discharge, Suspended Sediment Concentration, Suspended Sediment Discharge, Channel Sediment Yield, Malmo Stream and Goruba St.