Morphologic Response of a Stream Channel to Extensive Sand Mining

Abstract

This study assesses the impact of sand mining on the morphology of Kano River channel. The river channel was divided into three sites consisting of site upstream of active mining site, active mining site and downstream of active mining. The upstream site was assumed to be unaffected by the mining activity. The mining site was an area of current active mining. The downstream area is downstream of mining site but with no mining activity. A morphometric assessment of 50 sample points in each of the three sites from a cross section was made where width of the channel was measured from one end of the channel to the other horizontally on transect; depth was measured from the lowest point in the flood plain to the top of the bank; channel slope was determined following standard survey technique from points located from the top of one riffle to the top of another within the entire cross section. One-way ANOVA between groups was employed to test the differences between the measured mophometric variables in the three sites. The results revealed that mining activities has resulted in modification of the channel with great variations in depth between the sites (p<0.01) with the mining site having 7.5 m the upstream site 2.3 m and downstream 2.5 m deeper than the average channel depth; width also vary between the sites (p<0.01); mining site has a mean width of 110 m, downstream site, 75 m and 50 m in the upstream site. Field observation indicate that downstream pools are longer but upstream pools are deeper, expected spacing of riffles given as five to seven stream widths was not observed but riffle interval was however as expected in the mining site.