Morphologic Response of a Stream Channel to Extensive Sand Mining

Aliyu Baba Nabegu

doi:10.19026/rjees.6.5747

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.

Highlights

A considerable number of studies have shown that human activities such as sand mining within river channels have greatly accelerated natural geomorphologic processes with negative consequences which includes modification to channel morphology; ground water table lowering, stream-bank instability; flood flow increase and several other biological impacts (Leopold et al, 1964; Lagasse et al, 1980; Chang, 1987; Kondolf, 1997, 1994; Desprez, 2000; Rinaldi et al, 2005; Rovira et al, 2005; Chen and Lui, 2009; Nabegu, 2012)
It is on account of this that this study evaluates the impact of sand mining on the river Kano channel morphology
Sand mining in Kano river is manual in operation, in contrast to other places where heavy dredgers are used, the continuous removal over a long period of time results in the loss of considerable amount of sediments from the river system

Summary

INTRODUCTION

A considerable number of studies have shown that human activities such as sand mining within river channels have greatly accelerated natural geomorphologic processes with negative consequences which includes modification to channel morphology; ground water table lowering, stream-bank instability; flood flow increase and several other biological impacts (Leopold et al, 1964; Lagasse et al, 1980; Chang, 1987; Kondolf, 1997, 1994; Desprez, 2000; Rinaldi et al, 2005; Rovira et al, 2005; Chen and Lui, 2009; Nabegu, 2012). The observed impacts have led to numerous studies in Europe, Asia and United states, using a variety of methods and techniques such as by experiments exemplified by the work of Lee and Chen (1996) and Neyshabouri et al (2002), field observations by Neyshabouri et al (2002) and Rinaldi et al (2005), analytical models by Cotton and Ottozawa-Chatupron (1990) and since the late 1980s, by the use of sophisticated numerical modelling by Cao and Pender(2004) and Chen and Liu (2009) Very few of such studies have been undertaken in Africa and in Kano Region in particular where, the main source of sand is from river bed mining and demand has continued to increase as a result of its utilization as cheap material for housing and infrastructure construction which has been exacerbated by high population growth estimated at 3% per anum and unprecedented urban growth of 40% per anum (Nabegu, 2012). It is on account of this that this study evaluates the impact of sand mining on the river Kano channel morphology

MATERIALS AND METHODS

RESULTS AND DISCUSSION

CONCLUSION