In-stream Sand Mining in Kano River: Implications for Sustainable Resource Utilization By

1. In-stream Sand Mining in Kano River: Implications for Sustainable Resource Utilization By Aliyu Baba Nabegu Department of Geography, Kano University of Science and Technology, Wudil Email: prepra@live.com Paper presented at the 54th Annual Conference of the Association of Nigerian Geographers held at the Department of Geography, Kano University of Science and Technology Wudil, From 19th—23rd November,2012

2. Introduction • Sand mining is the removal of sand from its natural configuration including river channels. • Sand on riverbeds have been considered as an attractive high quality and low cost source of building material for centuries ( Rinaldiet al., 2005). • Although, the economic and social benefits of sand mining is recognized, it can also create alterations to river system that have accelerated the natural geomorphologic process with serious negative consequences (Leopold, et.al., 1964; Largasse, et.al., 1980; Chang, 1987; Pringle, 1997; Kondolf, 1997; Rinaldi, 2003; Rinaldiet al., 2005; Roviraet al., 2005). • In Kano region, the main source of sand is from in-stream mining and this has continued to increase due high population growth, unprecedented urbanization and economic development.

3. Aim of the Study • Present understanding of alluvial channel systems like the Kano River is generally not sufficient to enable understanding of the response of the channel to mining disturbances quantitatively and with confidence (Richards, 1980, Lu,2007). • Qualitative response models based on water and sediment supply are useful for predicting the general direction of geomorphic responses (Lane 1955, Schumm 1969, Grant et al. 2003), but, predicting the magnitude of morphologic adjustments and physical-habitat changes is extremely challenging because many stream channels are still adjusting to historical legacies that produce ongoing, lagged geomorphic responses (Trimble 1977, 1995). • Also, several other factors influence channel response to alteration. For example, whether a channel incises or widens can depend on local variations in boundary materials (Booth 1990). Riparian vegetation may also influence channel adjustment and migration (Dunaway et al. 1994). • The aim of this study is to assess the impacts of sand mining on themorphology of Kano River

4. Materials and Methods • This study was conducted between November 2011 and May 2012. • Kano River at Wudil was surveyed to ascertain the number and location of active sand mining points. • The channel was divided into three sites based on the method used by Brown, et. al., (1998) consisting of (i) Upstream of the active mining (ii) Active mining area (iii) Downstream of active mining area • Ten sample points were selected in each of the three sites for morphometric assessment • Dendrogram - shows similarities in cluster group of the sample points. • Data analysis • ANOVA • Multiple comparisons were made with Turkey’s least-squares mean tests

5. Study Area • Kano River is part of the complex system of the Hadejia river basin in which three principal tributaries of Kano, Challawa and Watari streams join above Wudil to form what it referred to as the Upper Hadejia • Downstream of Wudil, the basin is underlain by the Chad basin formation. • Upstream, it is underlain by the Basement Complex of Precambrian rocks. • The typical relief is 300 m • Aeolian sand derived from wind deposits cover most part of the area with thickness of about 5m in the upland, and 10m along the lowland plains. • River has been impacted by Dam and other structures

6. Results and Discussion • The mining site is wider than upstream and downstream sites P , 0.01,(99%) • The depth characteristics of the three sites indicate uniformity • Downstream pools were significantly increased (P , 0.01), but the depths were not (P . 0.10) • The expected spacing of riffles (five to seven stream widths, Leopold et al. 1964), did not occur in the mining or downstream sites. • The riffle interval in all three sites was longer than predicted by Leopold et al. (1964). • There were large areas of exposed bedrock in mining and downstream sites than upstream • Incision and braiding is dominant in the mining site than upstream and downstream(Plate 1) • Conclusion • Sand mining within Kano river channel seems to create serious impairment to the physical structure of river channel. Decreased flow depth, increased water speed and the resulting increase in erosion forces create an unstable river channel that moves around within the river bed, or meanders, much more rapidly than a natural river channel.The removal of the riverbed armoring that occurs in stream mining and the flattening of the stream bed creates a rapidly changing and unstable environment for a stream. • . In order to capture the scale of change that occurred in Kano river, baseline data which extends far enough upstream to capture geomorphic changes of the magnitude that occurred is crucial to improving our understanding of the impacts. Sediment transport modeling should be done in reaches where mining modifications are observed. Sediment transport modeling upstream and downstream would provide reach-scale aggradations and degradation patterns so that changes in sedimentation patterns could be identified, and the stability of engineered structures evaluated.

7. Plate 1 Braided channel – in the Mining site

8. The wider channel in the mining site results from the decreases in the streambed stability because of the removal of streambed armoring by mining activity • The incision of channel occurs through two primary processes, either, head cutting or due to incision that occurs when sand removal increases the flow capacity of the channel • Removal of sediment than the system can replenish due to mining results and also increased lateral erosion that cause widening of channel • A further cause of the widening channel in the mining site is the removal of riparian vegetation which weakens the channel bank leading to collapse (Plate 2). • Downstream impacts result from increased amounts of floodwater and increased floodwater speeds.

9. Plate 2 Weakened Channel Bank that is Susceptible to Collapse

10. Implication on Sustainable resource utilization • The continuity of sediment transport is interrupted by removal of sediment from the channel by mining - the flow becomes sediment-starved (hungry water) and prone to erode the channel bed and banks • The resulting imbalance in sediment supply and capacity modify physical habitat and ecological potential via a wide variety of mechanisms. • )Altered channel morphology and bed material, hydraulic environments, and the magnitude, frequency, and timing of sediment-transport events adversely affect aquatic life and their life cycles (Trimble 1997, Waters 1995, Konradet al. 2005). • ) Also, channel enlargement, bank instability, degradation of physical habitat, and numerous other geomorphic responses have been associated with such alterations (Hammer 1972, Arnold et al. 1982, Booth 1990, Booth and Henshaw 2001, Jacobson et al. 2001). • Sand mining in stream channels also damage public and private property. For instance, channel incision caused by sand mining undermine bridge piers and expose buried pipelines and other infrastructure. • Wider channel in the mining site means larger cross-sectional areas, so flooding exceeding bank-full capacity may be less frequent, since the effective capacity of the stream is increased. • .

11. Conclusion • Sand mining within Kano river channel create serious impairment to the physical structure of river channel. • Stream channel form was altered by increased widths, lengthened pools, and decreased riffles in mining and downstream sites. • The removal of the riverbed armoring that occurs due to mining and the flattening of the stream bed creates unstable environment. • In order to capture the scale of change that occurred in Kano River, baseline data is crucial to improving our understanding of the impacts. • Sediment transport modeling using RS & GIS in upstream and downstream would provide reach-scale aggradations and degradation patterns so that changes in sedimentation patterns could be identified.

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