A. B. Nabegu 225 African Scientist Vol. 11, No. 4 December31, 2010 1595-6881/2010 $12.00 + 0.00 Printed in Nigeria © 2010 Klobex Academic Publishers http://www.klobex.org/afs AFS 2010121/11402 Response of the Jakara stream channel to urbanisation Aliyu Baba Nabegu Department of Geography, Kano University of Science and Technology, Wudil Email: marpelione@hotmail.com (Received August 7, 2010; Accepted September 6, 2010) ABSTRACT: This study assesses the morphological response of the Jakara stream channel to the effect of urbanization of its catchment. The proportion of the Jakara catchment under urbanization was determined using black and white air photographs taken in 1961and 1981, landsat imagery of 1987, 1995 and 2006. These were used together with land use maps, road maps and layout plans and ground truthing and three sites were identified thus: An upper watershed dominated by urbanization – Urban; A middle section that is under going urbanization - Semi urban and - A lower catchment that is primarily rural –Rural. Detailed field survey was conducted in six reaches of the Jakara channel, two each in urban, semi urban and rural sites to measure morphological variable. Morphological variables of the Jakara channel reaches under different levels of urbanization were compared. Consistent and significant differences in the sites were demonstrated in bankfull width, depth, cross section and wetted perimeter. Jakara channel is demonstrated to be consistently larger in the reach under urban land use than those under non-urban land uses, with capacity ratio of 2.36, width ratio 1.94, depth ratio 2.25. Most studies in humid tropical areas of Nigeria and temperate areas elsewhere reported smaller urban river channels enlargement. Sinuosity was 68.58% less in urban than rural reach. Channel density increased by 28.6% due to storm sewers, culverts and other runoff removal. The results of the study has implications for urban channel management and suggest that different strategies may be required for channel reaches based on the type of land use and that the selection of a mitigation strategy is dependent upon the extent to which the channel has been impacted by urban within the catchment. Key Words: Channel site, Channel reach, Catchment, Impervious cover, Channel morphology 1. Introduction Urbanization of catchment has been associated with serious problems that dramatically degrade both the form and function of stream ecosystems that can be difficult to mitigate (Booth and Jackson 1997). The complexity of urban land use and the varying responses reported present challenges for understanding the mechanisms by which urban impacts change channel structure and function (Booth et al., 2004). These and several studies have shown that progressive urbanization of a catchment can result in among others changing channel morphology and hydraulic geometry of stream channels. A single disturbance event may trigger a variety of disturbances that differ in frequency, duration, intensity, and location (Klein 1979; Arnold et al. 1982; Booth and Jackson 1997; Trimble 1997; Nilsson et al., 2003). These impacts have recently been referred to as Urban Stream Syndrome (Paul and Meyer, 2001, Walsh et al., 2005a). Despite the recognition of the problem, few studies have evaluated streams of semi-arid climates that have different hydrological characteristics with perennial streams. In Nigeria in particular, studies of