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The suspended sediment concentration response of three small streams draining quartzites and quartz-schists in southwestern Nigeria to storms of varying magnitude are presented. A total of 1468 water samples from 62 storm responses with peak stream discharge values ranging from 80 to 120 I s-' were analysed and storm and suspended sediment concentration hydrographs and hysteresis loops were used to depict the response patterns. The six different types of responses identified include the single and multiple discharge peak rises with sediment lead and lag and also the mixed response patterns. Both valley slope and channel erosion constituted important sources of suspended sediment. However, sediment availability, exhaustion, and flushing effects determined the variation in the different response types.

This study focuses on the effects of urbanisation on the morphology and hydraulic geometry of the Ekulu River in Enugu, southeastern Nigeria. Measurements of channel properties were taken along a 25 km stretch at 45 sites grouped into three sections: section A, upstream of the town (15); section B, within the town (15); and section C, downstream of the town (15). Spatial interpolation techniques were used to predict channel morphometric properties within and downstream of Enugu on the basis of upstream relationships. The independent variable in the analysis was drainage area, used as a surrogate for discharge. In section A, channel parameters increased systematically downstream with basin area. Within the town, channel parameters exhibited sudden dimensional increases. Based on sectoral relationships, measured channel dimensions showed moderate increases above the expected values, with average enlargement ratio indices of 34 per cent, 91 per cent and 65 per cent in width, channel capacity and depth, respectively, between sections A and B. Between B and C the channel exhibited average reduction ratio indices of 21 per cent and 27 per cent in capacity and depth, respectively, and an average enlargement ratio index of 17 per cent in width relative to the expected value. The increase in channel dimension within the town is explained by: (1) the confluence with a third‐order tributary; (2) the poorly structured, loose, incoherent and highly erodible channel bank materials; (3) high volumes of runoff generated from the impermeable urban surfaces; (4) urban hydrological routing due to urban drainage; (5) human traffic across the river banks; and (6) the huge volume of garbage and solid wastes dumped into the channel.

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The hydrological response patterns of some third order rivers in southwestern Nigeria are described in terms of regime, discharge variability and recession of flow from peak discharge in the rainy season to the lowest discharge in the dry season. The maximum and minimum discharges of the rivers coincide with the rainy and dry seasons respectively. Most of the rivers exhibit erratic flow with quick responses to storms and storm water abating quickly, while some have a very low groundwater contribution to streamflow, a phenomenon which accounted for their drying up for considerable periods in the year. The variability indices of discharge of the rivers range from 0.25 to 2.12 while the recession constants range from 0.64 to 0.98. The variability indices are much higher than those of basins of similar size reported from other studies. Three types of rivers are recognizable on the basis of their hydrological response patterns. It is observed that the nature of the surficial and solid geology has a greater influence on discharge characteristics than other factors such as depth of regolith and rainfall.

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