Abstract
This study examined the development of urban gullies in a part of Southwestern Nigeria. This was done with a view to determine the volume and amount of sediment loss from the 1st and 2nd order gullies in a cascade system. Twenty (20) towns were randomly selected from where thirty (30) gully systems comprising forty (40) 1st order and five (5) 2nd order gullies were measured with Tape and Total Station (TS). The gully dimensions measured include gully lengths, depths and cross sectional areas. The core samples were also taken from the study gullies for the determination of the soil bulk density. The results showed that the mean volume of soil loss from the 1st order and (2nd) order gullies in the study area are 1612.633 m3 and 1629.922 m3, respectively. The weight of the estimated sediment loss from the 1st order and 2nd order gullies are 2661.621 and 2657.318 tonnes, respectively. The result further showed that the total soil loss of 119661.442 tonnes was obtained from the study gullies and that the 1st order gullies accounted for 87% (106,375 tonnes) of the total soil loss. This was an indication of soil degradation in the area.
Highlights
Gullies have been recognized as an important environmental threat in many parts of the world [1]
The values obtained in this study was in the same range for the values obtained for urbanized city of Miami-Dade and Gainesville in Florida which were averaged at 1.63 g/cm3 and 1.52 g/cm3, respectively [34,35]
This study investigated the development of urban gullies in southwestern Nigeria
Summary
Gullies have been recognized as an important environmental threat in many parts of the world [1]. Past studies, for example, [13,14] in AdoEkiti; [15] and [16,17] in Ilorin, focused on the contribution of rainfall parameters on sediment generation and distribution from various land use surfaces in the urban areas. These studies showed that increase in volume of runoff generated from large areas of impermeable urban surfaces coupled with loose and incoherent nature of the soil on steep surfaces and from unpaired drains contributed largely to gully formation/development in urban areas [see 10]. The main objective of this study is to document sediment loss from 1st and 2nd order gullies in urban areas of southwestern Nigeria
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