Estimate of bed load transport and scour depth in Kwadna watershed in Minna, Niger State, Nigeria

Abstract

Knowledge of sediment transport has been used to determine whether erosion or deposition will occur beneath the hydraulic structures, especially the magnitude of this erosion or deposition, and the time and distance over which it will occur. This paper, utilizes the stream gauging by wading method in estimating the bed load transport and scour depth in Kwadna Basin. The estimate of bed load transport enhances the understanding and design of the hydraulic structures overlying water bodies. The current meter was used in measuring stream flow velocity in three critical points along the Kwanda stream. The measurement was used to derive an equation for depth of scour and the rate of erosion after a period of time. Laboratory tests such as sieve analysis and specific gravity were carried out on the samples obtained from the field which showed that the sediment is poorly graded gravelly sand material. The results of the laboratory tests as well as the stream flow parameters of the stream were used to compute the expected volumetric total sediment load transported daily as 889.33 m3/day with annual value of 338347.158 m3/year. Kwadna stream bed material had a geometric mean particle size, D50, of 0.993 mm and consequently, the river transported bed material of larger diameter which explains why there are more deposits of sediments in the basin. The depth of scour for points 1, 2 and 3 after 365 days of high peak rainfall were estimated to be 1.0238, 1.7753 and 1.7019 m, respectively. The findings of this work will help in selecting suitable cross sections for the river structures having observed problems arising from sediment transport and deposition so as to reduce the sediments negative impacts on such structures.