Assessment of Sediment Deposition Rates in Orashi River, Nigeria

Abstract

The dynamic nature of rivers as a result of natural and anthropogenic factors such as hydrology, geology, climate, land use, deforestation, urbanization, dam construction, dredging, pollution etc is of monumental consequences to its inhabitants and its surroundings. These dynamic natural and anthropogenic factors are observed in Orashi Rivers in the form of fluctuations in the volume of water, changes in depth due to sediment, and changes in geometry. These vagaries have remained unpredicted and hence the focus of this study. The aim of this research is to assess the rates of sediment deposition in Orashi river. The objectives are to determine the depth of some sections (catchments) of Orashi river bed for 2012, 2018 and 2024; determine the hydrodynamics parameters of some sections of Orashi river for 2018 and 2024, determine the surface runoff water of some sections (catchments) to the river, determine the volume of sediment deposition of some sections of Orashi river in two epochs, determine the most contributing factor to the sedimentation of the river using linear regression analysis. This study employed mixed methods of research using classical survey methods such as river current measurement, river cross-sectional area evaluation, river water discharge rate estimation, bathymetric operation, runoff water computation, sediment computation and multiple regression analysis. The linear regression by Least Squares Method (LSM) was carried out using data obtained for 2018 and 2024. Runoff water peak discharge (Qp) and River water discharge rate (Q) were used as the independent variables while the rate of sediment deposition was used as the dependent variable. The result shows the average velocity of the catchments in Orashi river for dry and wet season as 0.61m/s and 0.76m/s and the average discharge flow rate of each catchment in Orashi for dry and wet season as 711.75m3/s and 1594.54m3/s. The result shows the average sediment deposition ranges from 0.3m to 0.6m (3cm to 6cm) in Orashi river between 2012 to 2024. The linear regression analysis showed 46% by river water discharge and 54% by run-off water peak discharge. The research recommends, among other things, the dredging of Orashi river so as to avoid the overflow of river which causes flooding of their farmlands and residence.