Application of Churchill and Fishers’ models in assessing dispersion coefficient and assimilative capacity of a natural river channel in Benue State, Nigeria

Abstract

This paper is aimed at using Churchill and Fishers’ models to predict dispersion coefficients and assimilative capacity of a natural river. In order to achieve this, river hydraulic data were generated from field sampling of Ngo River combined with data from literature and applied to the models. Results showed that slightly low to higher values of dispersion coefficients with increasing river distance along the study stretch were obtained using Churchill and Fisher’s models. The hydraulic characteristic of Ngo River show that the river channel varies from 5 to 22m during peak flow and 2 to 12m during normal flow period, the river can be considered as a small river with an average width of 8 to 26m, the depth of 0.8 to 2.0m and velocity of 0.3 to 22m/s. From the hydraulic measurement, it was established that the ratio of re-aeration rate constant (K2) to that of the de-oxygenation constant (K1) in all cases exceeded the minimum value of 2 needed to improve the oxygen level in a river. It was therefore found that the river has a fair assimilative capacity that can withstand reasonable level of shock loads. The values of the analyzed models performance of MAE, BN, RMSE, RRMSE, R2 and NSE gave a good fit.