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Evaluation of the Longitudinal Dispersion Coefficient for Dor-Nwezor-Bodo River using Tracer Experiment and Theoretical Measurement

Uyigue L and Achadu M. Abah

This paper is focused on determining the longitudinal dispersion coefficient of pollutants in the Dor-Nwezor-Bodo River, located in Ogoni land in the present Rivers State, Nigeria. The measurement of the longitudinal dispersion coefficient for this River will help to ascertain the degree to which the concentrations of pollutants introduced at upstream will dilute at downstream. This parameter will help in the effective control and management of the River Water pollution. Basic hydraulic properties of the River that was measured for this study: flow velocity=0.22 m/s, test travel length (between tracer injection and sampling)=450 m, River depth=10.5 m, channel width=5.2 m, and hydraulic radius=2.7 m. Tracer experiments and theoretical (or empirical) model predictions were the methods adopted for this study. The tracer experiment is an indirect measurement that also adopted the constant distance-variable time method, for which the measured value of the longitudinal dispersion coefficient for the River is 6.572 m2/s. This value is an indication of a moderate response of injected pollutants to hydraulic mixing and dilution in the River Water within a travel distance of 450 m. The longitudinal dispersion coefficient for the River Water was also predicted using several theoretical models, while their levels of accuracy were assessed with respect to the measured value. Models from Seo and Cheong and that combined with Kashefipour and Falconer showed close approximations to measurement obtained from the Tracer experiment.