Reservoir Released Waves as a Transient Riverine Pollution Mitigation Tool: An examination of the feasibility of using waves of water released from a reservoir as a response to pollution spills.

Pollution spills are a serious threat to rivers causing fish kills, and lasting damage to the biological systems of rivers. At present financial penalties are used to deter such incidents but no mitigation system exists. A multiple method approach involving a hydrological and water chemistry based field study, a flume tank experiment, a computer fluid dynamics model and a 1D flow model was under taken to examine the feasibility of using a wave of water released from a reservoir to dilute pollution spills. Nine waves were released from reservoirs on three different catchments. Water quality was measured downstream of sewage treatment works and the progress of the wave was tracked down the river with gauges. Additionally in one experiment a slug of rhodamine dye was released into the river ahead of a wave. To understand the impact of a wave on mixing processes within the water column, in particular longitudinal dispersion, a series of flume tank and computer fluid dynamics experiments were ran. In both experiment sets a wave was released from one end of a tank and a slug of either rhodamine dye, or tracked particles was released mid tank, the interaction between the wave and the dye was then captured as footage and analysed. Across the three sets of experiments waves were found to move significantly faster than the baseflow with mean velocities ranging between 0.86ms-1 1.63ms-1. In the Holme River a dye slug would be caught within 3 hours and 46 minutes. Catch up times and response times were both demonstrated with a dye test and estimated with a 1D model providing management focused results previously unreported in the literature. Dilution of water quality parameters including NH4 and conductivity was recorded during wave passage at the sewage treat works outflows in the majority of experiments. Peak dilutions of 59% for NH4 and 58% for conductivity were recorded. An increase in longitudinal dispersion with wave magnitude was observed in the computer fluid dynamics model but unclear within the flume tank.