Reservoir inflow monitoring for improved management of treated water quality - a South Australian experience

Abstract

Large tributary inflows into water supply reservoirs caused by heavy catchment rain may be of concern due to problems associated with high levels of natural organic matter (NOM) present in the inflows. Themovement of these inflows within a reservoir is dependent on its relative density to the receiving waters. For example, if the inflow is denser (colder) than the recipient water it will travel along the base of the reservoir as an underflow and can penetrate as far as the dam wall water off-take to a water treatment plant (WTP). Field studies were conducted to track the passage of underflows through two South Australian reservoirs, Little Para and Myponga. Samples were collected before and during storm event inflows and analyses undertaken to determine NOM concentration, alum demand, disinfection by-product formation potential, and quality of the water. We demonstrate that by monitoring the movement of inflows into reservoirs, combined with changes in reservoir off-take levels, that the risk of NOM entering a water treatment plant can be reduced which in turn will lower water treatment costs by reducing alum dosing levels and lessen the risk to human health by reducing disinfection by-product formation.