Overview
Runoff from the urban environment is a major contributor of non-point source contamination for many estuaries, yet the ultimate fate of this stormwater within the estuary is frequently unknown in detail. This study investigated the relationship between catchment rainfall and estuarine response within the Sydney Estuary, Australia.
Model Setup
A verified hydrodynamic model — the Environmental Fluid Dynamics Code — was used in concert with measured salinity data and rainfall measurements to determine the relationship between rainfall and discharge to the estuary, with particular attention to a significant high-precipitation event. A simplified rational method for calculating runoff, based on daily rainfall, subcatchment area, and runoff coefficients, was found to replicate discharge into the estuary associated with the monitored event.
Key Findings
Determining freshwater supply based on estuary conditions is a novel technique that may assist researchers studying systems where field-measured runoff data are unavailable. The study concluded that because the monitored freshwater plume broke down within the estuary, contaminants associated with stormwater runoff from high-precipitation events (daily rainfall greater than 50 mm) were retained within the system for a longer period than was previously recognised.