Sources and management of urban stormwater pollution in rural catchments, Australia

Abstract

This paper assesses the impact and quantifies the relative contribution of stormwater runoff (diffuse pollution sources) and point pollution sources on the quality of receiving water in the urban catchment of Orange. The study results were employed to develop management strategies to control stormwater pollution at the catchment level. The Orange urban catchment has experienced moderate to high levels of pollution in terms of nutrients (P and N), suspended solids (SS), heavy metals, fecal coliforms, and, to a lesser extent, salinity (TDS). Treated sewage effluent (point source) contributed, on average, 5% SS, 29% total nitrogen (TN) and 41% total phosphorous (TP). The nutrient yield per unit area was 2-31-folds higher than those reported for other Australian urban catchments. The overall contribution of the urban sources accounted for 93% and 94% of the TP and TN mass loads, respectively. In contrast, stormwater pollution in coastal urban catchments, that have similar population and land use, is dominated by rural diffuse sources contributing 81-99% of nutrient mass loads. This striking difference is attributed largely to the position of the catchment with respect to the hydrological system. Orange urban catchment is situated at the headwater of its river system and as such rural runoff into the urban part of the catchment was limited. The coastal catchments, on the other hand, are located at the end of their river systems and thus rural inflow into the urban area is substantially higher than those in upland catchments. This comparative assessment may suggest that the relative impact, per capita, of urban stormwater pollution on the receiving water is more significant in the upland catchments than in the coastal catchments. A stormwater management plan (SMP), consisting of structural and non-structural strategies, was developed to control stormwater pollution and enhance the quality of receiving water.