Overview of Urban Stormwater Impacts on Receiving Waters

Frequently reported degradation of urban waters indicates that discharges of urban stormwater may cause a variety of impacts in receiving waters [1]. Such impacts can be characterised with respect to their nature, time scales, spatial scales, and the types of receiving waters. The nature of the impact is usually classified as physical, chemical, microbiological or combined. Examples of physical impacts include increased flows (and reduced recharge of groundwater aquifers), erosion and sediment transport/deposition, temperature rise, and densimetric stratification. Chemical impacts contribute to changes in water quality through dissolved oxygen depletion, nutrient enrichment and eutrophication, and toxicity (both acute and chronic). Microbiological impacts may affect both recreational waters and shellfish harvesting areas. Finally, it should be recognised that these types of impacts usually occur in various combinations, which may be referred to as combined impacts and further described by ecological impacts and impairments of beneficial water uses.