Urban Stormwater Runoff: A New Class of Environmental Flow Problem

Christopher J Walsh,Tim D Fletcher,Matthew J Burns,Jack Anthony Gilbert

doi:10.1371/journal.pone.0045814

Christopher J Walsh, Tim D Fletcher + Show 2 more

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https://doi.org/10.1371/journal.pone.0045814

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Journal: PLoS ONE	Publication Date: Sep 19, 2012
Citations: 277	License type: CC BY 4.0

Affiliation: University of Melbourne, Monash University

Abstract

Environmental flow assessment frameworks have begun to consider changes to flow regimes resulting from land-use change. Urban stormwater runoff, which degrades streams through altered volume, pattern and quality of flow, presents a problem that challenges dominant approaches to stormwater and water resource management, and to environmental flow assessment. We used evidence of ecological response to different stormwater drainage systems to develop methods for input to environmental flow assessment. We identified the nature of hydrologic change resulting from conventional urban stormwater runoff, and the mechanisms by which such hydrologic change is prevented in streams where ecological condition has been protected. We also quantified the increase in total volume resulting from urban stormwater runoff, by comparing annual streamflow volumes from undeveloped catchments with the volumes that would run off impervious surfaces under the same rainfall regimes. In catchments with as little as 5–10% total imperviousness, conventional stormwater drainage, associated with poor in-stream ecological condition, reduces contributions to baseflows and increases the frequency and magnitude of storm flows, but in similarly impervious catchments in which streams retain good ecological condition, informal drainage to forested hillslopes, without a direct piped discharge to the stream, results in little such hydrologic change. In urbanized catchments, dispersed urban stormwater retention measures can potentially protect urban stream ecosystems by mimicking the hydrologic effects of informal drainage, if sufficient water is harvested and kept out of the stream, and if discharged water is treated to a suitable quality. Urban stormwater is a new class of environmental flow problem: one that requires reduction of a large excess volume of water to maintain riverine ecological integrity. It is the best type of problem, because solving it provides an opportunity to solve other problems such as the provision of water for human use.

Highlights

Humanity faces a major challenge to provide the world’s growing population with reliable and affordable water supplies, while protecting the ecological integrity of freshwater ecosystems [1]
While the imported water supply and exported wastewater of urban areas substantially alters the water balance of cities [5], in most modern cities with separate stormwater drainage and sanitary sewerage systems, these elements of the urban water system bypass, and have relatively little influence on, the flow regime of streams and rivers of the city themselves. It is the third element of the urban water system–stormwater, generally of a similar volume to imported water [6], but rarely considered by water resource managers, that has the largest effect on flow regimes of urban streams and rivers
The similarity of flow regimes in Olinda and Sassafras creeks (Figure 3) and their good water quality and ecological condition (Figure 1) demonstrates the potential for streams with substantial catchment urbanization to retain important elements of the flow regime and water quality that are likely to be required for the protection of in-stream ecological values

Summary

Introduction

Humanity faces a major challenge to provide the world’s growing population with reliable and affordable water supplies, while protecting the ecological integrity of freshwater ecosystems [1]. While the imported water supply and exported wastewater of urban areas substantially alters the water balance of cities [5], in most modern cities with separate stormwater drainage and sanitary sewerage systems, these elements of the urban water system bypass, and have relatively little influence on, the flow regime of streams and rivers of the city themselves. It is the third element of the urban water system–stormwater (runoff from impervious surfaces during and immediately after wet weather)–, generally of a similar volume to imported water [6], but rarely considered by water resource managers, that has the largest effect on flow regimes of urban streams and rivers

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