Baseflow water quality behaviour: implications for wetland performance monitoring

Abstract

A study was undertaken in Melbourne, Australia, to monitor pollutants conveyed in urban runoff during stormflows. Water quality monitoring was extended beyond the storm hydrograph, enabling post-storm baseflow samples to be collected. The study aimed to gain insights into the interaction between inter-event water quality behaviour and current wetland monitoring strategies used to report baseflow and storm event treatment performance. Extending water quality monitoring identified a secondary pollutograph for total nitrogen (TN) and total phosphorus (TP) (consisting predominantly of dissolved nitrogen and phosphorus constituents) suggesting that inter-event concentrations do not exhibit steady concentrations even when flow remains relatively constant. Monitoring strategies for baseflow and storm events need to be amended to account for the secondary pollutograph, which may originate from delayed stormflows conveyed through pervious media. The inter-event water quality behaviour suggests that storm events may impact on water quality well beyond the period of the storm hydrograph typically used to distinguish storm events. Consequently, treatment performance of wetland systems may have been frequently incorrectly estimated, given that higher concentrations of delayed dissolved stormflow pollutants entered the wetland after the storm hydrograph monitoring had ceased. Results from this study provide greater insights into the implications of elevated inter-event concentrations on monitoring (and reporting) wetland treatment performance. The combined effect of elevated inter-event concentrations and ambient water quality in wetland storage require further investigation, since current monitoring strategies used to ascertain baseflow and stormflow treatment performance are more suited to systems without permanent (ambient) storage

Keywords:

• Dissolved nitrogen
• urban runoff
• inter-event
• wetland water quality monitoring
• baseflow

Additional information

Notes on contributors

Geoff D Taylor

Geoff Taylor is a postgraduate research student for the Institute for Sustainable Water Resources, in the Department of Civil Engineering at Monash University. Geoff’s research focuses on urban wetlands and stormwater quality, with a specific focus on the nitrogen cycle and the conveyance of nitrogen constituents through constructed stormwater wetlands. He was also a researcher in the Urban Stormwater Quality Program of the Cooperative Research Centre for Catchment Hydrology and is currently a Research Assistant in the Facility for Advanced Water Bio-filtration (FAwB). Prior to his postgraduate studies, Geoff undertook research into nutrient cycling at a whole-of-farm scale with the Water and Soils division of Agriculture Victoria. Geoff has a degree in environmental science with first class honors, where he undertook research into eutrophication of receiving waters from the Macalister Irrigation District in Gippsland.

Tim D Fletcher

Tim Fletcher is Director of the Institute for Sustainable Water Resources at Monash University and a senior lecturer within the Department of Civil Engineering. He was the Leader of the Urban Stormwater Quality Program within the Cooperative Research Centre for Catchment Hydrology and one of the creators of MUSIC.

Tim’s research focuses on the prediction of stormwater quality (and its uncertainty), treatment performance, aquatic ecosystem responses, and integration within the urban water cycle.

Tim has also held a number of senior roles in the water and waterway management industries, including Water Resources Manager with the Corangamite Catchment Management Authority, Senior Environmental Planner with Melbourne Water, and roles with Central Highlands Water.

Tim Fletcher co-chairs the UNESCO International Hydrologic Program project on data for integrated urban water management, and is on the Editorial Board of the Urban Water Journal.

Tony H F Wong

Tony Wong is a founding partner and director of Ecological Engineering, and Chief Executive Officer of the Facility for Advancing Water Biofiltration. He has over 25 years experience in the fields of water resources management in the rural and urban environment, with a recent focus on the water aspects of ecologically sustainable development, particularly integrated urban water cycle management and water sensitive urban design. His expertise has been gained through consulting, research, and academia, and has received a number of industry awards for the projects he has led.

Tony’s principal research and technical design contribution to stormwater treatment elements has resulted in over 100 international journal and refereed conference papers, a book, chapters in a further four books, and a number of national and international invited keynote addresses. He also initiated the 1998 revision of Engineers Australia’s Australian Rainfall and Runoff and the 2002 project to publish Australian Runoff Quality. Tony was the editor-in-chief of Australian Runoff Quality, published in April 2006, a document which sets Australia-wide principles for sustainable urban water management. He now chairs the International Working Group on Water Sensitive Urban Design under the auspices of the Joint IAHR/IWA Committee on Urban Drainage.

Hugh P Duncan

Hugh Duncan has over 30 years experience in a range of water resources issues. Specialised areas covered during this time include forest hydrology research and modelling, future water resources planning, water demand management, the analysis, modelling, and projection of urban water demands, and review and modelling of urban stormwater quality. Since 1994 Hugh has been working with the Cooperative Research Centre for Catchment Hydrology and more recently its successor the eWater Cooperative Research Centre, in the area of urban stormwater quality research and modelling, on full time secondment from Melbourne Water.