Hugh P Duncan

A Model for Urban Stormwater Improvement Conceptualisation

Catchment urbanisation leads to increased hydraulic and pollutant loadings into receiving waterbodies. Issues concerning pollution that endangers the sustainable utilisation of water resources have focused government authorities towards integrated catchment management, where both causes and effects of pollution are addressed. Recent research has provided a platform for improving urban stormwater management. The CRC for Catchment Hydrology (CRCCH) has recently developed a Model for Urban Stormwater Improvement Conceptualisation (MUSIC), which serves as a decision support system (DSS) that packages the results of many research activities undertaken at the CRCCH and other organisations into an easily used tool. MUSIC enables urban catchment managers to (a) determine the likely water quality emanating from specific catchments, (b) predict the performance of specific stormwater treatment measures in protecting receiving water quality, (c) design an integrated stormwater management plan for each catchment, and (d) evaluate the success of specific treatment measures, or the entire catchment plan, against a range of water quality standards. This paper describes the operation of the model, the principal algorithms, and research activities undertaken in the CRC directed at further enhancing the system.

New Insights into the Quality of Urban Storm Water in South Eastern Australia

Quantifying the quality of urban storm water is an important prerequisite to the effective management of urban runoff, which is recognized as the major nonpoint source of pollution in urban areas. Although data on urban storm-water quality are widely available, they are often based on relatively limited data sets, usually containing few samples per event and/or few events per catchment. This paper reports on a large scale monitoring of the key storm-water pollutants found in urban discharges during both wet and dry weather from seven urban catchments in South Eastern Australia. The catchments are all separately sewered (with wholly piped systems) with varying sizes and land uses. Using the same monitoring technique, between 16 and 52 pollutographs were captured at each site for total suspended solid (TSS), total phosphorus, and total nitrogen (TN), while event mean concentrations (EMCs) of heavy metals and major ions, as well as species of N and P, were recorded at a subset of sites. It was found that EMCs of TSS were around 50% less than have been typically reported in earlier literature. During wet weather, nutrients were similar to previously reported, as were most metals concentrations. However, zinc concentrations were significantly higher than previously reported. EMCs of TSS were higher during storm flows than in baseflow, while TN concentrations were consistently higher during baseflow. EMCs of all pollutants monitored were poor with simple hydrological parameters (e.g., event rainfall depth); however, event pollution loads correlated very well with the rainfall intensity to a power, summed over the event duration. It was not possible to distinguish an impact of land use on pollutant concentrations. The first-flush effect was found not to be significant at all sites except the smallest catchment with the simplest drainage layout (the roof of a large building). All these findings have significant implication for treatment strategies with the significantly lower than previously observed TSS requiring consideration in future modeling and treatment design.

Testing and Sensitivity of a Simple Method for Predicting Urban Pollutant Loads

This paper tests a simple two-parameter regression model, based on rainfall intensity, for calculating event loads of total suspended solids, total phosphorus, and total nitrogen from urban catchments. It also examines the sensitivity of the model to its two parameters and to the rainfall time step. This was done by using large data sets collected at six urban catchments in temperate Melbourne. It was found that the two-parameter model typically explains approximately 90% of the variation in event loads at a site. The model also predicts the within-event behavior of pollutants when the flow lag time is taken into account, with R2 correlations greater than 0.6 in most cases for both loads and concentrations at a six minute time step. Despite its acknowledged correlation with flow, rainfall intensity over short time steps is shown to be the primary driver of pollutant mobilization, and provides a practical means of predicting pollutant loads by using readily available data.

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