Matthew J. Burns

Urban Stormwater Runoff: A New Class of Environmental Flow Problem

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.

Urban rainwater harvesting systems : research, implementation and future perspectives

While the practice of rainwater harvesting (RWH) can be traced back millennia, the degree of its modern implementation varies greatly across the world, often with systems that do not maximize potential benefits. With a global focus, the pertinent practical, theoretical and social aspects of RWH are reviewed in order to ascertain the state of the art. Avenues for future research are also identified. A major finding is that the degree of RWH systems implementation and the technology selection are strongly influenced by economic constraints and local regulations. Moreover, despite design protocols having been set up in many countries, recommendations are still often organized only with the objective of conserving water without considering other potential benefits associated with the multiple-purpose nature of RWH. It is suggested that future work on RWH addresses three priority challenges. Firstly, more empirical data on system operation is needed to allow improved modelling by taking into account multiple objectives of RWH systems. Secondly, maintenance aspects and how they may impact the quality of collected rainwater should be explored in the future as a way to increase confidence on rainwater use. Finally, research should be devoted to the understanding of how institutional and socio-political support can be best targeted to improve system efficacy and community acceptance.

Principles for urban stormwater management to protect stream ecosystems

Urban stormwater runoff is a critical source of degradation to stream ecosystems globally. Despite broad appreciation by stream ecologists of negative effects of stormwater runoff, stormwater management objectives still typically center on flood and pollution mitigation without an explicit focus on altered hydrology. Resulting management approaches are unlikely to protect the ecological structure and function of streams adequately. We present critical elements of stormwater management necessary for protecting stream ecosystems through 5 principles intended to be broadly applicable to all urban landscapes that drain to a receiving stream: 1) the ecosystems to be protected and a target ecological state should be explicitly identified; 2) the postdevelopment balance of evapotranspiration, stream flow, and infiltration should mimic the predevelopment balance, which typically requires keeping significant runoff volume from reaching the stream; 3) stormwater control measures (SCMs) should deliver flow regimes that mimic the predevelopment regime in quality and quantity; 4) SCMs should have capacity to store rain events for all storms that would not have produced widespread surface runoff in a predevelopment state, thereby avoiding increased frequency of disturbance to biota; and 5) SCMs should be applied to all impervious surfaces in the catchment of the target stream. These principles present a range of technical and social challenges. Existing infrastructural, institutional, or governance contexts often prevent application of the principles to the degree necessary to achieve effective protection or restoration, but significant potential exists for multiple co-benefits from SCM technologies (e.g., water supply and climate-change adaptation) that may remove barriers to implementation. Our set of ideal principles for stream protection is intended as a guide for innovators who seek to develop new approaches to stormwater management rather than accept seemingly insurmountable historical constraints, which guarantee future, ongoing degradation.

Will it rise or will it fall? Managing the complex effects of urbanization on base flow

Sustaining natural levels of base flow is critical to maintaining ecological function as stream catchments are urbanized. Stream base flow responds variably to urbanization. Base flow or water tables rise in some locations, fall in others, or remain constant. This variable response is the result of the array of natural (e.g., physiographic setting and climate) and anthropogenic (e.g., urban development and infrastructure) factors that influence hydrology. Perhaps because of this complexity, few simple tools exist to assist managers to predict baseflow change in their local urban area. We address this management need by presenting a decision-support tool that can be used to predict the likelihood and direction of baseflow change based on the natural vulnerability of the landscape and aspects of urban development. When the tool indicates a likely increase or decrease, managers can use it for guidance toward strategies that can reduce or increase groundwater recharge, respectively. An equivocal result from application of the tool suggests the need for a detailed water balance. The tool is embedded in an adaptive-management framework that encourages managers to define their ecological objectives, assess the vulnerability of their ecological objectives to changes in water-table height, and monitor baseflow responses to urbanization. We tested our framework with 2 different case studies: Perth, Western Australia, Australia and Baltimore, Maryland, USA. Together, these studies show how predevelopment water-table height, climate, and geology together with aspects of urban infrastructure (e.g., stormwater practices, leaky pipes) interacted such that urbanization led to rising (Perth) and falling (Baltimore) base flow. Greater consideration of subsurface components of the water cycle will help to protect and restore the ecology of urban fresh waters.

Flow-regime management at the urban land-parcel scale: Test of feasibility

AbstractOvercoming the hydrologic shortcomings of conventional approaches to stormwater management requires the protection or restoration of flow regimes at small scales. A better understanding of how stormwater management strategies can achieve this aim is needed. This study modeled 28,800 design configurations of a typical stormwater management strategy at the scale of urban land parcels across a range of urban densities and climatic conditions. Realistic design configurations that achieved three hydrologic response targets were identified as part of this modeling. It was found that meeting the targets required a combination of stormwater harvesting (using tanks) and infiltration (using rain gardens). This was possible primarily because the amount of harvested impervious roof runoff made a large contribution to a hydrologic target, which measured the ability to restore volumetric losses. Management of flow regimes at small scales will require policy mechanisms that necessitate both stormwater harvesting...

Building capacity in low-impact drainage management through research collaboration

Municipalities often play the principal role in the management of urban stormwater runoff. Dominant approaches involve routing urban stormwater runoff directly to streams, which has negative impacts on waterway health. Alternative management approaches, such as low-impact drainage management, have the potential to protect or restore urban streams, but remain rarely used. The Yarra Ranges Council (YRC), a municipality in Melbourne, Australia, collaborated with a team of researchers to construct stormwater-harvesting schemes, infiltration systems, and other measures (e.g., low-flow filters for water-quality treatment), as part of a catchment-scale experiment on low-impact drainage management. We held a workshop to elicit views of staff across a range of departments on insights gained from the experiment. We also gathered information on the design and construction of works to support findings from the workshop. Over time, research collaboration increased the capacity of YRC in low-impact drainage management. This increased capacity was linked to the temporary assignment of one of the researchers to work in the municipality’s engineering department. The researcher increased the confidence and trust of YRC in the use of new stormwater-management technologies. This temporary assignment into YRC helped support the long-term nature of the collaboration, which built trust over time. Our results support the views of scholars that civil experimentation can improve the capacity of municipalities to implement alternative approaches to urban stormwater management, with the aim of protecting or restoring streams.

Evaluating City Scale Surface Water Management Using a Rapid Assessment Framework in Melbourne, Australia

This research develops application of a strategic surface water management screening framework to enhance decision support in cities. Decision support in cities is typically constrained by resource costs of detailed analysis, this new methodology overcomes this through applying a simplified option screening process to evidence strategy and direct future detailed modelling of promising options. This study advanced on previous research by developing the methodology through option evaluation using a real world case study in collaboration with key catchment stakeholders. Research included stakeholder engagement workshops to identify catchment flood hazards and design potential management strategies, followed by application of the fast flood assessment framework to assess the flood reduction potential of each strategy. Theoretical implications indicate that city scale interventions demonstrate effective performance at managing design standard flood events. Practical findings indicate the framework to be an effective stakeholder engagement tool due to fast analysis of collaborative strategies. The key benefit to readers is understanding that fast, simplified urban drainage modelling can provide an opportunity to collaboratively screen flood hazards and generate evidence for prioritising detailed modelling in urban catchments.

Restoring in-stream habitat in urban catchments: Modify flow or the channel?: Restoring urban streams

Author(s): Anim, Desmond O; Fletcher, Tim D; Vietz, Geoff J; Pasternack, Gregory B; Burns, Matthew J

Stormwater harvesting: Assessing operational system performance

Abstract Recently, it has become apparent that stormwater harvesting has the potential to play a significant role in the sustainable management of water resources. However, it has been recognised that uncertainties concerning the operational performance of existing stormwater harvesting systems and also the lack of appropriate design standards are barriers to the widespread adoption and utilisation of stormwater harvesting. In this study, we gathered design and operational information regarding three stormwater harvesting systems located in Melbourne, as well as undertaking water quality and quantity monitoring. It was found that the design objectives of each system were developed in order to meet a range of environmental, social and economic outcomes, and while most of these objectives were met, some were rather qualitative and so were difficult to assess. The design of each harvesting system did not represent what was built and this is likely to be limiting operational performance. The ongoing drought has severely impacted on the volume of stormwater harvested from the two smaller systems, however, recent winter/spring rainfall has increased the volume of stormwater in storage. In comparison, the larger system has been able to provide significant amounts of stormwater during the very dry summer of 2007 and throughout the year. Preliminary water quality monitoring indicated that systems featuring WSUD devices are able to improve the water quality (in terms of TSS, TN and TP) of stormwater. Importantly, it appears that systems that do not have disinfection will more frequently have E. coli levels that exceed 10 orgs/100 mL.