William F. Hunt

SUDS, LID, BMPs, WSUD and more - The evolution and application of terminology surrounding urban drainage

The management of urban stormwater has become increasingly complex over recent decades. Consequently, terminology describing the principles and practices of urban drainage has become increasingly diverse, increasing the potential for confusion and miscommunication. This paper documents the history, scope, application and underlying principles of terms used in urban drainage and provides recommendations for clear communication of these principles. Terminology evolves locally and thus has an important role in establishing awareness and credibility of new approaches and contains nuanced understandings of the principles that are applied locally to address specific problems. Despite the understandable desire to have a ‘uniform set of terminology’, such a concept is flawed, ignoring the fact that terms reflect locally shared understanding. The local development of terminology thus has an important role in advancing the profession, but authors should facilitate communication between disciplines and between regions of the world, by being explicit and accurate in their application.

Field study of the ability of two grassed bioretention cells to reduce storm-water runoff pollution.

Two grassed bioretention cells including internal storage zones (ISZs) were monitored for 16 months in central North Carolina. Each cell had a surface area of 106 m2 and fill media depths were 0.75 and 1.05 m for the north (North) and the south (South) cells, respectively. Asphalt parking lot inflow and outflows were analyzed for nitrogen and phosphorus forms and fecal coliform (FC). Outflow volumes and peak flows for individual storms were generally less than those of inflow. Overall, except for N O2,3 –N , effluent nitrogen species event mean concentrations (EMCs) and loads were significantly (α=0.05) lower than those of the inflow, and nitrogen species load reductions ranged from 47 to 88%. Apart from fall and winter, during which a longer hydraulic contact time seemed to be needed, the ISZs appeared to improve denitrification. Total phosphorus (TP) and OP O4 -P EMCs were significantly lower than those of the inlet. Reductions were 58% (South) and 63% (North) for TP and 78% (North) and 74% (South) for ...

A Field Study of Green Roof Hydrologic and Water Quality Performance

Recent regulations intended to minimize the amount of nitrogen and phosphorus in stormwater runoff have resulted in interest in stormwater treatment practices to reduce nutrient loadings. In ultra-urban areas where typical treatment practices are not optimal because of large surface area requirements, green roofs are an option to improve stormwater runoff. The hydrologic and water quality performance of two extensive green roofs in eastern North Carolinas Neuse River basin were investigated. The two green roof designs were a flat 70 m2 area with an average media depth of 75 mm, and a 3% pitch 27 m2 surface area roof with an average media depth of 100 mm. Extensive green roofs typically have shallow media depths (less than 150 mm) with vegetation that requires minimal irrigation and maintenance. Each green roof retained a significant (p < 0.05) proportion of the rainfall observed, 64% of the total rainfall measured at each site. Peak outflow of runoff was significantly reduced (p < 0.05) from the green roof (average peak flow reductions of more than 75% were observed from each green roof), and each green roof substantially delayed runoff. On average, the total nitrogen (TN) concentrations in the green roof outflow were 2.7 mg L-1 higher than the rainfall (significant at p < 0.05) and 1.3 mg L-1 higher than the control roof outflow; TN amounts in the green roof outflow were 0.02 g higher than the rainfall and 0.12 g lower than the control roof outflow. On average, total phosphorus (TP) concentrations in the green roof outflow were 1 mg L-1 higher than the rainfall and 0.8 mg L-1 higher than the control roof outflow (both significant at p < 0.05); TP amounts in the green roof outflow were 0.07 g higher than the rainfall (significant at p < 0.05) and 0.05 g higher than the control roof outflow. It was determined that the media, composed of 15% compost, was leaching TN and TP into the green roof outflow. This field study demonstrated the importance of green roof media selection in locations where nutrient removal is a concern. Results from this study serve as a benchmark for the development of an optimal media that contains fewer nutrients initially within the media mix, yet provides adequate plant growth.

Ecosystem service provision by stormwater wetlands and ponds — A means for evaluation?

Stormwater control measures (SCMs) such as constructed stormwater ponds and constructed stormwater wetlands (CSWs) are designed to regulate runoff hydrology and quality. However, these created ecosystems also provide a range of other benefits, or ecosystem services, which are often acknowledged but rarely quantified. In this study, additional ecosystem services, including carbon sequestration, biodiversity, and cultural services, were assessed and compared between 20 ponds and 20 CSWs in North Carolina, USA. Carbon sequestration was estimated through the carbon content of pond and wetland sediments across a gradient of system age. Biodiversity was quantified in terms of the richness and Shannon diversity index of vegetative and aquatic macroinvertebrate communities. Cultural services were qualitatively assessed based on the potential for recreational and educational opportunities at each site. Ponds and wetlands were found to support similar levels of macroinvertebrate diversity, though differences community composition arose between the two habitat types. CSWs demonstrated greater potential to provide carbon sequestration, vegetative diversity, and cultural ecosystem services. This assessment provides an initial framework upon which future assessments of ecosystem service provision by SCMs can build.

Meeting Hydrologic and Water Quality Goals through Targeted Bioretention Design

AbstractBioretention is one of the most commonly used stormwater control measures (SCMs) in North America and Australasia. However, current design is not targeted to regulatory need, often reflecting an outdated understanding of how and why bioretention works. The purpose of this manuscript is to synthesize research to recommend a suite of design standards focused on the purpose of bioretention SCM. Both hydrologic (peak flow mitigation, infiltration, annual hydrology, and stream stability) and water quality [total suspended solids (TSS) and particulates, pathogen-indicator species, metals, hydrocarbons, phosphorus, nitrogen, and temperature] regulatory and stream ecology needs are addressed. Bioretention cells designed to meet a prioritized subset of those measures would be substantially different than cells that are designed for a different subset of needs. Designers have the ability to adjust bowl volume, media composition, media depth, underdrainage configuration, and vegetation type. This study exami...

Intra-event variability of Escherichia coli and total suspended solids in urban stormwater runoff

Sediment levels are important for environmental health risk assessments of surface water bodies, while faecal pollution can introduce significant public health risks for users of these systems. Urban stormwater is one of the largest sources of contaminants to surface waters, yet the fate and transport of these contaminants (especially those microbiological) have received little attention in the literature. Stormwater runoff from five urbanized catchments were monitored for pathogen indicator bacteria and total suspended solids in two developed countries. Multiple discrete samples were collected during each storm event, allowing an analysis of intra-event characteristics such as initial concentration, peak concentration, maximum rate of change, and relative confidence interval. The data suggest that a catchments area influences pollutant characteristics, as larger catchments have more complex stormwater infrastructure and more variable pollutant sources. The variability of total suspended solids for many characteristics was similar to Escherichia coli, indicating that the variability of E. coli may not be substantially higher than that of other pollutants as initially speculated. Further, variations in E. coli appeared to be more commonly correlated to antecedent climate, while total suspended solids were more highly correlated to rainfall/runoff characteristics. This emphasizes the importance of climate on microbial persistence and die off in urban systems. Discrete intra-event concentrations of total suspended solids and, to a lesser extent E. coli, were correlated to flow, velocity, and rainfall intensity (adjusted by time of concentrations). Concentration changes were found to be best described by adjusted rainfall intensity, as shown by other researchers. This study has resulted in an increased understanding of the magnitude of intra-event variations of total suspended solids and E. coli and what physical and climatic parameters influence these variations.

Hydrologic Performance of Bioretention Storm-Water Control Measures

The transportation and urban infrastructure relies heavily on impervious surfaces. Unmitigated rainfall runoff from impervious surfaces can lead to a myriad of environmental problems in downgradient areas. To address this issue, novel stormwater control measures (SCMs) are being emphasized and implemented widely to mitigate some of the impacts of impervious surface. Bioretention is a soil/media-based SCM that is often used for this purpose, but current design practices are highly empirical. This study compiles work from three research sites in three states to provide some fundamental underpinnings to bioretention design. Although all sites demonstrate different levels of performance, water volumetric performance trends are common to all. These trends are based on the available storage in the bioretention cell, termed herein as the Bioretention Abstraction Volume (BAV). The BAV is directly related to available media porosity and storage in the surface bowl. A finite capacity to completely store all runoff from smaller events is defined by the BAV. Normalization for this storage provides prediction for volumetric performance. Recommendations for bioretention design are provided.

OVERVIEW OF REGULATORY/POLICY/ECONOMIC ISSUES RELATED TO CARBON DIOXIDE

This is an overview of Session 2c dealing with the regulatory, policy and economic issues related to carbon dioxide and its impact on global climate change. The information is taken from the two papers presented in this session (the U.S. Perspective by Dennis Leaf and the European Perspective by Hans J.H. Verolme) and from the panel discussion that took place at the end of the session. The overview focuses primarily on the policy responses of both the United States (US) and the United Kingdom (UK) to changes in global atmospheric pollution. To a lesser extent, the progress of policy responses to these changes is discussed. The United Nations Framework Convention on Climate Change (UNFCCC) has been signed and ratified by over 180 countries. The UNFCCC contained no binding targets or timetables for emissions reductions. The Kyoto Protocol [United Nations. Kyoto Protocol to the United Nations Framework Convention on Climate Change. UNEP.IUC/99/10. Chatlelaine, Switzerland: United Nations Environment Programmes Information Unit for Conventions, for the Climate Change Secretariat, 1997] to the UNFCCC did contain targets and timetables for reductions of greenhouse gases on the part of developed countries. The US has signed but not ratified the Kyoto Protocol. The US has experienced some movement to reduce greenhouse gas emissions on the part of various levels of government, as well as the private sector. The UKs commitment to reducing green house gases is laid down in the UK Climate Change Programme 2000. The UK is a member of the European Union (EU). In this context, an example of EU-wide progress, the voluntary agreement with car manufacturers to reduce CO(2) emissions in new vehicles, will be discussed. In addition, there will be some discussion on the UK CO(2) trading scheme that created the first market in the world in April 2001. Overall, the policy process is constantly informed by scientific research. In the case of climate change, much of this work is carried out under the auspices of international scientific panels.

Indicator Bacteria Removal in Storm-Water Best Management Practices in Charlotte, North Carolina

Water quality degradation due to pathogen pollution is a major concern in the United States. Storm-water runoff is an important contributor to the transport of indicator bacteria from urbanized watersheds to nearby surface waters. With total maximum daily loads being established to reduce the export of indicator bacteria to surface waters, storm-water best management practices (BMPs) may be an important tool in treating indicator bacteria in runoff. However, the ability of these systems to remove indicator bacteria is not well established. A study in Charlotte, N.C., monitored nine storm-water BMPs (one wet pond, two storm-water wetlands, two dry detention basins, one bioretention area, and three proprietary devices) for fecal coliform and Escherichia coli (E. coli). A wet pond, two wetlands, a bioretention area, and a proprietary device all removed fecal coliform with an efficiency higher than 50%; however, only the wetlands and bioretention area had significantly different influent and effluent concentr...

Statistical evaluation of factors affecting indicator bacteria in urban storm-water runoff.

An urban watershed in Raleigh, North Carolina, was monitored for indicator bacteria during 20 rain events. Results showed elevated levels of E. coli, enterococci, and fecal coliform. Samples were compared based on seasonality and were found to be statistically different ( p<0.05 ) , with pairwise comparisons indicating significantly lower concentrations of E. coli and fecal coliform during the winter ( p<0.05 ) . Enterococci concentrations were substantially lower in the winter and fall, but no significant differences were found between seasons during pairwise comparisons ( p<0.05 ) . Correlation analyses showed multiple significant relationships between antecedent climate parameters, flow characteristics, and indicator bacteria concentrations. More detailed multiple linear regression yielded explanatory variables related to antecedent climate conditions. Variables were generally related to temperature and moisture conditions in the atmosphere and soil. The results of this study show indicator bacteria co...