Stormwater management is no longer a concern solely of large municipalities and quickly growing counties. Federal mandates to clean runoff are being implemented across the United States, and most developed countries have stormwater requirements. Bills such as the Energy Security and Independence Act of 2008, for example, requires all federal facilities at least 5000 ft2 in surface area to mitigate stormwater runoff using non-traditional techniques. Runoff has been documented to increase flooding, reducing ground water infiltration and shallow interflow. Pollutants in stormwater, such as nutrients, pathogens, and temperature, are all foci of watershed management plans, particularly those promulgated by EPA's Total Maximum Daily Load (TMDL) program. In response, universities and colleges have developed programs – both research and academic/teaching – focused on stormwater management. The purpose of this issue of the Journal of Contemporary Water Research and Education is to highlight how universities and other applied research-oriented organizations are responding to the new demands of stormwater management. The issue begins with a focus on alternative metrics that can be used to assess stormwater management. Most regulatory entities assess pollutant removal by implementing efficiency ratios (or percent of pollutants removed from stormwater). While this technique is simple to understand, many in the stormwater design community recognize that this methodology has become outdated (Strecker et al. 2001). Still, little change away from removal efficiencies has been observed among regulating authorities. Davis et al. present the fundamental pollutant removal unit processes employed by stormwater practices. They explain limits to how certain pollutants are mitigated and expectations associated with individual treatment practices. Battiata et al. present an alternative metric that focuses on annual volume reduction provided by stormwater management systems. Putting water into the ground or into the air to imitate what occurs naturally is clearly a design element that regulating authorities could require. Greenway explores an entirely different way of evaluating stormwater practices: assessing benthic health. She does this by presenting a few case studies from Australia. Much of the most innovative stormwater management has occurred in locations that are relatively wet (like the Pacific Northwest, the East Coast), but many federal mandates apply to drier regions as well. Gautam et al. discuss the unique nature of stormwater management in arid and semi-arid regions and point out how blind implementation of stormwater management plans from wetter locations will not work for much of the Western U.S. Selecting the appropriate practices to implement in a watershed or drainage catchment is a frequent challenge for designers and developers. Two articles, Young et al. and DeBusk et al., discuss practice selection for communities in the Mid-Atlantic U.S. Young et al. introduce an analytical heirarchy process (AHP) methodology that can be used to select practices without bias and test this method in Blacksburg, Virginia. DeBusk et al. examined several North Carolina watersheds to implement scores of practices. She and her colleagues identified ground-truthed limitations associated with land type and treatment need. As stormwater practices are implemented, many stormwater managers are discovering the need to have them maintained. Because millions of public and private dollars are invested to treat stormwater, if practices are not maintained, much of this money may prove wasted. Erickson et al. investigate how communities in Minnesota and Wisconsin are keeping practices in working order and which practices appear to be the simplest (or conversely the most tedious) to maintain. As its name, Journal of Contemporary Water Research and Education (my emphasis), implies, stormwater management does offer a wealth of opportunity to educate students. Stormwater practices can be integrated into college campuses and academic curricula. Welker et al. discuss exactly how this was done at Villanova University. The stormwater management on that campus not only serves to clean water, but also helps beautify the campus and unite the university with the surrounding community, perhaps changing the local population's opinion of stormwater management practices. Giacalone et al. surveyed public opinion in South Carolina regarding stormwater management needs and perceived costs. In what must be considered a very positive finding, communities that had active stormwater and watershed education efforts also had citizens who viewed the need for stormwater and watershed management favorably. The final article in the issue serves as a reminder for why innovative measures are needed and why the public would care about stormwater management. Chagnon provides a detailed account of very wet period in Illinois and the flooding it caused. Often the drivers for innovation of any kind are dramatic events. As guest editor for this special stormwater issue of the Journal of Contemporary Water Research and Education, I hope you enjoy this collection of articles from across the United States and Australia. The composite picture they paint of the future of stormwater management is very promising. William F. Hunt (“Bill”) is an Associate Professor and Extension Specialist in the Biological and Agricultural Engineering Department at North Carolina State University. He is actively involved with Stormwater Control Measure (SCM) research and is the leader of the Stormwater Engineering Research Group. Hunt is an active member of the American Society of Civil Engineers (ASCE) and the American Society of Agricultural and Biological Engineers (ASABE), where he has many committee leadership roles. Hunt conducts 20–25 workshops and other training events per year across NC and the USA, and is author or co-author of 33 peer-reviewed journal articles. He may be contacted at NC State University, Agricultural and Resource Economics, Box 8109, Raleigh, NC 27695, by phone: (919) 513–0185, or by email: bill_hunt@ncsu.edu.
Throughout the 2004 mosquito season, 52 stormwater retention facilities were sampled to characterize the seasonal occurrence and relative abundance of mosquito species in relation to the structural complexity and biological diversity of the facilities. The three different types of facilities included standard wet ponds (n=20), innovative ponds (n=14), and wetland ponds (n=18). All retention structures were sampled at the beginning, middle and end of the mosquito season so that seasonal changes in mosquito production could be characterized. Overall samplings, mosquitoes were collected from 34% of the retention structures. Fourteen species representing 7 genera were collected, but only 5 species (Culex erraticus, Cx. territans, Anophelesquadrimaculatus, An. punctipennis and Uranotaenia sapphirina) were commonly collected in all three types of stormwater management facilities. In general, the seasonal prevalence and relative abundance of mosquito species did not vary among three types of retention structures. A significant association (P<0.01) between the presence of mosquito larvae or pupae and the absence of mosquitofish was found for innovative and wetland stormwater retention facilities but not for standard retention facilities (P>0.05).
Low impact development (LID) stormwater practices are becoming more popular because of their ability to improve water quality and recharge groundwater. New regulations require water quality treatment of stormwater runoff in addition to reducing peak flows, especially in nutrient sensitive watersheds. Previously, the main focus of traditional stormwater practices had been on mitigating flooding and reducing peak flows; whereas, newer LID practices improve water quality and attempt to restore a site's natural or pre-developed hydrology. This is accomplished by promoting more evapotranspiration and infiltration. Three commercial shopping centers have been monitored from April 2008 to September 2009 to measure the performance of using LID stormwater treatment, traditional stormwater treatment, or no stormwater treatment. All three sites were monitored for water quality and hydrology, and they were located within 70-km of each other. The site with no stormwater treatment and the site with traditional stormwater treatment were located in Raleigh, NC, and the site with LID treatment was located in Nashville, NC. Since the sites did not receive the same precipitation depths for each storm, the hydrology data were normalized per area treated. The LID practices were designed to treat the first flush of runoff or water quality event. The LID site incorporated the use of bioretention, permeable concrete, and constructed wetlands. Seven bioretention cells of varying media depths (0.6-m and 0.9-m) treated the front asphalt parking lot, and permeable concrete treated the rear parking lot. Storage was added beneath the permeable concrete to completely capture a 2.5-cm event. The constructed wetlands treated rooftop runoff, miscellaneous paved areas, and outparcel lots. Each LID practice was monitored as a separate unit and the site was monitored as a whole system. Effluent was monitored from the retention basin at the site with traditional stormwater treatment. A mixture of parking lot and rooftop runoff was monitored at the site with no stormwater controls. In addition to the water quality and hydrology results, much was learned about the construction and implementation of multiple and large scale LID practices at one site. LID practices are typically more sensitive practices, so proper construction oversight, installation, and maintenance are vital to adequate functioning of these stormwater treatment devices. Errors at this site included: undersized bioretention cells, clogged bioretention cells, a continuously flowing bioretention cell due to interception of the water table, and constructed wetlands that remained flooded, resulting in vegetation die off.
Routine maintenance and proper construction oversight both need to occur during and after bioretention cell construction, in order to ensure proper functionality. Two sets of bioretention cells of varying media depths (0.6-m and 0.9-m) have been monitored for two, 12-month periods, in Nashville, NC. These bioretention cells are unique in that during the first monitoring period, the bioretention cells were (1) clogged with fine sediment from construction and (2) were severely undersized. Complete drawdown of the surface storage took 48 hours or more, as compared to the recommended 12 hours. Initially, the surface storage volumes for the 0.6-m and 0.9-m media depth cells were only 28 percent and 35 percent of the design storage volume, respectively. The design event for the bioretention cells at this site was 2.5-cm, but the system was overwhelmed frequently and overflow occurred for events as small as 0.9 cm. After one year of monitoring, the fines layer present in the top 7.6-cm was removed. Removal of this layer increased the surface storage volume of both sets of cells by 89 percent. With the increase in surface storage volume, more runoff was treated, and fewer events had overflow. The smallest event with overflow was 1.9 cm, and some events up to 2.8 cm were fully captured in the bowl. Overflow volume was reduced to approximately one-third of the volume from the first monitoring period. Moreover, removal of the fines layer increased the surface drawdown rate by up to a factor of 10. Pollutant load reductions increased for nitrogen species and total suspended solids because more runoff was treated. The results of this study highlight the reduced performance associated with improperly constructed and maintained bioretention cells. Even a small construction error in setting the base elevation for the bottom of the bowl or the emergency overflow structure can drastically reduce the bowl storage volume.
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