William G. Lord

Stormwater control measure (SCM) maintenance considerations to ensure designed functionality

Abstract Great investment is made in the design and installation of stormwater control measures (SCMs). Substantial research investment, too, is made to optimise the performance of SCMs. However, once installed, SCMs often suffer from lack of maintenance or even outright neglect. Key maintenance needs for wet ponds, constructed stormwater wetlands, bioretention, infiltration practices, permeable pavement, swales, and rainwater harvesting systems are reviewed with many tasks, such as the cleaning of pre-treatment areas and the preservation of infiltration surfaces, being common maintenance themes among SCMs. Consequences of lacking maintenance are illustrated (mainly insufficient function or failure). Probable reasons for neglect include insufficient communication, unclear responsibilities, lack of knowledge, financial barriers, and decentralised measures. In future designs and research, maintenance (and lack thereof) should be considered. Assessing the performance of SCMs conservatively and including safety factors may prevent consequences of under-maintenance; and requiring regular inspection may help to enforce sufficient maintenance.

Field Evaluation of Four Level Spreader-Vegetative Filter Strips to Improve Urban Storm-Water Quality

An assessment of the performance of four level spreader–vegetative filter strip (LS-VFS) systems designed to treat urban storm-water runoff was undertaken at two sites in the Piedmont of North Carolina. At each site, a 7.6-m grassed filter strip and a 15.2-m half-grassed, half-forested filter strip were examined. Monitored parameters included rainfall, inflow to, and outflow from each LS-VFS system. A total of 21 and 22 flow-proportional water quality samples were collected and analyzed for the Apex and Louisburg sites, respectively. All studied LS-VFS systems significantly reduced mean total suspended solids (TSS) concentrations (p<0.05), with the 7.6 and 15.2-m buffers reducing TSS by at least 51 and 67%, respectively. Both 15.2-m VFSs significantly reduced the concentrations of total Kjeldahl nitrogen (TKN), total nitrogen (TN), organic nitrogen (Org-N), and NH4-N (p<0.05), whereas results were mixed for the 7.6-m VFSs. Significant pollutant mass reduction was observed (p<0.05) for all nine pollutant f...

Effectiveness of LID for Commercial Development in North Carolina

AbstractThe purpose of this project was to characterize runoff and pollutant export from three commercial sites: one with no storm water control measures (NoTreat), one with a wet detention basin (WetBasin), and one with low impact development (LID) measures. The sites were located in the Piedmont and Coastal Plain physiographic regions of central North Carolina. Rainfall, runoff, and pollutant concentrations were monitored at each site for more than one year by using automated rain gauges and samplers. The storm event mean concentrations (EMCs) of total kjeldahl nitrogen (TKN), nitrate+nitrite nitrogen (NOx-N), and total phosphorus (TP) in runoff were generally less than corresponding EMCs for many other urban areas in the United States. Also, EMCs were similar to those found for eight parking lots in North Carolina. Storm runoff to rainfall ratio was greatest for the NoTreat site and least for the WetBasin site, which was anticipated because the NoTreat site had no detention/storage and the WetBasin sit...

Constructed Storm-Water Wetland Installation and Maintenance: Are We Getting It Right?

Constructed storm-water wetlands (CSWs) have become one of the more popular storm-water control measures (SCMs). CSWs offer a hybrid between larger detention technologies like storm-water wet ponds and newer green infrastructure technologies. The systems are characterized as being predominately shallow retention practices, with water elevations sufficiently low to support diverse flora and fauna. Figs. 1(a–c) illustrate several successful examples of CSWs. Many researchers have found that CSWs remove sediment, nutrients, and metals from storm-water runoff (Greenway 2004; Hathaway and Hunt 2010; Line et al. 2008; Kohler et al. 2004; Wadzuk et al. 2010). One of the principal drivers for the use of storm-water wetlands is the amount of credit awarded to them by various governmental agencies with respect to nutrient removal and sequestration [North Carolina Department of Environment and Natural Resources (NCDENR) 2009]. The apparent improvement in nutrient capture from storm-water runoff over that of storm-water wet ponds is one of the main reasons designers choose CSWs over the more traditional wet pond. Extensive coverage of vegetation allows for several pollutant removal mechanisms: filtration of particles, stabilization of sediments, nutrient uptake, microbialrhizophere interaction to promote nitrification and denitrification, and the provision of increased surface area for biofilm/periphyton growth (Greenway 2004). In regions where thermal loads threaten cold water fisheries, CSWs have been shown to release cooler water to streams than do wet ponds because of the shading caused by the vegetation—but absent from wet ponds (Jones and Hunt 2010). Some concerns have also presented themselves with respect to CSWs, which have prevented the practice from outright replacing the wet pond. Foremost among them is the threat of mosquito infestation that wetlands invariably face in relation to the public (QDNR 2000). Research has shown that exorbitantly high mosquito populations need not accompany CSWs, provided they are diversely vegetated (Greenway et al. 2003; Hunt et al. 2006). However, if wetlands are allowed to become monocultures of specific mosquito-protective plants, such as Typha spp. (commonly referred to as cattails in the United States), they can become the very mosquito breeding grounds that the public fears (Greenway et al. 2003; Hunt et al. 2005). If storm-water wetlands are to be constructed, they must both (1) meet their intended water quality (and hydrologic) design goals and (2) not be a public nuisance. Anecdotal observation of CSWs constructed worldwide shows how many well-intended CSW designs fail. Two principal reasons were identified: One appears to be that not enough care was taken to ensure the storm-water wetlands’ normal pool elevation was appropriately shallow (that is, often the elevation of water in CSWs is too deep). The cause has been previously identified by Greenway et al. (2007). The second is clogging of the outlet structure that artificially raises the elevation above normal pool for extended periods of time. In both cases, simple preventative actions could be taken to ensure constructed storm-water wetlands maintain their designed integrity. The purpose of this forum is to document how poor design and inadequate management of two CSWs caused each to effectively become wet ponds, which results in (1) a reduced efficiency in the removal of some pollutants; (2) a degradation of biodiversity, which leads to an increased risk of having the wetlands become mosquito breeding grounds; and (3) degraded aesthetics.

Inspection and Maintenance Guidance for Manufactured BMPs

ASCE/EWRI has assembled a Task Committee on guidelines for certification of manufactured stormwater BMPs. A nine-member subcommittee for maintenance was tasked by the larger committee to develop maintenance guidelines for manufactured stormwater BMPs. The subcommittee has developed recommendations for manufactured BMP maintenance in the following seven areas: (1) designing for maintenance, (2) defining standard maintenance triggers, (3) defining maintenance fundamentals for all manufactured BMPs, (4) defining maintenance tasks by BMP design; hydrodynamic or filter design, (5) identifying entities best able to maintain manufactured BMPs, and training requirements, (6) identifying entities to train maintenance providers, and (7) reviewing recommended disposal techniques for captured pollutants.

Stormwater BMP inspection and maintenance program in North Carolina - a 3 year update.

Stormwater BMPs are being installed across the United States and studies show they are not being properly inspected and maintained. If not properly maintained, stormwater BMPs will not perform as intended or fail, but little guidance or training on maintenance and inspection procedures is available. The North Carolina State University Cooperative Extension Service developed a 1.5 day Stormwater BMP Inspection and Maintenance program in 2007 that has trained and certified more than 1250 local government officials, design professionals, and landscape maintenance practitioners from across the United States. The course consists of 12 modules that range from stormwater regulations to parking lot BMPs. A learner feedback loop has been incorporated into ongoing development of the course and information is being gathered about whom does maintenance, how it is done, and how often it is performed. Upon passing an exam, the Extension Service certifies an individual for 3 years, when a 4 hour recertification class is being offered. To date, approximately 10 cities and counties in North Carolina are requiring certification for anyone who inspects or maintains stormwater BMPs.

Comparison of Low Impact Development Treatment, Traditional Stormwater Treatment, and No Stormwater Treatment for Commercial Shopping Centers in North Carolina

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 sites 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.