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Chapter 8 – Synthesis of Our Current Understanding of Stormwater Ponds in Coastal South Carolina


Bridget E. Cotti-Rausch, Ph.D., S.C. Sea Grant Consortium, Coastal Environmental Quality Program Specialist, Charleston, S.C. Currently at the U.S. Environmental Protection Agency, Washington, D.C.

Correspondence: Bridget E. Cotti-Rausch, Ph.D. (


In 2007, the S.C. Department of Health and Environmental Control-Office of Coastal Resource Management (SC DHEC-OCRM), in cooperation with the S.C. Sea Grant Consortium (SCSGC), published State of the Knowledge Report: Stormwater Ponds in the Coastal Zone (Drescher et al. 2007). This effort highlighted pond research topics including water quality, hydrology, pollutant removal, sedimentation, modeling, and social sciences. It also outlined research and informational needs. Here, we revisit 18 questions highlighted in the report, identify progress made in the past decade, and discuss past recommendations in the context of our current understanding. Throughout, we incorporate SCSGC-funded projects, and when appropriate, data from neighboring states and national studies. In the SCSGC Strategic Plan 2018-2021 (herein “Strategic Plan”) stormwater ponds are specifically identified as a priority area for ongoing research. Therefore, we cite how each topic corresponds to priorities outlined in the Strategic Plan. Ultimately, we seek to provide guidance that reflects the existing landscape of stormwater ponds in coastal South Carolina and advance efforts to refine stormwater pond practices to maximize functionality, effectiveness, and cost efficiency.

TOPIC 1. State Regulatory Standards in the Southeast U.S.

The 2007 State of the Knowledge report described stormwater management in the Southeast in order to provide context for South Carolina’s standards. In light of changes in North Carolina and Georgia, we begin by revisiting these standards here.

South Carolina (S.C.)

The regulatory standards for Stormwater Management and Sediment Reduction in South Carolina were last updated in June 2002. Briefly, these include water quantity (flood) controls on the post-development peak discharge rates that cannot exceed pre-development rates for the two- and 10-year frequency 24-hour storm event. Additionally, discharge velocities must be reduced. Water quality is also addressed: “When ponds are used for water quality protection, the ponds shall be designed as both quantity and quality control structures.” Permanent ponds must store and release the first ½ inch of runoff over a 24-hour period from the site. Sediment storage must be calculated, but only for the duration of the construction activity. Additional regulations are in place for coastal counties, and for ponds constructed in the Critical Zone (Chapter 5). The statewide stormwater design manual provided by S.C. DHEC was last updated in June 2005, though a revision is anticipated. This manual states the designed permanent pool volume should be equal to one-inch of runoff per impervious acre on the development site. An average pool depth of four to six feet is described as “optimal” for water quality treatment. Additional design recommendations are described, including inclusion of forebays, and minimal flow length-to-width ratios of 1.5:1 to prevent runoff short-circuiting the basin. The manual provides a table of average pollutant removal efficiencies, though these are not for enforcement purposes.

North Carolina (N.C.)

In September 2016 the N.C. Department of Environment and Natural Resources, now the N.C. Department of Environmental Quality (NCDEQ), initiated changes to their statewide stormwater program (NCDEQ 2016). These included design requirements for wet ponds that reflect research on pollutant removal effectiveness. Major Design Standards include (

  • Basin discharges must be distributed over a vegetative filter strip.
  • Discharge rate of the treatment pool be drawn down over two to five days.
  • Average depth of permanent pool is calculated using a series of equations that considers pond surface area (top and bottom), volume of the permanent pool basin, and forebay.
  • Surface area to drainage area ratios adapted from Driscoll (1986) must be used to determine permanent pool surface areas based on pollutant removal efficiencies and calculated for individual regions (e.g., coastal, mountain), considering percent impervious cover.
  • The pond must include a forebay with a volume that is ~20% of the permanent pool.
  • A 10-foot wide vegetated shelf must be installed around the pond perimeter.
  • Short-circuiting of pond must be prevented; minimum length to width ratio of 1.5:1.

The NCDEQ program includes credits for removal of total suspended solids, total nitrogen, and total phosphorus, but no volume reduction credits. Bacterial removal is linked to the reduction in total suspended solids, but there are no specifications for reductions in fecal coliform counts or other microbial indicators. Stormwater regulations require that runoff is released over a period of two to five days; this increased residence time is intended to allow most suspended sediments and associated pollutants to settle out of the water. The basin is sized with additional volume to account for this sediment storage; at least one additional foot in addition to the permanent pool volume (main pond and forebay). These requirements must be met in order for a licensed engineer to receive a permit to construct a wet pond in the state. Major Design Elements must also be met in order to achieve pollutant removal rates for credit. The NCDEQ design manual also details maintenance requirements, including monitoring water clarity and algal growth. In the coastal counties, inspections should occur once a month, and within 24 hours of rainfall that exceeds 1.5 inches. Records should be made available upon request from an NCDEQ or local government inspector.

Georgia (GA)

In the 2016 edition of the GA Stormwater Management Manual Volume 2: Technical Handbook (GA Environmental Protection Department 2016), a variety of practices were recommended to improve runoff volume reduction and water quality. This manual described the Unified Stormwater Sizing Criteria that is intended to holistically address stormwater impacts from development. The statewide water quality treatment volume is equal to the runoff from the first 1.2 inches of rain (equal to an 85th percentile storm). Specifications for stormwater ponds include a forebay, a minimum length-to-width ratio for the pond of 1.5:1, and a maximum permanent pool depth of eight feet. The pollutant removal efficiencies described for ponds are similar to those found in the S.C. manual. There are no pollutant removal credits in GA, and wet ponds do not qualify for a runoff reduction volume credit.

In GA the above standards are only recommended, while in N.C. design specifications must be met in order to obtain a construction permit. Therefore, while the GA design manual has been updated more recently than in S.C., permit requirements for water quality improvements in both states have not progressed to the levels found in our northern neighbor. However, now that six of the eight coastal counties are regulated MS4s, additional guidance, including more strict design standards, can be found in their manuals, which are updated more regularly than the state’s (Chapter 5).

TOPIC 2. Inventory of Ponds

2007 State of the Knowledge Report

Question 1: How many stormwater ponds exist in the coastal zone?
Question 2: What is the cumulative volume/coverage of ponds?
Question 3: At what rate are ponds expanding?
Question 4: Do we need to classify ponds by size, land use, etc.?

Prior to the analysis presented in Chapter 1 of this report, the last comprehensive stormwater pond inventory for the South Carolina coast reported approximately 8,114 ponds, using aerial photography from 1999 (Siewecki et al. 2007). In the current contribution, Smith and colleagues utilized 2013 satellite imagery to quantify pond numbers, estimate pond acreage, and classify neighboring land uses. The researchers also calculated the rate of expansion in pond numbers over a nearly 20-year time span (1993 to 2013) and the coverage area relative to total development for the Charleston and Myrtle Beach metro areas. While development has increased by approximately 2% per year, cumulative pond aerial coverage has increased by roughly 4% over this period. Because stormwater ponds have proliferated so rapidly, tools that help stormwater departments meet the high demand for pond inspections can improve regulatory compliance and the lasting effectiveness of ponds as flood and water quality control measures.

Application: The 2013 geodatabase is available by request from the SCSGC. The Compliance Office of Berkeley County’s Stormwater Department requested and received the data in October 2017 to use this resource to improve their MS4 inspection program for private ponds.

TOPIC 3. Pond Design and Management

Ponds work as water quality Best Management Practices (BMPs) largely by removing particles via sedimentation. As Chapter 2 describes, pollutant removal capability is dependent on particle density, size, chemical composition, and pond hydrodynamics. But basically, the longer stormwater is retained within a pond system, the more likely both large and fine grain particles will be removed through sedimentation and biological uptake can occur. A 2007 study compared sedimentation and pollutant removal efficiencies in a single residential pond and a multiple pond series (herein “pond series”), on Daniel Island, in Berkeley County (Messersmith 2007). In this study, the single pond demonstrated a greater loss of water storage capacity (36% loss) as compared to the terminal pond in the pond series (15% loss) over the sampling period. The Messersmith study also showed that the pond series drained more slowly than the single pond: 75% of water left the single pond in just seven hours while it took nearly 24 hours for the same amount to leave the pond series. Due to enhanced sedimentation and biological uptake, the pond series out-performed the single pond in terms of removal of nutrients (nitrogen and phosphorus), total suspended solids, and fecal coliform bacteria.

While those data are now a decade old, a recent article in The Daniel Island News (Bush 2017) demonstrated the development’s ongoing commitment to effective stormwater management, especially in terms of flood protection. The developers engineered their BMP systems to hold a 25-year storm event, as compared to the S.C. DHEC-mandated 10-year storm. Additionally, they credit much of their success in flood prevention in the wake of hurricanes Matthew in 2016 and Irma in 2017 on the interconnectedness of their pond systems. So that, in this case, superior pollutant removal appears to be linked to flood control. For more information on Daniel Island ponds’ system, see SCSGC’s fall 2017/winter 2018 issue of Coastal Heritage magazine.

While the ponds described above are connected through an “intricate piping and drainage system” (Bush 2017), runoff enters ponds from multiple sources. To better understand pond water budgets, a year-long SCSGC-funded study by Smith and Peterson quantified inputs to three stormwater ponds in Horry County (from 2014 – 2016). The researchers found groundwater contributed between 2 and 5% of pond inflow during rain events and 6 to 26% over the course of the entire two-year study (Smith 2017). Overland sheetflow contributed between 15 and 18% of total input to the pond during rain events. In many residential areas, including those evaluated by this study, sheetflow travels over mowed turf grass and enters the pond carrying a pollutant load representative of the land use practices of the surrounding drainage area. In fact, between 40 and 50% of the nutrient loading to ponds was found to be delivered via sheetflow (Smith 2017). Excess nutrients lead to eutrophication and can result in algal blooms, with consequences for poor water quality in the pond. Another study of 14 residential ponds along the Grand Strand showed that sediment composition in ponds across the region was correlated to impervious surface cover and carried a largely terrestrial signature (Schroer et al. 2018). As the majority of fill materials are sourced from upland vegetation and other particle sources, algal growth is either remineralized within the pond or transported in the outflow (Schroer et al. 2018). These two studies reinforce the need for good upland management to maintain pond functionality. Beneficial activities include careful treatment with fertilizers to minimize excess nutrients flowing into ponds, as well as bagging and removal of lawn debris to prevent material introduction to pond systems that results in volume loss over time. As ponds receive particle loads from the surrounding area, a major issue for pond owners and managers is how quickly ponds lose storage volume and require dredging.

2007 State of the Knowledge Report

Question 5: How fast are ponds “filling in”?

The study by Schroer et al. (2018) addressed sedimentation rates and showed that accumulation ranged from just 0.05 to 0.57 cm/year and varied throughout the pond basin. Overall, the median time for these ponds to lose 25% of their volume was estimated to be 68 years (Schroer et al. 2018). Both this and the Smith and Peterson studies intentionally targeted ponds described as “typical” for the Grand Strand: those with no forebays, and little or no shoreline vegetation. These results differ markedly from those presented by Messersmith (2007) for the single pond on Daniel Island (near Charleston, S.C.) that lost nearly 40% of its storage volume in five years. According to Schroer’s estimates, sediment dredging operations would be required less frequently than the five to 10 years predicted by S.C. DHEC, while Messersmith’s study indicated 25% volume would be lost rapidly (S.C. DHEC 2005).

The contrast in fill rates between the Messersmith and Schroer studies could result from differing land uses, such as construction in the pond’s vicinity, and regional dissimilarities between the Tri-County and Grand Strand. These differences illustrate the difficulty in extrapolating broadly from a single study and the importance of defining a useful geographic range for data. For pond owners and managers, the range in possible sedimentation rates suggests the need to characterize individual sites in order to inform maintenance activities. Considering that dredging costs are calculated in terms of the volume of sediment removed and can exceed $700 per cubic yard, depending on the method used, pond managers should consider evaluating pond bathymetry to focus dredging in areas where sedimentation is greatest. We reached out to several pond professionals for their thoughts on dredging, and their universal recommendation was for pond owners to invest in bathymetric surveys. For a one-acre pond, these surveys can cost less than $1,000 (Quality Lakes Inc., pers. comm.).

Pond Bacterial Removal Capabilities

Bacterial removal efficiencies are linked to particle sedimentation. And as microbes can pose a major threat to shellfish, and bacteria such as Vibrio are associated with human illness, these microbes are heavily monitored in coastal waters. Ponds have been shown to be highly effective at removing microbial pollutants from runoff. However, in the Drescher (2007) review of 511 ponds, these removal efficiencies ranged from -47% (pond = source to receiving waters) to 99% (pond = sink). Results from two ponds studied in the Grand Strand showed that removal efficiencies for suspended sediments and E. coli averaged 75 and 90%, respectively (Smith 2017), supporting previous research in N.C. for E. coli (Hathaway et al. 2009; Krometis et al. 2009). According to the S.C. DHEC design manual, wet ponds can be expected to remove 45 to 75% of bacteria in runoff. Exploration of county and city stormwater design guides found that bacterial removal rates by wet ponds are classified as “moderate.” Compared with the local research, these design guides may be underestimating the upper limit on microbial removal efficiencies of ponds.

Broadly, the effectiveness of ponds as water and pollutant storage devices relies on enhancing runoff residence time. For example, the Smith and Peterson study found pollutant removal capabilities for the third pond in their study were non-significant based on the “short-circuiting” of water through the pond. Bacteria, and other pollutants, are often associated with small particles that take longer to settle out of the water column. The difference in settling times between very fine sand (100 μm diameter) and medium clay (1 μm) is seconds versus days. In the 2016 Final Report of the International Stormwater BMP Database, which compared the differences in influent and effluent concentrations for a variety of BMPs, wet ponds were shown to significantly reduce E. coli and fecal coliform bacteria in the outflow leaving ponds. The median reductions in these pollutants ranged from 2.4 to 25-fold for the ponds evaluated. Because this is a national database, the specific characteristics that determined the effectiveness of a given BMP were poorly characterized. Much of the variability in pond removal capabilities likely stems from differences in the residence time of runoff within a given pond and associated land uses.

Pond size should also be appropriately scaled for the drainage area. During construction periods, to achieve more than 60% reductions in total suspended solids, the pond surface area should be at least 1.5% of the watershed drainage area (Pitt 2004). In Washington, a study by Comings et al. (2000) found that increasing pond surface area relative to the drainage basin from 1% to 5% allowed water to be retained seven times longer. The size, depth, and shape are therefore important design criteria. Pond designs that use horseshoe or snake-like paths to route runoff between the inflow and outfall structures are recommended. Considering that storm events can mobilize pond sediments, a S.C. study suggested that building a deeper permanent pool (8 to 10 feet) could help prevent resuspension of sediments on the pond bottom (Moore 2010). Additionally, as settling of fecal coliform bacteria and total suspended solid removal rates are linked, knowledge of critical particle sizes should factor into pond design. The majority of microbes studied by Krometis and colleagues (2009) in two N.C. ponds were found to be associated with particles less than 10 μm in diameter, while neither pond studied reduced concentrations of particles less than 5 μm. To evaluate pond placement within the landscape, they also compared particles in runoff, near the inflow of ponds and the outflow structures, as well as downstream locations. They found there were no fractionation differences between particle-associated microbes in runoff and inflow samples and concluded that ponds located in upland areas were most effective at trapping pollutants (Krometis et al. 2009).

TOPIC 4. Alternative BMP Designs

Returning to our previous example of Daniel Island, we learned from these developers that they closely considered the natural topography of the island in their stormwater management plan, taking advantage of different strategies depending on the specific site characteristics. Therefore, a freshwater wetland system runs through a portion of the island and is engineered to receive a large portion of runoff allowing stormwater to follow several paths through the system. Here we consider how the incorporation of diverse BMPs impacts stormwater management; as raised in the 2007 State of the Knowledge report.

2007 State of the Knowledge Report

Question 6: What stormwater pre-treatment procedures are most effective?

A common critique of pond systems is their limitation on sedimentation efficiencies for small solids; the smallest particles that can be reliably removed by this process are found to be 2 to 5 μm in diameter (Camp 1952). Therefore, pond systems benefit from pre-treatments or post-treatments that can retain finer sediments. This especially concerns clay particles, that we understand from the work cited in Chapter 2 and Chapter 3 are often associated with a variety of potentially harmful contaminants (e.g., cadmium, copper, microbes). A study by Hathaway et al. (2009) in Charlotte, N.C. compared the bacterial removal efficiencies for a variety of stormwater BMPs. All BMPs tested removed fecal coliform bacteria at efficiencies greater than 50%, while a bioretention swale and wetland had removal efficiencies of 89 and 98%, respectively. These exceeded the capabilities of the wet pond studied (70%); this study supports the use of a variety of treatment practices to improve downstream water quality.

Ponds also perform relatively poorly with respect to nitrogen; S.C. DHEC states the average removal capability of wet ponds to be between 30 and 45% (S.C. DHEC 2005). The Smith and Peterson study cited previously found total nitrogen was reduced by ~45% in two Grand Strand ponds. The 2016 International BMP Database Summary Statistics showed that ponds significantly reduce total nitrogen but at only a ~20% removal rate (inflow = 1.24 mg/L versus outflow = 1.00 mg/L) (Clary et al. 2017). Removal of nutrient pollutants is best accomplished by vegetated systems (Baker & Clark 2012; Lucas & Greenway 2008, 2011). Substantial uptake by plants can occur if low flow rates are achieved so that nutrients remain in contact with roots and soil microbes. Effective bioretention practices included those with underdrain systems that store water between storm events and allow denitrification to occur (Hunt et al. 2008). Phosphorus differs from nitrogen, as phosphate can be removed partially in ponds by sedimentation, with plant uptake serving as an additional treatment pathway. However, leaching of phosphate from sediments is possible if the environment turns anaerobic, as occurs in S.C. during periods of stratification, especially in summer. Therefore a properly aerated pond can help reduce this issue. Managers must consider both nitrogen and phosphorus loading when managing ponds, as research presented in Chapter 4 demonstrates both sources can promote unwanted and potentially toxic algal growth in fresh and saline systems. Unfortunately, the impact of vegetated buffers on nutrient uptake and cycling was identified as a major informational gap, as thorough studies on these topics are lacking for coastal S.C.

A retrofit to ponds that can be completed relatively inexpensively and may provide improved nutrient trapping ability is the addition of floating treatment wetlands (FTWs). In 2015, as part of the May River Action Plan, the Town of Bluffton used EPA 319 grant funds to build a 1.25-acre stormwater pond within the May River watershed in an area with elevated levels of fecal coliform bacteria (Jones et al. 2017). After the pond was built, the forebay exhibited algal blooms. The implementation of this BMP did not significantly reduce fecal coliform levels entering the watershed. Therefore, the town modified the pond using the “treatment train” approach, specifically, the addition of FTW and a filter sock at the outfall. Broadly, this approach uses a series of BMPs designed so that runoff flows from one to the next, which provides several opportunities to capture and treat runoff. Based on preliminary inspections, no blooms occurred following the implementation of FTWs, which the town attributed to uptake of nutrients by these plants (Jones et al. 2017). A study performed in Durham, N.C. evaluated the effectiveness of FTWs at removing nutrients and sediments in two ponds (Winston et al. 2013). In their study of pre- and post-retrofits, they found that the greater percent coverage achieved by the FTW resulted in better removal of pollutants. Overall, pollutant removal was modest for total phosphorus and total nitrogen, as the wetland plants took up a small fraction of these nutrients.

Low Impact Development Guidelines

In 2015, the S.C. Sea Grant Consortium and several partner institutions, including the North Inlet-Winyah Bay National Estuarine Research Reserve (NERR), the ACE Basin NERR, and the Center for Watershed Protection, published Low Impact Development in Coastal South Carolina: A Planning and Design Guide (herein “LID Design Guide” ). This manual discusses how LID practices can be incorporated into stormwater management in coastal S.C. Its purpose is to enhance access to LID implementation by providing engineering tools, planning guidance, and case study examples specific to the coastal zone. In Chapter 4 of the LID Design Guide, the authors discuss stormwater BMPs and the treatment train approach which can be used to maximize the utility of a given BMP for improving water quality. While this method can be advantageous, as shown in Daniel Island, there are challenges because it is specialized for variable site characteristics, including natural topography and various land use types. These challenges include design complexity, vegetation selections, and calculating practice depths. Most typically, the wet pond is the final step in a treatment train, while first-in-line BMPs include bioretention areas, green roofs, and mechanical stormwater filtering systems. A comprehensive national report by Clark and Pitt (2012) evaluated several general treatment mechanisms for removing particles in runoff, including sedimentation, physical filtration, and biological processes. This study also provided a useful table that summarizes notes for stormwater managers that can be used to determine effective pre-treatment and primary treatment options for a variety of pollutant classes.

From 2014 to 2016, researchers at Clemson University’s Baruch Institute of Coastal Ecology and Forest Science were funded by SCSGC to address the effectiveness of various stormwater treatment systems. Specifically, the work compared loading sources from forested land, natural wetlands, a wet detention pond, and a combined wetland-pond system (Hitchcock, unpubl. data). Both the pond and wetland-pond system reduced E. coli levels in discharge as compared to natural sites. Differences were also found between the basic pond and the modified pond-wetland system. They found that the addition of wetland plants and a baffle system (to increase retention times) to the pond resulted in significantly higher dissolved oxygen concentrations in the discharge. The pond had higher levels of solids discharged as compared to the pond-wetland system. The higher levels were attributed to the growth of algae in the pond but not present in the wetland-pond system, likely due to uptake of excess nutrients by the plants. This study also developed a GIS-based pilot LID Suitability Index for wetland (wet) and bioretention (dry) based applications in the coastal zone. Preliminary results showed that given varying soil types, topography, and seasonally high water tables, a larger percentage of land area favors bioretention systems in the Charleston area, while wetland-based systems were found to be preferable in the Myrtle Beach area. In the Beaufort area, bioretention is likely preferable on the sea islands, while the index recommends wetland systems to be used inland.

Application: This index can be found on Clemson’s Community Resource Inventory (CRI) data viewer , and is being improved through ongoing research by a graduate student at Clemson. The pond inventory 2013 layer (Chapter 1) will be added to the CRI so that existing stormwater practices can provide context for potential future LID applications.

TOPIC 5. Pond Lifecycles and their Role within the Coastal Landscape

Sediment Contamination and Health Concerns

2007 State of the Knowledge Report

Question 7: What is the level of sediment contamination?
Question 8: How often is sediment dredged, and where is dredged material placed?

The research summarized in Chapter 3 shows that ponds can be hot spots for contaminants. Because pollutants such as heavy metals are often associated with particles and ponds largely improve water quality by sedimentation, pond sediments can show elevated levels of toxicity as compared to natural sites. Contaminants with the potential for negative impacts on aquatic life that have been shown to be elevated in S.C. pond sediments include: cadmium, copper, and both contemporary-use and legacy pesticides.

At present there are no overarching requirements that pond sediments be tested for chemical or biological contaminants prior to excavation. In the absence of other regulatory mandates, recommended sediment testing guidelines are provided in Table 4.11 of the LID Design Guide, derived from the Wisconsin Administrative Code. However, this resource does not include guidance on copper or pesticide levels.

Sediment testing can be required if the dredging activity classifies for a Section 404 permit. Section 404 of the Clean Water Act, administered by the Army Corps of Engineers, regulates the discharge of dredged material into waters of the United States, including wetlands. We reviewed all public notices for Section 404 permits submitted statewide in 2016 and 2017 and found the majority of references to dredging stormwater ponds were as part of their initial construction phase. Over the two-year period we reviewed, a single permit was filed by the Sea Pines Plantation community (Hilton Head Island, Beaufort County) as part of a project to return their stormwater system to the original design standards. This permit concerned their network of 23 ponds, termed “lagoons,” constructed in the 1960s and 70s. The permit implied that this was the first effort by the community to dredge the accumulated sediments. From this information we can assume that these ponds were likely not filling in as rapidly as DHEC indicates. Though the Sea Pines permit for stormwater maintenance stated that the excavated material would be drained and hauled to “a suitable upland disposal site,” the permitting process was required in this case because this lagoonal system is tidally influenced and considered jurisdictional waterways. Our investigation into Section 404 permits, albeit narrow, suggests that dredged pond sediments are not regularly being used as fill material in areas that directly impact waters of the state.

However, we cannot draw from this record a comprehensive picture of what is happening with pond sediments. Perhaps private ponds are not being dredged often, or when dredging occurs the sediment is being disposed of in landfills or used as fill in ways that do not directly impact jurisdictional waterways. This information lies largely with pond management companies that are hired by communities to perform dredging operations. We learned through a local pond management company (Thomas Moore of Dragonfly Pond Works, pers. comm.) that they advise removing sediments when the pond has filled in and lost a third of its design capacity or when there is visible shallow water in the main body (< 1 feet). For this company, their preferred removal method is pump dredging as it is more efficient and environmentally friendly; this method also does not lower the water level or damage stocked fish populations. The costs of sediment removal per cubic yard typically run between $20 and $30, with nearby on-site disposal included. However, if the material needs to be transported to a further dump site, the costs can increase to between $55 and $65 per cubic yard. Disposal costs largely depend on where the dump site is located, with a ~$100 per hour charge associated with transport, and a roughly $75 fee for disposal at the landfill (per load; 14 to 15 cubic yards per load). For example, a disposal site located 30 minutes away that requires a 500 cubic yard dredge job adds up to $3,500 for hauling and $2,500 for disposal. Away from any wetlands or coastal waters, a dredge for a pond less than one acre would not require a permit. Echoing the recommendations of Quality Lakes, the representative from Dragonfly Pond Works also endorsed performing bathymetric mapping. As the research by Schroer et al. (2018) demonstrates, ponds do not necessarily fill in uniformly. Bathymetric mapping reveals where sediment has accumulated, allowing pond owners to target these operations and save the community money in the long run. Outside of dredging activities, we also considered the potential environmental impacts of accumulated pond sediments, discussed below.

2007 State of the Knowledge Report

Question 9: What public and environmental health risks might ponds pose?

Chemical Pollutants

Based on analysis of existing data from ponds in S.C., the heavy metals cadmium, chromium, copper, and zinc are elevated to levels in pond sediments that may pose significant ecotoxicological risks to benthic organisms. Legacy pesticides, those no longer used in urban applications, can also persist in pond sediments many decades after their last use. This may be due to their association with particles and exposure to low oxygen conditions in pond bottoms that increase their half-lives. While legacy pesticides persist at low levels, the pesticide found in highest concentrations in coastal pond sediments is the contemporary-use pesticide, chlorpyrifos. This insecticide was found in nine of 16 S.C. ponds tested by Weinstein and colleagues (2008), at levels that exceeded the Environmental Protection Agency (EPA) ecological risk assessment screening benchmarks. Chlorpyrifos is also synergistically toxic to aquatic invertebrates when found in the environment with the herbicide atrazine, another chemical commonly found in coastal S.C. pond sediments. Nationally, the U.S. Geological Survey (USGS) identified chlorpyrifos as one of a handful of problematic pesticides found often in urban areas due to its potential to cause pervasive ecotoxicology issues in aquatic systems (Stone et al. 2014). A 2012 report by an expert panel in California identified the need to include this insecticide in future monitoring efforts (Anderson et al. 2012). The S.C. Coastal Pesticide Decision Making Tool developed by University of South Carolina and many partners has Safety Rankings for the 100 most commonly used pesticides. This is a user-friendly, web-based tool designed for a broad range of audiences and can be used to improve upland management.

Sediment-associated pollutants derived from ponds are of greatest concern to human health if/when they become resuspended and transported into receiving waters, where they can come into direct contact with people engaging in various recreational activities. While chemical pollutants measured in S.C. ponds may be elevated to levels that pose a threat to benthic organisms, no published data show these sediments pose a risk to public health. However, much of the data presented in Chapter 2 and Chapter 3 of this report are derived from work published a decade ago. We can realistically hypothesize that contaminant levels in un-dredged ponds are likely higher now, as population growth and the associated increased coverage of impervious surfaces are linked to pollutant loading.

Harmful Algal Blooms (HABs)

Public health risks from exposure to stormwater ponds in coastal S.C. primarily include contact with HABs. Algal toxins in ponds have caused a variety of negative human health effects, including rashes, swelling, and respiratory ailments. Mycrocystins, a group of cyanobacteria toxins, have been found to be elevated in our coastal ponds to levels 10 to 100 times the World Health Organization limits for drinking water. From 2018 – 2020, mycrocystin (particularly the most potent form, LR) will be included in DHEC’s water quality monitoring in S.C.’s jurisdictional waters as part of the EPA initiative. While these do not now include ponds, broader guidance may result from these efforts.

Between the summers of 2014 and 2015, raphidophytes were associated with 40 blooms in coastal S.C. (Greenfield et al. 2015). Proliferation of these algae in ponds has been linked to nutrient loading and associated with certain bacterial species (Liu et al. 2008a, b). The diatom genus Pseudo-nitzschia is being reported more frequently in S.C.’s coastal stormwater ponds. This taxon is of particular concern because it produces the neurotoxin domoic acid, which has caused bivalve and dungeness crab fishery closures in other regions (Maine, west coast) of the U.S. A recent S.C. publication showed concentrations of the bacterial pathogen Vibrio were positively associated with dinoflagellate and raphidophyte blooms in coastal ponds (Greenfield et al. 2017). Vibrio was also positively associated with increased temperature, a further indication that climate change may result in increased incidences of Vibrio and HABs.

Application: Acknowledging that HABs are a leading public health and environmental health concern, SCSGC recently funded several projects that seek to improve our ability to rapidly detect, quantify, and ultimately respond more effectively to these threats. Drs. Dianne Greenfield and Joe Jones were funded in 2014 – 2016 to develop a novel molecular tool to identify HAB species that have been linked to numerous coastal fish kills and other public health concerns. Following upon the success of this research, Dr. Greenfield and colleagues developed a tool that focuses on the cyanobacteria genus Microcystis, which produces microcystin. The products of this project will enhance monitoring efforts and early warning detection systems.

Pond Impacts on Waterways

2007 State of the Knowledge Report

Question 10: What are impacts on receiving waters from pond discharges?

As ponds collect contaminants and promote HAB growth, there is concern over whether pond discharges are a source of pollutants to coastal waterways. As the inventory in Chapter 1 states, the majority of ponds in coastal S.C. are within the Critical Zone. This is an important issue along the coast. However, drawing from individual studies, it is not possible to provide a coast-wide answer as to whether ponds are a direct source of pollutants to waterways. The protection afforded by ponds to nearby receiving waters largely relies on the residence time of runoff within the pond. For flood control, the state requires that peak flows from two-year/24-hour and 10-year/24-hour storms be attenuated. The exact volume of runoff retained by a given pond then depends on the size of the development and proximity to nearby receiving waters and, in particular, shellfish beds. Some stormwater management programs have instituted stricter regulations, including the retention of a 25-year/24-hour storm event. However, in recent years S.C. has experienced heavy rain events that exceed even the 25-year storm event. In 2015 the state suffered a 1,000-year rain event, with some areas along the coast seeing rainfall that exceeded 28 inches in 24 hours. In these cases ponds can be overwhelmed, as indicated by measurements of fecal coliform concentrations and salinity of nearby tidal creeks. This has been noted by local stormwater managers and often attributed to poor pond designs. Some work by Greenfield and colleagues (2009, 2014b, 2017) shows that nutrient levels, HAB concentrations, and Vibrio spp. in ponds mimic trends recorded in receiving tidal creeks. On James Island, pesticide concentrations in a pond-tidal creek system were correlated, though pond chlorophyll and bacterial concentrations were not linked (Serrano & DeLorenzo 2008; DeLorenzo et al. 2012). This system demonstrated the importance of limiting introduction of pesticides and herbicides to ponds, as they can be a pathway to receiving waters.

Following up on her earlier work on stormwater and tidal creek systems (e.g., Blair et al. 2012; Sanger et al. 2013) Sanger and colleagues were funded by the SCSGC from 2014 – 2016 to evaluate the impact of 20 years of coastal development on tidal headwaters. These researchers also examined whether the widespread implementation of stormwater BMPs has a direct impact on tidal creek environmental quality within a watershed. Using models, the study found that use of BMPs in the suburbs does not alter the delivery of materials to tidal creeks as compared to what would be predicted based on the amount of impervious cover in a given area (Sanger et al. 2015).

Warning Signs

2007 State of the Knowledge Report

Question 11: What water quality indicators/levels may indicate an impaired pond or potential pollution sources for receiving waters?

While there are no water quality criteria for stormwater ponds, standards do exist for bodies of water that are classified as waters of the state (DHEC 2014). These standards vary depending on the use of the waterways, such as for recreational contact or for sustaining shellfisheries. For lakes greater than 40 acres in size and other freshwaters, nutrient and chlorophyll criteria are based on an ecoregional approach. For lakes in the coastal counties, total phosphorus must be less than 0.09 mg/L, chlorophyll less than 40 μg/L, and total nitrogen less than 1.50 mg/L. There are additional metrics for microbial pollutants (summarized in Chapter 3). The S.C. Estuarine and Coastal Assessment Program (SCECAP) developed various thresholds for establishing water quality indices for estuarine ecosystems (Bergquist et al. 2009, Sanger et al. 2016). This includes physical parameters (dissolved oxygen, pH), as well as chemical (nitrogen, phosphorus), and biological measures (chlorophyll, fecal coliform bacteria). Sediment thresholds and index are also included in this program. Smith (2017), based on the SCECAP thresholds for estuarine waters, found that the outlet waters of the majority of ponds were classified as “good” for total phosphorus measurements (< 0.10 mg/L), while more were characterized as “fair” (0.81 to 1.05 mg/L) or “poor” (> 1.05) as pertaining to total nitrogen concentrations. In their study, the ponds with highest nutrient levels were found to be associated with the greatest development densities. Failure to meet either DHEC standards for coastal lakes or SCECAP thresholds for quality indicates that a natural waterway is impaired. The application of these metrics to ponds should be used with caution because part of their designed function is to collect and store pollutants. The main concern is if ponds become a source of pollutants to natural waterways, as discussed in the previous section.

TOPIC 6. Modeling

2007 State of the Knowledge Report

Question 12: Which stormwater hydrological model is most applicable in coastal S.C.?
Question 13: Which commonly used models have been validated for coastal S.C.?

Federal Tools

The EPA’s Storm Water Management Model (SWMM) is used globally for planning, analysis, and design as related to stormwater runoff. The most recent iteration, SWMM 5, includes the hydrologic performance of LID controls. In 2017, the EPA released the National Stormwater Calculator (SWC), which is a free software application that accesses national databases on soil type, topography, rainfall, and evaporation for a given site. The SWC was created to be userfriendly and site-specific, so that anyone that needs to calculate and reduce runoff from a property can use the tool. This tool can analyze site hydrology for LID controls, and it provides an LID cost estimation module. Finally, this model lets a user evaluate runoff based on both historic controls and climate scenarios.

Local Models

Other commonly used stormwater modeling systems include the U.S. Department of Agriculture National Resources Conservation Service (USDA NRCS) curve number and unit hydrograph methods. These methods were modified by researchers in 2014 within NOAA’s National Centers for Coastal Ocean Science for coastal S.C.’s soil and topography to develop the stormwater runoff modeling system (SWARM) (Blair et al. 2014a, b). SWARM evaluates runoff for watersheds and sub-watersheds.

2007 State of the Knowledge Report

Question 14: Are designed storm events (the two- or 10-year rain event) reducing peak rates of flow to pre-development conditions? Are pre-development rates accurate for our low topography?
Question 15: What is the performance of ponds during small, frequent rain events versus large, infrequent events?

Managing Volume Control

During periods of high rainfall events in S.C., there is a possibility of ponds being overwhelmed by runoff. Managing runoff volume is an ongoing mission for Beaufort County, as shellfish are a valuable economic resource in the Lowcountry and fluctuations in salinity and the transport of microbial contaminants carried by runoff threaten the fishery. In 2006, Beaufort County evaluated pond basins in order to recommend improvements that addressed both volume control and water quality issues (Moore 2010 ). They proposed that ponds should be modeled for smaller, more frequent storm events rather than the large, less-frequent 10- and 25-year storms (EPA 2009). Ultimately this report concluded that the combination of wetland restoration and deeper permanent pools would improve volume controls and outflow concentrations. A recommended retrofit included the allowance for an eight to 10 foot permanent pool, and a freeboard that could detain a 25-year storm. The addition of a vegetated flood shelf was proposed to enhance volume control as well as promote evapotranspiration, sediment trapping, and bioretention of nutrients. As the proposed ponds would be designed to mimic nature, the study also indicated that the addition of wetlands would help retain microbial pollutants. By fall 2017, eight of the proposed projects were in process or had been completed. These were accomplished using 319 grants and public-private partnerships and the county plans to monitor these retrofits, including water quality indicators, as much as possible throughout their lifetime (Eric Larson of Beaufort County, pers. comm.).

A study for inland Richland County, S.C. was performed in 2010 to evaluate pond performance under seven design storm scenarios: one, two, five, 10, 25, 50, and 100-years with rainfall between 1.54 and 8.42 inches, along with storm durations of one, three, six, 12, and 24-hours (Huda & Meadows 2010). They found that during variable storm events the ponds frequently failed at protecting downstream waterways. In order to better prevent downstream flooding, the authors concluded that 24-hour extended detention of the one-year 24-hour storm is necessary and the permanent pool should be equivalent to the difference between post- and pre-development runoff volumes for the one-year 24- hour storm event (at least ½ inch from the entire watershed) in order to meet water quality standards. While models are powerful tools for determining effectiveness of stormwater management programs, they greatly benefit from ground-truthing with local data. Therefore the analyses of Huda & Meadows (2010) should be validated in the coastal region in order to verify similar results for coastal plain.

Application: Tweel and colleagues (2015) evaluated the volume sensitivity of tidal creeks in Beaufort County, with varying levels of development, using in-stream salinity, rainfall, and SWARM. Ultimately, the study identified six particularly volume-sensitive watersheds and developed BMP and climate change scenarios that can be used by the county to focus policy and management actions. Volume-control measures have since been included in Beaufort County’s stormwater design manual. A similar study in Charleston County is being conducted from 2018-2020 to assess the applicability of the findings to another coastal location.

TOPIC 7. Costs and Benefits of Stormwater Management

First, we considered the approximate costs of maintaining stormwater ponds, as they are the standard BMP in coastal S.C. We utilized the information from the survey of pond professionals conducted by researchers from the College of Charleston and presented in Chapter 6. Based on these data the average costs of constructing a new private pond ranges between $17,000 and $33,000 per acre. The survey also indicated that average annual maintenance costs are between $230 and $760 per year, or between 1 and 8% of the initial construction costs. This back-of-the-envelope calculation was made by applying a fixed pond size of 0.54 acres, determined to be the average size of development-related coastal ponds (Chapter 1). These data, while provisional, do compare well with the costs for the published studies described in Chapter 6.

As development continues to boom on the S.C. coast, future stormwater management costs will likely be impacted by changes to existing policies and regulations on the volume of stormwater discharged from a site. For example, in 2009 Beaufort County commissioned several studies evaluating the cost of a proposed change to an ordinance that would require all new developments or redevelopments limit their stormwater rates and volumes to remain at or below pre-development levels (Ramsey 2010; Thomas & Hutton Engineering Co. 2009). To control post-development runoff to pre-development levels, several methods were proposed, including runoff to be diverted and reused, stored in underground tanks, or channeled through LID structures. Thomas & Hutton Engineering Co. (2009) found that constructing ponds with additional storage volume to use for irrigation purposes increased the cost of residential development by 10 to 35%, depending on the exact land-usage. While this is expensive, it was deemed not cost-prohibitive by the county.

LID Implementation

2007 State of the Knowledge Report

Question 16: What are the comparative costs/benefits of more innovative practices?

Currently, nearly all design guides for S.C. coastal county stormwater programs include policies and standards to encourage developers to select LID practices such as bioswales, bioretention areas, rain gardens, and innovative technology BMPs like mechanical filtration devices. The level of detail provided in each guide varies by municipality. The LID Design Guide is directly cited by Horry and Georgetown counties as the recommended authority on implementing these practices. Specific LID requirements from individual county and municipal ordinances in coastal S.C. are briefly summarized in the LID Design Guide. Greater encouragement and/or direct incentivization of LID stormwater management practices are stated in the Comprehensive Plans of Charleston, Dorchester, Georgetown, and Jasper counties. Full-scale implementation of incentive programs through local ordinances has not yet occurred. In the Jasper County Stormwater Design Manual, LID practices such as revegetation, green roofs, and permeable pavements do qualify for quantifiable stormwater management credits through reduction in runoff and improved water quality protection. The LID Design Guide outlines various strategies for local governments to encourage and incentivize more innovative green infrastructure, and it appears that many are moving to do so. The national Center for Watershed Protection also provides general guidance on how to implement better site designs and evaluate and change development rules (CWP 1998; EPA 2008). The Oak Terrace Preserve community located in North Charleston, S.C. is a model community for implementing LID practices.

Application: The cost of implementing and maintaining LID practices is highly variable, and at present there are little data on how they compare to traditional BMPs, namely ponds. Research by Dr. Marzieh Motallebi at Clemson University is currently (2018-2020) being funded to evaluate a variety of stormwater control measures (SCMs) over their life spans, calculate marginal costs of the selected SCMs, and evaluate costs of both their economic benefits and ecosystem services provided. The proposed research will build on the LID Design Guide and help to answer what the comparative costs and benefits are of utilizing innovative stormwater management practices in coastal S.C.

TOPIC 8. Societal Impacts

2007 State of the Knowledge Report

Question 17: How can education and outreach to local government and homeowners be improved?
Question 18: What are economic costs/benefits?

Importance of Education and Outreach

The 2007 DHEC-OCRM report was completed just as coastal counties and cities were taking over responsibility for stormwater infrastructure within their jurisdictions. As the shift to largely MS4-based management occurred, stormwater education and outreach programs grew rapidly to meet the requirements of the NPDES minimum control measures (MCMs). The first two of these require public outreach, education, and public involvement. SCSGC was a founding education partner to the first of the education consortia, the Coastal Waccamaw Stormwater Education Consortium (CWSEC), which was initialized in the Grand Strand in 2004. In 2007, CWSEC became more formalized as they went through their first NPDES Phase II permit cycle. The Ashley Cooper Stormwater Education Consortium (ACSEC) has operated in the Tri-County region since 2007, while the Lowcountry Stormwater Partners, recently revitalized in 2016, operates in Beaufort, Colleton, and Jasper counties. Clemson Extension directs the activities for both the ACSEC and the LSP, while Coastal Carolina University is the academic partner of CWSEC. The SCSGC remains a lead educational partner for all three programs.

These platforms unite highly skilled education providers and communicators with a variety of partners, each with their own expertise (e.g., DNR, the NERR programs). As the networks have grown, they have largely met the need to improve education and outreach to local governments and homeowners proposed in the 2007 DHEC report. Staff of each consortium works directly with the MS4 liaisons and their respective communities. Activities that each provide include regional conferences, focused workshops, mass media and targeted outreach, teacher and classroom trainings, and formal professional training in pond management. The MS4 community relies heavily on these activities to educate homeowners and pond professionals in how to effectively manage the network of thousands of private ponds in the coastal zone. In Chapter 7 of this report, the authors discuss various strategies for communicating to a variety of groups on stormwater management.

As the economics chapter (Chapter 6) demonstrated through an international review of stormwater management practices, education is a best management practice for promoting improved, effective, and economically viable long-term strategies. Investing in educational programs, like those described above, is largely cost-effective for local government and can promote long-term behavioral changes. Because the majority of coastal S.C.’s programs are relatively new (< 10 years old), the long-term benefits of these programs have not yet been fully quantified.

Resources for Pond Owners

The EPA guidebook on stormwater wet ponds developed by the Center for Watershed Protection largely focuses on visual impairments related to the structure and functionality of the pond to retain water (EPA 2009). This guide focuses on pipe repairs and vegetation management, while water quality degradation related to bacteria, algal blooms, and low oxygen levels is only briefly addressed. Through the Master Pond Manager course offered by Clemson Extension, regional workshops, and local training efforts, pond owners are educated on what to look for that may indicate trouble in their own ponds. These programs cover topics related to dealing with nuisance animals, handling poor water quality, and managing plant growth and sedimentation around inflow and outflow structures. Primary water quality issues and causes include presence of algal blooms (= nutrients), fish kills (= toxins or low oxygen), and restricted flow (= sedimentation). Clemson Extension also provides soil testing services so if nutrients are a problem in ponds, the community can alter their fertilization routine to prevent nutrient over-loading to the system. These are vital programs, as private owners are responsible for the management and maintenance of the majority of coastal ponds. In 2018 Clemson Extension launched an online Master Gardener course that includes a variety of stormwater-related topics, such as planting and maintaining rain gardens.

Recognizing the need for ongoing education, Clemson Extension, in partnership with DNR, began hosting Stormwater Pond Working Group meetings entitled the “Healthy Pond Series”. This program was initiated in fall of 2017 and grew from an assessment performed after the 2016 Charleston Area Stormwater Ponds Conference. The content addresses informational needs that homeowners’ association (HOA) members and homeowners identified in a working group. Topics covered have included pond design and pond inspections. Each session features expert presentations, small group discussions, and a hands-on component, and they have proven to be popular free training opportunities for Charleston-area HOAs. Clemson Extension is evaluating whether they can expand the program to other regions.

Specialized Management Trainings

To promote good management practices, a variety of training options for pond professionals are available. Pond professionals, including those from out of state, benefit from Clemson Extension’s Master Pond Manager training. Clemson Extension also offers the Post-Construction BMP Inspector course that trains pond professionals to conduct routine, thorough inspections of stormwater BMPs. This is a statewide program that covers wet and dry ponds and green infrastructure practices.

Additional technical trainings are offered through the Center for Watershed Protection, a national nonprofit based in Maryland that works to protect waterways from the negative impacts of land-use activities. They offer tailored workshops to meet a variety of audiences, including stormwater managers, public officials, and developers. Topics include: development site design, residential stormwater practices, and regulatory compliance. In 2017 in Baltimore, the Center for Watershed Protection piloted a workforce development program, entitled the Clean Water Certificate Training Program, that helps participants gain skills and knowledge in green infrastructure practices. Education and public involvement is shown to be an effective strategy for ensuring proper pond management, and communication efforts need to identify and target the individual groups responsible for pond management over their life cycle.

Measures of Success

Each regional stormwater education consortium in S.C. develops strategies for public outreach and involvement, and documents the activities it performs as a way to evaluate how well the consortium is meeting its goals. They publish records of these activities and annual reports that are available on their respective websites. However, establishing if and how the implemented programs result in behavioral changes and cleaner waterways is a challenge. The California Stormwater Quality Association (CASQA; found that an effective stormwater management program should meet six outcomes, including changes in attitudes, knowledge and awareness, as well as behavioral changes in BMP implementation practices. CASQA developed an online portal where members of the stormwater community can access materials that will assist them in assessing the effectiveness of individual programs. While many of these materials are tailored for California, the Effectiveness Assessment Baseline Report includes guidance and specific metrics that could be applied to the evaluation of any stormwater management program.

TOPIC 9. Recommendations for Future Action

The 2007 State of the Knowledge report outlined several management recommendations to improve stormwater management practices by DHEC-OCRM to ultimately benefit our coastal receiving waters. These included:

  • Improve water quality by managing on a watershed basis.
  • Allow/encourage innovative stormwater management practices/standards (e.g., use vegetative options, install green infrastructure).
  • Research current use, feasibility, economic impact, and projected effectiveness of implementing pollutant removal efficiency standards for new systems.
  • Improve the Stormwater Maintenance Program (e.g., maintenance inspection procedures for emerging practices, sampling for sediment contaminants, include maintenance in realtor workshops, increase education to HOAs).

Over the past decade, the shift in responsibility from the state to the local level under the Phase II NPDES program means that direct management lies in the hands of county and municipal stormwater or public works departments. To better understand how stakeholders and decision-makers perceive current management needs, we convened a Stormwater Ponds Advisory Council (SPAC; Table 8.1), comprised of regulatory agents, private sector representatives, and nonprofits. Several of the issues listed above were addressed in preceding sections, including promotion of green infrastructure and educational practices. The remainder of the topics are addressed below, where we draw on conversations and feedback provided by SPAC members over a series of group and individual meetings, beginning in 2014.

Name Affiliation Subject Area
Jeff Adkins NOAA NOS – Office for Coastal Management Resource Economist
David Fuss Horry County Local Government – Stormwater
Shannon Hicks DHEC State Government – Resource
Eric Larson Beaufort County Local Government – Engineer
Chris Marsh, Ph.D. The LowCountry Institute Environmental Science and
Ed Oswald Private/Charleston Trident Association of Realtors Real Estate Agent
Calvin Sawyer, Ph.D. Clemson Extension Water Quality Specialist
Norm Shea Private Pond Management
Allen Smith Private/S.C. Aquatic Plant Management Society Pond Manager
April Turner S.C. Sea Grant Consortium Coastal Communities Extension
David Whitaker, Ph.D. S.C. DNR – Marine Resources
State Government – Resource

Table 8.1 The Stormwater Ponds Advisory Council (SPAC).

Watershed Management

Ensuring that stormwater is managed on a watershed basis is a challenge, especially in the era of MS4 programs, where greater than five political entities may be managing a single watershed. In some cases these disparate entities work together to design and implement strategies that are appropriate across jurisdictions. Therefore, it is paramount that agencies like SCSGC work across a variety of stakeholders to ensure science-based information is generated and utilized. For example, SCSGC was involved in a study conducted in the Beaufort area to identify tidal creek systems that are especially vulnerable to volume of runoff (Tweel et al. 2015). This included a watershed analysis across all major Beaufort County watersheds, which scaled up the results of this single effort. Importantly, the study utilized a new model (described above under Topic 4) that can assist other coastal counties and municipalities manage runoff on a watershed scale.

In the Grand Strand, the Waccamaw Watershed Academy (WWA), established in 2004 by Coastal Carolina University, is a unique program in the state. The research arm of the WWA addresses technical study of environmental problems and is performed at the Environmental Quality Laboratory, the only lab in the region with regulatory-level standards. Their mission is to understand the sources, transport, and impacts of pollutants in the Waccamaw River watershed. This includes the Volunteer Water Monitoring Program, a successful long-term initiative which helps local municipalities meet NPDES Phase II stormwater program requirements. The work of the WWA incorporates coastal S.C. research including work performed in the Tidal Creeks Project, led by DNR and co-funded by SCSGC (Sanger et al. 1999a, 1999b; Holland et al. 2004). This was seminal work in the field of evaluating and predicting pollution trends in tidal creek systems caused by development and associated increase in impervious surfaces.

Nationally, the EPA generates broad guidance for watershed management, while DHEC provides more specific watershed-based planning documents for the state. Additionally, DHEC has developed watershed-based plans for several specific watersheds, including the Savannah/Salkahatchie and the Broad/Edisto in the Lowcountry, and the Santee/Pee Dee in the Grand Strand. Section 319 grants, received from the EPA and administered through DHEC, are a source of funding for watershed-based planning activities that address NPS pollution. As part of the South Carolina Nonpoint Source Program, funds are dispensed through federal Section 319 grants and a state revolving fund; any state agency, local government, or public university is eligible to receive these grants.

Changes to Pond Design and Maintenance

Requiring that ponds, and other stormwater BMPs, meet minimal pollutant removal efficiency standards was proposed in 2007 and is still being discussed by DHEC and local managers. At this time there are no regulatory requirements for pond water quality, as mentioned previously in this synthesis. In meetings with the SPAC, we learned that information provided by the scientific community on water quality issues is valuable for agencies when proposing new policies to the legislature. Additionally, a better understanding of how effective (or not) ponds are at removing pollutants would be highly impactful. Our current report demonstrates that pollutant removal capabilities are highly variable and dependent on site characteristics and contaminant type. In order to provide more comprehensive management, we propose closer partnership with MS4 communities, as described under Recommended Priority 1 in the next section.

Other major challenges to proper pond maintenance, as cited by SPAC members, are related to the lack of knowledge of HOA members and property owners. Often, pond management decisions made by HOAs rely largely on aesthetic preferences, which in most places means clear cutting of grass to the pond’s edge. To combat misperceptions and promote positive changes, education is required at all stages of the pond life cycle as discussed previously. This opinion was reinforced by several SPAC members. In multiple conversations with stormwater managers, their greatest concern is about increasing awareness about ponds to the general public. At this time, BMP inspections required for Phase II MS4 programs cover structural function and not water quality measures. While structures can be a proxy for water quality issues, they cannot address function. And for many coastal counties and municipalities, even these inspection programs are in their infancy, so compliance rates are poorly characterized at this time. In Chapter 7 of this report, our communications team generated a detailed management booklet intended for a general audience and based on feedback from pond professionals. We describe additional strategies to address this issue below.

The Next Steps for the Stormwater Ponds Collaborative

Since 2006, SCSGC has funded 16 studies on stormwater BMPs, and an additional 11 studies on the impact of land use and runoff on downstream water quality issues. Not including the current effort, SCSGC and our partners have produced nine products that incorporate this science, including the LID Design Guide. At present, we are partnered with seven institutions and agencies working on stormwater management-related issues. Building on these successes, SCSGC now looks to the future and the next generation of stormwater management in order to best position ourselves so that we continue to serve as a helpful partner in the field. Because our involvement in stormwater is as both a research entity and educational partner, we work with a variety of stakeholders, each with unique relationships to both our work and stormwater in general. Below we outline some potential activity priorities we identified during the preparation of this report.

First, Sea Grant’s path forward in both stormwater research and outreach would benefit from an official needs assessment of our diverse partner groups. These include:

  • Coastal stormwater education consortia,
  • Academic institutions,
  • Local resource managers,
  • State agencies (e.g., DHEC, DNR),
  • Nonprofits (e.g., Charleston Waterkeeper, LowCountry Institute),
  • Private businesses,
  • Real estate professionals,
  • The development community, and
  • Local government stormwater managers.

The goal would be to identify priority needs and, together with the Homeowners’ Associations, to write a research prospectus for funding to address them. In the current report, knowledge or research gaps were identified by each project team and compiled in Appendix A8. Engaging our stakeholder communities to assist in prioritizing next steps from this curated list of knowledge gaps would be a useful step in creating a
comprehensive and meaningful prospectus. An additional resource that may help to facilitate this process is a needs assessment used by the Consensus Building Institute in their evaluation of Ohio’s stormwater management programs (Consensus Building Institute 2012). We recommend the list of questions generated in this report be used by SCSGC as an interview guide, with pertinent topics including:

  • Defining successful stormwater management,
  • Promoting positive behavioral changes,
  • Acknowledging citizen concerns,
  • Identifying inconsistencies and difficulties in implementation of various regulations,
  • Evaluating precipitation patterns and information needs,
  • Connecting users with trustworthy data sources, and
  • Determining an acceptable geographic range for projects.

The members of the collaborative and the SPAC are the appropriate first audiences to survey, but the process of preparing a prospectus can be extended to other partners with whom SCSGC regularly coordinates. Below we outline several priorities that were identified through previous meetings of the collaborative and SPAC that should be considered when developing the prospectus.

Recommended Priority 1

To evaluate the success of individual BMPs, as requested by stormwater managers, we believe the prospectus should continue and expand partnerships with local stormwater programs. Close partnerships with these programs would avoid the difficulties faced in extrapolating broadly from studies performed on private land due to ignorance of pond history and current management. This challenge is illustrated throughout the report. By partnering with local stormwater departments that manage BMPs on public property, these knowledge gaps are removed. As mentioned earlier, a potential funding source for monitoring is the 319 program administered by DHEC. The State Revolving Fund can also be utilized to explore the effectiveness of green infrastructure and innovative retrofits (e.g., inclusion of vegetated forebays, floating wetlands), especially in MS4s that have already identified, or even incentivized, the use of LID practices in their stormwater management plans. A priority area for future research, as identified by state and local regulators, should be developing the scientific basis for water quality thresholds in stormwater ponds. As described under Topic 5, creating standards or thresholds based on what is expected for natural waterways is not necessarily appropriate as ponds are small, often stagnant water bodies designed to collect pollutants. Therefore, a unique system should be considered to assess the health of a stormwater pond over the course of its lifetime.

As an example the Stormwater Action Monitoring (SAM), an ambitious monitoring project in the Puget Sound region, united municipal groups for monitoring needs. This program is paid for by nearly 100 cities, counties, state and federal agencies, and businesses. A portion of the monitoring strategy, developed by the State of Washington’s Department of Ecology, evaluates the effectiveness of various BMPs. This includes LID practices, retrofits, and structural and non-structural BMPs. While large in scope, SAM may be a useful guide for creating regional monitoring programs in coastal S.C.

Recommended Priority 2

To incorporate the societal aspects of pond management, volunteer monitoring programs could also be implemented. Lee County, FL has sustained a successful Pond Watch Program which utilizes citizen volunteers to monitor ponds for conditions such as nutrients and chlorophyll a that indicate problems with aquatic weeds and algae. The data collected through this program are used to calculate the Trophic State Index, a tool used in Florida to determine the biological productivity of a lake or pond. Elsewhere, a long-term citizen science stormwater pond monitoring effort in Toronto, Canada found nutrient concentrations (phosphorus and nitrogen) were often elevated relative to Canadian water quality standards (Scott & Frost 2017). Alongside local guidance from the WWA, successful citizen science pond programs such as these can be used as guides for developing and implementing new pond monitoring initiatives in coastal S.C. These would likely rely on state and local funds but could seek public-private partnerships with communities and businesses.

Engagement Opportunities

As stated earlier, SCSGC has a unique role as a funding entity, science-based information generator, and information broker. Therefore, we ensure that the results of relevant studies are communicated directly to those groups that can utilize the information. At present, SCSGC is an education partner to the three coastal stormwater education consortia. This provides a direct pipeline by which we educate the educators. For instance, in 2017 the Coastal Environmental Quality program specialist spoke at the Coastal Waccamaw Stormwater Education Consortium winter meeting to share information on recent and ongoing SCSGC-funded studies. Audience members included educational partners and MS4 representatives. One- or two-page progress reports, written by SCSGC’s Communications department in a language that speaks to stormwater managers and pond professionals, would be useful products. These could be disseminated via a bi-annual newsletter or linked to a SCSGC-hosted GIS application that highlights active research projects. An additional tool to assist in the dissemination of information is the South Carolina Coastal Information Network (SCCIN), a resource provided and maintained by SCSGC.

A final important aspect of communicating more frequently with our partners is to ensure we use a common language and reinforce a shared message. SCSGC will be partnering with Clemson Extension to create an interactive, online stormwater portal that will allow users to navigate science-based products alongside Clemson’s outreach and educational resources. We also are working with state and local agencies to revitalize a realtor training program. Through conversations with the real estate professional on the SPAC, we identified stormwater as an important issue facing agents and their clients along the coast.


While each chapter of this 2019 State of Knowledge Report highlights specific research gaps for given topic areas, we found that by evaluating the field holistically, an overarching need arose. Because the proliferation of stormwater ponds along the Southeast coast has created new aquatic habitat that lies in residents’ backyards, social, economic, and ecological issues are thoroughly intertwined. For example, mitigating the impact of nutrients on ponds and downstream water quality relies strongly on the behavior of community members. Therefore, all future research must apply an interdisciplinary approach to characterize the role of ponds within the landscape and their associated management challenges. The mission for SCSGC is to facilitate comprehensive research projects and diverse outreach materials that address the complex interdependence of pond systems and human actions.


Anderson PN, Denslow JE, Drewes A, Olivieri, Schlenk D, Scott GI, Snyder S (2012) Recommendations of a science advisory panel on monitoring strategies for chemicals of emerging concern (CECs) in California’s aquatic ecosystems. California Water Resources Control Board, Southern California Coastal Water Research Project, Costa Mesa, CA; Technical Report 692, 229 pp.

Baker KH, Clark SE (2012) Recycling vertical-flow biofilter: a treatment system for agricultural subsurface tile water. In: Garcia-Garizabal, Iker, Abrahao, Raphael (Eds.), Irrigation-water Management, Pollution and Alternative Strategies. InTech

Blair A, Lovelace S, Sanger D, Holland AF, Vandiver L, White S (2014a) Exploring impacts of development and climate change on stormwater runoff. Hydrological Processes 28(5):2844-2854

Blair A, Sanger D, White D, Holland AF, Vandiver L, Bowker C, White S (2014b) Quantifying and simulating stormwater runoff in watersheds. Hydrological Processes 28(3):559-569

Bergquist, D.C., R.F. Van Dolah, G.H.M. Riekerk, M.V. Levisen, S.E. Crowe, L. Brock, D.I. Greenfield, D.E. Chestnut, W. McDermott, M.H. Fulton, E. Wirth, and J. Harvey. 2009. The Condition of South Carolina’s Estuarine and Coastal Habitats During 2005-2006: Technical Report. Charleston, S.C.: South Carolina Marine Resources Division. Technical Report No. 106, 60 pp.

Bush E (2017) Daniel Island scores another good report card after Irma, but why? Daniel Island News, 20 September, 2017

Camp TR (1952) Water treatment. In: Davis CV (Ed.) Handbook of Applied Hydraulics, second ed. McGraw-Hill, Inc., New York, NY

Clark SE, Pitt R (2012) Targeting treatment technologies to address specific stormwater pollutants and numeric discharge limits. Water Research 46:6715-6730

Clary J, Jones J, Leisenring M, Hobson P, Strecker E (2017) International Stormwater BMP Database 2016 Summary Statistics. Final Report: The Water Environment & Reuse Foundation

Coastal Heritage magazine

Comings KJ, Booth DB, Horner RR (2000) Stormwater pollutant removal by two wet ponds in Bellevue, Washington. Journal of Environmental Engineering 126(4):321-330

Consensus Building Institute (2012) Assessment of Ohio Stormwater Management for the Stormwater Incentives in Lake Erie Basin Project. 15 pp.

CWP (1998) Better site design: A handbook for changing development rules in your community. Prepared for the Site Planning Roundtable

DeLorenzo ME, Thompson B, Cooper E, Moore J, Fulton MH (2012) A long-term monitoring study of chlorophyll, microbial contaminants, and pesticides in a coastal residential stormwater pond and its adjacent tidal creek. Environmental Monitoring and Assessment 184:343-359

DHEC (2005) South Carolina DHEC Storm Water Management BMP Field Manual

DHEC (2014) R.61-68 Water Classifications and Standards. Bureau of Water, DHEC, 65 pp.

Drescher S, Messersmith M, Davis B, Sanger D (2007) State of the Knowledge Report: Stormwater ponds in the coastal zone, South Carolina. S.C. Department of Health and Environmental Control, Office of Ocean and Coastal Resource Management

Environmental Protection Division (2016) Georgia Stormwater Management Manual, Volume 2: Technical Handbook

Greenfield DI, DeMattio K, Brock L, Keppler CJ, Williams SH, Wilde SB (2009) Temporal variability in plankton assemblages in three Kiawah Island, S.C., detention ponds and tidal creek systems during 2008. Poster. Southeastern Estuarine Research Society, Conway, S.C.

Greenfield DI, Keppler CH, Hilborn E, Moore J, Sandifer P (2014) Linking phytoplankton community composition with incidences of Vibrio in stormwater detention ponds. Proceedings of the 2014 South Carolina Water Resources Conference, Columbia, S.C.

Greenfield DI, Jones WJ, Mortensen R, Doll C (2015) Development of a sandwich hybridization assay approach to rapidly assess multiple harmful algal bloom species linked with fish kills and public health concerns in the southeastern U.S. Presentation. 8th Symposium for Harmful Algae in the U.S., Long Beach, CA

Greenfield DI, Moore J, Stewart JR, Hilborn ED, George BJ, Sandifer PA (2017) Temporal and environmental factors driving Vibrio vulnificus and V. parahaemolyticus populations and their associations with harmful algal blooms in South Carolina detention ponds and receiving tidal creeks. GeoHealth 1(8):306-317

Hathaway J, Hunt W, Jadlocki S (2009) Indicator bacteria removal in storm-water best management practices in Charlotte, North Carolina. Journal of Environmental Engineering 135(12):1275-1285

Hehman L (2014) The effects of aeration on phytoplankton community composition and primary production in stormwater detention ponds near Myrtle Beach, S.C. M.S. Thesis, University of South Carolina, Columbia, S.C.

Holland AF, Sanger DM, Gawle CP, Lerberg SB, Santiago MS, Riekerk GHM, Zimmerman LE, Scott GI (2004) Linkages between tidal creek ecosystems and the landscape and demographic attributes of their watersheds. Journal of Experimental Marine Biology and Ecology 298:151-178

Hostetler M (2017) Lessons learned: What does it take to create a more natural stormwater pond? The Nature of Cities

Huda MK, Meadows ME (2010) Critical assessment of management practices and policies for stormwater and sediment ponds in South Carolina. Proceedings of the 2010 South Carolina Water Resources Conference, Columbia, S.C.

Hunt WF, Smith JT, Jadlocki SJ, Hathaway JM, Eubanks PR (2008) Pollutant removal and peak flow mitigation by a bioretention cell in urban Charlotte, N.C. Journal of Environmental Engineering 134(5):403-408

Jones KW, Warren DA, Lewis B, Ritchie J, Connor S (2017) Management decision implications resulting from analysis of stormwater best management practice efficacy across temporal and varying spatial scales. Invited Speaker. 2017 Beaufort Area Stormwater Ponds Conference, Bluffton, S.C.

Low Impact Development in Coastal South Carolina: a Planning and Design Guide

LID Suitability Index on Clemson’s Community Resource Inventory:

Liu J, Lewitus AJ, Brown P, Wilde SB (2008a) Growth-promoting effects of a bacterium on raphidophytes and other phytoplankton. Harmful Algae 7:1-10

Liu J, Lewitus AJ, Kempton JW, Wilde SB (2008b) The association of algicidal bacteria and raphidophyte blooms in South Carolina brackish detention ponds. Harmful Algae 7:184-193

Lucas W, Greenway M (2008) Nutrient retention in vegetated and nonvegetated bioretention mesocosms. Journal of Irrigation and Drainage Engineering 134:613-623

Lucas W, Greenway M (2011) Phosphorus retention by bioretention mesocosms using media formulated for phosphorus sorption; Reaction to accelerated loads. Journal of Irrigation and Drainage Engineering 137(3):144-153

Messersmith M (2007) Assessing the hydrology and pollutant removal efficiencies of wet detention ponds in South Carolina. M.S. Thesis, College of Charleston, Charleston, S.C., 106 pp.

Moore (2010) Retrofitting regional stormwater quality BMPs for bacteria treatment and volume control in Beaufort County. Proceedings of the 2010 South Carolina Water Resources Conference, Columbia, S.C. Available online at: https://

N.C. Department of Environmental Quality (2016) Stormwater BMP Manual: 10. Wet Detention Basin

Pitt R (2004) Module 6: Temporary ponds for construction site sediment control

Pond Watch Program

Ramsey C (2010) Storm water worksheet for single family homes. Report prepared for Beaufort County Engineering Division by Allison Ramsey Architects, Inc.

Sanger DM, Holland AF, Scott GI (1999a) Tidal creek and salt marsh sediments in South Carolina coastal estuaries: I. Distribution of trace metals. Archives of Environmental Contamination and Toxicology 37:445-457

Sanger DM, Holland AF, Scott GI (1999b) Tidal creek and salt marsh sediments in South Carolina coastal estuaries: II. Distribution of organic contaminants. Archives of Environmental Contamination and Toxicology 37:458-471

Sanger DM, Johnson SP, Levisen MV, Crowe SE, Chesnut DE, Rabon B, Wirth EF (2016) The condition of South Carolina’s estuarine and coastal habitats during 2011-2014. SCECAP Technical Report No. 108, marine/scecap/reports.html

Schroer W, Benitez-Nelson CR, Smith EM, Ziolkowski LA (2018) Drivers of sediment accumulation and nutrient burial in coastal stormwater detention ponds, South Carolina, U.S.A. Ecosystems, 1-21

Serrano L, DeLorenzo ME (2008) Water quality and restoration in a coastal subdivision stormwater pond. Journal of Environmental Management 88: 43-52

Siewicki TC, Pullaro T, Pan W, McDaniel S, Glenn R, Stewart J (2007) Models of total and presumed wildlife sources of fecal coliform bacteria in coastal ponds. Journal of Environmental Management 82:120-132

Smith E (2017) It’s all connected: The role of stormwater ponds in coastal South Carolina. Invited speaker: 2017 Beaufort Area Stormwater Ponds Conference, Bluffton, S.C.

State of Washington Stormwater Action Monitoring Program (2010)

Stone WW, Gilliom RJ, Martin JD (2014) An overview comparing results from 2 decades of monitoring of pesticides in the nation’s streams and rivers, 1992-2001 and 2002-2011. U.S. Department of Interior, USGS, Scientific Investigation Report 2014-5154, 23 pp.

Thomas & Hutton Engineering Co. (2009) Opinion of potential infrastructure cost for stormwater runoff volume control. Prepared for Beaufort County, S.C.

Tweel A, Sanger D, Blair A, Montie E, Turner A, Leffler J (2015) Collaborative research to prioritize and model the runoff volume sensitivities of tidal headwaters. Final Report: NERR Science Collaborative

U.S. EPA (2008) Managing stormwater in your community: A guide for building an effective post-construction program. Prepared by the Center for Watershed Protection

U.S. EPA (2009) Stormwater Wet Pond and Wetland Management Guidebook. Prepared by the Center for Watershed Protection

Weinstein JE, Crawford KD, Garner TR (2008) Chemical and biological contamination of stormwater detention pond sediments in coastal South Carolina. Final Report for the S.C. Sea Grant Consortium and DHEC-OCRM

Winston RJ, Hunt WF, Kennedy SG, Merriman LS, Chandler J, Brown D (2013) Evaluation of floating treatment wetlands as retrofits to existing stormwater retention ponds. Ecological Engineering 54:254-265