Stormwater Wet Ponds Research Articles

Evaluation of pollutant removal efficiency of urban stormwater wet ponds and the application of machine learning algorithms

Wet ponds have been extensively used for controlling stormwater pollutants, such as sediment and nutrients, in urban watersheds. The removal of pollutants relies on a combination of physical, chemical, and biological processes. It is crucial to assess the performance of wet ponds in terms of removal efficiency and develop an effective modeling scheme for removal efficiency prediction to optimize water quality management. To achieve this, a two-year field program was conducted at two wet ponds in Calgary, Alberta, Canada to evaluate the wet ponds' performance. Additionally, machine learning (ML) algorithms have been shown to provide promising predictions in datasets with intricate interactions between variables. In this study, the generalized linear model (GLM), partial least squares (PLS) regression, support vector machine (SVM), random forest (RF), and K-nearest neighbors (KNN) were applied to predict the outflow concentrations of three key pollutants: total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP). Generally, the concentrations of inflow pollutants in the two study ponds are highly variable, and a wide range of removal efficiencies are observed. The results indicate that the concentrations of TSS, TN, and TP decrease significantly from the inlet to outlet of the ponds. Meanwhile, inflow concentration, rainfall characteristics, and wind are important indicators of pond removal efficiency. In addition, ML algorithms can be an effective approach for predicting outflow water quality: PLS, GLM, and SVM have shown strong potential to capture the dynamic interactions in wet ponds and predict the outflow concentration. This study highlights the complexity of pollutant removal dynamics in wet ponds and demonstrates the potential of data-driven outflow water quality prediction.

Monitoring the spatial distribution of water quality of an urban stormwater pond using satellite images

Stormwater ponds play a critical role in managing urban runoff and mitigating the impact of pollutants on receiving water bodies. This study investigates the potential of remote sensing (RS) techniques in retrieving water level and key water quality parameters in urban stormwater wet ponds. Specifically, the focus is on water level, chlorophyll-a (Chl-a), total suspended solids (TSS), turbidity, and Secchi depth (SD). The results indicate that RS techniques can provide reliable estimates of water level, Chl-a, turbidity, SD, and TSS in urban stormwater wet ponds. Results revealed that Chl-a concentrations are higher near the inlets and within the forebay, with a significant decrease downstream of the forebay. TSS and total dissolved solids (TDS) concentrations follow a similar pattern to Chl-a, being higher near the inlet and within the forebay, but significantly lower downstream. Notably, the highest concentrations of TSS, TDS, and Chl-a are observed in July, likely due to heavy rainfall events during that period. Through principal component analysis (PCA) and correlation analysis, the study effectively captured the interrelationships among the water quality parameters in the stormwater pond. The spatial distribution of TSS and Chl-a shows a correlation. Furthermore, the study uncovers a relationship between water temperature and Chl-a concentration, with Chl-a decreasing as the temperature exceeds 20 °C and increasing when it drops below 20 °C. This relationship is influenced by sunlight availability, which affects Chl-a growth, as evidenced by variations in Chl-a concentration between the water column's bottom layers and surface. Overall, this research highlights the potential of utilizing RS techniques to retrieve water quality parameters, providing valuable information for water managers and decision-makers. The ability to generate maps of these parameters using reflected light measurements above stormwater wet ponds also contributes to effective water quality management strategies.

Ecological design of Taman Merdeka as an alternative to the development of Depok city green open space

Taman Merdeka, Depok City, is an urban park that has experienced degradation in terms of quality, both functionally and aesthetically. This declining condition causes less satisfactory use of this park, even though this park is a way for the government to provide an area that functions as a recreational area for urban citizens. The current condition of the park, with its original concept no longer visible, needs a touch of comprehensive design that can solve the problems that exist on the site. This study aims to ecologically design Taman Merdeka so that it meets the needs of park users and is environmentally friendly. The method used in this study is a descriptive method through field survey and interview. The schematic design is developed based on the traditional Depok Batik pattern that features the city's iconic fruit, that is star fruit and then transformed into elements and landscape spaces. The principles of ecological design are implemented through green infrastructure for water management, conservation of existing vegetation, upcycling center for waste management, and the use of environmentally friendly materials. The design is developed in detail in all areas including the welcome area, sports courts, playground, plaza, bioswales, stormwater wet pond, food court, upcycling center, sitting area, elevated walkway, amphitheater, lawn, and promenade.

Field observations of stratification in stormwater wet ponds

Stratification is one of the fundamental physical processes that may have a significant impact on water quality in stormwater wet ponds. However, the role of thermal and chemical stratifications in governing water quality processes is not fully understood. This is in part due to the lack of detailed field measurements of sufficient governing parameters over time periods that span a wide range of environmental conditions. To fill this gap, a comprehensive 2-year field program was undertaken in two stormwater wet ponds in Calgary, Alberta, Canada, during the ice-free season from May to November in 2018 and 2019. At different locations in each pond, thermal and chemical stratifications were observed, thermocline depth and strength were determined, and continuous water velocity profiles were measured. In addition, the effect of local weather conditions on stratification, thermocline, and hydrodynamics was investigated. The results showed that the ponds had vertical water temperature differences >1 °C for 99% of the time, May to August. In addition, salt-laden inflows from road deicing salts led to strong chemical stratification up to five times stronger in the sediment forebays than in the main cells in spring. Wind-induced surface currents were insignificant, scaling at 0.3% of the wind speed with negligible impact on vertical mixing in the ponds. Our results demonstrate that the ponds' strong and prolonged stratification decreased pollutant retention capacity and caused the water at depth to become anoxic, degrading the quality of the water discharged downstream. Hence, additional consideration of stratification is required when designing new stormwater ponds.

Field Observations of Stratification in Stormwater Wet Ponds

Field Observations of Stratification in Stormwater Wet Ponds

Floating treatment wetland retrofit in a stormwater wet pond provides limited water quality improvements

Floating treatment wetlands (FTW) are an emerging management practice for improving water quality in stormwater wet ponds or other detention basins. Although there is substantial evidence of nutrient reductions by FTW in mesocosm-scale studies, findings from field-scale studies on the water quality benefits of FTW are less conclusive. A medium-sized stormwater wet pond (~0.8 ha) was partially divided using an impermeable liner and monitored for 280 d using a control and FTW treatment (~20–23% FTW coverage) to determine impact of FTW on concentrations of several water quality parameters at the field-scale. Discrete samples and high-frequency, multi-point monitoring were used to assess water quality differences. No significant differences between the two treatments were found for total nitrogen, total Kjeldahl nitrogen, or total phosphorus, based on discrete samples, and in situ monitoring showed dissolved oxygen was significantly lower in the FTW treatment by roughly 2.6 mg L−1. The FTW treatment had significantly higher nitrate concentrations in discrete samples, but this finding was not supported by the high-frequency data collected when considering the full monitoring period. The FTW had significantly lower total suspended solids, based on discrete and high-frequency sampling, and resulted in a 10–43% reduction in TSS (~25% mean reduction), relative to the control. Comparison of subsets of the high-frequency data to discrete sampling data demonstrated how limited discrete sampling can lead to partial information and potentially erroneous conclusions when assessing FTW treatment effect in stormwater, especially when differences in water quality chemistry are small.

Water quality before and after watershed-scale implementation of stormwater wet ponds in the coastal plain

Wet ponds have been used extensively for stormwater control throughout the US, including coastal areas. Despite the widespread application of these water control structures, few studies have investigated how watershed-scale implementation of wet ponds affects downstream water quality or how the pollutant removal efficacy of wet ponds changes over time in a coastal setting. This study utilizes a seven year data set of nutrient, total suspended solid, and chlorophyll-a concentration data collected during baseflow and stormflow from two coastal headwater streams draining a developed (28% impervious) and an undeveloped (1.2% impervious) watershed. The seven year record encompasses before, during, and after a large construction project and concurrent implementation of wet ponds in the developed watershed that drain 97% of the watershed area. Additional nutrient, total suspended solid, and chlorophyll-a concentration data were collected from within a wet pond in the developed watershed during baseflow over a single spring and summer. A comparison of stream water quality before and after the construction project and wet pond implementation in the developed watershed showed that mean chlorophyll-a, nitrate-nitrite (NOx−), organic nitrogen, and total suspended solid concentrations significantly increased, the mean orthophosphate (PO43−) concentration significantly decreased, and the mean ammonium (NH4+) concentration did not change. Over a three year time period after construction and pond implementation, developed stream chlorophyll-a, ammonium, and organic nitrogen concentrations decreased, and nitrate-nitrite, orthophosphate, and total suspended solid concentrations increased compared to the reference stream during the same period, indicating changes in pollutant removal capacity. A comparison of baseflow and stormflow samples during the Post period and samples from a wet pond in the developed watershed indicated that ponds were functioning as sources of chlorophyll-a and total suspended solids to the stream and sinks for nitrate-nitrite. Overall, watershed-scale implementation of wet ponds in the developed watershed failed to mitigate many negative water quality impacts caused by increased development. This study suggests that centralized stormwater management may not be optimal for maintaining water quality in coastal environments, and that pond retrofits combined with frequent excavation could improve pollutant removal by wet ponds. Further research on the effects of nutrient cycling in coastal wet ponds and wet pond maintenance is needed.

Water quality before and after watershed-scale implementation of stormwater wet ponds in the coastal plain

Water quality before and after watershed-scale implementation of stormwater wet ponds in the coastal plain

Nitrogen and Sediment Capture of a Floating Treatment Wetland on an Urban Stormwater Retention Pond—The Case of the Rain Project

Nitrogen is widely recognized as a chronic urban stormwater pollutant. In the United States, wet retention ponds have become widely used to treat urban runoff for quantity and quality. While wet ponds typically function well for the removal of sediments, nitrogen removal, performance can be inconsistent due to poor design and/or lack of maintenance. Retrofitting ponds to improve their nitrogen capture performance, however, is often expensive. By hydroponically growing macrophytes on wet ponds, floating treatment wetlands (FTW) may provide a cheap, sustainable means of improving nitrogen removal efficiency of aging stormwater ponds. Few studies have been performed on the effectiveness real-world stormwater systems, however. In this study, we investigated the nitrogen and sediment capture performance of a 50 m2 floating treatment wetland deployed for 137 days on a stormwater wet pond located within an urban university campus near Washington, D.C. A total of 2684 g of biomass was produced, 3100 g of sediment captured, and 191 g of nitrogen removed from the pond. Although biomass production was relatively low (53 g/m2), we found that nitrogen uptake by the plants (0.009 g/m2/day) was comparable to contemporary FTW studies.

System dynamics modeling with sensitivity analysis for floating treatment wetlands in a stormwater wet pond

Rapid urbanization and climate variability impacts increase with more extreme precipitation and drought events, challenging stormwater management in terms of both flood control and water quality. Traditional stormwater wet detention ponds have limited capacity to remove nutrient pollutants, specifically nitrogen, and the changing environment may exacerbate the problem. The use of floating treatment wetlands (FTWs) may become a viable best management practice to increase the efficiency for on-site removal of nitrogen pollution from traditional stormwater wet detention ponds before release into neighboring aquatic systems or to the groundwater. This study, which is deemed a companion study of the early ecological engineering practice of FTWs, presents a system dynamics model to improve understanding of the nitrogen cycle in relation to FTWs-based subtropical stormwater wet detention ponds. The model was calibrated and validated based on surface water samples collected in a thorough field campaign with R-squared values of 0.83 and 0.97, respectively. Final simulation runs with sensitivity analysis were conducted to investigate scientific questions about the experimental design and effects of urbanization impacts on the biological nitrogen cycling in stormwater ponds.

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.