A spatial life cycle cost assessment of stormwater management systems

Hydrologic and water quality performance of a subsurface gravel wetland treating stormwater runoff

Subsurface gravel wetlands are an emerging type of green infrastructure that can be used to manage stormwater through the capture and slow release of runoff. They are unique to other types of green infrastructure in that they have a distinct fully saturated gravel layer below an occasionally saturated soil layer that influences pollutant removal processes. While they have been widely applied to treat wastewater, our understanding of their efficiency in treating stormwater with variable pollutant inputs is limited. To fill this gap, this study monitored the flow and water quality (total suspended solids, total nitrogen, total phosphorus, and chloride) in a subsurface gravel wetland in Oshkosh, Wisconsin at the influent, effluent, and in an observation well. Results from nine storm events indicated that the wetland had a median volume reduction of 74% and a median peak flow reduction of 89%. The reduction in pollutant concentrations where highly dependent upon the influent concentration. Average reductions of total suspended solids, total nitrogen, and total phosphorus were 49%, -21% and -0.2%, respectively, indicating an increase in nutrients; however, where influent concentrations were above irreducible levels, total phosphorus was reduced by 45% (influent ≥0.25 mg/L) and total nitrogen was reduced by 38% (influent ≥2.5 mg/L). Overall, this study shows that the subsurface gravel wetland performed similar to other types of green infrastructure and could be a good management practice to mitigate the harmful effects of stormwater runoff.

Willingness to Pay for the Maintenance of Green Infrastructure in Six Chinese Pilot Sponge Cities

Due to the increasingly devastating impact of pluvial flooding on human beings’ lives and properties in cities, the use of green infrastructure to manage stormwater onsite is becoming more popular worldwide. The maintenance of green infrastructure to ensure its function has become one of the most pressing tasks facing policy makers. However, there is limited research regarding the willingness to pay the stormwater fee as a form of maintenance funding. This study utilized contingent valuation data obtained from a survey of 1101 respondents living in six pilot sponge cities in China to estimate the willingness to pay for the green infrastructure maintenance. The findings indicated that two-thirds of all respondents were willing to pay, 17% would like to pay around 6–10 RMB/month (0.95–1.59 US dollars/month), and 17.8% would like to pay more than 20 RMB/month (3.2 US dollars/month). The educational level and age of the respondents were significant determinants of the probability of willingness to pay and the amount they would like to pay. Knowledge of the concept of sponge cities was another significant influencing factor for the willingness to pay, but it did not influence the amount of payment. The findings could help policy makers make better strategies regarding the maintenance of green infrastructure and its costs.

Effects of low impact development on the stormwater runoff and pollution control

The frequent urbanization and extreme rainfall events have posed the threat to the urban environment. The implementation of low impact development (LID) practices with great potential for control urban flood and overflow pollution is not comprehensively understood yet due to the influence of complex factors (i.e., hydrological pattern, installation location, and vertical parameter setting). In this study, the hydraulic and water quality model were used to analyze the hydrological and pollution reduction of outfall and storage under different hydrological patterns, vertical parameter setting, and green infrastructure installation locations, which can determine the best implementation of the scheme for overflow pollution control. The results showed that nine parameters of the vertical layer regarding the four parameters impacted the peak value and load of suspended solids (SS). The combination scheme of the LID practices was further proposed based on the selection and analysis of the single LID practice. Besides, considering the installation location, the downstream installed location was a better choice. The horizontal connection of overflow runoff and pollution could be reduced by up to 9.75% and 36.46%, respectively. In addition, the horizontal connection can effectively reduce the peak value of inflow and pollutants at the time of assessing storage tank impact, which reach the maximum of 14.08% and 29.25%, respectively. The pollutants distribution became uniform and showed better resilience against rainfall intensity, which is beneficial to the management of stormwater. Our findings can provide guidance for Sponge City construction and effectively alleviate the combined sewer overflow.

Conflict or consensus? Stakeholders' willingness to participate in China's Sponge City program

In 2015, China initiated the Sponge City Program (SCP), an integrated urban stormwater management strategy, to mitigate the paradoxical challenges of urban flooding and water shortages. Very few studies have attempted to examine the willingness to participate of multi-level stakeholders in the case of storm-water management initiatives. To address this gap in the existing body of knowledge, this study took Guyuan city, Ningxia Province, a Stage 2 pilot city located in the arid northwest region of the People's Republic of China, as a case study. Members of three key stakeholder groups were surveyed, i.e., government, commercial entities and communities, and a total of 687 valid questionnaires were obtained in the SCP. Via a logistic regression model, the results showed that: (1) the stakeholders reached a consensus during the participation process that they were motivated by personal benefits and expected to improve water usage through the participatory process; (2) the government represented the public interest by prioritizing the overall improvement of the urban water environment and improving standards of living by contributing to the program; (3) the commercial entities prioritized the acquisition of knowledge and technical issues relevant to their business operations, and expressed concerns about how these operations might be affected by stakeholder participation; (4) both the commercial and community groups were more willing to participate if they perceived that the SCP would affect their daily lives, and the general public were willing to participate for multiple reasons. This study will help to guide future studies to continuously explore the diverse factors that influence the stakeholder participation of diverse stakeholders. The findings can also benefit the design of future projects with a view to enhancing stakeholder participation. Recognizing the quantifiable benefits of the SCP, this paper demonstrates how the evaluation of diverse stakeholders' priorities and the assessment of the drivers for their willingness to participate can further benefit the implementation of sustainable urban water initiatives, as in the case of this megaproject, and their enduring success.

Successful mitigation of stormwater-driven nutrient, fecal bacteria and suspended solids loading in a recreational beach community

Marine and estuarine waterways adjacent to urban areas are often the final recipient of polluted stormwater runoff. Microbial degradation of coastal water quality is a direct threat to human health through fecal contamination of bathing waters and shellfish, as well as distressing local economies through the loss of waterways to commercial (shellfishing) and recreational use. In coastal waters reduction of nitrogen loading is a key strategy for prevention of noxious and toxic algal blooms. Best management practices (BMPs) can be successful tools for mitigating such pollutants in runoff, but BMPs must be tailored to individual situations for maximum effectiveness. This study examines the efficacy of a set of BMPs installed in the coastal resort Town of Wrightsville Beach, North Carolina, USA. The BMPs targeted the highly-impervious (90%+) drainage area of two stormwater outfall pipes emptying into recreationally used Banks Channel. Mitigation measures included replacement of impervious pavement with pervious concrete and construction of an infiltration chamber in the parking lot of a local recreational seaside club. Significant reductions were achieved in total stormwater discharge (62%), as well as loading of the fecal indicator bacteria Enterococcus (76%) and total nitrogen (TN - 87% decrease). Additionally, there were reductions in loading of total phosphorous (TP) and total suspended solids (TSS) to estuarine waters following BMP installment. The set of BMPs applied here have wide management applicability to coastal ecosystems, as well as freshwater riparian areas characterized by sandy, porous soils.