Green stormwater infrastructure such as bioretention can reduce stormwater runoff volumes and trap sediments and pollutants. However, bioretention soil media can have limited capacity to retain phosphorus (P) or even be a P source, necessitating addition of P-sorbing materials. We investigated the potential trade-off between P removal by drinking water treatment residuals (DWTRs) and hydraulic conductivity to inform the design of bioretention media. Batch isotherm and flow-through column experiments showed that P removal varied greatly among three DWTRs and across methodologies, which has implications for design requirements. We also conducted a large column experiment to determine the hydraulic and P removal effects of amending bioretention media with solid and mixed layers of DWTRs. When DWTRs were applied to bioretention media, their impact on hydraulic conductivity and P removal depended on the layering strategy. Although DWTR addition in solid and mixed layer designs improved P removal, the solid layer restricted water flow and exhibited incomplete P removal, while the mixed layer had no effect on flow and removed nearly 100% of P inputs. We recommend that DWTRs be mixed with sand in bioretention media to simultaneously achieve stormwater drainage and P reduction goals.
A quantitative comparison of total costs between the traditional approach and the optimization approach for stormwater management is presented in this study. As the uniform sizing method is always associated with the traditional stormwater management practices, the optimization approach is well suited for the more recent stormwater management paradigm of low impact development (LID) practices. In the case study conducted for the town of Franklin in the Upper Charles River Watershed, Massachusetts, USA, the optimization method is able to identify stormwater management alternatives that cost 60% less than the traditional approach for meeting the Phosphorus loading reduction targets. The study highlights the comprehensive benefits from coupling optimization with the LID practices in stormwater management: 1. The LID practices’ focus on restoring the predevelopment runoff conditions ensures sustainable stormwater management, and 2. The optimization technique guarantees that the most cost-effective LID practices are selected throughout the decision-making process. The approaches outlined in this study can be very informative to many Asian countries that are under fast development and are in urgent need of scientific and sound approaches for achieving sustainable watershed management.
Habitat/aquatic impairments in an urban environment are often associated with multiple stressors, including known and unknown pollutants, storm water runoff, hydrologic modifications, riparian corridor encroachment, and channel alteration. Many of these stressors may be acting either in an individual or cumulative manner. However, it is very difficult to determine the exact role and significance each pollutant/stressor plays in contributing to the impairment to aquatic life. As a result, developing TMDLs for these impairments present unique and complex challenges. For example, it is very difficult to meaningfully identify appropriate loading capacities for each individual stressor and sufficient data/information are rarely available to isolate the relative strength of each stressor and to link each stressor independently to the impairment. As a result, innovative approaches are required to develop TMDLs that will address such impairments and also be the basis for implementing control actions. The impairments, in many cases, are related to excessive development in the watershed and the stressors are largely associated with a single source category such as storm water runoff. Therefore, using storm water as an umbrella surrogate for all stressors contributing to the aquatic life impairment may be appropriate for developing TMDLs if all stressors (pollutant loading, habitat destruction and hydrologic alteration) are related to storm water runoff. Also, this approach provides the necessary information to meaningfully guide storm water management implementation activities since many of the available storm water controls are capable of addressing excessive runoff rates and multiple pollutants. The use of surrogate indicators expressed as quantitative targets is an important tool for developing such TMDLs. This paper presents a simple and innovative approach utilizing flow duration statistics to identify a suitable surrogate hydrology target that supports healthy habitat/aquatic life. Two case studies are presented to highlight the approach, including the Shawsheen River Watershed in Massachusetts and the Penjajawoc Stream in Maine.
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