Initial impacts of rain gardens＇ application on water quality and quantity in combined sewer： field-scale experiment

Green infrastructures such as rain gardens can benetit onsite reduction ot stormwater runott, leading to reduced combined sewer overflows. A pilot project was conducted to evaluate the impact of rain gardens on the water quality and volume reduction of storm runoff from urban streets in a combined sewer area. The study took place in a six-block area on South Grand Boulevard in St. Louis, Missouri. The impact was assessed through a comparison between the pre-construction （2011/2012） and the post-construction （2014） phases. Shortly after the rain gardens were installed, the levels of total suspended solids, chloride, total nitrogen, total phosphorous, zinc, and copper increased. The level of mercury was lower than the detection level in both phases. E. coli was the only parameter that showed statistically significant decrease following the installation of rain gardens. The likely reason for initial increase in monitored water quality parameters is that the post-construction sampling began after the rain gardens were constructed but before planting, resulted from soil erosion and wash-out from the mulch. However, the levels of most of water quality parameters decreased in the following time period during the post-construction phase. The study found 76% volume reduction of stormwater runoff following the installation of rain gardens at one of studied sites. Statistical analysis is essential on collected data because of the encountered high variability of measured flows resulted from low flow conditions in studied sewers.

Plant Selection and Application of Rain Garden in Southern China

Based on the basic principles of rain garden infrastructure, optimal species for rain facilities such as vegetated buffer strip, vegetated shallow groove, artificial wetland were selected, characteristics, configuration principles and methods were summarized.

RESIDENTIAL STORMWATER:METHODS FOR DECREASING RUNOFF AND INCREASING STORMWATER INFILTRATION

INTRODUCTION Humans and plants depend on an adequate supply of clean water for numerous reasons,from food production to sustaining terrestrial and aquatic life.The average Virginia resident uses about 47 gallons(178 L)of fresh water daily(VDEQ 2008).While a majority of Virginians are provided water from a centralized,public utility,there are nearly two million Virginia residents who depend on well water as their main source(VDH 2008).Replenishing groundwater withdrawals depends on recharge(water moving from the surface to groundwater)from infiltration of precipitation through permeable surfaces in the environment;an important part of the hydrologic,or water,cycle(VDEQ 2010).Forests and grasslands provide much of the available recharge area due to their high capacities to infiltrate precipitation.However,the urbanization process is rapidly converting forested areas and grasslands to commercial,residential,or industrial developments.This conversion creates a significant increase in impervious surfaces such as concrete,asphalt,building roofs,and even compacted vegetated sites(U.S.EPA 2003).Impervious surfaces decrease infiltration and groundwater recharge.They also generate increases in stormwater runoff;defined as any precipitation from a rain or snow event that flows off of an impervious surface.As water runs off urban impervious surfaces,it picks up sediment,oils,debris,nutrients,chemicals,and bacteria.The runoff is then collected in a conveyance system,transported,and discharged to surface waters such as creeks and rivers;most of the time without any type of water quality treatment(U.S.EPA 2003;Paul and Meyer 2001).In addition to carrying pollutants,the runoff is also typically warmer than the receiving surface waters.The increased volume and velocity of the stormwater runoff erodes soil and stream channels and can lead to stream“blow out.”Water quality is degraded and aquatic habitats are adversely altered(Meyer,et al.2005,Booth and Jackson 1997).Due to the interconnected nature of watersheds,the degraded water travels downstream causing subsequent problems.The effect of increased development is an increase in stormwater runoff and associated pollutants into surface waters and a decrease in infiltration for groundwater recharge and stream base flows.Traditional practices for mitigating stormwater runoff impacts have targeted the management of peak runoff by using storage facilities such as detention and retention ponds.Mounting evidence that these methods are inadequate prompted the National Research Council in 2008 to advocate a shift to Low Impact Development(LID)practices to better meet stormwater quality and quantity management goals.LID is based on a set of techniques used in Prince Georges County,Maryland(Prince Georges County 1999).LID seeks to restore the natural hydrology of a site by minimizing the creation of impervious surfaces and increasing infiltration of runoff volume.The ineffectiveness of conventional management approaches and the implementation of the Chesapeake Bay and other critical watershed Total Maximum Daily Loads(TMDLs)caused Virginia to revise its entire process for regulating stormwater.LID and Environmental Site Design(ESD)practices are now used to design sites to meet hydrologic goals and to treat runoff to meet a net site nutrient export standard(Battiata et al.2010).As of the date of this paper,15 of these best management practices,or BMPs,have been approved for use by Virginia(Virginia Stormwater BMP Clearinghouse 2011).Similar approaches are being considered and adopted in other Chesapeake Bay jurisdictions,as well as nationally.The responsibility of stormwater management can be fragmented between state,local,and municipal government(Roy,et al.2008),often differing from watershed to watershed.Because LID is decentralized,it changes the management focus from a large,regional scale to a site scale.Changes at the residential lot level can generate much greater infiltration over the watershed.Each homeowner can significantly reduce the stormwater load leaving their property,thereby improving surface water quality and helping to recharge groundwater reserves.From a green building perspective,LID techniques can provide a substantial credit under the LEEDS-ND(Leadership in Energy and Environmental Design-Neighborhood Development)program.The objective of this paper is to provide a relative context for runoff at the site scale,and an overview of the available BMPs that may be applicable.

DESIGN AND PERFORMANCE OF BIORETENTION BEDS FOR REMOVAL OF STORMWATER CONTAMINANTS

Bioretention basins hold a volume of water that is filtered through sandy soil and allowed to infiltrate into the subsoil or drained to an outlet(Figure 1).Originally,bioretention basins were intended as a site-scale tool to improve the quality of urban stormwater runoff,but they have a demonstrated impact on reduction of runoff volume and time of concentration.Therefore,the design of basins are complicated by a range of possible goals.Recharging groundwater,improving runoff water quality to maintain or restore aquatic ecosystem health,reducing peak storm flows,extending time of concentration,and reducing runoff volume to prevent channel erosion and sedimentation are all possible goal options.Only a few states have guidelines or regulations for bioretention basins.Furthermore,some existing state design requirements do not reflect the range of goals or the research demonstrating the design and performance of bioretention basins.For example,the Idaho Department of Environmental Quality recommendations were published in 2005 but based information from 1993(IDEQ,2005).The first section below considers the original purpose-pollutant removal.