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With the purpose to study a solution based on Sustainable Urban Drainage Systems (SUDS) to reduce and treat stormwater runoff in urban areas, a bioretention pond (BP) was realized in the Agripolis campus of the University of Padova, Italy. The BP collected overflow water volumes of the rainwater drainage system of a 2270 m2 drainage area consisting almost entirely of impervious surfaces. Sixty-six Tech-IA&reg, floating elements, supporting four plants each, were laid on the water surface. Eleven species of herbaceous perennial helophyte plants, with ornamental features, were used and tested. The early growth results of the BP functioning showed that nearly 50% of the total inflow water volume was stored or evapotranspirated, reducing the peak discharge on the urban drainage system. Among plants, Alisma parviflora, Caltha palustris, Iris &lsquo, Black Gamecock&rsquo, Lysimachia punctata &lsquo, Alexander&rsquo, Oenanthe javanica &lsquo, Flamingo&rsquo, Mentha aquatica, Phalaris arundinacea &lsquo, Picta&rsquo, and Typha laxmannii had the best survival and growth performances. A. parviflora and M. aquatica appeared interesting also for pollutant reduction in runoff water.

The floating treatment wetland (FTW) is an innovative hydroponic device which can be installed on the surface of a stormwater retention pond to improve its pollutant removal efficiency. Limited full-scale experiments have been published, and no design or maintenance guidelines have been developed to date to promote their use. This paper presents implementation and maintenance considerations developed based on the monitoring of three full-scale ponds retrofitted with FTWs. Results suggest that the size and relative surface cover of the FTW, the relative root depth, and the capability of the plants to tolerate periodic anaerobic conditions are crucial factors to promote good removal across a spectrum of pollutants. Special attention to the location and anchorage of the FTW are thought to promote good performance and facilitate FTW maintenance. While zinc and copper sediment concentrations were unlikely to cause undue aquatic impacts after 2 years of operation, more frequent sediment removal will be ...

Hamrebäcken rinner genom östra delen av Västerås och har Mälaren som recipient. Under bäckens flödesväg tillkommer dagvatten och föroreningar i form av näringsämnen och tungmetaller från dess avrinningsområde. Bäcken utgör ett av de mest prioriterade vattendragen i Västerås gällande utsläpp av dagvatten. Detta examensarbete har utförts med syftet att utreda föroreningssituationen för Hamrebäcken och hur dess recipient Mälaren påverkas. Examensarbetet syftade även till att undersöka reningseffekten för en befintlig dagvattendamm samt att utifrån ett kostnads- och reningsperspektiv beskriva ett antal åtgärdsförslag för att uppnå en förbättring av bäckens ekologiska och kemiska status. Utvärdering av Hamrebäckens föroreningsbelastning samt reningseffekt för befintlig dagvattendamm och åtgärdsförslag utfördes med hjälp av den Excelbaserade dagvatten- och recipientmodellen StormTac. Resultatet från studien visade att den modellerade belastningen från flera av bäckens delavrinningsområden överskrider föreslagna riktvärden för mindre vattendrag. Den totala belastningen från Hamrebäckens avrinningsområde överskrider i fallet för föroreningarna bly och suspenderat material även föreslagna riktvärden för Mälaren. Modellering av den befintliga dammen indikerar att anläggningen är underdimensionerad i förhållande till dess belastningsyta. Dammens reningseffekt uppnår inte heller effektmålen i Västerås stads handlingsplan för dagvatten. Ett förslag om utbyggnation av dammen har tagits fram utifrån litteraturstudie och tillgänglig yta för åtgärden. Den simulerade ombyggnationen uppnådde inte uppsatta effektmål men gav en betydande ökning i reningseffekt. Åtgärder som syftar till att öka dammens avskiljningsförmåga bör därför utredas ytterligare. Fyra ytterligare åtgärdsförslag togs fram och reningseffekten av dessa modellerades i StormTac. Detta inkluderade två olika placeringar av dagvattendammar, en skärmbassäng med flytande våtmark, samt en konstruerad våtmark. Från genomförd modellering rekommenderas vidare utredning av åtgärdsförslagen inkluderande ett anläggande av en skärmbassäng med flytande våtmark, alternativt en konstruerad våtmark. Detta då dessa åtgärdsförslag uppnådde effektmålen för rening enligt Västerås stads handlingsplan för dagvatten. Åtgärdsförslagen skilde sig något åt gällande kostnadseffektivitet. Detta ansågs dock inte ensamt vara argument nog för att motivera anläggning av något åtgärdsförslag till följd av osäkerheter i det beräknade resultatet. Att en skärmbassäng kan utföras i närtid och inte kräver några ingrepp i avrinningsområdet kan anses som ytterligare argument för installation av anläggningen. En konstruerad våtmark kan i sin tur motiveras med att anläggningen bidrar till att höja det estetiska och ekologiska värdet av området. Dessa argument bör beaktas i valet av metod och det fortsatta arbetet med att minska områdets föroreningsbelastning och förbättra bäckens ekologiska och kemiska status. Hamrebäcken is a small stream in Västerås, which flows through the eastern part of the city. Along it’s course to Lake Mälaren, the stream receives polluted stormwater containing such as heavy metals and nutrients. The primary objective of this master thesis was to investigate the level of pollutants in Hamrebäcken. A secondary objective was to study the reduction efficiency of an existing wet stormwater treatment pond in the area, and propose ways in which to achieve a higher ecological and chemical status for the stream. The stormwater and recipient software model StormTac was used to estimate the level of pollutants and to investigate the reduction efficiencies of different stormwater treatment facilities. The study revealed that pollutant levels were too high for several of the subwatersheds, based on the recommended guidance for small streams. The pollutant load for the total watershed exceeded the guidance levels for Lake Mälaren for lead and suspended solids. Modelling the reduction efficiency of the existing wet pond indicated that the pond’s size was inadequate to cater for the quantity of incoming stormwater in need of treatment. Subsequently, the pollution reduction efficiency of the pond was not meeting those objectives set out in the Stormwater Action Plan developed by Västerås municipality. A proposal for rebuilding the pond was therefore developed, taking into account the existing conditions of the area and using recommendations from literature. When modeled in StormTac, the modified pond showed a substantial increase in reduction efficiency compared to that of the existing pond. Despite not reaching the objectives of the Action Plan, this suggested that it would be beneficial to investigate measures that increase the reduction efficiency of the existing wet pond further. As a result, an additional four alternatives for reducing the pollutant load of Hamrebäcken were developed using StormTac. These consisted of two wet stormwater treatment ponds at different locations within the watershed, a screen basin with floating treatment wetlands, and a constructed wetland. The modeling revealed that the most feasible of the investigated measures was an installation of either a screen basin with floating treatment wetlands or a constructed wetland, both measures adjacent to the outlet of Hamrebäcken. This was mainly due to the modeled reduction capacity of these measures where the reduction objectives of the Action Plan were reached. A difference in cost effectiveness was found between the different measures. This was however not considered to solely be argument to justify the implementation of a certain measure due to uncertainties in the modelled result. The fact that a screen basin can be installed in the near future and without occupying space in the watershed are additional arguments for the use of this measure. A constructed wetland can in return be motivated by a potential increase in esthetic and ecological value of the area. These arguments should be considered in the continued investigation of choosing a measure for reducing the pollutant load of Hamrebäcken and to achieve a higher ecological and chemical status for the stream.

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.