Beneficial Use of Stormwater - Opportunities for urban renewal and water conservation

University dissertation from Dept. of Water Resources Engineering, Lund University

Abstract: This thesis investigates the beneficial use of stormwater in Swedish urban environments. The focus has been on open stormwater systems for source control, as well as rainwater collection systems. To analyse the implementation of open stormwater systems, two case studies are presented: Augustenborg in Malmö and Bäckaslöv wetland in Växjö. The retention and detention effects of green-roofs have been also studied by means of experimental work. Ringdansen, a residential area in Norrköping, is used to discuss rainwater collection for urban applications. The aim of the Augustenborg study was to determine the effect of disconnecting impervious areas from a combined sewer system in favour of a new open stormwater system. The open system, which consists of a combination of structural best management practices (BMPs), was assessed by comparing synthetic hydrographs for the ½, 2, 5 and 10-year design storms assuming wet and dry initial conditions. It was found that the BMPs are able to lower the total runoff from the area and successfully attenuate storm peak flows for all the recurrence intervals considered. Bäckaslöv wetland in Växjö, is shown as an example of a multi-purpose urban stormwater facility. The wetland system has been the focus of studies into water quality and hydraulic processes, as well as surveys of plant and bird populations. Apart from stormwater management, the system benefits include urban renewal, habitat creation and the provision of an outdoor laboratory. In order to estimate the response of green-roofs to individual rain events, precipitation and runoff data from controlled experiments (with dry and wet initial conditions) on a sedum album green-roof were analysed by means of linear programming. The results indicated that slope does not influenced retention volumes. Under dry initial conditions, stormwater can be retained and detained, whereas under wet initial conditions only detention is possible. To further investigate the detention effect, a comparison between the response of an impervious roof and a green roof was carried out. Green-roofs can be implemented in combination with other BMPs to successfully detain stormwater. The Ringdansen study showed that rainwater collection systems are efficient elements in Swedish urban environments. They contribute to water saving by supplying water for domestic use where potable water is not essential. Rainwater collection systems are also shown to be important elements of stormwater management systems.

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