Stormwater retention park

OPTIMISATION OF WATER SENSITIVE URBAN DESIGN PRACTICES USING EVOLUTIONARY ALGORITHMS  
The development and application of a framework to incorporate WSUD into an optimisation
C McPhail, S Vial, R van der Pennen, B Heidrich, Prof. A Simpson, Dr. J Cantone
Publication Date (Web): 6 November 2017
DOI: https://doi.org/10.21139/wej.2017.031


Population growth and urban consolidation have resulted in a movement away from the natural landscape creating a greater proportion of impervious area and an increase in urban stormwater runoff. The increase in stormwater runoff has typically be handled using traditional drainage infrastructure such as pipes, pits and detention basins. A review of the literature identified that the optimisation of traditional drainage infrastructure can result in great cost-savings and ensure that other hydrologic and hydraulic performance criteria are met. An alternative to implementing traditional stormwater collection and conveyance infrastructure is Water Sensitive Urban Design (WSUD), which has been shown to counteract the effects of increased runoff by decreasing the proportion of impervious area and utilising natural retention/detention.

To date, the optimisation of WSUD practices has focused primarily on large-scale practices such as wetlands, detention basins, and stormwater harvesting schemes. It is evident that little research has been conducted to identify the impacts of utilizing lot-scale WSUD practices, such as rain gardens and rainwater tanks, on the catchment-wide hydrologic response.

This research aims to utilise evolutionary algorithms as a means of identifying the most efficient combinations of WSUD practices at the lot scale to meet designated hydrologic objectives at the catchment scale. Furthermore, this research will use optimisation to determine, and explore, the trade-offs between WSUD practices and more traditional drainage infrastructure practices.

A case study on the proposed South Campus Research Park at the University of Illinois Urbana Champaign (UIUC) was optimised to determine the optimal combination of traditional and WSUD infrastructure to meet flooding, freeboard and peak flow criteria at minimum cost. In order to facilitate this analysis decisions associated with implementing alternative WSUD practices were scripted in JavaScript and integrated into the Optimizer WCS software to allow alternative scenarios to be simulated and optimised. 

The optimisation results showed that for a variety of rainfall Average Recurrence Intervals (ARIs) it is cheaper to use a combination of traditional drainage infrastructure and WSUD than to only use the traditional drainage infrastructure. It is also apparent that optimising a combination of infrastructure types produces a cheaper cost when detention storage is used. These results show that for the proposed Research Park it is most cost effective to include WSUD in the final plan. The results generally showed that more WSUD was used at the downstream end of the catchment. The spatial placement of the WSUD was consistent for most optimised solutions suggesting that it is an important factor. For the 1 in 100 year rainfall ARI between 5 and 35% of the paved areas utilised permeable pavement. It was also found that rainwater tanks were applied to most buildings. The framework applied to this case study is generic and can be applied to any stormwater system.

 

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