Derwent Estuary WSUD Project

Client: The Derwent Estuary Program
Type: Water Sensitive Design
Date: 2010 - 2011

AILA AWARD WINNER: AILATasmania Water Sensitive Urban Design Award

The State of the Derwent Report 2010 prepared by the Derwent Estuary Program identified stormwater runoff as a major source of pollution to the Derwent estuary. Local councils surrounding the Derwent estuary, in cooperation with the Derwent Estuary Program, have monitored stormwater quality. The concentration of a number of pollutants regularly exceeds recommended guidelines for activities such as swimming in the estuary.

The Derwent Estuary Program has a dedicated stormwater project aimed at improving water quality by developing and implementing resources and programs for local government, business and industry, schools and the community. One of those initiatives is aimed at encouraging Water Sensitive Urban Design (WSUD) adoption in both new developments and for retrofitting into existing situations to demonstrate the need for stormwater management as part of the protection efforts for the Estuary. This project was a pilot project to select some sites for the retrofitting and establishment of WSUD in a few locations around the Derwent estuary. Four sites were nominated by the Derwent Estuary Program with a view of undertaking WSUD design and works. This project has been funded through the Caring for our Country program of the Australian Government. This Design Development report follows on from an Initial Site Appraisal of Opportunities and Constraints to using WSUD at each of four sites, prepared in March 2010.

WSUD Sites

Site 1 – Cadbury’s Car-park This carpark site is on the site for the Cadbury factory in Glenorchy. The car park covers an area approximately of 1.6Ha and generally drains to a drain on the south east side. The car park receives a high usage with up to 1000 visitors per day. The runoff from this area is likely to be contaminated with a range of pollutants such as nutrients, oils and greases including PAH’s and heavy metals. The concept was developed to harvest and reuse the runoff from the catchment for landscape water or reserve watering. Installation of education and interpretation signage at this high profile site is recommended.

Site 2 – UTAS Sandy Bay Campus Regent Street Union Car-park This is a small site at the University of Tasmania, Sandy Bay Campus, but is high profile being next to the student facilities. It is a high traffic zone with a lot of car movements. The drainage grade is very steep and is not suitable for standard vegetated swales systems and the kerb will have to be maintained. An additional constraint a rivulet passes under the site in a 1200mm diameter pipe and given that the upstream catchment is large, the overland flow issue has to be considered. The solution was to elevate the WSUD bio-filter in a gabion structure. The use of gabions was a functional response to the constraints as well as reflecting on established aesthetic used at the adjacent Pharmacy development and carpark.

Site 3 – Centro Glenorchy Car-park The site is a large Council owned carpark servicing the Glenorchy Shopping Centre incorporating the Centro development and Village Cinemas. The Glenorchy shopping centre is a large site that attracts a high customer use. The car park at this site is almost totally paved and currently covers approximately 1.1 Ha. The volume of traffic for this site is high. The drainage system has been placed over the pre-existing creek (Barossa Creek). Currently the runoff from the areas discharges to a piped local stormwater system that discharges to the Barossa Creek and thence to the Derwent Estuary.

Site 4 – Southern Water Depot Car-park, Huntingfield. This site is a works depot that sits immediately adjacent to Coffee Creek, Huntingfield. Whilst most the site stormwater is directed to the point of connection at the rear of the site to the existing in-stream retention pond in Coffee Creek to the south east, a number of stormwater drains from the site drain directly to the front of the site and fall via side entry pits in Patriarch Drive. The site has a medium traffic load on Patriarch Drive though low use in the site internally and is remote from any high visitation. The site is on a very restricted footprint and has a number of underground and above ground services. Site Inspection showed that the two areas identified on the site’s stormwater plan were in fact restricted for WSUD insertions due to a low unencumbered and available footprint for provision of WSUD services, taking into account the depth to invert and areas needed for such treatment elements. The available area between pavement and site perimeter fencing is restricted and steeply battered. The most suitable area for incorporation of WSUD devices is in fact on the neighbouring Coffee Creek drainage reserve.

Partners:  Aquatic System Management Derwent Estuary Program; University of Tasmania

For more information on the AILA Tasmania Awards 2011 see AILA http://www.aila.org.au/tasmania/AWARDS/2011/default.htm

Recent Article http://www.ewater.com.au/casestudies/music-case-studies/improving-water-quality-in-the-derwent-estuary/