Queens Domain WSUD Project, Hobart
Urban Initiatives Pty Ltd (Tasmania)
The necessity for this project had arisen from a need to assess impacts of overland flow and flow-pathway problems at the Royal Tasmanian Botanic Gardens (RTBG), which sit on the lower northern slopes of Queens Domain in Hobart. This report also outlines the opportunities to assess water management needs on the Queens Domain, Hobart.
Hobart City Council are the managers of Queens Domain and the Royal Tasmanian Botanic Gardens (RTBG) are managed by a state government statutory organisation, governed by the Royal Tasmanian Botanical Gardens Act 2002 and administered by the Department of Primary Industries, Parks, Water and Environment (DPIPWE).
Urban Initiatives in association with Aquatic Systems Management undertook and reported on the opportunities for the incorporation of Water Sensitive Urban Design (WSUD) at Queens Domain and Royal Tasmanian Botanical Gardens.
The is project sought to overcome a range of issues, including flooding damage at the Royal Tasmanian Botanical Gardens, through to seeking responsible reuse of stormwater for a variety of sustainable uses, plus also to reduce water quality impacts on the Derwent Estuary.
Subsequent to the identification of the opportunities, it was resolved to obtain an opinion on the probable order of cost to assist in future planning for staged implementation of the project.
Three key environmental objectives:
To reduce the impact of stormwater-bourne sediments and pollutants, including nutrients upon the downstream catchments including the Derwent River, and other downstream sites such as the Royal Tasmanian Botanical Gardens
To increase the ability of water-users on the Domain to harvest and re-use stormwater for irrigation and other uses. Also to increase the use of non-potable water that can replace increasingly costly and environmentally valuable potable water.
To reduce the impact of additional inflows from irrigation use upon the vegetation ecology of natural drainage lines such as Grasslands Gully.
The drainage and water management issues in the subject catchments are impacting on values of the Domain and Botanical gardens. There are also some key assets within the Domain and Botanical Gardens, which could benefit from an improved integrated management approach.
Potential Responses
Flooding Management
This issue was the key impact prompting this report. Flood management is normally handled by a range of interventions to bring back the flows regime to something akin to natural.
Water Quality Treatment and WSUD
The need to address the sediment and trash loads entering the RTBG were part of the original focus of this project, but the need to address impacts of higher nutrients and sediment loads on the Grassland Gully and also the overall impacts of export loads to the Derwent Estuary needs to be considered.
Rainwater Harvesting and Reuse
Rainwater or stormwater runoff from the urban environment is often regarded as the ‘Cinderella resource’ and is not used to great extent in the Hobart Urban environment. The reuse of stormwater is already practiced at the RTBG site through use of roof water at the Kiosk toilets. However, the historical use of potable water for garden and sports field maintenance has been favoured due to the low cost and current abundant supply.
Ecosystem Management
The Grasslands Gully receives an unnatural supply of water derived from the watering of the soccer pitch area with potable water. The vegetation response in the upper gully with a range of rushes sedges and weed species is probably unnatural also. The provision of a wetland in the bowl area below the information shelter will allow trapping of sediments and also treatment of nutrients prior to some controlled release, recirculation and reuse for the maintenance of other assets such as the Soldiers Memorial Avenue plantings. It is important to maintain a level of wetness within the Grasslands Gully that sustains the preferred native assemblages of grasses and sedges. Adjustments to the orifice controls at the wetland can allow this to occur.
more on this project (PDF)
