Gosford City Council music case study

Stormwater harvesting could ease mains water demand

A decade of drought and extreme rainfall unpredictability has left councils across Australia in no doubt of the pressing need to plan for infrastructure to secure future water supply.

Dam storage levels in many communities dropped below 30 per cent at the height of the drought. In response many utilities are diversifying sources to reduce reliance on rainfall run-off stored in dams.

Gosford City Council has been investigating the feasibility of using harvested stormwater for non-potable water use to diversify its water sources.

Image courtesy Gosford City Council

Outcomes and benefits

Many local government authorities are compiling year 2050 plans projecting expected growth and required infrastructure as a condition for receiving ongoing Federal funding.

Gosford City Council is engaged in such a planning process to help meet its responsibilities for supplying water to its residents. The research was undertaken to help with the exercise.

The project shows harvested stormwater could reduce mains water consumption by up to 38 per cent. However further investigation will be required to determine the viability of implementing these stormwater harvesting schemes.

The researchers warn the current price of recycled water is too low for stormwater harvesting schemes to be financially competitive, meaning subsidisation may be required. They also suggested future investigations should focus on stormwater harvesting schemes for catchments of at least 30 hectares, in order to achieve the greatest economies of scale.

The results are playing a valuable role in helping the Council with water recycling planning as it seeks to balance water demand and supply, while ensuring future water security. Being able to harvest stormwater for reuse would give the Council an alternative water source to add to the mix.

There are many water uses which do not require potable water, including irrigation, toilet flushing, and vehicle washing. Using water of lower quality like harvested stormwater could significantly reduce the demand on the mains water supply.

“Using music as the major tool in the project helped with high level conceptual modelling of potential stormwater run-off quantity. Where feasible, Council intends to use harvested stormwater for non-drinking water demands such as sports field irrigation, toilet flushing and car washing,” Mr Borg says.

“The Stormwater Harvesting research project has given the council some basic information to assist in our water security planning. It is one part of the puzzle to provide a secure water supply for Gosford. The council plans to undertake other studies, to determine the potential demands for stormwater reuse, and suitable locations for stormwater harvesting infrastructure.

music is the best tool available for this investigation and made the research project a lot easier to complete.”

Not a detailed design tool in itself, music rather aims to set out the alternatives for improving stormwater quality. The software is allowing planners to assess the pros and cons of various engineering systems for improving stormwater quality – biofilters, swales, wetlands and the like.

It includes major advances to the science and enhances the ability to model new stormwater technologies like porous pavements. It also includes raw rainfall data for 50 major population centres in Australia.

Using eWater’s urban stormwater modelling software, music (model for urban software improvements conceptualisation), a project team from the University of Technology, Sydney, assessed the viability of stormwater harvesting to supplement the existing water supply. Environmental and engineering consultants around Australia use music every day to design urban development proposals that meet water sensitive urban design standards.

“Council wanted to estimate the volume of harvestable stormwater runoff as it investigated different potential sources to secure a long term solution for the local water supply. music is a good modelling tool for planning stormwater reuse,” Gosford City Council’s Project Supervisor Mikell Borg says.

“We divided the Local Government Area into rural, semi-rural, and urban sub-catchments, focusing our attention on the urban sub-catchments. Using the music software, we estimated the annual volume of stormwater run-off of each of the urban sub-catchments. “

Applying music to the water balance modelling of the existing catchments allowed the researchers to determine the size of stormwater store required to meet the projected demand.

“We fed data into music, includingrainfall data from the Bureau of Meteorology, soil property information, catchment areas, evapotranspiration data, and landuse information” Borg says. “Based on these factors, music estimated annual stormwater run-off from each urban sub-catchment, allowing us to get an idea of the total run off from all urban sub-catchments in the LGA,” Mr Borg said.

“The software also allowed development of scenarios for application to each catchment area. The scenarios were useful in highlighting trends associated with any potential stormwater harvesting schemes.”