Little Stringybark Creek

Requirements > It is expected that new developments in the Little Stringybark Creek catchment achieve 70% of the maximum potential Environmental Benefit (EB) for the site. (Environmental Benefit is a score of how well stormwater is managed on the site).

How much? > Developers will be offered $1,500 for every unit of EB they score. For a site with 600m2 of roof and paving, $9,000 would be available if the full EB potential was achieved (EB Score of 6.0). If 80% of the maximum potential EB was achieved (EB Score of 4.8) then $7,200 would be available.

Why is it important > The Little Stringybark Creek catchment is degraded because of too much stormwater runoff. This catchment is part of a research project to monitor the improvements to the stream from implementing Water Sensitive Urban Design (i.e. treatment systems that retain and treat stormwater). Any new developments in the catchment will further degrade the stream and compromise restoration efforts unless the runoff from any new impervious surfaces such as roofs and pavements is directed to tanks or rain gardens.

Am I eligible? > To be eligible, the property you are developing needs to be located in the project area (click here). Also, it is expected that new developments in the Little Stringybark Ck catchment achieve 70% of the maximum potential EB for the site. For example a minimum of 2.1 EB units would be required for a new development with 300m2 of impervious area. To discuss your eligibility and decide the most appropriate treatment system please contact Darren Bos, the Little Stringybark Creek Project Coordinator on 8344 9248 or 0447 551 522.

How can developers minimise impacts > Tanks and rain-gardens benefit Little Stringybark Creek by keeping damaging stormwater out of the creek when it rains and allowing cleaner, filtered water to flow to the creek.

All proposed treatments in the creek's catchment are assessed for the benefit they provide to the creek. This is done via the Environmental Benefit (EB) Calculator. Doing so not only aids in the design of works (such as the required size of the rain-garden), but also provides us with a cost/benefit analysis of the proposed works.

The Environmental Benefit (EB) calculator lets you try different tank and rain-garden installation ideas to see which ones earn the best EB scores.

The intent of the Environmental Benefit Index is to:

· Maintain the predevelopment frequency of surface runoff

· Maintain the predevelopment volume of stormwater

· Maintain predevelopment infiltration rates

· Comply with State Environment Protection Policy objectives for nutrients and sediment

An overall index equally weights these metrics which is standardised to 100m₂. eg . A property with 200 m² of roof and 100 m² of paving (300 m² in total), connected to the stormwater drainage system, has the potential to earn 3 EB units.

What type of system do I need? > There is a range of ways to retain and treat stormwater running off your site.

The most effective way is to utilise a rainwater tank with the overflow of the tank connected to a rain garden. To make the best use of your tank and gain the most EB units the tank should be connected to a range of internal uses like hot water, toilet and utilised for garden watering.

Rain-gardens are very versatile and come in a range of designs from simple scoria filled infiltration trenches to planter boxes. Melbourne Water has developed a series of fact sheets for various types of rain-gardens.

Infiltration rain-garden (still in preparation)
Unlined rain-garden (still in preparation)
Lined rain-garden
Planter Box rain-garden
Swale (still in preparation)

Rainwater tanks can be used for a range of internal and external uses. The Plumbing Commission web site provides information regarding the use and installation of rainwater tanks. http://www.pic.vic.gov.au/www/html/477-rainwater.asp

What size tank or rain-garden will I need? > The table below shows typical treatment systems that can be utilised to achieve the minimum requirements for typical impervious areas in the Mt Evelyn catchment.

Building Type	Impervious Area Range (m²)	Recommended Treatment to Achieve Minimum Requirement
Garden Shed	<25	Consider a rain-garden* only (2m² by 1m deep in size)
Carport/Garage	25-50	Consider a rain-garden only (4m² +/- 2m² in size)
Large Barn	50-150	Consider a rain-garden only (8 +/- 2m² in size)
Townhouse	180	Consider a 2000L rainwater tank^ used for garden watering and toilet flushing with the overflow connected to a rain-garden (>1m2 )
Medium Size or Medium Density Dwelling	200	Consider a 2000L rainwater tank used for garden watering and toilet flushing with the overflow connected to a rain-garden (> 1m2)
Low Density Dwelling or Large House	375	Consider a 5000L rainwater tank used for garden watering and toilet flushing with the overflow connected to a rain-garden 8 +/- 2m² in size)

Note: *Rain-gardens must not feature slotted under-drains with uncontrolled outflow. If these systems are lined, they must feature a standpipe which allows controlled outflow out of the filter. The depth of these systems is typically around 1 metre which includes a 600mm infiltration zone (scoria layer). The ponding depth of these systems must be around 20 cm. ^Rainwater tanks should ideally be connected to around 80 to 100 percent of the available roof area.

Alternatively the graphs below also provide a simple guide to the size required to adequately retain and treat stormwater runoff from your site.

Firstly find the impervious area of your site from the bottom of the graph. Each line on the graph represents a different size system. The vertical axis of the graph then tells you what % EB you have achieved for your site. If you are above 70% you are eligible for funding. Ideally we’d like you reach 100% as this will assist in improving the health of Little Stringybark Creek.

Sizing graphs are currently provided for:

An infiltration rain-garden (Link)
A rainwater tank (Link)
A rainwater tank with overflow connected to an infiltration rain-garden (Link)

If you are interested in variations on these designs then you can input your specific design requirements into the on-line EB calculator.

Are you applying for a permit to subdivide under Clause 56? > Currently Clause 56 requires residential subdivisions to treat stormwater to current practice. The works in Little Stringybark Creek are aiming for higher treatment and retention. Melbourne Water currently allows payment towards regional water quality works in lieu of treatment for developments less than 1ha.

The payment for a 1ha residential subdivision in the Shire of Yarra Ranges is $6,195. Typical developments in Mt Evelyn region are around 2,000m2 or 0.2Ha. This would equate to an offset payment of $1,239. In order waive this payment and receive funding from the Little Stringybark Creek Stormwater Fund you will need to achieve 70% of the maximum EB for your site.

Case study> A developer recently submitted a application to subdivide a property within the Little Stringybark Creek Catchment into four lots in addition to the construction of three new. An environmental steward, the developer proposed to retain and treat runoff on the site through the use of water sensitive urban design techniques including rainwater tanks and an infiltration trench.

It was shown that the use of these techniques could achieve 3.8 environmental benefit units. This was greater than 70 percent of the maximum attainable environmental benefit (4.8 EBs) for the proposed development and as such, the Stormwater Fund payed the developer $1500 per environmental benefit – $5750. The developer was given approval to carry out the proposed works and construction is soon to be completed. The implementation of water sensitive urban techniques has likely increased the value of this development.

Who to contact > For further information and face to face consultation please contact Darren Bos, the Little Stringybark Creek Project Coordinator on 8344 9248 or 0447 551 522