Water Sensitive Urban Design (WSUD)

Posted on July 5, 2017

Water Sensitive Urban Design is the integration of urban, site & building design with constructed elements that can provide on-site stormwater quality treatment and its re-use in the built form.

Why is it important to treat Stormwater?

The primary purpose of treating stormwater is to protect surface water and ground waters in our lakes and rivers. The treatment will also help to reduce the effect of peak stormwater flows and protect the surface water from stormwater pollutants. Increased nitrogen and phosphorous in water ways can lead to unwanted growth of algae which can have a detrimental effect on plant life, aquatic life and animals due to a decrease of oxygen levels in water.

For example, the STORM tool sets the following criteria as the benchmark against which performance is measured:

•    Suspended solids (SS) – 80 per cent retention of the typical urban annual load
•    Total phosphorus (TP) – 45 per cent retention of the typical urban annual load
•    Total nitrogen (TN) – 45 per cent retention of the typical urban annual load
•    Litter – 70 per cent retention of typical urban annual load
•    Flows – maintain discharges for the 1.5 year ARI at pre-development levels

When is WSUD report or Stormwater Management Plan needed?

The councils of Bayside, Campaspe, Casey, Bass Coast, Monash, Moonee Valley, Yarra, Stonnington, Port Phillip, and Melbourne require any new development which is less than 3 dwellings in a subdivision, extensions which are 50 m² or greater and subdivisions in commercial zones to submit a WSUD report or Stormwater Management Plan.

In addition, all CASBE councils will require a BESS assessment which includes the STORM rating

What is the difference between a STORM Rating and WSUD Management Plan?

A STORM rating is only a component of a WSUD Management Plan. A WSUD Management Plan needs to clearly show the STORM calculation and a site plan which shows the areas included into the calculation and their method of treatment.
Furthermore, the rain harvesting and re-use strategy and stormwater maintenance plan are included along with the selected treatment option to deal with run off during construction.

Which councils require WSUD reports ?

WSUD policies are built into some council’s planning schemes (Bayside, Campaspe, Casey, Bass Coast, Monash, Moonee Valley, Yarra, Stonnington, Port Phillip, and Melbourne) and is a mandatory section in the Built Environmental Sustainability Scorecard (BESS).
BESS is a requirement for all CASBE councils within Victoria at the town planning stage of a project.

How important is the STORM rating  in the BESS tool?

Are there any other stormwater management options taken into consideration?

Within BESS, Stormwater is a mandatory credit in which you must receive 100% to pass a BESS assessment.

The total weighting of the stormwater section is 13.5% of the total score within BESS.

It is important to remember that the water section and stormwater section of BESS are different mandatory credits (water requires a minimum 50% score to pass BESS).

However, they are interrelated as the water section of BESS relates to potable water use reduction and stormwater treatment options (ie rainwater storage and reuse) have a big impact on this.

What are the most common strategies used to treat stormwater?

Common treatment methods include collecting rainwater from roofs and storing in rainwater tanks which can then be used to flush toilets or irrigate landscaped areas, or rain gardens which treat water run-off from hard surfaces such as driveways and pathways before discharging it to the municipal stormwater system.

Other options for water treatment which are less common for typical residential stormwater treatment but may be applicable in either are ponds, wetlands, buffer strips, sandy loams and gross pollutant traps. industrial or municipal stormwater systems.In some very large developments where a STORM rating of 100% cannot be achieved or is not practical, there is an option to pay a one-off Melbourne Water contribution to the creation of wetlands.  If complying via this method, you will need council approval.

Are there any issues with certain strategies?

All stormwater syStem treatments require regular maintenance depending on the type of treatment.
In the case of rainwater harvesting systems., roofs should be periodically cleaned to remove debris and stop any potential blockages in the piping of the system.

With regard to rainwater systems, sludge will accumulate in the tanks over time.That being said, sludge and biofilm is part of the purification process which occurs within the tank therefore it should only be removed when it is smelly or affecting the water quality.  only occurs when the tank level is Discoloured water or malodorous water is drawn from the sludge level. Only professional tank cleaners should clean rainwater tanks.

In the case of raingardens, filter media should be typically recommended to be inspected every 3 months and also after significant storm events for sediment build up at inflow and outlet points. Plants need to be checked periodically for overall health and general weeding should be carried out regularly. An annual test for adequate flow should also be undertaken.

How does a raingarden work?

Raingardens ideally contain drought tolerant plants which help filter stormwater (reducing nitrogen, phosphorus and suspended solids) run off before it enters our water ways. Storm water runs into the rain garden where it goes through a filter media which the plants are embedded. A filter media ensures that the stormwater drains before the stormwater enters waterways.

Where can I find more information about raingardens?

Melbourne Water has all the information relating to rain gardens and how to build and maintain them

SUHO has a wide range of experience producing WSUD reports and BESS assessments for projects in the planning stage whilst providing practical and cost effective solutions with developers & architects.

For more information about the various options give us a call.

Nick Sneddon

ESD Consultant