A Water Sensitive Urban Environment:

Water Sensitive Urban Design (WSUD) is also known as Low Impact Development (LID) in the United States, and Sustainable Urban Drainage Systems (SUDS) in the United Kingdom.

It all refers to the land planning and engineering design approach that integrates the urban water cycle, including stormwater, groundwater, and wastewater management and water supply, into urban design. This is done to minimise the environmental degradation as well as improve the look of the area.

Why use WSUD? According to the guidelines released by the South Eastern Councils in Melbourne Victoria, WSUD has been identified as a “means to control flows and filter stormwater to remove pollutants”.

Stormwater is the water that runs off urban surfaces after heavy rainfall. The report said it has been identified as the key cause of pollution and declining health of waterways.

“With increased urban development, the proportion of impervious surfaces in our catchments increases. This increases the velocity and amount of water running into our waterways, creating problems of erosion and flooding and changing natural flow regimes, with associated ecological damage. It also washes more pollutants into our streams, further impacting river health.”

Victoria councils, like other councils in Australia, have recognised the importance of sustainable water management such as WSUD. The release of various guidelines enables organisations to have a first point of reference for their projects.

The design “integrates urban water cycle management with urban planning and design, with the aim of mimicking natural systems to minimise negative impacts on the natural water cycle and receiving waterways and bays”.

Some of the key principles of WSUD as stated in the Urban Stormwater: Best Practice Environmental Management Guidelines (BPEMG) include:

• Protect and enhance natural water systems within urban environments.
• Integrate stormwater treatment into the landscape, maximizing the visual and recreational amenity of developments.
• Improve the quality of water draining from urban developments into receiving environments.
• Reduce runoff and peak flows from urban developments by increasing local detention times and minimising impervious areas.
• Minimise drainage infrastructure costs of development due to reduced runoff and peak flows.

Australian states started to release WSUD guidelines based on the federal government’s foundational research in the 1990s. Western Australia first released theirs in 1994 followed by other states like Victoria, New South Wales, Queensland and so on.

The Citygreen® products are designed to ensure it supports the effort for a sustainable water management. The Stratavell’s™ octagonal modules leave over 94 percent of its total volume for root growth and storm water harvesting. Find out more about the products here.

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Supporting Urban Trees:

It is common knowledge that in order for a tree to thrive, the root network must be able to access enough water. If there is insufficient water then the tree will be unable to absorb nutrients from the soil and will deteriorate as a result of the water loss that occurs during transpiration.

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What You Need For a Successful Urban Treepit Design:

The benefits that healthy urban trees provide to the environment are significant, but the environmental conditions in urban spaces can often be challenging for their establishment and long-term survival.

In order to provide urban trees with the best chance of survival, it is important to consider the conditions of soil, climate, and water availability that trees face when they are planted in towns and cities. The correct design and installation of tree pits will mitigate the negative effects of the urban environment.

There are several key factors to consider, including root volume availability. The following soil volumes at a minimum are recommended for healthy tree growth:

Small tree 5-15 m³

Medium tree 20-40 m³

Large tree 50+ m³

If in case this amount of space is not available, tree establishment can still happen provided that great care is taken with regard to species selection and root management. In all cases, the deployment of structural root cells can help to prevent soil compaction and ensure that the available rooting volume is fully utilized.

This is very important if the tree is to be located next to a road or another engineered structure, as the soil structure requirements for hard surfaces capable of sustaining large weights are diametrically opposed to those of a healthy tree root network.

Aside from providing sufficient volume for growth for tree roots, it needs to be appropriately directed to ensure that they do not damage surrounding surfaces or underground structures. Paved surfaces and utilities are particularly vulnerable to tree root damage and various types of root management products can be specified depending upon the item that requires protection.

For example, if a tree pit is to be located amidst a continually paved surface then the tree roots will need to be managed downwards by at least 300mm or the depth of the pavement structure to remove the possibility of paving heave.

Next, we’ll discuss more about proper irrigation, drainage and aeration to raise a strong tree network.

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