As a landscape architect, one of my key focuses is to create functional and sustainable outdoor spaces for my clients and the community. Recently, I've had the opportunity to work on some large-scale residential developments along the Central NSW coast. These projects often require careful engineering of the landscape to create roads and infrastructure, which can have an impact on water permeability and local habitats.

One of the most important features of these projects are the vegetation basins, which serve multiple purposes, including water quality management, community engagement, and providing habitat for wildlife.

Typically, the design of basins focuses mainly on water quality, with the goal of minimising earthworks and maximising water capture and filtration. However, as a landscape architect, our role I believe there are a number of ways we can improve the design of these basins to make them more resilient and sustainable. Basins offer an opportunity to rehabilitate the local vegetation communities, resolve existing and future soil erosion, and promote a stronger connection between people and our water.

1. Naturalising the Spillway

Spillways are an important component of vegetation basins and play a crucial role in managing water flow and preventing flooding.

Traditionally, engineers often used concrete culverts for spillways in basin design. While these solutions are low-cost and easy to calculate water volumes and speeds, they don't take into account the impact on the environment and visual aesthetics. In addition, during heavy rainfall or flood events, concrete culverts can become overwhelmed and cause erosion and damage to infrastructure.

An alternative solution, which should be recommended more often for vegetation basins, is the use of wide, vegetated spillways. This type of spillway can be achieved through a grassed swale or rock-clad design and can provide a number of benefits over traditional concrete culverts.

One of the key benefits of vegetated spillways is that they are more flexible and can better handle varying water volumes. This is because they have a larger surface area, which allows water to spread out and infiltrate the soil. This can reduce the risk of flooding and erosion, and can also help to improve water quality through filtration.

Vegetated spillways also have a lower carbon footprint than traditional concrete culverts, they can improve urban heat mitigation, and they can provide important habitat for native wildlife. They also tend to be more visually attractive and can create a more inviting and human-friendly space.

It's worth noting that vegetated spillways do require some ongoing maintenance, such as regular mowing, weed removal, and plant replacement. Also, it's important to choose the appropriate native plants for the local climate and conditions to ensure the spillway can function properly.

In summary, vegetated spillways are an effective alternative to traditional concrete culverts for vegetation basins in Australia. They provide more flexibility, better water management, and improved environmental benefits. These spillways not only improve the functionality of the basins but also create an attractive, peaceful, and functional space for human and native wildlife.

2. Connecting the dots through Basin Chaining 

Basin chaining is an effective way to improve the functionality and sustainability of vegetation basins in Australia. By connecting one basin to another, the water flow is spread out over a larger area, allowing for a greater holding capacity. This can be particularly beneficial in areas that are prone to flooding, as it allows for a more even distribution of water, reducing the risk of damage to infrastructure and property.

Basin chaining can also create a dedicated open space that can be used by the community and can provide important habitat for native wildlife. This can be particularly beneficial in urban areas where green space is often limited. The connecting swales can be designed to be visually attractive, featuring Australian native plants and rock features that can create a more appealing and naturalistic environment.

In addition, basin chaining allows for a more gradual water flow. When water flows in one basin, it will fill up and overflow into the next, this creates a gentle flow of water that is less likely to cause erosion and can be beneficial for plants and aquatic life. This also creates a peaceful atmosphere, as the water movement provides white noise.

Another advantage of basin chaining is that it is a more sustainable solution. It doesn't require the large scale of earthworks that traditional basin solutions demand, it also uses less materials and energy to construct. It also allows for greater retention and use of on-site water resources, this reduces the need for off-site water management solutions.

It is important to note that while basin chaining offers many benefits, it also requires careful design and planning. The chains of basins should be designed to handle the expected water flow, so that the basins don't become overwhelmed during heavy rainfall events. They also require regular maintenance, such as removal of weeds and debris to keep them functioning properly, and the native plants chosen should be appropriate to the local climate and growing conditions.

In summary, basin chaining is a versatile and sustainable solution for basin design that provides water management, community engagement, and habitat protection in Australia. By combining basin chaining with native plants and creating an attractive, peaceful, and functional space for both human and native wildlife, it can be a great way to improve the ecological health of urban and suburban areas.

3. Layering through terracing & vegetation

Terracing and vegetating basin designs are another effective way to improve the functionality and sustainability of vegetation basins.

Terracing involves creating different levels or ledges within a basin to create different water depths. This can be achieved through the use of retaining walls, berms, or other forms of earthworks. Terrace basins can be an effective way to create different microclimates within a basin, which can support a diverse range of plant species and aquatic life. This can be useful in creating a range of habitats and improving water quality by increasing the surface area of the plants and providing a greater range of filtration.

Vegetating a basin design means adding plants to the basin in order to create a more natural and visually attractive space, it also provides habitat and improves water quality through filtration. When choosing plants for basin vegetations, it is important to select species that are appropriate for the local climate and that can tolerate the conditions found within the basin, such as varying water levels and saturation.

One way of vegetating a terraced basin in would be to include a series of planting zones, with each zone corresponding to a different water depth. For example, in the shallowest zone, you might choose Australian native plants such as Lomandra or Schoenoplectus, which can tolerate standing water, while in the deeper areas, you could choose species such as native water lilies or native lotus (Nelumbo nucifera), which can tolerate deeper water. Refer to my previous blog for more information on planting zones in water basin design.

Terraced and vegetated basin designs also can have a positive impact on water temperature. During the summer, vegetated basins can reduce water temperature by up to 10°F as well as providing shade for fish and other aquatic life.

Terraced and vegetated basin designs also can be visually attractive and can provide an oasis for residents and visitors. This can be particularly beneficial in urban areas, where green space is often limited. They also can provide a sense of tranquillity, improve air quality and can reduce the urban heat island effect.

It's worth noting that terraced and vegetated basin designs require careful planning and maintenance to ensure that they are functioning properly and continue to support the intended range of plant and animal life. This includes regular monitoring of water levels, removal of invasive species, and replacement of plants as needed.

Overall, terracing and vegetating basin designs can be a valuable tool for creating functional and sustainable vegetation basins that support a diverse range of plant and animal life and improve the overall health and aesthetics of the surrounding environment.

As landscape architects, we have a variety of tools at our disposal to create functional and sustainable vegetation basins that provide essential water management, community engagement, and habitat protection. By considering these design improvements, we can create more resilient and sustainable vegetation basins that not only provide water management and filtration but also provide engaging spaces for human and native wildlife, making our surroundings a better place for all.

Thanks to Blacktown City Council for the fantastic examples of basin design pictured throughout. Check out the Water Sensitive Urban Design Guidelines for their initiatives and more information on best practice design.