5/2024 – Terracrete™ permeable hard lawn pavers play a vital role in sponge city design
The sponge city concept is an urban planning model that uses nature-based solutions (NbS) to manage stormwater and reduce the impact of urban development on ecosystems. The goal is to improve urban liveability by imitating the natural water cycle and increasing evaporation. Sponge cities are designed to absorb rain, prevent flooding, and improve the urban climate.
Terracrete™, a permeable interlocking concrete paver (PICP) developed by Terraforce®, retaining block developer based in South Africa in 1999, is ideally suitable for this purpose, as it is a paving block with larger openings (40% open), compared to paving blocks with widened joints (15% open). Says Rust, founder, Terraforce: “The bigger openings allow for coarse infill to be used which means better infiltration and easier maintenance. In addition, something that is often neglected, this allows tree roots to breathe, to absorb water and nutrients that get washed off the paved areas.”
For more technical information on Terracrete: Terracrete™ – Terraforce
WATCH: Terracrete for sponge city design
When used as part of sponge city planning, Terracrete blocks offers several benefits:
Permeability: The blocks are designed with multiple large voids, allowing water to infiltrate the ground below. This permeability helps to reduce surface runoff and mitigate the risk of urban flooding by allowing rainwater to be absorbed back into the soil, mimicking natural hydrological processes. In scenarios where the water table is high or the soil’s absorption capacity is exceeded, excess water can be managed through additional measures, such as underground storage tanks, existing drainage systems, bioswales and rain gardens.
Stormwater Management: By allowing rainwater to permeate through the openings, Terracrete blocks help manage stormwater effectively by allowing a more natural absorption of water into the native soil.
The blocks are designed with enough strength and stiffness to make them suitable (with the appropriate sub-base construction and in some cases wired together with galvanised fencing wire) for vehicular traffic, which makes them perfect for applications that would traditionally be impermeable, such roads, walkway and parking areas. This ultimately helps reduce runoff volume and velocity, alleviating flooding and soil erosion.
Groundwater Recharge: The permeable characteristics of the blocks facilitate groundwater recharge by allowing rainwater to infiltrate the soil through a drainage layer (typically gravel or crushed stone) that temporarily holds water, letting it percolate slowly back into the subsoil. This helps to replenish underground aquifers, which are vital sources of water for drinking, irrigation, and other uses, particularly in areas prone to water scarcity.
Pollution Reduction: Terracrete blocks can also help improve water quality by filtering pollutants and contaminants from stormwater runoff. The naturally occurring micro-organisms in the soil in the blocks and in the sub-base, digest oils and spills, another important advantage. Any grass or other suitable vegetation also acts as natural filter, cleaning the water further. This helps to reduce the number of pollutants entering water bodies, thereby protecting water quality and ecosystem health.
Aesthetic Appeal: The blocks can be laid in three different patterns, interlocking with or without additional wiring for strength, offering flexibility in design while enhancing the aesthetic appeal of urban spaces.
Says Rust: “from an aesthetic point of view, they are very versatile. A grass driveway, a rustic gravel driveway, or an attractive pattern of Terracrete pavers can add the finishing touch to a custom home looking to stand out. With a grass finish, they can add a park-like or pastoral feel to areas normally needing hard paving.” They can also be integrated into sidewalks, plazas, and other public areas such as parking spaces, adding visual interest and contributing to the overall attractiveness of sponge city environments.
Heat Island Reduction: Grassed Terracrete pavers help to mitigate the urban heat island effect by providing shade and evaporative cooling. The grass growing within and around the pavers transpires water, which evaporates and cools the surrounding air, while also providing natural shading to the underlying pavers, reducing the amount of heat absorbed by the surface. This contributes to a more comfortable urban environment and reduces energy consumption for cooling purposes.
Durability and Longevity: Terracrete blocks are durable and resistant to environmental degradation, making them suitable for use in various climate conditions. This longevity ensures effective stormwater management can be provided for an extended period, contributing to the long-term resilience of sponge cities. Damaged blocks can easily be replaced, when necessary, while the design of the substrate can assist in prefiltering water.
Adding vegetation is the ultimate goal
Grassing the Terracrete blocks adds to their ability to acts a green eco-surface in a sponge city design. Altus Eitner, Streets & Stormwater / Project Planning & Management, Mossel Bay Municipality, South Africa, commends the block: “Thanks to large holes and a unique interlock the blocks are fully permeable and plantable, which adds to their ability to fully integrate with any environment they are introduced to.
“The roots of the plants anchor the blocks and help to strengthen them, especially against floods. The holes also allow worms and bugs to pass through the block without sterilizing (smothering) the area. Added to this, maintenance of the installations is easy, as the blocks provide a stable platform for the mowing of the grass if needed.”
How to grass your Terracrete eco-surface:
Please note: Each site will be unique to area and country of installation.
- All blocks to be brush filled with a topsoil and organic fertilizer mix of a high compost fraction (40/60). Aim for a mix best suited for whatever plant species chosen, in this case Cynodon Dactylon, which is relatively drought resistance once established.
- Soil to be lightly compacted and watered, and finally seeded with 40g per m² of warm season grass such as Cynodon Dactylon or other grass / plants suited to local climate. Alternatively use cuttings.
- Plants to be carefully selected using the following criteria: Conduct an on-site survey to identify the locally indigenous vegetation naturally occurring on site and surrounding areas. It is suggested to consult a national vegetation book and to select species carefully based on site rehabilitation.
- Seeds to be scattered, racked/swept and recompacted.
It’s a no-brainer. Permeable surfaces are key for floodwater management
Overall, Terracrete permeable hard lawn pavers play a valuable role in sponge city planning by providing sustainable stormwater management solutions that help cities become more resilient to water-related challenges while enhancing their environmental sustainability and liveability.