Thoughts on designing with water. — LANDSCAPE ARCHITECTURE AOTEAROA

The 2023 floods that swept through Tāmaki were a wake-up call on the way we design our cities. The destruction and displacement caused by these unprecedented weather events brought to light the need for holistic approaches to urban development. Isthmus Principal Landscape Architect Grant Bailey has been thinking about the way we design to assure that resilient stormwater systems are a part of our future.

Go with the flow.

Cities need to embrace regional water planning and natural processes and create localised climate drainage policies. Trying to engineer water to stay in streams and rivers is a never-ending task. Water needs space to move; it passes as quickly as it arrives. The goal should be how best to keep people and property safe and secure at acceptable levels, not forcing the water to conform to human control. Ultimately, embracing water planning and natural processes aims to achieve a balance between human needs and the environment. This requires recognising that water is not just a commodity but a dynamic living environment that deserves respect, care, and protection. By creating adaptive climate drainage policies aligned with these values, we can ensure that our water resources are managed in a way that benefits all and creates a legacy of sustainable and resilient communities for generations to come.

Access indigenous knowledge – Ki Uta Ki Tai.

Cultural knowledge and traditional indigenous thinking have a powerful impact on shifting perspective and balancing solutions for managing risk. In the Māori worldview, water is a taonga, a treasure that sustains all life. Therefore, embracing water planning and natural processes is essential to ensure the well-being of the environment, the people, and the culture. This means acknowledging that water is a dynamic force that cannot be entirely tamed or controlled by human intervention. Instead, it requires working with the natural processes of the land and sea to manage water in a way that benefits everyone. This includes recognising and respecting traditional Māori knowledge and practices of water management, such as the principles of kaitiakitanga (guardianship) and waiora (water health). A river is not just the river, but the whole catchment, including tributaries – Ki uta Ki tai (from source to sea).

Mokihinui River, West Coast of the South Island. Conservation land and site of the proposed hydroelectric dam. Following initial approval of the application, the Department of Conservation (DOC) and other parties, including Isthmus, took a successful appeal to the Environment Court. Image Credit: Isthmus.

Suck it up.

Sponge cities and climate streets are great concepts. These successful ideas from other parts of the world need to be adaptable to geographically specific catchments. Planning and controls should respond to and work for local conditions, including soil permeability and proximity to the coast vs. inland floodplains. These ideas need consideration in both local natural and cultural contexts and within private and public land. Cloudburst in Copenhagen is a good example of balanced solutions, using Blue (water), Green (vegetated), and Grey (concrete) infrastructure. Surface storage and flow paths within hard landscapes of streets and plazas and streams (blue), greenways and open space (green) to hold back peak events, and overland flow paths or sub-surface tunnels (grey) to direct extreme flows directly to the coast.

Kopupaka Reserve, Tāmaki Makaurau. This hybrid park integrates infrastructure with natural features; it’s part stormwater reserve, urban park, playground and skate park. Image credit: Isthmus.

Capture the runoff.

Ensure the Resource Management Act (RMA) makes an appropriate assessment of development effects. Assessment should be climate-relevant and not limited to the effects of a 100-year event only. Hard surfaces and increased runoff from private and public development should be part of consenting assessments. Impervious surface controls help and are great for smaller events, but large extreme cloudburst events saturate the ground, causing it to act as impervious. This, in turn, causes topsoil and silt to wash into our streams and harbours at rates well beyond predevelopment flow rates.

Manage downstream effects.

We are still designing for a 100-year event in terms of risk. The design and development community will only design to the codes set by the Government and Council. We need to change the rules so the whole system will collectively contribute to managing downstream effects and an acceptable level of risk on an appropriate scale and event frequency. This is economically complex as insurance and liability create false ceilings on the increasing levels of risk. We could have a two-tier approach: one for agreed insurable risk and government liability, and another that accommodates extreme events beyond? Hobsonville is a good example of a systems approach to stormwater management, but it has very little downstream impact as it discharges directly on the coast. Other inland development sites are more complex and have greater catchment impacts; therefore, wider assessment of effects should be applied.

Detention at source.

Water should be held at the source; projects should capture all water on-site, even in high-density areas with full build lots. This puts more cost on the developer and on housing affordability, but it does not push all the problems to the Council and ultimately the taxpayer. In some countries, planning restricts discharge to the public system for anything under a 10-year event. They use rain gardens, green roofs, or underground cisterns to hold back water at the source.

Slow the flow.

Use existing parks and open space; this is easy to do in terms of using limited available space to accommodate water in a dense urban city. Greenslade Reserve and Awataha show that this can be done well with appropriate drainage and minimal disruption to recreational use after the storm event. We need to be careful not to put all the high-velocity water and energy into existing streams, as this might cause increased erosion and wash out sensitive ecology.

Allow roads to become rivers.

Water in the road is not necessarily a bad thing—it’s better than water being in people’s property. Planning of critical transport routes in times of flooding, like the motorway and key arterial routes, needs to remain open. However, residential streets, as long as people are safe in their homes, can accommodate overland flow paths that will allow water to move away quickly to the coast. We need to rethink our roads’ capacity to hold and move water. Cycleways that require less load than roads could be key to rethinking a softer, more permeable asset in unlocking capacity for water infiltration.

Te Ara Awataha project in Northcote has daylit the Awataha Stream along with critical infrastructure upgrades to the stormwater network, working with nature to mitigate against climate change and protect the town centre from flooding. Image credit: Isthmus.

Plant trees.

It’s not just the low-lying land that is vulnerable to water impacts—saturated ground on steep banks, cliffs, and escarpments arguably put more lives at risk. Keeping urban stormwater away from these landscapes requires careful attention. Slips and water-soaked soil mean the sponge is full, and when it’s full, it has no ability to absorb, causing it to become fluid again. These areas are vulnerable; planting trees will help hold the slope but this requires management as large trees can add weight that sometimes actually triggers slips. Kaitiakitanga principles and stewardship of vulnerable landscapes, including vegetation and pest management, including invasive species, could provide wider biodiversity benefits to our urban landscape.

Do density well.

We are building more dense cities. Affordable housing is driving more density, and in some areas, this is nearly four times the number of houses on the same land. Have we got the balance right between chasing affordability and ensuring resilience? Density done well should be balanced with a finer grain in water-sensitive areas. The water suburb could be a zone overlay that has less density and more permeability rules, emphasizing soft site development prior to yield. In less flood-prone areas, increase the detention requirements; parking must be permeable and/or grouped together – working with site contour instead of large retaining for flat sites that shed into all the driveways, which are often concrete and steep.

Value natural systems.

Water and the rhythm of nature are everyday experiences; we should celebrate the value of water. Rivers, streams, wetlands, and estuaries are rich biodiverse places – they can be designed to enhance community and the access to and the experience of nature in the city. Research has been done on the ability to use stormwater and rain intensity for energy generation – what could the hydro–city look like? How do we design to harness the power of water to give back spiritually, environmentally, recreationally, and economically?

Creating a climate drainage policy that aligns with these principles will require a shift in thinking from a human-centric approach to a more holistic and collaborative approach that involves the community, local iwi, and other stakeholders. This means understanding the interdependence of water systems, land use, and climate change and how they affect each other. It also means acknowledging that water management is not just a technical or engineering problem but a social, cultural, and environmental one that requires a multi-disciplinary and integrated approach. Therefore, the policy should focus on promoting sustainable land use practices, protecting and enhancing natural waterways and ecosystems, and building community resilience to extreme weather events.