Managing stormwater effectively is crucial for protecting our communities, waterways, and infrastructure. With increasing urban development and climate-related challenges, ensuring proper stormwater solutions is more important than ever.
Across New Zealand, councils are introducing stricter regulations to improve flood resilience and manage stormwater effectively. Plan Change 27 (PC 27) in Tauranga and Plan Change 14 (PC 14) in Waikato are two examples of how new flood modelling data is shaping the way developments must be planned. Property owners and developers must now consider flood maps, resource consents, and future climate impacts when planning new projects.
At CKL, we help clients navigate these challenges by providing expert stormwater management advice, flood modelling, and practical solutions to meet council requirements while supporting sustainable development.
This Q&A covers key aspects of stormwater management, including how PC 27 and PC 14 affect developments and what property owners can do to mitigate flood risks. Read on to learn more.
What is stormwater?
Stormwater is the runoff from urban surfaces, such as roads, roofs, and footpaths, caused by rainfall or melting snow. This water flows into drains and an underground pipe network before eventually being discharged into local waterways, such as rivers, lakes, or the ocean. Unlike wastewater, stormwater is often untreated, meaning any pollutants it picks up along the way can end up in the environment.
Why is stormwater management important?
When stormwater isn’t properly managed, it can lead to flooding, erosion, and contamination of waterways. In urban areas, hard surfaces like concrete and asphalt prevent water from naturally soaking into the ground, increasing the volume and speed of runoff. This can overwhelm drainage systems and cause damage to property and infrastructure. Effective stormwater management helps protect communities, waterways, and ecosystems from these risks.
How does poor stormwater management affect local environments?
Stormwater can carry contaminants such as sediment, oil, heavy metals, and chemicals into local rivers and coastal areas. Over time, sediment buildup can disrupt aquatic habitats, reduce water quality, and contribute to erosion. In areas where stormwater and wastewater systems combine, excessive runoff can lead to overflows, putting both public health and the environment at risk.
How can stormwater be managed effectively?
Modern stormwater management focuses on controlling water flow and treating contaminants as close to the source as possible. This is known as Water Sensitive Urban Design (WSUD), which mimics natural processes to manage runoff in a more sustainable way. Some effective stormwater management techniques include:
- Raingardens – Landscaped areas that absorb and filter stormwater.
- Pervious paving – Surfaces that allow water to soak through instead of running off.
- Swales – Shallow, vegetated channels that slow and filter water.
- Green roofs – Roofs covered with vegetation that absorb rainwater.
- Soakage devices – Systems that allow water to infiltrate into the ground.
Flood modelling helps predict how water will move across land during heavy rainfall. Councils provide general flood modelling, but it often doesn’t account for site-specific factors like existing buildings or changes to land use. At CKL, we conduct more detailed flood modelling to provide accurate, tailored solutions. This ensures developments can proceed while minimising flood risks.
What happens if a property is identified as being in a flood-prone area?
If a site is identified as flood-prone, property owners are often required to engage stormwater specialists before development can proceed. CKL works closely with councils and developers to assess flood risk, interpret flood models, and provide solutions such as adjusting site levels, designing appropriate drainage, or implementing stormwater attenuation measures.
What is Plan Change 27, and how does it impact developments in Tauranga?
Plan Change 27 (PC 27) is a regulatory update designed to ensure new developments in Tauranga are resilient to flooding caused by intense rainfall. The plan introduces a rule framework within the Tauranga City Plan, requiring developments in flood-prone areas to meet stricter requirements. Key aspects include:
- Checking flood maps – Tauranga City Council provides public flood maps based on LiDAR data to help property owners identify if their land is at risk.
- Managing development in flood-prone areas – Certain sites may require resource consent to proceed with building or subdivision.
- Ensuring appropriate floor levels – Developments must factor in flood resilience measures to reduce the risk of property damage.
- Considering long-term flood risks – Models now account for climate change and sea level rise through to 2130, ensuring future-proofed solutions.
What is Plan Change 14, and how does it impact developments in Waikato?
Plan Change 14 (PC 14) focuses on flooding resilience in the Waikato region. It incorporates new flood modelling data through Council's Floodviewer Maps, which now identify significantly more properties at risk of flooding. The provisions under PC 14 have immediate legal effect and will shape how properties in flood-prone areas can be developed. Key aspects include:
- Updated flood maps – The latest modelling has expanded the list of properties at risk.
- Regulatory changes – Stricter rules apply to developments in areas identified as flood-prone.
- Submission process – Submissions on PC 14 are open until 28 February 2025, giving stakeholders an opportunity to provide feedback.
Can stormwater issues be caused by nearby developments?
While it’s easy to assume that new developments are the cause of increased flooding, that’s not always the case. Water naturally follows flow paths, and changes to land use upstream or downstream can alter runoff patterns. CKL has worked on projects where property owners have attributed flooding to nearby construction, only to find that the issue was due to existing drainage constraints. Our expertise helps identify the true source of the problem and develop appropriate mitigation strategies.
How can CKL help with stormwater solutions?
CKL provides expert advice on stormwater management for residential, commercial, and industrial developments. Our team offers services including:
- Site-specific flood modelling and risk assessment
- Design and implementation of stormwater treatment and conveyance systems
- Compliance guidance for local council regulations
- Innovative stormwater solutions that balance development needs with environmental sustainability
