Summary
- Kāpiti Coast District Council (KCDC) manages stormwater across urban catchments, protects receiving environments, maintains water quality, and reduces flood risks.
- This is a major challenge in a naturally flood-prone region facing rapid growth and more extreme rainfall from climate change.
- Accurate flood hazard models are vital for proactive planning and mitigation.
- Councils’ models can become outdated due to urban expansion, major projects altering the landform, and revised climate predictions.
- Between mid-2020 and 2023, Awa Environmental rebuilt seven base flood models for KCDC using our advanced processes and technologies.
- The new models are more detailed, accurate, and user-friendly, while being faster and more cost-effective to manage and update.
- They are now widely used across the region to support flood mitigation projects, planning, and consent decisions.
- KCDC selected Awa Environmental for our leadership of stormwater modelling, deep local knowledge, and trusted partnership.
Challenges
Stormwater-related challenges
- Kāpiti is shaped by rivers and the coast, with much of its developed areas on low-land sand dunes and peatlands.
- Rapid population growth and more extreme rainfall events driven by climate change heighten the urgency for KCDC to better understand where flooding may occur, its potential severity, and how best to plan for it.
- Accurate, up-to-date flood models are essential to proactively mitigate flood risks to existing developments and help avoid adding new risks with future developments.
- Such models help councils prioritise stormwater upgrades, inform planning and consent decisions, support emergency management, and provide residents with local flood risk insights.
- Public accessibility and usability increase their value to businesses and the community.
Flood model challenges
- Modern high-resolution hydraulic models resemble complex computer systems more than scientific and engineering analysis tools.
- They are often built over time by multiple contributors in multi-stakeholder programmes, under pressure to deliver accurate results before completion.
- As models evolve through peer-review and scenario-testing, multiple versions may emerge.
- This complexity can make them expensive and time-intensive to build and maintain.,
- So, councils have typically updated them infrequently, meaning the models lose accuracy and usefulness over time.
KCDC’s old models
- KCDC’s previous models, developed after major flooding in 1998, were becoming outdated.
- In 2020, the Council engaged Awa Environmental to rebuild its seven stormwater models, using TUFLOW software.
- Objectives included:
- Incorporating recent development data
- Enhancing drainage network information
- Applying updated climate predictions
- Merging catchments as appropriate
- Leveraging improved software and computing power.
Solutions
The right people and processes
- Awa Environmental assembled a team of modellers and digital solutions experts – many familiar with KCDC’s legacy models.
- We applied our framework - Plan, Build, Evaluate, Implement, Use & Maintain - to clarify purpose from the outset, an essential step to maximise long-term value.
- Models were built to KCDC’s specification, adapted from Wellington Water’s (WWL) framework, which we had helped develop previously.
- We had also created the hydrological methodology used by KCDC and embedded it into our model build software to streamline delivery.
- Between mid-2020 and 2023, initial model iterations were completed.
- Along the way, information gaps emerged, prompting additional work such as extensive soil infiltration testing, commissioned by WWL and KCDC and carried out by Awa Environmental.
- This provided region-wide infiltration rates that informed the new models.
Optimised model and data management
- Effective and efficient model and data management is essential for accuracy, cost-effective updates, and long-term reliability and relevance.
- Awa Environmental has developed and refined industry best practices and specialist tools to achieve this.
- We are also leaders in supporting organisations to implement these processes and tools –helping maximise the return on their model investment.
- Alongside model construction, we optimised KCDC’s model and data management using innovative methods and solutions, including our Model Manager platform.
Digital solutions
- Model Manager is a scalable, cloud-based system that supports:
- Secure file uploads
- Service desk requests
- Metadata tracking
- Web-based mapping
- Knowledge base creation
- Activity monitoring
- Quality assurance
- Data archiving
- Additional tools included:
- Model Compare: identifies differences across model settings and assets
- Model Backlog: stores information for future updates, such as new developments
- mGIS: a GIS database covering all relevant assets, not just those owned by KCDC.
- All models were built for open use by any TUFLOW user, with no dependency on Awa Environmental or our software tools.
Benefits
Models fit for the future
- The new models significantly improve quality, accessibility, usability, and traceability.
- The Council now has state-of-the-art tools that:
- Serve as a single source of truth
- Deliver accurate, defensible outputs for policy, planning, operations, and consenting
- Produce stable results unaffected by data or software changes
- Support rapid turnaround from initial request to delivery of modelling work
- Enable fast scenario testing by non-experts
- Facilitate third-party use and streamlined model reviews
- Allow ready tracking and comparison of model versions, and easy retrieval of previous versions.
- Model Manager and related solutions and processes have been central to this transformation by:
- Ensuring a well-maintained database of base model and project model versions, with corresponding metadata, is available
- Supporting concurrent work by multiple modelers without data conflicts
- Enabling continuous and cost-effective improvements.
- Crucially, model updates are quicker, more efficient, and substantially cheaper – reducing potential timelines from years to weeks.
- This creates the opportunity for annual or more frequent updates, further increasing the relevance and value to the Council and community.
- The models are also more accessible to a wider range of users – including developers, engineers, urban designers, and residents.
- Awa Environmental continues to support KCDC with model management and maintenance, with work underway to enable future Council ownership – an important step towards broader use and greater long-term value.
Delivering value on the ground
- The models are already supporting a range of projects across Kāpiti. For example, the Kenakena waterway in Paraparaumu has long struggled from poor drainage largely due to undersized culverts and an overgrown outlet.
- To improve flood resilience, KCDC plans to build a fish-friendly pump station to move water into the downstream wetland and estuary.
- Awa Environmental assessed its effectiveness using a new hydraulic model.
- Beyond this, the models have enabled demonstration of hydraulically neutral development, informed recommended building levels, guided consultants and contractors on flood hazards, and supported consent decisions.
