This project will
Provide a natural recreation space
Improve the habitats for native fish and eels
Manage stormwater as Rotokauri grows
Project summary
What we’re doing
We’re creating a greenway - the mainstream channel next to wetlands and water storage ponds - to help manage and improve the stormwater that reaches our waterways. Rotokauri drain flows into Lake Rotokauri, into the Ohote Stream, the Waipa River and then to the Waikato River. The greenway will raise the quality of water that reaches the Lake. This will provide a gradual flushing effect, improving Lake water quality over time.
The Rotokauri greenway will be 3.8km long, 4-4.5m deep and up to 60m wide in places, with 750,000m3 of earth to be moved (enough to fill 300 Olympic swimming pools) during construction.
Why we’re doing it
To enable future growth in Rotokauri-Northwest, Council needs to properly manage stormwater in the area. We’ve identified that a central stormwater greenway corridor is the best way to do this.
Currently, there’s a drain running through Rotokauri which is home to native fish, but the quality of their habitat is poor. The Rotokauri greenway will improve the quality of water and ecological values through this waterway to Lake Rotokauri and Lake Waiwhakareke.
The greenway will help manage the increased volume of stormwater runoff created by the new residential development in the Rotokauri-Northwest area. The area accounts for about 18% - 20% of the actual water in Lake Rotokauri. This greenway corridor will hold stormwater behind the Exelby Road culvert in large storage basins, mitigating any negative environmental impacts.
The Rotokauri greenway will provide a central location for residents and visitors to meet, relax and play.
Construction of the greenway is planned to take three years and will be done in stages, working from Exelby Road to Rotokauri Road.
Fun fact
The Ohote Stream actually changes direction during a rain event and flows into Lake Rotokauri. It is only once the lake reaches a ‘tipping point’ or max level that the Ohote Stream reverses its flow into the Waipa River.
Programme blueprint
As well as managing stormwater in the area and improving the health of our waterways and habitats for local aquatic species, the Rotokauri greenway will become the main public recreation area for Rotokauri.
Project features
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Natural vegetation
Carefully considered plantings will mimic the natural vegetation in Rotokauri, connecting housing with natural spaces, through to wetland and riparian species. Clusters of trees will provide food for birds and shade for all. -
Recreation spaces
The Rotokauri greenway will provide biking and pedestrian infrastructure, green spaces, viewing platforms, picnic areas, fitness circuits, seating areas, boardwalks, bird watching areas, play areas, and barbeque shelters. -
Improved habitats
Rotokauri waterways are currently home to giant kokopu, longfin eel, and black mudfish. We’ll be protecting and bettering their habitats through improved water quality, smart design, and good construction management.
Where we're at with progress
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Stage 1 - Planning
2019-20
Following completion of the early investigation and design, we lodged the Notice of Requirement, which was approved to designate the greenway corridor area. -
Stage 2 - Planning
April 2022
We're preparing for construction e.g. undergoing consents and doing detailed design of the pipes, connections and community spaces along the greenway network. -
Stage 3 - Underway
In the future
Land acquisition and construction. This stage is dependant on funding and partnerships with developers to support construction. -
Stage 4 - Completed
In the future
Opening of greenway. This stage is dependant on funding and partnerships with developers to support construction.
Frequently asked questions
What is a designation?
The Resource Management Act 1991 (RMA) allows for areas of land to be designated for use as network utilities, such as roads and telecommunications facilities, and in this case stormwater drainage, or large public works (such as schools and prisons). These designated areas (or 'designations') are then identified in district plans, usually in the maps.
Why do we have to designate this land?
We need to protect the land required to help manage the additional stormwater caused by new development, before it's used for housing.
Why do we have to treat and manage stormwater?
Stormwater is often thought of as ‘clean’, but when it comes into contact with other surfaces, it collects and loosens contaminants such as sediment, phosphorus, copper and zinc. These collect in water bodies (such as streams and lakes) and can create poor water quality environments for our native fish, wildlife and plant life. In particular, Lake Rotokauri and Lake Waiwhakareke are sensitive to these contaminants.
When high rainfall hits our hard surfaces such as paths, roads and roofs, it accumulates and runs off those surfaces in a very short period of time. This can cause flooding and water can flow at such a speed that it can cause erosion and scour. We need to manage the direction and minimise high flows of stormwater so that flooding and erosion is minimised.
How will you manage flooding?
To manage stormwater runoff from development, we hold any additional water behind Exelby Road culvert. To mitigate the chance of Lake Rotokauri flooding due to a sudden inflow of water from the Rotokauri area will require a series of five storage basins requiring over 750,000m3³ of earthworks to build. The culverts will be sized to hold water back and slowly release it over time.
How does Council treat stormwater?
There are a number of ways to remove or reduce contaminants before they get into our waterways. This includes filtering (through land and plants) and allowing plants and soil to uptake or bond the nutrients that can cause problems in lakes. Treatment can also include collecting rainfall and slowing its release so that the network does not become inundated with stormwater. Devices include, but are not limited to, rain tanks and rain gardens.
What is a treatment train?
Sometimes it will take several devices to remove certain contaminants and manage water quantity. A treatment train is a number of individual treatment devices in a series that form a treatment system (or train) with the goal to remove a target rate of contamination. A treatment train can be on private and public property.
What treatment is needed for this catchment?
A treatment train in this area is required to remove up to 70% total phosphorus before discharging to the main conveyance channel. This will be achieved by:
- source controls: this includes devices on both public and private property, which will differ in size depending on what they need to do
- wetlands and main corridor wetlands on public property.
Why do we need such a large central green corridor?
- Treatment: the footprint of the central green corridor is driven by the planted area that will be required to treat the stormwater. We need to remove 70% of phosphorus to improve the water quality before it enters Lake Rotokauri.
- Storage: to also manage quantity and minimise property flooding, we have optimised the design of this area to accommodate a one-in-100-year storm event and account for future climate change. We still require storage of over 500,000m3.
Who will maintain the treatment devices?
Treatment devices located on private property such as rain tanks and rain gardens are maintained by the property owner.
Treatment devices that have been vested to us, such as rain gardens and wetlands, will be maintained by usl after a ‘contractor maintenance period’.
When will it be built?
Funding for the construction of the Rotokauri greenway was approved for year seven in the Council’s 2018-28 10-Year Plan. This does not prevent a Private Development Agreement (PDA ) being formed with residential developers to bring the project forward.
Will there be stagnant water?
There will be slow moving water as it passes through the treatment ponds. These will be heavily planted and provide an environment for native ecology, but not for mosquitos.
Will the slopes be safe?
While the detailed design has not been completed, the concept provides safe slopes and heavily planted areas that provides the ability for people to stop themselves. The slopes are of a safe angle that a tractor mower can cross.
Will we be kept updated on the greenway?
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Last updated 16 July 2022