The Ōpawaho/Heathcote River is the key focus of much of the Council’s Land Drainage Recovery Programme work. This update gives a snapshot of some of that work. You can find more information on Heathcote flood mitigation works here.

Bells Creek catchment in Woolston has seen one of the highest increases in flood risk as a result of land changes due to the earthquakes. Works in this catchment have been prioritised, with pipe upgrades already completed, new basin construction underway, and a major pump station to be installed in 2017. Bells Creek Flood mitigation works include:

• Upgrade of pipes in the Mackworth Street area – this work has been completed.
• A new stormwater detention pond is being constructed within the northern half of Edmonds Park, where the sports fields are currently located. This will be dual-use, with the park flooding only in large rainfall events, and otherwise still operating as sports fields. The new sports field (shown at right) is due to be completed early April, with remaining works, including planting, completed in May 2017.
• A new stormwater detention pond is planned within Linwood College's lower fields - We will be looking to consult with the community on this work in January, with construction starting after this, and running for approximately six months.

• A pump station on Richardson Terrace near the Heathcote River - Currently, Bells Creek comes out through a large piped outfall into the Heathcote River near the intersection of Richardson Terrace and Ferry Road.

The new pump station at 12 Richardson Terrace will direct stormwater flow from Bells Creek into the river during a large storm event and reduce flooding in the area. The pump station will incorporate a stormwater treatment device, which will improve water quality in the Heathcote River by treating stormwater runoff from a large catchment extending to Moorhouse Avenue and the southern central business district. Design is currently underway for the nearby outfall structure. It’s hoped construction on the pump station and stormwater device will start in March next year, and take around 10-12 months.

We are holding a street meeting to answer questions people may have about the Richardson Terrace pump station works, and hope to give you more information on the outfall. The meeting will be held on Wednesday 7 December, at 5:30pm, at Woolston Park, Richardson Terrace entrance.

• A screen in Woolston Park to prevent debris damaging a new pump station – Work will begin in January on changes to a culvert running underground in Woolston Park. Historically Bells Creek ran through the site that is now Woolston Park. In the 1950s the creek was buried underground within a large concrete culvert. The flood mitigation works will involve opening up a section of the culvert near the north-east boundary of the park. A screen will be installed in this open section, fenced off for safety, and surrounded by landscaping, as shown in the image above. The screen will trap debris to protect the new pump station to be constructed downstream on Richardson Terrace. The pump station will pump storm flows from the Bells Creek catchment into the Heathcote River. The screen will also help reduce the amount of litter entering the River. This work is expected to take around two months.

The Land Drainage team has identified sections of bank along the Heathcote River which have suffered damage from the 2010/11 earthquakes.

Some of these sections are considered a high priority for stabilising work due to the erosion that is taking place. Over the next two years, these sections will be repaired, with all works in keeping with the Mid Heathcote/Ōpawaho Linear Masterplan so that cultural, recreational, ecological, landscape and heritage values are taken into consideration.
The focus of these works are on repair, not flood mitigation, but where needed, the design will also look at opportunities to increase capacity to complement future flood mitigation works.

The Council has been looking into options for storing water in the upper Heathcote, to reduce flood risk above Colombo Street.

The first basins constructed in the upper Heathcote through the Land Drainage Recovery Programme were completed earlier this year, located on Sparks Road (shown in the image above). These provided additional storage to the existing basins there.
Investigations into further storage options to reduce flood risk above Colombo Street have now been completed and four storage basins identified. Modelling shows these four basins working together would bring significant benefit to properties at risk of flooding in the upper and mid-Heathcote River reaches during a storm event.
The full findings of the investigations will be released when the final report is available, but in the interim, the Council is looking at ways to fast-track delivery of all four storage areas to provide the flood reduction benefit in as short a timeframe as possible. It is anticipated they could be designed in the early months of 2017 with construction throughout 2017 and 2018.

To complement the work on developing more storage, a project is underway to develop a wider floodplain management plan to address areas not benefitted from storage downstream to Radley Street in Woolston. The project aims to:

• Look at the range of sustainable and resilient local, and catchment wide management options, including planning and policy responses (such as District Plan rules or house raising) as well as viable engineering options.
• Explore ‘Quick win’ opportunities, where flood levels can be managed in one area, without adversely affecting other areas.
• Consider the impact of sea-level rise and more extreme tide and rainfall events, to see how options could be adapted in the future in response to these events.
• Assess the resilience of the options, and land serviced by any option, if subjected to other hazards, such as an earthquake, tsunami, coastal inundation and erosion, increased groundwater levels and increased liquefaction vulnerability. Assess the costs and benefits of all options, and provide a plan of preferred options.

Once options are developed, the Council will be looking to work with the community and groups with an interest in the Heathcote to canvas their views and preferences. This engagement is likely to take place early next year. It’s expected the final plan will be completed in September 2017.