2km In-River Flatwater Sports Course with Renaturalised Margins

Floodable Land Scenarios: Integration concept for improving recreation & ecological values

Regeneration of the Ōtākaro Avon River red zone corridor produces many opportunities to reimagine the area in and around the river. The concepts below have been developed by AvON to stimulate discussions around the possibilities.

The starting point is to provide renaturalisation of the river and its flood plain and simultaneous improvement of recreational opportunities. The main focus is on management of the margins. A large proportion of the riverbank in these areas is currently engineered with stop-banks. Adjusting these to address earthquake change and better suit the future uses of land within the Red Zone offers an unprecedented chance to renaturalise the river margins. This can be done in a number of ways that integrates improved recreational access to the water in addition to improving recreational experience by enhancing the natural environment.

Examples of renaturalisation–recreation integration opportunities include:

A greater number of access points for kayaks, waka ama, and other water sports, integrated into the landscape.
Improved waterway connections.
Improved foot / wheelchair access connections. This can be achieved through integrating access facilities (eg. tracks) into restoration plans for renaturalising the river margins
Larger scale modifications to cater for specific activities.

Enhancements for flat-water sports at Kerrs Reach

The concept below shows an example for the Kerrs Reach area that attempts to incorporate a full size flat-water course into a re-engineered section of the river.

This would involve:

Small breaches in the stopbanks to allow small bridged side channels connecting to a lattice work of tidal waterways and wetland bush on both sides of the river, with outer stopbanks at the outer fringes protecting residential areas and/or other assets.
Naturalisation of the river bank and edge, using treatments that embrace new technologies for attractive river bank designs that utilise native plants, deter exotic geese and ducks, and dampen reflected wash from water craft thus removing the need for wide shallow-angled banks;
Re-positioning of the river stopbanks to accommodate a flatwater sports course 2,150m long x 160m wide x 4m deep, between the west corner of Avondale Bridge straight up to and into Avon Park; NOTE: Since we undertook this concept work East Lake Trust has raised significant concerns regarding the impact on river water quality of 'impounding' such a large volume of water for a 2km in-river course. While this still remains subject to further assessment by Regenerate Christchurch, we have continued to explore further options both in-river and off-river to meet enhanced provision for flatwater sports.
Improvement of hydrologic connectivity and restoration of wetland values in the the regeneration planning area near Horseshoe Lake / Waikākāriki, including use of the land for stormwater remediation. In general, managing water levels and connectivity in this area is tricky due to the need to maintain tidal defences and pumping capability to accommodate flood waters that coincide with high tides. However there are several possibilities for improving free flowing connection in the vicinity of the Horseshoe Lake confluence (this would still include provision to pump flood waters out). This and other aspects of renaturalising the margins will require adaptive management based on modelling the river’s response to natural hazards and climate change (eg. considering inundation from high rainfall, tidal inundation and sea level rise in a strategy for progressive ecological and recreational restoration of the river corridor);
Inclusion of a wider section at the northern end suitable for waka ama;
A network of interconnected pathways for cycling and walking and of waterways for exploring via small boats such as kayaks and canoes;
The west side of the river may offer a suitable location for the WHoW Wai Huka o Waitaha whitewater and surf park which will utilise small volumes of ground water (from an aquifer separate from those supplying our drinking water) in a way that allows the integration of the artesian flow into the natural river system akin to a spring-fed source with opportunities for swimming (as well as having space for swimming at the park itself);
Retention of New Brighton Road at its current location probably raised and with at least one further minor bridge allowing interconnection of minor waterways in the Dallington / Horseshoe Lake (ie. navigable by a kayak / small boat).

New Lake in River3Web.jpg

Developing Scenarios

The following maps provide further information on areas of floodable land within the regeneration planning area based on current ground levels. They can be used to assist in developing scenarios for renaturalising the margins.

The maps show one potential configuration for integrating the above flat-water course into the environment. Alternatively, small scale remodifications could be considered in the same general area to suit the level of need for different watersports in this area. There are also several options for integrating the flat-water facility proposed by East Lake Trust with these general principles.

The Challenges

Sedimentation – periodic dredging would likely be required to maintain the 4m depth and to prevent weed growth, which would be an ongoing cost. Sediment traps (at both ends of the deepened section) would be advantageous and may also be a useful approach for intercepting sediment (and sediment bound heavy metals) for removal. These are ongoing concerns for urban stormwater management and can lead to accumulation issues in the lower rivers / estuary if not addressed;
Flow – in the Kerrs Reach area both river flow and flood tide flow are experienced creating a variety of effects. However flow is not a notable issue for most flat-water sports. Competitive courses are often located in flowing waterways;
Re-shaping Kerrs Reach – this may be considered by some to be significant however it is already a highly engineered part of the river and a re-working of the stopbanks and river containment is likely to be needed for flood management anyway to provide a renaturalised floodplain;
Water quality – currently river water quality is poor – it still receives sewage overflows in high rainfall events - secondary contact sports do currently operate in this environment albeit with considerable care, but it is not suitable for primary contact (ie swimmable), however the public is now demanding significant improvements in river water quality that are being heeded by authorities. Enhancing the capacity for flatwater sports with an in-river course would provide further impetus for improving water quality;
Costs – this concept could be adapted in different ways and the costs are yet to be established. It is intended to promote discussion of integration concepts for river uses and naturalisation.

The Advantages

The overall concept is targeting a multiple-wins outcome. The recreational facility could meet many of the needs of flat water codes. Renaturalised river margins are created as an aspect of completing that engineering. Freeing up space and improving hydrologic connections in the surrounding lands will help restore a floodplain that produces the most benefit to the most people whilst also respecting its nature;
Offers a regeneration opportunity with high levels of resilience to sea level rise and flooding;
High synergies with other proposals for the red zone and tremendous tourism potential;
The promotion of in-river recreation opportunities may help motivate Christchurch to seriously tackle water quality in our urban rivers;
Greatly increased opportunities for improved mahinga kai values including enhanced inanga habitat in the Horseshoe Lake / Waikākariki area;
Retention in situ of current Kerrs Reach facilities;
Retention of significant infrastructure that would be expensive to move or re-direct including New Brighton Road.