Prior to Christmas each year Environment Canterbury gives nature a helping hand by forming low shingle banks to improve swimming in the Ashley River / Rakahuri.
Ashley River / Rakahuri
(Image: Environment Canterbury; click to enlarge) |
The engineering design of the Ashley River / Rakahuri, downstream of the Okuku confluence, calls for a wide, open 'braided' shingle bed with planting between the river and stopbanks. The sheltered and shady picnic spots are enhanced by the groynes and tree planting.
Rock, concrete and stone filled gabion "groynes" jut into the river at right angles to the stopbanks to constrain the river to its present course. Flood waters speed up at the groyne heads and the resulting increase in energy induces deepening of the shingle bed – often forming swimming holes. Groynes are identified by a number painted on railway-iron posts.
Likely good sites this summer include (subject to flood changes):
1. Taggarts sponsor "the Rangiora Picnic Area" - South bank, immediately downstream of the Rangiora/Loburn Bridge. Minor work will be carried out to encourage this site to re-establish. This may be more suited for families with younger children. Take a look at the Rivercare Group's Riverstone Information Panel in the Picnic Area, and then wander down the walkway and view native plantings downstream to the Railway Bridge.
2. No.3 Groyne – Turn off stopbank 1.5km upstream of Merten Road, past the Rangiora airport on the left, or alternatively access from Priors Road. Sheltered and shady grassed (mown) picnic areas with swimming in a hole around and downstream of the head of the groyne. Minor work will be carried out to encourage this site to re-establish. Avoid the riverbed downstream to No.1 Groyne as this is prime shorebird nesting area. Use the adjoining vegetated berms – the planted bit between the river and the stopbank instead.
3. No.10 Groyne - The River has once again changed the most popular site of recent years, infilling the groyne swimming hole with gravel after floods. Minor work will be carried out to encourage this site to re-establish. This is a great picnic spot with large grassed areas (some mown) and plenty of willows providing shelter. Access the river immediately downstream of the Groyne.
Popular areas unlikely to be as good this year include No. 1 and No.11 Groynes and any sites located in the vicinity of SH1 Bridge (subject to flood changes).
Possible Safety Issues
At the State Highway 1 Bridge (near the coast) Phormidium growth has increased to high levels upstream of the bridge with medium-thick to thick mats observed. Mats are detaching and any that accumulate along the river's edge continue to pose a risk to river users and dogs. We advise river users to avoid areas where there are large amounts of strong smelling algae present and areas of stagnant waters. Please check out the latest water quality information. Visit http://ecan.govt.nz/SERVICES/ONLINE-SERVICES/MONITORING/SWIMMING-WATER-QUALITY/Pages/river-warnings.aspx
Many Ashley River / Rakahuri groynes have armoured heads of stone-filled wire baskets resting on a concrete slab mattress. Some of these mattresses have sunk further than designed. This results in gaps and uneven edges. Also be aware that tree roots and branches can protrude underwater, and whirlpool currents can occur.
Watch for variations in water depth and overhanging branches. Channels away from the riverbanks are usually more constant in flow and depth and are safer for inexperienced swimmers and those using inflatables and canoes.
Floods And Water Levels
Beware of rising water levels. A forewarning is discolouring of the water. Having a foothills catchment, the Ashley River / Rakahuri floods less frequently than the mountain-fed Waimakariri, but floods can occur in any season.
Listen to the radio for flood warnings and use Environment Canterbury's river level and flood information service – 0900 RIVER (0900 74837). Note calls cost 50 cents/minute + GST.
For texters, enter the short code RV ASHG (for River Ashley at the Gorge) and the phone number ECAN (3226) to receive river gauge information. Internet users, go to the Council's Website www.ecan.govt.nz and select "Check River Flows" to show a table. Click on "Ashley Gorge" site for a graph of flows for the last seven days.
An Ashley Gorge flow at 3-6 cumecs (cubic metres per second) is ideal for swimming. Anything over 15 cumecs is likely to be discoloured and unsuitable. As a matter of interest the stop banked Ashley system is designed to carry floods of up to 3,000 cumecs.
In spite of very little surface abstraction, the surface flow in the Ashley usually disappears in the middle reaches. This can occur when the gorge flow drops below about 2 cumecs. Site 3 (Groyne 10) will usually have plenty of water, even when the Gorge flow is down to 1 cumec and surface flow has disappeared at other sites. Surface flows are more reliable downstream of SH1 where the river approaches the coast and where the bed has been lowered by gravel extraction.
Regional Park
A regional park has been established on the Ashley River / Rakahuri from the confluence with the Okuku downstream to the coastal marine reserve. Two of the key feedback objectives from the community were for the continuation of swimming hole enhancement over summer and the protection of rare river bird nesting species. This work will assist both these objectives.
Wildlife Values
The Ashley River / Rakahuri bed is the northern-most breeding area of the rare Wrybill Plover with its unusual curved beak.
The Ashley-Rakahuri Rivercare Group's (ARRG) chairman Nick Ledgard said: "This year, the Ashley-Rakahuri Rivercare Group's annual survey of the river has found record numbers of some birds - including two of the rarer species, the wrybill and black-fronted tern. Hence the Group is pleased to be able to assist in the siting of swimming holes for the summer season. If people swim in the right places, then there is no risk of unnecessary disturbance".
Please watch out for signs alerting the presence of rare birds nesting and rearing their young.
No shooting and no open fires are allowed in summer except gas barbecues in open areas, clear of vegetation.
Most of the Ashley River / Rakahuri riverbed land downstream of the Okuku River confluence is controlled by Environment Canterbury and unlike many Canterbury Rivers is available for public recreational use. It is maintained in a semi-wild state and appropriate care should always be taken.
Tracks for example, are maintained for river monitoring access only and are often one lane, rutted and may even be washed out. Do not expect motorways or city park safety standards, but DO enjoy yourself!
