To be leaders in Water Management providing Reliable, Economic and Sustainable Supply
Most of the following information is from the document Proposed Waimakariri River Regional Plan.
The complete document can be downloaded from the Canterbury Regional Council website.
The Waimakariri is one of the larger braided rivers in New Zealand. Its flows are controlled by the weather in its upper basin, the stronger and drier the Nor-West wind is on the plains, the greater the flow be from heavy north west rain in the upper basin. This rain seldom extends to the Plains.
The current demand for water abstraction from the river is low but growing . In 2001, Resource Consents for surface water takes, including 10.5 cumcs for WIL, totalled 16.237 cumecs. A Resource Consent application for 40 cumecs has been lodged with Environment Canterbury by the Christchurch City Council, the Selwyn District Council and the Ashburton Community Water Trust. The mean flow of the Waimakariri River is 126 cumecs.
The Eyre River rises in the western foothills and, unlike the Waimakariri river, is largely fed by easterly rains. As a consequence of the unreliability of these rains, for much of the summer it is dry. Its bed and banks are covered with gorse and broom. The only fish in the river live over a short length where it flows into the Waimakariri River.
The Cust River runs from the foothills behind Oxford, through the Cust valley and then into the Cust Main Drain. This drain was built in 1862 to drain the Rangiora Swamp, which covered all of the land from Rangiora to the Waimakariri River. When the drain was enlarged in 1868, it accidentally captured the Cust River and the drain is now this river’s main course. During the 1998 drought, sections of this river also dried up.
The Ashley River originates in the Puketeraki Range behind Lees Valley and is fed largely by Southerly rainfall and snow. When the snow melts in spring the flow is high, peaking in September, It dries up regularly above the Ashley bridge at Rangiora.
The significant difference between these three rivers, the Ashley, Cust and Eyre, and the Waimakariri River, are their east coast catchments. While hot north-westerly winds are drying out the Waimakariri Plains, the Waiamakariri River is often swollen by nor-west rain or snow-melt from its mountainous catchment.
Under their consent conditions WIL is required to independantly and regularly monitor nitrate levels in representative wells throughout the scheme area . Records have been taken in the subject wells back to 1980 allowing longer term trends to be seen.
The 2008 Wamakariri District Council report shows that since the introduction of WIL, 5 wells have shown no change in nitrate levels with 4 wells showing reduced nitrates in the ground water. The Councils report provides an explanation for these positive trends. The full report can be accessed via the home page of www.wil.co.nz.
The catchment water resources comprise_ (a) rainfall; (b) ice and snow, alpine bogs and streams; (c) the flow of the Waimakariri River and tributary rivers which include:
(d) a groundwater resource beneath the Plains which feeds the Cust, Kaiapoi, Styx, Otukaikino Creek, and other smaller streams on the lower plains
(e) more than twelve lakes and associated wetlands which include Lakes:
(f) Brooklands Lagoon 2
(g) Pines Beach wetland.
The flow in the Waimakariri River is continuously recorded at the Old Highway Bridge where there are some 30 years of records indicating that the river has a mean flow of 126 cubic metres per second (cumecs), flood flows which can exceed 4,000 cumecs, and flows as low as 25 cumecs. The mean annual daily low flow is 41.5 cumecs. Over 90% of the river flow is derived from precipitation in the upper catchment. Winter snow and ice is stored and released in spring, contributing to higher flows in the river during this part of the year. The period of lowest flows occurs in late summer. Flood flows can occur at any time.
Water leaves the bed of the river below Halkett and recharges groundwater to the north and south of the river. The estimated range of this recharge is 3-12 cumecs . A considerable groundwater resource is stored in the gravels beneath the plains and feeds a number of streams on the lower plains, including the Avon and Heathcote Rivers.
Beneath the Waimakariri-Ashley Plain is a groundwater resource of great significance to the communities that live there. It provides 90% of the area’s drinking water, mostly without any treatment.
The Waimakariri River presents a major flood hazard to Christchurch, a city of 300,000 people, which has developed on the southern floodplain, and to Kaiapoi (5,000 people), which has developed to the north. An extensive system of flood protection works has been developed along both banks of the lower river. (Refer to the Proposed Waimakariri River Floodplain Management Regional Plan.)
The Eyre River which drains foothills to the west of Oxford, bisects the plains between the Waimakariri and Ashley Rivers but rarely carries any surface flow in its reach across the plains.
Water is abstracted from the Waimakariri River for three community stockwater schemes and for Darfield’s community domestic supply. The Selwyn District Council scheme intake is at the Waimakariri Gorge. It takes water from the Waimakariri River and the Kowhai River and provides stockwater to some 47,500 ha. A second Selwyn District Council scheme, with an intake at Halkett, provides stockwater to about 17,000 ha. The Waimakariri District Council Scheme has an intake at Browns Rock and provides stockwater to some 45,000 ha. Domestic water supply to Darfield comes from a gallery system in the bed of the Waimakariri River.
Above State Highway 1 there are no significant point-source discharges to the Waimakariri River.Below State Highway 1 the Waimakariri River receives trade waste and treated sewage effluent.
The plains tributaries (Kaiapoi-Cam-Cust system, Styx and Otukaikino Creek) were once the most important sources of mahinga kai in the catchment but their use for this purpose has declined as the plains were developed and the streams altered to control flooding and improve drainage. Pollutants in runoff and from direct waste discharge to these rivers and the drainage network feeding into them, devalue them as sources of mahinga kai. The community uses the plains tributaries to dispose of stormwater, treated trade wastes and treated sewage effluent.
Within the Waimakariri River Catchment there are about 90 discharge permits to surface water, and 80 to land, mainly for storm water, agricultural wastes and industrial wastes.
The Waimakariri River, primarily because of its location in relation to Christchurch, is the most heavily used river for recreation purposes in Canterbury, with the possible exception of the Avon and Heathcote Rivers and their common estuary.
The Waimakariri River has potential for hydro-electric power generation, for groundwater recharge, and as a future source of water for Christchurch City. There is a small commercial eel fishery based on the river and there are opportunities for freshwater fish farming.
The source of the Waimakariri River is in the Main Divide of the Southern Alps amongst the spectacular scenery and natural landscape of Arthurs Pass National Park. Downstream from the National Park the river winds its way through the relatively little-modified Waimakariri basin with its scattering of attractive lakes, limestone outcrops and scenic backdrops before passing through the spectacular 25 kilometre long Waimakariri Gorge. It emerges from the gorge at Woodstock and flows to the sea in a wide, braided riverbed, with constricting narrow reaches at the Waimakariri Gorge Bridge and downstream from the motorway bridge.
In the catchment above Woodstock the Waimakariri River and tributaries are anintegral part of the landscape. Their unmodified form and natural setting contrast with other South Island rivers now controlled by dams and drowned by lakes. The natural untamed river and its landscape is sought-after for jet boating, rafting, canoeing and a range of other recreation activities.
The State Highway and railway through the upper catchment link Canterbury with Westland. Much of the upper catchment is included in Selwyn’s District Plan as a scenic corridor. The upper catchment has very high natural values and the reach of the Waimakariri River between the Mt White bridge and the upper gorge has very high habitat value for Wrybill plover.
Below Woodstock the Waimakariri River has its own identity, distinct from the adjacent plains. The braided section across the plains presents a special jet-boating challenge as well as attracting salmon and trout fishers, picnickers and others. The braided sections of the river are habitat for Wrybill plover, Black-fronted tern and the Banded dotterel, all threatened species of native wildlife.
The river below its confluence with the Kaiapoi River is within the Coastal Marine Area, which is outside the area covered by this plan. The Coastal Marine Area includes Brooklands Lagoon, which is both a wildlife refuge and a source of game birds in season, and the Waimakariri River mouth, which is a magnet for fishermen and whitebaiters.
The high country, the Waimakariri River, and the coast provide many opportunities for recreation while the plains provide for the material needs of the community, for food and fibre, and sites for housing and industry.