Operative Waikato Regional Policy Statement (October 2000)

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3  Significant Resource Management Issues, Objectives, Policies and Methods

3.4  Water

3.4.2 Surface Water Resources

Lake Taupo was formed as a result of an extensive volcanic eruption in 186 AD. The huge crater that resulted is now filled with high quality water. The lake surface is 359 metres above sea level. It measures 40 km long and is 30 km wide at its widest point.

The lake has two major population centres: Taupo township (21,257 population¹) at the northern end and Turangi (5,484 population²) at the southern end. The lake and its tributary rivers and streams support an internationally recognised trout fishery, a major contributor to the economy of the Region. The lake provides valuable habitat for indigenous fish and invertebrates, and other aquatic and biotic life.

The Waikato River catchment straddles the rohe of the Tainui, Ngati Tahu and Ngati Tuwharetoa. It is 425 km long from its source in the volcanic region of the Central Plateau to its mouth at Port Waikato, making it the longest river in New Zealand.

The predominant use of the river is for electricity generation. Below Lake Taupo, discharges to the river and the ponding effects of dams combine to significantly modify the nature, flow characteristics, water and habitat quality of the river. Natural inflows to Lake Taupo and therefore to the Waikato River are significantly increased by diversions from the Wanganui, Whangaehu and Rangitikei River Catchments. These diversions play a significant part in the NZ electricity generation system and add to water available for other uses in the Waikato River. The catchments from which water is diverted are located in the Manawatu-Wanganui Region and it is important that the adverse effects of the diversions in the Manawatu-Wanganui Region (principally on the natural character and ecological habitat of the water bodies concerned and Maori values) are considered as part of an integrated cross-boundary process which takes account of beneficial effects in the Waikato Region.

Water and habitat quality are further degraded by discharges from a number of sources (notably community sewage and agricultural sources)³.

The middle and lower reaches of the river are associated with a chain of lakes and wetlands. Catchment erosion and waste discharges have significantly reduced the water quality and habitat of indigenous aquatic species in this area⁴. In addition, lowering of the water table through land drainage practices and the depletion of surface water resources is likely to lead to further degradation of wetland areas. The lower reaches of the river are currently used for the extraction of sand and gravel. Extraction of such material has the potential to affect both the water quality and flow regimes of the Waikato River.

There are several species of introduced fish that are now firmly established in the Waikato River. Some introduced fish species are of concern because of their likely effect on native fish, and at least one (the koi carp) is recognised as a pest because of its effect on water quality through disturbance to banks and beds of rivers and lakes. The Waikato River provides a valuable recreational trout fishery of regional importance.

A history of flooding in both the Lower Waikato and the Waipa catchments resulted in a large-scale flood control scheme that was formally completed in 1983. Since then the Scheme has moved into a maintenance and small-scale works phase.

At 3060 km², the Waipa River catchment is the largest sub-catchment of the Waikato River. It joins the Waikato at Ngaruawahia, and at its confluence, contributes approximately 24 percent to the mean flow of the Waikato. This means that the hydrology of the Waipa catchment has a major bearing on flows in the lower Waikato River.

Water quality in the upper parts of the Waipa catchment is generally very high. The clearing of forests in the catchment, loss of riparian vegetation along the banks of tributaries, the draining of wetlands and intensive land use have also contributed to sedimentation. In addition, as with the Waikato River, community sewage, non point discharges, and farm effluent discharges into the river have resulted in a gradual downstream degradation of water and habitat quality.

The Waihou River system covers an area of some 2150 km² and has generally high water quality and flow regimes, although there are some concerns about the degradation of wildlife habitat. The upper catchment is dominated by the Mamaku plateau where around 80 percent of the river's base flow is generated.

Aquatic weeds associated with drainage channels and riverbanks can cause blockages and reduce water clarity.

Over the years, severe flooding on the Hauraki plains has given rise to various drainage and flood protection schemes, which resulted in a comprehensive scheme being introduced in 1965. Associated soil conservation work in this area includes upper watershed protection in the Kaimai Ranges, and channel planting throughout the catchment. The Scheme was completed in 1998 and provides the catchment with both flood protection and soil conservation.

The Piako and Waitakaruru catchment has a low surface water yield. The Waitoa River is the major tributary and at low flows, contributes significantly to the base flow of the Piako. Discharges of dairy farm effluent into the Piako river and its tributaries have degraded the water and habitat quality of the catchment. Other issues associated with water degradation include: nutrient enriched run-off, soil erosion and subsequent sedimentation. Aquatic weeds can also cause problems when they clog waterways and interfere with drainage.

Protection of remaining wetland areas is also an important issue in this catchment. Wetlands are an important but diminishing resource in the Waikato. Drainage, excessive abstractions and catchment works affect the habitat and character of wetlands. Stock access to wetland areas has the potential to destroy marginal habitats, increase sedimentation and raise nutrient levels. Land developments such as reclamations, peat mining and the depositing of land fill material also have an effect on wetlands.

In the past, flooding was a problem associated with this area, and flood protection is now provided through the Piako River Scheme.

Water quality in most of the streams on the Coromandel Peninsula⁶ is good, although there are problems in some areas. Major issues include: local water quality degradation caused by acid mine drainage from abandoned mines; water demand often exceeds supply in summer months; soil erosion and the subsequent silting of streams is an ongoing problem; and the clearing of land has left streams vulnerable to flash floods and high exposure to summer sun.

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Footnotes

1. 1996 Census.
2. 1996 Census.
3. Environment Waikato, Draft Lower Waikato Regional Plan, 1993.
4. Environment Waikato, Draft Lower Waikato Regional Plan, 1993.
5. Environment Waikato, Piako Catchment Draft Water and Soil Management Plan, April 1991.
6. Environment Waikato, Coromandel Management Strategy (Internal Draft), July 1992.