Appendix B: Environmental Sector Information
B.1 Potential Environmental Values Affected
The objective of this section is to describe the aspects of environmental or natural resource value within the Upper and Lower Waitaki catchment that are potentially affected by additional water allocation from the river and lake systems.
Environmental value is attached to both "in river" and "out of river" features within the Waitaki catchment and in this report have been assessed at different scales:
- macro ecosystem level (e.g., braided river),
- micro ecosystem level, and
- species level.
This demarcation recognises that the various components have their own value (e.g., braided river for providing fish and bird habitat, hydrological functionality (flood pathway and sediment transport) and intrinsic value of big river; fish species for recreation; wetland habitat for game bird and eel populations). Any loss or significant change to any part of the ecosystem is likely to impact on those values at other scales within the system.
The Meridian Energy Assessment of Environmental Effects (AEE) report and appendices for Project Aqua (referred to here forth as the "Project Aqua AEE") form the most comprehensive description of likely impacts from the impacts associated with Project Aqua canal and power stations development. These documents have been compiled by a number of independent environmental and engineering consulting firms.
The following section discusses values of the macro ecosystem, followed by other ecosystem values and then species values for the Upper and Lower Waitaki catchments independently.
B.1.1 Upper Waitaki
The Upper Waitaki catchment is notable for its high mountains, indigenous tussock and forest vegetation, and lakes and rivers that provide:
- a sense of remoteness;
- excellent water quality;
- excellent habitat for wildlife; and
- many recreational opportunities.
These qualities are becoming scarce within New Zealand (and globally) through intensification of land use and development.
B.1.1.1 Lakes
There are six main lakes in the Upper Waitaki, each of which is used for hydropower generation and have various environmental, recreational, social and cultural values. As previously indicated, the recreational, social and cultural values are covered in a separate report (Appendix E).
With the exception of Lake Aviemore, the lakes provide habitat for game birds and other dabbling and wading birds, due to the shallow margins, high natural water quality, plentiful food supply (macrophytes) and adjacent pasture.
Although overall water quality of the lakes in the Upper Waitaki is naturally high, there are a number of sites where because of the high level of human activity water quality is threatened. Smaller lakes in particular are more vulnerable to water quality problems (WCC, 1982).
B.1.1.2 Rivers and Tributary Streams
The Ahuriri, Hopkins, Dobson, Tasman, Godley and Cass Rivers are the only rivers with unchanged natural flows in the Upper Waitaki following the development of the hydroelectric schemes. However, the Ahuriri is the only fully protected river (WCC, 1982). Diversion of water from the Tekapo, Pukaki and Lower Ohau Rivers has meant that flow in tributary streams (e.g., the Maryburn and Fraser) have become more important as fisheries (pers. comm. Al Shearer, ECan Twizel, 5 November 2003).
B.1.1.3 Braided River Ecosystems
The South Island braided river systems are geologically unusual and have unique plant and animal communities (DOC, 1999; Boffa Miskell, 2003c). The dynamic ecosystem encompasses riparian wetlands, swift water, pools, ephemeral areas, braided channels and gravel islands. Numerous species have specialised for the environment. Some of these species are threatened or rare, including: 15% of the remaining 5,000 wrybills; 60% of the remaining 5,000 black-fronted terns; and 100% of the remaining 43 black stilt nest on the rivers and wetlands of the upper Waitaki Basin. Under international criteria, wrybills and black fronted terns are classified as "threatened" and black stilts are critically endangered (DOC, 1999). Game bird species are well represented in the Upper Waitaki, both in number and diversity. Many of the braided river birds need the variety of habitats found in the braided river system for various ecological and biological functions, from loafing in the shallows, nesting in the gravels to feeding on pasture.
Other particular species endemic to New Zealand found in the Upper Waitaki include Macan's skink, and many native fish including two distinctive high country species, the long-jawed and alpine galaxias (DOC, 1999).
B.1.2.2 Groundwater
We understand that Electricity Corporation of New Zealand commissioned a number of drilling and groundwater investigations over the years as part of the pre-feasibility studies for the Upper Waitaki hydroelectric scheme. However, it has not been possible within the scope of this report to collate and review this information. Besides this, information on groundwater in the Upper Waitaki is limited and this probably signifies that groundwater is currently not regarded as a valuable resource in the Upper Waitaki, primarily because:
- groundwater occurrence and quantities are generally inadequate to meet large abstractive water requirements, and
- many of the natural groundwater dependent ecosystems have dried up the since the hydroelectric scheme was developed.
WCC (1982) states that groundwater immediately downstream of the lakes tends to lie at great depths. It is unclear whether this refers to groundwater levels pre- or post- canal development. The report indicates that groundwater within the river valleys may be perched by glacial silt layers deposited in the riverbed. However, a systematic hydrogeological study to establish the relationship between the Post Glacial gravel and Pleistocene glacial till aquifers and the underlying Pliocene basement rocks has yet to be initiated in this area (Brown, 2001).
It is likely that the shallow groundwater within the fluvial glacial system has passively dewatered since diversion of the river water for hydroelectric generation. This is supported by anecdotal information from station holders, which suggests that tussock on the lower terrace flats has deteriorated significantly through prolonged moisture deficits following:
- canal development, and
- clearing of willows in the river which effectively allows more rapid drainage of the surrounding lands (pers. comm. Denis Frasier, Simons Hill Station, 4 December 2003).
In recent times, a number of bores have been drilled by individual station owners/managers prospecting for irrigation water supply. Results indicate that groundwater is encountered at significant depth (generally greater than 80m) however the variability in yield over short distances is significant and the yields obtained indicate that many bores would be required to meet typical irrigation water demands.
For example, Simons Hill Station drilled two 300mm diameter exploratory production bores in 2002-2003 to approximately 81m and 120m below ground, respectively. Results of these investigations were mixed with the shallow bore effectively dewatering after two hours at a discharge rate of 7.5L/s, while the deeper bore was step tested for 38 hours and yielded 33L/s with a 36m drawdown during the final test step.
B.1.1.5 Wetlands
The riparian wetlands of the Upper Waitaki basin are habitat for threatened and migratory birds, and form complimentary habitat for many species that also occupy the braided river and gravel island environments. Large areas of wetlands have been lost because of hydroelectric development due to lowered river and groundwater levels, and through agricultural development, and the remaining wetland areas are considered worthwhile protecting (DOC, 1999).
B.1.1.6 Basin Floor and Terrace Indigenous Plant Communities
The basin floor and terrace indigenous plant communities of the Upper Waitaki are classified as short tussock grasses occupying land below 1,000m and comprise predominantly hard tussock, adventive grasses including browntop and various cushion and mat herb communities (WCC, 1982). Little is published about the value of these ecosystems in the Upper Waitaki.
B.1.2 Lower Waitaki
B.1.2.1 Braided River Ecosystem
The braided ecosystem of the Lower Waitaki River is a natural resource of major ecological significance, providing a diversity of habitats for a wide range of aquatic and terrestrial species. O'Donnell (2000) in Boffa Miskell (2003c) ranked the Lower Waitaki River in the highest ecosystem category for habitat significance in an assessment of 41 braided river sections, and considered the section to be of national and international significance. This was based on the diversity of species, the viability of bird populations and the ability for many birds with the same ecological niche to coexist. The river system supported the highest number of threatened bird species in this assessment, and was ranked second overall for diversity of ecosystems (from open channels to backwaters and wetlands). Fish and Game also consider the Lower Waitaki River to be of national importance due to the game bird habitat.
Twenty eight species of bird were surveyed on the Lower Waitaki River in 2001, including the threatened wrybill, black stilt and black-fronted tern (Boffa Miskell, 2003c), along with popular game birds such as the paradise shellduck, Canada goose and mallard. Many of the braided river birds need the variety of habitats found in the braided river system for various ecological and biological functions, from loafing in the shallows, nesting in the gravels to feeding on pasture.
B.1.2.2 Groundwater
Groundwater is a valuable resource in the Lower Waitaki for a number of reasons including:
- Water supply - potable, domestic, stock and irrigation water supply to people in areas where access to river water or water from the Lower Waitaki Irrigation Scheme is not possible.
- Ecosystem dependence - has an important role in maintaining ecosystems that are dependent on it for water supply, such as springfed streams, wetlands and ponds.
- Maintaining soil moisture levels - in areas where groundwater is close to the surface, it is important for maintaining soil moisture levels in overlaying soils and reducing soil wind erosion.
Groundwater investigations within the Lower Waitaki have been undertaken since the late 1970s associated with the hydroelectricity generation investigations for the Lower Waitaki Scheme. Since then a number of small investigations have been undertaken by Waitaki Catchment Commission in 1986 and Otago Regional Council in 1993-1994. In 1999 Otago Regional Council commissioned a major investigation of the Lower Waitaki alluvium on the south side of the river. The study comprised a comprehensive bore survey, nine months of groundwater quality and level monitoring, and an assessment of groundwater quantity and sustainability (SKM, 2000). Since this time, additional information has been compiled and a broader study encompassing ORC and ECan data has been completed as part of the Project Aqua AEE (see URS, 2003b).
By far the highest yielding and important aquifers in the Lower Waitaki are the Pleistocene and Post Glacial gravel alluvium deposits representing the upper and lower terraces, respectively. These aquifers are used for potable and domestic, stock drinking water, dairy shed washdown and irrigation. The biggest consumptive use of groundwater on an annual basis is related to dairying (excluding dairy farm irrigation) however, while only a handful of bores used groundwater for irrigation, the irrigation peak take during summer nearly doubles that of non-irrigation use.
While most bores appear capable of yields between 2-5 L/s, groundwater is secondary to surface water sourced from the Lower Waitaki Irrigation Scheme for irrigation and stock water (SKM, 2000).
Other sources of groundwater in the Lower Waitaki include the cemented sedimentary and limestone aquifers of the Papakaio Formation and the Otekaieke Limestone, respectively (URS, 2003b). However, these are generally of lesser quality and yields.
B.1.2.3 Wetlands
There are approximately 190ha of river terrace wetland in the Lower Waitaki valley, which are fragmented and modified to varying extents (Boffa Miskell, 2003c). The diverse habitats range from indigenous flora and fauna to artificial irrigation or wastewater treatment ponds, which provide for a diverse range of wetland flora and fauna. It is estimated that there are approximately 3,000ha of riparian wetland along the Lower Waitaki, although much of this is ephemeral and of low ecological value (Boffa Miskell, 2003c).
The river terrace wetlands dominated by raupo, flax, Carex secta and bog rush, represent communities that were formerly more abundant in the valley. These are considered to have the highest ecological value, although due to the paucity of wetlands in the locality, most wetlands are considered to be ecologically significant (Boffa Miskell, 2003c). The nationally threatened Canterbury mudfish is present in a small number of streams on the north bank and bittern (vulnerable) are found in a range of small wetlands in the valley (Boffa Miskell, 2003).
Wetlands that are connected to the Waitaki River are particularly important as habitat for birds and fish that require breeding or spawning areas, feeding and sheltered habitat during various times of their life cycle.
B.1.2.3 Kurow Turflands
The Kurow indigenous turf ecosystem is a sustainable, semi-natural dryland turf ecosystem. It contains representative native turf vegetation, reptile, insect and bird communities once common on infrequently inundated river terraces. This site has no equals in the Waitaki Valley, and could be considered nationally significant due to the presence of threatened insects and plants (Boffa Miskell, 2003c).
B.1.2.5 Salmonids
Salmonid are introduced fish species from the Northern Hemisphere, of which the following are found in New Zealand:19
- Oncorhynchus mykiss (rainbow trout)
- Oncorhynchus nerka (sockeye salmon)
- Oncorhynchus tshawytscha (Chinook salmon)
- Salmo salar (Atlantic salmon)
- Salmo trutta (brown trout)
- Salvelinus fontinalis (brook char)
- Salvelinus namaycush (mackinaw)
In the Waitaki, rainbow trout, brown trout, sockeye salmon and Chinook salmon are the most important species.
The Waitaki River is one of the four most important Salmon fishing rivers in New Zealand20 and has the largest flow of the four (Waimakariri, Rakaia, Rangitata and Waitaki). The river is also unique in that brown trout, rainbow trout and salmon coexist (pers. comm. Martin Unwin, NIWA, 27 November 2003) In particular rainbow trout are more common in this river than in other large east coast braided rivers (Cawthron, 2003). New Zealand has the only self-sustaining Chinook salmon fisheries outside of North America (Fish and Game in Boffa Miskell, 2003). Cawthron (2003) and Boffa Miskell (2003c) consider the river to be of national significance due to the salmon and trout fishery, however Central South Island Fish and Game Council (in Boffa Miskell 2003a) go further to consider the river to be of international significance.
Due to the size and number of braids, and the variety of instream habitats that allow for spawning and juvenile security, the river can support more trout and salmon than most other New Zealand rivers (NIWA 2003b).
Salmon spawn slightly later in the Waitaki than in rivers to the north, with the peak in March compared to late January / early February. This has implications for the proposed flushing regime of the river.
B.1.2.6 Indigenous Fish
The species composition, distribution and abundance of native fish in the Lower Waitaki River appears to be typical of braided rivers along the East Coast of the South Island, although it provides habitat for the Canterbury mudfish, one of New Zealand's most threatened species. Two other species are considered rare, the alpine galaxias and a new specie of long jawed galaxias, both found in the upper tributaries. Native fish have customary, intrinsic and ecosystem values.
B.2 Description of Existing Conditions
The objective of this section is to describe the current environmental trends with respect to major impacts that have occurred in the catchment in recent times (last 50 years) and changes that are still occurring.
Many of the current environmental issues associated with irrigation and hydroelectric power development have been topical for at least 20 years. Under the discrete policy objectives for irrigation and hydroelectric power within the 1982 Waitaki Water and Soils Resource Management Plan the following environmental aims were discussed (WCC, 1982):
- prevent or control soil erosion (irrigation);
- avoid nutrient pollution in water (irrigation);
- allocation that recognises the wildlife habitat (irrigation);
- prevention of damage by flooding (hydroelectric power).
B.2.1 Upper Waitaki
B.2.1.1 River Flow
It is self evident that the river hydrology in the Upper Waitaki has experienced a greater impact from hydroelectric power development than the Lower Waitaki. This is particularly apparent in the Tekapo, Pukaki and Lower Ohau Rivers downstream of the respective lakes. The residual flows within these rivers comprise only infrequent spills during storms large enough to overtop the dam spillway, and inputs from tributaries further downstream, which occur predominantly during November to March when the lakes are filling or have filled (Hughey in Gough et al., 1986). For the majority of the time much of these rivers exist as dry riverbed (WCC, 1982).
The above situation occurs under the consented flow regime for the hydroelectric schemes and for the purposes of this study, it will be considered to be the base case assuming no significant changes in the consent envelope are likely.
B.2.1.2 Braided River Ecosystems
Water control through damming and diversion has caused a major reduction in the area and quality of braided river habitat in the residual riverbeds, and within the associated stable side channels and wetlands. In addition, the reduced size and frequency and changed timing of floods has resulted in increasing rates of exotic weed invasion (e.g., gorse, briar, broom and lupins). Weed invasion provides habitat for rabbits and mammalian predators that prey upon native fauna and chokes the riverbed causing channelisation and exacerbation of flooding (DOC, 1999).
The adverse effects of hydroelectric generation on rivers and wetlands was recognised and a number of compensatory agreements were reached. One of these between Electricity Corporation of New Zealand (now Meridian Energy Ltd) and Department of Conservation (DOC) was signed in 1990. This agreement, known as Project River Recovery, has the objective "to carry out jointly agreed programs of wetland habitat restoration and enhancement with the goal of providing habitat and conditions equivalent to or greater than the net loss of habitat and conditions attributed to the Waitaki hydroelectric power development" (DOC, 1999).
Project River Recovery has so far managed to control weed growth in the Lower Ahuriri, expanding habitat for the black stilt, removed willows from the Tekapo Delta and Ohau River. In the Tasman River lupin and wilding pine removal has been undertaken. The project has also created and enhanced wetlands, which are now protected with predator trapping and electric fences (DOC, 1999).
In other parts of the catchment, ECan (with part Meridian, part ratepayer funding) carries out some mitigation work (including vegetation clearance), however the funding is low and will continue to be low as long as the properties who benefit from the controls (i.e., adjacent to the rivers) have low value. The level of funding is considered sufficient to "just hold the line" against vegetation encroachment in the Upper Waitaki catchment (pers. comm. Bob Reid, ECan, 27 November 2003).
The future work of Project River Recovery will improve the quality and type of habitat in the Upper Waitaki. The project plans to increase the area of weed-free braided river habitat, enhance and protect further wetland areas and maintain predator fences. Bird populations, including game, are considered stable or in the case of the black fronted tern and black stilt numbers may be increasing (pers. comm. Graeme Hughes, Cental South Island Fish & Game, 3 December 2003; Ken Hughey, Lincoln University, 27 November 2003).
The fisheries are considered to be stable, allowing for the natural annual fluctuations (pers. comm. Ken Hughey, Lincoln University, 27 November 2003).
In summary, weed invasion and wetland diminution are the main environmental trends in the braided river ecosystems of the Upper Waitaki. However, through activities such as Project River Recovery, these trends have been slowed or mitigated to some extent.
B.2.1.3 Groundwater
The status of the groundwater resource in the Upper Waitaki is probably one of limited shallow groundwater adjacent to the Tekapo, Pukaki and Lower Ohau Rivers, although there are likely to be pockets where shallow groundwater is more prolific (e.g., adjacent to Lake Ruataniwha). There is likely to be groundwater in the hardrock aquifers underlying the fluvial glacial gravels, however these aquifer are generally of low permeability and storage capacity, meaning that the ability of these rocks to transmit and store water is limited. Localised exceptions to this will occur; in such cases where regional unconformities (rock type boundaries and fault zones) and localised rock defects exist. However, to achieve the yields required to irrigate average station requirements, either many typical spec production bores (up to 80-100m deep), or fewer significantly deeper bores (>150m deep) would be required, making it prohibitively expensive to achieve the quantities of groundwater required for irrigation.
B.2.1.4 Lakes
The lakes in the Upper Waitaki and New Zealand as a whole are coming under increasing pressure from changes in land use (farming intensification and urbanisation on the lake margins at Tekapo for example) and greater number of anglers from both international and local people.
Lake levels in the Upper Waitaki are controlled to maximise power generation. For example, Tekapo and Pukaki may undergo significant reductions in water level- usually during winter when power production is high (NIWA, 2001). It is unclear what effects such changes in lake level have on fish populations and their food supplies. A NIWA study (NIWA, 2001) found that the turbid lakes of the Upper Waitaki (due to glacial flour content) generally had poorer condition brown trout than in clear lakes elsewhere in the South Island. Brown trout in the turbid lakes were also restricted to shallower depths < 7m compared to depths exceeding 40m in clear lakes. However, the relative abundance of brown trout was greater in a stable turbid lake (Ruataniwha) than in a fluctuating turbid lake (Pukaki). On the other hand, rainbow trout size and condition was not closely related to water clarity or lake level fluctuations and they appeared to show variable depth preferences in different lakes (NIWA, 2001).
In summary, the effect on the aquatic ecology after the development of the Upper Waitaki power schemes is likely to have stabilised, but additional environmental trends are establishing, which are likely to put additional pressure on the aquatic ecology of the lakes (see also Appendix B.2.1.5).
B.2.1.5 Exotic Aquatic Weeds
In recent times Lagarosiphon major, an exotic South African oxygen weed that forms dense stands out-competes native vegetation, has been discovered on the Ahuriri delta in Lake Benmore. The weed propagates in clean clear waters and has become established in many New Zealand waterways (Lake Dunstan, Lake Taupo, Lake Karapiro to name a few) causing problems to native species, recreational users and hydroelectric facilities. Left uncontrolled, the weed is likely to fully colonise all available habitats in Lakes Benmore, Aviemore and Waitaki, as well as the Lower Waitaki within three years (Landward Management, 2003).
B.2.1.6 Soil Les
The sparse vegetation cover in the Mackenzie Basin provides little protection from frost heave in the winter and dry north west winds during spring and summer. The result is annual soil losses averaging 2.2 tonnes per hectare (pers. comm. Al Shearer, ECan Twizel, 5 November 2003), which constitutes not only destruction of the soil structure but major nutrient losses from the soil.
Anecdotal information provided by various parties (land holders, DOC staff) indicates that the significant areas of dryland plant communities on the river terraces, such as Pukaki Flats, have succumbed to the increased periods of soil moisture deficits (DOC, 1999; SHS, 2003). This has resulted in an increase in the area of bare land exposed to wind erosion.
Soil erosion in arid land is a natural phenomenon, however it would appear that the current environmental trend is of enhanced soil erosion through hydroelectric scheme development, which has resulted in generally lower soil moisture levels, and through fire, rabbits, and inappropriate use of arid land such as over grazing.
B.2.1.7 Basin Floor and Terrace Indigenous Plant Communities
The effect on basin floor and terrace indigenous plant communities through hydroelectric and agricultural development in the catchment has been a reduction in area of indigenous plant communities due to the permanent drying of soils (especially on the lower terraces adjacent to the now dry rivers) and cultivation.
B.2.2 Lower Waitaki
B.2.2.1 River Flow and Geomorphology
In the Lower Waitaki there is a perception among local river users (fisherman, boaties) that the river has not changed significantly over the last 40 years. Undoubtably however, there have been changes in river flow and water quality since the development of large hydropower storage dams in the Upper Waitaki and landuse intensification through dairy farming. Changes to the river hydrological regime and hence geomorphology have resulted in gradual effects or modification to the vegetation and terrestrial ecology of the river. Examples of these changes are documented in the following:
- Boffa Miskell (2003c), NIWA (2003b) - vegetation encroachment on the fairways due to wide daily river fluctuations providing ideal environment to disperse and germination of seeds and tree fragments;
- NIWA (2003h) - reduction in total area of riverbed (as a result of conversion to farmland), a reduction in the width of unvegetated fairway, and a tendency to become less braided and more stable in channel pattern;
- NIWA (2003h) - reduction in the transport of coarse bedload gravels and supply to the coast;
- Boffa Miskell (2003c); NIWA (2003b) - exacerbation of periodic flooding and bank erosion;
- Meridan Energy (2003b) summary of current vegetation, braided river, flooding, plant and animal trends.
NIWA (2003h) state that "the latest relationships from the scientific literature predict that in its unregulated state, before the 1930s the river lay just above the braiding/non-braiding threshold. Since then, the river has fallen below this threshold, and can be expected - irrespective of Project Aqua - to be within a long-term trend wherein it is evolving its platform to one of fewer more stable channels". The effect of this trend will be concentrated overbank flooding and bank erosion on specific bends in the river.
With the reduction in frequency and extent of flood flow overall, marginal areas to the river that were once frequently flooded have been commandeered for farming. People using these areas for a livelihood, may contribute to perception of "flooding problems" in the catchment.
While there has been changes in the catchment, some of these are undoubtably due to short and long-term variation in climate and ocean conditions. Overall, the bass case is considered to be the summation of NIWA (2003h), where the river is evolving to one of fewer and more stable channels.
B.2.2.2 Groundwater
Hamilton and Elliott (1994) report that groundwater levels increased between 2m and 6m following large-scale irrigation development in the Lower Waitaki during the early 1970's. Further increases in groundwater level are probably restricted by the relatively high permeability of the gravel aquifers which provides a high degree of coupling with surface water boundary conditions such as springs, drains, creeks and the river, acting to constrain further groundwater rise. The rise in groundwater level has a beneficial effect on groundwater supply and groundwater dependent ecosystems.
SKM (2000) indicates that while concentrations of nitrate-nitrogen (averaging 2.7mg/L) are below drinking water standards (11.3mg/L), there is a slight temporal trend of increasing nitrate concentration since monitoring began in 1993. This trend may be attributed to the intensification of dairy farming in the region, and is consistent with trends observed in various other significant dairy farming areas in New Zealand (e.g. Southland, Otago,Canterbury, Taranki, Lake Taupo, Bay of Plenty, and Waikato).
Recent studies focussing on Lake Taupo have found that urine leaching is the main cause of high nitrates in groundwater in that catchment. The nitrate leaching rates from dairy landuse in the Taupo area are approximately 50kg N/ha/yr compared to about 15kg N/ha/yr from sheep and beef farms (Elliott and Stroud, 2001; Ledgard, 2000).
The impact on the shallow groundwater quality of intensified dairy farming in the Lower Waitaki is unlikely to reach similar proportions to that in the Waikato and Lake Taupo. This is due to the shorter groundwater residence times, higher aquifer permeability, flushing rates and river recharge; and the fact that the catchment is already near full development.
B.2.2.3 Braided River Ecosystems
The ecological values of the Lower Waitaki were discussed in Appendix B.1.2, and while still of significance, they have been impacted by the high level of modification of the river and adjacent lands (Boffa Miskell, 2003). There are now very few gravel surfaces in the Lower Waitaki where native vegetation dominates, as the exotic species are generally more aggressive (Boffa Miskell, 2003c). Native plant species are continuing to decline as a result of the invasion of exotic species, and the predicted trend is increasing shrub species such as gorse and broom and a decrease in the exposed gravels and low-cover native species (Boffa Miskell, 2003c).
Boffa Miskell (2003c) state that endemic braided river specialists such as the wrybill and black billed gulls are probably declining nationally, although the black-fronted tern and black stilt populations show an increase in the Lower Waitaki. Most of the wetland bird species in the lower Waitaki River show similar patterns of increase and decline as national data (Boffa Miskell, 2003).
The key threat to bird populations is considered to be predation, followed by a decline in nesting habitat (clear gravels). Flooding is also a factor, although with the managed river regime, flooding is less of an issue now than under the natural river flow regime. Under the current regime there is considered to be further vegetation encroachment and a reduction in the number of braids, reducing breeding success and leading to a decline in the abundance and variety of bird species (Boffa Miskell, 2003c).
ECan does not have any plans to change their river management programme of vegetation clearance and other flood mitigation measures, but considers it may be "losing the battle" against vegetation encroachment (pers. comm. Bob Reid, ECan, 27 November 2003).
B.2.2.4 Wetlands
Boffa Miskell (2003) conclude that the wetlands in the Waitaki River valley are following a national trend of decline due to the intensification of agriculture, and this is likely to continue through the following:
- water diversion or draining of wet areas to allow for pasture establishment;
- encroachment of weed species on natural systems; and
- stock effluent and fertiliser affecting water quality.
Of some benefit is the creation or enhancement of pools and ponds for sport wildlife habitat, and the creation of artificial ponds for irrigation and wastewater treatment, both of which enable native flora and fauna to establish. Predators are considered a threat to wetland birds.
B.2.2.5 Indigenous Plant Communities
Indigenous plant communities in the Lower Waitaki has declined and is likely to continue to decline with further agricultural intensification.
B.2.2.6 Salmonid
Numbers of adult salmon returning to the Waitaki River range from 6,000 to 36,000 per annum and equal or exceed runs in any other salmon river in New Zealand (NIWA, 2003f). Trout abundance is estimated between 9,000 and over 20,000 fish. Salmon run from the sea to spawn in the braids of the upper and middle river and the Hakataramea River. Rainbow trout are largely an upper river species, dependent for spawning on the upper tributaries. Brown trout are common throughout the system and spawn in the tributaries and smaller braids of the main river (NIWA 2003b). The number of salmon running in any year depends on rearing conditions in both the river and the sea. Trout populations are dependent on spawning and rearing conditions, and competition for food.
Allowing for the natural annual fluctuations, the fisheries are considered to be stable (pers. comm. Ken Hughey, Lincoln University, 27 November 2003 and Martin Unwin, NIWA, 27 November 2003).
B.2.2.7 Indigenous Fish
Most populations are stable, however the recruitment of long-finned eels is in decline in the Waitaki River, as it is in most parts of New Zealand (NIWA 2003f).
B.2.2.8 Exotic Aquatic Weeds
Appendix B.2.1.5 summarises the Lagarosiphon problem in the Upper Waitaki and highlights the potential problem in the Lower Waitaki. However, the presence of Lagarosiphon in the Lower Waitaki at this time is unknown and no documentation of its existence is provided in the Project Aqua AEE. Information received at the forums subsequent to the draft report released indicated that more information regarding lagarosiphon in the lower catchment was available, however it was not received in time to include in the final report.
B.3 Environmental Impacts, Irrigation Sector Expansion
The development of additional irrigation in the Waitaki catchment has the potential to both improve and damage the natural environment and ecosystems. However, many of the damaging outcomes are both manageable and mitigateable if appropriate water allocations are made and land management techniques utilised.
Damaging environmental effects associated with additional irrigation relate primarily to the effects that result from intensification of farming, which are generic through many rural regions in New Zealand, and include:
- potential stress on river systems through reduction of the pre-existing flows. This is considered a specific risk to the smaller tributaries, that is some cases that might currently have allocations towards hydro-electricity.
- increased nutrient concentrations (primarily nitrate and phosphorus) in waterways through leaching into the groundwater system or direct runoff (depending on soil types), which eventually leads to increased biological oxygen demand, decreased dissolved oxygen levels and eutrophication of lakes, ponded areas, lowland river backwaters, and slower flowing lowland riversrivers;21
- increased microbial concentrations in waterways through stock excretement runoff from the riparian margins and directly through access to waterways;
- increased bank erosion and turbidity through increased stocking rates and access to waterways;
- changes in groundwater level due to irrigation and associated environmental effects.
A proportion of these environmental effects can be mitigated or reduced through appropriate farm management practices, such as controlling nutrient discharge rates in sensitive areas and at sensitive times of the year, fencing riparian margins and using biodegradable or environmentally friendly fertiliser, herbicides and pesticides.
The environment effects from farm intensification will vary in areas with different soil types and climate regimes because the various areas will be capable of supporting different types of farming. For example, the Lower Waitaki has experienced a significant increase in diary farming (SKM, 2000) which has been linked in many parts of the country to nitrate problems. Meanwhile irrigation in the Upper Waitaki is anticipated to provide a higher degree of security to beef and sheep farmers through higher stocking rates and crop diversification, which is anticipated to have less environmental impact than dairying. However, landuse intensification may lead to loss of biodiversity and landscape characteristics and degradation of water quality in smaller water bodies.
Positive environmental outcomes from irrigation include:
- less susceptibility to wind erosion;
- improved soil structure and moisture retention properties - leading to;
- enhanced stream baseflows during dry periods (i.e., maintenance of flow); and
- increased food sources for game bird populations.
B.3.1 Upper Waitaki
The following sections summarise the more significant effects of increased irrigation and pastoral development in the Upper Waitaki.
B.3.1.1 Visual Character
Large scale irrigation and agricultural development of the Upper Waitaki will bring a marked change to the general appearance and visual character of the landscape, changing the present muted tones and open appearance to the brighter greens and shelter-belt subdivided appearance of a farm landscape (WCC, 1982). This may lead to a loss of valued characteristics in an area that is a nationally outstanding landscape and an important setting for recreation and tourism.
B.3.1.2 Water Quality
As alluded to in Appendix E.3 irrigation development is likely to result in more intensive stocking rates, and further accruement of land for farms (i.e., reduction of wetlands and forested areas) have the potential to affect both groundwater and surface water quality. The magnitude of the potential effects is highly variable depending on soil characteristics, land gradients and climate of the areas under consideration.
Water quality concerns relate primarily to elevated:
- suspended sediment load and turbidity affecting macroinvertebrates and aquatic plants;
- nutrients (mainly nitrate and phosphorus) affecting algae growth rates and consequently dissolved oxygen levels;
- microbacteriological constituents, which pose human health risks; and.
- toxic compounds from herbicides and pesticides, which also pose human health risks.
A significant proportion of these adverse environmental outcomes are mitigateable by implementation of modern land management techniques including:
- restricting access to waterways through installation of riparian fencing and culvert crossings;
- carefully managing stocking rates and paddock selection during susceptible times of the year (i.e., during winter when groundwater recharge and flushing rates are greatest, and when shallow groundwater tables are near the surface);
- use of rapidly biodegradable fertilisers, herbicides and insecticides and appropriate application rates;
- managing effluent disposal via areal rather than point discharges; and
- appropriate irrigation rates that avoid surface runoff and excessive leaching to groundwater.
B.3.1.3 Braided River Ecosystem
The predicted impacts on the braided river habitat are considered similar to the base case scenario. Where this may differ is if irrigation causes property prices to rise and the land owners demand more erosion and flooding protection by Ecan (Bob Reid, Ecan, pers. com 27 November 2003). Because river works are demand-driven, then the demands of adjacent landowners will dictate whether vegetation clearance, riparian plant management and other in-river works are increased or not.
Game birds populations are predicted to explode with increased pasture following irrigation. This has been seen already in other parts of the catchment where irrigation has been successful (pers. comm. Graeme Hughes, Central South Island Fish & Game, 3 December 2003). Braided river specialist birds such as the black stilt may also benefit from the increased food source (pers. comm. Ken Hughey, Lincoln University, 27 November 2003).
Increased land intensification is anticipated to increase the recreational demands on the river and may in turn affect the competition on the gravel channels between anglers and between humans and birds. Lower river flows will also create better human access and more competition for the river bed.
B.3.1.4 Soil Erosion
Irrigation can have a positive impact on arid landscapes where soil wind erosion is an ongoing concern. Various submissions to the project team at the Fairlie workshop and the evidence of Clarke (2003) suggest that soil depth and water holding capacity build up rapidly under irrigation and the degraded soils quickly change to productive soils, with the ability to resist erosion. However, overgrazing and inappropriate use of arid landscapes is likely to exacerbate soil erosion.
B.3.1.5 Wetlands
Previous wetlands or areas bordering existing wetlands are obviously unlikely to require irrigation, implying that there are unlikely to be any directly damaging effects from irrigation on wetlands. However, land encroachment on wetland areas for farming, although not a permitted activity (for ecologically significant wetlands), has occurred in the past and may reduce the size of existing wetlands in the future.
Wetlands downgradient of irrigated areas are likely to experience varying degrees of lateral groundwater recharge depending on the soil characteristics of the irrigated area and irrigation efficiencies. Lateral groundwater recharge may improve the wetlands in these areas by providing a more secure water supply.
Fencing of wetland and riparian areas will mitigate the possible damaging outcomes of stock access to these sensitive areas, and is becoming a condition of consent for farm development and irrigation in many regions of New Zealand.
Overall, it is expected that remaining low terrace wetlands would improve with widespread irrigation, assuming that appropriate land management techniques are exercised, although these are not currently a requirement of consents.
B.3.1.6 Indigenous Grassland Ecosystems
There are large areas of indigenous grasslands identified by DOC that could be developed into intensive pastoral ecosystems under irrigation (Ken Hughey, Lincoln University, pers. com 27 November 2003). These grasslands are underrepresented and provide important habitat for indigenous invertebrates. Unless protected by covenant in the District Plan, these areas are likely to be affected adversely with intensification of irrigated agriculture.
B.3.1.7 Salmonids
Additional irrigation may affect salmonids through water quality (Appendix B.3.1.2) and instream loss of flow effects depending on where the water is sourced. If the water is sourced through existing power scheme canals then abstractions effects of additional irrigation are likely to be minimal. It is unlikely that large consents would be granted for additional abstraction from the rivers and tributary streams in the Upper Waitaki due to these remaining resources being already under pressure.
B.3.1.8 Groundwater
Groundwater levels would be expected to rise under additional irrigation scenarios in the Upper Waitaki, even under fully efficient irrigation. This is because the soil structure on the river terraces is stony and vertical percolation would be difficult to avoid, especially in the earlier years of irrigation before the soil structure and organic content has improved.
Groundwater level rise would not be seen as an adverse effect in the Upper Waitaki as it has positive secondary effects on wetlands, springfed streams and stream baseflows.
B.3.2 Lower Waitaki
As indicated in Sections E.3.8, irrigable agriculture in the Lower Waitaki is nearing capacity. This would suggest that irrigation water demands within the Lower Waitaki, and environmental effects of landuse change (out of river effects) and abstraction (in river effects) would be nearing a plateau. However, some areas currently not requiring irrigation, may in the future, through climate and/or land use change effects on shallow groundwater tables and there are also proposals to irrigate areas in North Otago outside of the Waitaki River valley catchment (see Appendix E.3.8). This indicates that in river effects from river abstraction may increase and the flow on effects of reduced river flushing and dilution may also occur, which will serve to exacerbate any existing water quality effects from intensive agricultural operations.
B.3.2.1 Water Quality
The discussion of water quality effects from irrigable agriculture intensification provided in Appendix B.3.1.2 for the Upper Waitaki is also applicable to the Lower Waitaki. However, due to the fact that the catchment is well developed any effects are anticipated to be less marked than that anticipated should widespread irrigation expansion occur in the Upper Waitaki.
The water quality effects due to reduced flow in the river as a result of abstraction are anticipated to be insignificant (without Project Aqua) as the maximum rate applied for in the Lower Waitaki is approximately 40m³/s, which is equivalent to approximately 30% of the 7-day mean annual low flow of approximately 127m³/s and insignificant compared to the mean flow of approximately 360m³/s.
B.3.2.2 Wetlands
Information pertaining to the impact on wetlands in the Lower Waitaki is provided in Boffa Miskell (2003c), and is summarised as follows.
Wetlands are expected to be impacted by:
- Increased demand for productive land leading to conversion of remaining wetlands on the river terraces to pasture.
- Increased stock damage to riparian wetlands due to increased stock numbers and better access to the river bed. River terrace wetlands also likely to experience more stock damage due to intensification of land use.
- Increased effluent and fertiliser runoff affecting water quality and potentially ecosystem function and diversity. This impact would vary depending on the type and size of wetland.
- Decreased connectivity between wetlands and the river due to less river flow during irrigation demand months.
- Increased groundwater in local areas due to irrigation recharge water, which may assist connectivity or water supply to wetlands.
As described in Appendix E.3.4, many of the damaging environmental outcomes are mitigateable if appropriate land management techniques are utilised. Mitigation in the form of fencing, maintaining water supply and other proactive ecosystem enhancements may offset many of these impacts, although they are not currently conditions of consent. Overall we would expect no noticeable change in wetlands to occur if these measures were implemented, however in reality continues degradation of wetlands is more likely Salmonids
The effect on the salmonid populations from changes in river flow are considered to be minor, as the quantity of water required for irrigation from the Lower Waitaki River is small in proportion to flow as discussed in Appendix E.3.4).
Water quality changes from intensification of land use in the valley is not anticipated to have an adverse effect on salmonids due to the size of the Lower Waitaki River and its ability to dilute runoff. It is anticipated that the water quality in the spawning tributaries of the Lower Waitaki River will not be adversely affected by adjacent land use intensification.
B.3.2.3 Native Fish
The scenario for native fish is likely to be similar to the Project Aqua scenario, albeit to a lesser extent due to the smaller relative size of irrigation compared to Project Aqua.
B.3.2.4 Braided River Ecosystem
The predicted impacts on the braided river habitat are considered similar to the base case scenario described in Appendix B.1.2.1). Where this may differ is if irrigation causes property prices to rise and the land owners demand more erosion and flooding protection (pers. comm. Bob Reid, Ecan, 27 November 2003). Because river works are demand-driven, then the demands of adjacent landowners will dictate whether vegetation clearance, riparian plant management and other in-river works are increased or not.
Increased land intensification is anticipated to increase the recreational demands on the river and may in turn affect the competition on the river between anglers and between humans and birds.
B.4 Environmental Impacts, Hydroelectricity Sector Expansion
The section summarises the main environmental impacts associated with additional power generation in the Waitaki catchment, with the assumption that irrigation demands remain as they currently are. Some further analysis as it applies to specific economic variables is also provided in the main body of the report under Appendix E.4.2.
B.4.1 Upper Waitaki
The information contained in the Project Aqua AEE regarding environmental impacts in the Upper Waitaki is limited. The only information on the lakes levels that we obtained is a statement in Appendix C of URS (2003a) that indicates all lakes modelled remain within their current consent conditions and operating criteria at all times. Having said this, it is likely that the combined lake storage levels will generally reside lower than under current conditions for the majority of time to meet additional Project Aqua flow requirements, which would include the canal, residual river and proposed river flushing. The net result is likely to be lower storage levels and more storage available for the majority of time to absorb high and flood flows. This would result in a further reduction in spill flows (i.e., reduction in size and frequency of major flood flows) into the residual rivers in the Upper Waitaki.
In the absence of data indicating otherwise, the following sections assume that additional pressure will be put on the water resources of the Upper Waitaki to meet the Lower Waitaki system requirements.
B.4.1.1 Lake Levels and River Flow
As alluded to above, the effect on river and lake hydrology in the Upper Waitaki of additional power generation in the Lower Waitaki is unclear and represents a significant information gap. Information provided in the URS (2003a) suggests that median daily flow22 over the Waitaki Dam with Project Aqua operational will be 13m³/s greater than historical conditions between 1980-2000 (386m³/s compared to 273m³/s). The net effect of this is likely to be an overall reduction in storage in the Upper Waitaki Lakes for the majority of the time.
The above analysis probably under predicts the actual impact on the Upper Waitaki system, due to the fact that the analysis has been carried out on the 1980-2000 period with mean daily flows 10.2% greater than data for the proceeding 50 years (Opus, 2003).
If the combined lake storage levels are generally reduced in the Upper Waitaki to meet the additional water requirements of Project Aqua, residual flows in the Tekapo, Pukaki and Lower Ohau Rivers are likely to experience further reduction. As indicated in the base case (Section 1.2), the rivers downgradient of the main hydropower storage dams are severely effected by existing hydroelectric generation, which may indicate that additional in-river effects are not likely to be significant. However, the overall effect of this will be to put more pressure on water resources within the lakes and tributary streams for other abstractive water users.
B.4.1.2 River Habitat and Wetlands
The effects experienced under the existing hydroelectric development (discussed in Appendix B.2.1.2) are likely to be exacerbated if lake levels and the frequency of spills in the residual rivers are reduced further. These effects are:
- reduction in area and quality of braided river habitat; and
- increased rates of exotic weed invasion.
B.4.1.3 Soil Erosion
Soil erosion is likely to be exacerbated by further reductions in river flow and water available for irrigation, which will have effect soil moisture levels in riparian and shallow groundwater areas.
B.4.2 Lower Waitaki
The environmental effects in the Lower Waitaki have been described extensively in the Project Aqua AEE. This section summarises the issues that have been identified through workshops and discussion with stakeholders as of most significance. This report, being a national cost benefit analysis, does not include some environmental effects that are generally considered important only within the local context.
It should be noted that as part of the consent process, Meridan Energy was in the process of developing a Waitaki River Management Strategy with relevant stakeholders. Its task in part would be to mitigate some of the impacts identified in the following sections and consequently the impacts noted may be over-estimates in the consideration of the Project Aqua proposal.
At the time of the report finalisation, the development of the Waitaki River Management Strategy to address issues of mitigation had not been completed due in part to the cessation of planning for Project Aqua.
B.4.2.1 Hydrology
The proposed change in flow regime under Project Aqua is described in NIWA (2003a) and URS (2003a) and reproduced here in Table 19.
Table 19: Summary of Current and Proposed Flow Regime in the Waitaki River (Waitaki Dam) and at the Aqua Canal Intake (Sources: URS (2003b); NIWA (2003a)). | Scenario | Minimum flow in residual river
(m³/s) | Median daily flow at Waitaki Dam
(m³/s) | Median daily flow at Priest Road (residual river)
(m³/s) | Median daily flow into canal
(m³/s) | Flushing flows
(m³/s) |
| Current | 120 | 373 | 379 | n/a | n/a |
| Project Aqua | 100-1401,2 | 386 | 119 | 265 | 450& 900³ |
Meridian have generated a synthetic historical (1980-2000) flow data set for the Waitaki Dam that optimises generation for the Upper Waitaki system with Project Aqua operational. From this, the proposed flow regime over the Waitaki Dam with Project Aqua operational is expected to reside within the envelope bounded by the historical regime of the last 20 years (NIWA, 2003d). The following provides a summary of the major changes anticipated:
- Minimum Flows - While minimum flows within the river will be similar under Project Aqua, minimum discharges from Waitaki Dam will need to increase (Meridian Energy, 2003b pg 7-3) in order to supply the additional minimum canal flow requirement of 75m³/s.
- Flow Regulation - The optimised flow series with Project Aqua operational is a change in the manner Meridian has operated the system. The fundamental difference is that flow in excess of the Project Aqua and residual river requirements (i.e., 340m³/s + 100-140m³/s, respectively) will be preferentially held in storage to maximise generation potential. The result of this is less variability in daily flows above the proposed residual river flow regime. For example, historically between 1980 and 2000, flows above 900m³/s and 1,200m³/s have occurred approximately 14 and 9 times respectively. In comparison flows of the same magnitude for the optimised Project Aqua data set are predicted to occur approximately 4 and 3 times, receptively. The statistical summary tables in URS (2003a) indicate that maximum daily flood flows will reduce by 45% from 2,649m³/s to 1,458m³/s.
- Flushing Flows - As indicated in Table 19, flushing flows in the residual river of 450m³/s for a 24 hour period are proposed once every 5-6 weeks during December to April.
- Median Flow - Considering the above flow regime changes, calculations with data provided in Table 2.9 and 4.2 of URS (2003b) indicate that the resulting median daily flow at Waitaki Dam will be increased by 13m³/s (Table 19). Data for this calculation was based on daily flow statistics for the Waitaki Dam for 1980-2000 historical and modelled optimised Project Aqua flows (includes flushing flows).
- Residual River Flow - Flow within the residual Waitaki River downgradient of the Project Aqua intake and Hakataramea River confluence will reside between 100m³/s and 140m³/s 90% of the time, and as shown in Table 19, a 69% reduction in median daily flow is expected from 379m³/s to 119m³/s.
The key implications of the above changes in river hydrology are:
- an overall reduction in the combined lake storage levels (for the majority of the time) in the Upper Waitaki system due to increased flow over the Waitaki Dam (see Appendix B.4.1.1);
- a greater degree of high and flood flow buffering in the Upper Waitaki system;
- a commensurate reduction in the frequency and size of flood flows within the Lower Waitaki River;
- a more noticeable seasonal pattern of higher flows in summer (i.e., proposed minimum flow of 140m³/s compared to 120m³/s, plus regular (5-6 weekly) 450m³/s flushing flows) and lower flows in winter compared to current conditions.
The NIWA (2003b) report focuses on predicting the impacts of the proposed Project Aqua flow regime on the river's form and processes, including:
- instream and terrestrial habitats;
- engineering issues;
- hazards such as bank erosion, flooding and erosion of the adjacent coast.
- Much of the information contained in the following sections, which discuss the consequences of the flow regime changes, was taken from NIWA (2003h).
B.4.2.2 Geomorphic Processes
The following summary of the anticipated effects due to flow regulation under Project Aqua has been compiled from NIWA (2003h) where else indicated:
- In the short term, the residual river would remain braided, but the average numbers of braids would reduce in number from approximately 9 to 6 (at Priest Road).
- Over a period of decades, with no change in riverbed vegetation control, the residual river would degrade and become less braided, with channel morphologies and positions tending to become more stable. The river is predicted to remain at least semi-braided (i.e., alternating downstream between a single channel and several channels).
- The proposed Project Aqua flood flow (or "maintenance" flow) releases would not be sufficient on their own to maintain the existing intensity of braiding in the residual river, as the extent of braiding appears to be decreasing under the present flow regime.
- The present supply of gravel to the residual river from tributaries would reduce, particularly in those tributaries that emerge some distance from main river channels.
- The annual rate of bedload transport in the river will reduce, with gravel supply to the coast reduced under the optimised Project Aqua regime by 70-90% within a few decades from the current level. In consequence, erosion along the coastline is expected to accelerate, although to what degree is unclear and difficult to predict.
- There will be an increased likelihood of chronic bank erosion where the river swings against one or the other bank downstream of the canal outlet upstream of SH1, which may affect the stability of SH1 road and rail bridge piles.
- The reduced frequency of flooding will tend to hinder barrier breaching and increase the likelihood and extent of northward extension of the outlet channel. This will result in the likelihood of erosion on the north side cliffs (NIWA, 2003h).
The main impact of Project Aqua on turbidity and water clarity is a reduction in the ability of flows within the residual river to dilute and flush suspended sediment delivered by freshes and floods from its tributaries. It is predicted that the average concentration of tributary derived suspended solids in the river are likely to double under Project Aqua, while suspended solids from the upper catchments would reduce slightly. Overall, there is likely to be no noticeable change in water clarity.
B.4.2.3 Braided River Ecosystem
The key effects of Project Aqua on the terrestrial ecosystem within the braided river as a result of reduced flow in the river include:
- initial gains in breeding habitat due to increased area of exposed gravels, but long term losses in breeding habitat through vegetation encroachment by willows, gorse, broom and others if left unmanaged;
- losses in breeding productivity of braided river bird species through predation;
- increased conflict between breeding birds, stock and human usage impacts (i.e., recreation, agriculture, river works and gravel extraction) of the river under low flows (pers. comm. Ken Hughey, Lincoln University, 27 November 2003);
- Bird species diversity may decline as those species that prefer open space leave the river due to vegetation encroachment (i.e., geese and swan) (pers. comm. Graeme Hughes, Central South Island Fish and Game, 3 December 2003).
These effects can be mitigated to a large extent through the River Management Strategy. However, the level to which aquatic communities (trout, salmon, native fish and invertebrate communities) are to be maintained as agreed in consent conditions has not yet been defined. Recommendations in the NIWA (2003d) report are designed to maintain the status quo or to improve habitat for instream communities. Whether the status quo is to be maintained or enhanced will be a mitigation-mandating matter for the River Management Strategy, the bilateral mitigation agreements between the parties, the Water Allocation Framework and the resource consent process. However, the bottomline is unlikely to be any worse than the current trend of ongoing degradation under the "status quo".
In practice, increased levels of vegetation control will be required to maintain the existing fairway width and an Adaptive Management Approach is proposed to determine the most suitable pattern of flood flows for environmental objectives. The proposed approach acknowledges that it is difficult to predict what the site-specific impacts of the reduced flow regime will be in practice.
B.4.2.4 Water Quality
Several aspects of the Project Aqua flow regime are likely to affect the residual river water quality (NIWA, 2003c). The main affect identified appears to be through reduced flows, which are likely to cause a reduction in turbidity (positive effect) and increased nutrient and microbial concentrations (negative effect). The increased nutrient and microbial concentrations will result from a reduction in the rivers ability to dilute contaminants (Meridian Energy, 2003c), however it should be noted that the source of these contaminants is related to landuse management not Project Aqua.
The effect of increased microbial concentrations can be mitigated by an increase in the degree of treatment required in cases where the water is used for potable supply. However, the existing water quality is reported to be below the New Zealand drinking water guidelines and treatment upgrades to municipal supplies are planned, so the effect of Project Aqua should not result in any additional treatment required (Meridian Energy, 2003b). Private potable water users may require additional treatment.
The likely increase in nutrient concentrations is reported as not being significant enough to affect salmonids (Meridian Energy, 2003b).
B.4.2.5 Salmonids
The reduction in flow and the change in invertebrate species may have a minor impact on trout populations, but overall there is anticipated to be no major change (NIWA, 2003f; pers. comm. Ian Jowett, NIWA, 20 November 2003). There may be a change to the balance of numbers between the brown and rainbow trout populations depending on the hydrology of floods and the extent of competition for habitat between the two species (NIWA, 2003f).
NIWA (2003f) state that salmon are more likely to be affected adversely by reductions in spawning habitat in the residual river than trout, although there should still be sufficient habitat for successful spawning.
Juvenile habitats for salmonids is expected to decline by 10 - 20% with the reduction in flow as backwaters and wetland areas dry up or are modified, although there is considered to still be an acceptable amount of habitat. In addition, any declines in physical habitat should be compensated by increased flow stability and food supplies, resulting in an insignificant change in numbers (NIWA, 2003f).
Ongoing river management as described in the Project Aqua AEE, including the proposed flow regime, management of river braids and vegetation, and wetland enhancement is designed to mitigate potential effects on salmonid populations.
B.4.2.6 Indigenous Fish
The reduction in flow expected from the development of the proposed canal structure will reduce the area of wetland and backwater environments that are needed by many native species, including short-finned eels, lamprey and inaka (NIWA 2003e). Fish associated with riffles and swift flowing environments (such as torrentfish and bluegilled bullies) are likely to be most at risk from a decline in habitat in the mainstream, whereas longfinned eels are most at risk from the 20% reduction in wetland / riparian areas (NIWA 2003e).
The reduction in flow expected from the development of the proposed canal structure will reduce the area of wetland and backwater environments that are needed by many native species, including short-finned eels, lamprey and inaka by approximately 20% (NIWA, 2003e). Fish associated with riffles and swift flowing environments (such as torrentfish and bluegilled bullies) are likely to be most at risk from a decline in habitat in the main stream, whereas longfinned eels are most at risk from the reduction in wetland / riparian areas (NIWA, 2003e).
The natural decline in eel numbers, particularly short finned, will be exacerbated by the loss in habitat. This will probably be mitigated by the creation and enhancement of wetland areas, but only if they form part of the riparian area of the river or maintain passage to the river for migration.
There are risks of entrainment from the canal intake that could affect fish migration and populations. However, this will be mitigated to a large extent by installation of fine mesh screens. It is anticipated that native fish species will migrate into the canal, particularly the juvenile eels and koaro and adult lampreys, putting additional pressure on native fish populations (NIWA, 2003e).
Overall, total indigenous fish numbers are likely to be unchanged. Native fish density may increase, as the stabilising effect of the low flow environment will favour most native fish and provide new habitat to compensate for that lost with the reduction in riparian and wetland environments (NIWA, 2003e).
B.4.2.7 Groundwater
The most significant effect of Project Aqua on groundwater levels is the widespread drawdown or reduction in groundwater levels within the gravel aquifer, through:
- reduction in the residual river levels (impact on both sides of the river); and
- dewatering associated with the construction and operation of below ground canal sections and power stations (impact on south side of the river only).
The groundwater level reductions associated with the residual flow regime are predicted to be widespread in the Post-Glacial Gravels (more recent gravels) that form the river floodplain of up to 0.5m. Groundwater level reduction in the Pleistocene Gravels (older gravels) associated with the construction and operation of the canals and power stations are more localised (URS, 2003b), although significantly greater at these locations than the depressurisation associated with the river. For example, at the power stations dewatering drawdowns in groundwater levels are anticipated to reach approximately 30m.
The impact of reduced groundwater levels would be experienced by groundwater users that obtain their water through excavated gravel pits, infiltration galleries, wells and bores. In some cases the effects can easily be mitigated by deepening abstraction points for gravel pits, infiltration galleries and shallow wells, which are usually located adjacent to the river in the Post Glacial gravels and will only experience a maximum of 0.5m groundwater level drop. For deeper wells and machine bores located in the Pleistocene gravels, the costs of deepening and extending submersible pumps will be significantly greater, especially in those areas affected by the cone of depression from dewatering of the power stations.
Groundwater level reductions will also affect a number of springs, springfed streams, groundwater dependent wetlands and riparian margins and farms adjacent to the river and springs with shallow groundwater. The potential effects will vary depending on the location with respect to the canal, as some reaches of the canal are above ground and potential exists for canal seepage to the groundwater system, which may enhance the groundwater dependent ecosystems. However, other section of the canal will be founded below ground level and below the groundwater table, and these section have the potential to dewater the adjacent aquifer.
URS (2003b) have adopted a conservative stance in their assessment of hydrogeological effects and assumed that no mitigation will be available. Mitigation measures are available to reduce the effects, but it is not clear at this stage what measures will occur, and whether the mitigation measures have been finalised. Levels of approximation have been used to determine the
B.4.2.8 Wetlands
As indicated in the groundwater section (Appendix B.4.2.7), wetlands will be affected by both:
- the altered river flow regime and consequent reduction in groundwater levels, and
- through dewatering effects associated with the construction and operation of the canals and power stations.
With the altered flow regime and the consequent reduction in the wetted perimeter of the river and lowered groundwater table, there will be a reduction in the extent and frequency of wetland flooding in the existing riparian zone (Boffa Miskell, 2003c). This will result in a reduction in habitat and further decline in the connectivity of wetlands with the river and other water bodies.
Of the 190ha of river terrace wetlands in the Lower Waitaki, 50ha will definitely be affected by groundwater changes and a further 34ha may be affected by groundwater changes. This includes Eckhold's Pond and Te Hua Taki Wetland, although Eckhold's Pond may be maintained by irrigation water. Those wetlands that experience long periods of drier conditions are likely to be invaded by species more tolerant to the dry (Boffa Miskell, 2003c).
Of the 190ha of river terrace wetlands, 30ha will be destroyed by the construction of the canal, including the destruction of Tewatapoki, Kurow and Duntroon wetlands and part of Cairns flax wetland. These are considered locally significant ecosystems. In addition, some of the riparian wetland areas will be affected by the construction of the intake and the outfall (Boffa Miskell, 2003).
Game birds and other braided river specialists will be affected by the loss of feeding, loafing, nesting and / or shelter habitat (pers. comm. Graeme Hughes, 3 December 2003, Central South Island Fish and Game,). Species diversity as well as populations may be affected, as wetland specialists such as the New Zealand shoveller lose habitat. Game bird populations may decline but due to the large numbers on the Lower Waitaki and flexibility in habitat, is thought that the observed impact to potentially affected parties (hunters) could be small.
The functions and values of these wetlands may be maintained by the Meridian's mitigation proposal to create new wetlands and connections with the river and groundwater system, and enhancement of existing wetland environments. However, it is acknowledged that establishment of new artificial wetlands is a difficult process to manage, and artificial wetlands may not attain to the ecological status of the natural wetlands they are intended to replace.
B.4.2.9 Dryland Turf
The construction of the settling pond, decanting facilities and canal will destroy approximately half of the remaining turfland at Kurow (which has no formal protection at present), although the highest ecological values in the raining area were planned to be formally (Boffa Miskell, 2003c). The construction will fragment the turfland ecosystem and interrupt the habitat sequence from the river at this location. The destruction of the lower value ecosystem areas within the turfland remove an important buffer zone of habitat between the high and low value areas which create a corridor for colonisation.
During construction there may be disturbances to the adjacent land that may affect native species populations and / or encourage weed species. A proposed exclusion zone for construction work may mitigate this to some extent.
The overall mitigation measures proposed will protect the remaining turfland, but will not adequately replace all the values lost with the construction of the Project Aqua infrastructure. Managing the remaining turfland will potentially improve biodiversity values.
Back to Top