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Doc #28 — NZ Water Resources Atlas

Rivers, Lakes, Aquifers, Dam Catchments, and Municipal Supply Sources

Phase: 1--2 (Print Early) | Feasibility: [A] Established --- reference compilation from existing NZ hydrological data

Unreliable — not for operational use. Produced by AI under human direction and editorial review. This document contains errors of fact, judgment, and emphasis and has not been peer-reviewed. See About the Recovery Library for methodology and limitations. © 2026 Recoverable Foundation. Licensed under CC BY-ND 4.0. This disclaimer must be included in any reproduction or redistribution.

EXECUTIVE SUMMARY

Water underpins everything in NZ’s recovery — hydroelectric generation, municipal supply, food production — and nuclear winter will reduce precipitation by an estimated 10–30% while imported treatment chemicals run out. If water resources are not mapped and managed, drought-vulnerable regions face supply failures, hydro output drops, and waterborne disease increases. New Zealand holds approximately 500 billion cubic metres of freshwater in rivers, lakes, and aquifers — one of the highest per-capita freshwater endowments in the world.1

This document catalogues NZ’s principal water resources: major rivers by flow rate and catchment area, lakes by volume and current use, groundwater aquifers by capacity and recharge characteristics, hydroelectric dam catchments, and municipal water supply sources for each major city. Its purpose is to provide planners, engineers, and regional authorities with a printed reference to data that currently exists only in digital systems maintained by NIWA, regional councils, and water supply authorities. Drought-vulnerable regions — particularly eastern Canterbury and Hawke’s Bay — face the tightest margins. Water quality risks arise from reduced capacity to maintain treatment infrastructure and from the loss of imported treatment chemicals (see Doc #48). The water itself is not the problem; treating it for safe consumption is.

This atlas should be printed and distributed to every regional council, civil defence office, and water supply authority in the country. It is a reference document, not an action plan — but it provides the factual foundation on which water management decisions depend.

Contents

COMPUTED DATA: WATER RESOURCES DATA

View the Water Resources Tables → — Major rivers, lakes, hydroelectric dams, municipal water sources, aquifers, and a water resources map.

View the generation script → — Python source code and data sources (NIWA, regional councils).

1. MAJOR RIVERS

NZ has over 425,000 kilometres of rivers and streams.2 The following table covers the principal rivers by mean flow, ordered by volume. Flow data is drawn primarily from NIWA’s National Hydrological Database and regional council monitoring stations.

1.1 South Island

River Mean flow (m3/s) Catchment area (km2) Key uses Notes
Clutha/Mata-Au ~614 20,580 Hydro (Clyde, Roxburgh), irrigation NZ’s highest-volume river3
Buller ~490 6,500 Minor hydro, drainage West Coast; high rainfall catchment
Waitaki ~370 12,000 Hydro (8 stations), irrigation Most developed hydro catchment
Waimakariri ~120 3,210 Canterbury aquifer recharge Christchurch’s indirect water source
Rakaia ~210 2,850 Irrigation, aquifer recharge Braided river; gravel aquifer connection
Waiau (Canterbury) ~95 3,340 Hydro (small), irrigation Modified by Manapouri diversion
Grey ~280 3,870 Drainage West Coast
Wairau ~85 4,440 Irrigation, Blenheim water supply Marlborough

1.2 North Island

River Mean flow (m3/s) Catchment area (km2) Key uses Notes
Waikato ~330 14,260 Hydro (9 stations), municipal supply (Hamilton, Auckland supplement), irrigation, cooling NZ’s longest river (425 km); flows from Lake Taupo4
Whanganui ~220 7,380 Navigation, conservation Granted legal personhood 2017
Rangitikei ~75 4,020 Irrigation Manawatu-Whanganui region
Manawatu ~110 5,890 Palmerston North supply (partial), irrigation Flows through the Manawatu Gorge
Waihou ~40 1,560 Hauraki Plains drainage Waikato region
Mokau ~35 1,370 Minor uses Taranaki/Waikato border

1.3 Nuclear winter impacts on river flow

Nuclear winter cooling of 5–8 degrees C reduces evapotranspiration, which partially offsets reduced precipitation. Net river flow changes are difficult to predict with confidence. NIWA climate modelling for drought scenarios (not nuclear winter specifically, but analogous in some respects) suggests that eastern catchments — Canterbury Plains, Hawke’s Bay, Wairarapa — are most vulnerable to flow reductions because they are already precipitation-limited.5 West Coast rivers, fed by orographic rainfall, are likely to retain higher flows even under reduced precipitation.

The Waikato River’s flow from Lake Taupo is buffered by the lake’s enormous storage volume (approximately 60 km3), so short-term precipitation changes have limited immediate effect on Waikato flows. Canterbury’s braided rivers (Waimakariri, Rakaia, Rangitata) are snow-and-rain-fed; reduced snowpack under nuclear winter would shift seasonal flow patterns even if total annual flow is not greatly changed.6

Key uncertainty: The magnitude and spatial distribution of precipitation change under nuclear winter is one of the most consequential unknowns for NZ water management. Global climate models for nuclear winter scenarios show wide variation for the Southern Hemisphere mid-latitudes. NZ-specific downscaling has not been done.7

2. MAJOR LAKES

NZ has over 3,800 lakes larger than one hectare.8 The following covers the most significant for recovery planning.

Lake Volume (km3) Area (km2) Region Key uses
Taupo ~60 616 Waikato Waikato River headwaters; hydro regulation; fishery9
Te Anau ~35 344 Fiordland Manapouri hydro scheme supply; conservation
Wakatipu ~17 291 Otago Queenstown water supply; tourism
Wanaka ~17 193 Otago Conservation; Clutha headwaters
Manapouri ~14 142 Fiordland Manapouri power station tailrace; hydro storage10
Hawea ~8 141 Otago Hydro storage; Clutha headwaters
Pukaki ~1.8 80 Canterbury Waitaki hydro scheme storage
Tekapo ~0.8 87 Canterbury Waitaki hydro scheme storage
Rotorua ~0.8 80 Bay of Plenty Rotorua city setting; geothermal influence; water quality challenges11
Ellesmere/Te Waihora ~0.08 182 (variable) Canterbury Shallow; brackish; fishery; ecological significance

2.1 Hydroelectric storage function

Lakes Taupo, Pukaki, Tekapo, Hawea, and Manapouri serve as storage reservoirs for NZ’s two largest hydro schemes (Waikato and Waitaki). Their combined storage represents several months of hydro generation capacity, providing the buffer that allows NZ to manage seasonal and annual rainfall variation.12 Under nuclear winter, reduced inflows would draw down these reservoirs more quickly, potentially constraining hydro generation during extended dry periods. Reservoir level monitoring and generation scheduling become even more critical than under normal conditions.

2.2 Water quality

Most large South Island lakes are oligotrophic (nutrient-poor) with excellent water quality. Several North Island lakes, particularly Rotorua, Rotoiti, and others in the Rotorua Lakes district, have significant eutrophication problems due to geothermal inputs, agricultural runoff, and historical land use. Post-event, reduced fertiliser use (imported fertiliser supply ceases) may actually improve nutrient loading in these lakes over time, though the response would take years to manifest.13

3. GROUNDWATER AND AQUIFERS

NZ’s groundwater resources store an estimated 613 billion cubic metres, though much of this is deep and not readily accessible.14 The following aquifer systems are the most significant for municipal and agricultural water supply.

3.1 Canterbury Plains aquifer system

Location: Canterbury, South Island — from the foothills to the coast, underlying approximately 8,000 km2 of plains.

Characteristics: A multi-layered gravel aquifer system, up to 600 metres deep in places, fed primarily by river recharge from the Waimakariri, Rakaia, Ashburton, and Rangitata rivers. Shallow aquifers (upper 50 m) are unconfined; deeper layers are confined and artesian in many locations.15

Capacity and use: The Canterbury Plains aquifer is NZ’s most important groundwater resource. It provides Christchurch’s entire municipal water supply (approximately 130–170 million litres per day depending on season, from over 50 artesian wells), irrigation for an estimated 400,000–500,000 hectares of farmland, and rural domestic supply for the region.16 Groundwater abstraction has been increasing, and some areas show declining water levels, particularly in the Selwyn-Waihora catchment.

Water quality: Generally excellent. Deep artesian water requires no chemical treatment for drinking — it is naturally filtered through tens of metres of gravel. Shallow groundwater in some areas shows elevated nitrate from agricultural activity, though levels generally remain within drinking water standards.17

Post-event vulnerability: Reduced river flows under nuclear winter would reduce aquifer recharge rates. The Canterbury Plains aquifer has large storage, so the effect on water levels would be gradual — years rather than months. However, continued irrigation abstraction at current rates combined with reduced recharge could draw levels down. The cessation of large-scale dairy irrigation (likely under the scenario, given fuel and infrastructure constraints) would substantially reduce abstraction, partially offsetting reduced recharge.

3.2 Heretaunga Plains aquifer

Location: Hawke’s Bay, North Island — underlying the Heretaunga Plains from Taradale to Havelock North.

Characteristics: Gravel aquifer system recharged by the Ngaruroro River and rainfall. Both unconfined and confined layers. Total area approximately 300 km2.18

Capacity and use: Supplies Napier, Hastings, and Havelock North municipal water, plus horticultural and viticultural irrigation. The Havelock North contamination event of 2016 demonstrated the vulnerability of the unconfined aquifer zones to surface contamination — sheep faecal matter entered the bore supply following heavy rain.19

Post-event vulnerability: The contamination pathway demonstrated in 2016 is the primary concern. Without laboratory water quality testing (which depends on reagents and equipment that may become scarce), contamination events are harder to detect. Protective measures — fencing stock from recharge zones, monitoring bore head integrity — become critical.

3.3 Hauraki Plains and Waikato lowlands

Location: Waikato-Hauraki region, North Island.

Characteristics: Alluvial aquifer systems in the Hauraki Plains and lower Waikato. Shallower and less extensive than Canterbury.20

Capacity and use: Rural and small-town water supply, some irrigation. Not a major municipal supply source — Hamilton draws from the Waikato River.

Post-event vulnerability: Shallow aquifers are more susceptible to surface contamination and respond more quickly to recharge changes.

3.4 Other significant aquifers

  • Hutt Valley (Wellington): Confined gravel aquifer beneath the Hutt Valley floor. Supplies part of Wellington’s municipal water (via the Waterloo wellfield). High-quality artesian water. Seismically vulnerable — the Wellington Fault runs through the valley.21
  • Waimea Plains (Nelson): Small but locally critical aquifer serving the Nelson-Tasman region. Already under allocation pressure pre-event.
  • Waipa / Piarere (South Waikato): Volcanic aquifers in the Taupo Volcanic Zone. Generally good quality but some geothermal influence.

4. HYDROELECTRIC DAM CATCHMENTS

NZ’s hydro schemes depend on specific catchments for their water supply. These catchments are detailed in Doc #65 (Hydroelectric Station Maintenance). The following summary links water resources to generation capacity.

4.1 Waikato River chain

Source: Lake Taupo (616 km2, ~60 km3 storage). The Tongariro Power Scheme diverts additional water from the Tongariro, Moawhango, and other rivers into Lake Rotoaira and thence into Lake Taupo, augmenting the natural catchment.22

Stations (upstream to downstream): Aratiatia, Ohakuri, Atiamuri, Whakamaru, Maraetai, Waipapa, Arapuni, Karapiro. Total capacity ~1,050 MW (Mercury Energy). Plus Rangipo (~120 MW) and Tokaanu (~240 MW) in the Tongariro Power Scheme (Genesis Energy).

Total catchment area: ~14,260 km2 including Tongariro diversions.

Water resource implication: Lake Taupo’s enormous volume provides multi-year storage buffering. Even substantial flow reductions do not threaten hydro generation in the short term. However, Taupo is used as a regulating reservoir — its level is managed within a narrow legal range (1.4 m). Under emergency conditions, expanding the operating range by even 0.5 m releases significant additional stored energy.23

4.2 Waitaki River chain

Source: Lakes Tekapo, Pukaki, and Ohau, fed by snow and rain from the Southern Alps.

Stations: Tekapo A, Tekapo B, Ohau A, Ohau B, Ohau C, Benmore, Aviemore, Waitaki. Total capacity ~1,800 MW (primarily Meridian Energy).24

Total catchment area: ~12,000 km2.

Water resource implication: The Waitaki scheme depends on alpine precipitation, including snowmelt. Nuclear winter cooling of 5–8 degrees C would lower the freezing level by an estimated 800–1,200 m, increasing the proportion of precipitation falling as snow rather than rain at altitude.25 This would build snowpack during winter but delay spring melt, shifting the seasonal flow pattern — potentially compressing high flows into a shorter melt season while reducing summer base flows. The net effect on total annual inflows is uncertain. Lakes Pukaki and Tekapo provide substantial storage, but the Waitaki system has less total storage relative to its generation capacity than the Waikato system.

4.3 Manapouri-Te Anau

Source: Lake Manapouri (~14 km3), fed by the Waiau River and Fiordland rainfall.

Station: Manapouri Underground Power Station, ~800 MW (Meridian Energy). NZ’s largest single station. Tailrace discharges to Doubtful Sound / Patea via the West Arm tunnel.26

Total catchment area: ~4,000 km2, predominantly within Fiordland National Park.

Water resource implication: Fiordland receives some of NZ’s highest rainfall (6,000–8,000 mm/year at the main divide).27 Even a 30% reduction leaves this among the wettest places in the temperate world. Manapouri is the least drought-vulnerable of NZ’s major hydro schemes.

4.4 Clutha River

Source: Lakes Wanaka and Wakatipu, fed by Southern Alps precipitation.

Stations: Clyde Dam (~464 MW) and Roxburgh Dam (~320 MW), operated by Contact Energy.28

Total catchment area: ~20,580 km2 — NZ’s largest river catchment.

Water resource implication: The Clutha carries NZ’s highest mean flow (~614 m3/s). Lake Wanaka and Lake Wakatipu provide substantial natural storage. Additional hydro development on the Clutha has been studied but not pursued due to environmental and social concerns pre-event. Under recovery conditions, the energy value of additional Clutha hydro development would be weighed differently.

5. MUNICIPAL WATER SUPPLY SOURCES

The following table identifies the primary water source for each major NZ urban area. This information is critical for post-event water management planning — different source types have different vulnerabilities and treatment requirements (see Doc #48).

5.1 Major cities

City Population (approx) Primary source(s) Source type Treatment required Key vulnerability
Auckland 1,700,000 Hunua Ranges dams, Waitakere dams, Waikato River Surface water Full conventional Coagulant chemical supply (Doc #48)29
Wellington 415,000 Hutt River (Te Marua, Waterloo), Wainuiomata River, Hutt Valley bores Mixed surface/groundwater Full for surface; minimal for bores Seismic disruption to infrastructure; single pipeline crossings30
Christchurch 390,000 Canterbury Plains artesian wells (50+ bores) Groundwater (artesian) Minimal (UV + chlorine, added post-2018) Aquifer recharge reduction; seismic bore damage31
Hamilton 180,000 Waikato River Surface water Full conventional Water quality dependent on upstream land use
Tauranga 160,000 Bores and surface sources Mixed Varies by source Growing demand; allocation pressure
Dunedin 135,000 Deep Stream, Silverstream, Ross Creek reservoirs Surface water Full conventional Ageing infrastructure
Napier-Hastings 135,000 Heretaunga Plains aquifer Groundwater Minimal for confined aquifer Contamination of unconfined zones (2016 event)32
Palmerston North 90,000 Turitea dams (surface) and Manawatu bores Mixed Full for surface Dam catchment vulnerability
Nelson 55,000 Maitai and Roding rivers, supplementary bores Mixed Full for surface Limited reservoir storage
Invercargill 55,000 Oreti River Surface water Full conventional No alternative source readily available

5.2 Key observations

Most resilient cities: Christchurch and Napier-Hastings are best positioned for water supply continuity under import cutoff. Their groundwater sources require minimal treatment and are not dependent on imported chemicals. Christchurch in particular operated without any water treatment for decades before chlorination was introduced in 2018–2019 following the Havelock North inquiry recommendations.33

Most vulnerable cities: Auckland is the most treatment-dependent major city. Its 1.7 million residents rely entirely on surface water requiring full coagulation, filtration, and disinfection. Auckland should be the highest priority for domestic treatment chemical production and alternative treatment infrastructure (Doc #48).

Seismic vulnerability: Wellington faces unique risks from its seismic environment. The bulk water supply crosses the Hutt Valley fault zone, and the 2016 Kaikoura earthquake demonstrated how widespread damage to infrastructure can occur. Wellington’s water resilience plan includes emergency water supplies and cross-connections, but a major Wellington Fault rupture during the post-event period would compound an already difficult situation.34

6. WATER QUALITY RISKS POST-EVENT

6.1 Treatment chemical supply

NZ’s municipal water treatment depends on imported chemicals — primarily aluminium-based coagulants (polyaluminium chloride, aluminium sulphate), chlorine compounds (sodium hypochlorite, gaseous chlorine), and polymer flocculant aids. Under permanent import cutoff, these stocks deplete within months to roughly two years, depending on rationing and demand reduction.35 Doc #48 (Water Treatment Without Imports) addresses this challenge in detail, including domestic chlorine production from salt electrolysis — which itself requires a reliable salt supply, corrosion-resistant electrodes (graphite or titanium), DC power, and containment vessels capable of handling chlorine gas — slow sand filtration as a partial coagulation bypass, and source protection strategies. Slow sand filtration removes turbidity and pathogens effectively but cannot match conventional coagulation-filtration for high-turbidity source water; Auckland’s dam-fed supplies after storm events, for example, may exceed slow sand filtration’s practical turbidity limits without pre-settlement.36

6.2 Infrastructure maintenance

Water treatment plants, pump stations, and distribution networks require ongoing maintenance — valve replacements, pipe repairs, instrument calibration, pump overhauls. Key imported dependencies include: pump impellers and seals (typically stainless steel or specialist polymers); SCADA control electronics and sensors; PVC and polyethylene pipe fittings; chlorine dosing equipment membranes; and UV disinfection lamps. The immediate risk is not catastrophic failure but gradual degradation: increasing leakage, declining instrument accuracy, pump efficiency losses, and eventually component failures that cannot be repaired with available materials. Water loss through pipe leakage (already approximately 10–20% nationally pre-event, varying by network age) would likely increase as repair capability diminishes.37

6.3 Agricultural contamination

Reduced fertiliser use (imported supply ceases) would gradually reduce nitrate and phosphorus loading in waterways and groundwater — a net positive for water quality, though groundwater nitrate levels respond slowly (years to decades, depending on aquifer turnover time).38 However, the transition period may see localised contamination as agricultural practices change: more animal waste relative to synthetic fertiliser, changes to stock management, potentially less effective effluent treatment from dairy farms if equipment fails.

6.4 Wastewater treatment degradation

If wastewater treatment plants lose capability (due to chemical supply, equipment failure, or workforce loss), contamination of downstream drinking water sources follows. This is the single largest water quality risk — a failure in wastewater treatment can render a functional drinking water supply unsafe, as demonstrated by numerous historical examples of waterborne disease outbreaks traced to sewage contamination of drinking water sources.39 See Doc #48, Section 8.

7. NUCLEAR WINTER IMPACTS ON PRECIPITATION AND WATER AVAILABILITY

7.1 Precipitation changes

Nuclear winter models project global precipitation reductions of 10–30%, driven by reduced ocean evaporation under cooler temperatures and altered atmospheric circulation.40 NZ’s position in the Southern Hemisphere mid-latitudes offers some protection — the Southern Hemisphere is less affected than the Northern — but the signal is still expected to be significant.

Regional variation within NZ:

  • West Coast (both islands): Orographic rainfall from prevailing westerlies may decline less than the national average, as the mechanism (moist air forced over mountains) is partially independent of sea surface temperature.
  • Eastern regions (Canterbury, Hawke’s Bay, Wairarapa): Already in rain shadow; proportional reductions here have larger practical impact because baseline rainfall is lower.
  • Northern North Island: Subtropical moisture sources may be more affected by ocean cooling, potentially reducing summer rainfall.

7.2 Snowpack and glacier changes

Nuclear winter cooling would increase snowfall at altitude relative to rain, potentially building snowpack. This shifts seasonal river flow patterns — less summer melt if spring temperatures remain depressed, larger spring melt if cooling eases seasonally. Canterbury’s braided rivers and the Waitaki hydro scheme are most affected by this shift.41

7.3 Net water budget

NZ’s total freshwater throughput (precipitation minus evapotranspiration) would decline under nuclear winter, but the reduction is moderated by reduced evapotranspiration at lower temperatures. The honest assessment: NZ is unlikely to face an absolute water shortage under plausible nuclear winter scenarios, given its high per-capita freshwater endowment and predominantly renewable water sources.42 The risk is regional and seasonal — eastern drought-prone areas in dry summers — not national water scarcity. This is a significant advantage relative to continental nations at higher latitudes, though confidence in this assessment is limited by the absence of NZ-specific nuclear winter precipitation modelling.43

8. DATA SOURCES AND VERIFICATION

This atlas draws on data from the following sources. Where NZ-specific modelling or verification is unavailable, this is noted.

  • NIWA (National Institute of Water and Atmospheric Research): National Hydrological Database, National Climate Database, river flow monitoring, lake level monitoring. NIWA is the primary custodian of NZ hydrological data.44
  • Regional councils: Each of NZ’s 16 regional and unitary councils maintains water resource monitoring networks, allocation databases, and environmental reporting. Canterbury (Environment Canterbury) and Hawke’s Bay (HBRC) have the most extensive groundwater monitoring programmes.
  • Taumata Arowai: NZ’s dedicated water services regulator (established 2021). Maintains the register of drinking water supplies and water quality compliance data.45
  • Watercare, Wellington Water, Christchurch City Council: Operational data for the three largest municipal water suppliers.
  • GNS Science: Geological and groundwater mapping, aquifer characterisation, geothermal water resources.46
  • MBIE / Electricity Authority: Hydro generation data, reservoir levels, generation capacity.

Critical gap: None of these datasets has been compiled into a single printed hydrological reference for NZ. The data exists across dozens of databases, reports, and web portals. This document is a first-order compilation. A full Water Resources Atlas, with detailed maps, tables, and per-catchment data sheets, would be a substantially larger document — estimated 200–400 pages — and should be commissioned from NIWA if the organisation remains functional. The present document provides the strategic overview; the detailed atlas provides the operational data.

CRITICAL UNCERTAINTIES

  1. Nuclear winter precipitation impact on NZ. Global models give wide ranges. NZ-specific downscaling has not been performed. Regional variation within NZ could be large. This is the single most important unknown for water resource planning.

  2. Canterbury aquifer recharge under changed conditions. The balance between reduced river recharge and reduced irrigation abstraction determines whether aquifer levels rise or fall. This depends on agricultural decisions as much as climate.

  3. Seismic events during the recovery period. NZ’s seismicity does not change post-event. A major earthquake (Alpine Fault, Wellington Fault, Hikurangi subduction zone) during recovery could severely disrupt water infrastructure. This is a contingency, not the baseline scenario, but it is a real and significant risk.

  4. Water quality monitoring capability. Laboratory testing of water quality requires reagents, instruments, and trained analysts. As reagent stocks deplete and instruments fail, the ability to detect contamination before it causes illness declines. Robust source protection becomes even more important when monitoring capability is limited.

  5. Flow measurement data currency. River flow and aquifer level data cited here are based on pre-event measurements and long-term averages. Actual conditions post-event will diverge, and the monitoring networks that would detect this divergence may be partially degraded.

CROSS-REFERENCES

  • Doc #48 — Water Treatment Without Imports: The companion document to this atlas. Addresses how to maintain safe drinking water as treatment chemical supplies deplete. Should be read alongside this document.
  • Doc #65 — Hydroelectric Station Maintenance: Dam catchment management and reservoir operations. Water resources and hydro generation are interdependent.
  • Doc #67 — National Grid: Transpower Operations: Water treatment plants and pump stations depend on grid electricity. Grid reliability is a prerequisite for municipal water supply.
  • Doc #8 — National Asset and Skills Census: Should establish actual chemical stocks, infrastructure condition, and workforce data that this document can only estimate.
  • Doc #74 — Pastoral Farming Under Nuclear Winter: Agricultural water demand and land use directly affect water resource availability and quality.
  • Doc #18 — NZ Climate Baseline Data: Provides the pre-event precipitation, temperature, and weather baselines against which post-event changes are measured.

APPENDIX A: QUICK-REFERENCE FLOW TABLE

Top 10 NZ rivers by mean flow (approximate)

Rank River Island Mean flow (m3/s)
1 Clutha/Mata-Au South ~614
2 Buller South ~490
3 Waitaki South ~370
4 Waikato North ~330
5 Grey South ~280
6 Whanganui North ~220
7 Rakaia South ~210
8 Waimakariri South ~120
9 Manawatu North ~110
10 Waiau (Canterbury) South ~95

APPENDIX B: MUNICIPAL WATER SOURCE TYPE SUMMARY

Source type Major cities served Post-event resilience Key action
Deep artesian groundwater Christchurch, Napier-Hastings High — minimal treatment needed Protect recharge zones; monitor bore integrity
Mixed surface/groundwater Wellington, Tauranga, Palmerston North Moderate — prioritise groundwater sources Develop groundwater capacity; build slow sand filtration for surface
Surface water only Auckland, Hamilton, Dunedin, Invercargill Lower — depends on treatment chemical replacement Domestic chlorine production; slow sand filtration (lower throughput than conventional treatment; limited effectiveness with high-turbidity source water) (Doc #48)

  1. Ministry for the Environment, “Environment New Zealand 2007” and subsequent updates. NZ’s per-capita freshwater availability is among the highest in the OECD. The 500 billion m3 figure includes all surface water and accessible groundwater; exact figures vary by methodology. https://environment.govt.nz/↩︎

  2. NIWA, “New Zealand Freshwater Fish Database” and hydrological datasets. The total length of rivers and streams is an estimate from GIS analysis of NZ’s river network. https://niwa.co.nz/freshwater↩︎

  3. NIWA National Hydrological Database. Clutha mean flow at Balclutha approximately 614 m3/s. Flow data from long-term gauging stations. Individual river flow figures should be verified against current NIWA records as they represent long-term means and recent years may differ. https://niwa.co.nz/information-services/nz-hydrometric-ne...↩︎

  4. Waikato Regional Council, “Waikato River Catchment.” The Waikato River is 425 km long, NZ’s longest. Mean flow at the mouth is approximately 330 m3/s. The river is heavily modified by nine hydro dams, the Tongariro Power Scheme diversion, and municipal/industrial abstractions. https://www.waikatoregion.govt.nz/↩︎

  5. NIWA, “Climate Change Projections for New Zealand” (various publications). While nuclear winter differs fundamentally from climate change, NIWA’s drought vulnerability mapping identifies eastern regions as most drought-susceptible under reduced precipitation scenarios. https://niwa.co.nz/our-science/climate↩︎

  6. Precipitation phase (rain vs. snow) under nuclear winter cooling is uncertain. Standard atmospheric lapse rate assumptions suggest the freezing level would drop by approximately 800–1,200 m under 5–8 degrees C cooling, significantly increasing the proportion of catchment area receiving snow rather than rain. The seasonal melt dynamics under these conditions have not been modelled for NZ alpine catchments.↩︎

  7. Robock, A. et al., “Nuclear winter revisited with a modern climate model and current nuclear arsenals,” Journal of Geophysical Research, 2007. Global precipitation reductions of 10–45% depending on scenario. Southern Hemisphere impacts are smaller than Northern but still significant. NZ-specific downscaling has not been published. The 10–30% range used in this document reflects the lower end of global estimates, appropriate for NZ’s Southern Hemisphere position.↩︎

  8. Verburg, P. et al., “Lakes in New Zealand,” in Endinger, S. et al. (eds), “The Lakes Handbook,” 2nd edition. NZ has approximately 3,820 lakes larger than 1 hectare, with a combined area of approximately 4,100 km2. Many are small and remote.↩︎

  9. Waikato Regional Council and Environment Court. Lake Taupo’s operating range is controlled by resource consent conditions. The lake’s surface area is approximately 616 km2, so each 1 cm of level change represents approximately 6.16 million m3 of water. The 1.4 m consented range represents approximately 860 million m3 of controllable storage.↩︎

  10. Meridian Energy, Manapouri Power Station. Lake Manapouri is maintained within strict environmental limits (the “Save Manapouri” campaign of 1969–73 is one of NZ’s foundational environmental moments). Under emergency conditions, operating limits may be reconsidered. https://www.meridianenergy.co.nz/↩︎

  11. Bay of Plenty Regional Council, “Rotorua Lakes.” Lake Rotorua has significant nutrient enrichment from both geothermal inputs and land-use-derived nutrients. Historical water quality has declined. Intervention measures (alum dosing, land use change, sewage diversion) have been implemented with partial success. Post-event, cessation of alum dosing would be offset by reduced fertiliser inputs — the net trajectory is uncertain. https://www.boprc.govt.nz/↩︎

  12. Electricity Authority, Electricity Market Information (EMI). Hydro storage data is reported weekly. Combined controlled storage across all major hydro lakes is approximately 4,000–5,000 GWh equivalent under normal operating ranges. https://www.emi.ea.govt.nz/↩︎

  13. Bay of Plenty Regional Council, “Rotorua Lakes.” Lake Rotorua has significant nutrient enrichment from both geothermal inputs and land-use-derived nutrients. Historical water quality has declined. Intervention measures (alum dosing, land use change, sewage diversion) have been implemented with partial success. Post-event, cessation of alum dosing would be offset by reduced fertiliser inputs — the net trajectory is uncertain. https://www.boprc.govt.nz/↩︎

  14. GNS Science, “Groundwater Resources of New Zealand.” The 613 billion m3 estimate is from White, P.A. et al., “Groundwater in New Zealand,” chapter in Rosen, M.R. and White, P.A. (eds), “Groundwaters of New Zealand,” NZ Hydrological Society, 2001. This figure includes all stored groundwater; the fraction that is practically abstractable is much smaller.↩︎

  15. Environment Canterbury, “Canterbury Water Management Strategy” and associated groundwater reports. Canterbury Plains groundwater characterisation is among the most detailed in NZ due to the region’s dependence on the resource. https://www.ecan.govt.nz/↩︎

  16. Environment Canterbury. Christchurch water supply data from Christchurch City Council. The 150 million litres/day figure is approximate average demand. Selwyn-Waihora groundwater level decline is documented in ECan monitoring reports and has been a significant resource management issue.↩︎

  17. Environment Canterbury, “Canterbury Water Management Strategy” and associated groundwater reports. Canterbury Plains groundwater characterisation is among the most detailed in NZ due to the region’s dependence on the resource. https://www.ecan.govt.nz/↩︎

  18. Hawke’s Bay Regional Council, “Heretaunga Plains Aquifer System.” Multiple technical reports characterise the aquifer system. https://www.hbrc.govt.nz/↩︎

  19. Government Inquiry into Havelock North Drinking Water, “Report Stage 1,” May 2017. Contamination of Havelock North’s drinking water bore supply caused an estimated 5,500 illnesses, 45 hospitalisations, and 3–4 deaths. The inquiry found that sheep faecal matter entered the aquifer through a poorly protected recharge zone following heavy rain. https://www.dia.govt.nz/Government-Inquiry-into-Havelock-...↩︎

  20. Waikato Regional Council, groundwater monitoring data. Hauraki Plains aquifer systems are less comprehensively characterised than Canterbury’s. Data availability is a limitation for this region.↩︎

  21. Greater Wellington Regional Council, “Wellington Region Water Supply.” Wellington’s bulk water supply system crosses multiple fault zones. The Waterloo wellfield in the Hutt Valley draws from a confined gravel aquifer beneath the valley floor. The Wellington Fault passes through the Hutt Valley. Seismic resilience is a longstanding concern. https://www.gw.govt.nz/↩︎

  22. Genesis Energy, Tongariro Power Scheme. The scheme diverts water from catchments that would naturally flow to the Whanganui River, redirecting it to the Waikato system via Lake Taupo. This is both an energy and a water resource management issue — the diversion augments Waikato flows at the expense of Whanganui flows.↩︎

  23. Waikato Regional Council and Environment Court. Lake Taupo’s operating range is controlled by resource consent conditions. The lake’s surface area is approximately 616 km2, so each 1 cm of level change represents approximately 6.16 million m3 of water. The 1.4 m consented range represents approximately 860 million m3 of controllable storage.↩︎

  24. Meridian Energy, Waitaki Hydro Scheme. Capacity figures are approximate and reflect current installed capacity. Some stations have been upgraded from original specifications. https://www.meridianenergy.co.nz/↩︎

  25. Precipitation phase (rain vs. snow) under nuclear winter cooling is uncertain. Standard atmospheric lapse rate assumptions suggest the freezing level would drop by approximately 800–1,200 m under 5–8 degrees C cooling, significantly increasing the proportion of catchment area receiving snow rather than rain. The seasonal melt dynamics under these conditions have not been modelled for NZ alpine catchments.↩︎

  26. Meridian Energy, Manapouri Power Station. Lake Manapouri is maintained within strict environmental limits (the “Save Manapouri” campaign of 1969–73 is one of NZ’s foundational environmental moments). Under emergency conditions, operating limits may be reconsidered. https://www.meridianenergy.co.nz/↩︎

  27. NIWA, climate data for Fiordland. Annual rainfall on the western slopes of the main divide reaches 6,000–12,000 mm in some locations. The Milford Sound area averages approximately 6,800 mm/year. Even under substantial reduction, this remains extremely wet by global standards.↩︎

  28. NIWA National Hydrological Database. Clutha mean flow at Balclutha approximately 614 m3/s. Flow data from long-term gauging stations. Individual river flow figures should be verified against current NIWA records as they represent long-term means and recent years may differ. https://niwa.co.nz/information-services/nz-hydrometric-ne...↩︎

  29. Watercare Services Ltd, “Auckland Water Supply.” Auckland’s system includes the Hunua Ranges dams (Mangatangi, Upper Mangatawhiri, Cosseys, Hays Creek, Wairoa), the Waitakere Ranges dams (Upper Huia, Lower Huia, Upper Nihotupu, Lower Nihotupu), and the Waikato River intake at Tuakau. https://www.watercare.co.nz/↩︎

  30. Greater Wellington Regional Council, “Wellington Region Water Supply.” Wellington’s bulk water supply system crosses multiple fault zones. The Waterloo wellfield in the Hutt Valley draws from a confined gravel aquifer beneath the valley floor. The Wellington Fault passes through the Hutt Valley. Seismic resilience is a longstanding concern. https://www.gw.govt.nz/↩︎

  31. Environment Canterbury, “Canterbury Water Management Strategy” and associated groundwater reports. Canterbury Plains groundwater characterisation is among the most detailed in NZ due to the region’s dependence on the resource. https://www.ecan.govt.nz/↩︎

  32. Government Inquiry into Havelock North Drinking Water, “Report Stage 1,” May 2017. Contamination of Havelock North’s drinking water bore supply caused an estimated 5,500 illnesses, 45 hospitalisations, and 3–4 deaths. The inquiry found that sheep faecal matter entered the aquifer through a poorly protected recharge zone following heavy rain. https://www.dia.govt.nz/Government-Inquiry-into-Havelock-...↩︎

  33. Christchurch City Council introduced chlorination to its water supply in stages during 2018–2019 following the recommendations of the Government Inquiry into Havelock North Drinking Water. Prior to this, Christchurch’s artesian water supply was distributed without chemical disinfection, relying on the natural filtration properties of the Canterbury Plains aquifer system. https://www.ccc.govt.nz/↩︎

  34. Greater Wellington Regional Council, “Wellington Region Water Supply.” Wellington’s bulk water supply system crosses multiple fault zones. The Waterloo wellfield in the Hutt Valley draws from a confined gravel aquifer beneath the valley floor. The Wellington Fault passes through the Hutt Valley. Seismic resilience is a longstanding concern. https://www.gw.govt.nz/↩︎

  35. Depletion timelines depend on pre-event stockholding, demand reduction measures, and whether alternative sources (e.g., domestic chlorine production) come online before stocks are exhausted. The “months to roughly two years” range reflects variation across chemical types: gaseous chlorine stocks at major plants may last 6–12 months; coagulant stocks (larger volumes held) may extend to 18–24 months under rationed use. Figures require verification via the skills census (Doc #8) against actual stockholding data from Watercare, Wellington Water, and other operators.↩︎

  36. Slow sand filtration is effective for source water with turbidity below approximately 10–50 NTU (nephelometric turbidity units); above this range, the biological layer clogs rapidly and flow rates drop to impractical levels. Conventional coagulation-filtration handles turbidity of hundreds of NTU. Auckland’s dam sources can spike well above 50 NTU after heavy rain. Pre-settlement (holding water in tanks to allow solids to settle before slow sand filtration) partially mitigates this but requires additional infrastructure and residence time. See Doc #48 for detailed treatment alternatives.↩︎

  37. Water New Zealand and Taumata Arowai. Reported non-revenue water (leakage plus metering losses) varies by network. National average is approximately 10–20% depending on the metric and network age. Older networks (e.g., Wellington) have higher losses.↩︎

  38. Groundwater nitrate response times depend on aquifer residence time and the depth of the contamination. Canterbury’s shallow unconfined aquifers may show improvement within 5–10 years of reduced nitrogen inputs; deeper confined aquifers may take decades. See Morgenstern, U. and Daughney, C.J., “Groundwater age, time trends in water chemistry, and future nutrient load in lakes,” Journal of Hydrology (NZ), 2012.↩︎

  39. The relationship between wastewater treatment failure and downstream drinking water contamination is well established in public health literature. NZ’s own Havelock North event (2016) demonstrated a related pathway; globally, the Walkerton, Ontario outbreak (2000) — where E. coli and Campylobacter from agricultural runoff entered a drinking water supply, causing 7 deaths and 2,300 illnesses — illustrates the consequences at scale. WHO, “Guidelines for Drinking-water Quality,” 4th edition, 2011.↩︎

  40. Robock, A. et al., “Nuclear winter revisited with a modern climate model and current nuclear arsenals,” Journal of Geophysical Research, 2007. Global precipitation reductions of 10–45% depending on scenario. Southern Hemisphere impacts are smaller than Northern but still significant. NZ-specific downscaling has not been published. The 10–30% range used in this document reflects the lower end of global estimates, appropriate for NZ’s Southern Hemisphere position.↩︎

  41. Precipitation phase (rain vs. snow) under nuclear winter cooling is uncertain. Standard atmospheric lapse rate assumptions suggest the freezing level would drop by approximately 800–1,200 m under 5–8 degrees C cooling, significantly increasing the proportion of catchment area receiving snow rather than rain. The seasonal melt dynamics under these conditions have not been modelled for NZ alpine catchments.↩︎

  42. Ministry for the Environment, “Environment New Zealand 2007” and subsequent updates. NZ’s per-capita freshwater availability is among the highest in the OECD. The 500 billion m3 figure includes all surface water and accessible groundwater; exact figures vary by methodology. https://environment.govt.nz/↩︎

  43. Robock, A. et al., “Nuclear winter revisited with a modern climate model and current nuclear arsenals,” Journal of Geophysical Research, 2007. Global precipitation reductions of 10–45% depending on scenario. Southern Hemisphere impacts are smaller than Northern but still significant. NZ-specific downscaling has not been published. The 10–30% range used in this document reflects the lower end of global estimates, appropriate for NZ’s Southern Hemisphere position.↩︎

  44. NIWA operates approximately 300 river flow monitoring stations and manages the National Hydrological Database and National Climate Database. These datasets are the authoritative source for NZ hydrological information. https://niwa.co.nz/↩︎

  45. Taumata Arowai. NZ’s dedicated drinking water regulator, established under the Water Services Act 2021. Maintains the register of drinking water suppliers and compliance records. https://www.taumataarowai.govt.nz/↩︎

  46. GNS Science, “Groundwater Resources of New Zealand.” The 613 billion m3 estimate is from White, P.A. et al., “Groundwater in New Zealand,” chapter in Rosen, M.R. and White, P.A. (eds), “Groundwaters of New Zealand,” NZ Hydrological Society, 2001. This figure includes all stored groundwater; the fraction that is practically abstractable is much smaller.↩︎

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