4 Creating a Water Supply and Demand Profile

4.1 Summary of land use profile by region

4.1.1 Profile by region

The following series of tables provide a regional breakdown of the landuse by sector and the extent of irrigation in each region/sector to provide a landuse profile.




4.2 Summary of existing water usage by region

The Canterbury and Otago regions dominate (in terms of land area under irrigation) accounting for an estimated 81% of the irrigated land in New Zealand in the year 2000. For presentation purposes these two regions have been separated from the remaining regions in the following two charts.

Figure 25

Dairy and the 'other pasture category are the leading uses for irrigation in Canterbury and Otago, while in the remaining regions, horticulture features more prominently.

Figure 26

Existing water use has been summarised in the report prepared for the Ministry of the Environment by Lincoln Ventures Ltd. (2000). MAF have also provided estimates of hectares irrigated by sector.

Figure 27: Regional breakdown of area in Land Use Class (LUC) I-III

Region

LUC I-III (km2)

ha

ha irrigated

percentage

Auckland

753

75300

6833

9%

Waikato

3486

348600

0%

Bay of Plenty

1051

105100

9435

9%

Gisborne

559

55900

0%

Manawatu-Wanganui

2417

241700

0%

Hawkes Bay

1497

149700

23242

16%

Taranaki

1591

159100

0%

Northland

819

81900

0%

Wellington

670

67000

9273

14%

Otago

3433

343300

84593

25%

Southland

4396

439600

0%

Tasman

502

50200

11737

23%

Marlborough

658

65800

19415

30%

Westland

195

19500

0%

Canterbury

6931

693100

400091

58%

Total

28958

2895800

564619

19%

Note: LUC I-III = Land use class 1-3 as defined by Landcare

4.3 Development of a demand profile for land use by region.

4.3.1 Water demand by land use type

The demand for irrigation is driven by the combination of

  • Contour and soil type
  • Climate and Evapotranspiration (a factor of solar energy, crop cover and wind)
  • Profitability of the land use

This demand is offset against the availability and cost of water and the irrigation investment required. As the potential evapotranspiration increases and the rainfall and soil moisture holding capacity of the soils decrease, the greater will be the economic response from applying water in addition to rainfall. Analysis of land suitable for irrigation must consider not only the contour, and soil moisture deficit factors but also the soil water holding capacity and how these three factors interrelate. In identifying the potential demand we have considered these factors, with a summary as follows:

4.3.2 Contour

The Land Use Capability Mapping system has been used to identify all relatively flat land (slopes less than 3 degrees) where there is no significant plant growth limitation caused from poor drainage characteristics. Soils that maybe relatively flat but which are so stony that they are not considered suitable for agriculture are not included. There are soils that fall outside this criterion that are irrigated, such as some peat soils and some soils that are steeper than 3 degrees, but these are relatively small areas.

Regional soils deemed physically suitable for irrigation by region are as follows:

Figure 28: Regional breakdown of soils suitable for irrigation

 

Region

LUC I-III (km2)1

ha

ha irrigated2

percentage irrigated

Northland

819

81900

4000

5%

Auckland

753

75300

6833

9%

Waikato

3486

348600

4500

1%

Bay of Plenty

1051

105100

9435

9%

Gisborne

559

55900

5000

9%

Hawkes Bay

1497

149700

23242

16%

Taranaki

1591

159100

2000

1%

Manawatu-Wanganui

2417

241700

8000

3%

Wellington

670

67000

9273

14%

Tasman

502

50200

11737

23%

Marlborough

658

65800

19415

30%

Westland

195

19500

0%

Canterbury

6931

693100

400091

58%

Otago

3433

343300

84593

25%

Southland

4396

439600

1500

0%

Total

20310

2031000

499526

25%

    1. Land use capability classes one to three
    2 The areas irrigated are taken from Information on water allocation in New Zealand 2000


4.3.3 Soil Type

Soils have been assessed for their available water holding capacity (this is deemed to be the water held between soil moisture tension levels of 5 kPa and 1500 kPa). The monthly deficits have been calculated. The approach is in line with that used by Landcare et al in "Crop water requirements for irrigation in the Waikato region".

Figure 29: Areas in ha by regions by water holding class

AW Class mm

200

125

87.5

62.5

37.5

12.5

Area ha

S_value

Value-1

Value-2

Value-3

Value-4

Value-5

Value-6

total

less than 37.5mm AWC

Northland

5800

32900

17300

0

25900

0

81900

25900

32%

Auckland

5500

14800

26800

0

20200

0

67300

20200

30%

Waikato

87800

140600

12900

17600

84600

5100

348600

89700

26%

Bay of Plenty

6000

46200

19600

0

29400

0

101200

29400

29%

Gisborne

2000

15500

37700

100

0

500

55800

500

1%

Hawkes Bay

18500

38300

46600

0

41500

4700

149600

46200

31%

Taranaki

800

138700

17700

0

0

1900

159100

1900

1%

Manawatu

83800

25300

126800

0

4200

1600

241700

5800

2%

Wellington

31300

3300

28600

0

500

3300

67000

3800

6%

Tasman

7100

24200

15700

3200

0

50200

0

0%

Marlborough

2800

29400

3500

11500

0

47200

0

0%

Westland

3600

15100

800

0

0

19500

0

0%

Canterbury

114700

87500

369500

121400

0

693100

0

0%

Otago

14500

12000

108300

206700

1800

343300

1800

1%

Southland

48700

1800

272800

116300

0

439600

0

0%

Note. The soils do not always tally with the totals as some soil groups in some regions have not been classified.

Figure 29 illustrates the problem faced with averaging data. The northern regions of Northland, Auckland, Waikato, Bay of Plenty and Hawkes Bay have about 1/3 of their irrigable soils with very low water holding capacities. This means that these soils will show evidence of moisture stress if they go for a week without rain in the summer months. By contrast almost none of the South Island soils fit this category.

The regions with a significant proportion (say more than 5 percent) of their soils in the low water holding capacity class, would potentially benefit from irrigation despite relatively low soil moisture deficit figures (due to reliable rainfall) . In this category would fall. Northland, Auckland, Waikato/King Country, Bay of Plenty, Hawkes Bay and Wellington. However, when all other factors are taken into consideration, irrigation becomes less practical for some regions.

The following table summarises the suitability of the six key regions to irrigation taking into consideration contour, soil type and climate.

Figure 30: Summary of key regions contour, soil and climate characteristics

4.3.4 Climate and Evapotranspiration

Having established the land area suitable for irrigation we have then used climate data to determine the mean monthly potential evapotranspiration, using the Priestly-Taylor method, and have applied an approximation of a 1 in 10 year low monthly rainfall to the regional soils.

Potential Evapotranspiration (Eto)

Potential evapotranspiration has been determined from the Landcare Climate Surfaces for New Zealand model for both mean and 10 percentile. This assumes a ground cover of pasture growing with water being non-limiting and deemed to have a crop factor equal to 1.0.

Actual Evapotranspiration (Eta)

As soils dry then the actual evapotranspiration reduces as the plants expend more energy to extract water from the soil. While irrigation systems are designed to replenish this soil moisture before the plants become significantly stressed, there is nonetheless a slowing down of evapotranspiration, even with irrigation. The table showing the average and "minus 1 standard deviation rainfall" deficits are derived for pasture and use the derived Eta.

4.3.5 Crop factor Kc

Different crops will use water at different rates depending on their stage of maturity and the percentage ground cover. The derivation of crop factors is an inexact science and little New Zealand work has been done on this subject. The following table was used by Landcare in the Waikato study and an estimate has been incorporated for grapes. Work at Marlborough and Hawkes Bay indicate that these figures are unlikely to understate the crop factor. It should be noted that the recent research work carried out by HortResearch on grapes was not designed to measure the crop factor, but to investigate the impact of soil moisture stress levels on grape production and wine quality.

The following table provides the Crop Coefficients (Kc) for various landuse types.

Figure 31: Crop demand relativity

Grass

Potatoes

Apples

Grapes

Squash

Vegetables

Spring

Summer

Autumn

Winter

January

1

0.9

0.8

0.9

0.4

February

1

0.9

0.8

0.9

0.7

March

1

0.9

0.7

0.6

0.8

April

1

0.7

0.5

0.4

0.4

May

1

June

1

July

1

August

1

September

1

1

0.5

0.9

October

1

1

0.6

0.7

0.4

0.5

November

1

1

0.7

0.8

0.8

December

1

0.7

0.9

0.8

0.6

0.8

Bare ground is normally regarded as 0.35 and all blank cells can be given this value. By way of explanation of table 3, where the grass demand factor is 1, the demand from apples in January is 0.9 or 90% that of grass.

Impact of crop type

The crop type being irrigated does reflect on the likely water requirements. In most cases pasture requires more water in any season than process crops, orchard trees and vines, although a crop with a very dense canopy could have a higher transpiration rate than pasture for a period of its growth. Generally cereal crops are regarded as having a similar rate of transpiration to spring sown crops. Grapes are often managed to stress the plants by maintaining lower levels of available soil moisture. This combined with various row spacings and inter-row cultural practices makes viticultural usage quite variable but typically a crop factor of .75 is common.

It should be noted that surveys of cereal crop water usage in Canterbury over the last five years show that some areas are having water applied at rates well in excess of the demand predictions used here.

In the overall scope of this report, the viticulture industry is very small and the reduced crop factor is making an insignificant impact on the total demand for water, although the impact is clearly important in Marlborough and Hawkes Bay where water is limited in supply and the viticulture sector is a significant user of water at local level.

In Canterbury the cereal crop industry is a big user of water and traditional levels of irrigation appear to be close to those used for pasture. The trend toward increased dairying at the expense of cropping in this region, means that the use of a pasture based irrigation requirement will not create significant demand anomalies.

Irrigation demand is a function of soil moisture deficit levels and the profitability of the potential agricultural activity resulting from irrigation compared with no irrigation. Irrigation does have an absolute ceiling that is fixed by the reliability and availability of water.

In Hawkes Bay there are changes taking place in landuse due to the availability of irrigation water in some areas. This is enabling land use to change from extensive agriculture to more intensive land use such as dairying and viticulture, but availability of water is becoming the limiting factor. While the profitability of these options is higher, the margins have not been sufficient to cover the costs of major community water supply schemes like those in Canterbury and Otago. As a result irrigation has been associated with proximity to reliable surface and underground supplies being accessed by individual operators.

May to August is not a period where irrigation is normally undertaken because deficits are minimal and there is usually no shortage of supply. These months can be ignored for the purpose of this analysis. This does not mean that irrigation is not carried out, but it is normally associated with "watering in" of young vegetable and nursery plants.

For most irrigation, the usual basis for assessment is to allow for the available waterholding capacity (AWC) to be replenished when it drops to 60% and not to allow moisture levels to be depleted below 50% for more than 10% of the time. For a given set of climatic conditions this means that soils with lower than average AWC will require more frequent irrigation and greater volumes of water in any given season.

The AWC is a function of the soil type, the plant rooting depth and the percentage of stone in the soil.

Actual evapotranspiration rates decrease as the soil water content diminishes. This has been incorporated in the deficit assessments in the accompanying tables. Most irrigation is designed to keep soil water content above 50% of AWC so the implication is that designers of irrigation systems will generally use an unadjusted transpiration rate which will give rise to a slightly higher deficit figure than shown here.

Average monthly rainfall deficits of non-irrigated soils based on varying profile using readily available water estimates from the Land Resource Inventory (LRI) extended legends have been included in the following table.

Figure 32: Monthly soil moisture deficit by region (mm)

Region

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Total

Northland

19.5

8.8

6.5

2.8

0.9

0.5

0.5

1.0

2.0

3.9

9.1

12.9

68.4

Auckland

22.3

14.2

7.8

2.7

1.2

0.4

0.4

1.0

2.6

5.5

8.7

13.1

79.9

Waikato

15.6

10.3

6.0

2.3

0.9

0.3

0.3

0.8

2.0

4.0

7.3

10.5

60.4

BOP

14.5

8.4

5.2

2.4

0.9

0.4

0.4

0.8

1.8

4.1

8.7

10.5

58.1

Gisborne

16.5

10.2

5.2

1.6

0.6

0.3

0.3

0.6

1.6

3.9

10.5

13.6

65.0

Hawkes Bay

22.7

17.7

9.5

2.8

1.1

0.5

0.5

1.0

2.8

7.3

16.6

18.9

101.2

Taranaki

11.6

7.3

4.2

1.4

0.5

0.2

0.2

0.5

1.1

2.4

4.3

7.5

41.2

Manawatu

15.3

12.1

7.0

2.0

0.6

0.3

0.3

0.6

1.6

4.0

8.0

11.1

63.0

Wellington

13.9

10.8

5.8

1.7

0.5

0.2

0.2

0.5

1.3

2.9

5.7

9.5

53.0

Tasman

17.4

13.4

6.1

1.4

0.5

0.3

0.2

0.4

1.5

3.0

5.8

9.4

59.5

Marlborough

24.5

21.3

11.7

3.1

0.7

0.3

0.2

0.6

1.8

4.9

10.0

18.3

97.3

Westland

6.2

4.3

2.1

0.6

0.2

0.1

0.1

0.3

0.6

1.2

1.8

4.1

21.5

Canterbury

22.6

21.0

10.1

2.5

0.6

0.3

0.2

0.7

2.2

6.5

12.7

20.7

100.0

Otago

21.4

19.7

9.7

2.8

0.6

0.3

0.3

0.9

2.8

6.8

13.1

21.1

99.4

Southland

11.1

6.2

4.3

0.9

0.3

0.1

0.2

0.6

1.4

3.5

6.1

10.4

45.1

Soil moisture deficits by region by month for 10-percentile2 rainfall are outlined in figure 33 below:

Figure 33: Soil moisture deficits by region in a 10 year low rainfall situation

Region

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Total

Northland

69.0

54.3

39.4

18.3

5.9

1.1

0.8

1.3

3.7

8.6

20.8

44.7

267.9

Auckland

61.4

61.3

48.5

19.4

5.6

0.9

0.7

1.5

3.4

10.9

23.5

39.0

276.1

Waikato

46.6

47.2

38.2

18.4

5.8

1.1

0.5

1.2

3.1

8.4

18.2

28.5

217.2

BOP

50.0

46.0

29.8

13.7

4.1

0.8

0.6

1.2

3.1

9.6

21.6

32.2

212.7

Gisborne

60.3

55.5

45.3

22.1

10.8

5.1

0.5

0.9

3.0

15.9

42.9

55.7

318.1

Hawkes Bay

66.5

60.4

46.3

26.3

16.2

8.4

0.8

1.6

6.6

22.8

48.8

54.8

359.7

Taranaki

43.5

42.2

31.0

12.2

2.4

0.3

0.3

0.7

1.8

6.5

13.8

26.7

181.5

Manawatu

49.2

47.0

37.2

18.0

7.3

2.8

0.4

1.0

3.3

11.5

24.9

35.7

238.3

Wellington

47.9

45.0

34.0

14.7

4.1

1.0

0.3

0.7

2.5

8.7

18.5

32.8

210.4

Tasman

59.2

60.1

43.1

18.0

5.1

1.2

0.3

0.8

4.0

12.6

24.9

39.9

269.2

Marlborough

64.8

59.0

41.5

17.9

6.8

3.3

0.4

1.2

6.8

20.3

34.8

50.0

306.8

Westland

17.8

23.8

15.2

3.3

0.3

0.2

0.2

0.5

1.0

2.1

3.6

9.2

77.1

Canterbury

63.7

52.7

41.5

21.8

11.6

7.0

0.7

2.7

10.8

28.5

43.9

60.3

345.2

Otago

51.4

42.3

34.4

15.9

6.7

3.6

0.7

2.9

10.1

23.6

36.8

50.1

278.3

Southland

34.1

30.8

20.7

5.8

0.8

0.2

0.2

0.8

3.2

8.6

18.0

28.5

151.8

The following chart picks up the key points from figures 32 & 33 above. By way of explanation the Hawkes Bay, Canterbury and Marlborough regions feature with a high (approx 100mm) annual mean deficit and a high soil moisture deficit in a 10 year low rainfall. At the other end of the scale, Southland, Westland and to a lesser extent Taranaki feature for having comparatively low annual mean deficits and limited susceptibility in a 10 year low rainfall situation.

Figure 34: Annual soil moisture deficits by region

4.3.6 Distance from water source

Where surface water is the main source of supply then land needs to be within 2 km of a supply source for reasonable access to the water. If the land is further than this, then it is likely to need a community scheme to make water accessible. [It was hoped that a map detailing the areas of suitable land within 2 km of a significant stream or river within each region would be made available however this has not been possible with the resources allocated to this project].

The interpretation of climate and soils has been done on a 1-km point grid and the soils vary considerably within this scale. The difficulty that this approach poses, is that irrigation design for best use of capital, normally involves systems watering between 8 - 15% of the design area on any one day, systems are usually designed to apply enough water to replenish the total readily available moisture at each pass. In addition, applicants are required to apply for their maximum likely requirement, which is usually based on a '1 year in ten' event prediction. Inevitably this means that water consents for irrigation tend to overstate the average demand.

4.4 Development of a likely supply profile given efficient allocation

Key water supply drivers:

The following key factors largely determine the water supply on a regional basis:

  • Rainfall
  • Balancing mechanisms such as storage dams and aquifers
  • Drainage
  • Regional allocation policies

A number of Regional Councils are in the process of trying to quantify available water from surface and groundwater resources that can be made available for use.

There are some simplistic approaches that provide a preliminary start point. The following series of tables for each key region list the factors considered when estimating water supply based on surface and groundwater supply. Demand for irrigation is calculated by assuming 50 percent growth in current irrigation plus 25 percent of low water holding capacity soils being irrigated. The second estimate is based on a Nimmo-Bell Ltd estimated market demand projection where market returns impact on landuse demand.

Demand for irrigation and availability of water for the main irrigation growth areas

The main growth in demand is expected from those regions where the combined moisture deficits are either high on average i.e. above 90 mm, (Hawke's Bay, Marlborough, Canterbury and Otago) or where the average deficit is moderate but the 10 percentile is high so that the sum of the two exceeds 350 (Gisborne). In addition there are some significant North Island areas in Northland, Auckland, Waikato and Bay of Plenty where there are soils with available water holding capacity of less than 37.5 mm. For Northland and Auckland, likely growth in demand for irrigation is not expected to be large as most of the intensively farmed areas that can irrigate are already doing so, or have chosen not to irrigate.

In the Bay of Plenty much of this land is in horticultural or dairy production already and growth in irrigation demand is not likely to be driven by change in land use so much as changes in the profitability of the existing landuse.

The other North Island area that is seeing an expansion in irrigation is the Wairarapa, but the climate data is masked because it is included in the Wellington region, which, overall is a relatively high rainfall area.

Regional Summaries

The regional summaries relate to those regions that have been identified as having significant growth in demand and therefore are likely to need more detailed assessments at local level. In these regions the demand for water for hydroelectric power generation and thermal power station cooling, has not been included in the figures. This is because the power stations are returning the water to the river systems. However, the stations do have a significant effect on the summer flows in the main rivers because of the management strategies of the major players. This has been ignored in this report because the main rivers concerned, outside Canterbury, are some way short of their potential allocation levels for irrigation and are therefore not yet limiting options for irrigation development.

Waikato region

In the Waikato Region there are large areas of low water holding capacity soils and the improvement in dairy returns is driving renewed interest in irrigation.

Figure 35: Waikato regional water supply and demand estimates

 

By way of explanation, current demand is 17,798 hectare equivalents. This is projected to roughly double to between 32,500-38,500 hectare equivalents in 2010, increasing the percentage utilisation from 9 percent to 18-21 percent.

The total water resource technically available is substantial, but the surface resource is concentrated in the Waikato River and to a lesser degree in the Piako and Waihou Rivers. These latter two have already been almost wholly allocated under the 10% of Q5 regime operated by the Waikato Regional Council. This condition in the proposed Regional Plan makes abstraction for irrigation a controlled activity up to the 10% of Q5 and a discretionary activity beyond this level. There are some streams that have been assessed as being able to sustain higher levels than 10% but they are relatively small and are unlikely to be significant in meeting the potential demand growth.

The vast bulk of the potential irrigation demand is located more then 2 km from the Waikato River and the demand on the smaller surface water sources is likely to rapidly exceed the 10% of Q5 on streams that have not already reached this situation. The Council is encouraging potential irrigators to use ground water, but the volume and quality suitability within the region is highly variable with vast areas having high iron concentrations. There are no proposals being investigated for community irrigation water supply schemes in the Waikato.

The region has huge water reserves and the potential growth in demand and subsequent potential growth in agricultural productivity is generally not appreciated because the Waikato is regarded as having a reasonably reliable rainfall. The substantial areas of sand and volcanic ash soils in the region dry out very quickly and the rainfall reliability is not sufficient to sustain adequate soil moisture levels in a significant number of years.

The issues are not as pronounced as in Canterbury or Hawke's Bay but they are still significant and need to be seriously addressed. Within ten years, the demand for water for irrigation is likely to become the biggest demand for this resource outside hydroelectric generation.

Hawke's Bay region

In the Hawke's Bay Region there are large areas of low water holding capacity soils, many with significant volumes of stones. There has always been a strong demand for irrigation in the traditional fruit producing areas on the Heretaunga plains, but the huge interest in viticulture development and the significant shifts towards large-scale dairy conversions are placing increasing pressure on the water resource.

Much of the land deemed suitable for viticulture development does not have ready access to surface or groundwater. As a result, availability of water is a major issue in the region constraining land use change options. The western areas of the region are likely to prove more popular with landowners (particularly dairy farmers) due to the more reliable rainfall (relative to the drier eastern areas).

The assessed level of natural leakage of groundwater appears to be a major water wastage issue. Off stream storage and community schemes seem to offer an opportunity but the Regional Council has not taken a major initiating role as yet.

The policy of only making water available from surface sources between Q95 (i.e. the stream flows that are exceeded 95% of the time) and MALF is seriously constraining available water for irrigation. Any adjustment to this policy will mean that the Council will need to address the issue of an effective rationing policy during periods of low flows, to maintain in-stream ecological and spiritual values.

The following diagram details the current and future projected supply and demand situation for the Hawkes Bay.

Figure 36: Hawkes Bay regional water supply and demand estimates

Current demand is estimated at 97 percent of potentially available supply from normal summer flows and aquifer recharge. The projected increase in demand driven by market forces puts the region in a deficit situation of 18-27 percent if the current allocation policy is maintained.

While a significant amount of land development is to viticulture, (which uses about 75% of the water used by pasture) the growth in demand still poses a serious regional problem. With the variation in location and site specific shortfalls, there are significant areas that cannot move into land use changes because water is not available from individual traditional avenues. This means that the productive and economic growth opportunities for the Hawke's Bay are being seriously limited by the lack of available water.

Much of the growth in the last five years has been as a result of an influx of outside investment coming into the Hawkes Bay. This investment will change to purchase of existing assets rather than new development unless the Regional and District Councils take some initiative in the development of community based irrigation schemes designed to make more water available.

Wairarapa district

In the Wairarapa district the soils are similar to many of the terraces in the Hawke's Bay and with the district located to the east of the main North Island ranges it suffers from similar low summer rainfall. The area has been traditionally dominated by sheep and beef farming, but as the value of other more intensive farming activities has increased, so have the opportunities for irrigation in changing land use patterns. The Wairarapa has been split out from the total Wellington region because it is significantly different from the rest of the region. Treating it as part of the Wellington region as a whole has the effect of masking the irrigation issues that exist.

Figure 37: Wairarapa regional water supply and demand estimates

From the existing use of water in the area, an amount equal to the summer available surface water is already being allocated. Nearly half of this water is being drawn from underground water. The major reasons for this being that many of the existing irrigators are either beyond easy access to suitable surface water, or because river flooding makes intake maintenance a major issue, or water is being drawn from local unconfined aquifers associated with the main Ruamahanga River system and associated tributaries.

The main demand drivers are dairying and the recent development of a fledgling viticulture industry.

Marlborough region

The Marlborough soils are free of volcanic influence and tend to have higher water holding capacities than many of the North Island soils. However, many of the viticulture areas have a significant stone content thereby reducing the water holding capacity. In addition, low rainfall over extended periods classes the region as being highly susceptible to regular drought conditions. Irrigation is therefore a major requirement for high value agricultural land use.

Figure 38: Marlborough regional water supply and demand estimates

Current demand levels are estimated at approximately 30 percent of potentially available water. We expect this to increase to between 43-45 percent.

The Regional Council has adopted a three-tier structure for the allocation of surface water in the region. This is Class A, Class B and Class C consents. Essentially Class A consents allow users to take water until the stream flows fall to what are regarded as ecologically critical levels and then the takes are progressively reduced to zero if conditions warrant.

The Class B takes are similar but set at a higher level so that restrictions are imposed on users at an earlier stage. Class C consents are such that irrigators are required to build significant off-stream storage to be able to irrigate through the dry periods. Consent holders may hold one, two or all classes of consents.

Virtually all class A & B water is already allocated for all but the Wairau River suggesting the smaller catchments are much more likely to be under demand stress in dry periods.

The Wairau has 75% of the allocable surface water, but most of the demand for water is more than 2 km from this river. There are two proposed community water schemes that will draw water from the Wairau and Awatere rivers. Both schemes are driven by the planned expansion in the viticulture sector. The Wairau scheme will involve piping water up to 70km. The schemes are at the feasibility stage and are viewed as crucial for the further development of viticulture, horticulture and agriculture in the region.

It would appear that community schemes are an urgent imperative if the Marlborough region is to continue to develop. The Wairau River does have available capacity for additional allocation. (Note: In the Marlborough data as reported in the Lincoln Environmental report # 4375/1 the area irrigated appears to be significantly understated. There is also an error in the calculation of the allocated water at 20 mm per week, which should read 62 mm per week.)

The groundwater is deemed to be almost at the maximum sustainable level and on the resources set out it would appear that allocations for irrigation alone would appear to be using 20% of the annual recharge. Some of the groundwater takes are from bores adjoining the Wairau and these are effectively shallow bores tapping into the unconfined gravels that are directly fed from the River.

The data base relating to the Marlborough District Council consents and water use may be causing some confusion in trying to determine the true position when it comes to discussions on the efficiency of water use. Our approach indicates that there is possibly more area being irrigated than the database suggests, or that there is a lot less water actually being used than the consented values, or there are very high water rates being applied compared with the 20mm per week suggested by Lincoln Environmental.

Canterbury region

Irrigation has always been an important input into the agricultural matrix on the Canterbury plains and the main river valleys. Community schemes were established in the first half of the 20th century, and a network of community water races has long provided a distribution system for the water from the main river systems. With the very fertile plains located on the east of the Southern Alps, hot dry summers and the north west winds have left no doubt as to the importance of irrigation in the development of the region's prosperity.

While there may appear to be adequate overall water supplies based on the allocations, some rivers are not able to supply the water allocated. The worst instance of this is the Ashburton River that has water allocations that exceed its average annual flow, let alone the mean low flow level. This means that there are serious shortfalls during the peak of the irrigation season that need to be addressed.

With the increase in dairying landuse that has occurred (and is projected to continue), there has been a substantial increase in the abstraction of ground water. Reports of delays of up to 18 months for landowners wanting bores to be drilled, are common.

In addition to the growth in underground water abstraction, new community irrigation schemes are being proposed and are at various stages of investigation. A recent feasibility study conducted for the Central Plains Water Enhancement Committee, Selwyn District Council and Christchurch City Council identified the potential to irrigate (via communal schemes) a further 192,000 hectares in mid and central Canterbury. The authors of the study have identified the benefits for expansion of this area at an additional 1,100 - 5,000 on-farm jobs and an additional 6,000 - 12,000 jobs in the Canterbury region as a whole. Further schemes are being proposed for 20,000 ha for South Canterbury near Waimate and 20- 30,000 ha from Lake Tekapo

The Regional Council is working through a major water resource study at the present time and hopes to have some preliminary results available by the end of 2001. That study will be significantly more detailed than is possible with this overview.

Figure 39: Canterbury regional water supply and demand estimates

Current demand is estimated at 66 percent utilisation. This is projected to increase to between 76 --85 percent utilisation in 2010. Community water schemes will be required to increase the utilisation as projected.

Otago region

The northern and central half of the Otago region has had a long history of droughts and irrigation, but further south the reliability and overall levels of rainfall have tended to increase and irrigation has been less important.

On the northern side of the region demand is very high and Meridian Energy is looking at extracting water from the Waitaki River and diverting it through to the Otago Region.

Most of the ground water is already fully allocated in the northern part of the region and has been included with the surface water allocations for summation purposes.

Figure 40: Otago regional water supply and demand estimates

Current demand is 61 percent utilisation. This is projected to increase to between 68-77 percent.

Like the Waikato and Marlborough, the total potential supply is dominated by a single river, in this case the Clutha, which accounts for 97% of the regions surface water.

Many of the water use consents date back to the late 1800's and were associated with the gold mining industry, when ecological values were not regarded as a significant. As a result many of the rivers have water allocated beyond the MALF levels. There are primary and secondary consents and these are currently being challenged in the Environment Court by the Department of Conservation (DOC) and the Fish & Game Council.

General comments on regional information

The report completed by Lincoln Environmental and the additional efforts that we have made to get reliable base data from the Regional Councils has shown that databases are variable and even within a single agency, are not necessarily consistent. While Councils may all ask for the relevant information in handling consent applications and may get annual monitoring data supplied from consent holders, the systems enabling easy extraction of meaningful data are lacking.

In many cases the regional plans may be many centimetres thick, but often the knowledge and understanding of the basic water resource and its true use appears to be inversely proportional to the weight of the Regional Plan. A large effort was made to obtain the data for the Report #4375/1 and some regional councils place greater credibility on this report's summaries, than they do on their own data.

The Resource Management Act has been in effect now for 10 years and the responsibilities on regional councils are clearly set out in this regard. Previously, the Soil and Water Act set out similar responsibilities. It is perhaps a reflection of the priorities set by Government and the regional councils, that the basic understanding of the national water resource and its importance to our economic development appears to be receiving less attention than the planning frameworks and ecological stream values.

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