Figure 4.1. The Kakanui River Catchment
Figure 4.1. The Kakanui River Catchment
The Kakanui River catchment lies to the west of Oamaru (Figure 4.1).
The Kakanui Mountains to the south, the Maerewhenua catchment to the west,
the Waitaki catchment to the north, and the Pacific to the east border
the area, and all water beneath its surface is classed as Kakanui Catchment
water. During drought most river flow comes from groundwater.
The administration of groundwater and surface water supplies rests with
the Otago Regional Council.
The Kakanui has three major tributaries: Kauru River, Island Stream
and Waireka Creek. During drought surface flows may cease.
Water is taken from the river and shallow aquifers for rural stock and
household water as well as for small township and rural water schemes,
which are permitted to take 57.4ls-1 in total (Stewart 1998).
The largest water users are irrigator farmers, the focus of this research.
In 1995, 31 irrigators had water rights to draw water from the Kakanui and Kauru Rivers or from shallow aquifers nearby (Manly and Niven 1998). The total permitted abstraction for the area is 1440ls-1, although not all permits are used at once. Flow rates in the Kakanui River are shown in Figure 4.2 and are often well below the fully allocated amount (Stewart 1998). Figure 4.2 also shows higher flow rates during late winter and spring when water is least needed, and lower in summer when irrigation demand is at its annual peak.
Figure 4.2. Box and Whisker diagram for
Clifton Falls daily mean flows sorted by month (Snelder et al 1998)
Permit holders may draw water from the river until the minimum flow
of 250 ls-1 is reached. At that point restrictions take effect.
A Water Allocation Committee administers restrictions, and consists of
irrigators elected by their peers. That Committee decides who
may irrigate, when, and by how much.
The Papakaio and Deborah are two deep aquifers in the Kakanui Catchment,
and they yield significant amounts of water for irrigation and other permitted
uses.
The Papakaio Aquifer is a layer of quartz gravel and occurs throughout
most of North Otago. It recharges in the western downlands,
where it lies closest to the surface, and descends to 120m below the surface
towards the coast. This aquifer is confined by sandstone, which
renders it artesian over much of its extent (Otago Regional Council 1992).
It discharges into a fault that is believed to feed the Deborah volcanic
aquifer and feeds 69ls-1 into the Kakanui River (Otago Regional Council
2000a).
Figure 4.3. Groundwater piezometric head
trend in the Papakaio Aquifer (from Otago Regional Council 2000b)
Water flows very slowly in this layer, and has been carbon isotope dated
to 5,000 - 30,000 years old (Otago Regional Council 2000a). As a result,
the water tends to be rather saline and only suitable for irrigation.
Five farmers draw water from the aquifer for irrigation, abstracting an
average of 1.25Mm3 per year (40ls-1) (Otago Regional Council 2000a).
Although abstraction began as recently as 1985 it has been increasing steadily
ever since. Currently, water permits account for an annual
drawdown of 4.83Mm3 (153ls-1) of water per year, with applications for
a further 3.7Mm3yr-1 (117ls-1) pending. Figure 4.3 shows that
piezometric head levels have dropped at one control well site over the
last 15 years. Under current abstraction rates it is expected
that outflow to the river will be steadily reduced (Otago Regional Council
2000a). A groundwater model was run at full abstraction rates with
users entitled to 153ls-1. Then the outflow from the aquifer
into the Kakanui reversed and 50ls-1 was lost from the Kakanui River as
opposed to the 69ls-1 it gains currently. A timeframe was not
available for this discharge reversal because the model was run in steady
state mode.
The Deborah Volcanic Aquifer is thought to be fed largely from the
Papakaio Aquifer, and water can be tapped from fissures. Water
quality is a limitation on its use for irrigation. Figure 4.4
shows overall decline in head of the Deborah Aquifer over the last 15 years.
There is concern about incursion of salt water from the coast, depletion
of the aquifer through excessive draw, and decrease in water quality as
a consequence of tapping supplies of older water deep in the aquifer (Otago
Regional Council 2000 b).
Figure 4.4. Piezometric Head for the Deborah
Volcanic Aquifer (Otago Regional Council 2000b)
Farming in North Otago was originally wheat dominated, a crop that
thrived in the dry climate. Over the last century, landuse
has changed from wheat through to predominantly pastoral, as is currently
the case, with sheep and beef farming the main operations.
Forestry, horticulture and dairying are the directions that North Otago
is moving towards, with horticulture and dairying relying on a steady supply
of water.
Currently, irrigated farms are located adjacent to the water source in the case of rivers, or immediately above the water source in the case of groundwater. Farther from a water source, dryland farming based on sheep and cattle predominates, notably on larger farms with lower stock/land ratios (Manly and Niven 1998). In recent years, dairy conversions have occurred wherever landowners have been able to access sufficient water for irrigation.
When posed with the theoretical proposal of a cut in irrigation water,
irrigator farmers were able to say how their operations would be affected
(Table 4.1.) Water supplies are essential on some farms, whereas
others could manage with less than their current permit.
Table 4.1. Likely changes in farming practise resulting from a 10% and a 25% cut in irrigation allocation, related to the percentage of farm income derived from irrigated land (from Manly and Niven 1998).
The Kakanui River harbours trout, although at flow rates of 400ls-1
or less trout tend to migrate out of the river (Snelder et al 1998).
Native fish can survive even lower flows, although 250ls-1 is described
as the absolute minimum (Department of Conservation 1998).
Other natural events, such as floods, will also reduce the fish populations.
Low flows may result in closure of the Kakanui River Mouth, given the right
oceanic conditions, and affect migration of fish. The Kakanui
River is used for recreation, food gathering, recreational fishing, boating
and swimming, all activities depending on a minimum flow of 400ls-1.
The Department of Conservation and the Central South Island Fish and Game
Council argue that a minimum flow of 250ls-1 is inadequate (Otago Regional
Council 1998), but this is a matter of contention between irrigators, in-stream
users and administrators.
The high value, demand and current over-allocation of irrigation
water in North Otago reflect the region’s dry climate and susceptibility
to drought. Most of the area’s rainfall falls in the Kakanui
Mountains, and is lowest in the flats and downlands where demand is highest
(Figure 4.5).
Figure 4.5. Mean annual rainfall in the
Kakanui Catchment in mmyr-1 (Stewart 1998).
Average annual potential evapotranspiration is consistently greater than rainfall. At the Oamaru Airport the average annual rainfall is 531mm and potential annual evapotranspiration is 569mm (Bee, 1984). The difference is greatest during periods of drought and in high summer. Drying föhn winds from the northwest worsen the situation. Demand for irrigation water is greatest in late summer, when river flows are seasonally low. There is clearly scope for water storage in ponds and dams on farms during winter when there is little call for irrigation and water is more readily available. The recently issued secondary water permits should allow irrigation to take advantage of this, because they allow water abstraction when flow rates in the Kakanui exceed 800ls-1.
There is growing pressure from customers for predictable supplies of farm produce. Freezing works lose money when they sit idle during a drought, and profitable niche markets may not be able to depend on dryland farmers for supplies during drought. The problem of assuring supply, as well as rising farm costs, makes irrigation a highly attractive option to more farmers.
Obtaining a water right in the Kakanui is made difficult by the shortage of water, yet those who hold water rights experience little pressure to ensure that they are making good use of the water to which they are entitled. Borderdyke irrigation has been considered an inefficient use for many years, yet the last of the borderdykes are only now being replaced. Water rights are currently tradeable if property is sold with a water right attached or if an amendment is made to the water permit. As a result the real value of a water permit may be less than could be realised on the open market.
Economic advantage currently lies with dairying, but in the dry climates
of North Otago access to irrigation water is imperative if landowners are
to convert. The experience of the last two decades shows that
the Kakanui River Catchment has insufficient water to meet the increasing
demands of irrigators and conservationists, making it an ideal site for
an evaluation of the current water allocation system, and the acceptability
of an alternative, market-based, system of allocation that assigns real
value to water.