Hurunui River: B Block allocation
review
NIWA Client Report: CHC2009 -017
May 2009
NIWA Project: ENC09511
Hurunui River: B Block allocation review
Maurice Duncan
Prepared for
Environment Canterbury
The information in this report is accurate to the best of the knowledge and belief of the Consultant acting
on behalf of Environment Canterbury. While the Consultant has exercised all reasonable skill and care in
the preparation of information in this report, neither the Consultant nor Environment Canterbury accept
any liability in contract, tort, or otherwise for any loss, damage, injury or expense , whether direct,
indirect or consequential, arising out of the provision of the information in this report.
NIWA Client Report: CHC2009-017
February 2008
NIWA Project: ENC09511
National Institute of Water & Atmospheric Research Ltd
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Contents
Executive Summary
1.
2.
Introduction
Background
1
1.2.
Key environmental values to conserve
2
1.3.
Tasks
3
Approach
Alternative approaches
Preferred flow ranges
4
4
4
3.1.
Periphyton and fine sediment flushing
5
3.2.
River bed nesting birds
6
3.3.
Salmon angling, passage and migration
6
3.4.
Invertebrate production
7
3.5.
An increase on the frequency of flows favoured by kayakers
and jet boaters
9
3.6.
4.
1
1.1.
2.1.
3.
i
Summary
Likely effects of alternative approaches
10
10
4.1.
Limiting the size of the B Block
10
4.2.
Providing a flow gap between the A and B Block allocations.
12
4.3.
Implementing a sharing regime whereby for each increment of
flow abstracted an increment is left in the river
12
Having a minimum flow for the abstraction B Block that varies
with time
13
Having rules to preserve particular aspects of the flow regime
such as small freshes to flush periphyton or large floods to
maintain channel forming flows and sediment transport
13
Summary
14
4.4.
4.5.
4.6.
5.
Should there be a C allocation Block?
15
6.
Simulations
15
6.1.
The effect of different size B Block allocations
16
6.2.
The effect of different sized gaps between the A and B Block
allocations.
18
6.3.
Summary of effects of gaps between the A and B Blocks
25
6.4.
Potential abstraction volumes for the B Block scenarios
25
6.5.
Reliability of supply
26
6.6.
Conclusions from the simulations
26
7.
Recommended B and C Block flow regimes
27
8.
Summary
28
9.
Acknowledgements
29
10.
References
29
Appendix 1:
Project brief
27
Reviewed by:
Approved for release by:
Doug Booker
Jochen Schmidt
Executive Summary
Environment Canterbury (ECan) wish to assess for the Hurunui River the environmental effects of
different sizes of B allocation blocks and gaps between the A and B Blocks as part of the review of the
minimum flows required by the proposed Natural Resources Regional Plan (NRRP) Policy WQN5.
The A allocation block for the Hurunui River is fully allocated and there are potential applications for
a greater allocation. ECan wish to explore the effect of various sizes of a B/C Block allocation and the
sizes of flow gaps between the A and B/C Blocks on environmental values.
This report reviews community concerns on environmental effects of B/C Block abstractions and
3 -1
determines that the critical issue is the need to have flows in the range 25-40 m s during September
3 -1
to December for riverbed nesting bird breeding and to have flows in the range 15-40 m s during
December to May for salmon passage and angling. If flows were sufficient for these activities then
there would be sufficient flow for kayaks and jet boats, benthic invertebrates, trout and native fish.
Other issues, such as flow regimes to flush periphyton and fine sediment and to preserve bedload
transport and channel forming capacity, are discussed.
The effects of allocation mechanisms such as abstraction limits, flow sharing and gaps between
allocation blocks on the critical values are discussed with flow limits and gaps between allocation
blocks appearing to be the most useful mechanism for preserving environmental values.
Simulations of the different allocation mechanisms were carried out on an unmodified flow record to
quantify their effects on the critical flows.
3 -1
A maximum B Block allocation of 10 m3s-1 and contiguous C Block allocation of 5 m s is
recommended, as larger allocation blocks would provide little extra water and supply would be quite
unreliable.
An allocation regime is recommended that allows certain freshes and large floods to pass without take
3 -1
after periods of low flow, a maximum 10 m s B Block allocation with a gap between the A and B
3 -1
3 -1
Blocks of at least 5 m s from September to January and 8 m s from February to March Any C
Block allocation should be without a gap between the B and C Blocks.
.
Hurunui River: B Block allocation review
i
1.
Introduction
1.1.
Background
Environment Canterbury (ECan) wish to assess for the Hurunui River the
environmental effects of different sizes of B/C allocation blocks and gaps between the
A and B/C Blocks and appropriate flow regime requirements to minimise these
effects. This work has been prompted by the proposed Natural Resources Regional
Plan (NRRP) Policy WQN5 that states that within 5 years of becoming operative,
rivers such as those in the Hurunui area will have their existing minimum flows
reviewed and incorporated into schedule WQN1 (Familton 2007).
Figure 1 explains some of the terms used in this report. At flows less than the
minimum flow water cannot be extracted for irrigation (or other out of stream use). At
flows greater than the minimum flow, A allocation block water can be abstracted but
the full amount cannot be taken until the flow is greater than 18.2 m3s-1 in this
example. There is a gap of 8 m3s-1 between the A and B blocks and that means the B
block water cannot be abstracted until the flow is greater than 26.2 m3s-1. The
minimum flow for the C Block is 36.2 m3s-1.
60
February and March
50
Flow m3/s
40
30
20
C allocation block 5 m3/s
B allocation block 10 m3/s
Gap 8 m3/s
A allocation block 6.2 m3/s
10
Minimum flow 12 m3/s
0
19620201:094453 0211
0221 MMDD
site 65104 Hurunui at Mandamus Flow m3/s
Figure 1.
An explanation of some of the terms used to describe the allocation system.
Hurunui River: B Block allocation review
1
No gap is shown between the B and C blocks as there are no environmental
advantages in having one. The point of having a B and C block is to give a greater
reliability of supply to the B block abstractors who gained their resource consents first.
If there was only one block, the first group of consent holders could not take their full
allocation until flows were greater than 41.2 m3s-1 but with a B and C block they could
take their full allocation once flows were greater than 36.2 m3s-1.
The A allocation block for the Hurunui River is fully allocated and there are potential
applications for a greater allocation. ECan wish to explore the potential effect of
various sizes of a B/C Block allocation and the sizes of gaps between the A and B/C
Blocks on environmental values.
While this report is primarily about the B allocation block, some information is
provided about the A Block so the reader can distinguish between the effects of A
block abstraction and combined A and B Block abstractions.
The report is about the reach between the Mandamus and Pahau River tributaries as
this reach has a higher proportion of its flow allocated. In the summer the Pahau
contributes more flow than is currently allocated downstream of the Pahau River and
much of the river downstream of the Pahau confluence is single thread and likely to be
deeper and so is less critical for salmon and jet boat passage.
1.2.
Key environmental values to conserve
Before deciding on an allocation framework the community needs to indicate the
instream and out of stream values that are important. Familton’s (2007) report
summarizes work by Mosley (2002), Duncan and Shankar (2004), and Duncan (2007)
on instream values and their flow requirements. Duncan et al. (2008) sets out the
requirements for the protection of river bed nesting birds from mammalian predators:
The key values and requirements are:
•
The need to maintain flows in a range suitable for providing the maximum
number of islands suitable for the breeding of riverbed nesting birds during
the breeding season,
•
The need to provide flow regimes that are not detrimental to invertebrate life
suitable as food for native fish, salmonids and river birds,
Hurunui River: B Block allocation review
2
1.3.
•
The need to maintain flows in a range suitable for salmon passage when
salmon are migrating from the sea to spawning grounds,
•
The need to maintain flows most favoured by jet boaters during the summer,
•
The need to maintain flows suitable for kayaking,
•
The need to retain freshes capable of flushing undesirable periphyton growths
that can smother the gravel any time of year when flows are stable, so
maintaining the rivers suitability as habitat for aquatic insects that are prey for
birds and fish,
•
The need for a flow regime that retains the channel forming flows that are
responsible for the morphology of, appearance of, and sediment transport in,
the river. Such flows need to be capable of removing, and preventing
encroachment of, exotic vegetation into the riverbed. Maintaining a bare
gravel river bed is essential to providing habitat for riverbed nesting birds.
Tasks
•
Consider different sizes of B Block and analyse their effect on:
(a)
flushing flows that remove periphyton and fine sediment;
(b)
floods that maintain sediment transport, riverbed appearance and
remove exotic vegetation from the fairway;
(b)
the availability of flows within the desired flow range for salmon
passage and fishing and riverbed nesting birds;
(c)
the frequency and duration of "flatlining" and whether this creates any
specific issues, e.g., promoting periphyton growth, impacts if any on
salmon/boat passage, encroachment of exotic vegetation;
•
Determine whether there should be a gap between the A and B Block, and/or
flow sharing within the B Block, along with a robust justification.
•
Simulation of the effect of full year round abstractions of the existing A Block
allocation and proposed B Block allocations in the range 7.5, 10, 15, and 20
m3s-1.
Hurunui River: B Block allocation review
3
2.
Approach
2.1.
Alternative approaches
There are a number of approaches to conserving the values outlined in Section 1.2. By
using the word “conserving” I wish to indicate not a preservation of the current flow
regime, but a regime that would allow most of the values to be retained at a level
acceptable to most of the community.
The alternative approaches to defining a B Block allocation could include
combinations of:
3.
•
Limiting the size of the B Block
•
Providing a flow gap between the A and B Blocks.
•
Implementing a flow sharing regime whereby for each increment of flow
abstracted an increment is left in the river.
•
Having a minimum flow for the abstraction block that varies with time.
•
Having rules to preserve particular aspects of the flow regime such as small
freshes to flush periphyton or large floods to maintain channel forming flows,
sediment transport and a vegetation-free, open gravel riverbed.
Preferred flow ranges
The information that follows has been obtained primarily from the documents listed in
Section 1.2. Some of the documents have appeared in peer reviewed literature and
some have not. Some of the flow requirements may be less certain than implied and
presented here but precise numbers were used in the report to enable simulations of
different take regimes to be carried out.
Most of the abstraction from the river is allocated to the Balmoral Irrigation Scheme.
The environmental flows adopted for that scheme that indicate flatlining (constant
flow caused by abstraction) of the flow will occur at the lower of the flows when the
flows are between 12 and 18.2 m3s-1 in January to July, 13 and 19.2 m3s-1 in August,
15 and 21.2 m3s-1 in September, 19 and 25.2 m3s-1 in October, 18 and 24.2 m3s-1 in
November and 13.5 and 19.7 m3s-1 in December. The flatlining at those flows is not of
value to all instream river uses, e.g., riverbed nesting birds need flows greater than 25
Hurunui River: B Block allocation review
4
m3s-1 in September to October, but such minimum flow would be suitable for adult
trout feeding.
In this section only physical habitat is considered and any effects of water quality,
water temperature and sedimentation of the substrate are not considered. Water quality
in the river is relatively high even though the tributary flows from the Pahau river
flows may be of low quality. High water temperature from time to time may delay
adult salmon migration. High flows are normally sufficiently frequent that
sedimentation of the substrate should not be an issue.
3.1.
Periphyton and fine sediment flushing
Mosley (2002) suggests that flows of about 70 m3s-1 would slough periphyton from the
river bed with and flows of 120 m3s-1 (three times the median flow of ~40 m3s-1)
would disturb the bed enough to remove the periphyton and flush out any accumulated
fine sediment from within the gravels.
Abstractions are likely to reduce the magnitude and frequency of small freshes capable
of flushing sediment and periphyton. In order to mitigate this effect, consent
conditions are required that maintain the frequency of flows greater than 70 m3s-1 and
preferably greater than 120 m3s-1 after a period of low flow of sufficient duration to
potentially allow the growth of periphyton to nuisance levels. Familton (2007) reports
that significant periphyton accrual occurs approximately 50 days after a fresh, with
accrual continuing for a further 30 days until peaking (Biggs and Stockseth 1996).
In a poorly armoured river like the Hurunui, the turbulent water in the steep rising
limb of the hydrograph is likely to entrain fine sediment capable of abrading
periphyton, and provide sufficient shear stress to flush periphyton, so a prolonged
period at 120 m3s-1 is probably not required. For flushes smaller than 120 m3s-1 a
longer duration (say 2 days) is required to provide the abrasion and stressing to
remove periphyton because there will be less sand in suspension than for larger
freshes.
Duncan and Bind (2008) show for the Waimakariri River, that flows of three times the
median flow are sufficient to turn over the river bed and reset periphyton and
invertebrate communities. That finding was consistent with that of Sagar (1983) who
found that a flow of three times the median flow in the Rakaia River was sufficient to
reset the invertebrate (and presumably the periphyton) communities. These two rivers
are similar in character to the Hurunui River and endorse the findings of Mosley
(2002) reported above.
Hurunui River: B Block allocation review
5
3.2.
River bed nesting birds
River bed nesting birds require predator-free and weed-free islands to breed on and a
large wetted area to maximise invertebrate feeding opportunities. Recent research
(Boffa Miskell and Urtica Consulting 2007) has shown that, providing trapping
reduces population pressures, the presence of water has a deterrent effect on potential
mammalian predators regardless of their swimming ability. Thus river bed nesting bird
breeding success could be enhanced by encouraging flows that maximise the number
of islands large enough to provide nesting sites. Duncan et al (2008) show that the
number of islands in the Hurunui River is maximised at flows greater than the median
flow of 40 m3s-1 and the number islands significantly increases at flows greater than 25
m3s-1 .The river bed bird breeding season is from September to December. Food
production for river bed nesting birds is optimal at flows of 5-30 m3s-1 (see Section
3.4).
Duncan and Shankar (2004) and Familton (2007) recommended lower flows than
those indicated above. Those lower flows were primarily based on feeding
requirements. It is arguable that given the current low population numbers of most
river bed nesting bird populations, that food is not limiting and that predation by
mammalian predators is probably exercising more control on populations.
Accordingly there is a need for high flows in the breeding season to reduce access to
nests by mammalian predators.
There is room for debate on the size of flow to provide for riverbed nesting birds and
hence the size of the gap between the A and B Blocks. The area of islands increases as
flows increase between 25 m3s-1 and 50 m3s-1, but the habitat for food production and
the habitat for bird feeding and their quality both increase and decrease over this flow
range depending on the food production measure used or the bird species and its
feeding mode (Duncan and Shankar 2004). Also the flow is very variable (there are
lots of floods) during the breeding season so that the higher the minimum flow the
more vulnerable the islands available for nesting at these flows are to the braids
forming those islands being dewatered and exposing the nests to predation. For
example over the September to December islands protected by 20 m3s-1 are exposed
9% of the time while those protected by 40 m3s-1 are exposed 33% of the time. Then
there is the issue with the small numbers of these birds as to whether the availability of
safe nesting sites is limiting riverbed bird populations. Thus it is debateable whether B
block minimum flows of 40-50 m3s-1 would provide optimum nesting habitat, but it is
clear minimum flows of 25-30 m3s-1 start to provide increasing amounts nesting
habitat. In this report the options explored were to provide a gap that would provide B
block minimum flows between 25 and 30 m3s-1.
Hurunui River: B Block allocation review
6
3.3.
Salmon angling, passage and migration
Most (77%) salmon anglers prefer to fish the Hurunui River near the mouth
Greenaway (2001) where the river is deep and mainly in a single channel. A further
18% of anglers fish between the Stoneyhurst and SH1 Bridges (Figure 2). Thus the
main requirement for most of the river is to have sufficient flow and depth for adult
salmon passage to spawning reaches upstream of the confluence with the Mandamus
River during January to May. Duncan and Shankar (2004) show that for the modelled
braided reach just downstream of SH7 there is sufficient depth (0.24 m) at a flow of
10 m3s-1 for salmon passage along the entire reach. The riffle depth survey for that
study found that the minimum thalweg depth over the shallowest riffle over a 17 km
long survey of the braided Amuri Plain reach was 0.25 m when the river flow
measured by the water level recorder at Mandamus was 13.5 m3s-1 on the day of the
survey. Thus flows greater than 15 m3s-1 during January to May should provide
sufficient water depth for unimpeded salmon passage to the spawning grounds.
Nevertheless radio tagging has indicated salmon migrate more slowly up river at low
flows than during freshes (Glova and Docherty 1986). Long periods of low flows
delay upstream migration, cause extra abrasion of their bodies and ultimately affect
reproductive success (Hayes 2008), thus flows higher than 15 m3s-1 would benefit
salmon.
Any B Block allocation would reduce recession flows and potentially impact on
upstream migration.
3.4.
Invertebrate production
Maintaining production of particular invertebrates is a key to providing food for birds
and fish. Those particular invertebrates are sensitive to excessive nuisance periphyton
growth and deposition of fine sediment. Thus there is a need for regular flushing of the
bed to remove the nuisance periphyton and fine sediment with the risk that the
preferred invertebrates will be flushed as well, although most preferred invertebrates
are expected to be affected less by flushing than less desirable species that are often
associated with periphyton proliferations.
Modelling work (Duncan and Shankar 2004) has shown that, in general, as the flow in
the Hurunui River increases, so does the suitable habitat characterised as Weighted
Useable Area (WUA) for food producing invertebrates. This appears to indicate that
any reduction in flow would reduce WUA and invertebrate production. However, to
use the habitat available at higher flows the flow must remain stable for a sufficient
Hurunui River: B Block allocation review
7
Mandamus
River
Amuri Plain Reach
SH7 Bridge
SH1 Bridge
Figure 2:
Stonyhurst
Bridge
The Hurunui River catchment.
Hurunui River: B Block allocation review
8
time (15 days (Sagar 1987)) for populations to build up to exploit the habitat.
Preliminary modelling of benthic invertebrate dynamics in the Waimakariri River
reported by Duncan (2008) suggests that abstraction from the river may have little
effect on overall invertebrate biomass.
The other factor that needs to be taken into account is that all freshes and floods are
which
likely to reduce invertebrate populations with floods greater than about 120 m3s-1
are likely to substantially reduce (reset) invertebrate populations (Duncan and Bind
2008). Duncan and Bind (2008) also showed that even in large floods there are
significant areas with suitable depths and velocities to act as refugia for invertebrates
that can then rapidly repopulate channels as flow recedes.
Duncan and Shankar (2004) show that the most efficient flows for invertebrate
production are between 5 and 25 m3s-1 and that the optimum flow is in the range 10-30
m3s-1. Accordingly flows that are sufficient for river bed nesting birds and salmon
passage will be sufficient for invertebrate production.
As the main stem of the river is not currently dammed there should be enough floods
and freshes to maintain a healthy and productive river. If the main stem is dammed or
the B Block is large, provision needs to be made to allow freshes to rejuvenate the
river if algal biomass increases to nuisance levels (See Section 3.1).
3.5.
An increase on the frequency of flows favoured by kayakers and jet boaters
Duncan and Shankar (2004) concluded that a flow of 15 m3s-1would provide passage
for canoes and jet boats, but R Gerard, an experienced jet boater suggests that the
Amuri plains reach would not be used by recreational boaters at less than 40 m3s-1
(Familton 2007). It is likely that kayakers too would find it easier to paddle the reach
at flows greater than 15 m3s-1 even though passage is possible at such flows. The
author has travelled much of the length of the braided Amuri Plains reach with a
skilled driver in a jet boat that is larger and heavier than most recreational jet boats
when the flow was 13.5 m3s-1. This experience suggests that Mr Gerard’s
recommended minimum flow is rather conservative and a flow of 20 m3s-1 is
suggested here as providing sufficient depth for recreational jet boats with moderately
experienced drivers. Most jet boating is assumed to be done during December to
March (Adams 2008).
Hurunui River: B Block allocation review
9
3.6.
Brown trout and native fish
Duncan and Shankar (2004) show that physical habitat for brown trout adults and
yearlings reduces as flow increase from 10 to 30 m3s-1, so if the abstraction regime
reduces the unmodified flows to place them in that flow range then the environment
for trout would be enhanced. This is because both juvenile and adult brown trout
prefer slower velocity water.
The physical habitat for torrent fish, shortfin and longfin eels was modelled by
Duncan and Shankar (2004). Torrent fish habitat varied little over the range of flows
10 to 50 m3s-1 so their physical habitat is unlikely to be influenced much by
abstractions. Habitat for large eels and small longfin eels is insensitive to flow rate.
Habitat for small shortfin eels decreases from 10 to 20 m3s-1 and increases from 20 to
40 m3s-1 but is 2-3 times that for the other eel species and sizes.
3.7.
Summary
Figure 3 shows a representation of the preferred flow ranges for each of the key values
of concern. The upper limits for salmon passage and riverbed birds are given as 40
m3s-1, the median flow, even though for some uses such as salmon angling and boating
higher flows may be suitable. It is clear that kayaks can use a large range of flows and
that any flows that are protected for other values will be suitable for kayaks. Thus the
flows to be protected for any new allocation regime should be 25-40 m3s-1 from
September to December and 15 to 40 m3s-1 for January to May. For June to August it
may be possible to apply fewer restrictions on takes because they would not impinge
on the key values of community concern.
4.
Likely effects of alternative approaches to allocation rules on instream
values
4.1.
Limiting the size of the B Block
There should be some limit on the amount of water in the B (or C) Block allocation. If
the B Block was large (more than 20 m3s-1) the river would be flat lined (unless there
was flow sharing) for a long period of time at flows much less than required to meet
the requirements for the key environmental values. In this situation flows would only
meet the required values for short periods of time.
Hurunui River: B Block allocation review
10
150
140
River bed birds
Salmon passage
120
Flow m3/s
100
80
60
40
20
0
0
40
60
80
100
Percentage of time flow is not exceeded
Percent
of time flow is not exceeded
site 65104 Hurunui at Mandamus
Flow m3/s
Unmodified flow
19570101 094453 to 20071231 231500
site 1062 Var8 min, 6.2 A block Flow m3/s
Variation 8 minimum
A Block
19570101flows,
094453
to 20071231 231500
site 1072 Var8 min, 6.2 A block, 6.5
3 -1 gap, 10 B block
Variation 8 minimum
A Block,
6.5 to
m20071231
s gap, 10
m3s-1. B Block
Flow m3/sflows,
19570101
094453
231500
Figure 3:
20
The preferred flow ranges for key values of community concern. The blue colour
shows the preferred flow range for salmon, and boating and the pink colour the
flow range for river bed nesting birds. The flow duration curves are for the whole
year for 1957 to 2007. A Block is 6.2 m3s-1.
If the B Block allocation was less than 20 m3s-1 there could still be long periods of
flatlining as flows are in the range just above the A Block allocation for a lot of the
time, but the time during which flows are in a useful range for key environmental
values would be longer than for larger B/C Blocks.
Accordingly, limiting the size of the B Block on its own may not be particularly useful
for enhancing instream values as water will be taken when flows would otherwise be
in a useful range.
Hurunui River: B Block allocation review
11
4.2.
Providing a flow gap between the A and B Block allocations.
B Block allocations could cause flatlining at flows of little value to river users and
reduce the time flows are in a useful range. Providing a flow gap between the A and B
Block has potential to mitigate this issue.
Providing a gap between A and B Blocks is a very useful tool for reducing the
ecological effects of water abstraction. It allows the flow to remain in the range most
useful to the key environmental values for the longest time, albeit detrimentally
affecting the reliability of the abstraction. B Block water is less reliable than A Block
water and storage may be needed to obtain a reliable water supply from B Block
water. Reducing the reliability of abstraction would require an increase in the storage
capacity to retain the same water supply reliability. One effect of allowing a gap
between the A and B Blocks is to create a flat line hydrograph at the level of the
minimum flow for the B Block. Thus if the gap between the A and B Block was varied
with season the flow at which the flat line occurred would maximise the flow in the
preferred range for the season.
4.3.
Implementing a sharing regime whereby for each increment of flow abstracted
an increment is left in the river
Instream values may be protected in several ways. One way is to have a relatively low
minimum flow where instream values are probably compromised, but reduce the
probability of flows getting that low by having, say, a 1:1 sharing ratio, e.g., the
Rangitata River flow regime. An alternative is to have a higher minimum flow that
adequately protects instream values and no flow sharing, e.g., the Waimakariri River
Regional Plan. While the two approaches are not mutually exclusive usually one or
other approach is used.
One of the arguments for flow sharing is that it moves some way to preserving the
natural flow regime. In fact, the widely fluctuating natural Hurunui flow regime is
responsible for severely limiting the productivity of the river and some flow stability
might enhance its productivity. However, there are aspects of the Hurunui River flow
regime that function to maintain the river ecosystem and need to be retained, e.g.,
flows sufficiently large enough to flush periphyton and fine sediment, and large floods
to move bed load and remove vegetation and so retain the natural character of the
river. Flow sharing is probably not the best way to ensure that these characteristics are
retained. Rather there should be particular rules and consent conditions that ensure
that these characteristics are retained (see Section 4.5).
Hurunui River: B Block allocation review
12
Flow sharing is a fairly blunt tool for getting particular flows to enhance or increase
the time the river spends in particular preferred flow ranges, but it is more likely to
keep the river within the preferred range of flows than allocation without flow sharing
and gaps between blocks.
One part of the flow regime that is required is flows that will flush periphyton.
Extending the principles from Duncan and Bind (2008) to the Hurunui River indicates
that flows between 80 m3s-1 and 120 m3s-1 are required in the Hurunui River to flush
periphyton and fine sediment to keep the river healthy. If the B Block minimum flow
is 26.2 m3s-1, the B Block take is 20 m3s-1 and there is 1:1 sharing, when the
naturalised flow is 66.2 m3s-1 the residual flow in the river is 40 m3s-1 (assuming 15
m3s-1 minimum, 6.2 m3s-1 A Block allocation and a 5 m3s-1 gap). That is well below the
threshold for periphyton flushing if the pre-existing flow was 20 m3s-1 (15 m3s-1
minimum plus 5 m3s-1 gap). In that case 1:1 sharing does not cause the flow to cross
the threshold for periphyton flushing and so would be of little value for that purpose.
But, in this example the naturalised flow (66.2 m3s-1) is less than that required for
flushing anyway.
4.4.
Having a minimum flow for the abstraction B Block that varies with time
As is shown in Section 3 the preferred flow ranges vary with time so by varying the
gap between the A and B Blocks the flat lining caused by the B Block allocation could
be varied to maximise the time the flow was the either at the optimum for the activity
(e.g. bird breeding or salmon passage) or possibly at the lower end of the preferred
range to enhance the reliability of any abstraction. The current and proposed minimum
flows already vary by month for the benefit of instream values and that effect could be
enhanced by varying the gap between the A and B Blocks, i.e., varying the B Block
minimum flows.
4.5.
Having rules to preserve particular aspects of the flow regime such as small
freshes to flush periphyton or large floods to maintain channel forming flows and
sediment transport
Regardless of the main B Block allocation rules (flow sharing, gaps between
allocation blocks or allocation limits) there needs to be specific rules to promote
periphyton and fine sediment flushing and to maintain channel forming flows.
Duncan and Bind (2008) show surface flushing of periphyton and fine sediment occur
at about twice the median flow, e.g., 80 m3s-1 for the Hurunui River and that deep
flushing and significant bed movement occurs at 3 times the median flow, e.g., 120
m3s-1. Thus during periods of low, stable flows when periphyton may grow to nuisance
Hurunui River: B Block allocation review
13
levels at between about 21 days (Biggs 2000) and 50 days (Biggs and Stockseth
1996), freshes occurring after 21-50 days of minimum or low flow should be allowed
to flow untapped until the flow has exceeded 80 m3s-1, or after two days, which ever is
the sooner.
Duncan and Bind (2008) also show that much of the river bed is being deep flushed at
flows greater than the FRE3 flow (120 m3s-1 for the Hurunui River at Mandamus) and
it can be inferred that at such floods channels are being formed and sediment transport
is occurring at significant rates. In theory (Davies 1988) any reduction in flow will
result in aggradation of the bed in the long term (many decades). In the short term,
pulses of more or less sediment will probably mask any long term aggradation.
Significant aggradation has not been apparent at any of Canterbury’s larger irrigation
take locations e.g., the Rangitata Diversion Race and the Waiau Irrigation Scheme
intakes. The largest of these has been in place for ~60 years and others for several
decades. To limit sediment input to irrigation infrastructure, prudent irrigation
company managers may voluntarily shut intakes when flows and sediment
concentrations are high. Thus requiring irrigation companies to cease abstractions
when natural flows are high is unlikely to impose any burden and may not be required.
However, new technology, such as infiltration galleries, could allow abstractions to
occur during large floods and so some restrictions may be necessary to future proof
the flow regime and preserve channel forming flows. An allocation cap goes some
way to preserving channel forming flows as the allocation becomes a smaller part of
the flow as flood flows increase. Large amounts of sediment transport, inferring
channel forming flows and rapid changes in channel form, occur at flows larger than
~700 m3s-1 in the Waimakariri River (Duncan and Bind 2008). The equivalent flow is
~300 m3s-1 in the Hurunui River and abstraction could be fully restricted when flows
are larger than 300 m3s-1. Such flows only occur about 2% of the time. An alternative
approach would be to require consent holders of large takes to monitor bed levels in
the vicinity of intakes and to review consent conditions if aggradation becomes
apparent.
4.6.
Summary
It appears from the discussion above that the ideal B Block allocation regime would
have the following characteristics:
•
A limit on the total maximum allocation,
Hurunui River: B Block allocation review
14
5.
•
Provide a gap between A and B Block allocations to better target the preferred
flow regime. This would be achieved by having a minimum flows within the
target band so the flatlining caused by the allocation would keep the flow in
that band for longer. In the winter months (June to August) between the
salmon angling season and the start of the riverbed nesting bird breeding a gap
would not serve any useful purpose and would not be necessary. Not having a
gap would assist in improving reliability for storage takes.
•
Have rules to promote surface flushing of fines and nuisance periphyton after
a specific duration of low flows when natural flow increases occur.
•
Have bed level monitoring at major intakes to measure any effects (possible
aggradation) of the abstraction on the bed load transport capacity. High flows
are necessary to preserve the transport capacity of the river at channel forming
flows and the bare, vegetation-free, braided character of the river.
Should there be a C allocation Block?
Allocation blocks have normally been used to retain priority and some provide
certainty about access to their allocation, for those first in time for consent allocations.
The purpose of a C Block would be to provide access to water to consent holders who
come later.
A C Block could be used to further enhance the possibility of keeping flows within the
preferred flow range. It should be contiguous with the B Block or there could be a gap
and still keep the flow in the preferred range if the B Block was aimed at keeping
flows at the lower end of the preferred range.
Any C allocation Block should be subject to the same rules as indicated in Section 4.6.
A C Block would provide the opportunity for new users to gain access to water should
the B Block allocation be fully allocated. However it would be quite unreliable if there
was a 20 m3s-1 B Block allocation as water could start to be taken ~36 % of the time.
See section 6.5 for more data on reliability of supply.
6.
Flow simulations
The flow simulations are for the Mandamus confluence to Pahau confluence reach
(see Section 1.1). The effects of alternative B Block allocations and flow gaps
Hurunui River: B Block allocation review
15
between the A and B Block allocations were simulated using the following data and
assumptions:
•
The flow record from the Hurunui River at Mandamus (site number 65104)
for 1957 to 2007 inclusive was used as the basis for the simulations and was
assumed to represent the natural or unmodified flow.
•
That the “variation 8” A Block minimum flows, based on information from
ECan, are:
o
15 m3s-1 for January and April to August,
o
12 m3s-1 for February and March and,
o
20 m3s-1 for September to December.
•
That the A Block allocation from September to May is 6.2 m3s-1, the A Block
allocation for June to August is 15 m3s-1 and there is no significant take of
stock water that needs to be taken into account. The simulations assume the
water is taken (all year) whenever flows are above the minimum monthly
flows as the resource consents allow the water to be taken all year.
•
That B block allocations would be taken all year, whenever flows permit.
•
Four scenarios with B block allocations of 5, 10, 15 and 20 m3s-1 were
simulated without a gap between the A and B block allocations.
•
Three scenarios with gaps of 0, 6.5 and 10 m3s-1 between the A Block and B
Blocks were simulated with a B block allocation of 10 m3s-1.
The flows were simulated using the simulation facility (PSIM) of the time dependent
data processing and archiving software TIDEDA.
6.1.
The effect of different size B Block allocations
Figure 4 shows flow duration curves for the whole year for each block size scenario,
the effect of increasing the size of the total allocation without gap between the A and
B blocks is evident. The predominant effect of increasing the B Block allocations is to
increase the duration that flow is flat lined at the minimum flows of 12 m3s-1, 15 m3s-1
and 20 m3s-1 (Table 1). With reference to Figure 3, flatlining the flow at flows equal to
Hurunui River: B Block allocation review
16
60
All year
River bed birds
50
Salmon
Flow m3/s
40
30
20
10
0
0
Figure 4:
20
40
60
80
100
Percentage of time flow is not exceeded
site
65104 Hurunui
Unmodified
flow at Mandamus Flow m3/s
19570101 094453 to 20071231 231500
site
1112 Var8
min,
6.2 A
block,
20 no
B block
Variation
8 min.
flows,
6.2
m3s-1nogap,
A Block,
gap, 20 m3s-1 B Block
Flow m3/s 19570101 094453 to 20071231 231500
site
1102 Var8
min,
6.2 A
block,
15 B
Variation
8 min.
flows,
6.2
m3s-1nogap
A Block,
noblock
gap, 15 m3s-1 B Block
Flow m3/s 19570101 094453 to 20071231 231500
site
1082 Var8
min,
6.2 A
block,
10 B
Variation
8 min.
flows,
6.2
m3s-1nogap
A Block,
noblock
gap, 10 m3s-1 B Block
Flow m3/s 19570101 094453 to 20071231 231500
3 -1
site
1092 Var8
min,
6.2 A
block,
5 Bno
block
Variation
8 min.
flows,
6.2
m3s-1nogap
A Block,
gap,Flow
5 mm3/s
s B Block
19570101 094453 to 20071231 231500
site
1062 Var8
min,
6.2 A
block
m3/s
Variation
8 min.
flows,
6.2
m3s-1Flow
A Block
19570101 094453 to 20071231 231500
Full year flow duration curves for the Hurunui River at Mandamus for the
unmodified flow, the A Block (6.2 m3s- and 15 m3s- June to September) and B
Blocks of 5, 10, 15 and 20 m3s-1, for (1957-2007).
Hurunui River: B Block allocation review
17
or greater than 15 m3s1 puts the flow in the suitable range for salmon passage, but the
time the flow is in the range for river bed nesting birds reduces as the total allocation
increases.
Table 1 shows the percent of the year when the flow is flat-lined (constant). The
duration at each level is primarily a reflection of the number of months per year that
the level is the A Block minimum flow.
Table 1:
The effect of different sized B Block allocations on flow statistics (full year, 19672007).
Mean flow
Median flow
Naturalised
flow
m3s-1
A Block
6.5 &15
m3s-1
A Block
6.5 &15
m3s-1
5 m3s-1 B
Block
52.2
44.7
40.9
37.6
35.0
32.7
A Block
6.5 &15
3 -1
ms
10 m3s-1 B
Block
A Block
6.5 &15
3 -1
ms
15 m3s-1 B
Block
A Block
6.5 &15
3 -1
ms
20 m3s-1 B
Block
39.1
30
26
21
20.0
20
3 -1
na
3
6
9
11
12
3 -1
na
10
17
23
28
32
3 -1
na
4
6
9
7.5
14
% time at 12 m s
% time at 15 m s
% time at 20 m s
Please note that Tables 1 to 3 contain rows that indicate the duration that flows are in
particular ranges.
6.2.
The effect of different sized gaps between the A and B Block allocations
The effect of different sized gaps between the A Block and B Block allocations is
illustrated with a single B Block size of 10 m3s-1, and gaps of 0, 6.5 and 10 m3s-1. The
minimum flow for the B Block varies by month and with the size of the gap.
Figure 5 shows flow duration curves for the full year for the unmodified flow, an A
Block and a 10 m3s-1 B Block with gaps of 0, 6.5 and 10 m3s-1 between the A and B
Blocks. It can be seen that having gaps increases the duration that the flow is in the
best range for river best nesting birds and for jet boats.
Table 2 shows the effects of gaps on annual flow statistics. There is flatlining, but it
occurs at different flows depending on the minimum flow and the size of gap (Figure
5). The durations and flow rates for flatlining are shown in the table. For the 10 m3s-1
take, as the gap size increases so does the mean and median flow of the residual river.
Hurunui River: B Block allocation review
18
60
All year
50
River bed birds
Salmon
Flow m3/s
40
30
20
10
0
0
20
40
60
80
100
Percentage of time flow is not exceeded
site 65104 Hurunui at Mandamus Flow m3/s
19570101 094453 to 20071231 231500
site 1082 Var8 min, 6.2 A block, nogap 10 B block
Flow
m3/s 19570101
094453 to 20071231 231500
Unmodified
flow
site 1072 Var8 min, 6.2 A block, 6.5 gap, 10 B block
Flow m3/s 19570101 094453 to3 20071231
231500
Variation 8 min. flows, 6.2 m s-1 A Block, no gap, 10 m3s-1 B Block
site 1122 Var8 min, 6.2 A block, 10gap 10 B block
Flow m3/s 19570101 094453 to3 20071231
231500
Variation 8 min. flows, 6.2 m s-1A Block, 6.5 m3s-1 gap, 10 m3s-1 B Block
site 1062 Var8 min, 6.2 A block Flow m3/s
19570101 094453 to 20071231
231500
Variation 8 min. flows, 6.2 m3s-1 A Block, 10 m3s-1 gap, 10 m3s-1 B Block
Variation 8 minimum flows, 6.2 m3s-1 A Block
Figure 5:
Flow duration curves for the unmodified flow, the A Block of 6.2 m3s-1 from
September to May an 15 m3s-11 from July to August Block plus B Block takes of
10 m3s-1 with gaps of 0, 6.5 and 10 m3s-1 between the A and B Blocks (1957-2007).
Hurunui River: B Block allocation review
19
Table 2:
The effect of different sized gaps between A and B Block allocations for a 10 m3s-1
B Block allocation for the whole year (1957-2007).
A
10 m3s-1 B
6.5 m3s-1 gap
A
3 -1
10 m s B
10 m3s-1 gap
Unmodified
A Block
A
3 -1
10 m s B
0 gap
Mean flow
52.7
44.7
37.6
38.8
39.3
Median flow
39.1
30.0
21.0
24.0
25.0
Flat-line time (percent
of time at flow rate)
na
3% @
3 -1
12 m s
21% @
12 m3s-1
3% @
12 m3s-1
Flat-line time (percent
of time at flow rate)
na
10% @ 15
m3s-1
23% @ 15
m3s-1
16% @ 15 m3s-1
16% @ 15 m3s-1
Flat-line time (percent
of time at flow rate)
na
4% @ 20
3 -1
ms
9% @ 20
m3s-1
5% @ 18 m3s-1
4% @ 20 m3s-1
Flat-line time (percent
of time at flow rate)
na
na
na
3 -1
6% @ 21.5 m s
5% @ 22 m3s-1
Flat-line time (percent
of time at flow rate)
na
na
na
3 -1
6% @ 26.5 m s
6% @ 25 m3s-1
Flat-line time (percent
of time at flow rate)
na
na
na
na
3% @ 30 m3s-1
% time at 15-40 m3s-1
46
57
62
67
67
3 -1
% time at 25-40 m s
32
25
10
22
22
3% @
12 m3s-1
This indicates that the volume able to be taken reduces with increasing gap size. The
time in the preferred flow ranges varies irregularly with gap size and preferred flow
range but is greater than for the naturalised flows and A Block take for salmon
passage (and boating) with the larger gaps having the most time in the preferred range.
For riverbed nesting birds the time in the preferred flow range is greatest for the
unmodified flows and the A block allocation, but if there is a B Block allocation
having a gap between the blocks puts the flow in the preferred range for longer.
Figure 6 shows flow duration curves for the various gap options for September to
December, when river bed nesting birds are breeding and rearing chicks. It can be seen
that either the 6.5 or 10 m3s-1 gap option results in the same duration in the optimum
flow range (between the two horizontal lines), and that the duration within that range
is longer than for the unmodified flow and the A block allocation options. By
interpolating between the 0 and 6.5 m3s-1 gap options it can be seen that a 5 m3s-1 gap
would satisfy the minimum flow criteria for riverbed nesting birds. Reducing the gap
to 5 m3s-1 would slightly increase the volume available for abstraction without
reducing the duration of flows within the optimum range. However, increasing the gap
would increase the number of islands for riverbed nesting birds.
Hurunui River: B Block allocation review
20
60
River bed birds S,O,N,D
50
Flow m3/s
40
30
20
10
0
0
Figure 6:
20
40
60
80
100
Percentage of time flow is not exceeded
site 65104 Hurunui at Mandamus Flow m3/s
Unmodified094453
flow to 20071231 231500
19570101
site 1082 Var8 min, 6.2 A block,
nogap 10 B block
Variation
min. flows,
6.2 m3to
s-120071231
A Block, no231500
gap, 10 m3s-1 B Block
Flow
m3/s 819570101
094453
site 1072 Var8 min, 6.2 A block,
6.5 gap, 10 B block
s-120071231
A Block, 6.5
m3s-1 gap, 10 m3s-1 B Block
Variation
min. flows,
6.2 m3to
Flow
m3/s 819570101
094453
231500
site
1122 Var8
min,
6.2 6.2
A block,
1010
B block
A Block,
m3s-1, 10 m3s-1 B Block
Variation
8 min.
flows,
m3s-110gap
Flow m3/s 19570101 094453 to 20071231 231500
3 -1 m3/s
site
1062 Var8
min, 6.2
A block
Flow
s A Block
Variation
8 minimum
flows,
6.2 m
19570101 094453 to 20071231 231500
Flow duration curves for the unmodified flow, the A Block allocation of 6.2 m3s-1
and B Block takes of 10 m3s-1 with gaps of 0, 6.5 and 10 m3s-1 between the A and B
Blocks for September to December (1957-2007). The optimum flows for river bed
nesting birds are those between the two horizontal black lines.
Figure 7 shows flow duration curves for the various gap options for December to
March, when the river is most likely to be used for jet boating and kayaking. It can be
seen that the 10 m3s-1 gap option gives the maximum duration in the optimum flow
range (between the two horizontal lines), and that the duration within that range is
longer than for the unmodified flow and the A block allocation options. By
interpolating between the 6.5 m3s-1 and 10 m3s-1 gap options it can be seen that an 8
m3s-1 gap would satisfy the flow criteria for jet boating and kayaking. Reducing the
gap to 8 m3s-1 would slightly increase the volume available for abstraction without
reducing the duration of flows within the optimum range.
Hurunui River: B Block allocation review
21
60
Jet boats D,J, F, M
50
Flow m3/s
40
30
20
10
0
0
Figure 7:
20
40
60
80
100
Percentage of time flow is not exceeded
of time the flow is not exceeded
site
65104 Hurunui
at MandamusPercentage
Flow m3/s
Unmodified
flow
19570101 094453 to 20071231 231500
3 -1 nogap 10 B block 3 -1
site
10828Var8
6.2
Am
block,
Variation
min. min,
flows,
6.2
s A Block, no gap, 10 m s B Block
Flow m3/s 19570101 094453 to 20071231 231500
3 -1 6.5 gap, 10 B
-1
site
10728Var8
6.2
Am
block,
Variation
min. min,
flows.
6.2
s A Block, 6.5 m3sblock
gap, 10 m3s-1 B Block
Flow m3/s 19570101 094453 to 20071231 231500
3 -1
site
11228Var8
6.2
Am
block,
10 m
B3block
Variation
min. min,
flows,
6.2
s A 10gap
Block, 10
s-1, 10 m3s-1 B Block
Flow m3/s 19570101 094453 to 20071231 231500
3 -1
site
10628Var8
6.2
Am
block
Flow m3/s
s A Block
Variation
min. min,
flows,
6.2
19570101 094453 to 20071231 231500
Flow duration curves for the unmodified flow, the A Block allocation of 6.2 m3s-1
and B Block takes of 10 m3s-1 with gaps of 0, 6.5 and 10 m3s-1 between the A and B
Blocks for September to December (1957-2007). The optimum flows for jet boats
and kayaks are those between the two horizontal black lines.
Hurunui River: B Block allocation review
22
Figure 8 shows flow duration curves for the various gap options for December to May,
when adult salmon are migrating from the sea to spawning areas upstream of
Mandamus. It can be seen that the 6.5 m3s-1 and 10 m3s-1 gap options give the
maximum duration in the optimum flow range (on and between the two horizontal
lines) and the maximum volume for abstraction and a similar duration within that
range to the unmodified flow and the A block allocation options. A 3 m3s-1 gap would
provide the same time in the optimal zone as the larger gap options
60
Salmon D,J, F, M, A, M.
50
Flow m3/s
40
30
20
10
0
0
40
60
80
100
Percentage of time flow is not exceeded
Percent of time flow is not exceeded
site 65104 Hurunui at Mandamus Flow m3/s
Unmodified
flow 094453 to 20071231 231500
19570101
site 1082 Var8 min, 6.2 A block, nogap 10 B block
3 -1
s A to
Block,
no gap,
10 m3s-1 B Block
VariationFlow
8 min.
6.2 m
m3/sflows,
19570101
094453
20071231
231500
site 1072 Var8 min, 6.2 3A -1
block, 6.5 gap, 10 B3 block
s A to
Block,
6.5 m
s-1 gap, 10 m3s-1 B Block
VariationFlow
8 min.
6.2 m
m3/sflows,
19570101
094453
20071231
231500
site 1122 Var8 min, 6.2 3A -1
block, 10gap 10 B3block
VariationFlow
8 min.
6.2 m
s A to
Block,
10 m231500
s-1, 10 m3s-1 B Block
m3/sflows,
19570101
094453
20071231
site 1062 Var8 min, 6.2 3A -1
block Flow m3/s
s A Block
Variation19570101
8 min. flows,
6.2tom
094453
20071231
231500
Figure 8:
20
Flow duration curves for the unmodified flow, the A Block allocation of 6.2 m3s-1
and B Block takes of 10 m3s-1 with gaps of 0, 6.5 and 10 m3s-1 between the A and B
Blocks for December to May (1957-2007). The best flows for salmon are those
between the two horizontal black lines. Flows at the bottom of the range are
adequate for salmon passage while those at the top of the range are more suitable
for angling.
Hurunui River: B Block allocation review
23
Instream habitat modelling down-stream of SH7 indicates that 15 m3s-1 will provide
continuous fish passage depths greater than the 0.25 m minimum depth requirements
for salmon passage (Hayes 2008). Nevertheless radio tagging has indicated that
salmon more slowly migrate up Waimakariri River at low flows than during freshes
(Glova and Docherty 1986). Long periods of low flows delay upstream migration,
cause extra abrasion of their bodies and ultimately affect reproductive success (Hayes
2008).
Table 3 lists the time the flow is in the appropriate range for each instream use for the
period of that use for the various flow options. For riverbed nesting birds gaps of 5-10
m3s-1-will give far more time in the preferred flow range than other options including
the unmodified flow. For jet boats and kayaks there is less difference between the
options, but if there is a 10 m3s-1 B Block then a gap of 8-10 m3s-1 provides the longest
time in the preferred flow range. For salmon passage a gap of 5-10 m3s-1 provides the
longest time in the preferred flow range when there is a 10 m3s-1 B Block.
Table 3:
List of the mean and median flows and the durations that flows are in the
appropriate range for various instream uses for the appropriate season.
Unmodified
A Block
A
3 -1
10 m s B
0 gap
A
3 -1
10 m s B
3 -1
6.5 m s gap
A
3 -1
10 m s B
3 -1
10 m s gap
67.5
60.9
52.6
53.8
54.4
51.4
45.0
35
35
35
6
15
45
17
17
27
30
17
41
41
67
55
42
42
42
42.9
36.8
30.1
31.9
32.7
32.4
26
20
21
22
16
31
50
42
31
49
43
32
40
51
35
26
18
18
18
43.6
37.2
31.0
32.8
33.5
32.5
26
19
21
24
Riverbed birds
September - December
Mean flow
Median flow
3 -1
% time at <25 m s
3 -1
% time at 25 -40 m s
3 -1
% time at >40 m s
Jet boats and kayaks
December - March
Mean flow
Median flow
3 -1
% time at <20 m s
3 -1
% time at 20 -40 m s
3 -1
% time at >40 m s
Salmon
December - May
Mean flow
Median flow
3 -1
% time at <15 m s
3 -1
% time at 15 -40 m s
3 -1
% time at >40 m s
Hurunui River: B Block allocation review
6
11
22
11
11
59
62
58
69
69
35
27
20
20
20
24
6.3.
6.4.
Summary of effects of gaps between the A and B Blocks
•
The minimum gap size to provide optimum flows for riverbed nesting bids is
5 m3s-1.
•
The minimum gap size to provide optimum flows for jet boats and kayaks is 8
m3s-1.
•
The minimum gap size to provide optimum flows for salmon passage is 3
m3s-1.
•
Optimizing the gaps would result in a 5 m3s-1 gap for September to January for
riverbed birds and jet boats and an 8 m3s-1 gap for February and March for jet
boats and kayaks, with no gap from April to August. These gaps would also
put flows in the optimum range for salmon passage.
•
If jet boat and kayak passage was not seen as a priority for the Amuri Plan
reach of the river then there could be a gap of a least 5 m3s-1 for September to
March and no gap for April to August.
Potential abstraction volumes for the B Block scenarios
Table 4 shows the maximum take volumes for the A Block take plus selected B Block
take scenarios. The larger the rate of take the larger the volume able to be taken.
Increasing the gap between allocation the A and B Blocks reduces the volume of take.
For example, a 10 m3s-1 take with a 10 m3s-1 gap would result in ~12% less water able
to be taken than having no gap.
Table 4:
Maximum take volumes for selected B Block take scenarios.
B Block take rate m3s-1
3 -1
(m s )
Potential take
(m3 x 106)
No gap
0
237
No gap
5
351
No gap
10
461
No gap
15
543
No gap
20
615
0 m3s-1 gap
10
461
6.5 m s gap
10
423
3 -1
10
407
Take scenario
3 -1
10 m s gap
Hurunui River: B Block allocation review
25
6.5.
Reliability of supply
Table 5 shows the annual reliability of supply for selected take scenarios. Column
three lists the percentage of time that the A Block take can start to be taken and
column four the percentage of time that the full take can occur. The A Block starts to
become available for 99% of the time. As the size of the take increases the reliability
of supply for the full take decreases. Having gaps reduces the reliability of full supply
and as the size of the gap increases the reliability of full supply decreases. The
reliability of supply for a September to April irrigation season would be lower than
that shown in Table 5.
Table 5:
The reliability of supply of selected allocation scenarios. Column three lists the
percentage of time that the total take can start to be taken and column 4 the
percentage of time that the full take can occur during the full year
B Block take rate
(m3s-1)
Start take
% time take available
Full take
% time take available
No gap
0
99
71
No gap
5
99
61
No gap
10
99
50
No gap
15
99
42
No gap
20
99
36
0 m3s-1 gap
10
99
50
6.5 m s gap
10
99
40
3 -1
10
99
37
Take scenario
3 -1
10 m s gap
Note that Table 5 does not take into account any reduction in supply that might occur
because of any flushing rule that might be applied.
6.6.
Conclusions from the simulations
Optimizing the gaps would result in a 5 m3s-1 gap for September to January for
riverbed birds and jet boats and an 8 m3s-1 gap for February and March for jet boats
and kayaks, with no gap from April to August. These gaps would also put flows in the
optimum range for salmon passage.
As the allocation increases, so does the potential take, but the reliability of full supply
goes down significantly. With a 10 m3s-1 B Block take the volume of water able to be
taken and reliability of full supply reduces by 12% and 26% respectively as the flow
gap between allocation blocks increases from 0 to 10 m3s-1.
Hurunui River: B Block allocation review
26
7.
Discussion
One outcome from the study was to recommend the gaps between allocation blocks
only for September to March as the winter minimum flows have been set to maintain
the instream values and there are no values that require higher flows. One outcome of
such a gap suspension is the likelihood of increased flatlining in winter if the allocated
water is diverted for storage or some other reason. Flows are often low in winter
because the precipitation is held in storage as snow and this increases the likelihood of
low flows and the probability of having prolonged flatlining. Prolonged flat lining is
conducive to the proliferation of long filamentous green algae and cyanobacteria mats
and this possibility needs to be managed. The appropriate management for this issue is
to allow any freshes/floods occurring after an appropriate period of flatling or low
flows (e.g., 21 days) to move through the river without being harvested, rather than to
maintain a gap as a gap would not allow enough water to remain in the river to flush
it.
As detailed in Section 3.2 there is room for debate about the best flow and hence the
size of the gap from September to December to provide the best combination of
nesting and feeding habitat for riverbed birds. So although this report appears to
favour a 5 m3s-1 gap to provide a B block minimum flow of 25 m3s-1 this is a minimum
requirement and the community may wish to provide greater protection, albeit at the
expense of reliability of supply for abstractors.
8.
Recommended B and C Block flow regimes
•
Periphyton biomass should be monitored after 21 days of flat lining and if
periphyton biomass reaches nuisance levels, there should be no B or C Block
takes during freshes or floods until the measured flow has exceeded 80 m3s-1
or has persisted for 2 days if the peak flow rate does not reach 80 m3s-1.
•
Riverbed levels should be monitored in the vicinity of large takes and if
aggradation occurs, consent conditions should be revised so that when the
naturalised flow is more than 120 m3s-1, B Block abstractions should cease
until the flow has reduced to less than 120 m3s-1.
•
The maximum B Block allocation should be 10 m3s-1 with at least a 5 m3s-1
gap between the B Block and A Block allocations during September to
January and an 8 m3s-1 gap in February and March.
Hurunui River: B Block allocation review
27
9.
•
A maximum C Block allocation of 5 m3s-1 with no gap between B and C
Blocks.
•
A gap between A and B Blocks is not required from April to August as the
minimum flow for this period of 15 m3s-1 is sufficient for salmon passage and
there are no other instream values that require higher flows during this time.
The purpose of the gap removal would be to increase the reliability of supply
of abstractions.
Summary
The values associated with instream uses and community concerns about abstraction
from the Hurunui River were reviewed. From this information the critical flows and
their timing were assessed.
The effects on instream values of alternative approaches to setting a flow regime were
discussed.
Simulations were made of the alternative take regimes and assessed against the critical
flows.
The preferred flow regime allowed for:
•
Periphyton and fine sediment flushing,
•
Preservation of channel forming and bedload transporting flows,
•
A maximum B Block allocation of 10 m3s-1 with at least a 5 to 8 m3s-1 gap
between the A and B allocation blocks,
•
A maximum C Block allocation of 5 m3s-1 with no gap between the B and C
allocation blocks,
•
Suspension of the gap requirement between A and B Blocks from April to
August.
Hurunui River: B Block allocation review
28
10. Acknowledgements
The constructive comments of NIWA and Environment Canterbury staff are gratefully
acknowledged.
11. References
Adams, R.H. (2008). Evidence presented to the Central Plains Water Enhancement
Scheme Hearings. http://www.ecan.govt.nz/Resource+Consents/Central+Plains+
Water/PlansAndReports.htm.
Biggs, B.J.F. (2000). Eutrophication of streams and rivers: dissolved nutrientchlorophyll relationships for benthic algae. Journal of the North American
Benthological Society 19(1): 17-31.
Biggs, B.J.F.; Stockseth, S. (1996). Hydraulic habitat suitability for periphyton in
rivers. Regulated Rivers 12, 251-261.
Boffa Miskell and Urtica Consulting. (2007). Black-fronted tern trial: effects of flow
and predator control on breeding success. Report prepared for Meridian Energy
Ltd, April 2007. 15 p
Davies, T.R.H. (1988). Modification of bedload transport capacity in braided rivers.
Journal of Hydrology (New Zealand) 45: 63-82.
Duncan, M.J. (2007). Hurunui River habitat 2-D modelling: habitat for periphyton.
NIWA Client Report: CHC2007-039 for Environment Canterbury, Christchurch.
Duncan, M.J. (2008). Waimakariri River: B/C Block allocation review. NIWA Client
Report CHC 2008-107. 27 p.
Duncan, M.J.; Bind J. (2008). Waimakariri River bed sediment movement for
ecological resetting. NIWA Client Report: CHC2008-016. 32 p.
Duncan, M.J.; Hughey, K.F.D.; Cochrane, C.H.; Bind, J. (2008). River modelling to
better manage mammalian predator access to islands in braided rivers. Pp.
487–492. In: Sustainable Hydrology for the 21st Century. Proceedings of the
10th BHS National Hydrology Symposium, Exeter.
Duncan, M.J.; Shankar, U. (2004). Hurunui River habitat 2-D modelling. Technical
Report U04/19, prepared by NIWA for Environment Canterbury, Christchurch.
Hurunui River: B Block allocation review
29
Familton, H. (2007). Planning Report Hurunui River and tributaries: environmental
flow and water allocation. ECan Report no. U07/60. 259 p. ISBN 978-1-86937687-1.
Glova, R.G.; Docherty, C. (1986). Waimakariri River – radio tracking of adult salmon.
Freshwater Catch 29: 4-5.
Greenaway, R.; Associates.( 2001). Hurunui River Recreational study 2000/01. Client
report 936, Technical Report U01/19 Environment Canterbury and North
Canterbury Fish and Game Council, Christchurch.
Hayes, J.W. (2008). Evidence presented to the Central Plains Water Enhancement
Scheme Hearings. http://www.ecan.govt.nz/Resource+Consents/Central+Plains
+Water/PlansAndReports.htm.
Mosley, M.P. (2002). Hurunui River: Instream values and flow regime. Report R02/1.
Environment Canterbury, Christchurch. ISBM1-86937-437-1
Olsen, D.A. (2008). Evidence presented to the Central Plains Water Enhancement
Scheme Hearings. http://www.ecan.govt.nz/Resource+Consents/Central+Plains
+Water/PlansAndReports.htm.
Sagar, P.M. (1983). Invertebrate colonisation of previously dry channels in the Rakaia
River. New Zealand Journal of Marine and Freshwater Research 17: 377-386.
Hurunui River: B Block allocation review
30
Appendix 1:
Project brief
Environment Canterbury Project Brief for a technical report on the Hurunui
River to assess the environmental effects of different sizes of the B allocation
block and appropriate flow regime requirements to minimise these effects
1.
Background
The Hurunui River instream values were reviewed by Mosley (2002) and he
recommended a minimum monthly flow regime. Duncan and Shankar (2004) used 2D
modelling as a basis for IFIM assessment of the physical habitat requirements for fish,
invertebrates, riverine birds, recreation and periphyton (Duncan 2007). Duncan and
Shankar (2004) also recommended minimum monthly flows.
Partly on basis of these reports ECan settled on a monthly minimum flow regime and
an A Block allocation. That minimum monthly regime is now under review and there
is a need to consider a B Block allocation and the rules around that allocation, such as
the size of any flow gap between the A and B allocation blocks.
Small freshes are important for the river’s ecological health because they flush off
undesirable slimy periphyton growths that can smother the gravel during mid-late
summer when flows are lower and the water warmer. Freshes also help to flush fine
sediment that settles between the gravel, maintaining its suitability as habitat for
aquatic insect larvae that birds and fish feed on.
The proposed Variation 8 did include a 5 cumec gap between the A and B allocation
blocks, and this figure is being questioned by several submitters, who question the
need for and the justification for a gap.
Whatever sized B block is put into Variation 8, it is important that it does not reduce
the frequency, duration, and magnitude of these freshes to such an extent that the
aquatic ecosystem and other instream values are adversely affected.
2.
Tasks
•
Analyse different sizes of B block and their effect on: (a) flushing flows that
remove periphyton and fine sediment; (b) the availability of flows within the
desired flow range for salmon fishing; (c) the frequency and duration of
"flatlining" and whether this creates any specific issues eg promoting periphyton
growth, impacts if any on salmon /boat passage and riverine nesting birds
•
Determine whether there should be a gap between the A and B block, along with a
robust justification. This shall include the options of no gap and a gap of 5
cumecs.
•
Prepare a technical report that addresses the above points
•
The report to include:
•
An assessment of the key environmental and recreational values and the
preferred flow ranges for those values.
Hurunui River: B Block allocation review
31
•
Simulation of the effect of full year round abstractions of the existing A
Block allocation and proposed B Block allocations in the range 7.5, 10, 15,
and 20 m3s-1.
•
Estimates of the reliability of supply in terms of the % of time allocations
could be accessed.
The report should be based on earlier work “Waimakariri River B/C Block allocation
review”, ECan report R08/67, as discussed between Maurice Duncan and Herb
Familton.
3.
Outputs
The consultant is to provide the following:
•
A draft report three weeks ahead of the completion date
•
A copy of the final report as a bound copy; an unbound copy; and an
electronic copy
4.
Timetable for outputs
Draft report is to be received by ECan three weeks ahead of the final report
completion date. ECan staff will provide comments within 5 working days of
receiving the draft. A meeting may be needed during this period to discuss any issues
The date for receiving the final report is 29 February 2008.
5.
Price estimate
The work will be charged on a time and materials basis with an estimated price of
$10, 000, plus GST to be paid upon satisfactory completion of the contract.
However, because of the difficulty in accurately assessing the work required, a
variation of the contract may be needed should the work required cost more than
$10, 000. Any such variation is to be in writing, and is to be agreed by both parties,
prior to NIWA incurring any costs that exceed the initial contract price of $10, 000.
6.
Progress payments
Full payment upon receipt of the final report
7.
Contract management
The contract will be managed by Herb Familton for ECan.
8.
Information Provision
ECan shall supply NIWA with a copy of ECan Planning report R07/60 Hurunui River
and Tributaries: Environmental flow and water allocation. (2007).
Hurunui River: B Block allocation review
32