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HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL
Hume and
Dartmouth Dams
Operations Review
Options Paper
N O V E M B E R 1 9 9 8
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E PA N E L
Hume and
Dartmouth Dams
Operations Review
Options Paper
N O V E M B E R 1 9 9 8
Please note!
The deadline for
comment on this
paper is Wednesday
10 February 1999
For details see page 1 (‘About this Options Paper’)
iH U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
Published by: Hume and Dartmouth Dams Operations
Review Reference Panel
Postal address: c/- MDBC, GPO Box 409,
Canberra ACT 2601
Office location: c/- Murray-Darling Basin Commission,
2nd Floor, 7 Moore Street,
Canberra City,
Australian Capital Territory
Telephone: (02) 6279 0100;
international + 61 2 6279 0100
Facsimile: (02) 6248 8053;
international + 61 2 6248 8053
E-mail: info@mdbc.gov.au
Website: http://www.mdbc.gov.au
Map on cover: © Copyright Commonwealth of Australia 1985
Remainder of publication: © Copyright Murray-Darling Basin
Commission 1998
This document may be reproduced in whole or in part,
provided that the information in it is not sold for commercial
benefit and its source is acknowledged. Dissemination and
discussion of the document is encouraged. For further
copies and assistance contact the Reference Panel at the
above address.
ISBN 1 875 209 92 1
ii H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E WContents
1. About this options paper 3
2. Overview 5
3. Introduction 7
3.1 History of River Murray water regulation 7
3.2 Roles of Hume and Dartmouth storages 7
3.3 The Operations Review 8
3.4 Work related to the review 8
3.5 Community consultation 9
4. Water regulation issues 11
4.1 Identification of issues 11
4.2 Issues that do not involve competing claims for water 11
4.3 Issues that involve competing claims for water 12
5. Issues that do not involve competing claims for water 13
5.1 Economic impact of Dartmouth Dam on the Mitta Mitta valley 13
5.1.1 Effect of Dartmouth Dam on pasture productivity 13
5.1.2 Flood duration in the Mitta Mitta valley 14
5.1.3 Adverse effects on agricultural land at peak regulated flow 16
5.1.4 Erosion on the Mitta Mitta River 16
5.2 Economic impact of Hume Dam on the floodplain below 17
5.2.1 Adverse effects on agricultural land at peak regulated flow 17
5.2.2 The need for a comprehensive river management plan between Hume and Yarrawonga 17
5.3 Effect of dams on non-flow environmental values 19
5.3.1 Impact of Dartmouth Dam on water temperature and quality 19
5.3.2 Effects of regulated flows and rain rejections on natural drying cycles in wetlands 20
5.4 The need to better manage minimum flows downstream of Mildura 21
5.5 The need for improved communication 21
1H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
6. Issues that involve competing claims for water 23
6.1 Issues and approaches to solving them 23
6.2 Testing single operational changes 24
6.2.1 Natural conditions 26
6.2.2 Benchmark (B42800) 26
6.2.3 Fill and spill (B42810) 26
6.2.4 Provision of airspace (B46770) 27
6.2.5 Relaxed pre-release rules (B42840) 27
6.2.6 Translucent flows (B46750) 28
6.2.7 Use of Dartmouth power station during floods (B42801) 28
6.2.8 “Sharing the Murray” proposal for the Barmah-Millewa forest (B47850) 29
6.2.9 Increased pre-release from Hume Dam (B46160) 30
6.3 Scenarios outside the scope of the review 32
6.4 Combined scenarios 33
7. Summary of options and preliminary panel views 37
Appendix A: Terms of reference for the Operations Review 41
Appendix B: Reference panel 43
Appendix C: Key issues identified in scoping study 45
Appendix D: Details of “Backgrounder” papers 47
Appendix E: Issue register 49
Appendix F: Supporting documents and references 51
Glossary 53
2 H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E W1. About this options paper
In December 1996 the Murray-Darling modelling group has carried out the necessary
computer simulations.
Basin Ministerial Council agreed that This options paper is the result of the review to
November 1998. It describes the issues that have been
the way in which Hume and identified as needing attention, the way in which the
panel has gone about its task, the tensions that arise
Dartmouth dams are operated should because of competing objectives for managing the
be reviewed. regulated Murray, and possible improvements and
changes to the balance between competing objectives.
T he review has been guided by a reference panel
consisting of members representing different
interest groups and drawn from the general
At this stage the panel has reached no fixed
conclusions. The paper presents options, and in most
cases also presents a preliminary panel view.
community, and supported by relevant government The work to date now needs to be exposed to the
agencies. wider community.
The Murray-Darling Basin Commission appointed A series of public meetings will be held to present
the reference panel, and the panel’s final product will and explain the material in the paper, discuss the
be a report and recommendations to the Commission. options, and stimulate comment and feedback. The
However the panel is fully independent and its work panel expects to refine its views in the light of public
has not been influenced or directed by the comment before making its recommendations to
Commission, nor has the Commission considered or the Commission.
endorsed this options paper. Comments may be made to any member of the
The technical work has been managed by a small panel (see contact numbers in appendix B) or can be
project team. The team has utilised private addressed to Clarke Ballard, c/o Murray-Darling Basin
consultants, expertise available in government Commission, GPO Box 409, Canberra ACT 2601;
agencies and the internal resources of the Murray- telephone 02 6279 0176; fax 02 6230 6005;
Darling Basin Commission. The Commission’s email: clarke.ballard@mdbc.gov.au
The deadline for comment is 10 February 1999.
H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E W 32. Overview
The terms of reference of the review (see — for example, the fact that water temperatures are
lowered and steady regulated flows diminish
appendix A) are essentially to review the riverbank vegetation and can aggravate erosion.
operating procedures for the Hume and The panel has been able to arrive at preliminary views
on most of these issues, which tend to be reasonably
Dartmouth Dams and to recommend self-contained.
The second group of issues essentially revolves
how they might be amended to better around trade-offs between different management
address the competing objectives of water objectives, and judging where the balance between
them should lie. Computer models were used
supply, environmental enhancement and extensively to analyse different possible operational
scenarios. These led the panel to a fairly clear
flood mitigation. A broad perspective is understanding of the effects of each strategy and those
required, including consideration of a strategies — or packages of strategies — that might be
useful in achieving a different balance. However, no
wide range of economic, social and option was found that resulted in improvements from
the viewpoint of every interest group.
environmental factors. The panel has therefore been unable, so far, to
reach a definitive view on strategies that should be
T he reference panel visited many areas of interest
along the river, and spent a lot of time collecting
input from interested groups. The result was a long list
recommended. Despite this, it has formed a view that
the likely direction is towards a package that includes:
• arrangements for effectively watering the Barmah-
of issues that were seen as important by one or more Millewa forest using the water already allocated for
interest group. It was necessary to be rigorous in that purpose,
pursuing only those issues that are related to dam • continued “harmony” operation of Hume and
operation. Dartmouth storages,
Another difficulty in maintaining focus has been the • some form of varied pre-release strategy to mimic
other processes, programs and inquiries (such as the natural variability in flows below the storages, and
Snowy Inquiry and work on environmental flows) that • possibly the acquisition of easements over
are under way at present. It has been necessary to frequently flooded land between Hume and
minimise potential duplication and overlap by forming, Yarrawonga.
as clearly as possible, a picture of the boundaries
between the various activities and where the review fits Such a package could be implemented with minor
into the larger picture. environmental benefits and little adverse effect on
The panel has found that issues fall into two distinct consumptive users, beyond that already in train because
groups: those that do not involve finding a balance of the water already committed to Barmah-Millewa
between competing claims to water, and those that do. watering. However, there would be further environmental
The first group of issues includes: benefits, and further adverse effects on consumptive use,
• the need for better communication between the if pre-release targets were revised to introduce a higher-
Commission’s operational arm and interested than-current risk of storages failing to fill.
community groups; Floodplain dwellers would obtain some benefit from
• economic impacts of the dams on human uses of these strategies, but those benefits would not
the floodplains below them; necessarily increase as the specified risk of storages
• management of flow variability in the river failing to fill was increased.
downstream; and The panel seeks opinions from the wider
• environmental impacts of the dams (excluding the community on where the balance between the various
impacts of extraction of water further downstream) competing interests should lie.
H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E W 53. Introduction
3.1 History of River Murray water regulation • erosion was increased by high regulated flows in
In its natural state, the Murray was quite different from some reaches of the river system.
the present regulated river. During severe droughts it Many of these impacts were unforseen when construction
was sometimes reduced to a chain of waterholes, but of major storages commenced. The community has
flows generally followed a yearly cycle. This included generally considered that benefits of river regulation
late winter and spring flooding in most years, with high greatly outweigh the costs. With increased knowledge of
flows continuing into summer and then gradually impacts caused by our actions, however, community
receding until, between February and May, the flow values have changed. Therefore, the way in which the
was reduced in places to a small saline stream. The Murray is regulated may need to be adjusted to take
Murray was too unreliable in that state to allow its account of these changes in community attitudes towards
valley to be intensively settled. riverine health.
Regulation of the Murray by the construction of
3.2 Roles of Hume and Dartmouth storages
large storages has guaranteed a reliable supply of water,
which has contributed greatly to the development and Hume storage is the primary regulating storage
prosperity of the region. operated by the Murray-Darling Basin Commission (the
Without the Hume Dam (completed in 1936), the Commission). Hume is drawn down in the summer
natural River Murray would almost certainly have and autumn of every year. In contrast, Dartmouth
ceased to flow in 1939, 1945, 1968 and 1983. Instead, a storage (completed in 1979) is primarily used as a
flow has been maintained along the river even during reserve storage to supplement Hume in dry years or
severe droughts. Without this regulation of water flow sequences of years. Dartmouth has a less regular
much of the development and prosperity of the region annual cycle of operation than Hume, and its levels
would not have been realised. tend to reflect longer cycles of wet and dry climate. In
The largest economic benefit of the storages has been the long term it is expected to be full or close to full in
a secure supply of water for irrigation and other about 30 percent of years, but it may remain below full
purposes. The value of irrigated agricultural production for periods of many years.
from the regulated Murray system is in the order of $700 Although the primary purpose of Hume and
million annually. Many towns and cities, the largest of Dartmouth is to store water for consumptive use, they
which is Adelaide, also depend on the Murray for their are also operated to mitigate flooding in the valleys
water supply. The regulation of Murray flows has also: below them. The two main strategies used to achieve
• greatly reduced extremes in salinity levels that this are pre-releases and harmony operation.
occurred under natural conditions; Pre-releases may be made in the winter or spring if
• mitigated flooding that would have affected human storage levels and inflows are high and the storage is
activities on the floodplain; and certain, or almost certain, to fill. The aim is to delay
• enhanced recreational opportunities. filling and so provide additional flood mitigation.
However, regulation has not been without cost: Harmony operation is the transfer of water from
• valuable land was flooded to provide storages; Dartmouth to Hume when the level of Dartmouth is
• weirs and storages raised and maintained water high. Harmony operation provides more flood
levels, causing salinisation and drowning trees; mitigation below Dartmouth Dam and enhances
• wetlands became too wet or too dry; recreational use of Lake Hume without jeopardising
• diversity of in-stream biota was reduced by release water supply. Harmony rules are complex, but in
of cold water; general tend to equalise the chance of spill of the
• more water in summer and less in winter reversed two storages.
the natural seasonality of flows; Operational principles and rules are described in
• natural flow variability and flooding were suppressed; more detail in background papers which were
• red gum forest growth and regeneration were distributed as the review progressed and can be found in
adversely affected by reduced spring flooding; and the support papers (see appendix F).
H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E W 7H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
3.3 The Operations Review make sure that duplication does not occur, but some
Against the above background, and because of overlaps are unavoidable.
The most important and relevant other work
suggestions from landholders below the two dams, the
currently under way includes the following:
operation of Hume and Dartmouth Dams has been the
• Development of River Murray bulk water
subject of a detailed review. This document is the result
entitlements in Victoria, which is well advanced —
to date of the review process.
including proposals for an enhanced environmental
The Murray-Darling Basin Ministerial Council
entitlement for the Barmah-Millewa forest.
defined the terms of reference for the review in
• Catchment-by-catchment development of river flow
December 1996, as shown in appendix A. and water quality objectives, which is under way in New
To oversee the review and ensure that all views were South Wales but has yet to be applied to the Murray.
represented, the Commission appointed a reference • An inquiry into the need for environmental releases
panel. Panel members represent various interested from the Snowy Scheme. The results of this inquiry
community groups and agencies (see appendix B) and have the potential to decrease water passed to the
have been fully involved in all aspects of the project. Murray. Concurrently, relaxation of current fixed
The final product of the review will be a report (to be water proportions passed by the Snowy Scheme to
prepared after further consultation) that the panel will the Murray and Tumut rivers is being examined.
present to the Commission. • An Interstate Working Group on River Murray
Flows has been established to develop a River
3.4 Work related to the review Murray flow management plan that balances
human and environmental needs. Some work
To fully address the terms of reference in this review, it
conducted by the Operations Review — in
is tempting to expand the review to consider:
particular, the modelling tools developed for the
• operation of the whole river system; review — is likely to augment the work of the
• water allocations and in-stream flows throughout Interstate Working Group.
the Murray; and To ensure that the scope of this review was
• the impacts of the Snowy Mountains Scheme and achievable in an a reasonable time-frame, the review
possible changes in its operation, etc. has concentrated on issues that can actually be
This would create an immense and unrealistic task and affected by the way in which Hume and Dartmouth
overlap with work being undertaken by other groups. It Dams are operated. Figure 1 illustrates the manner in
is important to be aware of other work in progress to which the various activities interact.
Figure 1: River Murray Flow Management
Stand-alone solutions
Hume and Dartmouth Dams from Operations Review
Operations Review
Inputs including:
Scientific Panel report
NSW water reforms and
Murray-Darling Basin
Interstate Working Group
environmental flows
Commission
on River Murray Flows:
Barmah-Millewa forest plan • Community representation
Victorian bulk entitlement • Agency representation
process Murray-Darling Basin
• Dedicated resources
Snowy Inquiry Ministerial Council
Snowy corporatisation
Future
review River Murray Flow
process
Management Plan
8 H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E WH U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
3.5 Community consultation • A series of background papers was produced (see
An essential requirement for conducting the review has summaries in appendix D), describing aspects of the
been wide consultation with stakeholders in aspects of review or present operation. A register of interested
River Murray management defined in the terms of stakeholders was compiled and all background
reference. The broad membership of the reference panel papers and information about the review were
has been an important part of the consultative process. distributed to these people. The register is constantly
Members of the panel have ensured that their interest being updated. To add a name to the register, please
groups are informed of review progress. In addition, the call 1800 630 144.
following arrangements were made to ensure that
stakeholders’ interests were fully represented. This options paper is the next step in the consultative
• The Australian Research Centre for Water in Society process. It is intended to inform people of progress to
identified issues that people along the river saw as date and to gather feedback on the options being
important, as the first step in conducting the review. considered. The final step in the review will be the
Identification of these issues was achieved by preparation of a report to the Commission based on
telephone interviews with people from a broad responses to this paper.
range of interest groups. A summary of the issues
identified is shown in appendix C.
The closing date for comment on this paper is
Wednesday 10 February 1999.
H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E W 94. Water regulation issues
4.1 Identification of issues of this sort of issue are as follows:
As mentioned earlier, the Australian Research Centre • Provision of space in storages to provide flood
for Water in Society identified important issues as the mitigation. This space may decrease reliability of
first step in conducting the review. In addition, a supply to irrigators and remove environmentally
number of interest groups expressed a desire for the desirable flooding over the broader floodplain.
panel to visit their local areas. The panel visited these • Allowing a percentage of winter and spring inflow
areas, discussed issues with local people, and conducted through a storage to reinstate some elements of the
field inspections in conjunction with scheduled panel natural flow regime. This policy may be beneficial to
meetings. the environment but may reduce reliability of
Field inspections were conducted in the following areas: irrigation supply and increase downstream flooding
• the Mitta Mitta valley; of agricultural land.
• the floodplain between Hume and Yarrawonga; • A pure “fill and spill” policy maximising supply to
• municipal areas of Albury and Wodonga; irrigators. This policy provides fewer benefits to
• (by air) irrigation areas around Deniliquin and the floodplain agriculture and lack of flow variability for
Barmah-Millewa forest; and the environment — particularly before spill and
• the Sunraysia area. throughout non-spill years.
Written submissions were also received from: Issues identified by the review are shown in appendix E
• interested parties in the Mitta Mitta valley; in terms of:
• Mitta Mitta Community Action Group; • relevance of issue to each river reach;
• Upper North-East River Management Authority; • rating of issue according to relevance to the review;
• River Murray Action Group; • priority for computer modelling or other assessment
• Corowa caravan parks; by the review.
• New South Wales irrigators (Deniliquin area); The review addressed most issues that have a
• Victorian gravity irrigators; and medium or higher rating. In many cases, issues with
• interested parties of the Sunraysia Region of Victoria lower ratings will need to be addressed by other
and NSW. processes.
An issue register was compiled from these sources The panel has devised options and developed
(appendix E), and was progressively updated and preliminary views on many issues that do not involve
reviewed to identify all issues important to balancing competing claims for water. They are
stakeholders. included in this paper under each section and the
The issues were then categorised into two groups: conclusions. The panel expects to be able to make firm
• issues that do not involve balancing competing recommendations to the Commission about most of
claims, and these issues.
• issues that involve balancing competing claims. Firm views have not yet been reached on issues
Issues that do not involve balancing competing claims are that do require trade-offs between competing claims for
largely equity-based: they can be remedied by water. However, options have been narrowed to what
compensation, engineering works, etc., and do not the panel believes are realistic alternatives. The panel
require trade-offs between competing claims for water. needs wider input on the process by which these
An example is the adverse effect of high regulated flow competing claims should be balanced.
between Hume and Yarrawonga on agricultural land.
4.2 Issues that do not involve competing
Issues that involve balancing competing claims are concerned
claims for water
with balancing competing management objectives from
different stakeholders. These issues require analysis by Major issues that do not involve balancing competing
simulation modelling to compare different operating claims — i.e., issues that do not require balancing of
strategies. Some of the costs and benefits of each competing objectives — were identified as:
strategy can be quantified in dollar terms but some, • Economic impacts of Dartmouth Dam on the Mitta
particularly the environmental ones, cannot. Examples Mitta valley.
H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E W 11H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
• Impact of peak regulated flow on agricultural land. • providing regular and secure water for irrigation,
• Lack of comprehensive river management plans. domestic and industrial consumption;
• Impact of water releases from storages (particularly • mitigating floods below storages to maximise
Dartmouth) on water temperature and quality. economic benefits to human floodplain users; and
• Impact of regulated flows and rainfall rejections on • making releases in a way that better meets the
natural drying cycles in wetlands. needs of the riverine environment.
• Management of minimum flows downstream of Due to the complexity of issues that involve balancing
Mildura. competing claims, computer modelling has been used
• The need for improved communication. to assist in decision making. This modelling has allowed
These issues are addressed in the following sections objective analysis of changes in flow advocated by
(5.1 to 5.5). stakeholder groups in both dollar and non-dollar terms.
Considerable effort was devoted to developing a model
4.3 Issues that involve competing claims
examining results of operational changes in daily time-
for water
steps rather than through traditional models that work
The major issues identified as requiring simulation in monthly time-steps. This approach enables closer
modelling were a complex interaction of competing examination of benefits and costs of these operational
objectives broadly classified as follows: changes, particularly for flood events.
12 H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E W5. Issues that do not involve competing claims
for water
5.1 Economic impact of Dartmouth Dam on The panel has examined the economic impact of
the Mitta Mitta valley Dartmouth on agricultural profitability under the
There is no doubt that Dartmouth Dam has heavily following headings:
modified the hydrologic regime of the Mitta Mitta • Effect of Dartmouth Dam on pasture productivity.
valley. The change in flow regime since construction of • Flood duration in the Mitta Mitta valley.
Dartmouth Dam has probably been the largest change • Adverse effects on small areas of land at peak
experienced anywhere along the River Murray. regulated flow.
The flow regime differs from the natural regime in the • Erosion on the Mitta Mitta River.
following manner:
5.1.1 Effect of Dartmouth Dam on pasture
• very low flows (less than 500 ML/day) are less
productivity
common than under natural conditions;
• flows between 500 and 2500 ML/day are slightly Independently of the panel’s review, a study of the
more common over all, but less common in effect of Dartmouth Dam on pasture productivity in the
summer and autumn; Mitta Mitta valley was commissioned by Goulburn-
• flows between 2500 and 6000 ML/day are slightly Murray Water and the Commission. This study was
less common over all, but significantly more guided by a steering committee consisting mostly of
common in summer and autumn; local landholders and was required to determine:
• flows between 6000 ML/day and channel capacity • the effect of changes in river flow regimes and
of 10 000 ML/day are significantly more common subsequent water table levels on productivity of
— particularly in summer and autumn; and dryland and irrigated pastures;
• flows above channel capacity are less common, • the effect of water temperature on irrigated pasture
especially at high flood levels, but the duration of productivity; and
floods that do occur is extended at some levels. • water usage on irrigated pastures and the effects of
This simple description does not fully represent the impact water table variation on this usage.
that construction of Dartmouth has had on the flow The study found as follows:
regime. There are really two river regimes — either of • Dartmouth Dam has typically reduced winter/spring
which may last for many years on end — as follows: flows, flooding and water table levels.
• When Dartmouth is filling (after being drawn down • Irrigation releases have been irregular in frequency,
to supply water for consumptive use), it fully timing and duration. However, moderate autumn
controls inflow and the valley downstream is almost releases have been made on a more regular basis
entirely flood-free. since 1990.
• After filling, Dartmouth Storage may remain close • Soils are highly permeable in general, and water
to full for extended periods — being drawn down table levels are often affected by river height,
under harmony rules in the autumn and refilling, rainfall, irrigation, run-off and adjacent lagoons.
with pre-releases, in winter and spring. Under this After rainfall or irrigation, water tables generally fall
regime, flood duration may be increased but within two weeks to a height related to the river
frequency is still less than that which occurs under height. Further from the river, groundwater levels
natural conditions. are less clearly related to river height.
Landholders are particularly concerned about the • Close to the river (say within 200 m), average
negative impacts that the dam appears to have exerted spring water table levels are estimated to be as
on agricultural profitability. As a result of fewer floods much as 1.5 m lower than before Dartmouth Dam
and lower water tables, pasture growth has been was constructed. Irrigation releases in summer or
reduced to the extent that irrigation has become a autumn result in water table levels as much as 2 m
necessity. Irrigation can improve production to greater higher during major releases.
than pre-Dartmouth levels. However, irrigation • Dryland pasture productivity is reduced by
increases operating risks and costs, and requires more Dartmouth Dam where the water table was
intensive management and capital investment. previously within 70 cm of the surface —
H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E W 13H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
particularly during dry spring conditions. Little from Dartmouth during spring/early summer would
effect is felt on dryland pasture productivity where reduce the effects of cold water on irrigation
water table levels were previously deeper than 70 productivity. These releases would also provide a
cm. However, productivity during wet seasons is higher water table in spring/early summer,
increased because current water tables are lower emulating natural regimes and enhancing pasture
and drainage is better. productivity.
• In a well-managed irrigated pasture, there is little Landholders believe actions required to remedy
pasture productivity benefit from a higher or problems highlighted by the report include increased
lower water table. With less capable management, water allocations and water pricing concessions.
a water table less than 70 cm will improve Goulburn-Murray Water, which is responsible for water
productivity. licences in the valley, is currently assessing these claims.
• Simulations of water releases at 10°C for an entire To address concerns relating to temperature of
irrigation season showed that pasture productivity water releases, the issue of a multi-level offtake at
would be reduced by up to 15% as a direct result of Dartmouth is considered in section 5.3.1.
application of cold water. This situation represents
the upper limit of the effect of cold water on pasture Based on the results of this study, the panel (noting that
productivity, as irrigation releases associated with the possible increased water allocations and pricing concessions
coldest river temperatures would rarely be made for are currently being assessed by Goulburn-Murray Water
an entire season. However, colder river temperatures and are now unable to be directly influenced by this
occur during releases from Dartmouth. Where colder review) has identified the following options:
water releases occur, greater productivity loss than a • Investigate earlier pre-releases in years when
10°C scenario may occur. Dartmouth Dam has spilled, to avoid periods of low
• Over 40% of diverted water can be lost through flow between spring spills and autumn harmony
infiltration past the root zone of flood irrigated releases.
pasture, and through channel seepage, evaporation • Investigate lower and earlier releases in years when
and run-off. Modelling shows an average annual resources must be transferred from Dartmouth to
irrigation requirement, without losses, of 3.7 ML/ha Hume for supply.
to 11.3 ML/ha depending on rainfall. However,
actual irrigation applications are less than those The panel’s preliminary views are as follows:
suggested by the model. • Goulburn-Murray Water is dealing adequately with
• High and low water table simulations show that possible increased water allocations (in the context
annual irrigation water requirements could be of the Murray-Darling Basin Commission Cap),
reduced from 8.5 ML/ha to about 6 ML/ha if a pricing concessions and any other compensation
shallow water table of less than 30 cm were measures for adverse effects on individuals.
maintained for the entire irrigation season under • Current harmony rules provide for releases as soon
optimal irrigation conditions. If the water table were as practicable following Hume ceasing to spill, and
maintained at 50 cm, water requirements would this provision should be retained.
only be reduced to 8.3 ML/ha. • When Dartmouth releases are needed for supply
Conclusions derived from these results applicable to purposes, there may be some scope for earlier
river flow management are as follows: releases at lower rates; however, this could involve
• More regular summer flows would provide: increased risk of loss of water for consumption.
– improved pump management,
– reduced pumping costs, and 5.1.2 Flood duration in the Mitta Mitta valley
– reduced irrigation water requirements because
It is well understood that Dartmouth markedly reduces
of higher water tables and higher pump flow rates.
the frequency of flooding in the valley below —
• Timing of irrigation releases can have an impact on
virtually eliminating flooding for long periods when the
dryland and irrigated pasture productivity. Releases
storage does not spill. However, there has been much
14 H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E WH U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
Table 1: Modification of flood regime at Tallandoon since construction of Dartmouth Dam
Flow at Average no of floods/year Average flood duration (days) Average days flooded/year
Tallandoon Pre Post % Pre Post % Pre Post %
ML/day Dam Dam change Dam Dam change Dam Dam change
10 000 (channel 3.59 1.78 -50 7.2 6.3 -12 25.8 11.2 -57
capacity)
13 000 2.75 0.87 -68 5.3 6.3 +19 14.4 5.5 -62
19 000 1.49 0.33 -78 3.5 4.6 +31 5.2 1.5 -71
(minor flooding)
27 000 0.62 0.16 -74 2.8 2.0 -29 1.7 0.3 -82
(moderate
flooding)
discussion about the effect of the dam on duration of The panel has reached the conclusion that the dam has
floods occurring when the storage is full. a powerful effect in reducing both frequency and peaks
Some landholders state that before Dartmouth was of floods in the Mitta Mitta valley. As discussed in
constructed “floods never lasted longer than a few days, section 5.1.1, this reduction in frequency and peaks
and were beneficial”. However, in a survey conducted provides both advantages and disadvantages to
during early stages of dam construction, beef and dairy agricultural productivity.
farmers listed fear of catastrophic floods as a major
barrier to farm development. While it is true that some floods are extended in
To objectively assess the impact of the dam on duration (at the 10 000 ML/day level at Tallandoon), it
flooding, the flood frequencies and durations under is equally true that some are decreased in duration. Over
pre-Dartmouth and post-Dartmouth conditions were the 63 years modelled, there were 13 such floods that:
compared using computer simulation models (see • lasted more than ten days under both the pre-
section 6 for a description of the models and the Dartmouth and post-Dartmouth scenarios, and
support papers for a detailed report on Mitta Mitta • were individual floods that could be directly compared.
flood duration). Comparison of those floods showed that the dam could
Modification of the flood regime by Dartmouth extend flood duration by as much as eight days, but
Dam at Tallandoon is summarised in table 1. conversely could reduce it by as much as eight days. The
This table shows that Dartmouth Dam removes average effect was an increase in duration of 2.4 days.
about half the low-level floods and three-quarters of
higher level floods. It also reduces average flood days Stakeholders have expressed some concern that the
per year by a similar proportion. At some levels, dam sometimes increases the duration of floods at
duration is increased for floods that are not removed; at particular levels, despite the powerful overall flood
other levels, average duration is decreased. mitigation effect. The review panel believes that it is
At the nominal river channel capacity at Tallandoon possible to change storage operation so that duration
(10 000 ML/day), average flood duration is somewhat above nominal channel capacity at Tallandoon is not
decreased. However, some floods at that level are increased. However, this change would cause increased
extended in duration by the storage. This effect is flood peaks.
particularly apparent for floods that occur when the
storage is already full. This option and the views of the panel are discussed
further in section 6.2.7 (‘Use of Dartmouth power
station during floods’). In summary, however, the panel
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considers that initially the question of using the power 5.1.4 Erosion on the Mitta Mitta River
station to assist in controlling flood duration is a matter The Mitta Mitta stream and floodplain are relatively
for the Mitta Mitta community to reach an agreed steep and there are few geomorphic controls — such as
position on. bedrock bars — that limit on-going fluvial geomorphic
processes. Erosion was prevalent on the river prior to
5.1.3 Adverse effects on agricultural land at
construction of Dartmouth Dam. In 1955, almost 25
peak regulated flow
years before completion of the dam, the Mitta Mitta
The nominal channel capacity of the Mitta Mitta River River Improvement Trust was formed to manage the
for regulated releases has been set at 10 000 ML/day. erosion problems.
In 1984, several regulators were installed with When Dartmouth Dam was constructed, possible
Commission funds on lagoons and anabranches adverse effects on river stability were anticipated. The
alongside the lower reaches of the river. These Commission has therefore contributed to erosion
regulators were intended to prevent high regulated control work. This work is now conducted by the North
flows from backing out on to the floodplain. East Catchment Management Authority (NECMA).
Unfortunately, the regulators were generally Most erosion work conducted since formation of the
unsuccessful because of construction problems and Mitta Mitta River Improvement Trust has used willows
permeable soils allowing lagoon levels to vary with and selective rock beaching as the primary control
river levels. Waterlogging, as distinct from inundation, method. This approach has led to two problems:
also occurs on a number of properties in this area. • expensive control measures for excessive willow
During 1997–98, slightly lower (9500 ML/day) growth, and
regulated releases were trialled. The lower releases • lowered environmental values caused by gradual
resulted in the affected area being reduced. However, at conversion of the stream to a rock and willow lined
least two properties were still affected by waterlogging channel.
and/or inundation. In a submission to the review, the Upper North East
River Management Authority (the predecessor of
The panel considers that there are three options for NECMA) stated that division of responsibilities between
resolving this problem: it, Goulburn-Murray Water and the Commission were
• investigate nominal channel capacities in the range unclear. Accordingly, the authority identified a need to:
9000 to 10 000 ML/day; • formalise management roles,
• investigate construction of regulators where • resolve management requirements, and
appropriate; or • clarify funding arrangements.
• take flood easements over affected land and pay The submission also suggested that an integrated program
appropriate compensation. of waterway and floodplain management should be
The panel has further considered these options in light developed for the Mitta Mitta River. It recommended that
of the following factors: this program should include plans for:
• problems may be minimised by carefully selecting • Floodplain management — including pasture, flood
the regulated release figure; and drought management.
• regulators may only be required on one or two • Stream health — including stream geomorphology
properties; and and stability, riparian vegetation and habitat, in-
• easements could be taken over the affected land if stream ecological conditions, and water quality.
no structural solution is possible. • Stream operational requirements — such as release
rates, drawdown rates, and community awareness
It is the view of the panel that further investigations provisions.
should be conducted to ascertain the most beneficial
option for each affected property.
16 H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E WH U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
Based on the submissions received and analysis Sometimes it takes days or weeks of high regulated flow
conducted by the panel, the following options have before waterlogging occurs. Affected areas can be identified
been identified: by changes in vegetation — typically weeds replacing
• Continue with existing stream erosion control paspalum — even in the absence of visible waterlogging.
methods, accepting that the result over time will be As part of the review, Hassall & Associates inspected
a willow and rock lined river channel of limited most of these areas in December 1997 to assess the spatial
environmental value. extent and cost of mitigating the effects of this waterlogging.
• Fund further research into mechanisms and factors They found that about 250 to 300 ha was affected, and
contributing to slumping of banks on the Mitta estimated the value of the affected land at about $375 000.
Mitta River.
• Develop an integrated program of waterway and The panel considers the options for dealing with this
floodplain management along the lines suggested by problem are to:
the NECMA. • reduce peak regulated flow level to a figure
significantly lower than 25 000 ML/day;
The panel’s preliminary view is that an integrated • do nothing, on the basis that the negative impacts
program of waterway and floodplain management are outweighed by flood mitigation benefits to
along the lines suggested by the NECMA should be agricultural land; or
developed. • take flood easements over the affected land and pay
appropriate compensation.
5.2 Economic impact of Hume Dam on the
floodplain below It is the view of the panel that, for equity reasons, taking
flood easements over the affected land and paying
5.2.1 Adverse effects on agricultural land at
appropriate compensation is the only reasonable option.
peak regulated flow
Channel capacity of the Murray between Hume and
5.2.2 The need for a comprehensive river
Yarrawonga has been regarded for many years as
management plan between Hume and
25 000 ML/day at Albury. Although nominal channel
Yarrawonga
capacity — and therefore peak regulated release from
Hume — have not changed, regulated diversions from
River regulation and flow regimes
the system have increased steadily over the past three
decades leading to longer periods of high regulated flow. Regulation of the River Murray between Hume and
This part of the Murray is not a single river, but rather Yarrawonga has progressively increased since
a main stream with many anabranches (refer to back construction of the original Hume Dam in the 1920s.
cover). In some places the anabranches carry more flow Since then, the Snowy Mountains Scheme has been
than the main stream During the late 1970s, regulated built, capacity of Hume has been doubled, and
flows of increasing magnitude led to concerns that access Dartmouth Dam has been constructed. Irrigation
to islands of freehold land was being cut off by development has matched the increased storage
anabranches. In particular, many formerly intermittent available, and the flow regime is now very different
anabranches started to run throughout the irrigation from the natural regime, in that:
season. Many of these problems have been resolved by • Low flows (1200 – 5000 ML/day) are more common
establishing a program in which the Commission — particularly in winter and early spring as storages fill.
contributed to the cost of access bridges or acquiring • Flows between 15 000 and 25 000 ML/day are more
easements where provision of access was not justified. common — particularly in summer and autumn
Another problem, however, is emerging. Areas of when natural flows would be lower. In most years,
freehold land on some properties are being inundated there are now extended periods of flow close to
at peak regulated flow, or are being waterlogged, 25 000 ML/day during the irrigation season. Pre-
because the land is marginally above river level and lies release of water at this rate, to mitigate potential
above sand/gravel lenses connected to the river. flooding in winter and spring, is also quite common.
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Table 2: Effect of Snowy and Murray River development on floods below Hume
Flow at Average no of floods/year Average flood duration (days) Average days flooded/year
Albury Natural Present % Natural Present % Natural Present %
ML/day change change change
25 000 (channel 4.37 2.10 -52 13.27 14.88 +12 57.99 31.25 -46
capacity)
31 500 4.25 1.51 -64 9.52 13.60 +43 40.46 20.02 -51
36 000 3.79 1.35 -64 8.33 12.00 +44 31.57 16.20 -49
(minimal
flooding)
43 000 0.62 0.16 -74 2.8 2.0 -29 1.7 11.20 -49
(minor flooding)
• Flows significantly above 25 000 ML/day are less downstream of Howlong. There has been little
common because of the flood-mitigating effect of change in depth between those locations. The depth
the storages. However, the duration of low-level throughout the Hume-Yarrawonga reach is now
flooding can be extended at times. fairly stable and the bed has become armoured by a
• Seasonality of river flows has changed markedly. coarse layer of gravel.
Much higher flows are experienced in summer and • The river has historically moved over the floodplain
autumn, and lower flows in winter and spring. by a process of lateral migration of bends. This
• Total water volume is about 6% more than under migration is occurring at present, but it is not clear
natural conditions as a result of water diverted from whether or not the regulated flow regime has
the Snowy catchment. affected the rate of migration of bends.
Effects of water storages and the Snowy Mountains • In contrast, there is a clear link between river
Hydro-electric Scheme on River Murray floods below regulation and general channel widening. River
Hume have been quite significant. Table 2 illustrates regulation, in conjunction with other land
changes in flooding as a result of these water control management practices, has led to a general
structures. widening of the river channel of about 160 mm per
The table compares natural and present-day year. It is likely that river regulation has been a
frequency, duration and total annual days flooding at major contributor to depleting the incidence and
various flow levels. Figures are for events exceeding extent of vegetation on the river bank. The long
one day’s duration occurring from June to December periods under regulated flow soften the banks and
inclusive. lead to higher rates of bank erosion.
• Banks are generally retreating in a parallel fashion
— notch erosion at high regulated flow level is not
River regulation and erosion
the main mechanism. Erosion is occurring across
Between Hume and Yarrawonga, erosion is more active the full height of the bank.
than in other reaches of the River Murray. Consultants • Anabranches carry large volumes of water under
Ian Drummond and Associates (1993 and 1997) regulated conditions. In one location, the main
investigated the nature and extent of channel stream carries less than half the peak regulated flow.
instabilities in the reach. They concluded as follows: Anabranches need to be examined individually to
• The river channel has deepened between Hume assess changes and the possibility of capture of the
Dam and Albury, and has become shallower main river channel.
18 H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E WH U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
• Regulation of flows causes a higher proportion of • a decision on the extent to which anabranch
flow to pass along the river channel and less along development needs to be contained;
the floodplain. It is estimated that re-regulation • setting desired levels of protection for aquatic,
within Hume increases the energy within the river riparian and floodplain habitats; and
channel (hence potential erosive power) by about • documenting desired aesthetic and recreational values.
6%. Re-introduction of elements of the natural flow Based on the strategic framework, a comprehensive
regime, combined with other management tools, river management program should be developed. This
may help to control channel erosion. program would:
• Erosion rates are high during floods, but the majority • establish an agreed management arrangement
of erosion is occurring from flows within the (which needs to work in two states, have proper
channel. The flows within the channel are mostly local input, etc);
irrigation releases, but also include flood pre-releases. • establish links with associated land management
• It is not possible to quantify the relative effects of programs in each state;
irrigation releases, flood releases and Snowy • establish agreed funding arrangements — with
diversions on channel erosion in the reach. consideration of funding from such sources as the
• Factors such as de-snagging (which tends to increase Commission, catchment management authorities
both channel capacity and erosion rates), changes in and local government, and input (cash or kind)
vegetation (partly but not solely because of increased from landholders;
regulation) and boating (probably quite limited) also • set a works program — including both an annual
contribute to changed rates of channel erosion. program of necessary patch-up works (done now to
The panel accepts that flow regulation has had a major a modest extent with Commission funding) and a
coordinated strategy of activities designed to achieve
influence on channel stability in the Hume-to-
the long-term goals; and
Yarrawonga reach of the Murray. However, the panel is
• monitor progress and the extent to which the
also aware that the river has historically migrated
strategic framework might need to be changed.
around the floodplain. This fact is obvious from aerial
photographs or maps of the area — including the map
5.3 Effect of dams on non-flow
on the cover of this paper.
environmental values
The panel considers that future options for 5.3.1 Impact of Dartmouth Dam on water
management of this reach of the Murray are to: temperature and quality
• retain the present management arrangement — under Water from Dartmouth Dam is normally released through
which the Commission provides limited funding to the the high-level outlet, except when storage content drops
NSW Department of Land and Water Conservation to below about 30% and the low-level outlet must be used.
treat actively eroding sites on a priority basis; or The high-level outlet draws water from about 60 m
• develop a comprehensive and properly funded below the full supply level of the storage.
program for management of the reach. The temperature of water from the high-level outlet
is considerably lower than river temperature prior to
The panel believes that this issue can only be fully construction of the dam — particularly in summer and
addressed by developing a comprehensive and properly autumn. Water quality of releases from the high-level
funded program for management of the reach. The outlet is also lower than water near the surface. The
management program will initially need a strategic low-level outlet exhibits similar, but amplified, water
approach to articulate a vision for the future desirable quality and temperature problems. Releases of low-
state of the river. The strategic framework will require: temperature water and/or poor quality water from
• developing criteria for acceptable and unacceptable these outlets may be responsible for:
erosion rates (& acceptable methods of erosion control); • declining habitat and native fish population in the
• setting limits to acceptable rates of channel river (temperature is identified as the critical factor);
widening and bed degradation; and
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• landholders being unable to achieve the full • Install shutters on the existing high-level outlet to
potential of pasture productivity improvements by provide limited improvement.
irrigation partly because of low water temperatures • Raise the top of the existing structure to above full
— see section 5.1.1 (‘Effect of Dartmouth Dam on supply level and install a fully functional multi-level
pasture productivity’). offtake.
During construction of the dam, provision was made in • Agree in principle that a fully functional offtake is
the existing high-level-outlet offtake tower for future required, and conduct detailed investigations into
extension above full supply level if required. It has been the cost, benefit and optimum way to achieve a
provisionally estimated that the extended tower with fully functional offtake.
multi-level offtakes would increase temperatures
significantly and improve other water quality factors. The panel’s preliminary view is that it agrees in
However, it is highly unlikely that the extended tower principle with the last option: that a fully functional
would restore temperatures and water quality to offtake is required and that detailed investigations into
natural pre-dam levels. A feasibility stage cost estimate the cost, benefit and optimum way to achieve a fully
of the extension is $11 million. functional offtake must be undertaken.
An alternative to the tower extension would be to
add shutters to the existing tower, which would be much 5.3.2 Effects of regulated flows and rain
cheaper. These shutters would vary draw-off levels to a rejections on natural drying cycles
limited extent, but would provide little improvement in in wetlands
water temperature or quality over the current situation. Too much flooding can be as damaging to a naturally
In assessing the benefits of extension or ephemeral wetland as insufficient flooding. Many
modification of the existing high-level outlet, the panel plants need a wetting and drying cycle for their seeds to
considered the following issues to be important: germinate and their roots to be aerated. Drying also
• Likely temperature increases will probably not permits oxygenation of sediments — a crucial step in
restore pre-Dartmouth conditions to the extent that the process of nutrient cycling — which in turn
suitable spawning habitat for all native fish will supports aquatic food webs.
return. Conditions may well be favourable for Some wetlands along the Murray are inundated at
Murray Cod and Macquarie Perch but not for some peak summer regulated flow. Others are not, but can be
other species. This needs to be investigated. affected when summer rain causes rain-rejection of
• The dam itself will remain a barrier to fish irrigation water which is returned to, or left in, the river.
migration.
• Water quality from the low-level outlet will not be The panel considers that this issue will require
improved. The low-level outlet was used in 1983 and considerably more work, integrated into river flow
briefly during the early 1990s, so its historic frequency management plans, and that solutions are likely to
of use is low. However, the storage can remain low for involve the following:
years on end: in the long term it is estimated that it will • Improved river operation. Improved river operation
be used 15% of the time. Water quality from this outlet may be possible from better weather forecasts, more
is potentially poor, with low dissolved oxygen levels accurate ordering from irrigation agencies, and
and considerable dissolved iron, manganese and improved estimation of river losses.
hydrogen sulphide. • Retention of rain rejections in storage of some kind. Four
possibilities have been identified, as follows:
Based on submissions received and analysis conducted – storage on-farm, particularly as drainage
by the panel, the following options have been recycling dams become more popular;
identified: – storage in distribution channels;
• No action — accept that temperatures in the Mitta – continued emphasis on drainage diversion
Mitta River will remain depressed, and that the river permits to encourage irrigators to pump from
ecology will remain altered from its natural state. authority drains, which contain a proportion of
20 H U M E A N D D A R T M O U T H D A M S O P E R A T I O N S R E V I E WYou can also read
