MDBA Submission
Submission in respect of the Guide to the proposed
(Murray-Darling) Basin Plan By Ian Mott
The original submission can be seen at http://www.mdba.gov.au/files/submissions/Ian%20Mott%20-%20Landholders%20Institute.pdf
The original submission can be seen at http://www.mdba.gov.au/files/submissions/Ian%20Mott%20-%20Landholders%20Institute.pdf
Comprising evidence and issues that are capable of establishing that the process outlined in the document described as the Guide to the proposed Basin Plan is;
A. A grossly improper exercise of power within the meaning of Sections 5 & 6 of the Administrative Decisions (Judicial Review) Act, 1977
http://www.austlii.edu.au/au/legis/cth/consol_act/adra1977396/s5.html and,
B. A planning process that is in serious breach of both the letter and the spirit of the Intergovernmental Agreement on the Environment, 1992.
http://www.austlii.edu.au/cgi-bin/sinodisp/au/legis/cth/consol_act/nepca1994432/sch1.html?stem=0&synonyms=0&query=%22intergovernmental%20agreement%20on%20the%20environment" and,
C. Conduct that is in grossly negligent abrogation of Professional Duty of Care to take all reasonable and practical steps to prevent entirely foreseeable and avoidable harm to all persons with an equitable interest in the proper management of all waters of the Murray-Darling Basin.
Overview:
The Murray-Darling Basin Authority (MDBA) has misinterpreted the objects of the Water Act, 2007 in a way that assumes that only the fresh water resources of the basin are available for achieving the purposes of that Act. The interaction of fresh and tidal waters of the Coorong and Murray mouth is the critical element in ecosystem health and end of system dynamics. Yet, the character, frequency and volumes of these tidal flows have not been included in the inventory of Basin water resources and no meaningful attempt has been made to consider the enhanced management and augmentation of this resource for achieving the objects of the Water Act, 2007.
This appears to have its roots in one of the most appalling intellectual cop-outs ever incorporated into a policy process, the second conclusion of Walker [1](2002) who said;
“The build-up inside the mouth is believed due to a combination of inadequate river flows and near shore coastal processes related to wave and tide climate. Engineers and managers have no control over the latter”.
The second sentence is a gross, and inexcusable, misstatement of fact, by omission of the incredible range of works carried out all over the world, and over more than 3000 years of history, to mitigate and manage the impacts of wave, tide and storm events.
Executive Summary:
A. The major determinants of the condition of the Murray River mouth are the asymmetric tidal patterns and storm induced wave heights that produce a build up of beach sediments in a standard “flood tide delta” inside the mouth.
B. Half of all daily tide patterns (week about) involve approximately 8 hours of rapid inflow that deposits sand, followed by 16 hours of slow outflow that doesn’t remove it.
C. The shear stress of a flow (its capacity to move sediment) increases at approximately the square of the flow speed. So an inflow that is twice as fast as the outflow will transport four times more sand than the outflow will remove.
D. Half of all river flows take place at times of each lunar cycle when the tidal variation is minimal and the capacity to remove sediment is severely retarded. So half of the 3 million ML of buy-back water will not do the job intended for it. Nor will half the 5 million ML of existing flows.
E. An increase in total river flows that removes sand will simply increase the capacity of tides and storms to put it back again.
F. The function required of increased outflows is purely hydrological. It can be done equally well by additional sea water that has not already come through the mouth. Sea water is in essentially unlimited supply and comes at zero cost.
G. Storm events compound the deposition problem by increased turbulence (transportability) and increasing inflow volume and velocity. Of the annual average 77 storm events, only 38 coincide with large tidal variances and only 14 of those have their storm surges coinciding with rapid tidal intakes. The latter can deposit up to 46,000m3 of sand in a single event and cause most of the deposition problem.
H. These events can only be countered by timely and fully proportionate outflows that negate the deposition multipliers. A continuous modest flow after or between these events cannot redress the original deposition problem.
I. Large dimension, unidirectional pipes under the dunes, with intakes below the wave zone and above sea bed sand, can passively deliver the volumes of clean sea water needed to ;
a. First, retard deposition through reduce volumes and velocities of river mouth inflows as a larger portion of the tidal prism is supplied via the pipes, and
b. Then produce the increased volume and velocity of outflows by blocking the reverse flows back out the pipes so the outflow is diverted to the Murray mouth where its greater volume and velocity will increase sand removal to equilibrium levels.
J. Two pipes at the far end of the Coorong, and one north of The Narrows, could produce a complete cyclical discharge of the hypersaline volume of both lagoons out through the Murray mouth, and its replacement with cool, oxygenated sea water.
K. Less than 13 pipes either side of the Murray mouth could negate the deposition of all major storm events and do a better job, much cheaper, than all current river flows and additional buy-back water combined. Dredging will reduce the number of pipes required.
2.44 Pipes under the dunes, on the other hand, have major advantages over open channels for delivery of additional sea water to barrier estuarine systems;
- They can deliver precise and standardised volumes of sea water over a much shorter distance in a fraction of the time taken by passive tidal systems,
- They can be replicated to deliver sea water to any desirable location along a barrier system,
- They can provide variable delivery of sea water to optimise flows in the system,
- They can be completely covered once in place to restore visual values,
- Their oceanic intake can be placed lower than the wave zone to reduce risk of storm damage,
- The oceanic intake can project a sufficient distance out of the sand body to ensure that it free of sand in suspension and hence, sand will not be transported through the pipes in any sea condition or intake velocity.
- The pipe will not form a groyne-like barrier to lateral movement of sand along the beach and no (internal) flood tide deltas will form at the other end that would otherwise continually restrict the pipes function.
2.45 Such a system would operate passively, responding immediately to various levels of tidal flux without management input and in direct proportion to the height of any storm surge. But the presence of a simple valve system would also enable complete or partial shutdown if or when required.
2.46 The system could function at a number of levels;
- As a simple source of fresher water to overcome seasonal hyper salinity and replace evaporation losses in the closed end system.
- As a general augmentation of existing volumes into the far reaches of the Coorong to produce an increase over normal water levels and create a net outflow which will discharge excessive and unsustainable saline build-up out through the river mouth.
- As a tool for accurate, timely and proportionate adjusting of flows in and out of the mouth so normal rates of sand deposition can be reduced and countered by increased rates of sand discharge.
- As a tool for timely and proportionate responses to reduce the extent of major storm surge sand deposition events as and when they occur.
2.47 The Coorong is now a closed end system. Variations in water levels at the front of it have minimal impact at the far end. In the absence of pre-settlement flows along its length from the South East Drainage System, no amount of fresh water flows adjacent to the northern end can deliver adequate ecosystem services.
2.48 The North Lagoon is 48km long. Its average width at AHD is 1.5km, depth is 1.2m, surface area is 7,200ha and volume is 86,400 ML (CFMI[10], 1992). Mean annual pan evaporation is 16 ML/ha so the actual (80%) is more like 12.8 ML/ha. Mean annual rainfall is 5 ML/ha giving a net evaporative loss of 7.8 ML/ha. It requires an average 56,160 ML each year (65% of volume) to replace net evaporation losses.
2.49 Even if all this volume came from fresh water delivered over the Tauwitcherie Barrage in the upper left corner it would only serve to temporarily dilute saline levels rather than reduce existing salt loads. The current, totally inadequate, policy of reliance on tidal “sloshing” of fresh water to maintain water quality requires a much greater volume of fresh water that is delivered in a poorly targeted manner by an extremely inefficient method.
2.50 Year round direct injection of tidal water to the southern end of the North Lagoon, in volumes capable of keeping pace with mid summer evaporation rates, by pipes will fully restore and maintain all ecological values and ecosystem services through a complete replacement of water volume.
2.51 Summer evaporation is 0.056 ML/ha/day with a gross loss of 403 ML/day. In the absence of storm surges only half the days of each cycle will have tidal variation capable of producing useful inflows so the daily pipe flow must be in the order of 806 ML/Day, over an 8-9 hour high tide interval.
2.52 The passive flow rate will vary as the tide height outside the dunes rises and falls in relation to the mean sea level inside the dunes. An average cycle of the type shows at left of the graph at 2.13 above would have two hours (first and last) of a 10cm drop, 2 hours each of a 20cm, 30cm and 40cm drop, and a peak hour of 50cm drop that defines the rate of inflow.
2.53 Over a single1000m pipe of 3.6m diameter this would produce passive flow of;
2 hours @ 7.83m3/sec for 56 ML
2 hours @ 11.39m3/sec for 82 ML
2 hours @ 14.18m3/sec for 102 ML
2 hours @ 16.56m3/sec for 119 ML
1 hours @ 18.68m3/sec for 67 ML
For a total discharge of 426 Megalitres a day.
2.54 A 20cm storm surge on such a day is likely to add another 295 ML to the peak flow and 168 ML to the lower flows, taking the daily discharge to 890 ML.
What else do we need to know?
4.01 The average duration of storm surges, (i.e., the time taken for frontal systems to pass) and their range of variation, needs additional study, as does their mean height and their range of variation in height. Without this information the more accurate determination of the likely range of passive flow pipe yields cannot be made.
4.02 For the proper management of Murray mouth sand deposition we need to know the proportion, number, and range of scale variations, of storm surges that coincide with the periods of peak tidal variation. Storm surges that coincide with ebb and neap tides are likely to produce much less deposition because their rising inflows counteract the tidal outflows. Storm events where maximum surge takes place during maximum tidal inflow will present the highest volume and velocity inflows and produce the highest volumes of sand deposition.
4.03 We then need to know the extent to which these major deposition events must be negated and the extent to which their deposition volumes can be carried forward for remedial action by subsequent normal tidal outflows and benign phase storm surge outflows. This information will be essential for the ultimate design specification.
4.04 We need to know the proportion of total inflows that will need to come via conduits other than the Murray mouth to ensure equal deposition and removal on each tidal cycle. That is, when the combined outflows through the mouth can remove the deposition that took place on the previous inflow. At Alternative 5.50 below, we have assumed this to be 50% but the actual is likely to be much less because a unidirectional diversion system reduces deposition by diverting mouth inflows to the alternative conduit and increases sand removals by increasing the total volume of mouth outflows via improved efficiency of the tidal prism.
4.05 We need to know the optimum size, volume, cost relationships in both pipe construction and installation. This analysis has used 3.6m diameter pipes as a standard but we need to know, for example, if smaller ones provide substantially lower cost advantages that outweigh the resulting reduced flow volumes. It may also be possible that larger pipes produce flow gains that outweigh their increased cost and installation difficulties.
4.06 Optimum pipe size will also be influenced by installation issues on the seaward side with questions over a single large prefabricated sub-surface interface or an on-site construction with coffer dams etc.
4.07 The trade-offs between large capacity passive flow systems that only function for part of the time, and smaller capacity pump based systems that can function all of the time would also merit detailed consideration.
4.08 The full evaluation of alternatives for keeping the Murray mouth open, carried out by the Sand Pumping Technical Committee in 2002 must be made public to properly inform the policy process. Some of these options, while appearing to be more costly than dredging appeared to be in 2002, may prove to be valuable contributors in a combined approach. For example;
“The Southern Alexandrina Business Association[19] has sent (9/04/09) a proposal to SA Water Security Minister Karlene Maywald for a break-water for the neighbouring Coorong. Association president John Clark says the cost would be roughly the same as dredging but would have longer-term benefits for the internationally-recognised Coorong wetlands”. http://www.abc.net.au/news/stories/2009/04/09/2540147.htm
If the local Business Association’s costing is anywhere near the reality then a mix of pipes, dredging and breakwaters is likely to be even more effective than each option in isolation. And the cost is certain to be substantially less than the MDBA’s perverse fresh water fetish.
5.00 Alternatives:
5.10 The Buyback of 3 million ML of irrigation water to maintain a higher continuous outflow. This option has a total cost in the order of $6 billion, with annual costs of $600 million. It uses high value, and highly variable supplies of fresh water to do a simple hydrological function. It wastes more than half the total volume supplied because it is delivered at a time when there is next to zero assistance in sand removal from tidal outflows.
5.11 It is incapable of responding in the time and scale needed to deal with the key storm surge deposition events. It is a continuous, static solution to a set of dispersed, variable impacts. And it will not alter the fact that the capacity of the tides to fill-in the Murray mouth is in direct proportion to the degree to which the river flows might open it.
5.12 In economic terms it is an even bigger waste. It takes water that is currently put to profitable use in an important national value chain. It involves water that must be purchased at considerable cost to the Commonwealth and it involves a significant ongoing reduction in the tax base and a serious undermining of the cost base for major storage infrastructure like Dams etc.
5.13 It will achieve little additional benefit to what has been delivered by a single dredge for the past three (worst case) years at an annual cost of $2.33 million.
5.14 And none of the wealth transfers involved appear to be incorporated into the Commonwealth Grants Commission processes, the body responsible for the fair and equitable distribution of Commonwealth funds between the states.
5.15 And it will not go anywhere near to restoring the ecological values of the lower Coorong, the very wetland used to justify the use of this water.
5.20 Removal of the Barrages to restore the tidal prism. This option has been promoted as the obvious solution to the major evaporative losses that take place within the lower lakes in severe drought.
5.21 But in a context of a current 5 million ML mean annual discharge of fresh water out the Murray mouth, and the prospect of an additional 3 million ML from buy-backs for the same end, the increase from a pre-settlement 400,000 ML fresh water evaporation to a current 500,000 ML net figure, makes this very much a second order issue.
5.22 The contribution of partial openings during drought to maintain internal water levels etc is certainly an option that needs proper consideration.
5.23 However, the permanent opening of the Barrages will actually exacerbate problems of excess deposition in the mouth by increasing the volume and velocity of the tidal inflows.
5.30 The construction of open channels through the dunes to introduce more sea water into the Coorong Lagoons. This option would be comparatively cheap to implement but would be quite short lived. If the Murray mouth, with its additional discharges of fresh water, cannot combat the internal sand build-up from tidal inflows and storm surges then additional man made channels will be closed by the same forces in even less time. Open channels must function in the same littoral zone as the Murray mouth and the resulting exposure to the forces at play in that zone would require continual maintenance expenditure and render the option unviable.
5.31 The closure of open channels would take place even faster if gates were fitted to allow for unidirectional flows.
5.40 The installation of large diameter, in-flowing pipes under the dune system to the Coorong, one supplying the North Lagoon and two supplying the South Lagoon, each delivering approximately 100,000 ML of sea water each year, sufficient to produce a net flow along the full length of the system and ultimate discharge through the Murray mouth.
5.41 The two, located near Fig Tree Crossing, would be capable of replacing all annual evaporation losses and, within a single year, push the entire hypersaline volume into the North Lagoon. The third pipe, just north of the Narrows, could then push the remaining volume out through the Murray mouth.
5.42 It is the first step in restoring the essential ecological values, especially normal salinity levels, to the system. The reliance on “tidal sloshing” has proven to be a consistent failure, especially for the South Lagoon. The delivery of fresh water from the Murray to the most useful parts of this system cannot be achieved without considerable additional capital outlays. And the volumes required cannot be sourced from the Upper South East Drainage Scheme.
5.43 This option substitutes a comparatively small amount of cheap, well targeted, sea water for a very large and indeterminate volume of expensive, poorly targeted fresh water that does not even perform the function assigned to it.
5.44 With this direct injection of tidal water into the Coorong system the full suite of environmental values and ecosystem services can be maintained with a substantially higher level of certainty. And the system can be maintained in a circumstance that remains connected too, but is no longer dependent on, the vagaries of Murray mouth hydrodynamics.
5.45 If the overriding aim of the MDB Guide’s requirement for 3 million ML of expensive buy-back water is to keep the Murray mouth sufficiently open so tidal sloshing might keep the Coorong ecosystem just above the point of ecological collapse then the need for this entire mouth open objective can be negated by just 300,000 ML of cheap sea water delivered directly to its point of maximum benefit.
5.46 The capital buy-back value of fresh water is $2000 per megalitre so the opportunity cost of a pipe that delivers 100,000 ML of sea water to do a better job is $200 million. Any capital outlay less than $600 million on these three pipes represents good value. Given that the concrete in a 1000m pipe of 3.6m diameter and 20cm thick only amounts to 2,400m3, and costs only $720,000 at retail prices, one must conclude that it would take some seriously monumental departmental bungling to push the installed cost above $100 million a pipe.
5.47 This option serves the first two functions outlined at 2.46 above, that is;
- As a simple source of fresher water to overcome seasonal hyper salinity and replace evaporation losses in the closed end system.
- As a general augmentation of existing volumes into the far reaches of the Coorong to produce an increase over normal water levels and create a net outflow which will discharge excessive and unsustainable saline build-up out through the river mouth.
5.50 The provision of additional pipes under the dunes either side of the Murray mouth to improve the management of normal flows and to respond in time and scale to retard the impact of storm surge deposition events.
5.51 These would need to be in sufficient number to deliver half the total tidal prism that would result from the onset of a 0.5m storm surge during the nine hour inflow phase of a 1.1m peak tide or 16 ML/ha. The total inflow would be 13,000 ML so the capacity of the pipes must be 6,500 ML over the same period to ensure that the volume flowing out the river mouth is double the volume flowing in the mouth.
5.52 Unlike pipes flowing into the Coorong where the outlet water level remains near AHD, pipes near the mouth would start inflows from the moment the low tide turned, and would continue to the tidal peak. The water velocity and discharge rates would be defined by the slope obtained from the water levels on either side of the dunes. And in the absence of more detailed analysis we should assume this to be a drop of 0.1m over 700m of pipe.
5.53 This would discharge 9.5m3/sec, or 34.2 Ml/hour, or 308 ML over a nine hour tidal inflow. The 6,500 ML capacity in that circumstance would require 21 pipes. This would mean one pipe for each 39ha of tidal area so the Goolwa channel would need 8 while the Tauwitcherie channel would need 13 pipes.
5.54 This would reduce the storm surge flow through the mouth to the same volume as a modest 0.8m tidal flow under natural conditions. A normal peak tide of 1.1m range would produce the even more modest 0.55m tidal inflow through the mouth with the full 1.1m outflow.
5.55 This across the board halving of river mouth inflow volume and velocity would produce a much more than proportionate decrease in sand deposition. The increase in river mouth outflow volumes and velocity through improved efficiency of the tidal prism would also produce an increase in sand disposal. And this gives us strong grounds for suspecting that this number of pipes may be significant over-kill.
5.60 Maintain dredging in a post flood open Murray Mouth. Once the mouth is open, it is an incontestable fact of history that a single dredge was able to maintain that open mouth during a period of zero fresh water discharges at a cost of only $2.33 million a year. The current capacity to move a minimum of 2000 m3 of sand in a 24 hour day along a pipeline up to 2km in length, is an asset that could be used elsewhere in the estuary to enhance the tidal prism. The sand bank just outside the Eastern end of the Tauwitcherie Barrage is a good first candidate and modification of The Narrows would also be justified. A system of pipes and breakwaters may produce additional need for dredging too.
5.61 It is obviously more economical to prevent a channel from degrading than it is to open a channel that has already closed. The current flood discharges have already opened the channels much wider than the dredge ever could but in subsequent years this maximum opening must contract. In a $10 Billion budget with $1 billion annual outlays, this $2.33 million punches well above its weight.
6.00 Conclusions
6.01 The option that least serves the purposes of the Water Act 2007 is option 5.20 Removal of the Barrages. The restoration of the original tidal prism may provide a temporary improvement in tidal sloshing into the North Lagoon but this would be a very short lived improvement as the asymmetric tidal patterns will increase deposition at the Murray mouth and substantially retard the efficiency of that enlarged tidal prism. Any benefits to be gained by introducing sea water into the Lower Lakes during drought can be achieved by simply opening the Barrages. Their removal is not necessary.
6.02 Option 5.30 Construction of open channels to the Coorong does not serve the purposes of the Water Act 2007 any better. The benefits of direct injection of sea water into the hypersaline ecosystem would be very short lived as the same processes at play at the Murray mouth would close any open channels even faster. This option would require continual maintenance at great expense.
6.03 Option 5.10 the buy-back of 3 million megalitres to increase regular flows is a static, continuous response to a variable, intermittent need. It also demands the scarcest and most valuable water to do a simple hydrological task that can be done better by cheap, abundant and reliable sea water. The scientific community has made no secret of their view that the volume is totally inadequate for the requirement. But the need to balance ecological, social and economic values for the up-stream communities will ensure that the required amount will not be forthcoming.
6.04 Option 5.60, Dredging, has already demonstrated its capacity to maintain an open Murray Mouth, at very low relative cost, and in worst case river flow circumstances. It has clearly earned the right to be included in any mix of solutions and is entirely compatible with other options as an outcome multiplier.
6.05 Option 5.40, Pipes under the dunes to the two Coorong lagoons, deals directly with the need to restore and maintain ecosystem services by delivering sufficient volume of fresh, fully oxygenated sea water to the exact locations that will meet the obligations under the Water Act 2007. It does so in a way that is in direct proportion to the need and it considers the highly relevant matters of timing, flow direction, adequacy and efficacy of water volumes delivered. It maintains the ecological integrity of the whole system but with a fully flexible stand alone management system. It operates in an incremental framework that deals with the most pressing ecological problem, South Lagoon hypersalinity, first and can then play its part in the broader issue of maintaining the Murray mouth.
6.060 Option 5.50, Pipes under the dunes to manage the Murray mouth, becomes a lesser priority once the ecological integrity of the Coorong has been restored by Options 5.40 and 5.60. The health of the Coorong need no longer be dependent on the state of the Murray mouth.
6.061 However, any pipes near the mouth will be better than no pipes because every pipe will enhance the contribution already made by river flows. The economics of trenching and subsequent dune restoration dictate that three or four pipes should be installed in each excavation. And the need for balanced hydrology in both channels would demand a minimum of eight pipes with four on each channel. The reality is that sea water is a superior, more abundant, lower cost, less disruptive and more proportionate substitute for all fresh water discharges through the Murray mouth. And there is no excuse for not doing so.
6.062 If the Australian community has already accepted a budget in excess of $6 billion for the buy-back then the mandate is already in place to spend up to the same amount on pipes to do a much better job.
6.063 When that $6 billion opportunity cost of the 3 million megalitre buy-back is spread over the estimated 16 pipes needed to completely restore the Coorong and keep the Murray mouth wide open we get an extraordinary $375 million for each pipe. The $200 million/pipe figure used in 5.46 above does not factor in the improved water use efficiency delivered by proportionate sea water over disproportionate fresh water.
6.064 And given the savings to be gained from placing 3 or 4 pipes side by side in the one excavation we can safely conclude that the cheapest and best option is undoubtedly the pipes.
6.065 In fact, with the Barrages in place for more than 70 years now, the demarcation of sea and fresh water ecosystems is well established. And this means that further substitution of sea water for existing flows is also feasible as a source of additional fresh water for up-stream wetlands. With adequate sea water systems in place there is no longer any justification, either logical or ecological, for a single drop of fresh water to go over the Barrages. All of existing fresh water outflows (up to 5 million ML) could be used for delivery of up-stream ecological services at zero cost to the economic, social and ecological values of the Basin.
6.066 I advise accordingly, and request that the MDBA considers all relevant matters outlined in this submission, and takes all reasonable and practical steps, to ensure that it does not;
- give effect to any improper exercise of power, or
- apply measures that are not cost effective, or
- apply disproportionate measures, that may
- cause entirely foreseeable, and avoidable detriment to people or communities in the Murray-Darling Basin.
Copyright: Ian Mott, 8th December 2010.
38 Jellicoe Street Manly West QLD 4179
Ph. (07) 3893 0612
talbank@bigpond.net.au
References:
[1] Walker, DJ. (2002) ‘The Behaviour and Future of the River Murray Mouth’ pp 14
[2] Harvey, N. (1996) ‘The significance of coastal processes for management of the River Murray Estuary’, Australian Geographical Studies, vol.34, no. 1, pp 45-57.
[3] Walker, DJ. (1990) ‘The role of river flows in the behaviour of the Murray Mouth’. South Australian Geographical Journal, vol. 90, pp. 50-65.
[4] Webster, IT. (2005) An Overview of the Hydrodynamics of the Coorong and Murray Mouth. Technical Report #/2005. CSIRO Water for a Healthy Country National Research Flagship. pp 4
[5] WBM Oceanics (2003), Murray River Mouth – Morphological Model Development Stage 2 – Model Set Up, Calibration and Verification, Report prepared for Murray-Darling Basin Commission & SA Dept. for Water, Land & Biodiversity Conservation.
[6] Chappell, J. (1991) Murray Mouth Littoral Drift Study, Report prepared for the Engineering and Water Supply Department, South Australia.
[7] Walker, DJ. (2002) op. cit. Fig. 4.3 pp 7
[8] Webster, IT. (2005) op. cit. pp 7
[9] http://www.calctool.org/CALC/eng/civil/hazen-williams_g
[10] CFMI (1992) Mathematical Modelling of the Hydrodynamics and Salinity in the Coorong Lagoons, Report CNG-1-12-12/92 prepared for the Engineering and Water Supply Department, South Australia.
[11] CFMI (1992) ibid.
[12] Chappell, J. (1991) op. cit.
[13] Webster, IT. (2005) op. cit. pp 16-17
[14] Dredging reduced at Murray Mouth, Earth Mover Magazine, (11/2020)
http://www.earthmover.com.au/news/2010/newswire/november/november-4th/other-top-stories/dredging-reduced-at-murray-mouth
[15] Campbell, T. Brown, R. Erdmann, B. (2008) Murray Mouth Sand Pumping: Keeping the Tided Flowing. Report by the Contract Manager, SA Water Corporation. pp 1
[16] Campbell, T. Brown, R. Erdmann, B. (2008) op. cit. pp 6
[17] Campbell, T. Brown, R. Erdmann, B. (2008) ibid. pp 6-7
[18] Campbell, T. Brown, R. Erdmann, B. (2008) ibid. pp 12
[19] The Southern Alexandrina Business Association. (2009) Submission to SA Water Security Minister on construction of Breakwaters. http://www.abc.net.au/news/stories/2009/04/09/2540147.htm
- They can deliver precise and standardised volumes of sea water over a much shorter distance in a fraction of the time taken by passive tidal systems,
- They can be replicated to deliver sea water to any desirable location along a barrier system,
- They can provide variable delivery of sea water to optimise flows in the system,
- They can be completely covered once in place to restore visual values,
- Their oceanic intake can be placed lower than the wave zone to reduce risk of storm damage,
- The oceanic intake can project a sufficient distance out of the sand body to ensure that it free of sand in suspension and hence, sand will not be transported through the pipes in any sea condition or intake velocity.
- The pipe will not form a groyne-like barrier to lateral movement of sand along the beach and no (internal) flood tide deltas will form at the other end that would otherwise continually restrict the pipes function.
2.45 Such a system would operate passively, responding immediately to various levels of tidal flux without management input and in direct proportion to the height of any storm surge. But the presence of a simple valve system would also enable complete or partial shutdown if or when required.
2.46 The system could function at a number of levels;
- As a simple source of fresher water to overcome seasonal hyper salinity and replace evaporation losses in the closed end system.
- As a general augmentation of existing volumes into the far reaches of the Coorong to produce an increase over normal water levels and create a net outflow which will discharge excessive and unsustainable saline build-up out through the river mouth.
- As a tool for accurate, timely and proportionate adjusting of flows in and out of the mouth so normal rates of sand deposition can be reduced and countered by increased rates of sand discharge.
- As a tool for timely and proportionate responses to reduce the extent of major storm surge sand deposition events as and when they occur.
2.47 The Coorong is now a closed end system. Variations in water levels at the front of it have minimal impact at the far end. In the absence of pre-settlement flows along its length from the South East Drainage System, no amount of fresh water flows adjacent to the northern end can deliver adequate ecosystem services.
2.48 The North Lagoon is 48km long. Its average width at AHD is 1.5km, depth is 1.2m, surface area is 7,200ha and volume is 86,400 ML (CFMI[10], 1992). Mean annual pan evaporation is 16 ML/ha so the actual (80%) is more like 12.8 ML/ha. Mean annual rainfall is 5 ML/ha giving a net evaporative loss of 7.8 ML/ha. It requires an average 56,160 ML each year (65% of volume) to replace net evaporation losses.
2.49 Even if all this volume came from fresh water delivered over the Tauwitcherie Barrage in the upper left corner it would only serve to temporarily dilute saline levels rather than reduce existing salt loads. The current, totally inadequate, policy of reliance on tidal “sloshing” of fresh water to maintain water quality requires a much greater volume of fresh water that is delivered in a poorly targeted manner by an extremely inefficient method.
2.50 Year round direct injection of tidal water to the southern end of the North Lagoon, in volumes capable of keeping pace with mid summer evaporation rates, by pipes will fully restore and maintain all ecological values and ecosystem services through a complete replacement of water volume.
2.51 Summer evaporation is 0.056 ML/ha/day with a gross loss of 403 ML/day. In the absence of storm surges only half the days of each cycle will have tidal variation capable of producing useful inflows so the daily pipe flow must be in the order of 806 ML/Day, over an 8-9 hour high tide interval.
2.52 The passive flow rate will vary as the tide height outside the dunes rises and falls in relation to the mean sea level inside the dunes. An average cycle of the type shows at left of the graph at 2.13 above would have two hours (first and last) of a 10cm drop, 2 hours each of a 20cm, 30cm and 40cm drop, and a peak hour of 50cm drop that defines the rate of inflow.
2.53 Over a single1000m pipe of 3.6m diameter this would produce passive flow of;
2 hours @ 7.83m3/sec for 56 ML
2 hours @ 11.39m3/sec for 82 ML
2 hours @ 14.18m3/sec for 102 ML
2 hours @ 16.56m3/sec for 119 ML
1 hours @ 18.68m3/sec for 67 ML
For a total discharge of 426 Megalitres a day.
2.54 A 20cm storm surge on such a day is likely to add another 295 ML to the peak flow and 168 ML to the lower flows, taking the daily discharge to 890 ML.
What else do we need to know?
4.01 The average duration of storm surges, (i.e., the time taken for frontal systems to pass) and their range of variation, needs additional study, as does their mean height and their range of variation in height. Without this information the more accurate determination of the likely range of passive flow pipe yields cannot be made.
4.02 For the proper management of Murray mouth sand deposition we need to know the proportion, number, and range of scale variations, of storm surges that coincide with the periods of peak tidal variation. Storm surges that coincide with ebb and neap tides are likely to produce much less deposition because their rising inflows counteract the tidal outflows. Storm events where maximum surge takes place during maximum tidal inflow will present the highest volume and velocity inflows and produce the highest volumes of sand deposition.
4.03 We then need to know the extent to which these major deposition events must be negated and the extent to which their deposition volumes can be carried forward for remedial action by subsequent normal tidal outflows and benign phase storm surge outflows. This information will be essential for the ultimate design specification.
4.04 We need to know the proportion of total inflows that will need to come via conduits other than the Murray mouth to ensure equal deposition and removal on each tidal cycle. That is, when the combined outflows through the mouth can remove the deposition that took place on the previous inflow. At Alternative 5.50 below, we have assumed this to be 50% but the actual is likely to be much less because a unidirectional diversion system reduces deposition by diverting mouth inflows to the alternative conduit and increases sand removals by increasing the total volume of mouth outflows via improved efficiency of the tidal prism.
4.05 We need to know the optimum size, volume, cost relationships in both pipe construction and installation. This analysis has used 3.6m diameter pipes as a standard but we need to know, for example, if smaller ones provide substantially lower cost advantages that outweigh the resulting reduced flow volumes. It may also be possible that larger pipes produce flow gains that outweigh their increased cost and installation difficulties.
4.06 Optimum pipe size will also be influenced by installation issues on the seaward side with questions over a single large prefabricated sub-surface interface or an on-site construction with coffer dams etc.
4.07 The trade-offs between large capacity passive flow systems that only function for part of the time, and smaller capacity pump based systems that can function all of the time would also merit detailed consideration.
4.08 The full evaluation of alternatives for keeping the Murray mouth open, carried out by the Sand Pumping Technical Committee in 2002 must be made public to properly inform the policy process. Some of these options, while appearing to be more costly than dredging appeared to be in 2002, may prove to be valuable contributors in a combined approach. For example;
“The Southern Alexandrina Business Association[19] has sent (9/04/09) a proposal to SA Water Security Minister Karlene Maywald for a break-water for the neighbouring Coorong. Association president John Clark says the cost would be roughly the same as dredging but would have longer-term benefits for the internationally-recognised Coorong wetlands”. http://www.abc.net.au/news/stories/2009/04/09/2540147.htm
If the local Business Association’s costing is anywhere near the reality then a mix of pipes, dredging and breakwaters is likely to be even more effective than each option in isolation. And the cost is certain to be substantially less than the MDBA’s perverse fresh water fetish.
5.00 Alternatives:
5.10 The Buyback of 3 million ML of irrigation water to maintain a higher continuous outflow. This option has a total cost in the order of $6 billion, with annual costs of $600 million. It uses high value, and highly variable supplies of fresh water to do a simple hydrological function. It wastes more than half the total volume supplied because it is delivered at a time when there is next to zero assistance in sand removal from tidal outflows.
5.11 It is incapable of responding in the time and scale needed to deal with the key storm surge deposition events. It is a continuous, static solution to a set of dispersed, variable impacts. And it will not alter the fact that the capacity of the tides to fill-in the Murray mouth is in direct proportion to the degree to which the river flows might open it.
5.12 In economic terms it is an even bigger waste. It takes water that is currently put to profitable use in an important national value chain. It involves water that must be purchased at considerable cost to the Commonwealth and it involves a significant ongoing reduction in the tax base and a serious undermining of the cost base for major storage infrastructure like Dams etc.
5.13 It will achieve little additional benefit to what has been delivered by a single dredge for the past three (worst case) years at an annual cost of $2.33 million.
5.14 And none of the wealth transfers involved appear to be incorporated into the Commonwealth Grants Commission processes, the body responsible for the fair and equitable distribution of Commonwealth funds between the states.
5.15 And it will not go anywhere near to restoring the ecological values of the lower Coorong, the very wetland used to justify the use of this water.
5.20 Removal of the Barrages to restore the tidal prism. This option has been promoted as the obvious solution to the major evaporative losses that take place within the lower lakes in severe drought.
5.21 But in a context of a current 5 million ML mean annual discharge of fresh water out the Murray mouth, and the prospect of an additional 3 million ML from buy-backs for the same end, the increase from a pre-settlement 400,000 ML fresh water evaporation to a current 500,000 ML net figure, makes this very much a second order issue.
5.22 The contribution of partial openings during drought to maintain internal water levels etc is certainly an option that needs proper consideration.
5.23 However, the permanent opening of the Barrages will actually exacerbate problems of excess deposition in the mouth by increasing the volume and velocity of the tidal inflows.
5.30 The construction of open channels through the dunes to introduce more sea water into the Coorong Lagoons. This option would be comparatively cheap to implement but would be quite short lived. If the Murray mouth, with its additional discharges of fresh water, cannot combat the internal sand build-up from tidal inflows and storm surges then additional man made channels will be closed by the same forces in even less time. Open channels must function in the same littoral zone as the Murray mouth and the resulting exposure to the forces at play in that zone would require continual maintenance expenditure and render the option unviable.
5.31 The closure of open channels would take place even faster if gates were fitted to allow for unidirectional flows.
5.40 The installation of large diameter, in-flowing pipes under the dune system to the Coorong, one supplying the North Lagoon and two supplying the South Lagoon, each delivering approximately 100,000 ML of sea water each year, sufficient to produce a net flow along the full length of the system and ultimate discharge through the Murray mouth.
5.41 The two, located near Fig Tree Crossing, would be capable of replacing all annual evaporation losses and, within a single year, push the entire hypersaline volume into the North Lagoon. The third pipe, just north of the Narrows, could then push the remaining volume out through the Murray mouth.
5.42 It is the first step in restoring the essential ecological values, especially normal salinity levels, to the system. The reliance on “tidal sloshing” has proven to be a consistent failure, especially for the South Lagoon. The delivery of fresh water from the Murray to the most useful parts of this system cannot be achieved without considerable additional capital outlays. And the volumes required cannot be sourced from the Upper South East Drainage Scheme.
5.43 This option substitutes a comparatively small amount of cheap, well targeted, sea water for a very large and indeterminate volume of expensive, poorly targeted fresh water that does not even perform the function assigned to it.
5.44 With this direct injection of tidal water into the Coorong system the full suite of environmental values and ecosystem services can be maintained with a substantially higher level of certainty. And the system can be maintained in a circumstance that remains connected too, but is no longer dependent on, the vagaries of Murray mouth hydrodynamics.
5.45 If the overriding aim of the MDB Guide’s requirement for 3 million ML of expensive buy-back water is to keep the Murray mouth sufficiently open so tidal sloshing might keep the Coorong ecosystem just above the point of ecological collapse then the need for this entire mouth open objective can be negated by just 300,000 ML of cheap sea water delivered directly to its point of maximum benefit.
5.46 The capital buy-back value of fresh water is $2000 per megalitre so the opportunity cost of a pipe that delivers 100,000 ML of sea water to do a better job is $200 million. Any capital outlay less than $600 million on these three pipes represents good value. Given that the concrete in a 1000m pipe of 3.6m diameter and 20cm thick only amounts to 2,400m3, and costs only $720,000 at retail prices, one must conclude that it would take some seriously monumental departmental bungling to push the installed cost above $100 million a pipe.
5.47 This option serves the first two functions outlined at 2.46 above, that is;
- As a simple source of fresher water to overcome seasonal hyper salinity and replace evaporation losses in the closed end system.
- As a general augmentation of existing volumes into the far reaches of the Coorong to produce an increase over normal water levels and create a net outflow which will discharge excessive and unsustainable saline build-up out through the river mouth.
5.50 The provision of additional pipes under the dunes either side of the Murray mouth to improve the management of normal flows and to respond in time and scale to retard the impact of storm surge deposition events.
5.51 These would need to be in sufficient number to deliver half the total tidal prism that would result from the onset of a 0.5m storm surge during the nine hour inflow phase of a 1.1m peak tide or 16 ML/ha. The total inflow would be 13,000 ML so the capacity of the pipes must be 6,500 ML over the same period to ensure that the volume flowing out the river mouth is double the volume flowing in the mouth.
5.52 Unlike pipes flowing into the Coorong where the outlet water level remains near AHD, pipes near the mouth would start inflows from the moment the low tide turned, and would continue to the tidal peak. The water velocity and discharge rates would be defined by the slope obtained from the water levels on either side of the dunes. And in the absence of more detailed analysis we should assume this to be a drop of 0.1m over 700m of pipe.
5.53 This would discharge 9.5m3/sec, or 34.2 Ml/hour, or 308 ML over a nine hour tidal inflow. The 6,500 ML capacity in that circumstance would require 21 pipes. This would mean one pipe for each 39ha of tidal area so the Goolwa channel would need 8 while the Tauwitcherie channel would need 13 pipes.
5.54 This would reduce the storm surge flow through the mouth to the same volume as a modest 0.8m tidal flow under natural conditions. A normal peak tide of 1.1m range would produce the even more modest 0.55m tidal inflow through the mouth with the full 1.1m outflow.
5.55 This across the board halving of river mouth inflow volume and velocity would produce a much more than proportionate decrease in sand deposition. The increase in river mouth outflow volumes and velocity through improved efficiency of the tidal prism would also produce an increase in sand disposal. And this gives us strong grounds for suspecting that this number of pipes may be significant over-kill.
5.60 Maintain dredging in a post flood open Murray Mouth. Once the mouth is open, it is an incontestable fact of history that a single dredge was able to maintain that open mouth during a period of zero fresh water discharges at a cost of only $2.33 million a year. The current capacity to move a minimum of 2000 m3 of sand in a 24 hour day along a pipeline up to 2km in length, is an asset that could be used elsewhere in the estuary to enhance the tidal prism. The sand bank just outside the Eastern end of the Tauwitcherie Barrage is a good first candidate and modification of The Narrows would also be justified. A system of pipes and breakwaters may produce additional need for dredging too.
5.61 It is obviously more economical to prevent a channel from degrading than it is to open a channel that has already closed. The current flood discharges have already opened the channels much wider than the dredge ever could but in subsequent years this maximum opening must contract. In a $10 Billion budget with $1 billion annual outlays, this $2.33 million punches well above its weight.
6.00 Conclusions
6.01 The option that least serves the purposes of the Water Act 2007 is option 5.20 Removal of the Barrages. The restoration of the original tidal prism may provide a temporary improvement in tidal sloshing into the North Lagoon but this would be a very short lived improvement as the asymmetric tidal patterns will increase deposition at the Murray mouth and substantially retard the efficiency of that enlarged tidal prism. Any benefits to be gained by introducing sea water into the Lower Lakes during drought can be achieved by simply opening the Barrages. Their removal is not necessary.
6.02 Option 5.30 Construction of open channels to the Coorong does not serve the purposes of the Water Act 2007 any better. The benefits of direct injection of sea water into the hypersaline ecosystem would be very short lived as the same processes at play at the Murray mouth would close any open channels even faster. This option would require continual maintenance at great expense.
6.03 Option 5.10 the buy-back of 3 million megalitres to increase regular flows is a static, continuous response to a variable, intermittent need. It also demands the scarcest and most valuable water to do a simple hydrological task that can be done better by cheap, abundant and reliable sea water. The scientific community has made no secret of their view that the volume is totally inadequate for the requirement. But the need to balance ecological, social and economic values for the up-stream communities will ensure that the required amount will not be forthcoming.
6.04 Option 5.60, Dredging, has already demonstrated its capacity to maintain an open Murray Mouth, at very low relative cost, and in worst case river flow circumstances. It has clearly earned the right to be included in any mix of solutions and is entirely compatible with other options as an outcome multiplier.
6.05 Option 5.40, Pipes under the dunes to the two Coorong lagoons, deals directly with the need to restore and maintain ecosystem services by delivering sufficient volume of fresh, fully oxygenated sea water to the exact locations that will meet the obligations under the Water Act 2007. It does so in a way that is in direct proportion to the need and it considers the highly relevant matters of timing, flow direction, adequacy and efficacy of water volumes delivered. It maintains the ecological integrity of the whole system but with a fully flexible stand alone management system. It operates in an incremental framework that deals with the most pressing ecological problem, South Lagoon hypersalinity, first and can then play its part in the broader issue of maintaining the Murray mouth.
6.060 Option 5.50, Pipes under the dunes to manage the Murray mouth, becomes a lesser priority once the ecological integrity of the Coorong has been restored by Options 5.40 and 5.60. The health of the Coorong need no longer be dependent on the state of the Murray mouth.
6.061 However, any pipes near the mouth will be better than no pipes because every pipe will enhance the contribution already made by river flows. The economics of trenching and subsequent dune restoration dictate that three or four pipes should be installed in each excavation. And the need for balanced hydrology in both channels would demand a minimum of eight pipes with four on each channel. The reality is that sea water is a superior, more abundant, lower cost, less disruptive and more proportionate substitute for all fresh water discharges through the Murray mouth. And there is no excuse for not doing so.
6.062 If the Australian community has already accepted a budget in excess of $6 billion for the buy-back then the mandate is already in place to spend up to the same amount on pipes to do a much better job.
6.063 When that $6 billion opportunity cost of the 3 million megalitre buy-back is spread over the estimated 16 pipes needed to completely restore the Coorong and keep the Murray mouth wide open we get an extraordinary $375 million for each pipe. The $200 million/pipe figure used in 5.46 above does not factor in the improved water use efficiency delivered by proportionate sea water over disproportionate fresh water.
6.064 And given the savings to be gained from placing 3 or 4 pipes side by side in the one excavation we can safely conclude that the cheapest and best option is undoubtedly the pipes.
6.065 In fact, with the Barrages in place for more than 70 years now, the demarcation of sea and fresh water ecosystems is well established. And this means that further substitution of sea water for existing flows is also feasible as a source of additional fresh water for up-stream wetlands. With adequate sea water systems in place there is no longer any justification, either logical or ecological, for a single drop of fresh water to go over the Barrages. All of existing fresh water outflows (up to 5 million ML) could be used for delivery of up-stream ecological services at zero cost to the economic, social and ecological values of the Basin.
6.066 I advise accordingly, and request that the MDBA considers all relevant matters outlined in this submission, and takes all reasonable and practical steps, to ensure that it does not;
- give effect to any improper exercise of power, or
- apply measures that are not cost effective, or
- apply disproportionate measures, that may
- cause entirely foreseeable, and avoidable detriment to people or communities in the Murray-Darling Basin.
Copyright: Ian Mott, 8th December 2010.
38 Jellicoe Street Manly West QLD 4179
Ph. (07) 3893 0612
talbank@bigpond.net.au
References:
[1] Walker, DJ. (2002) ‘The Behaviour and Future of the River Murray Mouth’ pp 14
[2] Harvey, N. (1996) ‘The significance of coastal processes for management of the River Murray Estuary’, Australian Geographical Studies, vol.34, no. 1, pp 45-57.
[3] Walker, DJ. (1990) ‘The role of river flows in the behaviour of the Murray Mouth’. South Australian Geographical Journal, vol. 90, pp. 50-65.
[4] Webster, IT. (2005) An Overview of the Hydrodynamics of the Coorong and Murray Mouth. Technical Report #/2005. CSIRO Water for a Healthy Country National Research Flagship. pp 4
[5] WBM Oceanics (2003), Murray River Mouth – Morphological Model Development Stage 2 – Model Set Up, Calibration and Verification, Report prepared for Murray-Darling Basin Commission & SA Dept. for Water, Land & Biodiversity Conservation.
[6] Chappell, J. (1991) Murray Mouth Littoral Drift Study, Report prepared for the Engineering and Water Supply Department, South Australia.
[7] Walker, DJ. (2002) op. cit. Fig. 4.3 pp 7
[8] Webster, IT. (2005) op. cit. pp 7
[9] http://www.calctool.org/CALC/eng/civil/hazen-williams_g
[10] CFMI (1992) Mathematical Modelling of the Hydrodynamics and Salinity in the Coorong Lagoons, Report CNG-1-12-12/92 prepared for the Engineering and Water Supply Department, South Australia.
[11] CFMI (1992) ibid.
[12] Chappell, J. (1991) op. cit.
[13] Webster, IT. (2005) op. cit. pp 16-17
[14] Dredging reduced at Murray Mouth, Earth Mover Magazine, (11/2020)
http://www.earthmover.com.au/news/2010/newswire/november/november-4th/other-top-stories/dredging-reduced-at-murray-mouth
[15] Campbell, T. Brown, R. Erdmann, B. (2008) Murray Mouth Sand Pumping: Keeping the Tided Flowing. Report by the Contract Manager, SA Water Corporation. pp 1
[16] Campbell, T. Brown, R. Erdmann, B. (2008) op. cit. pp 6
[17] Campbell, T. Brown, R. Erdmann, B. (2008) ibid. pp 6-7
[18] Campbell, T. Brown, R. Erdmann, B. (2008) ibid. pp 12
[19] The Southern Alexandrina Business Association. (2009) Submission to SA Water Security Minister on construction of Breakwaters. http://www.abc.net.au/news/stories/2009/04/09/2540147.htm
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