LETTER: Removing sand from the Todd makes no sense as a flood mitigation measure

Sir – There have been recent calls for the removal of sand from the Todd as a flood mitigation measure. It has recently been announced that AS Town Council is about to commence doing this.

As far as I can determine this is based on no scientific evidence whatsoever, and in fact is contrary to the best advice. If this is the case, I object in the strongest possible terms to my rates being wasted in this way. Can the Mayor come up with any evidence to justify the sand removal?

The Alice Springs Flood Plain management plan (1996) is the primary document in this issue. I was a member of a Steering /Advisory Committee that oversaw the development of this plan (I recently dated it to ’89, but that was incorrect).

The plan documented the fact that some members of the public claimed that the river bed has more sand than in the “good old days”. The Power and Water authority has good data on this, they have been monitoring it for 50 years. There have been no significant changes. The plan notes that local variation occurs, high points and banks can change and move around. However this is offset by correspondingly deeper low points.

The plan looks at the effect of the causeways, and concludes that the “bed-level” causeways (Schwarz and Tuncks) have no effect on the river flow. The obvious conclusion from this is that these causeways are on the “natural” bed level. It also follows from this that deepening the river bed by sand removal would do nothing for the river flow capacity unless the causeways were also removed and deepened, or replaced by bridges. Even if this were done, the sand would settle to its natural level after the next flow, and cover the below “bed level” causeways.

To achieve a significant increase in the river flow through town a host of works would have to undertaken:
• Several pipelines would have to be relocated.
• All the causeways would have to be rebuilt.
• The river would have to be deepened by 1.5m, and widened to 100 metres.
• All the trees would have to be removed.
Essentially the Todd would be turned into a concrete drain.

The plan does not explicitly address the Gap, but presumably to make the “concrete drain” work it would also have to be widened and deepened. Forget it.

And, to emphasise the fact again, removal of sand from the river bed would have no significant effect. It would be a waste of money. Our perception and memory of a build up of sand is wrong. 50 years of measurements document this.

My information comes from The Alice Springs Flood Plain Management Plan 1996. It is available in the Alice Collection in the Library.

Charlie Carter

Alice Springs

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11 Comments (starting with the most recent)

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  1. Hal Duell
    Posted November 13, 2012 at 12:27 pm

    @Alex
    Thanks for the explanation.
    I will admit that I still think it was better to remove the built-up sand, couch and all, rather than wait for a flood to do it. Chinaman’s Creek drains most of Alice Springs west of the Stuart Highway, more or less, and I like the idea of any water coming down that system exiting thru The Gap as quickly as possible.
    (Where does the run-off from the old Racecourse area go?)
    I agree with your comments about a river’s ability to alter its own banks. I too have seen that happen, although a bit further downstream. I have been told this phenomenon is known as a “hungry river”, and not much can stop it once it gets its teeth in.
    Perhaps that is another reason to remove any built-up sand before a flood – let any flood go through without getting its teeth in.
    To minimise the chance of that happening between the Telegraph Station and The Gap, I hope the sand currently being removed be ASTC is only being taken from the middle channels, and not from the sides.
    One more comment about the Taffy Pick crossing – in answer to a question at last night’s committee meetings, I learned that the crossing belongs to the NTG. This means that if it is to be knocked down to a level crossing, they are the ones to do it.

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  2. Posted November 13, 2012 at 10:44 am

    Perhaps I can answer your query, Hal – in short, yes, the removal of the sand at the junction of the Todd River with Chinaman’s Creek (yes, that was its name) at the north entrance to Heavitree Gap was unnecessary. This same area was sprayed with Roundup to kill the couch and buffel grass all the way to Taffy Pick Crossing and the sand was excavated only 10 years ago (I took photographs). It was a complete waste of public money.
    For a good example of where to see the effect of unimpeded water flow of the Todd River, it’s worth checking the river bank adjacent to the Arid Zone Research Institute. You’ll see an extensive indentation carved into side of the river with a sheer drop of three metres; it looks rather like a miniature version of the Great Australian Bight. This feature was caused by the flood of 1988, when the river water carved out a chunk of land (at least in the hundreds of tons of soil, perhaps more) and completely swept it away.
    All the trees and grasses on the side of the river bank did nothing to prevent that erosion, they all vanished downstream. Shortly after that flood, when I went exploring out that way to see what had happened (I was living nearby at the CSIRO Field Station at the time, now the Centre for Appropriate Technology) I observed trees and grasses teetering on the edge of that bank, with partial exposure of the roots dangling metres above the riverbed (again I took photographs). This stretch of the riverbank is the largest natural sudden change of the land I’ve seen occur anywhere in this region’s vicinity.
    The point here is that when there is a major flow of the river, piles of sand and sediment held together by grasses will simply be swept away.
    It’s also worth noting that the slope of the riverbed through town between the Charles Creek junction at Schwarz Crescent and Heavitree Gap to the south is a drop of 10 metres. Thus the impact of floodwaters backing up at Heavitree Gap itself has a minimal effect on the town further upstream.

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  3. Hal Duell
    Posted November 11, 2012 at 1:33 am

    @Charlie
    Are you saying that it was either wrong or unnecessary to remove the built-up sand earlier this year from the junction of the Bradshaw and Bloomfield drainage systems and the Todd River. (Is that Chinaman’s Creek? I heard that somewhere, but now can’t find it anywhere.)
    The Todd’s bed was about one meter higher than the bed of the drainage system, and was heavily anchored with couch grass too thick to walk through.
    I don’t know if grasses like couch and buffel are why sand builds up, but I suspect they help hold it when it does.
    Also, do you think that when flood water is checked, it drops some of its load? And if it does, does that impact on the flow of subsequent floods? This question leads into the Taffy Pick crossing, so don’t answer it if you don’t want to.

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  4. Posted November 10, 2012 at 11:20 am

    Peter Driscoll’s comment highlights why so much inaction has occurred with flood mitigation and management of the Todd River through Alice Springs during the period of time almost equivalent to self-government of the NT. Essentially the NT Government’s attitude (under CLP rule) was that the single most effective measure to counter flooding of the Todd River would be the construction of a flood mitigation dam in the hills upstream of Alice Springs.
    Two locations were proposed during the 1980s; the first was at the Old Telegraph Station, the second at Junction Waterhole further north. Both sites were strenuously resisted by Arrernte traditional owners concerned about the impact the dams would have on sacred sites.
    Technically a “dry dam” for flood mitigation would be the most effective measure against large floods but this would require extensive re-negotiation with TO’s who undoubtedly remain wary in light of the bitter diviseness this matter has generated in the past. The project would stand a much better chance of success, I think, if any suggestion of permanent inundation for recreational purposes (as insisted upon by the NT Government in the past) is ruled out completely.
    But that still leaves us with the need for dealing with localised flooding of the Todd River through town and for adequate management of it at all times.
    Currently the Todd River, for most of its length in town, is at or below the natural bed level of the sand. This is evident (as Charlie Carter pointed out on ABC radio a few days ago) by observing the bases of old river gum trees which predate the existance of Alice Springs – many of them now sit well above the natural bed level of the river at the time of their germination with significant root exposure. River gums never grow naturally with their roots exposed. This is particularly evident just downstream of the Wills Terrace Causeway, which was extensively excavated just six years ago. This same stretch of the river is now slated as Stage 3 for the current sand-mining of the Todd River by the Alice Town Council, as stated by Greg Buxton on ABC radio!
    There is also photographic evidence, too – the best example I know is a photo taken by Rev. John Flynn from the top of Meyers Hill in 1926 with a view towards what is now the CBD. The riverbed and west bank adjacent to the Civic Centre has not changed in almost 80 years.
    Equally I know of a photo held at the Olive Pink Botanic Garden taken during the drought of the 1960s, which views Olive Pink’s flora reserve from across the Todd River. Again, the riverbed and bank adjacent to the OPBG has not changed.
    In the 1950s my father regularly camped in the Todd River adjacent to May’s Guest House (now the Institute for Aboriginal Development on South Terrace), where the riverbank is quite high and steep. It was so in the 1950s and remains the same today, it hasn’t changed.
    The only part of Charlie Carter’s letter I disagree with is where he states The Alice Springs Flood Plain Management Plan 1996 concluded that the Tuncks Road causeway has no effect on the bed level of the Todd River. That’s clearly not the case now, where there is an obvious drop in the river bed on the downstream side – so much so, that just a little further downstream it is easy to observe the concrete capping that marks the position of the Palm Valley gas pipeline for the old power station. This was constructed in 1983, and the concrete capping was buried beneath the sand level at that time. Now it is exposed.
    Only the Schwarz Crescent causeway shows no impact on the Todd riverbed, yet that is where the Council has, and is, removing sand from the Todd!
    Finally, the cause of sand and silt buildup in the Todd River through the town is regularly attributed to the presence of exotic grasses, especially buffel and couch. While these grasses are most undesirable from an environmental perspective, they clearly are not the main cause (if any) of the perceived buildup of sand and silt. These grasses dominate along many of the rivers and creeks in the Central Australian region yet nowhere else have they caused any major flow restrictions; for some reason, they only do so (according to many) within the confines of the town’s urban area.
    Strangely, that’s the only stretch of the river where we have all these causeways, too.

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  5. Peter Driscoll
    Posted November 9, 2012 at 11:00 pm

    Seems like the easiest solution is to build a flood mitigation levy north of the town, to only be closed in pending flood emergencies for a short period of time to slow water flow through the town. I hope with a new government we can revisit this with the Feds.

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  6. Charlie Carter
    Posted November 9, 2012 at 9:50 pm

    Hal and Steve,
    Note, my letter deliberately DID NOT mention the Casino causeway. I did not want to muddy the water. I wanted to concentrate on the sand removal issue. The point about the bed-level causeways is that they reflect the “natural” level of the river bed. The Casino causeway is more complex. In smaller flows (up to a 1 in 20) it reduces the river “cross-section” and therefore increases the water velocity. You do not see a sand build-up below a constriction. What happens above is complex, and beyond my expertise.
    I was trying to avoid putting my relatively inexpert opinions forward, and am suggesting that we listen to the experts. I have had the benefit of sitting through the meetings and briefings that were part of the process of compiling the Flood Plain Management Plan. However, it’s 16 years ago, and like the people who see sand build up in the river, my memory is not perfect. That is why I went back to the document before I wrote. I suggest others do the same. Greg Buxton from ASTC responded to my comments on ABC Radio on Thursday.
    When asked for the science to support the decision to remove sand he blustered and waffled and finished up with “observations” Peter Latz has often observed that scientific conclusions are sometimes “counter-intuitive”.
    I would prefer to rely on the science in the ASFPMP than Mr. Buxton’s observations. He also misunderstood, or misrepresented, the FPMP. It does not recommend sand removal. Nor does it recommend “building bridges”. It does canvas these options, and dismisses both.
    Charlie Carter

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  7. Posted November 9, 2012 at 11:18 am

    Dealing first with Hal Duell’s comments, the Taffy Pick Crossing (originally the Casino Causeway) was constructed in 1981, and opened in July that year simultaneously with the opening of the Federal Hotels Casino. Federal Hotels and the NT Government jointly funded the construction of the Casino Causeway.
    Amongst the earliest critics of the new causeway was Taffy Pick in a letter published in the Centralian Advocate in early December 1982 – three months later the flood of March 1983 swamped the foyer of the casino and ripped out an 11 metre wide chunk of the causeway.
    A study was undertaken from 1984 onwards by the NT Government for the construction of a full size bridge to replace the Casino Causeway; and in 1986 the NT Government announced a $5.7 million project for the reconstruction and re-alignment of roads at the north entrance of Heavitree Gap and South Terrace, including a large roundabout at the Gap, re-alignment of South Terrace, a new bridge downstream from (and replacing) the Casino Causeway, a roundabout on the east bank of the Todd linking Stephens Road and Barritt Drive with the bridge, and extension of Stephens Road to link with Sadadeen and Undoolya. Only the roundabout at Heavitree Gap has been built, and that was a separate project in 1994 that was part of the NT Government’s plans for the rejuvenation of Alice Springs (which in itself sounds awfully repetitive, doesnt’ it?).
    The NT Government transferred responsibility for the Casino Causeway to the Alice Springs Town Council in early 1987. Following the flood of April 1988, the mayor Leslie Oldfield begged the NT Government to urgently replace the Casino Causeway with a properly constructed bridge.
    The NT Government has long publicly recognised that the Casino Causeway exacerbates flooding of properties by the river for a distance of 400m upstream from the causeway but has never done anything to resolve this problem of its own making.
    To my knowledge and recollection, there have been four major occasions in the past 30 years or so when sand has been removed from the Todd River within the urban area. The first was in the early 1980s but was suspended in 1982 following assessment by the NT Conservation Commission that showed that sand removal was having an adverse effect on the river gums.
    The second was in August / September of 1988, when the Department of Transport and Works removed sand that had accumulated next to the Casino Causeway. This was only a few months after the flood that year and coincided with the Flynn by-election campaign, during which the effect on flooding by that causeway was a major concern of voters in that electorate. (The CLP polled last and Labor topped the poll on that occasion, the only time this has happened in an urban electorate of Alice Springs. The CLP’s preferences helped NT Nationals candidate Enzo Floreani to win).
    The next major sand extraction that I recall was a decade ago, when the Alice Springs Town Council was granted $400,000 for the extraction of sand from Heavitree Gap to Taffy Pick Crossing, which also included extensive spraying of couch and buffel grass. This was a part of the NT Government’s Alice in 10 project; and this particular project was meant to be the first stage of cleaning up the river all the way to the top of town. It never progressed beyond that first stage; and (as predicted on the ABC by both my father and myself) this was a complete waste of money.
    The last major sand extraction from the Todd River occurred in 2006, in a project funded by the Martin Labor Government. This involved an upgrading of the Wills Terrace Causeway and extraction of sand downstream along the CBD, which cost (from memory) $600,000.
    So now we have yet another publicly funded program of removal of sand from the bed of the Todd River, based on utterly spurious documentation upon which the Alice Springs Town Council relies to justify the expenditure of public monies.

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  8. Hal Duell
    Posted November 9, 2012 at 5:11 am

    Since my last post, I have been informed that the Taffy Pick Causeway was built with money from the NTG, the Commonwealth and a contribution from Hotels Australia, or whoever the home page of the first casino operators belonged to.
    The responsibility for its maintenance was accepted by (dumped on?) a reluctant Alice Springs Town Council in the late 1980s.
    But who owns it today? Before it can be replaced with a level crossing, or even a bridge if that kind of money is available, that question needs answering.

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  9. Hal Duell
    Posted November 8, 2012 at 10:27 am

    When the Todd floods, the water carries a quantity of sand. Is that fair?
    Then, if the flow is slowed, some of the carried sand drops. Is that fair?
    The causeways, but especially the Taffy Pick crossing, slow all floods. Is that fair?
    Economic constraints dictate that we will never get rid of, or even rebuild, all the causeways. But we could lose the Taffy Pick crossing, not by replacing it with a bridge (economic constraints again, and possibly geographic ones as well), but by replacing it with a level crossing.
    If we did that, in the next flood wouldn’t at least some of the recently deposited sand from either side of the crossing flow out through the Gap?
    I question if this work would mean a rate hike. I thought the crossing was the responsibility of the NT government who, I have been told, insisted that the original builders of the casino put that crossing across the Todd. If this is true, who owns it now?
    Surely the removal of up to one meter of sand from the junction of the Bradshaw and Bloomfield drainage systems with the Todd River increased the flow of flood water through the Gap. I don’t know if that counts as sand-mining or not, and I don’t see it making, or even hinting at, a “concrete drain”.
    I too am all for “best practice” in the Todd, but what is best practice? If anyone thinks we can find one clear scientific opinion on this, I suggest they try to follow the global warming debate in which scientists of all stripes seemingly cannot find any common points of agreement.
    This may change after Cyclone Sandy, but I doubt it.
    While we look for that elusive best practice, and await funding and process for a flood-mitigation dam, how about we petition the NT government to level the Taffy Pick crossing. It would be a start.

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  10. Steve Brown
    Posted November 7, 2012 at 5:52 pm

    When the water flows so does the sand. When it stops being carried by the water it settles at the height of the highest sand dam, stopping its movement, the causeways.
    So the sand Level is determined by the height of the causeways. This means that when a logjam dam is formed against the casino crossing (Taffy Pick) the sand height rises towards that level and if the water runs long enough, will eventually reach that height with a corresponding increase in sand level all the way back up the river.
    It would be great to take this crossing out and replace it with a bridge but for the moment it is too expensive, unless you are volunteering huge rate rises, Charlie.
    It is a simple engineering fact (scientific) that if you concentrate the water flow into a channel it increases the velocity of the water. This in turn means that the water carries more sand which in turn has the effect of clearing a deeper wider channel through the sand which increases in dimension with the water flow. In short, you use the water to clear the built up sand. If you cast your mind back a while, Charlie, can’t give you a date, but this method has been successfully several times in the past.
    Given that sand is always being taken from the river further down I don’t see any reason that if sand is to be removed rather than pushed aside to form a channel, that those who are mining it further down couldn’t take advantage of mining it a little closer to town for a while, creating the channel for us at little or no cost.
    @ Dave if you mean by ominous that we might actually take the matter in hand and do something as opposed to running around espousing all encompassing motherhood statements such as Best Practice then you are probably right Dave: We really are ominous.

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  11. Posted November 7, 2012 at 3:59 pm

    @ Charlie Carter, ‘Removing sand from the Todd makes no sense as a mitigation measure.’ Posted November 7 2012.
    Great letter Charlie Carter! Despite the rhetoric from ASTC over the years, the signs coming from the new Ryan-Brown team are rather ominous concerning the management of the Todd River.
    I would guess that you share the sentiment of those like Mike Gillam who stated on 20/11/11: “We need best practice in the Todd.”
    I would also guess that, down your street, this issue is at least as important as that of cattle welfare as expressed in the Alice Springs News by Gehan Jayawardhana who has 22 years as research vet for NT DPI.
    The ball is well and truly in your court Mayor Damien.
    Regards,
    D. R. Chewings aka THE lone dingo.

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