Sands in Todd more stable than you think (re-published with Maxine Cook’s comment)

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ALEX NELSON

 

The river bed of the Todd is more stable than many assume. These photos were taken from exactly the same vantage point on Meyers Hill (originally called Nannygoat Hill). The first was by John Flynn in 1926; the brand new hospital Adelaide House is clearly visible left of centre of the photograph. I took the second this year.

 

There are two prominent river gums in the bed of the Todd River at the lower left of Flynn’s photo. These trees still exist next to the Stott Terrace Bridge, as seen in my photo. The tree in the middle of the riverbed has suffered extensively from dieback, a widespread disease problem which reached its peak in the 1980s, but in the last decade this tree has staged a remarkable recovery. This is typical of many of the rivergums in the Todd and other river systems in Central Australia.

 

In my photo there is a prominent “island” covered in buffel grass on the eastern side of the riverbed. This island is also observable in Flynn’s photograph, although it was devoid of vegetation at the time. It therefore cannot be argued this island of sediment has been caused by the presence of exotic grasses – rather, the grasses have taken advantage of the relative stability of this site upon which to establish and thrive.

 

As an afternote of interest, the name “Nannygoat Hill” but the name would be of the same vintage as Billygoat Hill. It was during the early part of last century that settlers relied heavily on flocks of goats for milk and meat. It’s for this reason that much of the landscape around Stuart (as it was then) was heavily denuded of vegetation. Goats were kept at the base of Nannygoat Hill in the area that is now the Olive Pink Botanic Garden – there is still an old Dead Finish shrub at the rear of the visitor centre which displays a clear browse line in the canopy from the time when goats must have sheltered beneath it.

 

RELATED READING: Removing sand from the Todd makes no sense as a flood mitigation measure – letter and comments.

 

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5 Comments (starting with the most recent)

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  1. Maxine Cook
    Posted December 25, 2012 at 4:12 am

    I was told the oldest river gums were having a problem in the 80s because the town area was no longer drawing the amount of water it used to from the immediate town water basin and with the good rainfall years from 1965-1985, raising the water level, then 85-86 being a drought, then 86-2007 being good seasons again.
    I was told the remedy was to start pumping a certain amount of water from the basin to keep the water to the desired level as the older trees, having longer roots, were not able to avoid the rising salty water.
    For quite a few years the creek had water above ground for most of the year which would have waterlogged a lot of the old trees. In the late 50s to early 60s, a lot of the wells people had in their back yards were not very deep but were becoming salty and contaminated. You had to be 100 yards from Billy Goat Hill, to be able to have a septic system in your yard but it didn’t say you couldn’t have one if your neighbour had a well in their yard, which I know was the case at our place!
    The increase in the number of trees in the newer photos of the town is really noticeable, when you compare them with the old original history photos.
    We had constant dust storms in the early days also, that would blow away any top soil that had developed from the silt and mulch. The lack of dust storms now must be a spin-off from having the amount of development and trees in the town and surrounding areas now?
    With more vegetation up in the catchment area the water would also be carrying more sediment with it in each flow as it cleans out the ground cover silt from the catchment areas.
    This is all being dropped as it goes past the islands building up more, and helping with the regeneration of our trees and protecting their roots. As the river can’t be made wider it can only be made deeper, or otherwise a dam could be the only other option?
    Before the guttering and storm drains were put in around the town the water during rain used to just flow through the town along the streets but now it all has to flow down around town and down the river towards The Gap. I think the engineers have done a great job of draining the town even just since 1984, as prior to that just a minor rainfall used to cause quite bad flooding through certain areas.
    The constant rainfall we had in 2010 was a good test for the drainage around town as the areas I used to notice flooding didn’t that year!
    I think our creek and its banks look a picture when the lush green couch is mowed. Now that we don’t have untidy camping in the creek bed it is really something for the council to be proud of.
    They must have been doing something right for the amount of trees that have regenerated and are in top condition. The infrastructure is very attractive and something the town should be proud of.
    The lack of vegetation in the 1926 photo was not caused by over grazing! The place may have been primitive but the goats etc. were not just roaming around the town.
    During the drought in 58-65 the only green places outside people’s own yards in town, were where the drain outlets into the creek supplied water for the couch grass, in between the odd rain and spurt of natural herbage for a week after rain, with the couch lasting a lot longer. Couch only goes to ground after frost but comes alive again after the frost stops.

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  2. Maxine Cook
    Posted December 24, 2012 at 10:59 pm

    The area referred to on the river used to silt up from deposits of silt dropped by the water coming from the eastern drainage areas, meeting with the Todd. They used to be very muddy after rain and flooding. Yes, the vegetation thrived in the moisture holding mulch left by the water flows.
    I have photos of the opposite side of the river below the Meyer’s Hill (Miss Pink’s Hill), in her day! That shows that there was no river bank 60 yrs ago the hill rocks just went straight into the river.
    The two big trees on the corner of the of the hill were not much smaller than they are now, but the now bank would be protecting them from flood damage in the future as the river sand on that corner is now quite a deal lower than it was when my photos were taken, with the trees looking like they were sitting in the river sand at the bottom of the hill rocks.
    Maybe a properly constructed walk way and bank on this corner would prevent further erosion and possible damage to the old trees. The fact that the bank has built up at the base of the hill shows the water flows slower on the corner as it is being pushed to the west by the water coming from the east.

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  3. Hal Duell
    Posted November 16, 2012 at 4:04 pm

    @Alex
    Thank you for your clearly stated answers to my questions.
    It is a bit of a shame, and a continuing problem that will always need managing, that Alice Springs was built where we find it. But after 124 years we’re still here, so we must not be doing everything poorly.
    I agree with you when you state that the river and the ranges are our two most valuable natural assets, but I would like to add one more – the night sky. We can’t do much about the sky except keep any industrial smoke our of it, nor about the ranges other than keep them from burning down and/or eroding. But we can impact better on the river through good management.
    And that’s the key – managing.
    It’s too late to pretend it will ever again be a “wild river” along the stretch between The Gap and the Telegraph Station. And above the Telegraph Station a flood mitigation dam with no allowance for a residue of standing water would severely impact on any tendency for wildness there and immediately downstream. I suggest we let it go wild again once it leaves us, and agree to manage what has become part of our shared urban landscape.
    Surely there are enough people with enough knowledge living here to come up with an acceptable plan. It doesn’t have to degenerate into a rancorous climate-change type debate.

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  4. Posted November 16, 2012 at 11:08 am

    Hal, both processes of deposition and erosion are occurring on this site and similar situations along the bed of the Todd River through town. There is clearly accumulation of sediment that has occurred on that sand island which has raised its height; simultaneously there is erosion now occurring on the margins of that deposition, and it is most noticeable at its termination closest to the Stott Terrace Bridge, where clumps of buffel grass are on the verge of being washed away in the next major flow. The same process is happening on the river bank on the far side of the photo. That is all part of a quite normal and natural process.
    Contrary to popular opinion, the Todd River appears to have long been comparitively narrow and shallow adjacent to the area now developed as the town’s CBD, and this was the situation before any European settlement of this vicinity. This is evident from the distribution of the oldest river gums in this area, where the junction of the tree trunks and root systems indicate the soil level at the time of germination. They clearly show the Todd River was more shallow and constricted than is the case today. Alice Springs’ town centre (which, incidentally, is 124 years old this month) was founded on a natural flood-plain verging on a flood-out.
    As you state, Hal, not all floods are raging events – in fact, the overwhelming majority of river flows are of low volume and duration and only carry water visible above the sand surface for short distances. In the past most flows of the river from the hills north of town terminated in the vicinity of where the CBD now exists; consequently, this is the location where a lot of sediment built up into the flood-plain/flood-out upon which the town centre is located.
    This pattern is repeated downstream on Undoolya Station in the vicinity of Rocky Hill, east of Amoonguna, where the bed of the Todd River disappears into a large flood-out area (as do Roe Creek and Laura Creek from west of town). This is where most big flows of the Todd River that run through Heavitree Gap terminate. It’s only the really big and comparatively rare flood events which manage to push water past this flood-out on Undoolya Station which re-converges into the Todd River further downstream; this lower stretch of the Todd River is augmented by river flows from Jesse Gap, Ross River and other streams that flow from the eastern MacDonnell Ranges.
    However, as far as Alice Springs (especially the town centre) is concerned, the primary problem is that it has been built in the wrong location; and this situation has been exacerbated by the construction of several causeways that interfere with the natural flow of the river. Extracting sand from the riverbed and spraying grasses is never going to redress these fundamental engineering errors, they are just exercises of throwing taxpayers’ good money after bad and it comes at the risk of considerable ongoing damage to the Todd River in town.
    Sadly the Todd River has never been properly managed in Alice Springs, especially so in recent times – yet it has the potential to be a major natural asset that complements the scenery of the magnificent MacDonnells in which this town is set.

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  5. Hal Duell
    Posted November 15, 2012 at 4:02 pm

    Alex
    I’m not arguing, just asking a couple questions.
    In the first photo there is a not particularly visible sand island that is not covered with any anchoring vegetation. In the second photo there is a clearly visible sand island that has been covered with vegetation that would help keep it anchored in place.
    Does a sand island seen in the same spot in photos taken so many years apart imply the possibility of a natural eddy at that spot in any flow of the Todd? And if so, could today’s floods coming upon an anchored island build up that island until it becomes an obstruction? This is assuming that any flow of a river, coming upon an obstruction and therefore being checked to some extent, will drop at least some of the sediment it is carrying.
    I think it is worth remembering that not all floods are raging events. Some are quite lazy, but they all carry sediment that can be left behind to be anchored with grasses.
    Is couch with its root system more effective in that regard than buffel? if so, could it be the couch on the banks that is protecting the banks and keeping the Todd confined to its present course?

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