The following post is a reprint of an article published in our local “Landcare Perspective” which is a newsletter put out by the Upper-Shoalhaven Landcare Council (a district level Landcare association, or ‘DLA’). The post was prompted by the article shown below, which appeared in the Winter-Spring 2014 edition of the Perspective….
….and, to a lesser extent by this ‘placestories’ video, which is also about ‘the Bank Job’ project.
The most stimulating aspect of these reports about ‘the Bank Job’ was that they both repeatedly blamed a single willow for causing the 10m deep incision that it was growing at the bottom of! No other causes were ever mentioned.
I could have made my own article more pointedly about rebutting this ridiculous claim, but wanted to avoid embarrassing anyone or hurting anyone’s feelings (I know! Shoot me please!). The Bank Job is a great example of how Landcare is able to motivate volunteer community input. But it’s also an example of how complex and dynamic environmental realities are often dumbed down to a predictable nonsense: “the willow did it”.
Another educational opportunity missed!
This story is about more than a group of volunteers wanting to do good things in their local environment. There’s a back story of misguided and misdirected ‘experts’ too. If you look at all of the organisations mentioned as contributing to this project, it is obvious there was a considerable investment of wages from various agencies. As such, total project cost would have been more than the $26,000 grant mentioned in the article above.
Anyway….here’s my take on ‘the Bank Job’ and why I think it’s a project that is missing the point. The problem evidenced here is not just one eroding bank, it’s an entire catchment with an elevated stream-energy regime. As a learning community of Landcarers, we need to join the dots and not simply blame the first non-native we see.
Landcare learning about landscape function
An article in the last Landcare Perspective gave an update on ‘the bank job’, a Landcare project on the Mongarlowe River. Apparently, a willow causing bank erosion was removed, and rock groins installed along with native vegetation, but the bank continues to erode. The article finished with the welcome suggestion that an evaluation of project outcomes now take place to inform future work at the site. I hope that the following contribution will help.
Flow-lines are in the business of handling varying flows of water and the erosive stream-energy that comes with them. If they are functioning well, they slow the water to limit stream energy and associated erosion. There’s a commonplace perceptual maladjustment in this country whereby people see a creek or river and assume that it functions to take the water away; whereas—as a matter of fact—flow-lines naturally develop in ways that will slow the water and hold it back as much as possible. This is achieved in multiple ways: overflowing across a floodplain is one of these, but many flow-lines are now significantly incised, so high flows don’t access floodplains as they once did. Where flows are contained within an eroded channel, stream-energy may also be dissipated by the process of meander development. Figure 1 shows how a direct path between two points of different elevation creates the steepest slope while a meandering route creates a longer path and correspondingly-lesser inclination; this lowers stream-energy and associated erosive force.
So meanders are a good thing, but how do they form in creeks and rivers? Well, it’s to do with the natural growth of vegetation. During recent fieldwork in an incised swampy meadow near Orange, I studied the development of pools and meanders caused by vegetatively-fixed bars of sediment situated along the base of the incision. Figure 2 compares a 1954 aerial photograph with another image taken in 2013, over this period of time a significant meander (indicated within the black rectangle) has emerged in the course of the incised flow-line.
The processes which led to this deviation are illustrated in Figure 3. The left side of this figure (A) shows the vegetatively-fixed bar and the pool below it—note the eroding bank on the right and the recently deposited sediment at centre. The right-hand image (B) is a close-up of this patch of sediment 4 weeks later—note how grasses have grown and stabilised (aggraded) it into the existing bar; this bar of sediment is actively growing.
Peak flows travelling over the bar are slowed and energy is dissipated at this point so that new deposition occurs after every high-flow event. At the same time, remaining stream-energy is deflected into the opposite bank causing erosion and channel deviation. The bar is expanding because stream-energy is lower where the plants have established; the bank is eroding because energy is being deflected to the opposite side from the bar. Over 60 years this process has created a pool–riffle sequence and a meander at this location. These slow the high flows and help dampen overall stream-energy within the incision.
Note that there is no ‘problem-willow’ at this location. This bank erosion is being caused almost entirely by grasses. Does the NRM lexicon have a term to describe these ‘problem-grasses’? This example illustrates the fact that all vegetation able to stabilise sediment is capable of causing bank erosion. Willows are often undeservedly singled out for the status of “problem-species” because they are particularly good at establishing in high-energy locations. Since meander development is a beneficial natural response to excess stream energy, it seems obvious that what we often see in ‘problem’ situations is actually ‘problem-urbanisation’, or ‘problem-property-boundaries’ which have been placed too close to dynamic natural flow-line systems.
The observations presented above demonstrate energy-dissipation processes within an incised flow-line. I suggest this is also happening at ‘the bank job’ site. Figure 4 is an aerial photograph of the bank job with the eroding bank and rock groins indicated. Also indicated is the existence of a gradually-developing bar of sediment, known as a ‘point-bar’, slightly upstream and on the opposite side of the river from the eroding bank. Successional ecological processes are indicated on this bar by a change in observable texture (indicating height or species differences) from upstream to down.
This is the initial stage of an energy-dampening repair process: the natural development of a river meander. It is promoted by vegetation spreading on one side of the river (the relatively low-energy side with the point bar) which causes energy deflection and corresponding erosion on the other side. Those rock groins may one day form part of the southern bank of the river! Alternately, they may succeed in preventing meander development, but protecting one part of the stream against bank erosion only exports the erosive energy further downstream, possibly creating problems elsewhere. Taken to an extreme, consistently armouring flow-lines against erosion and meander development promotes a higher-energy flow regime throughout the entire catchment, in spite of natural tendencies towards stream-energy dissipation.
As humans we often employ reductive thinking methods. These limit our perception of reality to a manageable problem or threat that we feel able to solve. You can see this happening in Australia right now in current obsessions over ‘the problem’ of asylum-seekers…or Muslims…or willows; take your pick. In each of these cases the underlying causes of the perceived situation are not adequately addressed because “the problem” has been narrowly defined to a single component. Community discourse is constrained so that the subject is culturally-constructed as having no redeeming features whatsoever. As such, “the problem” simply becomes the presence of the demonised subject. The solution must therefore be its removal (like when the RTA wanted to cut down Braidwood’s avenues of poplar). Often, explicit militarisation accompanies the goal of removal: ‘sovereign borders’, ‘war on terror’, ‘willow warriors’. Real causes of various issues, and better-informed ways to respond, are ignored because they are only apparent when we look beyond the narrowly defined “problem” and consider a broader context. Too much time, effort, and money (mainly it’s the money) is currently targeted in NRM to fight narrowly-defined “problems” in ways that ignore and actually undermine natural landscape function.
A more productive way to consider ‘the bank job’ situation might be to re-define excess stream-energy as a kind of water pollution. Like other pollution, it can be ‘point source’ or ‘diffuse’ and it represents a potential resource not being properly diverted or utilised—in this case to replenish nutrients and rehydrate floodplain landscapes. Also like other pollution, if we observe symptoms at the bottom of a catchment we look higher up to find the source.
Stream-energy pollution is embedded within multiple landscape processes, not simply in component features. As a concept it may help broaden perspectives beyond a simplistic focus upon “problem components”, to encapsulate the wider processes driving natural landscape function. A better way to deal with stream-energy pollution would be for upstream land managers to adopt practices which maintain all riparian vegetation and allow natural succession within flow-lines. Instead of armouring banks and exporting stream energy, we could slow and spread run-off using structures that create pools and bring peak-flows out of incisions, back onto their natural floodplains. This would reduce stream-energy thereby assisting natural processes of stabilisation lower down. Benefits would cascade through the catchment: rehydrated landscapes without destructive stream energy. Understanding underlying processes can stimulate beneficial ways of working to support natural landscape function and repair. Members of our Landcare community should pay close attention to ongoing Natural Sequence Farming trials happening in our local area to learn more.