In some locations with deeply incised gullies, both the goal of channel-floodplain reconnection and the goal of lateral floodplain rehydration are pretty much out of the question, at least in any way that will benefit most species on the floodplain (other than deep rooted trees).
One such example is the Natural Sequence Farming demonstration on the home farm at Mulloon Creek Natural Farms. To achieve either of the above goals would require a large engineered structure, which in a named perennial stream doesn’t sit too well with the existing regulations (extraction is achievable but would require a costly irrigation licence).
Currently, despite regulation exemptions which allowed some of the structures to already be quite large, the water level still remains 4-7m below much of the floodplain. This results in little benefit to the vegetation on the floodplain, but I believe the works have still been a success in a number of ways, one of which is setting the natural repair processes in action. (See the Mulloon Institute website for details of the research that’s been conducted)
The locations where chains of ponds and swampy meadows existed in abundance at the time of Euro settlement, such as Mulloon Creek, are known as ‘cut and fill landscapes’.
The ‘fill’ phase referred to in ‘cut and fill’ is relatively well understood. As Peter Andrews has popularised, dense wetland vegetation choked the discontinuous channels, slowing the water flow, trapping sediment and then binding it within vertically growing root mats.
The ‘cut’ phase isn’t quite so well known. Although these systems could remain stable for thousands of years, they weren’t permanent. A natural disturbance could set a period of degradation into action, with erosion gullies cutting through the floodplain sediments. Eventually, the ‘cut’ phase stabilised and the ‘fill’ process would begin again (Johnston and Brierley, 2006).
This rebuilding phase has in fact begun in some places. Zierholz et al (2001) wrote a great paper on the process, outlining the natural establishment of instream wetlands. In some places, their study found that dense reedbeds had accumulated up to 20 years worth of sediment from the associated catchment. That is, the floor of the gully is aggrading, nutrients and sediment are being held, valuable wetland is being created, erosion is being prevented, and the main reason: lots of reeds have established.
On Mulloon Creek, there are sections which before the NSF works were completed were either cut down to bedrock or basically gravel deserts, and had been that way since the degradation began, which likely occured in the early to mid 19th Century (Hazel et al. 2003). Those same sections now look very similar to the photo from the paper above.
What’s been the trigger? As they say, just add water:
As Craig Sponholtz of Dryland Solutions in New Mexico puts it, “This type of restoration work uses earthworks to create a foothold for natural processes. The structures then get assimilated into the ecosystem as natural healing processes take over.”
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Disclaimer: Where water flow is concerned there are substantial risks involved. While the information and images we publish are formulated in good faith, with the intention of raising awareness of landscape rehydration processes, the contents do not take into account all the social, environmental and regulatory factors which need to be considered before putting that information into practice. Accordingly, no person should rely on anything contained within as a substitute for specific professional advice.
Article and Images © Cam Wilson, Earth Integral, 2012
Hazell, D., Osborne, W. and Lindemayer, D. 2003. Impact of post-European stream change on frog habitat: southeastern Australia. Biodiversity and Conservation, 12: 301–320, 2003.
Johnston, P. and Brierley, G. 2006. Late Quaternary river evolution of floodplain pockets along Mulloon Creek, New South Wales, Australia. The Holocene 16 (5): 661-674.\
Zierholz, C., Prosser, I., Fogarty, P. and Rustomji, P. 2001. In-stream wetlands and their significance for channel filling and the catchment sediment budget, Jugiong Creek, New South Wales. Geomorphology, 38: 221-235.