This is a pictorial tour of the degradation and dehydration process that the Australian landscape went through post European settlement, along with one of the major aims of Peter Andrews’ Natural Sequence Farming approach, namely the rehydration of the Australian landscape.
If you were one of the early explorers, walking into a wide floodplain system in the early 1800s, more than likely you would have found some form of discontinuous watercourse. One example is known as a ‘chain of ponds’, in which you’d find small bodies of open water, about a metre below the level of the floodplain, held in place and separated from the next pond by a marshy plug of reeds such as Phragmites.
These ponds weren’t the whole story though. They were just the tip of the iceberg and indicated the level of the water table under the rest of the floodplain-step. That is, moisture within a metre or so of the toes of all of the plants on the floodplain.
When a decent flow occurred, rather than it rushing downstream, the reed beds would slow the water causing it to gently rise and flow over the banks onto the floodplain. This gave the water plenty of chance to infiltrate and recharge the aquifer below (a wise move for a landscape to make when the next generous rain might be a few months away). You might also notice something strange; the banks of the creek are higher than the rest of the floodplain. This is because when the water spills over the banks, the largest sediment settles out first, building up a levee over time.
With the landscape scouted, settlers soon arrived with their animals, ring barking as they went. There weren’t many stock troughs in those days, so of course the animals had to drink from the creeks.
The hard hooves soon cut tracks into the reeds and were one of the ways the marshy plugs were killed off.
With the plugs gone, coupled with the cleared, burnt and overgrazed hillside up above the floodplain, water could now build some momentum, and soon scoured out the deep erosion gullies we still see today.
With the ponds no longer in place, the gully turned into a really efficient drain….
… lowering the alluvial aquifer….
… down to the base of the incised channel. Once this occurred, rather than plants having moisture 1m below, they’re high and dry and at the mercy of the infrequent rainfall patterns experienced in much of the Australian landscape.
Once a channel is deeply incised, in many places even a large rainfall event is confined to the channel. This deprives the floodplain of the soaking sheets of water and fertile sediment of yesteryear.
Peter’s approach is about replicating the job that wetlands used to do. He creates ‘leaky weirs’ using locally available materials. Vegetation is an important component of the leaky weirs, with the fibrous root system of bioengineering plants such as willow used to tie the boulders together. This approach results in structures that are a fraction of the cost of the highly engineered structures commonly built by authorities. Peter also believes that the exclusion of livestock is important, except for periodic crash grazing.
The weirs enable chains of ponds to re-form, which begin to raise the alluvial aquifer (particularly through buried old creek lines which act as gravelly intake areas along the banks).
The rehydration will obviously happen faster in sandy soils than it will in heavy clay, but slowly the aim is for the alluvial aquifer to be raised. This is water harvesting in the form of reinstating a natural landscape process.
Eventually, the goal is to reinstate a drought-proof landscape.
At such time, flood processes become important once again, by creating a freshwater lens on top of the heavier, saline groundwater
If you’re interested in implementing strategies similar to these on your property, please contact us
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 Diagrams © Cam Wilson, Earth Integral 2012