The Food Forest

8.11.05: 8.11.2005 | Flooding of the Gawler River

flood mapThe Gawler River broke its banks on 8 Nov causing some $40M worth of crop damage on the Adelaide Plain, however the permaculture design of The Food Forest stood up to the swirling waters.

The flood resulted from 2005's wet spring, culminating in the filling of all major Adelaide Hills reservoirs and upstream storages on the Gawler River (by 7 Nov) at which point most of the rain falling in our catchment ran into watercourses feeding the Gawler River. The normal depth of the river at The Food Forest is approximately 60cm; this rapidly increased to 6 metres and the speed of the flow increased from 3km per hour to a maximum of almost 25km per hour. The flood persisted for several days.

Flooding is a normal occurence here as The Food Forest is located in the ancient bed of the Gawler River which is almost kilometre wide at this point, however floods have become relatively rare since the building of major reservoirs and thousands of farm storages in the Adelaide Hills and many people now get upset when the river breaks out of its main channel and invades their land where, in many cases, structures and crops have been placed unwisely on low ground.

house underwater

At The Food Forest we 'planned for catastrophe' (which can come in the form of wildfire, flood or tornado) by planting our very low ground (flood-flat) with species that are adapted to short term flooding. The design is called a 'floodable forest' and features Acacia slicina (Broughton Willow), Acacia stenophylla (River Cooba), Casuarina cunninghamiana (River Oak) and a range of sedges, grasses and ground covers. The concept is that the floodwaters can run unimpeded across the flood flat with the clean single stems of the timber trees allowing water to run around them and the seges and grasses simply lying down as the water rushes over them. In large measure this is what happened, however significant damage was done to outcrops of Atriplex nummalaria (Old Man Saltbush) which caught water-borne debris and thus presented a major obstacle to water flow.

Only one tree out of several hundred acquired a permanent lean and will need to be sawn off to promote the growth of a new, straight sucker.

The floodable forest is thus expected to have benefited from the thorough wetting of the soil profile and growth rates this summer should be outstanding. The trees are destined to become ultra-high-value timber for furniture or veneer manufacture over the next 25 years.

Sequential shots below show a young floodable forest disappear and reappear, somewhat worse for wear. 

acacia salicina

Form-pruned Acacia salicina trees allowing the water to flow freely across the flood flat

new planting

floating log


These young trees straightened themselves up within a week!

Below is a somewhat more frustrating sequence showing the fate of a revegetation effort on the actual channel bank. Sedges and grasses had been planted and mulched for the dry summer ahead just a week before the flood came and washed all the mulch and some of the new plants away. The team moved back after the water subsided and repaired the planting... hopefully the plants will be well established by the time the river next floods!

planting and mulching

Planting and mulching

mulch floating away

There goes the mulch!

bank stripped of mulch

The bank stripped by the flood; amazingly most plants survived

repairing the banks

The planting team quickly repairs the damage