The 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.
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.
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The 'thickening' of the river under the arrow
is not part of
The Food Forest so the photos below come from the more westerly 'bulge'.
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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 |
There goes the mulch! |
The bank stripped by the flood; amazingly most plants survived |
The planting team quickly repairs the damage |