CLM20-2 full issue-1 - Flipbook - Page 9
Saltmarsh restoration through flash re-creation
Practicalities
In both restoration and
creation, the water-retaining
structures – dams or berms
– are made from saltmarsh
sediments which can be
extracted from within the flash,
allowing for greater variation
in topography to be established.
To ensure good bedding-in, it
is important to turf-strip the
drain before blocking; leave
a dam that is slightly elevated
above the surrounding marsh to
Restored flashes are used for feeding by migrant waders, such as
allow for settling; and compact
dunlin. Bart Donato
the sediment after construction
of the dam. Ideally, the layer of saltmarsh
when the flashes are full. In their absence, water
vegetation is returned to the surface of the dam
will exploit weaknesses in the berm, which is
after installation to help with stabilisation.
invariably more porous than naturally settled
Where livestock are likely to trample the dam, it
saltmarsh soils; or it will enhance surface-flow
should be noted that this will potentially weaken
pathways over the berm top (often a product of
the structure – hence, it is a good idea to overthe poaching actions of livestock), which then
engineer it. Deepening the middle of the flash area erodes. Having a flow pathway through the better
can also be beneficial, as water can be retained
consolidated soils should relieve pressure on
for longer, but bear in mind that one of the
dams and berms and reduce the risk that they will
advantages of these natural landforms is that the
develop leaks while settling in.
flash edges have very shallow gradients, allowing
We have found that these flash features settle
for the development of large areas of bare mud
rapidly into the marsh and are readily adopted
during drawdown periods.
by birds within weeks of establishment. The full
If the landform is being enhanced by digging
process of settling and naturalisation, however,
down it is advisable to pay attention to the
takes a couple of years as fine sediments settle
substrate. In some estuarine systems, surface
and vegetation becomes well anchored. In light
layers of fine and relatively impermeable sediment of this, when undertaking a works programme
can overlie deposits of sand or gravel, especially
it is sensible to allow for aftercare in the first
close to river channels. Where this is the case it
couple of years in the event of issues that
is possible to deepen scrapes too much, exposing
need remediation, such as leaks developing
the more porous material beneath. The new flash
through a weakly compacted area of berm,
might then drain rapidly, at least until a fresh
water overtopping a dam or erosion caused by
layer of silt settles on the flash bottom.
livestock trampling.
Both damming drains and creating berms
allow for the establishment of extensive, shallow
Case study: Campfield Marsh RSPB
flashes. Most flashes we have restored are around
Campfield Marsh, 52ha of saltmarsh near Bowness0.5–1ha in extent when full, but restoration
on-Solway, north Cumbria, was bought by the
over larger areas is possible where space and
RSPB in 1987. Traditionally the area was drained
topography allow; the largest flash on Rockcliffe
and then grazed by livestock, but after the RSPB
Marsh covers approximately 17ha when full, but
purchased the marsh the management was changed
only rarely exceeds 50cm in depth.
to make the site more attractive to breeding waders
Experience also suggests that where long
and wintering wildfowl.
lengths of berm are being established it is better
In 1996 two parallel drains were bunded by
to have an overflow channel to let water escape
hand using sheet piling and sods of earth. This
Conservation Land Management Summer 2022 | Vol. 20 No. 2 7
