The Environment Agency remains the principal
body which manages main river whereas the Internal Drainage Board manages
key ditches. Although flood defence is an important function of these
bodies, they also have a responsibility to manage watercourses for
wildlife conservation. Some of the reactionary responses and 'solutions'
put forward to reduce flood risk may not be proven and can in fact be very
damaging to river ecosystems.
One such preoccupation is the rigorous removal of
aquatic plants, unfortunately termed as 'weeds', from rivers and ditches.
It is important to remember that these aquatic plants are a primary food
source in rivers. They provide wildlife habitat for mammals such as water
vole, for invertebrates such as dragonflies, and shelter for fish.
It is true that excessive growth of aquatic plants can
cause problems by impeding flow, increasing siltation and by blocking mill
and weir structures. This growth is likely to be exacerbated in part by
run off from arable fields, which is why the work of KSCP to encourage
buffer strips and arable reversion beside rivers is so important.
Traditionally, 'weed' has been cleared from the full width of
watercourses, and in flood situations there is pressure to continue this
approach. It has however, been proven that it is not necessary to weed cut
a whole channel and that the same improvement in flow can be achieved with
a 80% cut. In wide shallow rivers as little as 65% needs to be cleared. In
2000 the Environment Agency pioneered a weed cut regime on the Little
Stour above Littlebourne, leaving a wide marginal fringe of vegetation and
most submerged plants. According to an EA report, the improvements to
biodiversity were marked with several species of mayflies and caddis flies
colonising the river. Increased water velocity in the narrowed channel
scoured out clean gravel with water crowfoot appearing for the first time.
The in river vegetation also helped maintain summer flows. Unfortunately
the channel was severely weed cut in summer of 2002, the crowfoot
disappeared and a thick deposit of silt returned to the channel.
The pilot on the Little Stour showed for a brief time
the ecological improvements achieved by altering the weed cut regime. A
thoughtful compromise needs to be reached whereby our rivers can be
managed effectively for flood defence without compromising their wildlife
value enabling the Environment Agency to truly fulfil its dual role rather
than bowing to public pressure.
Judith Baker
