Duck Broad Island
Island Creation at Duck Broad, Heigham Sound
In June 2010 The Broads Authority started work on an innovative scheme to re-create reeded swamp lost due to erosion.
Duck Broad, a medium water body located on the starboard side as you leave Candle Dyke heading towards Hickling Broad, used to be separated from the navigation channel by a large reeded swamp. Wild fowl grazing on the reed bed and the action of the wind and tides slowly eroded this land, leaving Duck Broad open to the navigation channel. The shallow water within Duck Broad means is only suitable for small craft and due to the area being designated as a site for over wintering bird, access is prohibited between April and November.
Using gabion baskets made of reinforced steel, lined with geo-textile bags and dressed with coir roll, the Broads Authority Dredging crews began creating a 20m x 20m enclosure. The baskets were placed as single units and joined together using a steel spiral. This helped the baskets act as a solid wall as they were placed in the water.
Each basket was then slowly loaded with dredged material to form the outer walls of the island. This process continued until an area of approximately 400m2 was created. The next phase of the trail was to remove sediment from the navigation channel to fill the void we had created.
One of the concerns raised about dredging in Heigham Sound came from the Angling community. Prymnesium, a naturally occurring algae, lives in the water within Heigham Sound but occasionally has bloomed and can become stressed. When the Prymnesium algae reach this state of stress it can release toxins into the water which poisons fish. Historically algae blooms have been recorded within the Sound since the 1800.
To ensure the construction works did not exacerbate any possible Prymnesium outbreak we deployed a ‘Impermeable Silt Curtain’, which stopped any fluidised sediment entering the main water body. As well as the silt curtain we have been carrying out a rigorous water quality sampling regime which has seen weekly and daily water sampling to monitor the conditions within the work area and within the Sound. This was married with a robust action plan if water quality became adversely affected by our operation.
(Picture courtesy of Mike Page)
The first phase of the construction has now been completed with approximately 1000m3 of sediment being placed within the baskets and void to create a small spit of land.
The next phase is to plant reed and typher into the sediment to begin establishing flora on the island.
Last year seed was taken from reed and typher growing locally and has been propagated into saplings ready to be planted into the baskets. Trialling different techniques and methods, to see what establishes best, the baskets will be dressed and planted during September 2010.
We are also transplanting some established reed and typher, which is currently growing on the banks of the River Bure.
These larger ‘clumps’ of reed will be placed within the main body of the island to see if more mature reed bed establishes better.
The trail island will be constantly monitored over the winter months (2010/2011) and if the structural integrity of the baskets hold, and the reed and typher establishes then the hope is to progress onto creating the whole spit of land totalling 1 hectare.
