CANAPE: Hickling 2 - Return of the 20 tonne excavators

18 November 2019 - Published by Harry Mach
7 months ago, having completed the first phase of our work on Hickling Broad at Chara Bay, we packed up and left the site for the summer. Now we are back for the 2nd season of work.

Last year we completed the outline of the site, this year we will begin the process of backfilling, using more sediment dredged from the bottom of the lake. We will also take the opportunity to “de-sludge” Catfield dyke, which is adjacent to the site, and keep it open for navigation. Normally when doing this type of work an area of agricultural land has to be found to re-use the mud; however, the presence of the lagoon gives us the opportunity to support the creation of new habitat.

Additionally, this year we are trialling an innovation – using DNA testing to quantify levels of Prymnesium parvum. This is known as the golden algae, and it can release a toxin that is deadly to fish. This test has recently become commercially available, and the project will be the first use in the Broads. The method isolates particular DNA markers unique to Prymnesium parvum, and provides a greater accuracy compared to the previous method of counting specimens under a microscope. There are also benefits greater speed of analysis and allowing the processing of more samples in a day; all of which help safeguard against impacts to fish populations.

Aerial Picture of construction site, dredging rig and mud pumping rig both in view.

Aerial Footage of the work at Hickling Broad, November 2019. Copyright Mike Page. 

Dredging work at Hickling Broad will always only take place in winter, as disturbing the water during the summer months can cause algal blooms in this area. Fortunately, our construction crew are tough as nails are regard working in the face of icy northerly winds as “just part of the job.”

Like last year, work is carried out using two 20 tonnes excavators working with 2 barges. One Dredges the sediment from the lakebed, the other then loads the dredging into a re-purposed concrete pump which pumps the sediment into the lagoon that has been constructed. 

Last year we moved 5,850 cubic metres of sediment from the lakebed. This year, the objective is to move 8,000 cubic metres. By keeping this organic rich material wet, we estimate that there is an additional carbon storage of 50 to 100 tonnes of CO2 compared to spreading and drying the material on a neighbouring agricultural field.   

Placing the dredged within the geotextile “ring” will raise the sediment level closer to the surface of the water, and near to the level necessary for us to begin planting the reed, and restoring it to a more natural fen. This fen will become a major carbon store, and will begin accruing peat, taking CO2 out of the atmosphere.

Alongside the work at Chara bay, our construction team will also work on an earlier project site that needs a little more help to get it towards a natural state, by planting 250m2 of plants on the site. This will build on work previously done at Churchill’s bay (foreground) and accelerate its return to a natural habitat.

Boat wake leading away from the dredging platform