'When the fish leave, we'll close the door behind them': How Natural England's £4.5m project will restore life to Hoveton Great Broad
PUBLISHED: 13:54 03 March 2017 | UPDATED: 14:44 03 March 2017
Copyright: Archant 2017
A £4.5m project is under way to transform one of Norfolk's Broads from a mucky brown lake into a pristine, clear wildlife haven.
Natural England is managing the five-year Lottery-funded restoration scheme at Hoveton Great Broad – once rich in plant and animal life, but now choked with algae due to poor-quality polluted water entering it from the River Bure.
The first major phase of work involves removing 50,000 cubic metres of sediment from the shallower western end of the broad – only half a metre deep in places – and depositing it to create new species-rich fen habitats at the eastern end.
Dredging machinery is currently at work digging out mud which is pumped into huge “geotubes” – 50-metre tunnels of tough synthetic material – to create an artificial new coastline for the broad, behind which the rest of the sediment will be dumped to create the new fen.
When two years of winter dredging has been completed, a second technique of “biomanipulation” will be employed to remove tonnes of fish from the broad to allow zooplankton to flourish, which would usually eat the algae in the water.
Project manager Chris Bielby said: “Ideally we want the water in the lake to be like an aquarium. It is very shallow and it should be full of water plants, but it is very turbid, brown and mucky.
“We’re going to do that in two ways.
“First is sediment removal, but the real key to restoration is biomanipulation.
“It immediately changes the ecology of the broad and the water will go crystal clear. It allows sunlight to get in and for plants to germinate.”
The project team hopes that within 10 years, much more wildlife will be flourishing in the water and on the reed banks at the site, which has a host of protected designations and has been a National Nature Reserve since 1958.
BIOMANIPULATION: HOW IT WORKS
“We’ll let the fish leave of their own accord, and then close the door behind them”.
In simple terms, that is how the project team eventually aims to bring about the ecological renaissance of Hoveton Great Broad, through a process known as biomanipulation.
The water which once hosted an abundance of water plants like water lilies and reed has now turned a muddy brown colour due to the prevalence of algae.
When the Broad was healthy, most of this algae was eaten by water fleas (zooplankton). However, now the plants are gone, the water fleas have nowhere to hide and most of them are eaten by fish.
So the fish will be removed from the broad to give the water fleas a chance to thrive and feed on the algae, clearing the water.
This involves state-of-the-art underwater sonar cameras to monitor fish movements, using their natural behaviour to time the closure of mesh barriers behind them when they voluntarily leave the broad to go into the Bure.
Project officer Rhiannon Evans said: “Using these underwater cameras, we have been able to monitor the fishes’ behaviour. We can see at certain times of day fish enter or exit the broad of their own accord.
“The cameras monitor what the fish do during that period and we hope that by using their natural behaviour we can place fish barriers against these entrances and exits to the broads so when they leave we can close the door behind them.
“By doing it that way it is the least possible stress for the fish. If we had to physically catch and move them all it would be much more stressful.”
ACCESS AND ENJOYMENT
The project will also improve visitor access and enjoyment of the Broad, which cannot be reached by private boats from the River Bure.
A boardwalk nature trail – accessible by ferry from Salhouse Broad during the summer – has been open since 1969, but Natural England hopes to improve this with a floating boardwalk section over the water and a raised viewing platform. There are also plans to bring visitors in from the north via a new boat trail.
The project has already funded a new trail warden, which has allowed the nature trail to open seven days a week from the start of April, which has helped visitor numbers increase from an annual average of 3,500 during the previous three years to more than 6,000 since the start of the project in October 2015.
Rick Southwood, Natural England’s senior reserves manager for the Broads, said: “We want people to come out and see the wildlife and see how wonderful it is and re-connect with it.
“In terms of the wildlife and biodiversity, I have known this site for nearly 40 years and all this time it has been a mud-filled dirty pool. What we are aiming to get back is some depth and that gin-clear water that attracted people here in the first place.
“Once we get that we can get plants back rather than just algae and then we get a much more varied aquatic animal community, with all the invertebrates, damselflies and dragonflies, otters, fish and ospreys. We are looking for better spawning conditions for fish and a more varied population so you get the perch and tench coming back and, because it is connected to the river, we hope it will have an improvement for the fish population in the Bure.”