Coastal erosion at Tunstall has seen the sea take away chunks of cliff, leading to fears that in a storm water could surge into the drain, flooding fields and villages and even cutting off a large chunk of southern Holderness.

Now the Environment Agency is conducting studies looking at options including setting defences a mile inland.

Tony Ellis, whose family has owned Sand-le-Mere caravan site, Tunstall, for 40 years, said the sea was now only 50 yards from the drain. He fears the drain flooding from the sea could leave Burton Pidsea and Roos inundated.

The sea was already up to a man-made flood embankment protecting the drain and sometimes water came over, with salt water seeping through a pipe in the cliff. He said: "This year they may get away with it – next year it will be very risky."

The NFU's representative, Ed Davey, said seawater getting into the drainage system would be devastating for wildlife while any flooding would take agricultural land out of production for years.

He said: "The concept of water getting into that system from an environmental standpoint would be absolutely catastrophic – it would kill every water vole along there for a start." He added: "They are talking about putting a defence line about a mile or so inland. The concept is that they are going to end up abandoning a certain proportion of land so if the sea does come over the top of the bank it will flood and fall back to the new bank."

The Environment Agency is conducting a feasibility study and expects results by the year end. Flood risk manager Peter Holmes said: "We are aware there's a risk there and we are looking at options to overcome that. What we are talking about is a break-through of the cliff face there which would cause flooding and problems further down. I don't think we are going to have Withernsea Island or South Holderness Island – that's not going to happen."

Mr Holmes said there needed to be talks with the community. "There has to be a sense of perspective. It's a risk that exists but it is a risk that we are in the process of managing."