Boston Tidal Barrier

The Environment Agency has determined that there is a 1 in 25 year chance of a tidal flooding of Boston, and a 1 in 50 chance of flooding in any given year.

They have proposed as a solution having a tidal barrier, possibly with gates like on the Thames Barrier, which will move to a 1 in 300 chance of flooding in any given year.

Another reason to have a barrier is as part of the Fens Waterways Link, a flagship project of The Environment Agency designed to connect the Cathedral Cities of the East of England from Lincoln through Boston and Spalding to Peterborough and on to Ely and Cambridge, and beyond.

Putting in a barrier and running it the right way changes the access times from about 2 hours at high tide when nobody else needs to use that bit of water to over 14 hours.

Given the range of reasons for having a barrier, the case seems clearly made that we should have one in Boston, and indeed the agencies involved have decided we should have one, and got funding not just for studying the issues, but also for construction as well.

The next issue that arrises is where should such a barrier. A case could be made for putting it anywhere from the mouth of the Haven, right up to just downstream of the Black Sluice Lock.

Taking the mouth of the Haven as the first option, it has a number of problems, especially with cost, and the problems caused to wildlife, with the only thing to recommend it being the possibility to cover both the Haven and the River Welland.

Moving further up the Haven, there is another obvious place to put it, which is just past the Pilgrim Fathers Memorial. If you move it past Marsh Lane industrial estate, you could have a marina, and boat repair yard there, with provisions for launching one of the new lincolnshire fireboats from there. You could also station pumping barges there which could provide large amounts of water from the river to shore based fire engines to help deal with major fires anywhere near the river.

Another place is just past the Maud Foster Drain, which loses the advantages with it being past the industrial estate.

Both of these have the advantage of joining the Maud Foster with the Witham, forming a loop from Boston Dock out to Anton's Gowt down the Maud Foster Drain, and then back down the Witham. They also enable you to move ships about during low tide so that you can empty a ship, then swap it with another ship waiting to unload.

Unfortunately, there are serious complications to both of these options. You have to cope with large ships passing the barrier, which constrains you to only being able to use the Thames Barrier design, covering the full width of the river, with the maximum draft of the ships using the Docks, and the ability to cope with being hit by very big and heavy ships, all of which adds to the cost. Another problem is that if a ship does hit it, the captain's insurance company is liable for the cost of fixing it. All of these factors make the cost so high that the Agencies involved have had to rule out putting a barrier downstream of the Docks.

From this information, it leaves you having to have the barrier downstream of Black Sluice Lock (to get the advantages of connecting with spalding and beyond) and upstream of the docks (to avoid the costs of dealing with the big ships), which is what the agencies have concluded.

One issue that arises is that if it is put just near black sluice lock, and you get a lot of water in the forty foot drain, the pumping station kicks in and starts pouring water into the Witham, with the only place for it to go being back towards the sluice bridge.

There are questions about how it is operated. Is it used only for the tidal flooding event, or do you take advantage of it to keep the water levels higher in town during low tide? If you use it to equilise the water levels with the freshwater drains and rivers, a lot more of them suddenly become navigable.

You have three options as to how to run the barrier. You could only raise the barrier during times of flooding, but as the Barrier is going to cost millions, this doesn't seem good value for money, and you loose the advantages of connecting the waterways during low tides.

You could have the barrier raised all the time, but this leads to problems for those who need access to the sea, like fishermen and people who do sea cruises. It also causes a lot of problems for the drainage boards, as a lot of the drainage in lincolnshire is based on a gravity feed model, which would then fail, and need expensive pumps.

The only other option is to keep the barrier raised when the daylight high tide is lower than the river level, and lowered at night during low tide, to get almost all of the advantages of keeping the barrier raised, but without the disadvantages of the permenently raised plan.

This is why the agencies are confident that this is the model they will end up using.

This still leaves the issue of which design to use for the barrier, and the current thinking seems to suggest that a half barage, half barrier design might be what ends up being used, but the work to determine the design in detail depends on where the barrier is, and thus has not been done yet.

One thing you can do in the detailed design is to look at power generation options which you get if you divert a little of the water around the barrier, and make use of the massive flows we get from such a large catchment area to generate electricity.

Our understanding is that the options for power generation are on the table to be considered as part of the detailed design work.