Weir repair 2013

The concrete weir across the River Monnow probably dates from around the 1930s. It is not a large structure, varying from a maximum height of 70cm above the riverbed to a minimum of 20cm. In spite of the low height it has an old fish ladder, which is used by brown trout.

At some time before 2000 a minor breach had occurred at the eastern end where the weir is lowest. This did not prevent the mill working except during extended periods of drought. However, in the spring of 2012, when the river was exceptionally high, two large tree trunks came down the river and knocked out about half the width of the weir. Without major repair work we would no longer be able to operate the mill.

Any work in a river requires a Flood Defence Consent. Because our section of the river is classified as an ordinary watercourse and not a main river the consent authority is the county council. In October 2012 we applied to Herefordshire’s engineering contractor for consent to repair the weir.

After six months struggling with the bureaucrats we were getting nowhere, so we asked our local county councillor for assistance. Things then started moving. We completed the forms and provided drawings and method statements. The only outstanding detail was when could the work begin? Our friendly bureaucrats then decided that they needed to consult the Environment Agency to find out about fish movements.

The first response from the Environment Agency was that we could not repair the weir as it went against the European Water Framework Directive (with which we’re sure you are all familiar). Could we not get water to the mill using a pump powered by a solar panel? We argued that the millrace is an ordinary watercourse under the EA definition and is therefore subject to the same protection as the river. Therefore the weir had to be repaired. They then informed us that we would need to commission an engineer to design a fish pass and hire an environmentalist to write a European Water Framework Directive compliance assessment. This would have added thousands to the repair cost.

Eventually it was agreed that the existing fish ladder was adequate and that we could write the European Water Framework Directive compliance assessment ourselves. We submitted this within the week. After a further 5 weeks with no response, we informed the council’s contractor that we were starting work, whereupon they threatened us with legal action on the grounds that they had not received our EWFD compliance assessment. So we resubmitted it only to be informed that we needed to submit a pollution incident response plan as well. Having provided this, we were finally given consent, a long nine months after starting the process.

It had been a great summer, with the river low and the weather set fair. But thanks to the bureaucratic delay it was now the end of August. When we started work the river was lower than it had been for two or three years.

We were able to divert the flow away from the work area with just a low wall of sandbags. Loose concrete was removed, shuttering was bolted down, stainless steel anchor rods were set into the riverbed and steel reinforcement was assembled.

We even steam cleaned the riverbed to ensure a good key for the new concrete. And then the rain started and the river rose. The shuttering was inundated and logs and other debris were deposited on top of it.

After a week or so the river went down. We repaired the shuttering, steam cleaned the riverbed again and ordered the concrete – a first load of six cubic metres to be followed by a part load. On the chosen day, the concrete pump arrived but no concrete. Somehow our order had been lost. When the mixer truck eventually arrived they’d sent eight cubic metres – which miraculously turned out to be precisely what was needed to complete the first pour. Not a single bucketful was left over. Something was going right at last!

Now there was only a three metre gap left to fill, but the entire flow of the river was pouring through this gap. So we built a timber caisson around the gap to divert the water over the newly built part of the weir. We borrowed submersible pumps to pump out the space inside the caisson, built the shuttering and installed steel reinforcement. The concrete was ordered, but had to be cancelled when the rain started again and the river completely inundated the caisson.

After three days the river had fallen again. We pumped out the caisson, repaired the shuttering and finally poured another 3 cubic metres of concrete to close the gap. It was a short window of opportunity. In less than 12 hours the river rose again and once more overflowed the caisson.

It was another 10 days before the water level was low enough to remove the shuttering and see what we’d achieved. Fortunately concrete sets well under water and there had been no wash-out.

The work was finally completed in November 2013 and we again have a working weir, which hopefully will last for the next two hundred years or more.

The completed weir.

Postscript

After the weir was damaged in 2012 the visits from otters to this stretch of the river became far less frequent. Soon after we repaired the weir in 2014 the otters returned with their previous regularity. This does suggest that they find the weir attractive. If a weir like this is good for otters it means it's good for fish as well.

Historically, when there was a weir and a working mill approximately every two or three miles along its length, this part of the River Monnow was a famous trout and grayling fishery . The mill races also supported a large eel population. Now most of the weirs have gone, some because of a misguided policy of removing them. Now there are far fewer fish. Draw your own conclusions.

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