With low­ish lev­els be­ing a con­cern this year on some canals the reser­voirs have come un­der scru­tiny – but it’s not just too lit­tle wa­ter the en­gi­neers worry about

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Just how would the CRT man­age an emer­gency in the event of a breach

The cold Pen­nine win­ter of 1830 saw a thick layer of ice cover the surface of the Lan­caster Canal’s Killing­ton Reser­voir, high up in the hills west of Sed­burgh. But then the weather turned milder, the ice be­gan to break up and thaw­ing snow on the sur­round­ing hills swelled the waters. The wind veered around to the north, blow­ing the bro­ken ice down to­wards the dam, where it blocked the over­flow spill­way. With nowhere else to go, the ris­ing waters over­topped the dam and be­gan cas­cad­ing into the val­ley be­low…

The reser­voir-keeper saw what was hap­pen­ing and, show­ing quick-think­ing and pres­ence of mind, grabbed a spade and set about cre­at­ing a de­lib­er­ate breach along­side the dam to get rid of the ex­cess wa­ter. His prompt ac­tion pre­vented what would have been a ma­jor dis­as­ter if the dam had col­lapsed.

Al­most two cen­turies later, we can still see what is prob­a­bly the re­mains of the chan­nel washed out by the wa­ter as the reser­voir emp­tied it­self through his makeshift cut. I’m vis­it­ing the reser­voir with David Brown, a se­nior reser­voir engi­neer with the Canal & River Trust, who is su­per­vis­ing work tak­ing place at this site as part of a regime of in­spec­tion, main­te­nance and im­prove­ment work aimed at en­sur­ing that the events of 1830 will never be re­peated at any of the Trust’s reser­voirs.

This isn’t just a CRT mat­ter: all of Bri­tain’s reser­voirs are subject to statu­tory le­gal re­quire­ments – and with good rea­son. Dis­as­ter may have been averted at Killing­ton, but the peo­ple of Cwm Carn on the Mon­mouthshire Canal weren’t so lucky in 1875, when heavy rain caused the dam to over­flow and fail, killing 12 peo­ple.

Fail­ures of two drink­ing wa­ter sup­ply reser­voirs in the 1920s re­sult­ing in 31 deaths led to the 1930 Reser­voirs Act, and to to­day’s ten-yearly in­de­pen­dent in­spec­tions and re­ports by mem­bers of a panel of qual­i­fied civil en­gi­neers – backed out by more re­cent leg­is­la­tion, with fail­ure to com­ply be­ing a crim­i­nal mat­ter. And, to date, there haven’t been any more deaths from reser­voir fail­ures since then.

Of­ten tucked away in val­leys some dis­tance from the canals they serve, CRT’s reser­voirs form a part of its sys­tem that many boaters prob­a­bly rarely think about – other than when their wa­ter stocks start to run low in a dry sum­mer, as looked like be­ing the case this year.

But it’s the op­po­site issue that most

con­cerns the Trust, which is spend­ing £4.3m this year to en­sure ad­e­quate pro­tec­tion against the risk of too much wa­ter – and it’s largely driven by those ten-year re­ports.

So what’s in the re­ports? Firstly, gen­eral in­for­ma­tion such as details of the reser­voir and its catch­ment area; in­for­ma­tion about the ‘draw-down plan’ (for emp­ty­ing it in an emer­gency); con­struc­tion details and the lo­cal ge­ol­ogy. Se­condly, the find­ings of the in­spec­tion (with lots of de­tail about leak­age and seep­age).

Then the con­clu­sions: is the draw-down plan ad­e­quate? Is su­per­vi­sion sat­is­fac­tory? Will it survive a ‘once in 10,000 years’ flood event com­pletely un­scathed? Will it deal with the ‘worst me­te­o­ro­log­i­cally pos­si­ble’ event with only mi­nor dam­age? And, fi­nally, there are rec­om­men­da­tions on works needed to bring it up to scratch.

Killing­ton is a rel­a­tively early reser­voir dat­ing from 1819 – and typ­i­cally for this era, there are few records of how the dam was con­structed. It’s be­lieved to have a pud­dled clay core, but no­body can be sure with­out dig­ging down. It’s quite nor­mal for builders to have sim­ply used what soil was avail­able (such as sand or even peat) and not to make any at­tempt to dig down to a solid base be­fore build­ing it – of­ten the orig­i­nal top­soil is still there un­der the dam.

It’s also been al­tered sev­eral times: the dam was raised to in­crease ca­pac­ity (early en­gi­neers of­ten un­der­es­ti­mated wa­ter re­quire­ments) and we can still see where a large block of stonework was added to raise the height of the over­flow

‘The re­port con­cludes that the dam will cope with all the weather can throw at it, the over­flow is ad­e­quate, the level can be low­ered in a hurry if nec­es­sary and, in gen­eral, it’s ad­e­quately main­tained – but with a few pro­vi­sos’

chan­nel – and then a sec­ond over­flow chan­nel was added af­ter the 1830 in­ci­dent. The draw-off sys­tem has been changed more than once, as a siphon pipe set in the dam re­placed the orig­i­nal cul­vert, and was then sup­ple­mented by a sec­ond siphon.

Un­usu­ally, rather than sup­ply­ing a canal feeder chan­nel, the wa­ter from the reser­voir is fed back into the stream be­low the dam. It is then taken out sev­eral miles down­stream (me­tered, to make sure the same amount is taken out as is put in), where a feeder car­ries it to the un­nav­i­ga­ble north­ern reaches of the canal, and it even­tu­ally runs down the dis­used lock flight at Te­wit­field to reach the nav­i­ga­ble length, a full 15 miles from where it left the reser­voir.

But the re­port con­cludes that the dam will cope with all that the weather can throw at it, the over­flow is ad­e­quate, the level can be low­ered in a hurry if nec­es­sary and, in gen­eral, it’s ad­e­quately main­tained – but with a few pro­vi­sos.

There are var­i­ous rec­om­men­da­tions which are mainly main­te­nance is­sues – so we can see one team at work re­plac­ing sec­tions of the over­flow chan­nel’s base in con­crete to deal with ero­sion, while an­other group are us­ing a dye to in­ves­ti­gate leak­age in a fur­ther sec­tion of the over­flow, and in the block of stonework men­tioned above, prior to grout­ing work to seal the leaks.

In­ter­est­ingly, two un­re­lated projects are tak­ing ad­van­tage of the low­er­ing of the wa­ter lev­els for this work. Firstly, a lo­cal com­mu­nity hy­dro­elec­tric scheme is be­ing set up, tak­ing its feed from the cast iron draw-off pipe (which has in­volved some clever tap­ping into the pipe while still un­der some pres­sure).

Its tur­bine is cur­rently work­ing in par­al­lel with the 1930-built valve house to con­trol the take-off of wa­ter from the reser­voir; in fu­ture the en­tire main flow to the Lan­caster Canal will pass through the hy­dro sys­tem and gen­er­ate 30kW for the lo­cal area, with the prof­its go­ing to the com­mu­nity. All the work has been done by lo­cal com­pa­nies, and it’s be­ing cham­pi­oned as a demon­stra­tion of the ca­pa­bil­i­ties and pos­si­bil­i­ties of

part­ner­ships with com­mu­ni­ties, en­ergy groups and CRT. The other project is to in­stall a float­ing land­ing stage for a sail­ing club based on the reser­voir and used a great deal by groups sup­port­ing dis­ad­van­taged chil­dren.

Our sec­ond site visit is to Foul­ridge Up­per Reser­voir, built to sup­ple­ment Foul­ridge Lower Reser­voir, which in turn feeds into the Leeds & Liver­pool Canal just west of Foul­ridge Tun­nel – and it’s quite a con­trast. A much later reser­voir dat­ing from 1866, it’s hardly been al­tered since it was built, other than ad­ding a low con­crete wall along the top of the dam in the 1950s to de­flect waves. But here, the is­sues aren’t about main­te­nance: they’re about cop­ing with even­tu­al­i­ties.

The in­spec­tion re­port in­di­cates that an ex­treme flood would over­top the dam, wash­ing away the path be­hind the con­crete wall and ul­ti­mately threat­en­ing the dam it­self; and that in ad­di­tion, wa­ter pass­ing down the over­flow spill­way could over­flow the sides, wash out the ad­ja­cent ground, and again dam­age the dam.

The work in progress in­volves rais­ing the dam crest wall by ad­ding an­other half a me­tre of re­in­forced con­crete – as we watch, a team are at work dis­man­tling the wooden shut­ter­ing around a sec­tion that has re­cently been cast. Mean­while the soil along­side the over­flow spill­way chute is be­ing dug out and re­placed in a way that will be bet­ter able to with­stand a heavy flow of wa­ter. This in­volves putting con­crete be­hind the chan­nel side walls, in­stalling a geo­tex­tile mem­brane and gabions (wire cages filled with stones) and re­in­stat­ing the top­soil on top.

We’ve looked at just two of CRT’s 72 reser­voirs re­quir­ing reg­u­lar in­spec­tion. Work in progress else­where in­cludes grout­ing spill­ways at Slip­per Hill Reser­voir, in­ves­ti­gat­ing leak­age at Bar­row­ford, and in­ves­ti­gat­ing the state of the crest wall at Win­ter­burn (all on the Leeds & Liver­pool).

Then there’s rais­ing the dam at Tarde­bigge and lin­ing the cast iron draw-off pipe at Up­per Bit­tell (both on the Worces­ter & Birm­ing­ham), ad­ding new siphons to in­crease the draw-off ca­pac­ity at Bosley on the Mac­cles­field and deal­ing with min­ing sub­si­dence at El­ton on the Manch­ester, Bolton & Bury – the fact that the canal has been aban­doned doesn’t free CRT of its re­spon­si­bil­i­ties.

But if, de­spite all this work, the worst came to the worst and an emer­gency arose, how would CRT cope? There are in­un­da­tion maps in place for ev­ery reser­voir, show­ing the max­i­mum ex­tent of flood­ing in the event of a breach, and for those with the more se­ri­ous con­se­quences there are emer­gency plans de­tail­ing which build­ings would need evac­u­at­ing, and which roads would be un­us­able.

To find out if the plans work, a re­cent ex­er­cise was car­ried out by the Trust in con­junc­tion with the Bri­tish Dam So­ci­ety (yes, there re­ally is such an or­gan­i­sa­tion). At the start, none of the staff knew that it was just an ex­er­cise – it be­gan with a phone call in the mid­dle of the night to say there was an emer­gency at Foul­ridge Lower Reser­voir, and it ended with them demon­strat­ing that it ac­tu­ally was pos­si­ble to get one cu­bic me­tre per sec­ond of emer­gency pump­ing ca­pac­ity set up to deal with it by the end of the same day.

So there are grounds to be re­as­sured that even if, de­spite the in­spec­tions, re­ports, and rec­om­men­da­tions, the worst were to oc­cur, the sit­u­a­tion could be han­dled with a rather less des­per­ate re­sponse than one man and his spade.

And let’s hope that with wa­ver­ing wa­ter lev­els on some canals this sum­mer there will be plenty in store for next year.

Re­build­ing sec­tions of Killing­ton’s over­flow spill­way base

Pres­sure grout­ing the spill­way base

The Foul­ridge dam, with con­crete crest wall

Good for a ‘once in 10,000 years’ flood? The 1819-built Killing­ton dam

Re­pairs to Killing­ton’s over­flow spill­way

Foul­ridge Up­per Reser­voir: re­build­ing the spill­way chan­nel sides

Rais­ing the Foul­ridge dam crest wall

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