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eggsarascal

Whaley Bridge Evacuated

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1 hour ago, difflock said:

No, apparently the spillway was only concreted 50 year ago.

Yes but did the dam not have a spillway before or was there an earlier spillway than the 1968 one?

 

Also while I'm asking; is there another outlet and to which canal or does it feed the canal system via the river Goyt?

 

I ask because the High peak canal is higher than the Goyt at Whalley station and it looks like there is a feed to it via a mixture of cut and pipe from the reservoir.

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26 minutes ago, openspaceman said:

Yes but did the dam not have a spillway before or was there an earlier spillway than the 1968 one?

 

Also while I'm asking; is there another outlet and to which canal or does it feed the canal system via the river Goyt?

 

I ask because the High peak canal is higher than the Goyt at Whalley station and it looks like there is a feed to it via a mixture of cut and pipe from the reservoir.

In ma simple heid, there must always be provision for overspill, ergo a spillway, at any dam.

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29 minutes ago, openspaceman said:

 

 

Also while I'm asking; is there another outlet and to which canal or does it feed the canal system via the river Goyt?

 

I ask because the High peak canal is higher than the Goyt at Whalley station and it looks like there is a feed to it via a mixture of cut and pipe from the reservoir.

I've just asked this question on another forum where just about everyone is a liveaboard, I'm pretty sure the Goyt doesn't feed the cut. I stand to be corrected mind.

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55 minutes ago, eggsarascal said:

I'm pretty sure the Goyt doesn't feed the cut. I stand to be corrected mind.

Looking at the map  I think it is fed  directly from the middle of the dam by a cut running NE alongside reservoir road then under canal street to the terminus of transhipment warehouse.

 

This means the only viable way to discharge was into the todbrook under the dam and into the Goyt. Even if the canal system could take it this the  cut and pipe  wouldn't have capacity to take much and excess falls into the Goyt at the terminus weir anyway.

 

So the only way to get rid of the excess and not flood the Goyt would be to hold back outflow from the two other reservoirs to the South at Fernlee.

 

Apart from this gazing at the map my only direct experience is climbing and walking some ten miles to the west

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From a bloke that used to run a business on the cut in that area.

 

The Macc is fed by Toddbrook, not the river Goyt. Toddbrook is fed by a smaller stream, not the Goyt. Further south the other feeders are Sutton reservoir just south of Macclesfield, then Bosley reservoir. Given that there are no locks on this 21 mile stretch the 2 latter waters should be capable of keeping navigation open this year, given that both are full. Last year though, Bosley locks were closed for 3 months despite all 3 reservoirs being available.


 

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“We have got a three paragraph section which contains the bemusing phrase that ‘based on estimated annual probability of failure of the embankment the fatality rates are classed as being within a broadly acceptable number’. Could I ask what is a ‘broadly acceptable’ number of fatalities?”

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Oh and to top it off, turns out the hydro power scheme won't actually generate any electricity!! It is pumped storage, with the headpond above ground level, and nothing feeding in to it :vollkommenauf:

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23 hours ago, eggsarascal said:

From a bloke that used to run a business on the cut in that area.

 

The Macc is fed by Toddbrook, not the river Goyt.
 

Okay so the Todbrook after it leaves the dam is largely enclosed as it follows the route I suggested, the slipway and spillway take excess to the Goyt.

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9 hours ago, difflock said:

An annotated map would be wile useful in these meanderings debates about wot water flows where an why.

Here's a quick sketch of my take on this from looking at the map.

 

The Combs  and Toddbrook reservoirs (dark green) feeders (yellow) fill the High Peak Canal (canals use a lot of water when boats go through the locks, about 30 tonnes in our local canal as the locks hold two 70ft narrow boats).

 

Because the canals follow the contour and the Goyt is lower than the canal after Whalley bridge it has to be filled from Toddbrook and Combs reservoirs. Eggs has said it is also filled via the Macclesfield canal and the Bosley reservoir which is 25km from the junction with the high peak canal which starts in Whalley bridge  about 9km south of the junction.

 

The Fernlee and Errwood reservoirs do not seem to feed the canal but presumably also have the function of controlling flow on the Goyt. The trouble is the maps only show open water so I do not know what any of the reservoirs also serve by underground pipes.

 

So the only ways out of the Toddbrook reservoir are via the feeder to the High Peak canal, the weir at the northern tip  and then the overflow that runs  curving clockwise   in front of the dam and thence into the Goyt and the spillway over the top of the dam which meets the above overflow.

 

Any excess that ends up in the High peak canal ( shown red) flows over a weir and into the Goyt (shown light green) near the start of the canal at Whalley bridge.

 

As the Toddbrook reservoir was full, and following very heavy rain, all the excess ended up in the Goyt, which seems to have coped with it, as I said in an earlier post there was the possibility of holding back water at the Fernlee and Errwood reservoirs plus the Combs reservoir if the Goyt could not handle the excess from the Toddbrook system.

 

So it looks like everything worked as planned except the spillway  was damaged when it was over-topped with an unprecedented flow.  I can see the spillway was poorly constructed or maintained for the flow that came over it, Eggs asserts this was predictable and attempt should have been made earlier to lower the level of the Toddbrook reservoir via the overflow into the Goyt if I infer his post correctly.

 

whalleybridge.thumb.jpg.a6dbb099bd59535820ba809994788afe.jpg

 

My personal guess is that there wasn't much of a void below the spillway slabs prior to it being over-topped and the damage was all done during the surge because the joints between the slabs had  deteriorated.

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