Tag Archives: headrace

Navigating Ardnacrusha

The Western Mail & South Wales News of 19 April 1929 had an article by M Franklin Thomas about “Ireland’s Big Engineering Scheme”. The article was illustrated with a map and three photographs were reproduced on the newspaper’s “picture page”. It had a couple of interesting points about the headrace and tailrace considered as navigations; I can’t recall seeing these points made elsewhere.

Current

This [headrace] canal is level, but a flow of about 3½ miles per hour will be maintained owing to the water released through the turbines and navigation locks.

I don’t recall seeing a figure for the current. I presume that that is with three turbines running flat out.

There is an interesting account of the laying of the concrete apron that protects the banks against the “wave action set up by navigation, and the flow of the stream, wind, &c”. And the lock was to have an “ingenious arrangement by which the entering streams of water neutralise each other’s effect”.

Tailrace

Mr Thomas says

The tail race is one mile and a half long, cut from the solid blue limestone, and one of the most interesting points was the method adopted to permit barges to ascend the tail race against the enormous scour from the turbine discharges.

A special navigation channel is cut from the locks to a point some 200 yards below the outfall, and the bed of the tail race rises 20ft in the mile and a half, so that the depth of water will be 35ft at the outfall from the turbines and 15ft at the junction with the Shannon.

This will give a cushioning effect, and the rate of flow will be thus reduced to enable barges to navigate upstream. A bend is also provided where the special navigation channel joins the tail race and the rate of flow is estimated to be the same as that of the head race — 1.5 metres per second, or about 3½ miles per hour.

I would be glad to hear from anyone who can cast further light on this, and especially on whether the rising bed does have the intended effect.

What’s a cumec, Daddy?

I don’t know, but here’s a picture of 415 of them flowing through Castleconnell. [Update 13 December: that may be only 405 cumec.]

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415 cumecs on 12 December 2015

Actually, a cumec is one cubic metre of water per second, which is roughly one ton per second, which is a lot of water. And 415 cumec is the amount that, according to the blatts, the ESB is currently letting down the original course of the Shannon from Parteen Villa Weir; the minimum flow in that channel, as seen in summer, is 10 cumec.

Castleconnell 12 December 2015

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Younger trees getting their feet wet

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Who’d have guessed?

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Below the bridge

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Above the bridge

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Stormont

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Pump

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Sandbags

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Sandbag Central

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Sandbags filled here for distribution

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Army engineers

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More equipment arriving

Clonlara 11 December 2015

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Ardnacrusha headrace, said to take 400 cumec

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Errina bridge on the Plassey-Errina Canal

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The stop planks seem to be quite effective …

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… as there is little water getting down the canal to Clonlara bridge

Park Canal 9 December 2015

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Depth gauge at Park Lock

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Lock chamber

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Full canal upstream

 

Keeping a clean bottom

The upper chamber at Ardnacrusha lock