TRANSACTIONS OF SECTION G. 705 



navigation at Killaloe was stopped by the floods for an unusually long time that 

 season. Such has been the state of the Shannon navigation during the last thirty 

 years. 



Improvement of the Navigation. — The necessary works for improving this navi- 

 gation are : — To replace the protecting embankment at Killaloe by a concrete wall. 

 Fortunately they did not cut it all away. A length of 800 feet is enough to build. 

 When that wall would be built the proposed movable weir could be operated with- 

 out injury to navigation. It would be well to dredge a foot deep of dredgable 

 clay from Deny Shoal and White's Ford. A jetty 20 feet wide might be built 

 at the pier head. The Meelick Canal, two miles long, should be cleaned. The 

 obnoxious corner called the Devil's Elbow above the canal should be cut off. 

 These are all that are required for the navigation in order to improve the drainage. 

 _ Upwards to Athlone and Oarrick-on-Shannon, the state of the navigation is 

 quite good enough ; but it is almost. wholly useless for want of trade above Athlone. 

 The tolls received at the eight landing quays amount to but £100 a year, which is 

 £12 10s. a year to pay each lock-keeper or receiver. The four weir mounds there 

 are firmly maintained for the destruction of crops, and the disgrace of the govern- 

 ing power. Is it an enemy who maintains them so ? 



The Storage Capacity of the Lakes.— Taking the area in square feet of the 

 Shannon lakes, and the depth in feet of the legal navigation level under the surface 

 of the land, there results 6,000,000,000 cubic feet. If at the beginning of great 

 rain-falls the lakes were all down to the navigation level, which they will be with 

 removable weirs, there would be a storage reservoir of 6,000,000,000 cubic feet. 

 This woidd store 300,000 cubic feet of flood water per minute for fifteen days, while 

 the rest would be ppssing off to the sea through the open weirs. 



The greatest autumn flood lasted but seven days, and then fell regularly for and 

 remained low for twenty-six days. The lakes would store 500,000 cubic feet per 

 minute for eight days. Would these storage reservoirs have failed just when 

 wanted on that very important occasion ? Surely not. 



The Injurious Effects of the Weir Mounds.— In ordinary wet weather, during all 

 seasons, they keep the water so high as to saturate the lands, which is a great evil 

 to the crops and to the agricultural and sanitary state of the country. In medium 

 wet weather, as no opening can be made to let oft" ordinary surplus water, they 

 cause the lakes to be filled to the brim, which is 2^ feet over the legal navigation 

 level. When that occurs there is a natural fall from Carrick-on-Shannon Bridge 

 to Killaloe Bridge of 37 feet, and out of that 37 feet no less than 21 feet fall are 

 wasted by the weir mounds, leaving only 16 feet fall in the surface of the river 

 to propel the stream. In the highest autumn floods 16 feet are so wasted.* 



Mitchell Henry, M.P. for Galway, and I boated over many miles of meadows 

 where the hay lay, part in grass, cocks half covered, part in swarths wholly covered, 

 between Athlone and Meelick. When we got to Meelick there was a cataract over 

 the weir mound of 5 feet. There was but 1 foot to 2 feet of flood water rotting 

 the hay. 



If in planning for the improvement of the drainage of a river we begin by 

 robbing the surface of the stream of half of its natural fall, of course we must 

 estimate for very large excavations. Take, again, the channel at Killaloe as an 

 instance. The natural actual fall there in great autumn floods will be from the 

 deep wide water of Lough Derg down to the bridge 1 foot 3 inches in 2000 feet, or 

 3£ feet per mile. The present channel is 470 feet wide, and with this fall aud a 

 depth of 6 feet of running river it would as it is cany off 900,000 cubic feet of 

 flood water at a level that would keep Lough Derg and the river at Portumna 

 under the low lands. 



Now I beg your careful attention to a fact. The Government engineer, after 

 building the protection wall which would protect the navigation channel from 

 the river, proposes to construct a weir across the river that will of itself occupy 

 2 feet of the natural fall, and deprive the river surface of it. Of course he must 



* See Report to the Lords of the Treasury, by J. Lynam, C.E., printed by order of 

 the House ( f Commons, May 15, 1867. 



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