226 REPORT— 1874, 
The Fiver Shannon Drainage and Navigation*. By James Lynam, C.Z. 
The flood-waters of navigable rivers, such as the Shannon, may be far more 
easily, quickly, and economically regulated, and the crops on the adjacent lowlands 
preserved from inundations, by using wholly movable weirs, such as the French 
“ barrages mobiles,” than by wholly solid stone weir-mounds, such as those built by 
the Board of Works, and now existing in the Shannon, or by the dmmovable iron 
walls with submerged sluices recently designed for the Shannon by an eminent 
civil engineer. 
Works on a very large scale for the improvement of the river Shannon for both 
drainage and navigation were designed under the Act 5 & 6 William IV. chapter 6, 
and were carried on under the Act 2 & 3 Victoria, c, 61. The expenditure was 
about £586,000, of which one half was a free grant, and one half was levied on 
and paid up with interest by the riparian counties, 
In 1850 the Commissioners reported the works complete and effective, but that 
was a double mistake. It is now ascertained by measurements and admitted that 
large portions of the works are still unexecuted, and that 24,000 acres of land are 
periodically damaged by the inundations. In August 1861 an inundation destroyed 
the whole of the crops, and nearly every year great damage is done. During the 
last thirteen years the subject has been much discussed. A Select Committee of 
the Lords and another of the Commons have sat on the subject, heard much 
evidence, and reported. Two engineering surveys of the river have been made and 
lodged in Parliament, together with designs and estimates for the improvement of 
the drainage. The cost of all these amounts to about £12,000, but no work has 
yet been done. The landowners have asked from the Board of Works permission 
to construct sluices in the solid stone weir-mounds, but the Board refused. At 
length, last session of Parliament, the present magnanimous Government got an 
Act passed appropriating £300,000 of public money for the improvement of the 
river, of ‘which, as before, one half is to be a free grant, and one half is to be levied 
on and paid by the landowners with interest in thirty-five years. This half, viz. 
£150,000, is to be levied on an area of 18,000 acres, being at the rate of £8 6s. the 
English acre. Most of the owners of the flooded lands think this sum is more than 
the value of the benefit that would result to the lands from the drainage, and thus 
it remains very uncertain whether these landowners will give the formal legal 
asseuts to the project which the Act requires before works can be commenced. If 
works can be designed sufficient to improve the river to the extent necessary and 
desired for the sum of £200,000, one half of which, £100,000, levied on the lands 
would be but £5 11s. an acre, the landowners would freely give their assents, and 
a ae of £100,000 would be saved. That this can be done is what I here propose 
to show. 
Under the recent Act of Parliament it is not proposed to improve the whole of 
the river Shannon, but only three out of the eight divisions or reaches, leaving 
one level or reach at Limerick below and four reaches above unimproved, and 
their lands still subject to injurious flooding. 
The design for the improvement of those three levels at a cost of £300,000 to 
improve 19,000 acres comprises two principles, viz. increasing the water-way by 
excavation, and keeping up a depth of 6 feet to 7 feet of water on all the shoals 
and locksills in driest summer for steamboat navigation by regulating-weirs, 
The existing regulating-weirs, as built across the Shannon by the Commissioners, 
are wholly solid stone mounds of a half-horseshoe form, with the leg lying very 
obliquely to the stream. There is no sluice or flood-gate in any of them. In wet 
weather and in floods they act as an artificial barrier to the passage of the surplus 
water. From Carrick on Shannon to Killaloe Bridge in mid flood is 35 feet 9 inches 
in the surface. Of this fall 20 feet is wasted in useless cataracts at six weir- 
mounds, and 15 feet 9 inches only in the intermediate reaches to propel the stream. 
The regulating-weir proposed and designed recently by the Government in lieu 
of the existing weir~mounds is an immovable iron wall with submerged opes for 
sluices. Each ope is 6 feet broad and 4 feet deep, and surrounded on the top, 
sides, and bottom by the edges of the iron plates of the wall. The weir is 8 feet 
* Printed in extenso in ‘The Engineer,’ vol. xxxviii. p, 273, 
