TRANSACTIONS OF SECTION Q. 689 



where the flood waters were collected from 273 square miles. It has heen already 

 stated, that the flooded ground seldom averages seven per cent, of the catchment- 

 basins, and in the Inny District, above referred to, it equalled an average breadth 

 of 1237 feet, or seven per cent. If, then, a number of tributary rivers, with catch- 

 ment-basins some two miles in breadth and some eight or ten miles in length, branch 

 off' at nearly right angles to the main river along which this seven per cent, flooded land 

 exists, then if you divide these lateral catchment-basins each into 100 parts, allowing 

 the seven parts near the river to be flooded, it will be evident that the maximum 

 flood due to the maximum rainfall on the seven parts or seven per cent, at the 

 junction of the tributaries with the main river will have passed away into the 

 main river before the maximum floods from the second, third, or tenth miles, 

 &c., could reach the last-named junction, provided the rivers were not dammed up 

 with shoals, &c. 



So that the time required to allow of the river valleys being covered with 

 water before the execution of the works would, if properly utilized, be more than 

 sufficient to allow of the water passing down a properly constructed river-channel 

 before the maximum floods could reach the main river from the second, third, or 

 tenth mile back from the main river. 



If this holds good in narrow tributary catchment-basins, so will it be applicable 

 to all forms of catchment-basins, no matter what their direction with regard to the 

 main channel. 



The author believes, then, that the effect of arterial drainage works is to enable 

 the floods from the fractional 4, 7 or 8 per cent, flooded lands, near the main arteries, 

 to pass off after the execution of the works many hours or days sooner, according to the 

 magnitude and length of the rainfall and district, than before the execution of the 

 works ; andthat, by securing a longer interval of time for the discharge t>f a flood of 

 given magnitude, arterial drainage works cannot increase the maximum flood- 

 discbarges of a district. 



As this view of the case is confirmed by the author's observations, he invites 

 discussion in order to test its accuracy. 



When once it is established that the floods in a river valley are not increased by 

 the enlargement or improvement of either an upper or lower section of the river 

 passing through the valley, the author believes that the public and the Govern- 

 ment would find it more practical to deal with the improvement of rivers in the 

 following way. 



Whenever any considerable portion of a country is flooded by the overflow of 

 a river or its tributaries, and the parties injuriously affected are desirous of apply- 

 ing to Government, through the Commissioners of Public Works in England, Ire- 

 land, or elsewhere, for a loan to improve their land, they should be required to 

 furnish a section of the rivers to be improved, taking care to extend the sections 

 down the river whether 1 or 100 miles in length imtil a sufficient outfall is ob- 

 tained for the successful carrying out of the proposed works. 



Should the Board of Works report in favour of the project, the Treasury could, 

 after the usual formality, advance the necessary funds, thus enabling useful works to 

 be carried out under the superintendence of Drainage Boards acquainted with the 

 localities with which their interests are connected, instead of losing many years in 

 endeavouring to embrace all the tributary districts in one large, costly, and un- 

 manageable scheme. By this method the works could be commenced in divisions 

 corresponding to the natural sub-outfalls of the country, commencing at the fall 

 nearest to or furthest from the sea. 



_ Should this method be sanctioned by Government on any large scale, now that 

 it is proposed to grant loans for river works on a moiety of the proprietors assenting 

 to the project, instead of requiring two-thirds as formerly, a great impetus would be 

 given to the extension of such works, conferring great benefits upon the country by 

 increasing the value of land, and giving at the same time additional employment, 

 and circulating large sums of money among the working classes in agricultural 

 districts. 



Although the facts thus briefly set/ forth in this paper are now publicly brought 

 forward by the author for the first time, still in the case of the Great Barrow 

 River Scheme, which embraces a country of 625 square miles, he has succeeded in 

 1878. y t 



