50 THE SALMON RIVERS OF SCOTLAND 



come to be a spring fishing loch of some repute, instead of a 

 rather second-rate loch as at present. The success attained 

 by impounding water in the upper Helmsdale is an example 

 of what can be done by the operation suggested, and refer- 

 ence to this will be found in the chapter dealing with that 

 river. 



The catchment basin of Lochs Doine, Voil, and Lubnaig is 

 calculated as 73 '39 square miles by the officers of the Bathy- 

 metrical Survey, reference to whose reports has already been 

 made, and in dealing with the rainfall and water of the area it 

 is stated, 1 " The usual practice among engineers is to add 2| 

 per cent, of rainfall for each 100 feet of height above rain- 

 gauges. . . . Applying this rule to Loch Lubnaig catchment 

 basin, where we have an observed rainfall of 16-25 inches at an 

 average height of 538 feet, we must add 20 per cent, ior the 

 additional 809 feet of mean height, making an average annual 

 rainfall over the entire catchment basin of 91*5 inches." In 

 the same valuable paper, from information supplied by the 

 late Dr. Buchan, it appears that the total catchment basin of 

 Lochs Vennacher, Achray, Katrine, and Drunkie is about 

 75'29 square miles, and the mean height above sea-level 

 1035-185 feet. The rainfall is reduced to cubic feet in each 

 case, and the totals given according to three methods of 

 estimating rainfall described by Dr. Buchan. In comparing 

 in this way the Vennacher catchment with the Lubnaig 

 catchment, the following figures are arrived at : 



Vennacher. Lubnaig. 



1st method . . 14,857,214,000 15,600,760,000 



2nd method . . 14,991,815,000 15,750,446,000 



3rd method . . 12,424,867,000 12,737,328,000 



Means in cubic feet . 14,091,299,000 14,696,178,000 



From these calculations, which are no doubt as accurate as 

 can possibly be obtained, it appears that there is rather more 

 water in the Lubnaig than in the Vennacher system, and this 

 in spite of the fact that Loch Katrine is the largest loch in 

 either chain. 



From a table given on p. 213 of the paper already quoted, I 

 extract the following particulars as to the lochs in each chain. 



1 Scottish Geographical Magazine, xvi., No. 4, p. 221. 



