of the Fishery Board for Scotland. 



15 



however, the river rises, if the rise be not communicated to the pass, the 

 attractiveness of the pass is lessened, the water does not assert itself as 

 formerly, it is in much smaller proportion. Apart from these matters, 

 sluices always require someone to work them on each material alteration 

 of water-level. 



But, it will be argued, if the pass is open at the intake and flood water is 

 allowed to descend, the water will become a raging torrent and the pass 

 useless for fish. To this I am inclined to reply that if the pass is in the 

 form of a gradual and even slope, the result will be as stated, and that, 

 especially when the waterfall is high and the pass a long one, this result 

 will be pronounced. Under such conditions also rows of upright stones are 

 quite insufficient to check the water ; they rather break it up and increase 

 the foam. The arrangement of the pass must provide a much greater 

 check to descending water, so that in moderate flood it will still be possible 

 for fish to ascend if it is possible for them to run through the fall-pool. 

 In really high floods, however, no fish need be looked for close to high falls. 



At the Invermoriston new pass, two powerful sluices were fitted, 

 opening, it is true, from the river at a point where the current is always 

 considerable, and where in times of flood the current is very powerful 

 indeed. After some experience of the working of this pass, one of the 

 sluices was permanently opened and a substantial barrier of concrete was 

 erected outside of it in such a way that water coming to the intake had to 

 follow a narrow but deep and tortuous channel, the commencement of 

 which channel opened at an acute angle to the line of the river's flow. 

 This is found to work much better than the partial closing of the sluice. 



I have seen an effective method of a simpler kind in the passes of the 

 Sand River in Norway. A barrier is here constructed of rough hewn logs 

 placed horizontally one above another outside the inlet of each pass. This 

 log barrier allows water to pass below it, and is arranged at such a height 

 as to have no influence upon the pass at ordinary levels. When the river 

 rises, however, the surface flood water is at once impeded, and, owing to 

 the oblique direction of the barrier, turned off to a considerable extent. 

 Ascending fish pass up below the barrier. 



The Single Intake to a. Pass from a Loch. 



I have already, under the heading of * 'Recent Passes of Uniform Gradient," 

 dealt with the difficulty of satisfactorily making two or three intakes at 

 different levels from a loch to a pass, and given several instances of 

 attempts to solve this difficulty. 



If, however, the water of a loch is not required to supply artificial floods 

 to the river, and is in other respects completely under the control of the 

 river interest, it is possible to have a single intake and to regulate the loch 

 to suit the pass. These conditions have, I think, been practically met at 

 Glengalmadale, near Kingairloch, in Argyll. The loch is an artificial one of 

 no very great size, and there is a pass with a single unsluiced inlet. To 

 provide against flooding, a bye-wash channel, quite separate from the pass, 

 has been constructed in a wide sweep of easy gradient. This joins the 

 river below the foot or entrance of the pass. At ordinary levels this 

 channel is dry, but in high floods it will form an easy pass in itself.' 

 Owing to the steep nature of the surrounding hills, and the very consider- 

 able rainfall of the neighbourhood, floods are apt to be sudden and 

 violent ; a large storm-overflow has therefore been found necessary. To 

 regulate the loch so as to suit the level to the pass, a further device is, 

 however, necessary. This takes the form of a valve outlet passing through 

 the base of the embankment, but drawing water only from the surface of 

 the loch, down a vertical water tower. By opening or closing this flume, 

 the surface of the loch is manipulated independently of any storm-water 



