of the Fishery Board for Scotland. 



13 



upper of the two pools would flood the existing chute so that it would 

 harmonise with the two other rises of 3 feet. If only one large pool were 

 constructed, the velocity of the existing chute, with its gradient of 1 in 5, 

 would still be very considerable, and it might be necessary to deepen it 

 and project it into the pool above the weir so as to reduce the gradient. 

 The two-pool pass is, in my opinion, the better plan. 



Arrangements are now in progress for the alteration of Mugiemoss 

 obstruction, so that, I trust, a suitable pass may be erected. 



Recent Passes of Uniform Gradient Without Pools. 



A type of pass has recently been much employed which is constructed 

 with the floor of uniform and easy gradient, usually from 1 in 20 to about 

 1 in 24, and having as u breaks " to the descending water rows of upright 

 stones at intervals. It has been employed a good deal in the neighbour- 

 hood of Perth, at the outlet from the Shochie Loch, the Dupplin cruive 

 dyke on the Earn, the Bertha dyke on the Almond, and also on a large 

 scale at the second Invermoriston pass,* the Loch Yennacher outlet,t 

 and more recently at the Loch More outlet in the Thurso district, as well 

 as at the Airthrey dyke on Allan Water, already referred to. 



Loch More was previously 170 acres in extent ; now the level has been 

 raised by the erection of a massive dam dyke at the outlet, and the 

 acreage of the loch has become 511. The dyke is constructed with an 

 angle, the one arm being longer than the other. The pass runs along the 

 outer side of the long arm, and is 200 feet in length, 12 feet wide at the 

 top, and 25 feet wide at the foot or fish entrance. The gradient is 1 in 

 20. To provide for a flow of water down the pass when the level of Loch 

 More has sunk below the top of the pass, two apertures in the clam dyke 

 have been constructed. These outlets are 3 feet square and are sluiced. 



This introduces the consideration of a condition which has not yet been 

 touched upon. In the case of a pass at an obstruction in the course of a 

 river, I have pointed out the great value of determining the level at which 

 fish chiefly run, and of adapting the pass to suit that level. In the case of 

 a pass at a loch outlet, the pass becomes virtually a portion of the river 

 flowing from a sheet of water subject to considerable fluctuation of level. 

 It is, perhaps, very natural that an attempt should be made to adjust the 

 pass to various levels of loch, because any level of loch can supply the pass. 

 At the Loch More pass the highest level at the head of the pass is 

 unsluiced. To provide for lower levels of loch, the two sluiced openings, 

 as already mentioned, enter the pass at the side through the substance of 

 the retaining wall. These side openings send in water, therefore, at right 

 angles to the pass, and this water spreads out in thin fan-like shape and 

 strikes against the opposite side of the pass before it is conveyed down the 

 direct line of the structure. I cannot think that fish will find these side 

 openings easy to negotiate. The dam at Loch More was, however, 

 primarily intended to impound water which could be used for flooding the 

 river Thurso, and the possibility of arranging a pass to suit such conditions 

 is beset with peculiar difficulty, when at the same time the loch above is to 

 be regarded as an important angling water. In the Helmsdale arrange- 

 ment, Badanloch is not so regarcle;!, the angling tenants preferring that 

 the river should be primarily improved, and giving comparatively little 

 heed to the fishing for salmon in the loch. It is manifestly not easy, 

 while securing a good run of fish in the river by lowering the loch, to 

 arrange a pass which will take fish into the loch at different levels. The 

 pass would require to work at its best when the level of the loch had 



* Described and figured in the Twenty-second Report, Part II., p. 109. 

 f Described and figured in the Twenty-sixth Report, Part II., p 1. 



