THE FRESH- WATER LOCHS OF SCOTLAND. 121 



Loch Benachally (see Plate XXXIII.). Loch Benachally, a good 

 trout loch in the Forest of Clunie, is used by the Blairgowrie Corpora- 

 tion as the source of the town's water-supply. It flows by the Lornty 

 burn into the river Ericht, which further on joins the river Isla. Its 

 shores are of shingle and stones, except at the north-western corner, 

 where the material brought down by the Craigsheal burn has formed 

 an extensive flat covered with short weeds. This flat was dry at the 

 time of the survey, the water in the loch being very low. It is sur- 

 rounded by low hills covered with heather and grass. It is almost 

 triangular in outline, the base towards the north-west and the apex 

 pointing south-east, and is over a mile in length, with a maximum 

 breadth of over half a mile, the mean breadth being about a quarter of 

 a mile, or 23 per cent, of the length. Its waters cover an area of about 

 163 acres, or a quarter of a square mile, and it drains an area of over 

 3 square miles an area 12 times greater than the area of the loch. 

 About 60 soundings were taken, the maximum depth observed being 

 64 feet. The volume of water contained in the loch is estimated at 

 177,566,000 cubic feet, and the mean depth at 25 feet, or 39 per 

 cent, of the maximum depth. The length of the loch is 87 times the 

 maximum depth, and 220 times the mean depth. Loch Benachally 

 forms a simple basin, the bottom sloping more or less regularly on all 

 sides down to the deepest part, which is approximately centrally placed. 

 The slope of the bottom is in some places rather steep for instance, off 

 the northern shore near the north-western angle, and off the southern 

 shore near the middle, where soundings of 22 feet were taken about 60 

 feet from the shore, giving a gradient in each case of 1 in 2'7. The 

 loch is on the whole comparatively deep, very few of the soundings 

 being under 10 feet. The area of the lake-floor covered by less than 

 25 feet of water is about 91 acres, or 56 per cent, of the entire area of 

 the loch; that covered by water between 25 and 50 feet in depth is 

 about 58 acres, or 36 per cent. ; and that covered by more than 50 feet 

 of water is about 13 acres, or 8 per cent, of the total area of the loch. 

 Loch Benachally was surveyed on June 3, 1903, and the elevation of 

 the surface of the water was determined, by levelling from bench-mark, 

 as being 1004'9 feet above sea-level. 



Temperature Observations. Temperature observations taken in the 

 deepest part of the loch gave the following results : 



Surface 57"2Fahr. 



10 feet 55-8 ,, 



15 54-3 



20 49-0 



*' 47'4 , 



*> , 47 -2 



><> 47-0 



, 46'8 



