34 BATHYMETRICAL SURVEY OF 



LOCHS OF THE DUAETMOEE BASIN. 



WITHIN this basin two lochs were sounded by the Lake Survey, viz. 

 Loch Allt na h-Airbhe and Loch Duartmore, which drain by a short 

 stream into the small arm of the sea called Loch na Creige Ruaidhe. 

 Between these two lochs lies Loch Eucail, which is overgrown with reeds 

 and apparently shallow. 



Loch Allt na h-AirbJie (see Plate XIII.). Loch Allt na h-Airbhe (or 

 Upper Loch Duartmore) is the largest in the basin, and trends in a north 

 and south direction, being nearly two-thirds of a mile in length and one- 

 third in maximum width. Its waters cover an area of about 83 acres, and 

 an area of about 8| square miles drains into it. The maximum depth of 

 60 feet was observed in the south-western part of the loch. The volume of 

 water is* estimated at 110 million cubic feet, and the mean depth at over 

 30 feet. The loch was surveyed on September 11, 1902, when the elevation 

 of the lake-surface above the sea was determined, by levelling from bench- 

 mark, as being 119*5 feet. 



Loch Allt na h-Airbhe is a comparatively deep loch with an uneven 

 floor. The 25-feet contour-line follows approximately the shore-line, in 

 some places approaching close to the shore, while the 50-feet basin is 

 irregular, approaching the eastern shore in its northern portion, and 

 widening out and approaching the western shore in its southern portion. 

 In the central portion of the loch is an extensive shoaling, covered by less 

 than 30 feet of water, surrounded on all sides by deeper water. The deepest 

 sounding in 60 feet was recorded about 120 yards from the western shore 

 and about 200 yards from the southern shore. The soundings indicate a 

 steep off-shore slope in certain positions, as, for instance, off the western 

 shore near the southern end, where a sounding in 35 feet was taken about 

 50 feet from shore ; off the same shore, farther north, a sounding in 18 feet 

 was taken about 20 feet from shore ; while off the eastern shore, near the 

 northern end, a sounding in 25 feet was taken about 20 feet from shore 

 the last-mentioned giving a gradient exceeding 1 in 1. The following 

 table, giving the approximate areas between the contour-lines and the 

 percentages to the total area of the loch, shows that a larger area of the 

 lake-floor is covered by water between 25 and 50 feet in depth (equal to 

 nearly one-half of the total area) than by water less than 25 feet in 

 depth : 



