18 ON THE RECLAMATION 



I may here remark in passing, that the currents of large rivers 

 vary as the place of observation is narrow or wide, and also as 

 the flow is that of ordinary or of flood water, and that the velo- 

 city of such rivers as the Thames, the Tay, or the Clyde may, 

 according to their different conditions of flood, be found to vary 

 from about one mile per hour as a minimum, to about three 

 miles per hour as a maximum velocity. Smaller rivers with 

 steeper slopes have higher velocities. I have found the cur- 

 rents of such rivers as the Water of Leith, for example, in flood 

 at places where the gradient of the bed varies from 25 to 32 

 feet per mile, to run at rates varying from 3f to 5| miles 

 per hour. Still more rapid currents will be found where the 

 bed is still steeper, until we reach the mountain torrent carrying 

 everything before it in its rapid descent. 



The details of two very good examples of checking the flooding 

 of land by widening and straightening rivers, and thus increasing 

 their power of discharge, are to be found in the Transactions of 

 the Society the one an account of the improvement of the pas- 

 turage lands on the Torran in Caithness, by Mr James Purves,* 

 and the other a paper by Mr Blaikie on the Improvements of the 

 Don in Aberdeenshire.^ But it is not often that the divisions 

 between the properties of conterminous proprietors admit of 

 extensive deviations of a river's course, and even when no such 

 difficulty occurs, the formation of the country itself may render 

 such a work impracticable. Proprietors are, therefore, generally 

 obliged to resort to artificial embankments for the protection 

 of their own lands, and such works are, as is well known, 

 extensively employed for that purpose. Their proper construc- 



* Series iv. vol. ii. p. 439. t Ibid. ii. vol. ii. p. 75. 



