148 KOYAL SOCIETY OF CANADA 



stead of remaining warmer at the bottom, as it would if the stream were 

 quiet — as shown in Fig. la — is thus mixed with the frazil and probably 

 wliolly reduced to the ice-making temperature. Under favourable atmos- 

 pheric conditions the Ottawa Eiver becomes a stream of frazil instead 

 of water. The " kneading " and spray-crystallizing procedure is enacted 

 again and again in the two other rapids, en route to the power plants at 

 Ottawa and Hull. With a knowledge of the above conditions it is not 

 surprising that the water power plants near Ottawa encounter frazil 

 troubles. The destruction of rapids, by the erection of dams, will 

 prevent the continuous — all winter — formation of ice spicules, or frazil, 

 but the impracticability of shielding the surfaces of long open water 

 reaches from the action of the early winter wind is quite apparent and 

 the frazil question will, in my opinion, always demand some attention 

 at water power plants. 



Frazil attacks are never experienced at hydraulic power plants when 

 the sun is shining, but they may be expected — under favourable condi- 

 tions — at any other hour of the day or at night. While the sun is shin- 

 ing it imparts enough heat to the water to prevent frazil from being 

 formed. Frazil has the peculiar tendencies of growing in the water and 

 of clinging to everything with which it comes in contact. It has on 

 several occasions within my own observation temporarily choked up the 

 total flow of the Ottawa Eiver by blockading the rapids. A view of a 

 rapid blockaded by frazil and anchor ice is presented in Fig. 3 thr'ough 

 the kindness of Mr. J. B. McEae, C.E., who also supplied photographs 

 5 and 6. The newspapers last winter stated that anchor ice caused the 

 St. Lawrence Eiver to rise 25 feet and flood a portion of the town of 

 Cornwall, Ont. 



It is this tendency of frazil to cling to other objects and to form 

 itself into impervious masses that makes it cause so much trouble at 

 power plants. Instead of flowing quietly through a power plant, as water 

 does, frazil clings to the edges of every opening, thus reducing 

 their areas, and often closing them altogether. Large rectangular 

 sluices, 6 feet long by 3 feet wide, have been blocked by frazil so com- 

 pletely in a few hours that a drop of water could not flow through them. 



One of the earliest attempts to cope with the frazil difficulty, which 

 came to my notice, was the hanging of cedar boughs from a stout rope 

 stretched across the surface of a channel. This was done by grist millers 

 many years ago, and the cedar bough barrier floating in the water soon 

 became covered with frazil and served as a starting point for the forma- 

 tion of surface ice. Tlie idea was a good one, but as these barriers soon 

 formed dams which were torn from tlieir moorings by the force of the 

 water, and the whole mass was sometimes carried into the racks at the 



