2QO NOTES ON DOCKS AND DOCK CONSTRUCTION. 



cubic yards. The total number of times the sluices were 

 opened was 56, 1 and the aggregate time 22 J hours; therefore, 

 the quantity removed at each operation was practically 2000 

 cubic yards within an average period of 24 minutes. 



" The largest body of water run out of the great float at one 

 time reduced it in depth 5 feet 3 inches. Some difficulty was 

 experienced in arriving at the quantity run off, owing chiefly to 

 the long oscillating wave that came into play immediately the 

 sluices were closed. The extreme length of the float equalled 

 about two miles ; and when the flow from it commenced, a 

 current was established throughout the whole length. The 

 sudden check in the flow by the closing of the paddles caused a 

 rise in the water against the wall of the float nearest the 

 sluices of 12 to 15 inches above the previous level, producing 

 the wave which afterwards began to roll back to the further 

 end, to return and roll back again and again, with lessening 

 volume, for upwards of an hour, until entirely spent. 



" The mean head of water during the time of sluicing was 

 from 21 to 24 feet. 2 The calculated velocities due to these 

 heads would be 36'82 feet and 39'44 feet per second, or 25'67 

 and 26*86 miles per hour respectively. 



" It soon became evident, during these operations, that the 

 running of the water was attended, not only with much 

 inconvenience and hindrance to business, but with a considerable 

 amount of danger. The rapid lowering of the water in the 

 great float was highly objectionable. The low- water basin 

 had to be cleared of vessels before the sluices were raised, 

 and delays arose at times on this account. The injury to the 

 chambers showed the dangerous nature of the operations, for 

 it indicated a tendency to destroy the foundations, and, by form- 

 ing a sub-communication between the great float and the low- 

 water basin, to lead to the ultimate destruction of the works. 



"The danger to be apprehended was shown early by the 

 carrying away of the gates, and the uneasiness was not 

 diminished when the sluicing had to be conducted in the dark 

 mornings and evenings. 



"The power let loose was of immense force, and a feeling 

 arose that some great and sudden calamity, unforeseen and 

 uncontrollable, might at any moment arise; sluicing in the dark 

 was therefore discontinued. 



1 M.F.I.C.E., yol. xxviii. p. 528. f Hid., p. 530. 



