530 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 1923 



OPERATION 



Beginning with low tide, we may at first leave gates G, G, etc., 

 open and allow the water from the tailrace to discharge directly into 

 the tidal supply (Shepody Bay) , but the head will gradually decrease 

 as the tide rises, and at about 2^ hours rise the attendants close 

 gates G, G, etc., and open gates G 1 , G 1 , etc., allowing the discharge 

 from the tailrace to enter the low-level basin; into this the tailrace 

 will continue to discharge for about 6% hours, or through the last 

 oy 2 hours of flood tide and through the first 3 hours of ebb tide, after 

 which time the water in the low-level basin will have so risen, and 

 the water of the tidal supply will have so dropped, that it will now 

 be profitable to close gates G 1 , G 1 , etc., and open gates G, G, and 

 once more allow the discharge to occur directly into the source of 

 tidal supply and give the low-level basin time to again drain out on 

 the ebbing tide. I think you will at once grasp from this the sim- 

 plicity of the system itself, but in order that we should study more 

 fully one of the engineering problems involved I will call your 

 attention to the next figure (No. 5) , the typical tidal cycle at Hope- 

 well; this curve shows a copy, in per cent of range plotted against 

 time, of an actual tidal record, obtained at the ordinary neap tides 

 by the tide gauge established in 1919 at Hopewell by the Canadian 

 Tidal Survey, and furnished to me by the courtesy of Mr. H. W. 

 Jones, of that department. You will note how exceedingly regular 

 the tide is and how little affected by estuary flow, and this is one of 

 the great advantages of Bay of Fundy tides in general. At certain 

 places in the world the diurnal inequality becomes so great that for 

 several days there is only one tide in 24 hours, and at Southampton 

 there is a second high water occurring about 2 hours after the first. 



In dealing with the question of tidal power at Hopewell we must 

 remember that although the tide is regular in type, nevertheless the 

 range of the tide and not the rise is the limiting factor of our power 

 calculations, and it becomes necessary to establish and work on what 

 might be called a " standard " range. For this purpose I have 

 analyzed approximately the ranges that will occur in the course of 

 a year. I call spring tides those whose range exceeds 42 feet; they 

 occur about 15 per cent of the time, and I think no attempt should 

 be made to utilize them especially ; I call subnormal neap tides those 

 whose range is less than 32 feet ; they also occur about 15 per cent of 

 the time, and some means, which are discussed later, would need to 

 be employed to avoid the impairment of our "standard" amount 

 of power. 



All other tides I call ordinary neap tides, with a range at Hopewell 

 of 32 feet to 42 feet; they occur about 70 per cent of the time, and 

 it is the lower range of 32 feet which I think we should adopt as our 



