540 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



well ahead of the future requirements and thus improve the average 

 head ; and yet another method would be to build a fresh-water dam. 

 say, just below Turtle Creek, about 5 miles west of Moncton, in 

 which fresh water would be impounded and released only to make 

 up the deficiency in head at subnormal neaps. Still another method 

 would be to employ auxiliary steam power to assist the water power 

 during the water deficiency. One of the last two devices is nearly 

 always resorted to in the case of ordinary hydroelectric plants sit- 

 uated on fresh-water rivers. In nearly all districts the amount of 

 rainfall varies enormously during the different months of the year 

 ana the amount of run-off and discharge varies in a direct relation 

 to the rainfall. As an example of this, the discharge at Grand Falls, 

 on the St. John River, reached a maximum in May, 1909, fifty times 

 greater than the maximum of October, 1909, and the mean discharge 

 for the whole month of May was twenty times greater than the mean 

 for October. In fresh-water rivers a certain power may run into 

 thousands of horsepower in the spring, but be reduced to hundreds 

 in the fall of the year, unless adequate means are resorted to to in- 

 crease the deficiency of head. 



In this matter a tidal power scores heavily over a fresh-water 

 power. In the case of the fresh-water power neither the time nor 

 quantity of a head deficiency can be predicted, but with a tidal 

 power Jboth the time and the deficiency are predicted by the tide 

 tables several j^ears in advance, and it would thus be much easier to 

 provide for our head deficiency, which only, after all, amounts to 35 

 per cent in quantity and occurs only 15 per cent of the total time. 



The best means of making up the deficit in the case of the Hopewell 

 tidal plant would be best figured out in the final estimates as that one 

 which would maintain the normal output at a minimum of cost. 



The other two engineering items I wish to discuss are sediment 

 and ice. 



At the present time the never-ceasing current flow up and down 

 the two rivers keeps the river stirred up, and the waters of both 

 rivers show a considerable amount of sediment, and one would at 

 first jump to the conclusion that this muddy grit, fine though it is, 

 would produce much unusual wear on the turbines. However, what 

 will happen as soon as the mouth of the Petitcodiac is closed by a 

 dam? The mud in the water above the dam will undoubtedly settle, 

 for it will have time to do so, and the water of the Petitcodiac will 

 become clear. At present the water is never still, but with a dam the 

 rise and fall would be reduced to a few feet and the current would 

 be sluggish. 



In a similar way the building of the dam would entirely alter the 

 ice conditions. Once the dam was built, the whole river would freeze 

 over in severe weather and the sheet of ice would rise and fall with 



