ELECTRIC POWER FROM THE MISSISSIPPI RIVER CLARK. 205 



dined surface (pi. — ). An observer with a short metal sounding 

 rod can hear the clear ring of the solid rock bottom all the way 

 across. The regularity of the bottom and the rock of which it is made 

 are charted on the facsimile of the United States Government map 

 shown opposite page 200. 



A well constructed concrete dam, power house, dry-dock, and lock 

 on such foundations should last as long as the old Roman concrete- 

 work made of natural cement, a great deal of which has been standing 

 2,000 years and is still in good condition' where not destroyed by the 

 hand of man. 



STORAGE OF WATER. 



In the interests of navigation below the dam, particularly during 

 the open period from March to December in each year, there are 

 certain restrictions placed upon the complete interruption of the 

 flow of the river. The Mississippi River Power Co., successor to the 

 privileges and franchises of the Keokuk & Hamilton Water Power 

 Co., is allowed to cut down the flow only during the night to 15,000 

 cubic feet per second for two hours, 10,000 cubic feet per second for 

 six hours and 5,000 cubic feet per second during the balance of the 

 time between sunset and sunrise. If the wheels do not pass the above 

 amounts then the deficiency must be made up by letting water 

 through the gates. 



From an operating point of view these restrictions are not a gross 

 handicap, for the storage of water during the night, when the load 

 is light, will still be possible for use during the next day when the 

 load is heavy. 



In backing up this water, the amount of which can of course be 

 regulated as will be seen from the description of the dam construc- 

 tion below, in the ultimate development, there will be formed a lake 

 from 3 to 5 miles wide and about 40 miles long, overflowing the low- 

 lands and thereby changing the topography of the country immedi- 

 ately adjacent to the river. It will also submerge the Government 

 canal mentioned above which is being supplanted by the new lock 

 and dry dock. 



DETAILS OF THE DAM CONSTRUCTION. 



Resting on the solid river bottom described, the plant is being 

 built out from the bluffs on either side almost a mile apart. The 

 construction is handled by two distinct organizations — the Illinois 

 division building the dam, the Iowa division the locks and dry dock. 

 Each construction plant consists of a concrete-mixing plant, a stone- 

 crushing plant, a central power plant supplying compressed air and 



