KEOKUK DAM 
93 
the passage of ice and drift -when the gates are open. The gates are of steel, 11 by 
32 feet (3.4 by 9.8 meters), and, working in deep slots in the concrete, may be 
raised so as to give free passage to the water or may be lowered so as to hold back 
the water entirely, except such as washes over when the wind is high and such as 
escapes by leakage. The volume of water passing Keokuk, and therefore the water 
levels above and below, is regulated by opening and closing these gates. The varia- 
tions in the number of gates that are open is said to range from none to 100. One 
hundred and sLx observations made during the period April 16 to September 15, 
1916, each on a separate day, and one or more at nearly or quite every hour of the 
day and night, showed a range of 2 to 57 and an average of 28 + . The average for 
the whole year, including the period of low water in winter, might well be much less. 
On June 9, 1915, 74 gates were seen to be open at one time. The gates are raised 
and lowered by a traveling electric crane, and a complete operation, including the 
movement of the crane from the adjoining gate, required about 26 minutes previous 
to 1916; during that year improvements were made, so that a complete operation 
could be performed in about 6 minutes, and only one crane is needed now. 
The head, or difference in water levels, varies considerably, being affected by 
flood conditions above and below the dam and doubtless by backwater from the 
Des Moines River prior to July, 1917 ; according to information supplied by the power 
company, the head on the turbines had been as low as 21 feet and as high as 37 feet; 
it was thought that the head at the dam might be as much as 1 foot greater. When 
a gate is open there flows over the spillway a stream of water about 10 feet deep (at 
the crest) by 30 feet wide. 
We thus have at each spillway in use a waterfall of considerable volume, de- 
flected at the bottom, where the water shoots out with tremendous force in the form 
of a raging, foaming torrent, which makes a striking spectacle. Only an inadequate 
idea of it can be gained from Figure 3. The mass of rapid water cuts a deep, sharp 
trough in the surface of the river, so that the surrounding water is at a considerably 
higher level than the race water below the open spillways. It may be possible to 
grasp this from the figure; the dark area in the foreground is the relatively still water, 
which is always flowing down into the trough made by the water coming over the 
dam. During most of the year the water makes a terrific commotion when it hurls 
itself against rocks that extend above the surface of the water. When the stage of 
the lower river exceeds 11.34 feet (or 495 feet, Memphis datum), all rocks, as they 
existed in 1916, are submerged. The turbulence of the water is then less spectacular, 
but the force is still so great that no fish can get to the base of an open spillway. 
They do, however, come to the dam at a point where spillways are closed, and often 
work along the base until they are carried by the eddy into the troughlike race, by 
which they are instantly swept down the river. Sometimes a fish drawn into the 
edge of the race in this way is tossed high into the air; but in any case its inability 
to stem the swift current is manifest. 
It is evident then that the dam itself (as distinct from the power house and 
lock) is insurmountable for fish coming from -below. Not only can fish not ascend 
the spillways, but they can not even buffet the current for a distance of several 
hundred feet below the open spillways. 
There are several conditions that might cause fish to approach the base of the 
dam. In the first place, if there were an upstream movement at the time of the 
reproductive activity, the fish naturally would be led to follow the swift current as 
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