96 
BULLETIN OF THE BUREAU OF FISHERIES 
So far, then, as regards the dam structure proper, which comprises about three- 
fourths of the total barrier, we find that no fish can pass upward but that the fish 
may pass down, particularly those that feed or swim near the surface. The vertical 
upstream face of the spillways is a factor that must tend to lessen the chance of 
bottom fish being drawn over with the current. Aggregations of fish at the base 
of the dam, as if endeavoring to find a way up, have been observed, but with no 
such regularity as might have been expected. In the few instances, when such 
conspicuous gatherings of fish came under notice, different species were present each 
time, and in one case the presence of food brought over the dam was the obvious 
occasion for the gathering. Such observations do not afford adequate basis for dis- 
missing the possibility that the dam acts detrimentally as a barrier to upstream 
migrations, and this question will be considered more carefully in later sections of 
the paper. 
POWER HOUSE 
The power house, built out in the water and nearly parallel to the Iowa shore, 
from which it is some 700 or 800 feet distant, forms the eastern boundary of the 
fore bay. It may be remarked that the fore bay is a semi-inclosed portion of the 
lake, bounded below by the lock and the dry dock, on two sides by the power house and 
the Iowa shore, respectively, and above by a long ice fender of concrete, which 
extends from the upper end of the power house to the Iowa shore, being interrupted 
by a wide opening of about 300 feet for the passage of boats between fore bay and lake. 
The superstructure of the power house is completed for only one-half of the total 
length as planned (1,718 feet), but the entire foundation walls are in place, being- 
essential to hold back the upper water. The outside wall toward the Iowa shore 
is not built solidly to the bottom but rests on a series of arches, so that the water 
from the fore bay has free access to an inner or head bay within the building and 
extending its entire length. The outer wall of the building, which faces the Illinois 
shore, rises from the downstream bed of the river and is flanked by the tailrace. 
(Fig. 4.) The head bay and the tailrace are connected by as many passages as there 
are turbines, and each main passage consists of four narrow intake passageways; 
a single large scroll chamber, 38 feet in diameter, around the turbine (fig. 13); the 
turbine chamber; and the draft tube below. The turbines, of which there are now 15 
installed, are arranged in a single linear series from end to end of the house. The 
tailrace itself is excavated about 25 feet below the bed of the Mississippi; its width 
is 80 feet at the end, broadening to 230 feet at the lower end of the power house; the 
precise width below this point does not appear to be known, but the excavation was 
carried considerably farther down. 
The water from the head bay is admitted to each turbine through four gates, 
each 22 feet high by 7 feet 6 inches wide, consisting of iron gratings, which prevent 
the passage of large drift but which can exclude only those fish that are of unusually 
large size, the openings being 6 by 23 inches. The structures within the buildings 
are more particularly described later in discussing injuries to fish. It is sufficient 
at this point to state that upward movements of fishes would be stopped absolutely 
by the turbines. Undoubtedly it would be impossible for a fish to pass upward from 
the tailrace, through the draft tubes, and beyond the turbines. 
To find passage downstream through the power house, a fish must first pass 
the ice fender, either through the boat channel or through the deeply submerged 
archways; it must then enter the power house through the arches of the foundation 
