98 
BULLETIN OF THE BUREAU OF FISHERIES 
Another significant feature of the lock is the head wall, locally called a “sill,” 
at the upper end of the lock. An examination of Figure 6, from a photograph taken 
while the lock was unwatered, will give an idea of this particular difficulty to be over- 
come by a fish using the lock to pass upstream. In the illustration the two swinging 
lower gates are shown wide open and in their niches in the respective side walls; the 
wall or sill is in the middle background. A fish entering the lock finds a depth of 
10 to 25 feet of still water. The lower swinging gates having been closed, the water 
is admitted in miniature geysers, as shown in Figure 5, until, after 7 or 8 minutes, 
it is from 21 to 37 feet (6.5 to 11.3 meters) higher than when the lower gates were 
closed. The upper gate (black in fig. 6) is submerged until its surface is level with 
the upper wall, shown light in the background. The fish is now in an inclosure 110 
by 400 feet (33.5 by 122 meters) containing about 47 feet of still water. The only 
exit is the area 110 feet wide and 12 to 14 feet deep over the wall or sill. There 
is no current to guide the fish to this small opening at the upper edge of one part of a 
large area of concrete, and, as will be shown hereinafter, this opening exists for only 
a few minutes, the water being then lowered to the level of the river. 
INTERVALS OF FREE PASSAGE 
As has already been pointed out, there is no opening by which fish may leave 
the lock above, except while the upper gate is down. An effort was therefore made 
to learn during how much of the time this gate is submerged. Since the lock masters’ 
records show the number of lockages, it was necessary only to learn how long, on the 
average, the gate is down at each lockage. 
Without any selection, and just as happened to be convenient, 54 ordinary 
operations were timed. These operations were made in the usual way for the passage 
of boats, and, except in a few instances, the persons doing the work did not even 
know that an observation was being made. The gate remained beneath the water 
from 1% to 17% minutes, and the average for the 54 cases was 4.5 minutes. Of these, 
there were for the passage of boats northward 29, averaging 3.3 minutes, for the pas- 
sage of boats southward 22, averaging 6 minutes, and for the simultaneous passage 
of different boats into and out of the upper end of the lock 3, averaging 4.5 minutes. 
The longer average time for boats passing downward was due to the fact that for 
steamboats it was the practice to have the gate ready a few minutes before the boat 
arrived, so as to run no risk of causing it to stop above the lock. Steamboats passing 
up out of the lock simply cast off from the wall of the lock and leave, so that there 
is no corresponding delay. For smaller craft the time of submergence was not 
affected by the direction in which they are going. 
To allow for this difference, and because the observed cases include 7 more 
“ups” than “downs,” we may add 7 imaginary “downs” of 6 minutes each to the 
54 observed cases, which gives an average of 4.7 minutes. To simplify the arithmetic 
involved, 5 minutes will be taken as the average time when there exists a possible 
passageway for fish during each operation of the lock. 
In 1915 the lock was operated from March 1 to November 29, inclusive, or 274 
days, and the total number of lockages was 1,489, being an average of 5% times 
a day, or almost precisely 38 times a week. Complete records for 1916 are not at 
hand, but during the 114 days from March 24 to July 15, inclusive (the season of 
supposed upward migration of fish), there were 477 lockages, an average of 4.2 times 
a day, or 30 times a week. The actual number per week (excluding fractional weeks 
