232 ILLINOIS NATURAL 
dug across the channel. Then the trench 
was filled with gravel, which buried the 
lower edge of the netting so deep that it 
would not pull loose. 
On all censuses, the stilling basin at 
the base of the concrete surface spillway 
was used for holding fish to be returned 
to the lake. Weep holes in a 4-foot header 
wall across the lower end of this basin 
were plugged, and the basin above the 
History Survey BULLETIN 
Vol. 26, Art. 2 
the valve open usually 18 to 24 inches 
and with frequent closing of the valve 
for cleaning the screen. The valve was 
never left open at night or when it was 
unattended. 
When the lake level was down 12 to 
15 feet, fish came through the outlet valve 
in small numbers; it was not until the 
lake level was down 18 to 20 feet that 
the fish came through in quantity. When 
Fig. 8—Temporary fish screen used in draining censuses. 
1947, a temporary screen constructed of 1-inch-mesh poultry netting was installed across the 
stream channel below the outlet of Ridge Lake. 
wall was pumped full of water from the 
lake before any water was_ released 
through the outlet valve. 
Through tests run in the first two 
draining operations, it was discovered that 
no fish came through the outlet valve until 
the lake level had been lowered more than 
10 feet (lake depth 25 feet from the spill- 
way crest to the bottom of the outlet). 
As the valve gate is + feet square, the 
lake probably could be drained in 24 
hours with the valve wide open. How- 
ever, the flow resulting from a wide-open 
valve would top almost any screen that 
could be built across the stream channel 
and cause erosion of the stream banks be- 
low the outlet. The most the valve was 
ever open in actual draining operations 
was 36 inches and then only for a matter 
of minutes. Draining of the lake was 
accomplished in about + or 5 days with 
For fish censuses in 1945 and 
the lake level was down about 18 feet, 
the valve was opened for a few minutes, 
and then closed while the fish that had 
come through were being handled. Fish 
to be saved for restocking the lake were 
separated out and moved immediately in- 
to the spillway stilling basin. Those of 
value for stocking new lakes and ponds 
were weighed, counted, and placed in a 
tank truck. All other fish were sorted by 
species and_ sizes, and_ representative 
samples were weighed and measured indi- 
vidually; the rest were weighed in groups 
of 100 to 200 and counted. When all or 
most of the water, except that constantly 
running in the stream channel, had flowed — 
out of the lake basin, the valve was closed, 
and water was allowed to collect behind — 
the valve for an hour or so. The water 
was then released, and usually more fish | 
were washed through with it. This pro- 
ne 
mS ieee A 
