392 
(d) Copperas CreEK Dam To Havana (16.8 MILEs) 
Hydrography—One is at first surprised to find that although at 
the low water of 1901 there was a decidedly greater decline in elevation 
of water surface between the foot of the dam at Copperas Creek and 
Havana (0.78 inch per mile for 16.8 miles) than between Pekin and 
the head of the dam (0.14 inch per mile for 16.2 miles), average flood 
velocities in the section below the dam are less than in the section of 
similar length above it. The average velocity at a gage of 18 feet, 
Peoria, March, 1903, was 83.81 feet per minute between Banner—about 
2 miles above the dam—and Havana; and was 114.40 feet per minute 
- between Pekin and Banner. The average slope of high water surface, 
however, is in close correspondence with these flood velocities—equal- 
ing 1.43 inches per mile between Pekin and the dam, as compared with 
1.18 inches per mile between the dam and Havana at a gage of 22.6 feet, 
Peoria, March 31, 1904; and 1.36 inches per mile between Pekin and 
the dam, compared with 1.11 inches between the dam and Havana at a 
gage of 19.0 feet in March, 1903. As the low flood velocities through 
Peoria Lake are a joint consequence of the high bar above the mouth 
of Farm Creek and the unusual opportunity for expansion in the broad 
and low flats above it, the retardation of the flood current between Cop- 
peras Creek dam and Havana may be explained also as due jointly to 
the increased impounding area in this section* and to the high mud bar, 
superimposed upon an older sand bar, which attains its summit about a 
mile above the mouth of Spoon River. The top of this bar has an 
elevation only 0.6 foot below the level of the channel floor just below the 
dam at Copperas Creek, and is 13.8 feet higher than the deepest part of 
the channel between Liverpool and Havana. The artificial pool behind 
the dam at Copperas Creek, on the other hand, lies toward the lower 
end of a stretch of river with relatively steep natural slope, and at the 
higher gages the flood water moving through that section tends to follow 
the old slope-lines of water surface as they existed in the years antedat- 
ing the construction of the dam. 
Quite consistently with what has just been noted, both at flood 
stages and at the 1901 low levels, average slope and current are ap- 
preciably greater in the first than in the second half of the 16.8 miles be- 
low the dam, the average velocity (66.00 feet per minute) in the eight 
miles immediately above the Havana bar at a flood gage of 18 feet, 
Peoria, being in fact not much more than half that in the first eight miles 
(105.01 feet) and less than that of any other considerable reach of 
channel in the whole river below Peoria. 
In the first seven miles of channel below Copperas Creek dam the 
upper bottom stratum as shown by the government borings of 1902-1905 
was sand and shells or plain sand to a depth of 4 to 21 feet for the 
greater part of the distance; though dirty sand or sand and shells oc- 
curred at a few of the boring stations and was found by us just above 
* Table, p. 378. 
