14 BULLETIN 304, IT. S. DEPARTMENT OF AGRICULTURE. 
The quantity of run-off from the bluff lands will depend upon their 
topography and the natural watershed boundaries; the task of dis- 
posing of the run-off is often one of the most serious problems to 
be solved in the planning of a district. The amount of water thus 
entering the district should be reduced as much as possible by proper 
location of the levee and by a diversion ditch wherever the latter 
is feasible. The rate of run-off from the higher lands is likely to be 
several times as great as that from the bottom lands, so that the 
diversion of the run-off from a relatively small amount of hill land 
may greatly reduce the necessary capacities of the internal drainage 
ditches and pumping plant and diminish the annual operating 
charges. 
Owing to their high velocities the hill streams carry a great amount 
of silt, and as the slopes of the channels in the bottom lands are very 
flat the velocity of flow is reduced and the larger percentage of the 
silt is deposited soon after the water leaves the hills. On many of the 
districts along the Illinois and the Mississippi Rivers the silting of the 
interior drainage ditches by waters from hill streams has entailed a 
heavy expense for its removal. During 1914 a contract was let by 
the Hillview Levee and Drainage District to remove an estimated 
total of 90,000 cubic yards of silt from the interior drainage ditches 
at a unit price of 18 cents per cubic yard. On the Mississippi River 
the surveys showed that on the newly organized Indian Grave Drain- 
age and Levee District certain natural channels had been silted by 
hill streams to such an extent that it was considered necessary to 
construct new artificial channels, although at a very recent date the 
natural streams were of ample cross section to serve as main drainage 
channels for the district. It is estimated that because of this silting 
it will be necessary to excavate several additional miles of channel 
at a cost of from $30,000 to $40,000. It is evident that the damage 
which the silting of interior channels may cause will justify in most 
cases a considerable expenditure for protection. 
The only district known on either of the above rivers where diver- 
sion has been tried on an extensive scale for any considerable length 
of time is the Coal Creek Levee and Drainage District near Beards- 
town, 111. (See fig. 1.) A large diversion ditch and levee were con- 
structed about 10 years ago along the base of the bluff for a distance 
of about 4 miles, from the point where Coal Creek debouches from the 
hills to the lower end of the district. The levee is on the lower side 
of the ditch; that is, on the side toward the district. Not only is 
the flow of Coal Creek received by the diversion ditch, but several 
smaller streams also flow into it. This ditch, though sufficiently 
large at first, became too small by being filled with sediment brought 
down from the hill during floods, so that the various streams over- 
topped the levee and flowed into the district. In 1909 another ditch 
