14 BULLETIN 304, U. 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 



