DRAINAGE METHODS FOR COUNTY EOADS. 17 



gutter would be made of different material from the road crust, and constructed 

 at a different time or by a different force of laborers. 



11. The maintenance of side ditches consists in keeping them free from ob- 

 structions, and in reshaping them whenever this is desirable in order to prevent 

 erosion. While a limited amount of vegetation may be advantageous to ditches 

 on steep grades, it should not be such as to interfere seriously with the flow 

 of water in the ditch. Where drops are employed they should receive frequent 

 attention to see that they are not being undermined and that the water is not 

 cutting around them. The design of drops sometimes calls for the use of brush, 

 logs, saplings, cut stakes, etc., as. these often are the only inexpensive local 

 materials available in rural .sections. While such designs, if carefully con- 

 sidered, may produce drops effective for a considerable period, their use is not 

 recommended because of the great danger that the drop will break up under 

 stress of unusual conditions and the floating parts seriously obstruct the 

 ditch. 



12. The following examples have been selected from notes regarding some of 

 the existing side ditches which have been observed : 



Example No. 1. — Side ditch on Rock Point road, Charles County, Md. : 

 Age of road, IJ years. 

 Original shape of ditch, flat V. 

 Width of roadway, 24 feet. 

 Width of gravel surface, 15 feet. 



Average width drained by side ditch, including slope, 2.5 feet. 

 Character of soil, very light clay. 

 Slope of ditch (grade), 2 per cent. 



Length from summit to where erosion begins, 400 feet. 

 Ditch empties into cross drain at 500 feet. 



Example No. 2. — Same road and same conditions as example No. 1, except 

 slope of ditch is 3 per cent : 



Length from summit to where erosion begins, 200 feet. 



Ditch maintained with considerable difficulty below the 200-foot point by 



means of wooden breakers. 

 Example No. 3. — Side ditch on Owings-Prince Frederick road, Calvert County, 

 Md. : 



Age of road, 4 years. 



Original shape of ditch, flat V. 



Width of roadway, 23 feet. 



Sandy-clay surface. 



Average width drained by side ditch including slope, 22^ feet. 



Character of soil, very light clay with small percentage of fine sand. 



Slope of ditch (grade), 6 per cent. 



Length from summit to where erosion begins, 100 feet. 



At 300 feet the ditch has eroded 1 foot below the original section, and below 



5.50 feet it is maintained Avith great difficulty by means of wooden 



breakers. Below 650 feet, in fact, the entire road has been washed out 



at least twice, notwithstanding the breakers. 

 Example No. 4. — Same road as Xo. 3. 

 Original shape of ditch, flat V. 

 Width of roadway, 24 feet. 

 Sand-clay surface. 

 Average width drained by side ditch, including slope, 25 feet. 



66998°— 18— Bull. 724 2 



