246 PARKS 



hydraulic gradient for ground water in a sandy loam, and therefore the 

 spacing of the laterals will depend to some extent upon the depth at which 

 the laterals are installed. 



The depth for the installation of tile drains will vary with the type 

 of soil in which the lines are installed, more than the spacing does. In a 

 heavy clay soil the laterals should be laid slightly deeper (approximately 

 3 to 3^ feet) while in the lighter clay loam two and a half to three feet is 

 ample. The general rule is that the deeper the laterals are located, the 

 slower the action, but the wider the area which can be drained. Therefore 

 quick drainage of ground water would require the minimum depth of 

 laterals with the minimum spacing. 



The following are some notes on the average depth of laterals in 

 different kinds of soil and for different drainage purposes: Underdrainage 

 of normal lawn areas on heavy clay loam, 3 to 3^ feet; on lighter clay loam, 

 2 to 3 feet; of roads and walk areas, 12 to 18 inches below the subgrade 

 of such areas; of garden areas on the lighter clay soils, 2 to 3^/2 feet; of 

 areas in the vicinity of graves, 7 to 8 feet; of wooded areas, 3^ to 4^ 

 feet (intervals of 30 to 40 feet between laterals) ; underdrainage of intensely 

 used recreational areas, 18 inches to 2^ feet (spacing between laterals,. 

 10 to 15 feet). 



Determining location for drainage lines. The location for drainage lines 

 should be selected with a view to reducing as far as possible the total length 

 of drain pipe required and especially the lengths of deep laid pipe or of 

 pipe of large diameter. Whenever it is necessary to connect shallow pipe 

 with deep pipe, this may be accomplished in a manner similar to that shown 

 in figure 4 and figure 5 on Plate 108. It is quite essential that important 

 drainage lines should be installed within the boundaries of any extremely 

 wet portions of the area being drained. Drainage pipes should also be 

 located where if in the future it is necessary to get at them in order to 

 correct any clogging condition of the pipes or condition where pipes are 

 out of alignment, such excavation can be made without destroying finished 

 surface conditions which cannot be easily repaired. 



Setting lines and grades. All drainage lines should be carefully laid out 

 on the ground with stakes at least twenty-five or fifty feet apart along the 

 center lifie of the drain. Batter boards should be erected as shown in 

 figure 6 on Plate 108 at a uniform height over the flow line of the pipe 

 and a nail or tack driven into each batter board directly over the center 

 of the drain. The posts supporting these boards should be at least twelve 

 inches and preferably farther from the sides of the proposed ditch in order 

 not to be disturbed by excavating operations. Batter boards should be 

 carefully erected for each catch basin or inlet and allowance made for the 



