DRAINAGE OF IRRIGATED LAND. 
17 
always be provided. This device costs little and occupies but small 
space. If desired, the top sod ion may be removed at any time, a cap 
provided, and cultivation carried on directly over the top. Such a 
device may also be installed between regular manholes, for inspection 
purposes. Figure 17, page 22, illustrates the application of observa- 
tion wells. 
SURFACE INLETS AND FLUSHING WELLS. 
A vertical stack of tile is also useful as a surface inlet and flushing 
well. Figure 10 shows how it should be installed. The bottom 
Grave/ 
Sfeef Cho/'n or/ron 8ondw/fh ft/ngs 
Grour?d Co ^M 
Fig. 
-Observation well and sand trap con- 
structed of tile. 
Fig. in.— Standpipe, built of tile, for flushing 
drain or to act as surface inlet. 
should be paved with coarse gravel and the top provided with an iron 
grating and a mound of gravel or crushed stone. Such an inlet should 
be installed wherever a drain crosses a depression or flat, so that the 
waste water or storm water may not pond for a sufficient length of 
time to puddle the soil or "burn" the crop. One of these should 
also be placed at the upper end of each branch line as is indicated 
in figure 17, page 22. 
FLUMES. 
Flumes should be provided for all canals and ditches that cross 
underdrains, and care should be taken to prevent large quantities of 
water from flowing across these drains, particularly during the first 
two seasons after the installation of the latter. 
77733°— Bull. 190—15 3 
