DRAINAGE OF IRRIGATED SHALE LAND, 27 
water had two sources of supply, the main one being an underlying 
shale ridge coming in from the north. This ridge is not sharply 
defined, but is broad and flat, being a part of the larger and exposed 
shale ridge mentioned above. The other source of supply seemed 
to be the shallow draw. 
The system was laid out as shown in figure 3. The main.line runs 
up the draw, following as closely as possible the edge of the fill next 
to the seepage area. The most important part of the system is the 
lateral, 200 feet long, which follows up the shale ridge. Consider- 
able difficulty was encountered in constructing the main line, but in 
the shale construction was less difficult. In this line about 12 holes 
were bored with a 2-inch auger. The initial flow in them was strong, 
and they spouted above the bottom of the trench. This discharge 
gradually decreased, but the wells still furnish nearly all of the flow 
obtained in the small system. After a few months the surface of the 
affected area became so dry and hard that it was difficult to plow. 
This tract is a good example of drainage for prevention. The 
drains were installed before the affected area had spread and before 
the land had become highly impregnated with salt, and as a result 
the land was easy to reclaim. If the condition on this tract had not 
been attended to at once there is little doubt that it would have spread 
over most of the tract, and the soil would have become so filled with 
alkali that it would have required two or three years of washing and 
careful farming, with little or no returns, to reclaim the land. Fur- 
thermore, it would have been necessary to install many more drains. 
That this is a logical conclusion can be deduced from the quality of 
the drainage water developed by this system as indicated by analysis 
J in Table I. | 
EXAMPLE III. 
This tract slopes to the southeast as indicated in figure 4. The soil 
is a dense adobe. Small spots of alkali appeared about four years 
ago. The steady rise of the water table and the consequent accumu- 
lation of an excess of alkali at and near the surface was gradually 
killing out the alfalfa. With the exception of the southwest. corner, 
all of the alfalfa was in poor condition. At the time of the prelimi- 
nary examination there were large spots that produced no alfalfa 
at all, and the water table was practically at the surface which was 
covered with a thick crust of alkali in which sodium sulphate pre- 
dominated. There were no indications of black alkali. There were 
two main alkali spots. One strip extended north and south through 
the middle of the tract and was broader at the south end, where a 
bunch of tulles were growing. The other spot, which was very wet, 
was at the northwest corner and extended across the road to the west. 
The road was impassable and a large portion of the tract on the west 
was affected. 
