DEAIISTAGE 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 cpnclusion 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. 



