20 BULLETIN 502, U. S. DEPARTMENT OF AGRICULTUEE. 



this point are available. Information of this character has been 

 difficult to collect because it is almost impossible to measure the dis- 

 charge of the well except by noting the increase of flow at the outlet 

 of the tile as the wells are installed. This could be done readily if 

 the wells were installed after the line was completed, but construe - 

 . tion in bad ground often necessitates the drilling of the wells as the 

 work progresses, and this makes it impossible to determine how much 

 water is developed by the tile line and how much by the wells. The 

 following data were collected on a line of tile 350 feet long and 7 

 feet deep : When completed, the drain without relief wells discharged 

 3.2 gallons per minute. Six wells were installed in one day, imme- 

 diatel}'' after which a measurement was made, which showed a dis- 

 charge of 21.4 gallons per minute. Two of the six wells installed 

 did not flow at all. Another line in this same system, and with the 

 same length and depth, discharged 37.5 gallons per minute after 

 completion. Twelve wells were installed in one day, after which the 

 discharge was 85.7 gallons per minute. This latter example prob- 

 ably is more nearly representative of average results. About 300 

 feet of each of the above two lines were in shale. 



CONSTRUCTION. 



Construction of drainage systems in shale lands has varied greatly 

 in respect to difficulty of installation and cost. Much of the shale 

 is quite hard, or contains hard concretions, which makes necessary 

 the use of picks. Trenches where the greater depths are in solid 

 shale stand well and need little or no bracing if the work is handled 

 properly. Shale makes a very good foundation for laying tile, and 

 the coarse, broken shale is good material for blinding the tile. 



Generally speaking, the worlc in shale is not difficult, but trenching 

 in the saturated adobe soil is a real problem. Outlet lines usually 

 have to pass for considerable distances through soil not imniediately 

 underlain by shale, and in many lines the upper several feet of the 

 trench must be excavated through the soil before the shale is reached. 

 With the exception of saturated fine sand or quicksand, no class of 

 material is more difiicult to handle than adobe. When partly satu- 

 rated it becomes sticky and adheres to the materials and tools with 

 a tenacity that makes progress difficult and tedious. The skeleton 

 spade is the only tool that will handle it with any degree of success. 

 The ordinary shovel will not scour. When this soil becomes com- 

 pletely saturated it often assumes a semifluid state that makes the use 

 of tight sheeting necessary ; frequently, not only must the sides of the 

 trench be sheeted, but also the face. 



The most successful cribbing in such material consists of two heavy 

 timbers, held apart by trench jacks, behind which is driven the 



