1904 



FORESTRY AND IRRIGATION 



177 



The lo-inch tile in the main drain 

 have a capacity sufficient to remove 

 4 inches of water per week from the 

 adjacent lands, or lands underlain by 

 laterals Nos. i to 7. Ordinary opera- 

 tions for reclamation do not overload 

 the drains, however, since the factors 

 of summer evaporation and subdrainage 

 through the soil play important parts 

 in the disposal of the water added in 

 flooding operations. 



Over the great part of the tract the 

 drains were laid at a depth of 4 feet. 

 In that part nearer the lake a somewhat 

 shallower depth was necessitated in or- 

 der to obtain a gravity outlet for the 

 drainage water. The drains were laid 

 on a grade of not less than one-tenth 

 foot in 100 feet, except where 3 -inch 

 tile was used when the grade was some- 

 what higher. The illustration (Fig. i), 

 is a plan of the completed system, and 

 shows the supply canals, position of the 

 weirs, drains, and the position and ex- 

 tent of the different sizes of tiles. The 

 system as installed has proven adequate. 

 Flooding has been carried on system- 

 atically, the land being divided into 

 checks and plats by levees, and each 

 plat treated in rotation. During each 

 flooding water has been added to an 

 average depth of 4 inches. The move- 

 ment of the water into the soil has been 

 regular, and, considering the character 

 of the clay subsoil, rapid, and the drains 

 have quickly filled after the floodings 

 and have run freely throughout the 

 experiment. 



During the last season (1903) the 

 land was flooded once each week, with 

 occasional longer intervals when the 

 supply canal was being repaired or dur- 

 ing times when the land was being 

 plowed or the levees repaired. 



Before any water was applied to the 

 tract a detailed survey was made to de- 

 termine the alkali content of the soil. 

 This initial survey was made in Sep- 

 tember, 1902. The land was then 

 flooded once and allowed to remain 

 until the next spring. 



In May, 1903, before work was com- 

 menced, a second survey was made, and 

 a third survey of the tract was made in 

 October, 1903, after the close of the 

 season's operations. 



The following table gives the tonnage 

 of alkali in the tract, as shown by these 

 surveys : 



a Shows the proportion of the salts removed as com- 

 pared with the salt originally present in the various 

 depths. 



The data given in the above table 

 shows that between September, 1902, 

 and the following May, 3,171 tons of 

 salt had been removed from the soil to 

 a depth of 4 feet, and that between Sep- 

 tember, 1902, and the following Octo- 

 ber, 5,430 tons had been removed, or 

 82 per cent of the alkali originally in the 

 first 4 feet of soil. It is also seen that 

 a greater proportion of the alkali has 

 been washed out of the surface foot than 

 out of the lower depths, and that the 

 movement of the salts is less pronounced 

 as the depth increases. Thus originally 

 the fourth foot carried 30 per cent of the 

 total salt, while in October, 1903, the 

 fourth foot carried 49 per cent of the salt 

 then remaining in the soil. There has 

 been, however, a marked decrease in the 

 quantity of salt at all the depths, and 

 the fourth foot has in reality lost 69 per 

 cent of the quantity of alkali originally 

 present. 



It must be understood that these 

 changes have taken place through the 

 movement of the salts downward by per- 

 colating water and not through washing 

 them from the surface of the land. 



The following table shows the volume 

 of water added to the tract from Sep- 

 tember, 1902, until October, 1903. The 

 table shows also the volume of drain- 

 age over the outlet weir, and the salts 

 (alkali) removed from the tract in the 

 drainage water. The results are ob- 

 tained from continuous measurements 

 and daily collections of water samples 

 for the entire period. 



