126 HORTICULTURE, FORESTRY, FLORICULTURE 



for each spot will be necessary. Wells as outlets for water-bearing 

 porous substrata should be located at the end of the pocket if it 

 pinches out, and on the lowest ground if it extends all the way under 

 the tract. 



Lateral and main outlet drains should be clear to a depth of 5 

 feet, especially if they are intended for farm outlets on such land. 

 The depth of covered drains for arid soils is determined by two fac- 

 tors. The first is the depth of the drained soil necessary for different 

 crops. Fruit trees and alfalfa should have from 5 to 6 feet, and 

 still greater depths are advantageous. The other factor in alkaline 

 lands is capillary attraction. The height to which water will rise 

 and evaporate in large quantities is the minimum depth allowable 

 for ground-water level. Generally the water should be kept from 4 

 to 6 feet below the surface to satisfy these requirements. The mini- 

 mum grade is 0.1 per cent and may be increased to as much as 5 

 per cent if necessary. Sizes from 4 to 6 inches will be sufficient for 

 laterals in clay soils, with larger sizes for coarser soils. Fewer drains 

 are needed in the irrigated sections than in the humid. 



Plans for drainage other than small inexpensive lines should 

 always include surveys. Level surveys, both preliminary and final, 

 are absolutely necessary. The need of surveys for expensive tile or 

 open ditch work ought not to be questioned. The enormous losses to 

 farmers and co-operative companies in the past, when constructing 

 irrigating works without competent engineering supervision, should 

 be a lesson, and similar mistakes should not be repeated in undertak- 

 ing expensive drainage works. At the time when final surveys are 

 made the lines should be tied up to or located w r ith reference to per- 

 manent marks, and a map of the system made. Such a map may 

 prove valuable in planning future extensions and in other ways, 

 when otherwise the exact location would be forgotten. 



Field Construction. The tools most used for digging trenches 

 are trenching spades, shovels, and tile scoops. The digging for farm 

 drains should always begin at the outlet, finishing the work as it pro- 

 ceeds, except completing the back filling. For trenches not deeper 

 than 5 feet and for sizes of tile up to 12-inch, the top width need not 

 be more than 18 inches. To insure proper alignment one side should 

 be lined for the first spading. The last 1'6 inches should be removed 

 in the last spading and the bottom graded at the same time. The 

 work is much more easily done this way than if the digger were 

 lower in the trench, and the bottom will remain firmer if not mushed 

 up by constant tramping. Very few trenches can be finished in the 

 irrigated districts without the trouble caused by the banks caving 

 in, so that it is necessary to keep the tile laid and the trenches partly 

 back filled up to within a few feet of the finished trench, and for that 

 reason two or three diggers with one tile layer make the best team. 

 With proper care the grade should only vary within one-fourth inch 

 of true grade. 



Laying tile is an important part of the proper construction of 

 drains, even when the trench is made straight and on a uniform 

 grade. The first item of importance is providing a firm foundation 



