THE IRRIGATION AGE. 



209 



most effective way of treating such cases. There are 

 also long level sloughs having steep side slopes which 

 furnish a constant supply of water by seepage at the 

 base of the slope. Drains at the upper edge of the 

 saturated strip will intercept the seepage water before 

 it is forced to the surface by the pressure of the water 

 above. 



SURVEYS AND GRADES. 



Whatever may be said to the contrary, it remains 

 a fact that in order to get the best results in a system 

 of drainage the work should be laid out with a leveling 

 instrument and executed in accordance with the survey 

 made. No one can be relied upon to guess a grade 

 correctly, nor can any one arrange a system of grades 

 with economy and at the same time get the best pos- 

 sible work out of the system without first knowing the 

 facts as determined by the level in the hands of one 

 who is able to use it. The drainage engineer can stake 

 out the lines, adjust the grades, and put the work in 

 such shape that it can be executed with precision, either 

 by contract or day labor. The results of the work can 

 be predicted with reasonable certainty before a ditch is 

 opened. The drainage engineer, with the aid of the 

 farmer who is familiar with the soil, can plan and lay 

 out the work to far greater advantage than the inex- 

 perienced man. The farmer or superintendent can then 

 give his attention to the execution of the work and in- 

 sist on having it done according to the plans and sur- 

 veys without the misgiving that it may be entirely 

 wrong. Where there are large tracts of level land, or of 

 land so nearly level that it can be drained successfully 

 only by the most accurate work with instruments, the 

 services of an engineer are indispensable. Where the 

 land is somewhat rolling, the farmer may be able to 

 .adjust the grades himself. 



The slight grades upon which lines of tiles may be 

 laid with satisfactory results are a surprise to many; 

 indeed, they were regarded as entirely impracticable 

 until the experience of recent years proved the con- 

 trary. Lines of drain tiles laid on a grade as low as 

 one-half inch per 100 feet in firm soils will operate suc- 

 cessfully, provided the lines are not too long, while 

 drains laid on grades of one to two inches per 100 feet 

 may be counted by the hundreds of miles, and their suc- 

 cessful operation is attested by thousands of acres of 

 cultivated lands. It is not difficult to impress upon the 

 jmind of anyone who will give the matter attention the 

 fact that such work must he laid out with accuracy and 

 executed with thoroughness and skill. It should lie ob- 

 served in this connection that the fact of a drain hav- 

 ing a good grade should not be made an excuse for 

 careless and inaccurate work, though it is conceded that 

 the consequences would be less serious -than where the 

 grade is necessarily light. Where a grade can he ad- 

 justed as may be desired, three inches per 100 feet or 

 one-half inch to the rod is regarded as ample for tile 

 drains. The increase of the size of the drain as the 

 #rade is diminished is a principle that should be kept 

 in mind in laying out work, since grades must be largely 

 controlled by the natural slope of the land. 



It is not intended here to convey the idea that 

 drains can not be laid by guess by observing the flow of 

 water or by the hand level, nor that apparently good 

 work has not been done in this way; but numberless 

 mistakes, involving great waste of labor, and failures in 

 the attainment of the best results from the work, em- 

 puhasize the wisdom of securing the best possible pre- 

 liminary plans as well as their intelligent execution. 



SIZE OF TILES TO BE USED. 



. The proper size of tiles to be used in the con- 

 struction of drains is a matter upon which there is 

 great difference of opinion, and accordingly of practice. 

 It is doubtful if there is any part of the work requir- 

 ing more careful consideration than this. Much differ- 

 ence of opinion on this subject arises from the fact that 

 various soils respond differently to drainage work. 



There are several questions to be considered in de- 

 termining the size of tiles that should be used, espe- 

 cially for mains to a drainage system : 



(1) What depth of water per acre will it be neces- 

 sary to remove from the land in a given time, say 

 twenty-four hours, in order to secure the desired condi- 

 tion of the soil? 



(2) How rapidly will the water be brought to the 

 main drains i 



(3) What surface drainage does the tract have 

 that will be available for carrying unusual rains? 



(4) What is the nature of the soil as regards its 

 drainage properties that is, is it open or retentive ? 



(5) What are the grades upon which the drains 

 must be laid? 



As to the first question, it may be answered that 

 there are times during the growing season when the 

 entire ordinary rainfall will be taken up by the soil. 

 At other times, when the rains are frequent and heavy 

 and the soil becomes filled with water, it may be neces- 

 sary to remove a large part of what falls in twenty-four 

 hours. There are times when the rainfall is so heavy 

 that the water can not pass through the soil fast 

 enough, even if the drains are sufficiently large to carry 

 it off, but a part must run off the surface, by its vari- 

 ous depressions and channels, and these it is always 

 wise to provide. 



The total rainfall varies in the different States 

 and sections quite materially. Drainage, however, has 

 to deal with the extremes of rainfall rather than with 

 the mean, when the size and efficiency of drains are con- 

 sidered, although it is generally true that the sections 

 having the larger arinual rainfall are subject to heavier 

 storms. There are so many unforeseen conditions to be 

 met with that to treat the problems in an analytical 

 way in this connection will not contribute to any clearer 

 understanding of the best practice now followed. 

 Laboratory experiments made for determining the rela- 

 tion of rainfall to drainage are often so different from 

 field conditions that they aid us but little in practical 

 drainage problems. Deductions from the actual work- 

 ing of drains in lands of varied character and in dif- 

 ferent localities give us the most valuable data upon 

 this point, and these have been the guides used in the 

 following discussion. 



If the main drains have a capacity to remove one- 

 half inch in depth of water from the entire tract in 

 twenty-four hours, they afford what may be regarded 

 as good farm drainage, for, as ascertained_ by observa- 

 'tion, even one-fourth or one-third inch in that time is 

 the limit of capacity of many drainage systems in well- 

 improved alluvial soils. The soil is a great reservoir 

 and will hold from 25 to 40 per cent of its volume of 

 water. In localities where no advantage can be taken 

 of the surface flow for relief in times of heavy rain- 

 fall, mains may be used large enough to carry off one 

 inch of water in twenty-four hours. Ordinarily for 

 lateral drains no smaller than three-inch tile should be 

 used. 



(TO BE CONTINUED.) 



