DEAIlsTAGE OF lERIGATED LAND. 9 



little maintenance. There is little danger of irrigation water getting 

 into the drains, and the only way in which vegetation may do damage 

 is by the entrance of water roots from certain trees and plants. This 

 trouble may be avoided by keeping such trees as willows, cotton- 

 woods, tamaracks, etc., well away from the drain Hnes, and by cutting 

 away a narrow swath of such plants as the sugar beet from directly 

 over the tile line. Black willows will send out roots to a distance of 

 200 feet and choke a drain, while sugar beets planted directly over a 

 line will reach and obstruct a drain 5 feet deep. These roots penetrate 

 only the disturbed soil of the trench, however, so it is necessary to 

 remove but a narrow swath. 



In deciding whether a large covered drain or an open canal shall 

 be employed, it is necessary to calculate the original cost of each, 

 taking account of all auxihary and protective devices required, and 

 then to add to each sum an amount large enough to give an annual 

 return, at current rates, sufficient to cover the cost of maintenance. 

 The consideration of the first cost alone gives very misleading results, 

 as it has often been found that the difference in the cost of a very 

 few years' maintenance would have more than paid the difference in 

 first cost between the two types of drains. Thus, if a covered drain- 

 age system costs SI per foot to construct, and the annual mainte- 

 nance is 1 per cent of the first cost, 20 cents per foot must be added 

 to yield an annual income of 1 cent per foot at 5 per cent interest, 

 which makes the total cost $1.20 per foot. An open drain having 

 the same capacity will cost about 30 cents per foot for excavation, 

 25 cents per foot for right of way, and 10 cents per foot for inlets, 

 flumes, bridges, culverts, fences, etc. If the annual maintenance be 

 taken at 10 per cent of the excavation cost, which is reasonable, 

 60 cents per foot must be added to yield an income of 3 cents per 

 foot at 5 per cent, which gives a total of $1.25 per foot. The covered 

 drain is to be preferred, therefore, even from the standpoint of actual 

 cost ; and when the other factors are considered there is no room for 

 comparison between the two types. 



Practice in the humid section is leaning more and more toward the 

 covered drain, and tile having an inside diameter of 3 feet are not 

 uncommon, while still larger sizes are sometimes employed. Until 

 quite recently, very little tile over 12 inches in diameter had been 

 used in the arid section. However, conservative estimates based on 

 pres^mt prices and conditions show that it would }>e economical to 

 u.se 20-incli tile, rather than the open canal of the same capacity; 

 whil(! improvement of methods, increase of land and crop values, 

 and the decrease in the cost of niat(Tials that are now being wit- 

 nessed, nuikf! it seem reasonable to pndict that yory shortly the 

 eastern standards of practice will be adopted. 



7773.3°— Jiull. 190—16 2 



