80 



THE IRRIGATION AGE. 



A CORRECTLY PROPORTIONED DITCH. 



The Requisites in a Ditch to Form a Permanent Water- 

 way. 



Land reclamation, whether it be the removal of 

 hydrostatical, or excess, water from the soil in humid 

 climates or conveying water to the land in arid regions, 

 involves primarily the construction of ditches or canals. 

 In lands too wet for cultivation, even when reclaimed 

 by an underdrainage system, the outlet is nearly always 

 by means of an open ditch and since means for the re- 

 moval of the water from the end of the drain must be 

 provided before laying the tile, the first consideration 

 is the outlet ditch. In irrigated districts ditches are 

 not only required to deliver the water to the land, but, 

 experience has proved, they are also necessary to remove 

 the surplus water else the productiveness of the soil is 

 quickly dstroyed by the accumulation of alkali. What 

 constitutes a perfect ditch, therefore, ought to be of 

 special interest to every one interested in land tillage. 



The velocity of water flowing in an open ditch 



gives the following table of mean velocity of water at 

 different depths in a rectangular ditch 10 feet wide 

 with a grade of 3 feet to the mile. 



Mean Velocity in 



Depth in Feet. Feet per Second. 



0.5 1.4 



1.5 2.3 



2.0 . 2.6 



2.5 2.8 



3.0 2.9 



4.0 3.2 



5.0 3.4 



6.0 3.6 



8.0 3.8 



While the above table shows the more rapid flow 

 of deep ditches, it is manifestly not the proper shape 

 for a drainage ditch for several reasons. It is desirable 

 in a ditch for drainage purposes that the current shall 

 scour the bottom sufficiently to prevent the accumula- 

 tion of silt. When flowing only 6 inches deep and 10 

 feet wide it is obvious that the friction of the large 

 surface over which the water is spread will so retard 

 the flow that all silt will be deposited on the bottom and 



Fractional Map of Wisconsin. * Indicates Location of Shiocton Garden 

 Land Company's Property. 



depends upon the grade, the depth of the stream and 

 the character of the banks and bottom. Drainage en- 

 gineers recommend that a ditch be of sufficient size 

 that it will flow only four-fifths full at flood height. 

 If the flow were constant a rectangular shaped ditch 

 would have greatest capacity, but since the quantity of 

 water carried by all drainage ditches is variable and 

 nothing but solid rock will stand when the banks are 

 vertical, a perfectly shaped drainage ditch is one whose 

 bottom has the shape of the arc of a circle and with 

 banks sloped to an angle which enable them to withstand 

 the action of the elements. In fine clay soils this is 

 usually 1 to 1. In loose, loamy or sandy soils slopes of 

 1% to 1 or 2 to 1 are usually required. 



In engineering for land drainage, Mr. C. G. Elliott 



rapidly fill the ditch. It is also evident that where a 

 ditch is made with vertical sides the banks are certain 

 to cave through the action of frost and erosion, not 

 only obstructing the waterway, but through deflection 

 of the current from side to side the distance the stream 

 must flow is increased and as a consequence diminishes 

 the grade. It is also well known that once an irregular 

 channel is formed, the tendency of flowing water is to 

 increase the deflected movement undermining the banks 

 and adding to the quantity of silt in the stream. 



.In laying out a drainage ditch, therefore, the first 

 consideration should be that the banks are sloped to an 

 angle that will enable them to withstand the action of 

 the elements and the ditch should be as deep as prac- 

 tical with the available outlet. When the grade is 



