44 BULLETIN 652, U. S. DEPARTMENT OF AGRICULTURE. 



reclaimed the interior canals were too small and too shallow either to carry 

 the water rapidly to the pumping plant or to store up water for pumping. As a 

 result it was necessary to operate the pumping plant for a few hours almost 

 every day, and at times of heavy rainfall the portions of the canals remote 

 from the pumping plant were too full of water to give outlet to the ditches. 

 These canals ultimately were made wider and deeper. 



Since' the land is flat, flow in the canals can result only from a piling up of 

 water in one portion or from the lowering of the water by the action of the 

 pumps. If the canals are small, the velocity of the water in them must 

 be high in order to bring water to the pumps ; this will mean a large surface 

 slope and a large difference in the elevation as between the water surface at 

 the pumps and that in the remote portions of the district. Although immedi- 

 ately after very heavy precipitation the water may safely stand level with the 

 lowest land for several hours, the canals should be of such cross section that 

 they will be able to deliver enough water to allow the pumps to be operated 

 when the water stands at least 4 feet below the surface of the land. The 

 surface slope of the water in a canal of this size necessarily will be small; it 

 should be between 0.2 and 0.4 feet per mile. The minimum depth for such 

 canals is 7 feet, and the depth should increase gradually toward the pumping 

 plant so that the bottom shall have a slope at least as great as that of the 

 water surface. This will allow a depth of 1 or 2 feet of water to be main- 

 tained in the canals at all times, which is sufficient to discourage the growth 

 of weeds and grass. Experience on such reclamation districts has shown that 

 shallow canals become choked with weeds and grass very quickly and require 

 frequent cleaning. 



Reservoir canals have been excavated with a number of types of dredge. 

 Owing to the soft nature of the land a floating dredge is always required. 

 Where there is considerable standing timber and sunken logs and stumps, a 

 dipper dredge is the best machine for cutting the canals — at least for taking 

 out the top 4 or 5 feet. It has been found best to cut the canals in two layers, 

 allowing the banks and the material excavated the first time over to solidify 

 before placing an additional load on them. 



Where the prairie is free from stumps, or where the stumps have been taken 

 out of the way with a clipper dredge, a long-boom, gravity-swing, orange-peel 

 bucket dredge is a very satisfactory means of cutting such canals. This dis- 

 turbs the material much less than does a dipper dredge, and the canal cut with 

 the orange-peel bucket will be much freer of soft mud than one cut with the 

 dipper dredge. In any case, such dredges should be equipped with vertical 

 spuds instead of bank spuds, which have caused serious caving on all canals 

 whore they have been used in the soft prairie land. The berms between the 

 side of the canal and the spoil bank should be at least 10 feet and preferably 15. 



The hydraulic dredge is perhaps the most satisfactory means of cutting 

 interior canals. The top 4 feet might first be taken off with a dipper dredge, 

 thus forming low retaining walls to keep the material placed by the hydraulic 

 dredge from running back into the canal. Such canals will be free from soft 

 mud, and the side slopes can readily be controlled. While the side slopes of 

 the canals are limited more or less by the character of the excavating ma- 

 chinery, if operated with care a dipper dredge can easily give a slope of \ to 1 

 on the canals: If the material is placed well back from the banks this slope 

 has been found to be satisfactory. The excavating of such canals has been 

 done by dredges owned by the district at a cost per cubic yard of from 3 to 5 

 cents. The work has frequently been contracted for at from 6 to 8 cents. 



