30 BULLETIN 71, U. S. DEPARTMENT OF AGRICULTURE. 



seepage occurred. At ordinary stages of water the levee is hard and dry, al- 

 though the base always is submerged. However, the condition of the levee was 

 so unsatisfactory that during the latter months of 1911 a new reservoir canal 

 was cut parallel to and about 40 feet distant from the old one, and the old 

 canal was filled and considerable material deposited along the inside slope of 

 the levee. This improvement should greatly reduce the seepage. 

 • Experience on this tract seems to show that it is not good practice to place 

 the reservoir canal immediately inside of the levee, especially if the base of the 

 latter be below ordinary water level. Figure 7 shows cross sections of these 

 levees, the stages of water in the canals, and the curve of the ground water 

 through the levees at various times. It is apparent that there is considerable 

 advantage in allowing a liberal cross section for such levees. 



Reservoir Canals. 



As this tract has a slope from front to rear of nearly 4 feet, the location of 

 the reservoir at the lowest end of it was perhaps the best that could have been 

 made to act as an outlet to the laterals. Originally it was about 35 feet wide 

 and 5 feet deep. The storage capacity at this time was about 0.35 inch of water 

 over an area of 647 acres. During the growing season of 1909 and the winter 

 of 1910 it became partially filled with silt. In the spring of 1910 a 6-inch 

 hydraulic dredge was employed to pump out this silt. The dredge did not work 

 satisfactorily, but finally succeeded in taking out sufficient material to give the 

 reservoir its former capacity. However, with a pumping capacity of about 1.1 

 inches in depth over the whole area in 24 hours the cross section of the canal 

 was not large enough. After the water was lowered at the pump to the bottom 

 of the canal it was still about 2 feet deep at the farthest part of the canal, a 

 distance of 1.3 miles. It was then necessary to shut down the pump for per- 

 haps 5 hours, after which an additional run of about 2 hours would take the 

 water that had collected during the interval. 



As above mentioned, this canal was reexcavated in 1911, and now has a depth 

 of 8 feet and a width of 40 feet. The capacity is 0.45 inch in depth of water 

 over the entire area. Even before the reservoir was reexcavated the combined 

 capacity of the pumping plant and reservoir was sufficient to keep the land 

 from flooding except for a few hours at times of extreme storm. With the larger 

 canal the pumping plant is operated continuously until practically all of the 

 water is removed. 



Ditches. 



Due to the fall of about 4 feet to the mile in the surface of this tract it was 

 considered feasible to extend the lateral ditches the full length, 1 mile. The 

 ditches are of about the usual cross section — i. e.. top width 4 feet, bottom width 

 1.5 feet, and depth 3 feet. They are spaced uniformly 160 feet apart. This 

 seems to be a satisfactory arrangement, as the ditches have always given good 

 drainage and have never been flooded for any great length of time. A length 

 of 1 mile does not appear to be too great for ditches of this cross section and 

 fall. In this case each of these ditches is draining about 25 acres of land, or 

 carrying off 1.5 cubic feet per second on a basis of 1.5 inches run-off per 24 

 hours. 



The cost of maintenance on these ditches is no small item. It is necessary 

 to cut the weeds out of them at least twice each year and it is sometimes done 

 three times. Once in two years it is necessary to take out about 1 cubic foot 

 of material per linear foot. On this basis the annual cost of maintenance is 



