54 BULLETIN 115, U. S. DEPARTMENT OF AGRICULTURE. 



It amounts to a lined section of canal with a shallow cut-off wall at 

 each end and a delivery tube through the bank, regulated by a sheet- 

 iron gate. Debris is kept out of the delivery by a screen extending 

 across the recess in which the gate is set. For most systems this 

 screening would not be necessary. If the water in a lateral using 

 this type of structure is to be checked up more than 2 feet above the 

 bottom it would be well to extend the lined section farther down the 

 channel and carry the lower cut-off deeper into the bed of the ditch. 

 This depth will be determined in all cases by the material of the bed. 

 In adopting this plan a cheaper installation is made by omitting 

 the recess for the gate shutter, allowing both banks of the lined sec- 

 tion to slope uniformly to the bottom of the ditch. The gate shutter 

 can be set on this slope, using the connections and gates as made by 

 the manufacturers for a connection with a tube at 45° or 60° with the 

 gate standards. 



SAND GATES. 



Some designers attempt to exclude the sand before it enters the 

 canal by installing a sluice gate with a sill below the intake of the 

 canal, adjoining the river gates on the downstream side, but as a rule 

 the water is so agitated at the heading that only the heavier sand 

 remains on the bottom and the lighter particles, whirling about in 

 the water, are passed on through the gate to settle in the canal at 

 some point lower down where the velocity is reduced to such an 

 extent that the sand is no longer rolled along the bottom. 



It is probably much better to install a separate sand structure far 

 enough below the head of the canal so that the latter will have gained 

 enough elevation over the bed of the stream to obtain a good flushing 

 velocity, and scour out the sand deposit from time to time as water 

 is available. If the water rights on the stream are such that there are 

 other consumers on the stream below the sand gate entitled to water 

 at all times, then an arrangement may be effected so that a surplus 

 amount of water can be run and the sand gates left open throughout 

 the season, returning the surplus water to the stream. Kansas recog- 

 nizes this benefit by legislation in its favor. 



THE SUMP GATE. 



There are three general types of gates to remove the sand belosv the 

 headgate of a canal system. The first consists of a sump connected to 

 a discharge ditch or natural channel by gates located below the 

 normal grade of the canal. This construction makes a combination 

 sand and waste gate. Such a gate as this may be partly opened all 

 the time or it may be closed completely except when a flushing head 

 is available and then opened wide and all the water in the canal used 

 for a short period to wash out the sand which has accumulated. The 



