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



DIVERSION OR RIVER GATES. 



As much depends on the diversion gate and it is close to the river, 

 whose performance is always more or less uncertain, it is recom- 

 mended that a substantial and, if possible, permanent structure be 

 built as soon as possible. Even where the general policy of the con- 

 structors is to hold the initial expenditures down to the lowest limit, 

 it has come to be recognized that a substantial river gate inspires a 

 feeling of confidence in the system. As long as the control remains at 

 the river the canal below the diversion gate is not subject to ruin from 

 floods. Local storms may injure portions of the banks, but should 

 the river gate fail there is not much limit to the damage that can 

 result through the lack of this control. The trouble from the Colo- 

 rado River in the Imperial Valley during the years prior to 1907 was 

 caused by this lack of control at the river. 



LOCATION OF THE GATE. 



Most diversion gates are located in one of the four following 

 topographic situations : 



(1) At the point where the center line of the excavated canal 

 intersects the river bank; (2) out in the main river channel, with a 

 built-up canal bed between the gate and upper end of the true exca- 

 vated canal; (3) some distance down the canal from the point where 

 the latter leaves the stream, with open channel between the stream 

 water and the gate ; (4) at the upper end of the canal where it in- 

 tersects the bank of a secondary channel of the stream. 



Variations in local conditions surrounding the sites of such gates 

 preclude the adoption of any plans as standard, but some of the sug- 

 gestions in the plans shown will be of benefit in the designing of 

 gates under conditions which approximate those of the gate shown. 



Headgate at the bank of a stream. — If the conditions of topog- 

 raphy, anchorage, and stream flow permit, it is customary to install 

 the diversion gate at the true excavated head of the canal. As a rule, 

 this should be at a point where the main current of the river, espe- 

 cially at low-water stages, will sweep past the gate openings and 

 carry much of the silt not in suspension on down the stream. This 

 is partially effected by means of sand sluices adjoining the canal open- 

 ings, but the results with gates built on this principle show that the 

 designer should not expect to rid the canal of all sand at this point. 

 There are too many whirls and eddies to insure all the sand being on 

 the bottom of the stream, and for this reason some of it will enter 

 the canal. 



Gates placed at the original line of the river bank are not, as a rule, 

 subject to the full force of the current during high water. Neverthe- 

 less, the general factor of safety should be much higher than for 

 other structures farther down in the canals of the system. The great- 



