430 peterson. PROBLEM OF GULLYING [Ch. 23 



also cut off, no opportunity is afforded for the channel to fill except 

 from bank caving or from wind deposition. The reservoir behind the 

 diversion dam provides limited storage for sediment carried by the 

 stream, but once this is filled the problem of sediment disposal again 

 is met. As the very act of water spreading reduces the carrying 

 capacity of the stream, an alluvial fan immediately begins to form at 

 or near the diversion point. The tendency is for this fan to increase in 

 height until a new gradient on which the stream can carry its sediment 

 load is established. Unless a protective vegetative cover becomes 

 established, gullying is likely to develop on this higher gradient. Evi- 

 dence of this trend is already becoming apparent in some of the older 

 installations. 



One disadvantage in water spreading is the loss of water occasioned 

 by the spreading operation. Where supplies are ample for all needs, 

 the point has no significance, and the right to spread will probably 

 never be contested. On the other hand, however, should the practice 

 of spreading become widespread in the Colorado River Basin with its 

 limited supply, compared with existing and planned demands, it is 

 quite easy to visualize strong objections being raised from downstream 

 users. This precise situation developed on the Gila River in 1940, 

 where irrigators in the San Carlos District supplied from the San 

 Carlos Reservoir took the stand that the C.C.C. structures in the 

 Safford and Duncan valleys were interfering with and reducing the 

 normal runoff on the river. A special investigation authorized by the 

 National Resources Planning Board * showed that the supposed re- 

 ductions were more fancied than real, and thus not significant enough 

 to warrant action, but the attitude of irrigators, in this instance, is in- 

 dicative of the developing conflict for the use of water in western 

 streams, no matter for what purpose, and any gully treatment or other 

 type of conservation program must eventually, if not at present, give 

 it consideration. 



Efforts to prevent bank cutting and meandering in gullies has been 

 tried on a limited scale and with varying success in a number of 

 localities. Possibly greatest progress has been achieved in the Navajo 

 Indian Reservation, where several miles of the Chinle Wash and Keams 

 Canyon Wash gullies have been stabilized against widening under the 

 conditions of flow thus far experienced. The treatment consists es- 

 sentially of tree and willow plantings, some started without pro- 



* Upper Gila River Report by the Technical Committee, National Resources 

 Planning Board, Oct. 21, 1940, unpublished. 



