Ch. 23] CORRECTIVE TREATMENT FOR GULLIES 427 



ment or in reducing runoff crests to any appreciable extent. Old gullies 

 and erosion scars have not healed, and in many instances new ones 

 have developed. 



It is obvious from these results that in the more arid areas, like that 

 represented by the Upper Gila Basin, this type of treatment is of little 

 value. The reasons for this are not so obvious, but apparently the 

 flashy type of runoff produced by the higher intensity summer storms 

 characteristic of this locality is greater than these small-dimensioned 

 structures can cope with. Lack of vegetative recovery may be at- 

 tributed to drought and erratic distribution of rainfall together with 

 continuous grazing. Effect of the latter factor is hard to determine, but 

 the fact that herds were not reduced to any appreciable extent re- 

 flects the lack of confidence of the stock grower in the success of this 

 type of program. A more successful demonstration is needed before 

 this confidence can be restored. 



Recently the practice of water spreading has been greatly expanded, 

 and in some instances it has been used on major gullies. Success of 

 this treatment depends on complete diversion of flood flows onto a 

 spreading area sufficiently large to absorb all the water, because, if any 

 is allowed to return to the channel, new cutting immediately starts 

 at the bank. One of the most successful installations of this type has 

 been on the deep Polacca gully in the Hopi Reservation, Arizona, where 

 water has been spread a distance of 15 miles below the point of diver- 

 sion. Sand dunes, distributed along the bank, act as a natural barrier 

 to prevent water from returning to the channel for part of the distance ; 

 training dikes parallel with and close to the channel have been con- 

 structed for the same purpose along the remaining part. Similarly 

 treated areas located upstream on the Polacca Wash and in the tribu- 

 tary Wepo Wash utilize a system of dikes strategically placed so as 

 to direct the water away from the channel at needed intervals. Other 

 water-spreading areas using the same system are located in parts of 

 the Tularosa Valley in New Mexico and in the Alzada district in the 

 Little Missouri River basin in Montana. 



Although the projects have not yet been in operation long enough 

 to permit decisive evaluation, results to date appear to be promising 

 particularly from the standpoint of range rehabilitation. Increase in 

 forage as a result of water spreading has been of the order of several 

 hundred percent in some reported instances — enough to justify con- 

 siderable expenditures for such treatment. 



The final effect this treatment will have on the gully has yet to be 

 demonstrated. Naturally, erosion in the channel downstream from 

 the point of diversion is stopped, but, since the supply of sediment is 



