Ch. 23] CORRECTIVE TREATMENT FOR GULLIES 431 



tection, others in association with tetrahedrons or other types of revet- 

 ments. Figure 7 shows views of this treatment. 



Although plantings offer certainly the cheapest and most promising 

 field for this type of treatment, their use is limited to reaches where 

 water is available for plant growth. This condition automatically ex- 

 cludes the vast majority of gullies from treatment of this sort, because 

 most are cut in dry valley floors where the surface flow is too infre- 

 quent or ground water is too deep to support vegetation. Protection 

 of banks in this type of gully remains for future solution. 



A permanent solution of the overall problem presented by gullying 

 in the western valleys can be achieved only where the gullies have been 

 refilled and the valley floors restored to a condition approaching that 

 existing before cutting occurred. This involves substituting aggrada- 

 tion for degradation within the channels themselves. In theory, as 

 shown by Lobeck (1939, p. 168), the construction of a barrier to the 

 height of the gully wall or slightly above should accomplish this, and, 

 given time enough, perhaps it will. However, the results observed at 

 numerous barriers, some of which have been installed for more than 20 

 years, furnish little promise for results within the foreseeable future. 



Surveys conducted by the Soil Conservation Service * and the Geo- 

 logical Survey f to determine the gradient assumed by the fill above 

 these barriers show a minimum of 0.07 percent or 3.7 feet per mile and 

 a maximum of 0.76 percent or 40 feet per mile. These results apply to 

 localities where the fill was composed of sand and silt only. In every 

 case the gradient was less than 50 percent of the slope of the valley 

 floor. Textural analyses of the sediments constituting the deposits 

 failed to furnish any information about the disparity in the fill 

 gradients, although, as might be expected, coarser sediments were gen- 

 erally associated with the steeper slopes. 



Numerous observations indicate that vegetation forms one of the 

 most effective traps for sediment, and, where it is dense enough, even 

 fine-textured sediments will deposit on the floors of gullies. This action 

 is demonstrated in the Chinle and Keams Canyon washes, previously 

 mentioned, where as much as several feet of sediment has been de- 

 posited within the fringe of trees and willows planted primarily for 

 bank protection. Gradual filling of numerous gullies tributary to the 

 Powder River near Broadus, Montana, has been noted during the past 

 few years of favorable precipitation, during which dense growths of 



* G. A. Kaetz and L. R. Rich. Report of surveys to determine grades of depo- 

 sition above silt and gravel barriers, U. S. Soil Conservation Service manuscript, 

 1939. 



t Information in U. S. Geological Survey file in Salt Lake City, Utah. 



