408 peterson. PROBLEM OF GULLYING [Ch. 23 



or whether they occurred as discontinuous segments, each developed 

 individually with no relation with its neighbor, except for being aligned 

 along a common drainage course. Both types exist today, so it may 

 logically be presumed that they occurred previously. 



Although possibly the most destructive and certainly the most spec- 

 tacular in appearance, gullies represent only one phase of water erosion. 

 They may even be subordinate so far as silt removal from a given 

 locality is concerned, being surpassed in this respect by rilling or by 

 the much less prominent sheet erosion occurring on interfluviatile areas. 

 What constitutes their critical and insidious threat is the lowering 

 of the base level within the drainage system, which exposes to potential 

 removal all material within the basin above this level. A long gully 

 of narrow dimensions may represent the removal of only a few thou- 

 sand acre-feet of silt, but potentially it has set the stage for removal 

 of hundreds of thousands. 



That gullying is not confined to the arid and semi-arid West is 

 shown by its widespread evidence in other localities, but when con- 

 sideration is given to the problems involved in attempting to control 

 or ameliorate western gullies, complications of unique nature im- 

 mediately become apparent. As will be shown, the area affected by 

 gullying is of tremendous extent, but the value of the land on a per-acre 

 basis is extremely low, so low that treatment of only a minor nature 

 can be justified on the basis of land improvement alone. Despite the 

 low value, however, the lands are the major support of the western 

 livestock industry, and practically every acre is utilized for grazing 

 to the full limit of its forage production. Authority for such use is 

 established on the basis of either direct ownership or legally recognized 

 leases or permits. The vegetative cover that supports the livestock 

 also forms the major, if not the only, effective protection against ero- 

 sion. Sparse and erratically distributed precipitation in which droughts 

 of several years' duration alternate with flash floods of tremendous 

 eroding power is characteristic of almost the entire area. The problem 

 of maintaining a vegetative cover under these conditions is readily 

 envisioned. 



Further to complicate the problem, many of the remedial measures 

 applied thus far to a limited extent in an attempt to correct erosion 

 have been of very doubtful success, thus raising the pertinent question 

 whether our knowledge of the meteorologic, ecologic, hydrologic, and 

 geologic aspects of the problem is extensive enough to permit designing 

 a practical treatment program that will have a reasonable chance of 

 accomplishing the desired results. 



As an example of western gullies, one embodying the common history 



