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Show PART III CURRENT WATERSHED CONDITIONS AND PROBLEMS, AND EFFECTS OF PROBLEMS 1. Erosion as a result of overgrazing and related land abuse. 2. Erosion as a result of climatic variations. 3. Erosion as a result of infrequent intense storms. 4. Erosion as a result of an upset of balance among natural forces. This appendix is generally based on this theory which states that valley trenching and related forms of erosion should not be attributed to a single cause, but rather may result from any upset in the natural balance among the various environmental factors within a drainage basin. This explains many of the apparent conflicting opinions by suggesting that pre-settlement periods of erosion were initiated largely by cli- matic vagaries or shifts, whereas the present period of erosion was brought on largely by land misuse. Floods probably have always played an important role in local erosional patterns. Whatever the cause, however, this type of erosion, once started, appears to be a natural sequential process that typically occurs in arid and semiarid environ- ments the world over. Experience indicates that the erosion phase in a given area may be greatly prolonged by continued land misuse, or may be significantly shortened by devising effective erosion-control measures. The question is what constitutes "effective" erosion-control measures? Various treat- ments have been tried on arid and semiarid lands in the past with some success, but no treatment or combination of treatments has been devised that has successfully restored the lost environment in a trenched valley. A final solution to the erosion problem must provide a practical means of preventing valleys such as these from trenching and for restoring those trenched valleys. Erosion on forest and rangeland General Approximately 29,119,000 acres of forest and rangeland within the region are affected by erosion. Approximately 47 percent of the affected acreage is in the Green River Subregion, 37 percent in the San Juan- Colorado Subregion, and the remaining 16 percent is in the Upper Main Stem Subregion. |