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-23 ,~ area. Hydrologic degradation would include both temporary and long- term obstruction of the flood plain by debris that would, in the nor- mal course of events, be deposited mostly in areas above the Crystal River flood plain. Unfavorable side effects would include occasional damming, and a general condition of backwater upstream from the dis- charge point during flood flows of the Crystal River. Direct discharge of the mudf10w debris in or near the river would greatly, increase the sediment supply which could be expected to affect game fish, and the general stream aesthetics in the downstream direction. If such a solu- tion is proposed, it would almost certainly require approval from the U.S. Forest Service, Colorado Division of Game, Fish and Parks, Colo- rado Water Pollution Control Commission, and other interested agencies. Debris Dams as Possible Solution An alternative solution would consist of somewhat similar channel- ization of Slate Creek, but with addition of debris dams or catchment basins which would be designed to intercept and hold a large part of the flood debris within retaining structures adjacent to the channel. There are several complications with such a possible solution which has been tested in parts of California and the Wasatch Front area of Utah. The mudf10w events (not ordinary flood waters) are the basic problem, and the solid matter ("sediment") content of these probably constitutes 70 to 75% of the mass, and nearly all of the volume. The "sediment" volume is, therefore, roughly equal to the total flow of a mud flood event. Although we have made no estimate of sediment production in the Slate Creek drainage basin, it must be extremely high judging from the rapid backwasting of Gallo Bluff and the sizeable and frequent debris sheets deposited in the lower reaches of Slate Creek.