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...r< IN REPLY REFER TO: United States Department of the Interior BUREAU OF LAND MANAGEMENT Colorado State Office 2850 Youngfield Street Lakewood, Colorado 80215,7093 .~. www.co.blm.gov CO-932 7250 DEe 20 2002 Mr. Dan Merriman Colorado Water Conservation Board 1313 Sherman Street, Room 721 Denver, Colorado 80203 Dear Mr. Merriman: The Bureau of Land Management (BLM) is writing this letter to formally communicate its in stream flow recommendation for Cottonwood Creek, located in Water Division 5. . Location and Land Status. Cottonwood Creek is tributary to the Colorado River in Glenwood Canyon, approximately three miles southwest ofDotsero. The reach that was surveyed starts at the confluence with Slaughter Spring Gulch and terminates at the headgate of the Anderson Ditch. Of the 2.5 mile reach, approximately 40 percent is located on [ederallands. Biological Summary. Fishery surveys indicate that the stream environment is in stable condition, and supports a self-sustaining brook trout fishery. Spawning substrate, cover, and food availability are good for salmonids. However, the stream experiences occasional low flow events and pool habitat is very limited. This underscores the importance of protecting flows to maintain adequate depth and physical habitat where pools are not available. R2Cross Analysis. BLM collected one data set on the creek and the resulting recommendations were within the confidence interval for the R2Cross model. BLM's data analysis indicates that the following flows are required to protect the fishery and natural environment to a reasonable degree: 1.70 cubic feet per second is recommended for the high temperature period from April 1 to October 31. This recommendation is driven by the average velocity criteria, as expected in a stream with only a moderate gradient. Providing sufficient velocity is important for creating suitable spawning habitat, because much ofthe stream corridor is occupied by beaver ponds with slow-moving water and unsuitable spawning substrate. . 1.3 cubic feet per second is recommended for the low temperature period from November 1 to March 31. This recommendation is driven by the average depth criteria. This flow should maintain pools during the winter and allow passage between pools.