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II" , 1\ I, ~ ~ ~ ~ ~ ~ ~ ~ ,~ ~ ~ ~ , , , , GRAVEL PITS IMPACT FLOODING ALONG UPPER DOLORES RIVER, MONTEZUMA COUNTY, COLORADO This report presents inforniation gathered over many weeks about the nature of the Dolores River, the siting of numerous gravel pits upriver from Dolores town, and the potential for catastrophic impact upon people living along the river and in the town. Facts will be related to their sources, and opinions will rely upon affidavits from fluvial experts, geologist James B. Johnson, Ph.D., of Mesa State College, and geologist Robert W. Blair, Ph.D., of Ft Lewis College, and also upon my field work with them and conversations. 1 do not claim to be a professional geologist but have spent years in minerals research and have completed all coursework for a degree in geology. I am the expert repository of information related to river and gravel pit interactions and that is why it is I writing this report. CONCLUSIONS: A short conclusion to studies by Johnson, Blair, and myself to date (June 2001) is that we see definite threat to lives and property caused by continuing to site gravel pits close together along the floodplain of the Upper Dolores River. This threat goes beyond the sort of overbank flooding that people normally accept when building close to a flood-prone river. Our work reveals that virtually everyone living in the Dolores River Valley could be hit by the entire channel of the river. If a string of reclaimed gravel ponds captures the river, there is no way to certify where the river might then flow. With 28 ponds in a five-mile stretch upriver from the town, the Dolores River soon will have several man-made pathways to shift its channel and send powerful flows upon citizens. Much of the town of Dolores could be wiped out. RIVER TYPE: The Upper Dolores River above McPhee Reservoir is a high-gradient, gravelbed river with relatively straight channel sections that alternate with low-radius-of- ' curvature bends and one or two nearly right-angle turns. It moves tons of cobbles and boulders with ease. Latest research by fluvial geomorphologists indicates that channel shape and gradient of rivers depend upon discharge and bedload. A river with heavy , , bedload such as the Dolores keeps its gradient steep to produce streampower. The Upper Dolores between Rico and Dolores drops 54 feet per mile compared, for example, to the Colorado River through Grand Junction dropping only 10.2 feet per mile and carrying much more sand. Average bedload over millennia maintains the average gradient. Pulses of bedload moving downriver, however, cause changes in channel pattern to fine- tune the gradient to what is carried short-term. When a pulse of gravel enters a reach of channel, the channel gradually straightens to increase gradient. When that pulse has passed through, the channel will create bends to reduce gradient. A very large plug of gravel currently occupies the channel just below the Line Camp Pit along Akin Ranch. In this section the river in 1983 used a 6,000-cfs flood event to shift ovemight 100 feet; it is braiding through that section-an even more efficient means of moving bedload.