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I( II II II II - - ~, ~ - - - - - , , , ~ - Recently abandoned channels show relict bends similar to those seen today. These channels are as yet unfilled by sediment and can be seen on topographic maps and aerial photographs literally from valley wall to valley wall. It appears, therefore, that in a time frame of a few hundred years extending to the present, the Dolores is prone to move rather rapidly back and forth. We can expect this habit to continue. Several relict channels have amplitudes of about 600 feet and that size of meander-cutting into the land also can be expected to continue. A new bend along Akin Ranch has cut 250 feet in the past 15 years. People look upon this land and upon the gravel ponds and believe they are permanent. But in truth this is all amazingly ephemeral. It is difficult for non-geologists to grasp this truth-and so far they have not. FLOODING FACTS: The Upper Dolores River is located on the southwestern edge of the San Juan Mountains, and it catches great snowfalls in winter and rainstorms in summer enlarged by orographic effects, It is especially vulnerable to moonsoon rains coming up from storms in the Gulf of Mexico. The Bureau of Reclamation says the Upper Dolores drainage basin is 809 square miles; the U,S.G.S. stream data gathered near the town says the drainage area is 504 square miles. No attempt has been made by us to rectify these figures. Dr. James B. Johnson in his guest editorial for the Cortez Journal wrote, "Expect large floods." On October 5, 1911, the U.S.G.S. stream gauge recorded a pealdlow ofIO,OOO cfs. Given the depth of the river's channel through town, this flood must have put the river 4 feet above its banks; it flooded almost all of the town. Though the Army Corps of Engineers has no records dating back that far, oldtimers say the Corps came in after this flood and moved the whole river channel out of its accustomed position near downtown, ' over against the south wall of the valley. It is still there today and has been rip-rapped and leveed as it approaches McPhee Reservoir. Dr. Robert W: Blair noted that the Animas River at Durango also recorded its greatest-ever flood on October 5, ,1911, He believes a hurricane in the Gulf of Mexico was. the source of both floods. But according to Blair the event in Delores was oUly a 90-year flood. ' To assess flood frequency along 10 miles of river upstream from town, the following method was used: A resident, Pat Blackmer, 6 miles upstream, observed water running under severa! houses when the U.S.G.S. gauge in Dolores registered 5,300 cfs. If the river flooded upstream at this volume, it would have flooded upstream at all higher recorded peak volumes. This reasoning is reliable because along this entire 10-mile stretch, the river maintains a similar distance everywhere between water level and floodplain level. Also, there are minimal tributaries to the river along this 10 miles. Italian drainage comes from the north rim of valley wall but barely maintains enough flow to create wetlands. Other small drainages off the south wall are limited by the fact that the surface for 20 miles up there dips away from the river, so most run-off travels away from the river, not toward it. By the above line of reasoning, Dr. Blair counted 16 floods since the one of 1911. Eight floods' of greater than 6,000 cfs he termed large floods, and three floods of greater than 8,000 cfs he tenned very large floods, which he said could reconfigure the Dolores channel-that is have the power to move the entire channel to a new position,