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`' RIVER IN YOUR BACKYARD Marilyn Boynton Since March 2001 I have gathered information about the Upper Dolores River and have grappled with how new gravel pits along the floodplain may impact people. It has been a pleasure learning facts and insights. These should be passed along to decision makers and to citizens, especially to those living in the floodplain. United States Geological Survey has collected flow data since 1898 at their river guage in Dolores. The river has flooded 17 times. Every year, spring run-off crests around the last days of May, but the greatest flood danger is from summer monsoon rains when hurricanes hit the Gulf of Mexico. It was in Water Year 1912, actually October 5, 1911, that the largest flood was recorded, 10,000 cfs, a 90-year flood. One 97-year-old lady said this flood crest was augmented because a debris jam burst in Bums Canyon, up in Rico. By my calculations, water must have been 4 feet above banks through Dolores then. In the geologic record upstream from town, however, there is evidence of floods 3 to 5 times larger than that of 1911. This is shown by the size of boulders in the river and by truncated contours where tributaries enter the Dolores. Just like people, rivers have distinct personalities. That of the Dolores is to spend long periods alternating between straight channel reaches and those with lazge, low-amplitude meanders. Suddenly a big flood will come, and discharge will surge so rapidly that the entire channel will shift perhaps 100 feet. In that new position, it will return to the old habit of creating straight and gently bending channel pattenrs. Both topographic maps and aerial photos reveal floodplains covered in remnant, abandoned channel ghosts. Those shapes several thousand years old have tighter-circling meanders than we see today. But for yeazs numbering in the hundreds, low-amplitude relict bends appear much like those at present. One such abandoned curve lies along the Line Camp field next to the river. Another forms the crescent-shaped pond on Jack Akin's ranch. Another was used as a pond on land downriver now owned by John Sutherland. The Dolores maintains equilibrium of its gradient by changing gradually back and forth between periods of straight channel and periods of slight meanders-all applied as pulses of gravel bedload move downstream. When bedload increases, the stretch of river through which it moves steepens its gradient by straightening. When that pulse of gravel is past, the channel gradually creates new bends, reducing gradient. Thus it is that bedload itself determines channel shape in this river. Steepness gives water- power. Today between Rico and Dolores, the river drops 32 feet per mile, three times steeper than the Colorado River through Grand Junction, which drops 10.2 feet per mile. The Dolores River carries a bedload of cobbles and boulders; the Colorado carries much more sand. Because of the high gradient and a large drainage basin positioned to catch snow from the northwest and rain from the south, the Dolores River certainly is prone