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South Boulder Creek is a major tributary to Boulder Creek. This stream runs a parallel course to Boulder Creek through the mountains and emerges at Eldorado Springs. South Boulder Creek then turns north and joins Boulder Creek approximately 2 miles east of Boulder. . . . The Bear Canyon, Skunk, Twomile, and Fourmile Canyon Creek basins originate in the foothills west of the City of Boulder. The terrain of these upstream subbasins is steep and rocky, and consists of topsoils in the C and D hydrologic soils group, as classified by the SCS, The entire reaches of Bear Canyon, Skunk, Fourmile Canyon, and Eimers Twomile Creeks consist of well-defined channels. Wonderland Creek has a well-defined channel, except for the reach southeast of Valmont Road. Both Twomi Ie and Goose Creeks have extensive reaches without well-defined channels. The Lefthand Creek watershed extenrls about 3D miles eastward from its headwaters in the Roosevelt National Forest to its confluence with Saint Vrain Creek at Longmont. Most of the watershed lies in the mountains and varies in elevation from 5,600 to 11,000 feet. The remainder of the watershed lies in the high plains. The St. Vrain Creek is a continuous-flowing stream that drains the east slope of the Continental Divide by way of North and South St. Vrain Creeks. From the confluence of these creeks at Lyons, Colorado, St. Vrain Creek flows southeasterly through Longmont, then northeasterly to the South Platte River. Lefthand Creek, Dry Creek No. I and Spring Gulch join the St. Vrain Creek within Longmont. " Leflhand Creek passes within 5 miles of Boulder's northern corporate limits and extends through the expanding suburbs of Longmont. Until recently, the floodplain was devoted entirely to agriculture. Now, because of expanding population and industrialization, urban development has begun at both ends and in the middle of the study reach. The City Park Channel, Nissen Reservoir, Gay Reservoir, and the West Lake Reservoir drain a total area of approximately 8.4 square miles in the vicinity of Broomfield, Colorado, and are bounded on the northeast by a rise at an elevation of approximately 5,400 feet. The streams generally flow southeasterly, emptying into Big Dry Creek at an approximate elevation of 5,200 feet. The drainage boundaries of the individual basins are indistinct, being located at the crests of the east-west rolls of the high plains. The creeks are generally shallow, with no distinct channels. The climate of the study area is classified as semiarid. The average annual preClpltation is 18.3 inches, which includes an average annual snowfall of 83 inches (Reference 2). Location with respect to the foothills west of Boulder has a slight influence on the total precipitation depths in the study-area subbasins. Those 4