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<br />STREAM CHARACTERISTICS <br />Boulder Creek in the Boulder area is a fast-flowing stream that has a <br /> <br />slope of about 42 feet per mile at the upstream end of the study reach <br /> <br />and 18 feet per mile at the downstream end. It has a natural bed width <br />of approximately 30 feet and a top width of about 60 feet. The creek <br />bed is composed of sand, gravel, and boulders and meanders through a <br /> <br />flood plain which averages approximately 2,500 feet in width. <br /> <br />The channel of Boulder Creek upstream from Boulder Is generally well <br /> <br /> <br />armored and is not subject to severe erosion. Bank erosion is a serious <br /> <br /> <br />problem in Boulder, particularly along the left bank and the right bank <br />downstream from 24th Street where the banks are composed of alluvial and <br /> <br />fill soils. Shale bedrock outcroppings on the right bank upstream from <br /> <br />24th Street resist erosion. <br /> <br />I <br />I <br />I <br />I <br />I <br /> <br />earlier and result in improved water qual ity of Boulder Creek in and <br /> <br />downstream from Boulder. <br /> <br />The streamflow of Boulder Creek is partially regulated. Barker Reser- <br /> <br />voir located on Middle Boulder Creek about 12 miles upstream from <br />, <br />Boulder, is a privately developed power generation dam. Four thousand <br /> <br />acre-feet of its storage capacity of 11,500 acre-feet is used for water <br /> <br />supply for the City of Boulder. <br /> <br />Presently, there is no gross or obvious evidence of pollution in Boulder <br /> <br />Creek. It can be assumed that terrestrial and aquatic ecological condi- <br /> <br />tions are fairly stable, especially as contrasted with conditions in <br />similar small streams. Any major future physical or chemical distur- <br /> <br /> <br />bances would undoubtedly have the effect of altering the existing <br /> <br /> <br />ecological conditions including the fauna, flora, chemistry, and physics <br /> <br /> <br />of the stream. <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Boulder Creek is a perennial stream. Discharges vary widely throughout <br /> <br />the year. Streamflow recorded at the Oroclell gage on Boulder Creek <br /> <br />three miles west of Boulder has ranged from a low of 1 c.f.s. to a high <br /> <br /> <br />of 2,500 c.f.s. Prolonged high runoff occurs in late spring and early <br /> <br /> <br />summer as a result of snowmelt. During this period, streamflow often <br /> <br /> <br />exceeds 100 c.f.s. and sometimes 300 or 400 c.f.s. During the remainder <br /> <br />of the year, flows normally do not exceed 100 c.f.s. The average <br /> <br />discharge for the period of record is about 90 c.f.s. <br /> <br />Flood velocities in Boulder Creek are high. Average velocities in the <br />channel are about lO feet per second and point velocities may approach <br /> <br />15 or more feet per s~cond. Considerable bank erosion has accompanied <br /> <br /> <br />past floods. The 1894 flood resulted in the loss of every bridge in <br /> <br /> <br />Boulder. Buildings and long sections of roads and railroads were also <br /> <br /> <br />washed away. The 1969 flood, which was minor, resulted in loss of many <br /> <br />trees along the creek, loss of a bridge, and damages to building <br /> <br />foundations. <br /> <br />I <br />I <br />I <br /> <br />I <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />1 6 <br />