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<br />spill along Vine Drive flows into the drainage for Dry Creek and returns to the Cache La <br />Poudre River below the Timnath Reservoir Canal diversion via Dry Creek. <br /> <br />Downstream of Taft Hill Road, there are two diversion structures (for Larimer and Weld <br />Canal and Arthur Ditch) and large excavations on both sides of the river. Most of the <br />effective flow was on the left bank during the I-percent annual chance flood due to the <br />protective berms. Upstream of Taft Hill Road, split flow occurs during the D.2-percent <br />annual chance flood. <br /> <br />The same Manning's "n" value of 0.035 for the channel in the 1989 study was used for this <br />restudy. For the overbank areas, the values were revised to reflect existing conditions. The <br />values for the overbanks range from 0.04 to 0.104. <br /> <br />Starting water-surface elevations for the main channel of the Cache La Poudre River were <br />taken from the 1993 Flood Insurance Study report for Larimer County, Colorado. <br /> <br />Cross sections on Dry Creek were taken from topographic maps at a scale of 1 : 1 ,200, with <br />a contour interval of 2 feet (Reference 25). Roughness coefficients were estimated by field <br />inspection. Channel values ranged from 0.03 to 0.05, and overbank values ranged from <br />0.015 to 0.10. Water-surface profiles were computed using the USACE HEC-2 computer <br />program (Reference 22). <br /> <br />Cross section data for Fish Creek and the Fall River were taken from topographic maps at a <br />scale of 1: 1,200, with a contour interval of 2 feet (Reference 26) and were supplemented <br />with field surveyed cross sections. Roughness coefficients were estimated by field <br />inspection. The channel value was 0.04, and the overbank values ranged from 0.03 to 0.08. <br />Water-surface profiles were computed using the USACE HEC-2 computer program <br />(Reference 22). <br /> <br />Cross section data for Black Canyon Creek were taken from topographic maps at a scale of <br />1: 1,200 with a contour interval of 2 feet (Reference 19) and were supplemented with field- <br />surveyed cross sections. Roughness coefficients were estimated by field inspection. The <br />channel value was 0.04 and the overbanks were 0.06. Water- surface profiles were <br />computed using the USACE HEC-2 computer program (Reference 22). <br /> <br />Cross section data for the Fall River were field-surveyed. A water supply dam located in <br />the upper watershed failed in July 1982 and changed the channel. Roughness coefficients <br />were estimated by field inspection. The channel roughness ranged from 0.04 to 0.05and <br />the overbank roughness ranged from 0.03 to 0.06. Water-surface profiles were computed <br />using the USACE HEC-2 program (Reference 22). <br /> <br />Approximate flood elevations for the Little Thompson River were determined from a <br />USACE Flood Plain Information report (Reference 27). <br /> <br />Starting water-surface elevations for the Big Thompson River upstream of Lake Estes and <br />Fish Creek were the maximum normal operating level of Lake Estes. Starting water- <br />surface elevations for Dry Creek were computed assuming critical depth. On Fall River, <br />Black Canyon Creek, Boxelder Creek, and Cooper Slough, starting water-surface <br /> <br />33 <br />