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<br />. ()ti0()O <br />Vuo.... <br /> <br />turbidi'ry, which would have a temporary, adverse effect on aquatic <br />life in 'rhe South Platte River. Water re I eased f rom the dams wou I d <br />be of a quality simi lar to the surface water presently flowing in the <br />river. Below the high dams the present relatively low turbidities <br />would be further lowered due to entrapment of incoming sediment. <br /> <br />FRAZIL ICE <br /> <br />The occurrence of frazi I ice in wintertime is the major operational <br />problem that impacts upon the reliabi I ity of a diversion structure in <br />Waterton Canyon for furnishing an uninterrupted supply of raw water from <br />the South Platte River. <br /> <br />Frazil consists of sma I I ice particles mixed with the flow of a <br />turbulent stream. Concentrations vary from a few particles in the <br />flow to concentrations so high that the flow becomes slush. When <br />frazi I pi les up and Is al lowed to drain, it has the appearance of a <br />snow cone. <br /> <br />Frazll ice in flowing streams presents serious problems at <br />diversions. It clogs intakes and can block conduits. Although It can <br />be diverted with the water and conveyed through aqueducts, it must be <br />kept moving, for an interruption of flow could result in a blockage. <br />Both Denver and Aurora have fought the frazi Ikepr()bi.ems a.t their <br />intakes for many years. Blockages have occurred in both the Denver <br />and Aurora systems and there have been times when both cities have <br />been dependent upon diminishing raw water storage whi Ie maintenance <br />forces strove to clear the aqueducts. A water treatment plant is not <br />des I gned to operate wi thf raz il in the raw water; therefore, a settling <br />pond must be provided ahead of the plant. An alternative solution for <br />excluding frazi I ice from intakes is to draw the water from a reser- <br />voir. This is the ice control measure that is anticipated for the <br />alternatives which cal I for high dams. <br /> <br />The Missouri River Division has called on the Corps of Engineers <br />Cold Regions Research Engineering laboratory (CRREl) at Hanover, New <br />Hampshire, for an evaluation of the susceptibi I ity of each alternative <br />to operational problems from frazl I ice. CRREL concludes that the low <br />dam alternatives would be subject to continuing operational problems <br />from frazi I ice and could not be depended on for uninterrupted base load <br />operation during the winter months. CRREL also concludes that the high <br />dam alternatives should provide a continuous, ice-free base load water <br />supply, if appropriate operational procedures are fol lowed. <br /> <br />13 <br />