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Show earns • General Discussion " During interglacial periods of the last 12 million years, streamflow rates were many times greater than those observed today. The high runoff transported vast amounts of broken and crushed rock made available by glaciation, and filled the canyon bottoms. Introduction of flows from Strawberry Reservoir began a new period of instability. Due to the large elevation difference between the reservoir and the natural stream in Sixth Water, the water possessed extremely high energy levels ( the basis of proposed power generation). Very little of the energy was converted directly to down channel velocity. Instead, strong erosive currents were produced resulting in the excavation and transport of large volumes of previously stable material. The upper stream reaches were degraded 35 to 40 feet, and depositional areas were established between Three Forks and the mouth of Diamond Fork Canyon. The cutting action in the upper reaches of Sixth Water Creek created serious problems ( the large land flow area between Dip Vat and Sixth Water bridge is a good example). Deposition below Three Forks forced the channel to migrate rapidly. The situation was further compounded by the large fluctuations in flow rates. Under natural conditions, Diamond Fork experienced a mean monthly discharge of 140 c. f. s. during spring runoff ( flows exceeding 200 c. f. s. 6 or 7 days each year). Under the artificial situation, mean monthly flows were more than 200 percent ( 300 c. f. s.) of the natural peak and persisted for several months. Artificially induced flucutations occurred varying the flow from less than 200 c. f. s. to over 450 c. f. s. - sometimes within a single day. Both the high flow rates and their associated energy levels created a highly mobile streambed ( rocks as large as fourteen ( 14) inches in diameter were bounced along the bottom). As the volume of flow declined, the river was forced to deposit the larger material with the consequent formation of rock and gravel bars parallel to the direction of flow. As the water level continually dropped, more and more materials were deposited. When the trend was reversed and water level was again increased, 256 |