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<br />Fault. A fracture or fracture zone in the earth crust along which there has <br />been displacement of the two sides relative to one another. <br /> <br />Fault, Active. A fault which, because of its present tectonic setting, can <br />undergo movement from time to time in the immediate geologic future. <br /> <br />Fault, Capable. An active fault that is judged capable of producing macro- <br />earthquakes and exhibits one or more of the following characteristics: <br /> <br />a. Movement at or near the ground surface at least once within the past <br />35,000 years. <br /> <br />b. Macroseismicity (3.5 magnitude Richter or greater) instrumentally <br />determined with records of sufficient precision to demonstrate a <br />direct relationship with the fault. <br /> <br />c. A structural relationship to a capable fault such that movement on <br />one fault could be reasonably expected to cause movement on the other. <br /> <br />d. Established patterns of microseismicity which define a fault, with <br />historic macroseismicity that can reasonably be associated with the <br />fault. <br /> <br />Fetch. The straight line distance across a body of water subject to wind <br />forces. The fetch is one of the factors used in calculating wave heights in a <br />reservoir. <br /> <br />Filter (filter zone). One or more layers of granular material graded (either <br />naturally or by selection) so as to allow seepage through or within the layers <br />while preventing the migration of material from adjacent zones. <br /> <br />Flashboards. Structural members of timber, concrete, or steel placed in <br />channels or on the crest of a spillway to raise the reservoir water level but <br />that may be quickly removed in the event of a flood. <br /> <br />Flip bucket. An energy dissipator located at the downstream end of a spillway <br />and shaped so that water flowing at a high velocity is deflected upwards in a <br />trajectory away from the foundation of the spillway. <br /> <br />Flood. A temporary rise in water levels resulting in inundation of areas not <br />normally covered by water. May be expressed in terms of probability of <br />exceedance per year such as one percent chance flood or expressed as a <br />fraction of the probable maximum flood or other reference flood. <br /> <br />Flood routing. A process of determining progressively over time the amplitude <br />of a floodwave as it moves past a dam or downstream to successive points along <br />a river or stream. <br /> <br />Flood, Safety Evaluation (SEF). The largest flood for which the safety of a <br />dam and appurtenant structure is to be evaluated. <br /> <br />-6- <br />