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I Ie I I I I I I I . I I I I I I I I. I Estuary - Tidal reach at the mouth of a river. Fabriform - Grout-filled fabric mattress used for stream bank protection. f ascine - A stream bank protection technique consisting of wire mesh or timber attached to a series of posts, sometimes in double rows; the space between the rows may be filled with rock, brush, or other materials. Fences may be placed either parallel to the bank or e~:tended into the stream; in either case these structures decrease the stream velocity and encourage sediment deposition as the flow passes through the fence. Fetc!:l - The area in which waves are generated by wind having a rather constant direction and speed; sometimes used synonymously with fetch length. Fetch Lenqth - The horizontal distance (in the direction of the wind) over which wind generates waves and wind setup. fill-Slope - Side or end slope of an earth-fill embankment. Where a fill-slope forms the streamward face of a spill-through abutment, it is regarded as part of the abutment. Filter - Layer of fabric, sand, gravel, or graded rock placed, or developed naturally, where suitable in-place materials exist, between the bank revetment and soil for one or more of three purposes: to prevent the soil from moving through the revetment by piping, extrusion, or erosion; to prevent the revetment from sinking into the soil; and to permit natural seepa'Je from the streambank, thus preventing buildup of excessive hydrostatic pressure. Filter Blanket - A layer of graded, intermediate-size gravel laid between fine-grained material and riprap, to prevent wash-out of the finer material. Filter Cloth, Fabric - Synthetic fabric that serves the same purpose as a granular filter blanket. Fine Sediment Load (or wash load) - That part of the total sediment load that is composed of particle sizes finer than those represented in the bed. Normally the fine-sediment load is finer than 0.062 mm for a sand-bed channel. Silts, clays and sand could be considered as wash load in coarse gravel and cobble bed channels. Flankinq - Erosion resulting from streamflow between the bank and the landward end of a river-training or a grade-control structure. Flashy Stream - Stream characterized by rapidly rising and falling stages, as indicated by a sharply peaked hydrograph. Most flashy streams are ephemeral but some are perennial. Flood Envelope Curve - An empirical relationship developed between the maximum flood discharge and drainage area for a given region. Flood-Frequency Curve - A graph indicating the probability that the annual flood discharge will exceed a given magnitude, or the recurrence interval corresponding to a given magnitude. xlv