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<br />1 erminolOQY <br />Bed layer: The flow layer, several grain diameters thiek (usuaIly taken as two <br />grain diameters thick), immediately above the bed. <br />Bed load: Sediment that moves by roIling or sliding along the bed and is <br />essentiaIly in contact with the stream bed in the bed layer: <br />Bed material: The sediment mixture of which the stream bed is composed. <br />Bed sediment discharQe: That part of the total sediment discharge which is <br />composed of grain sizes found in the bed. The bed sediment discharge is assumed <br />equal to the transport capacity of the flow. <br />Contact load: Sediment particles that roIl or slide along in almost continuous <br />contact with the stream bed. <br />Density of water-sediment mixture: The mass per unit volume including both <br />water and sediment. <br />DischarQe-weiQhed concentration: The dry weight of sediment in a unit volume <br />of stream discharge, or the ratio of the discharge of dry weight of sediment to the <br />discharge by weight of water sediment mixture normally reported in parts per <br />miIlion (ppm) or parts per liter (ppl). <br />Load (or sediment load): The sediment that is being moved by a stream. <br />Sediment (or fluvial sediment): Fragmentary material that originates from <br />weathering of rocks and is transported by, suspended in, or deposited from water. <br />. Sediment concentration (by weight or by volume): The quantity of sediment <br />relative to the quantity of transporting fluid, or fluid-sediment mixture. 1 he <br />concentration may be by weight or by volume. When expressed in pprn, the <br />concentration is always in ratio by weight. <br />Sediment discharQe: 1 he quantity of sediment that is carried past any <br />cross-section of a stream in a unit of time. <br />Sediment yield: The dry weight of sediment per unit volume of water -sediment <br />mixture in place, or the ratio of the dry weight of sediment to the total weight of <br />water-sediment mixture in a sample or a unit volume of the mixture. <br /> <br />Suspended load (or suspended sediment): Sediment that is supported by the <br />upward components of turbulence in a stream. and that stays in suspension for an <br />appreciable length of time. <br />Susoended-sediment discharQe: The quantity of suspended sediment passing <br />through a stream cross-section outside the bed layer in a unit of time. <br />Total sediment discharQe: T~ totai sediment discharge of a stream. It is the <br />sum of the suspended-sediment diSCharge and the contact sediment discharge, or the <br />sum of the bed sediment discharge and the time rate of washload, or the sum of the <br />measured sediment discharge and the unmeasured sediment discharge. <br />Unmeasured sediment discharQe: Sediment discharge close to the bed that is <br />not sampled by a suspended load sampler. <br />Wash load: That part of the total sediment load which is composed of particle <br />sizes finer than those found in appreciable quantities in the bed and is determined by <br />