Contact load: Sediment particles that roll or slide along in almost continuous contact with the
stream bed, i.e., bed load.
The mass per unit volume including both water and
Density of water-sediment mixture:
Discharge-weighed concentration: The dry weight of sediment in a unit volume of stream
discharge, or the ratio of the discharge of dry weight of sediment to the discharge by weight of
water-sediment mixture normally reported in parts per million (ppm) or parts per liter (ppl).
Load (or sediment load): The sediment that is being moved by a stream.
Sediment (or fluvial sediment): Fragmentary material that originates from weathering of rocks
and is transported by, suspended in, or deposited from water.
Sediment concentration (by weight or by volume): The quantity of sediment relative to the
quantity of transporting fluid, or fluid-sediment mixture. The concentration may be by weight or
by volume. When expressed in ppm or mg/l, the concentration is always in ratio by weight.
Sediment discharge: The quantity of sediment that is carried past any cross-section of a
stream in a unit of time.
Sediment yield: The dry weight of sediment per unit volume of water-sediment mixture in
place, or the ratio of the dry weight of sediment to the total weight of water-sediment mixture in
a sample or a unit volume of the mixture.
Suspended load (or suspended sediment): Sediment that is supported by the upward
components of turbulence in a stream and that stays in suspension for an appreciable length of
Suspended bed load: The portion of suspended load which is composed of grain sizes found
in the bed.
Suspended-sediment discharge: The quantity of suspended sediment passing through a
stream cross-section outside the bed layer in a unit of time.
Total sediment discharge: The total sediment discharge of a stream. It is the sum of the
suspended-sediment discharge and the contact sediment discharge, or the sum of the bed
sediment discharge and washload, or the sum of the measured sediment discharge and the
unmeasured sediment discharge.
Unmeasured sediment discharge: Sediment discharge close to the bed that is not sampled by
a suspended sediment sampler.
Washload: That part of the total sediment discharge (load) which is composed of particle sizes
finer than those found in appreciable quantities in the bed and is determined by available bank
and upstream supply rate. Also called fine sediment discharge (load).