chapter 3 fundamentals of fluvial geomorphology and stream ...

outcrops, other non-erodible materials or inputs of relativelyimmobile sediments by steep tributaries. Repeat thalweg profilesare particularly useful in identifying bed level adjustments throughaggradation, degradation, local scour, and fill. When employingdifferent slopes to calculate stream power, it must be kept in mindthat the thalweg, water surface, and energy slopes are notnecessarily equal.3.4 SEDIMENT TRANSPORTOne aspect of river engineering that causes considerableconfusion and misunderstanding is the terminology associated withsediment transport. When discussing sediment transport, it isimportant to be familiar with the terminology adopted and thenature of the load being discussed. Over an extended period, acommon terminology has emerged and while it is not universallyagreed or applied, it does provide the basis for at least reducinginconsistency.Total sediment load is the mass of granular sedimenttransported by the stream. It can be broken down by source,transport mechanism, or measurement status (Table 3.1). Bedload is a component of total sediment load made up of particlesmoving in continuous or frequent contact with the bed. Transportoccurs at or near the bed, with the submerged weight of particlessupported by solid-solid contact with the bed. Bed load movementtakes place by processes of rolling, sliding, and saltation.Suspended load is a component of the total sediment load madeup of sediment particles moving in continuous or semi-continuoussuspension within the water column. Transport occurs above thebed, with the submerged weight of particles supported byanisotropic turbulence within the body of the flowing water. Bedmaterial load is the portion of the total sediment load composed ofgrain sizes that are found in appreciable quantities in thestreambed. The bed material load is the bed load plus the coarserportion of the suspended load, that is, particles of a size that arefound in significant quantity in the streambed. Wash load is theportion of the total sediment load composed of grain sizes finerthan those found in appreciable quantities in the streambed.Measured load is the portion of the total sediment load sampledby conventional suspended load samplers. The sediment sampledin deriving the measured load includes a large proportion of thesuspended load, but excludes that portion of the suspended loadmoving very near the bed (that is, below the sample nozzle) and allof the bed load. Unmeasured load is that portion of the totalsediment load that passes beneath the nozzle of a conventionalsuspended load sampler, moving in near-bed suspension and asbed load.32 Fundamentals of Fluvial Geomorphology and Stream Processes