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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
Table 3.1 – Classification of theSediment LoadMeasurementmethodTransportmechanismSedimentsourceUnmeasured LoadBed LoadBed Material LoadMeasured LoadSuspended LoadWash Load3.5 CHANNEL-FORMINGDISCHARGEMorphological studies have revealed that channel formdepends on a delicate balance between the flows of water andsediment that shape the stream, the processes by which channelform is changed, and the ability of the boundary materials to resistchange. Variability of the water and sediment discharges is acharacteristic of the watershed and, if maintained over asufficiently long period, the morphology of the stream will adjust toaccommodate the range of flow events responsible for regulatingthe balance between the erosive and resistive forces that mold thestream. Consequently, the shape and dimensions of an alluvialriver channel are adjusted to and reflect the wide range of flowsthat entrain, transport, and deposit boundary sediments (Lane1955). The concept that there is a single discharge which, if itprevailed all the time, would produce the same width, depth, slope,hydraulic roughness, and planform as those produced by theactual range of discharges, is attractive, but viewed in this contextit is clearly a gross simplification. The single discharge best ableto represent the actual spectrum of sediment-transporting eventsto yield the same bankfull morphology as that shaped by thenatural sequence of flows is referred to as the channel-formingflow or the dominant discharge. Dunne and Leopold (1978)defined stream maintenance flow as the most effective dischargefor moving sediment, forming or removing bars, forming orchanging bends and meanders, and generally doing work thatresults in the average morphologic characteristics of streams.Their definition of stream maintenance flow is very similar to theconcept of channel-forming discharge.In a regulated canal system, the dimensions of the streamcan appropriately be based on a single design discharge andempirical analysis of the relationship between that discharge andthe dimensions for a stable, unlined canal formed in alluvialmaterials produced the regime theory. Early work on regimetheory stems from design of straight canals in the Indian sub-Fundamentals of Fluvial Geomorphology and Stream Processes 33
Page 6 and 7: materials. Also, the threshold mobi
Page 8 and 9: ank of a large river. From an engin
Page 10 and 11: eddies in a stream do not scale on
Page 12 and 13: aiding. Braid bars are sediment fea
Page 14 and 15: Sinuosity (P) is a commonly used pa
Page 18 and 19: continent (Inglis 1941, 1947, 1949)
Page 20 and 21: instances where the bankfull discha
Page 22 and 23: uses readily available mean daily f
Page 24 and 25: of flows. The results are plotted a
Page 26 and 27: Similarly, in regime theory the con
Page 28 and 29: 3.7 STREAM STABILITY ANDINSTABILITY
Page 30 and 31: It should be noted that the map coo
Page 32 and 33: and slope of the reach are not sign
Page 34 and 35: (a) Bed and Bank InstabilityFigure
Page 36 and 37: the downstream limit of the system
Page 38 and 39: dam, where degradation was expected
Page 40 and 41: Figure 3.13 - Channel PatternClassi
Page 42 and 43: definition of a graded stream in wh
Page 44 and 45: midwestern experience, while Rosgen
Page 46 and 47: Schumm et al. (1981, 1984) and thei
Page 48 and 49: ut at a much reduced rate. The sedi
Page 50 and 51: • integration of results into eng
Page 52: 68 Fundamentals of Fluvial Geomorph

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