Total sediment transport rate or total sediment load

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Unformatted text preview: iment-transport rate, or total sediment load is the sum of the suspended-sediment and bed-load transport rates; it is the total quantity of sediment, as measured by dry weight or volume, that moves past a site during a given time. Often the suspended-sediment transport rate is measured, but the bed-load transport rate must be estimated. Total suspended solids (TSS), when used as a regulatory concept in the hydrologic subdiscipline of sedimentology, is a measure of the suspended-solids, or solid-phase, content of a water sample. According to Standard Methods for the Analysis of Water and Wastewater (1995), TSS is determined from a sub-sample of an original water sample, whereas the American Society for Testing and Materials (ASTM) advocates that the determination be made from an entire sample of the water-sediment mixture; the two approaches are not compatible. Transect is a line or path along which measurements or observations are taken, generally at equal intervals, as a means of compiling data for an investigation. As applied to geomorphology or sedimentology, for example, it could be the measurement of the diameter of each sediment particle or rock fragment occurring at 1-m intervals along a 100-m length of channel bed or hillslope; as applied to plant ecology, a transect is a line along which observations of vegetation are made, often within quadrats, that might include presence or absence of species, height or truck diameter of trees, or surface area covered by individual plants, as a means to study characteristics of a particular assemblage of species. The use of transects in geomorphic or ecological investigations is a means to minimize the potential for introducing bias into the study. 45 Transmission loss is the abstraction, or reduction, of flow in ephemeral or intermittent stream channels as discharge migrates downstream; the loss occurs by infiltration of streamflow into normally dry (unsaturated) sediment forming the channel bed and banks and therefore much of the flow abstraction becomes recharge to the ground-water reservoir. Transpiration is the process by which water in living organisms, primarily plants, passes into the atmosphere. Transport is the movement, shifting, or carrying away by natural agents of sediment (and dissolved load) from one place to another on or near the earth’s surface. Transport-limited is a term to describe the short-term ability of a specified flow rate to transport a specified type of fluvial sediment or a specified range of particle sizes of sediment; when a transport-limited condition occurs, the sediment load, or flux, is limited by the flow rate of the stream, not by the availability of sediment. Less commonly, transport-limited is applied to hillslope-erosion studies, for which it recognizes a condition of insufficient overland flow to move all eroded sediment down the slope. Tree is a woody plant having a single main stem or trunk at least to some measurable height above the surface; exceptions are caespitose trees, generally willows and cottonwoods, with trunks growing in clusters or tufts because the main trunk was sheared at the surface by a destructive flood. Turbidity is the optical property (state, condition, or quality) of opaqueness or reduced clarity of a fluid, due to suspended, colloidal, and organic matter and dissolved solids that provide color, that causes light to be scattered, absorbed, and diffracted rather than being transmitted directly through the water. Turbulent flow, as a hydrologic term, is water movement (flow) in which the lines of flow are erratic and mixed and in which flow direction at all sites changes frequently and nearly instantaneously; turbulent flow is typical of stream and other surface-water bodies whereas laminar flow is typical of slowly moving ground water. U Underflow is the down-valley movement of water in a near-surface alluvial aquifer that is hydraulically connected and directly related to the stream channel; underflow is most descriptive of near-surface ground-water movement beneath stream channels of arid and semiarid areas where it typically provides water adequate to sustain phreatophytic trees such as cottonwoods despite unreliable amounts of streamflow. Understory is the undergrowth, or underlying layer of plants (shrubs, herbs, etc.) of forest vegetation; the understory plants of a forest generally are adopted to conditions of limited light owing to shade caused by trees that form the canopy. The understory affects erosion by intercepting that rainfall penetrating the canopy, by causing evaporation of a portion of it and preventing that portion from reaching the surface to become runoff, and by protecting soil particles at the surface from erosion by rainsplash impact.. 46 Unmeasured sediment-transport rate, or unmeasured sediment load, is the difference between the total-sediment rate and measured suspended-sediment discharge. V Variable source area is a geomorphic concept acknowledging that within a drainage basin the amounts of water, sediment, and organic matter entering the drainage network from subbasins (or source areas) vary depending on local characteristics such as climate, geology and soils, topography, and history (especially floods, fires, and land use). Viscosity, o...
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This document was uploaded on 02/26/2014 for the course ES 322 at Western Oregon University.

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