Allometric growth a concept applied to landforms and

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Unformatted text preview: wth, a concept applied to landforms and especially stream systems, is derived from the study of allometry, the recognition that the proportional sizes of rates of growth of parts of organisms are comparable and often quantifiable; as an example of its application to fluvial geomorphology, it includes the measurement of increases in stream-channel width and depth with increases in discharge of the stream. Hydraulic-geometry relations are based on an inference of allometric growth. Alluvial aquifer is a partially saturated deposit of alluvium that yields water to wells; most alluvial aquifers are unconfined and are composed of channel and flood-plain sediment; the water that partially saturates an alluvial aquifer is largely derived from the stream that transported and deposited the sediment. Alluvial fan is a wedge-shaped deposit of recent stream alluvium (erosion products) or poorly consolidated rock debris that radiates outward and downslope as, in plan view, an open fan from a site draining an area of high relief or topography, such as the mouth of a mountain valley, onto a gentler slope, typically a pediment or an alluvial plain; the deposit is thickest at the fan apex, near the valley mouth, and thins to a feather edge at the distal edge of the fan. Active alluvial fans are surfaces of net deposition whereas inactive alluvial fans generally exhibit erosion and stream incision at the apex, the depth of incision decreasing with distance downslope to the distal edges of the fan. Alluvium is a general term for sediment deposited in a streambed, on a flood plain or other bottomland feature, delta, or at the base of a mountain during comparatively recent geologic time. 4 Anabranch of a stream is a separate channel that has diverged from the main channel and rejoins the stream at some downstream site; an anabranch is a discrete, semi-permanent channel that may be of equal or smaller size as the main channel, thereby distinguishing it from channel braids that are not discrete and may be highly ephemeral. Angle of repose is the maximum departure from horizontal, expressed as an angle, at which a slope formed of loose, cohesionless sediment retains stability. The angle of repose is a function of the frictional properties of the sediment and the angularity of the sediment grains; it varies from about 30 degrees for coarse, rounded particles to about 39 degrees for angular particles of sand, and is typically 32 to 34 degrees for dry sand of dunes. Annual flood is the maximum instantaneous discharge, typically expressed in cubic meters per second (m3 s-1), that occurs at a stream site in a water year (October 1 through September 30). Annual flood series is a list of annual floods measured at a streamflow gage site for the period of record or a selected part of the period of record. Antidune, in a fluvial setting or on a stream bed, is a transient sand wave or dune that moves upstream by processes in which erosion of sand particles occurs on the downstream slope of the bedform followed by deposition of the sand particles on the next upstream slope. Aquiclude is a nearly impermeable rock body that can absorb water very slowly and hence can only release the absorbed water to springs or seeps very slowly; where an aquiclude is at or near a lowland surface, swampy conditions may occur owing to the inability of surface water to infiltrate readily. Aquifer is any rock body or geologic deposit of alluvium or similar rock debris that is partially or fully saturated with ground water and has properties of permeability (transmissivity) and porosity that enable it to yield the ground water to a well or spring at a rate significantly high to fulfill a specified purpose; aquifers are grouped as unconfined, those controlled by near-surface gravitational and atmospheric-pressure conditions, and artesian, those that are poorly connected to the land surface due to an impermeable layer separating it from the land surface. Aquifuge is an impermeable rock body that cannot absorb water and hence cannot release water to springs or seeps very slowly; where an aquifuge is at or near a lowland surface, swampy conditions may occur owing to the inability of surface water to infiltrate. Archaeology is a composite science involving the study and understanding of both recent-past and ancient peoples and cultures through the excavation of sites of habitation and the recovery of artifacts; the practice of archaeology typically requires the application of disciplines including soil science, paleontology, hydrology, geomorphology, chemistry, and sedimentology, and the use of analytical techniques such as the identification of clays and rock fragments, particle-size analysis, and dating by radiocarbon analysis. Arête (from the French term for fishbone) is a sharp-edged, serrated ridgeline feature of a high alpine area sculpted by progressive back erosion of steep bedrock walls above two or more cirques formed by the glaciers occupying the cirques. A specific typ...
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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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