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Unformatted text preview: pt of bankfull discharge, which often approximates
the mean annual flood for perennial streams, includes the flood plain as a unique, identifiable
geomorphic surface, all higher surfaces of alluvial bottomlands being terraces, and
acknowledgement that bankfull discharge occurs only when stream stage is at flood-plain level.
Bankful stage, a fluvial-geomorphic term, is the water-surface level at the tops of alluvialstream banks that corresponds to the level of adjacent flood-plain surfaces, if present. Thus,
bankfull stage is the level at which bankfull discharge occurs, the upper limit of channel
capacity. As such, the concept of bankfull stage requires an interpretation of site-specific
landforms, especially bank. Although bankfull stage can refer to various channel-bank levels, it
generally applies to alluvial-stream channels (1) having sizes and shapes adjusted to recent
fluxes of water and sediment, (2) that are principal conduits for discharges moving through a
length of alluvial bottomland, and (3) that are bounded by flood plains upon which water and
sediment spill when the flow rate exceeds that of bankfull discharge.
Bank material is the sediment of which the mostly sloping sides, or banks, of a stream channel
are formed; like bed material, it is generally reflective of the size range of the total sediment
load of the stream, may be partly residual, but for regime channels is mostly indicative of the
suspended-load transported by streams during non-flood periods. 7 Bank storage is the process by which water, during periods of above-normal streamflow,
infiltrates into and saturates typically aerated bank sediment (alluvium) higher than the normal
stream surface; as the flow event recedes and stream stage declines, bank-storage water seeps
from the alluvium and reenters the stream.
Bar is in-channel sediment of relatively coarse bed material, typically coarse sand through
cobbles in size, that is generally deposited during the recession of a high flow and is mostly
exposed during periods of low flow; the upper surface of bars of perennial streams is typically
equivalent to a stage of about 40-percent flow duration.
Barranco, a Spanish term applied to incised channels of the water-deficient southwestern
United States, refers to a deep, rectangular to steep-sided trapezoid shaped ravine or arroyo in
partially consolidated bottomland alluvium; barroncos are indicative of an erosive drainage
network and are maintained by channel-bed erosion and the collapse of the arroyo walls during
brief periods of ephemeral streamflow..
Base flow is sustained, low, or fair-weather flow of a stream; base flow (m3 s-1) generally is
derived from ground-water inputs to the stream channel.
Base level is the lowest level or elevation for which a stream of flowing water hypothetically
can effect erosion. The ultimate base level is the sea surface or slightly lower, but as a
geomorphic concept, base level refers to more transient conditions such as an erosion-resistant
dike over which a stream flows and is unable to alter during a short interval of geologic time.
Bed, or stream bed, is the bottom surface of a water course, generally of a stream channel,
upon which water and sediment move during periods of discharge .
Bed load, or sediment discharged as bed load, is the sediment that is moved by saltation,
rolling, or sliding on or near the stream bed, essentially in continuous contact with it.
Bed material is the sediment of which the mostly horizontal bed of a stream channel is formed;
it is generally reflective of the size range of the total sediment load of the stream, in many cases
may be partly residual, but is mostly indicative of the bed-load sizes transported by the stream.
Bias, as used in scientific investigations in general, but particularly in hydrology and plant
ecology, is systematic error introduced to the investigation by inappropriate sampling,
inadequate sampling or testing of hypotheses, or by the purposeful favoring of one hypothesis
over one or more others; an example of unintentional bias is the sampling for suspendedsediment concentration at one site of a stream channel without accounting for other
concentrations at other sites of the channel section.
Billabong is an Australian term, derived from the aboriginal word for “dead river”, describing
blind or discontinuous anabranches of complex channel systems; billabongs are typically dry
but seasonally may be filled with water.
Biomass is the amount, expressed generally as mass (or weight) per unit area or the volume of
the environment, of near-surface living organisms in a specified area at a specified time.
Biome is a mature ecosystem that characterizes a particular natural environment. 8 Biophysical continuum is a complex, dynamic gradient of habitat types from headwaters to
oceanic confluence. Riverine flora, fauna, and physical features are usually distributed rather
predictably along the gradient according to the requirements specified by each stage in a
species life cycle, and by downstream change in fluvial-geomorphic process.
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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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