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Hydroperiod is the annual or otherwise repeatable period of time, typically expressed in days
or weeks, during which either alluvium underlying a bottomland area is persistently saturated
or the bottomland area is covered by water.
Hydrophyte is a plant that is adapted to a habitat of water or very wet conditions (including
Hyperarid refers to a climatic zone that receives average precipitation of less than 100 mm
annually. 25 Hyporheic zone is the ill-defined volume of sediment, adjacent to and beneath an alluvial
stream channel, through which ground water moves roughly parallel to streamflow. Water of
the hyporheic zone generally is readily exchangeable with stream water, receiving water as
bank storage through influent reaches of channel and yielding water as seepage through
effluent reaches. Processes of the hyporheic zone help control water temperature, dissolvedsolids and sediment transport, and near-channel ecology. Along intermittent-stream channels,
flow in the hyporheic zone at and slightly below channel level is commonly referred to as
underflow or perennial underflow that generally supports cottonwood trees or other
Hypoxia literally is the condition by which a deficiency of oxygen reaches tissues of the body; as
applied to hydrologic systems, it is a deficiency of dissolved oxygen in water and thus an
inadequate concentration of oxygen to maintain a healthy aquatic ecosystem. I
Illuviation is the movement of soluble and fine-grained material downward with descending
soil water into sites of the B horizon, where deposition or re-precipitation of the dissolved
minerals occur; illuviation is a specific form of eluviation.
Indicator species, as applied to plant ecology, refers to a plant whose natural presence on a
particular surface, soil, or landform is indicative of that surface, soil, or landform; as examples,
in moist parts of North America black walnut (Juglans nigra) is indicative of the flood plain,
whereas sacaton (Sporobolus airoides) is a bunchgrass of arid and semiarid parts of western
North America that is typically indicative of alkali soils of alluvial bottomlands.
Infiltration refers to the movement of water, from rain, snowmelt, runoff, and storage, from
the land surface through the air-soil interface and into the soil zone.
Infiltration rate of porous rock or a soil signifies the rate, often expressed in mm sec-1, at which
the rock or soil can absorb water provided to it from the surface by rainfall or snowmelt;
infiltration rate replaces the previous term, infiltration capacity, which was the maximum rate
at which infiltration could occur.
Inselberg (German, meaning island hill or island mountain), as applied to the American
Southwest, is a rock prominence surrounded and partially submerged by unconsolidated to
loosely consolidated sediment mostly of fluvial origin; inselbergs are common in the Basin and
Range Physiographic Province, where bedrock segments of mountain blocks, relative to the
land surface, have become separated or detached from the main mountain block through
alluvial-fan deposition around the bedrock segment.
Instability, as a descriptor of geomorphic processes and landforms, refers to a condition of
imbalance between inflows and outflows of matter through or over a landscape feature. As a
geomorphic concept, instability is often expressed as some state of dynamic- or quasiequilibrium, signifying that geomorphic processes and landforms are almost always in a
condition of dis-equilibrium and are almost always adjusting to regain relative stability; an
objective if applying the term is to determine the degree to which a process or landform
deviates from stability or equilibrium. 26 Interception is that portion of precipitation that wets vegetation or other surface cover and
returns to the atmosphere by evaporation during and following the precipitation event.
Interfluve is the area between sites of concentrated flow, particularly stream channels but
including gullies and, at a smaller scale, even rills, for which interrill area may be a preferred
Intermittent stream, as a hydrologic term, is intermittently or seasonally flowing water in a
natural, intermittent-stream channel; the flow of an intermittent stream typically is derived
from wet-season runoff or snowmelt, and the surface of an intermittent stream, or the bed of
the channel upon which flow occurs, typically is higher than the level of the zone of saturation
in the adjacent water-bearing alluvium or rocks. This characteristic is fundamentally different
from that of an ephemeral-stream channel, which at most times is separated from the zone of
saturation by a variable thickness of unsaturated alluvium or rock.
Irrigation is the application of water, by means of canals, pipes, sprinklers, or controlled
flooding, onto a land surface to augment the water that otherwise would be inadequate to
promote growth of crops or other vegetation.
Isohyet is a line, or contour on an isohyetal map, that connects points of equal precipitation;
isohyets and isohyetal maps generally refer to amounts of mean annual precipitation (as
examples, 50 mm or 100 mm), but also can be generated for other periods of time such as
months, seasons, or the duration of a single storm. J...
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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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