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The Science of Instream Flows: A Review of the Texas Instream Flow Program Appendix A Glossary Adaptive management —A process through which management decisions can be changed or adjusted based on additional information. Aggradation —(1) Geomorphic process in which sediment is carried downstream and deposited in streambeds, floodplains, and other water bodies resulting in a rise in elevation in the bottom of the water body. (2) The occurrence when the supply of sediment is deposited and stored in the active channel. Allocation —See Water allocation. Alluvial stream —A stream with a bed and banks of unconsolidated sedimentary material subject to erosion, transportation, and deposition by the river. Appropriation —A specified amount of water set aside by Congress, other legislative body or state or provincial water regulatory authority to be used for a specified purpose at a specified place, if available. Aquatic life —All organisms living in or on the water. Bankfull discharge —The discharge at channel capacity or the flow at which water just fills the channel without over-topping the banks. Base flow —Average streamflow in the absence of significant precipitation or runoff events. Also known as “normal flow.” Bedload —Material moving on or near the streambed. Bedload discharge —The volume of bedload passing a transect in a unit of time. Beneficial use —A cardinal principle of the prior appropriation doctrine. It has two components: the nature or purpose of the use and the efficient or non-wasteful use of water. State constitutions, statutes, or case law may define uses of water that are beneficial. Those uses may be different in each state, and the definition of what uses are beneficial may change over time. Bypass —(1) A channel or conduit in or near a dam that provides a route for fish to move through or around the dam without going into the
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The Science of Instream Flows: A Review of the Texas Instream Flow Program turbines. (2) That stream reach below a dam that is essentially skirted by the flow used to generate electricity. Channel —That cross section containing the stream that is distinct from the surrounding area due to breaks in the general slope of the land, lack of terrestrial vegetation, and changes in the composition of the substrate materials. Channelization —The mechanical alteration of a natural stream by dredging, straightening, lining, or other means of accelerating the flow of water. Connectivity —Maintenance of lateral, longitudinal, and vertical pathways for biological, hydrological, and physical processes. Discharge —The rate of streamflow or the volume of water flowing at a location within a specified time interval. Usually expressed as cubic meters per second (cms) or cubic feet per second (cfs). Diversion —A withdrawal from a body of water by human-made contrivance. Drainage area —The total land area draining to any point in a stream. Also called catchment area, watershed, and basin. Flood —Any flow that exceeds the bankfull capacity of a stream or channel and flows out on the floodplain. Floodplain —(1) Land beyond a stream channel that forms the perimeter for the maximum probability flood. (2) A relatively flat strip of land bordering a stream that is formed by sediment deposition. Flow —(1) The movement of a stream of water or other mobile substance from place to place. (2) Discharge. Flow regime —The distribution of annual surface runoff from a watershed over time such as hours, days, or months (See also Hydrologic regime). Fluvial —Pertaining to streams or produced by river action. Gradient —The rate of change of any characteristic, expressed per unit of length. (See Slope.) May also apply to longitudinal succession of biological communities. Groundwater —In general, all subsurface water that is distinct from surface water; specifically, that part which is in the saturated zone of a defined aquifer. Sometimes called underflow.
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The Science of Instream Flows: A Review of the Texas Instream Flow Program Habitat guild —Groups of species that share common characteristics of microhabitat use and selection at various stages in their life histories. High flow pulse —A short-duration, high flow within the stream channel that occurs during or immediately following storm events and serves to flush fine sediment deposits and waste products, restore normal water quality following prolonged low flows, and provide longitudinal connectivity for species movement along the river Hydraulic control —A horizontal or vertical constriction in the channel, such as the crest of a riffle, which creates a backwater effect. Hydrograph —A graph showing the variation in discharge over time. Hydrologic regime —The distribution over time of water in a watershed, among precipitation, evaporation, soil moisture, groundwater storage, surface storage, and runoff. Hyporheic zone —The interface between the stream bed and shallow ground water. Index of biotic integrity —A numerical gauge of the biological health of stream fish communities based on various attributes of species richness, species composition, trophic relations, and fish abundance and condition. Instantaneous flow —(1) Discharge that is measured at any instance in time. (2) Flow that is measured instantaneously and not averaged over longer time such as day or month. Instream flow —The rate of flow in a natural stream channel at any time of year. Instream flow requirement —(1) That amount of water flowing through a natural stream course that is needed to sustain, rehabilitate or restore the ecological functions of a stream in terms of hydrology, biology, geomorphology, connectivity and water quality at a particular level. (2) That amount of water flowing in a stream needed to sustain the protection of fish and wildlife habitat, migration, and propagation; outdoor recreation activities; navigation; hydropower generation; waste assimilation (water quality); and ecosystem maintenance, which includes recruitment of fresh water to the estuaries, riparian vegetation, floodplain wetlands, and maintenance of channel geomorphology. Instream flow requirements are typically recognized and administered under the authority of some type of legal means such as a water right, permit or operating agreement.
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The Science of Instream Flows: A Review of the Texas Instream Flow Program Instream Flow Incremental Methodology (IFIM) —Modular decision support system for assessing potential flow management schemes. It quantifies the relative amounts of total habitat available for selected aquatic species under proposed alternative flow regimes. Instream use —Any use of water that does not require diversion or withdrawal from the natural watercourse, including in-place uses such as navigation and recreation. Large woody debris —Any large piece of woody material that intrudes into the stream channel; often defined as having a diameter greater than 10cm and a length greater than 1m. Synonyms: Large organic debris, woody debris, log. Macrohabitat —Abiotic habitat conditions in a segment of river controlling longitudinal distribution of aquatic organisms, usually describing channel morphology, flow, or chemical properties or characteristics with respect to suitability for use by organisms. Main stem —The main channel of a river, as opposed to tributary streams, and oxbow lakes or floodplain sloughs. Mesohabitat —A discrete area of stream exhibiting relatively similar characteristics of depth, velocity, slope, substrate, and cover, and variances thereof (e.g., pools with maximum depth <5 ft, high gradient riffles, side channel backwaters). Microhabitat —Small localized areas within a broader habitat type used by organisms for specific purposes or events, typically described by a combination of depth, velocity, substrate, or cover. Minimum flow —The lowest streamflow required to protect some specified aquatic function as established by agreement, rule, or permit. Natural flow —The flow regime of a stream as it occurs under completely unregulated conditions; that is, a stream not subjected to regulation by reservoirs, diversions, or other human works. Naturalized flow —Managed flows that are adjusted to mimic flows that would occur in the absence of regulation and extraction. Normal flow —See base flow. Open channel hydraulics —The analysis of water flow and associated materials in an open channel with a free water surface, as opposed to a tunnel or pipeline. Overbank flow —An infrequent, high flow event that overtops the river banks, physically shapes the channel and floodplain, recharges ground water tables, delivers nutrients to riparian vegetation, and
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The Science of Instream Flows: A Review of the Texas Instream Flow Program connects the channel with flood plain habitats that provide additional food for aquatic organisms. PHABSIM —The Physical HABitat SIMulation system. A set of software and methods that allows the computation of a relation between stream flow and physical habitat for various life stages of an aquatic organism or a recreational activity. Q710 —The lowest continuous 7-day flow with a 10-year recurrence interval. Sometimes called 7Q10. Reach —A comparatively short length of a stream, channel, or shore. One or more reaches compose a segment. Riffle —A relatively shallow reach of stream in which the water flows swiftly and the water surface is broken into waves by obstructions that are completely or partially submerged. Riparian/riparian zone —Pertaining to anything connected with or adjacent to the bank of a stream or other body of water. The transitional zone or area between a body of water and the adjacent up-land identified by soil characteristics and distinctive vegetation that requires an excess of water, including wetlands, marshes, and floodplains that support riparian vegetation. Riparian vegetation —Vegetation that is dependent upon an excess of moisture during a portion of the growing season on a site that is perceptively more moist than the surrounding area. Sediment —Solid material, both mineral and organic, that is in suspension in the current or deposited on the streambed. Sediment load —A general term that refers to material in suspension and/or in transport. It is not synonymous with either discharge or concentration. (See Bedload). Segment —A relatively long (e.g., hundreds of channel widths) section of a river, exhibiting relatively homogeneous conditions of hydrology, channel geomorphology, and pattern. Stream—A natural watercourse of any size containing flowing water, at least part of the year, supporting a community of plants and animals within the stream channel and the riparian vegetative zone. Streambed —The bottom of the stream channel; may be wet or dry. Subsistence flow —The minimum streamflow needed during critical drought periods to maintain tolerable water quality conditions and provide minimal aquatic habitat space for the survival of aquatic organisms.
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The Science of Instream Flows: A Review of the Texas Instream Flow Program Suspended sediment —Particles that are suspended in the moving water column for long distances downstream. Much of this material settles out when water movement slows or ceases. Time-series analysis —Analysis of the pattern (frequency, duration, magnitude, and time) of time-varying events. These events may be discharge, habitat areas, stream temperature, population factors, economic indicators, power generation, and so forth. Tributary —A stream feeding, joining, or flowing into a larger stream (at any point along its course or into a lake). Synonyms: feeder stream, side stream. Turbidity —A measure of the extent to which light passing through water is reduced due to suspended materials. Water allocation —Determining the quantity of water from a given source that can or should be ascribed to various instream or out-of-stream uses. May be referred to as water reservation in some settings. Water resources —The supply of ground water and surface water in a given area. Water right —A legally protected right to use surface or groundwater for a specified purpose (such as crop irrigation or water supply), in a given manner (such as diversion or storage), and usually within limits of a given period of time (such as June through August). While such rights may include the use of a body of water for navigation, fishing, hunting, and other recreational purposes, the term is usually applied to the right to divert or store water for some out-of-stream purpose or use. Watershed —See Drainage area. Wetted perimeter —The distance along the stream bottom from the wetted edge on one side to the wetted edge on the other measured at a given discharge. SOURCE: Adapted from IFC, 2002.
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