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Home , Antidune, Billabong, Body of water, Channel pattern, Point bar, Revetment

L L unit: fast -turbulent, .... 17

L dimensions, and patterns that determines how water movement as it passes over a steep well it adjusts to and recovers from the changes channel bottom with gradients exceeding L in quantities of flow or . 8%. Most of the water surface is broken by short, irregular plunges creating white- L channel storage Volume of water at a given time water, frequently characterized by very in the channel or over the of large substrates, and a well-defined stepped C in a or reach. longitudinal profile that exceeds 50% in supercritical flow. C channel type A system for characterizing channels based on features such as channel and chute Rapidly flowing water within narrow, C confinement, gradient, and erosional and deposi- steep slots of bedrock. tional processes, such as: C falls Free-falling water with vertical or Confinement Gradient Sediment process nearly vertical drops as it falls over an C Confined >4% Source obstruction. Falling water is turbulent and Moderately appears white in color from trapped air confined 1.5-4% Transport bubbles. C Unconfined <1.5% Response classic falls Well-defined falls over a C Note: See Tables 1-3 for various systems for charac- sheer drop. terizing . C complex falls Falls with a series of drops, channel unit Relatively homogeneous areas of a breaks, or channels. C channel that differ in depth, velocity, and sub- strate characteristics from adjoining areas, curtain falls Falls with a broad, C creating different habitat types in a uninterupted face. channel. C falls Falls within a narrow, confin- fast water-turbulent Channel with a gradient ing channel. C that exceeds 1%. A channel unit of this type ribbon falls Elongate, narrow falls. possesses supercritical flow with hydraulic C jumps sufficient to entrain air bubbles and create . C L L

L rapids (from Helm 1985)

L cascade (from Helm 1985) rapids Moderately steep stream area (4-8% r gradient) with supercritical flow between 15 ~ cascade Highly turbulent series of short falls and 50%, rapid and turbulent water move- L and small scour basins, with very rapid ment, surface with intermittent whitewater

L TABLE1.-Channel Types of Paustian et al. (1983) L Type Hydrology-slope Sediment Valleyform A Sediment source L Precipitation headwaters Upper slopes steep B Precipitation transition zone Slope-valley interface L C Precipitation runoff Sediment Valley bottom D Glacial runoff L High sediment load Glacial outwash valleys E Tidal Sediment deposition Estuarine L C ~ :J 18 ... channel unit: fast water-turbulent, :J -., with breaking waves, coarse substrate, with ..J exposed boulders at low flows, and a some- -, what planar longitudinal profile. -..I -..I-, :J ---, run (from Helm 1985) ..J

sheet Shallow water reach that flows uni- :J formly over smooth bedrock. Also referred --, riffles(from Helm 1985) to as a slipface. -.I slow water Stream channel with a gradient of --.I riffles Shallow reaches with low subcritical less than 1% that is typically deeper than the flow (1-4% gradient) in alluvial channels of reach average with a streambed composed of -.J finer particles that are unstable, character- finer substrates and a smooth, unbroken water ized by small hydraulic jumps over rough surface. bed material, causing small ripples, waves, edgewater A shallow, quiet area along the and eddies, without breaking the surface margins of a stream with water velocity that -.I tension. Stable riffles are important in is low or nonexistent. Edgewater areas are maintaining the water level in the pool typically associated with riffles. immediately upstream of the . embayment An off-channel, -like water high gradient riffle A collective term for body that has a connection (sometimes rapids and cascades. Steeper reaches of narrow) to the stream channel. moderately deep, swift (greater than 4% gradient), and very turbulent . - Generally, these riffles have exposed substrates that are dominated by large boulders and rocks. See cascadeand rapids under fast water-turbulent under the main heading channel unit. low gradient riffle Shallow reaches with swiftly flowing (gradients less than 4%), turbulent water with some partially glide (from Helm 1985) --I exposed substrate, usually cobble or --, gravel. glide A shallow stream reach with a maxi- -.I mum depth that is 5% or less of the average step run Low gradient runs with small (0.5 stream width, a water velocity less than 20 to 2 m) riffle steps between runs. cm (8 in) per second, and without surface turbulence. fast water-nonturbulent Reaches that -J are deeper than riffles, with little or no pool Aquatic habitat in a stream with a supercritical flow. The water surface in gradient less than 1% that is normally such reaches has a smoother, laminar deeper and wider than aquatic habitats appearance. immediately above and below it. run Swiftly flowing stream reach with a dammed pool Pool formed by im- ---' gradient greater than 4%,little to no surface pounded water from complete or nearly agitation, waves, or turbulence, no major complete channel blockage caused by a flow obstructions, approximately uniform beaver , log jam, rock slide, or flow, substrates of variable particle size, and stream habitat improvement structure. A water surface slope roughly parallel to the dammed pool may form by substrate overall . deposition at the of a tribu-

~~ i , I L 0 channel unit ~ 19 0

0 TABLE2.-Channel Types of Rosgen (1996)

0 Type Description Slope

Aa Very steep, deeply entrenched with >10% High relief, deeply entrenched and erosional. 0 debris transport. Vertical steps with deep scour pools and . 0 A Steep, entrenched, step-pool with 4-10% High relief, entrenched and confined. Cascading high energy and debris transport. reaches with frequently spaced deep pools in a 0 step-pool bed morphology. B Moderately entrenched, moderate 2-3.9% Moderate relief, colluvial deposition and (or) [J gradient, riffle-dominated, residual soil, moderate entrenchment, and moderate infrequently spaced pools with width: depth ratio. Predominately rapids with [J very stable banks and profile. occasional pools in a narrow, gently sloping valley. C Low gradient, meandering, point <2% Broad valley with terraces associated with the [J -, riffle-, pool-, alluvial channels floodplain, alluvial soils, slightly entrenched, and with broad, well-defined floodplain. well-defined meandering channel. Riffle-pool [J streambed morphology. D Wide channel with longitudinal and <4% Broad valley with abundant sediment in alluvial [J transverse bars with eroding banks. and colluvial fans, glacial debris, and other depositional features exhibiting active lateral [J adjustment. Da Anastomosing channels that are <0.5% Broad, low-gradient valleys with fine [J narrow and deep with stable banks, and (or) lacustrine soil. Anastomosing geologic very gentle relief, highly variable control creating fine deposition with well-vegetated , and an expansive well- bars that are laterally stable and a broad [J vegetated floodplain and associated floodplain. . [J E Low gradient, riffle-pool with <2% Broad valley-meadow. High sinuosity with stable very efficient and stable well-vegetated banks and floodplain of alluvial [J meandering rate, low width: depth material. Riffle-pool morphology with very low ratio, and little deposition. width: depth ratio. [J F Entrenched meandering riffle-pool <2% Entrenched in highly weathered material with with a low gradient and high gentle gradient and a high width: depth ratio. [J width: depth ratio. Riffle-pool morphology with meandering channel that is laterally unstable with high . [J G Entrenched" " step-pool with 2-3.9% Gully, step-pool morphology with moderate slopes, moderate gradient and low low width: depth ratio, narrow valleys that are [J width: depth ratio. deeply incised alluvial or colluvial material. Unstable with grade control problems and high c rates.

c -prone area Bank-full stage

c range c Q DA E F G 4% <4% c <0.5% <2% ~ 2:4% Cross c section C Plan view L

Stream L types Aa+ L Channel type classification (from Rosgen 1994 with permission of ElsevierScience) L L r= 20 ~ channel unit:slowwater,pool,dammed pool,backwater :J\ :J

TABLE 3.-Channel Types of Montgomery and Buffington (1993) :J

Channel type Description :J Cascade High gradient stream with large substrate where the flow is strongly three- dimensional and energy dissipation is dominated by tumbling jet-and-wake flow ::J and hydraulic jumps. ::J Step-pool A large series of steps created by larger substrate that separate pools with finer substrates. :J Plane-bed Lack of a well-defined that is characterized by long reaches of relatively planar channel bed with occasional rapids. Pool-riffle Undulating channel bed with a sequence of bars, pools, and riffles. :Jf :JI Regime Low-gradient, sandbed channel that exhibits a succession of with increasing flow.

Braided Braided pattern of medial and longitudinal bars that are wide and shallow with a high :J sediment supply. ::J ::J beaver pool Pool formed behind a dam created by beaver. ::J debris pool Pool formed behind an a channel obstruction created by an ::J accumulation of woody debris. ::J landslide pool Pool created due to channel obstruction by materials ::J dammed pool (from Helm 1985) transferred into the channel from adjacent slope or channel failures. ::J tary stream with the river when water velocity decreases. ::J ::J ::J ::J ::J secondary channel (from Helm 1985) ::J backwater (from Helm 1985) secondary channel Relatively small ::J pools formed outside the mainstream backwater (1) A pool formed by water wetted channel, sometimes separated :J backing upstream from an obstruc- by formation of a bar deposited along tion, such as narrowing of the channel the margin of the main channel. Also by a bedrock or boulder constriction. referred to as an abandoned channel :J (2) Abandoned channel that remains or side channel pool. connected to the active main stem :J river. (3) Secondary channel in which side channel Elongated extension off the becomes blocked with the main channel that becomes a :J substrate deposition when water backwater under low streamf1ows ---, velocities decrease as the river sub- when the inflow to the channel ...J sides but the outlet remains connected becomes blocked from sediment with the active main channel. deposition. .-J J1 :=J i L L channel unit: slow water, pool, scour pool, ~ 21

L slackwater pool Pool-like depressions eddy A pool on the margin or off the on the floodplain with beds of rock or main channel of a stream that is L coarse material and higher formed and maintained by strong velocities flowing in a uniform direc- eddy currents. L tion that contain water only during high flow or after floodwaters recede, L more transient in than second- ary channel pools, and may contain L water for only a few days or weeks. C scour pool Pool created by the scouring action of current flowing against an C obstruction, causing an increase in lift and drag forces, a result of flow deflec- lateral scour pool (from Helm 1985) C tion, constriction, or increased local turbulence induced by a nonalluvial C obstruction. lateral scour pool A pool formed by the scouring action of the flow as it is L directed laterally or obliquely to one side of the stream by the configuration C of the channel or a partial channel obstruction. Usually confined to less C than 60% of the channel width. main channel pool A pool covering the C entire channel; typically associated with one bedrock bank and a bend in L alcove (from Helm 1985) the stream.

mid-channel pool A large pool formed L alcove A deeper area along the - by mid-channel scour that encom- line in a larger habitat where the passes greater than 60% of the wetted C stream is generally wide and shallow. channel with low velocity. C Also referred to as a sidepool. channel confluence pool (1) The L location where two streams converge. (2) A pool created by scour where two L channels meet that has more turbu- lence and higher water velocities than L found in many other types of pools. Also referred to as a channel conver- L gence pool. plunge pool (from Helm 1985) L L CORNER POOL plunge pool A pool created by water passing over or through a complete or L nearly complete channel obstruction, and dropping steeply into the stre- ambed below scouring out a basin in L ~ the stream substrate where the flow radiates from the point of water entry. L corner pool (from Helm 1985) This is an example of hydraulic L control in a stream that determines comer pool Pool formed by lateral how energy of moving water shapes a L scour and transverse currents near the channel. Also referred to as a falls pool concave bank of a curve. or plunge basin. L C r 22 ~ channel unit: slow water, pool, scour pool, pocket water

pocket water (from Helm 1985)

pocket water One or a series of small pools in a section of swiftly flowing underscour pool (from Helm 1985) water containing numerous obstruc- tions such as boulders or logs which create eddies or scour holes in the chemical oxygen demand (COD) Represents the channel substrate. Typically found in reduction capacity of organic and inorganic cascades and rapids. matter present, and is the amount of molecular oxygen required to stabilize the proportion of the residual pool The pool portion that lies sample which is susceptible to oxidation by a below the elevation of the down- strong chemical oxidant. stream outlet crest.

straight Straight, elongated pool in the chemical stratification Layering of water in a center of a channel that is created by because of density differences or differential concentrations of dissolved substances with an upstream constriction. depth.

chemocline See chemoclineunder stratification.

chronic toxicity Sublethal toxicity of long dura- tion that adversely affects an organism and may eventually lead to death. The sublethal toxicity is reflected through changes in productivity and population structure of a community. trench (from Helm 1985) chunk rock Formation of mixed sized, irregular- shaped rocks caused by gravity or erosion, trench A relatively long, deep slot-like usually found at the base of a bluff or cliff. depression in the streambed, typically with a V-shaped channel, coarse- grained or bedrock substrates, and high water velocities. Such reaches are usually found in highly confined, often bedrock-dominated channels.

underscour pool Form of scour pool created by a log or other obstruction near the surface that causes the water

to be deflected downward, scouring chute (from Helm 1985) out a pool in the substrate. Also referred to as an upsurge pool. chute (1) A narrow, confined channel through channel width Seechannelwidthunderdimensions. which water flows rapidly. (2) A rapid or quick descent in a stream, usually with a bedrock charco Seecharco under pond. substrate. (3) A short straight channel which See checkdam under habitat bypasses a long bend in a stream, and is formed enhancements. by the stream cutting across a narrow area L C cold ... 23 C between two adjacent bends. See also chute under closed basin A basin without a surface outlet, L fast water-turbulent under channel unit. from which water is lost only by evaporation or percolation. cienagas See cienagasunder wetlands. C closed lake See closedlake under lake. Rounded, bowl-like depressions in moun- C tains that are created by weathering, erosion, and clump A relatively dense aggregation of vegeta- glacial action. tion of the same species. See also clump under C large organic debris and remote sensing. cirque lake See cirquelakeunder lake. r: cluster See cluster under remote sensing. class See classunder remote sensing. r: coarse load See coarseload under sediment load. classic falls See classicfalls under fast water- L turbulent, falls under the main heading channel coarse particulate organic matter See coarse unit. particulate organic matter (CPOM) under organic C particles. clast An individual particle, detrital sediment or a C , initially produced by the coarse woody debris See large organic debris; also disintegration of a larger mass of bedrock, a synonym for large woody debris. classified according to size. C coast Land next to the . C clay Natural earthy material which is plastic when wet, and consists essentially of hydrated silicates coastal delta floodplain See coastaldeltafloodplain of aluminum, less than 4 j.Lm.Compare with under floodplain. C other substrate sizes under substrate size. coastal lake See coastal lakeunder lake. C clay bottom Bottom composed of clay or clay-like material. coastal plain A relative flat area, or plain, extend- C ing along a coast. cleanwater association An association of organ- C isms found in any natural, unpolluted environ- coastline Shape or pattern of an coast. ment that is characterized by species sensitive to C environmental changes caused by contaminants cobble Stream substrate particles between 64 and or pollutants. 128 mm (2.5-5 in) in diameter. Compare with C other substrate sizes under substrate size. cliff The high steep face of a rocky mass overlook- C ing a lower area; a precipice. See bluff. coefficient of storage See coefficientofstorage under . C The meteorological conditions including temperature, precipitation, wind, pressure, coffer dam Temporary structure constructed in a C evaporation, and transpiration that prevail in and water body to provide a dewatered area for characterize a location. construction of structures such as bridges. C climatic year A continuous 12-month period cohesion State in which particles of a single C during which a complete annual cycle occurs. substance are held together by primary or The u.S. Geological Survey uses the period secondary valence forces. C October 1 through September 30 in the publica- tion of its records of as a water year. col A pronounced dip in a ridge, or between two See water year. peaks, connecting a neck of land; often formed at C a divide where water courses flow in opposite climax succession stage See climax succession stage directions. C under succession. cold monomictic See coldmonomicticunder C clinograde See clinogradeunder stratification. mixing.

C clinolimnion See clinolimnion under stratification. cold spring Seecoldspringunder spring. C C .u :J 24 ~ coldwater fishes ::J coldwater fishes A broad term applied to fish compensation level Depth in a water body at ::J species that inhabit waters with relatively cold which the available light is reduced enough to temperatures (optimum temperatures generally cause photosynthesis to equal respiration. Also :J between 4-15°C (40-600P). Examples are salmon, referred to as the compensation point. trout, chars, and whitefish. Compare with :J coolwater fishes, warmwater fishes. competence Maximum size of particle that a stream can carry, which depends on water :J cold water lake See coldwaterlakeunder lake. velocity and gradient. Also defined as the critical stress necessary for grain movement. :J collectors See collectorsunder macroinvertebrates. complex falls See complexfalls under fast water- :J colloidal Particles which are 10-7to 5xlO-J;mm in turbulent, falls under the main heading channel diameter, larger than most inorganic molecules, unit. :J and that usually remain suspended indefinitely in the water column. complexity Term used to describe the presence of ::J a variety of habitat types within a defined area of colluvial Gently inclined surface at the base of a a waterbody. Increased complexity provides ::J slope that represents a transition zone between habitat for a greater variety of organisms or life . Colluvium is characterized by erosion stages, and is usually an indicator of better :J and transport, and downslope sites of deposition. habitat health. See also colluvial under streambank material. compound meander See compound meanderunder ::J meander. colluvial soil Recently transported soil derived :J from material eroded and deposited locally concave bank See concavebank under streambank. through sheet flow. In its extreme form, such as :J avalanche or landslide, the soil comprises concretion A localized concentration of chemical material of many sizes. compounds (e.g., calcium carbonate and iron :J colluvium A general term for loose deposits of oxide) in the form of a soil grain or nodule of soil and rock moved by gravity (e.g., talus). See varying size, shape, hardness, and color; concre- :J also colluvium under valley segments. tions of significance in hydric soils are usually iron oxides and manganese oxides occurring at :J colonization The establishment of a species in an or near the soil surface, the result of fluctuating water tables. area not previously occupied by that species. :J color The quality of water with respect to reflected conductivity A measure of the ability of a solution :J or refracted light, measured as a wavelength to carry an electrical current. Conductivity is pattern or hue. dependent on the total concentration of ionized ::J substances dissolved in the water and is mea- community An assemblage of plants and animals sured as microsiemens per centimeter. ::J occupying a given area; two or more populations of organisms interacting within a defined time conduit A pipe, tube, or the structure for convey- :J and space. ing water or other fluids. :J community tolerance quotient (CTQ) See commu- confined See confined under confinement. nity tolerancequotient (CTQ) under biological indices. confined An aquifer that is restricted in :J size by impervious materials. ::J compaction An increase in the density of a confined channel See confined channel under material by reducing the voids between the channel geometry. particles. The relative density of bed material, :J usually caused by sedimentation, mineralization, confined meander See confined meander under or imbrication. meander. :J compensation Creation or restoration of wetland confinement Degree to which the river channel is ::J areas that are equivalent to areas and functions of limited in its lateral movement by valley walls or destroyed wetlands. relic terraces. :J :J ::J C L controlstructure:gate, flapgate ~ 25 L channelization Deepening an existing stream river channel is prevented from migrating C channel or creating a new stream channel by laterally within the valley, usually by a bedrock human activity to increase the rate of runoff or ridge protruding from the valley wall. to lower the water table. C consumptive water use Occurs when water is confined channel A stream that is in continu- removed and not returned. L ous or repeated contact at the outside of major meander bends. contamination Presence of elevated levels of L entrenched channel A stream bend that is in compounds, elements, physical parameters, or substances that make the water impure or L continuous contact with bedrock valley walls unsuitable for use. or terraces. contents Volume of water in a . Unless L frequently confined channel A stream that is frequently confined by the valley walls or otherwise indicated, reservoir content is com- t: terraces. puted on the basis of a level pool and does not include bank storage. L secondarily confined channel A stream channel that has down into deposited contiguous habitat Habitat able to provide the life t: because a controlling structure has needs of a species that is distributed in a continu- been lost. ous or nearly continuous pattern. C unconfined channel A stream channel that is continuous gully Seecontinuousgully under gully. not touching the valley wall or terrace and is L capable of lateral migration. continuous stream See continuous stream under stream. t: confluence The location where two streams flow together to form one. contour An imaginary line of constant elevation C related to the surface of the earth. conglomerate Cemented material; rock consisting t: of rounded and waterworn gravel imbedded in a controlling breaching See controlling breaching finer material. C under breaching. conjugate points (conjugate principle points) See control station Any streamflow measurement site L conjugate points (conjugate principle points) under where a regulatory base flow has been estab- remote sensing. lished. C connate water Water trapped in deep geological control structure Artificial structure designed to sediments at the time the sediment was C regulate and control the movement of water. deposited. draft tube A conduit extended from a turbine. C connectivity Water exchange between the river channel and the associated floodplain. drop inlet A water level control structure with C a vertical tube connected to a horizontal tube consequent stream See consequent stream under that discharges through a dike or dam. L stream. drum gate A circular gate at the entrance of a L conservation pool The minimum water level that spillway. is normally reserved behind a dam for a variety gallery Area of a water intake structure behind L of purposes. a trash rack where water is distributed across L conservation storage Storage of water for later the face of a screen to prevent fish and small release for useful purposes (e.g., municipal water debris from entering the water system. L supply, power, or irrigation) in contrast with gate Moveable structures used to control the storage of water used for . movement, storage, and drainage of water. C constriction (1)A reduction in the channel width flap gate Moveable gate at a right angle to a L bya resistant structure. (2) Location where the pipe that responds to a change in flow. The L: C . 26 ~ controlstructure:gate,radialgate

current opens the gate to drain and pushes equipment of a power plant or other industrial the gate against the pipe to prevent re-entry facility. of water. coolwater fishes A broad term applied to fish radial gate A gate on pivotal arms. species that inhabit waters with relatively cool roller gate Similar to a sliding gate but temperatures (optimum temperatures generally operating on rollers. between 10 and 21°C (50 and 70°F). Compare with coldwater fishes, warmwater fishes. sliding gate Horizontal gate that is hoisted up or down between guides. copropel See gyttja.

high tube overflow Horizontal tube on a small coriolis effect (1) Force deflecting water currents impoundment that can accommodate spill. as a result of the earth's rotation. The deflection is natural spillway Natural, undisturbed ground to the right in the Northern Hemisphere and to sufficiently firm to handle overflow from an the left in the Southern Hemisphere. impoundment. (2) A force acting at right angles to horizontal path of particles in motion. ogee Spillway with an S-shaped . comer pool See cornerpool under slow water, pool, ~. outlet tower Structure that provides water scour pool under the main heading channel unit. control to a powerhouse inlet. --.. penstock Intake for a turbine. corrasion (1) The wearing down of underwater surfaces by chemical solutions. (2) The lateral --.. ski jimp Spillway shaped like a ski jump. and vertical cutting action of water courses, spillway Part of a control structure designed to through abrasive power of their loads. (3) The --.. allow water to spill over a dam without wearing down of underwater surfaces through weakening it. natural friction, as in the moving of --' . Sometimes referred to as . ~ stop log Box, logs, or planks with a drain pipe --' at the bottom that extends through the wall of counter dam A small wall built across the apron of an impoundment. the foot of a key dam to prevent it from being .... tin whistle Vertical riser tube connected to a undermined by erosion. -oJ horizontal tube through the wall of an im- course The direction of flow of water across the poundment. Stop logs are placed around the --, earth's surface. --' I riser so that the water level is higher than the top of the riser allowing water to spill over the A small indentation or recess in the shoreline ----. J logs into the vertical tube. of an aquatic system, sea, lake, or river; a shel- --. trash rack Protective structure used to intercept tered area. See , bay, embayment. J logs and other debris. cover Structural materials (boulders, logs, or -J----. turbine Rotary motor for converting the energy stumps), channel features (ledges, vegetation), of falling water into electricity. and water features (turbulence or depth) that ---' convex bank See convex bank under streambank. provide protection for aquatic species. See also cover under habitat enhancements. conveyance loss Loss of water in transit from a crater lake See calderalakeand volcaniclakeunder conduit or channel due to leakage, seepage, lake. evaporation, or evapo-transpiration...... convolution The sinuosity of a stream channel. creek A smalliotic system that serves as the The convolution index is the same as the sinuos- natural drainage course for a small drainage basin. See brook. ity index. See coolingpond under pond. creep Gradually and generally imperceptible downhill movement of soil and loose rock; a slow cooling water Water used to cool operating moving type of landslide. L L dammed pool <411 27 L creeping flow Seecreepingflow under flow. cuesta Coastal plain ridge that is steepest toward L the continent, due to the differential erosion of crenocole An organism living only in spring sedimentary deposits that gently dip seaward. environments. C cultural Accelerated addition of crenogenic meromixis See crenogenicmeromixis nutrients to a water body by human activities. L: under mixing. culvert A passage, usually a pipe, constructed t:: crenophile An organism that prefers spring beneath a road, railroad, or to transport environments but may be found in similar types water. c: of habitat. current Water moving continuously in one t:: crest (1) Top of a dike, spillway, or weir to which direction; the speed at which water is moving. water must rise to pass over. (2) The summit or Seevelocity. t: highest point of a wave. (3) Highest elevation reached by flood waters flowing in a channel. curtain falls Seecurtain falls under fast water- t: turbulent, falls under the main heading channel crib See cribunder habitat enhancements. unit. t: cribwell Seecribwell under habitat enhancements. cusps Triangular deposits of sand, or other current c: drift, spaced along a shore. critical depth Minimum depth that can occur as c: water flows over the top of a boulder, log, or See cut bank under streambank. crest of a spillway. Occurs slightly upstream of c: the brink. cutoff lake See cutoff lake under lake. c: critical flow State of water flow when one or more cutoff wall A wall (usually ) installed properties such as velocity undergoes a change. downstream of culverts to keep water and materials in place. c: critical location Location along a stream with a minimum concentration of dissolved oxygen. cutting back Upslope movement of a stream c: channel due to erosion. Seealso headcut. critical reach See critical reachunder reach. L cycle of erosion progressive stages in erosion of a critical slope Slope that sustains a uniform critical . c: flow.

t: critical velocity Seecritical velocity under velocity. Also referred to as critical flow. ~d t: cross- A ditch excavated across the road at an Dso See dsoor Dsounder sediment load. t: angle and depth sufficient to divert both road and ditch water off or across the daily Seedaily dischargeunder discharge. t: road. dam A barrier obstructing the flow of water that c: cross-over bar Seecross-overbar and transverse bar increases the water surface elevation upstream of under bar. Definition is provided with transverse the barrier. Usually built for water storage or to c: bar under bar. increase the hydraulic head. cross-sectional area See cross-sectionalareaunder damaging flood A flood of magnitude exceeding L: dimensions. the normal maximum discharge.

c: crown The growing tip of a tree. dam-break flooding Seedam-breakflooding under flooding. L: cryogenic lake See cryogenic lake under lake. dammed pool See dammedpool under slow water, L: cryptodepression Portion of a lake below sea level. pool under the main heading channel unit. C C ~- 28 ~ Darcy'slaw

Darcy's law See Darcy's law under groundwater. . This boundary is 2 m (6.6 £1)below low water or at the edge of emergent macrophytes, deadhead A log floating at or near the surface that whichever is deeper. Any open water in which presents a hazard to boating. See also deadhead the mean water depth exceeds 2 m (6.6 £1)at under large organic debris. mean low water in nontidal and freshwater tidal areas, or below extreme low water at spring dead lake Seedeadlakeunder lake. in salt and brackish tidal areas, or the maximum deadman A structure of wood, metal, or concrete depth of emergent vegetation, whichever is greater. that is buried in the ground to serve as an anchor for cables or other lines. deepwater zone An area of fairly great depth. dead storage The volume in a reservoir below the lowest controllable level. deflector See deflectorunder habitat enhancements. dead water Water without measurable currents. (1) Geologic process by which Generally refers to water in a stream behind an streambeds and are lowered in obstruction. elevation by the removal of material. (2) A decline in the viability of ecosystem func- debris Any material, organic or inorganic, floating tions and processes. Compare with . or submerged, moved by water. Geologists and hydrologists have used this term in reference to degraded channel See degradedchannel under inorganic material; more recently workers channel geometry. have used the term in reference to organic material. deliverability Likelihood that, as a result of one or more land-use practices or through cumulative debris avalanche See debris avalancheunder effects, a given amount of wood, water, sediment, landslide. or energy will be delivered to fish habitat in streams. debris fall See debrisfall under landslide. delivered hazard Adverse changes in the amount See debrisflow under landslide. or location of wood, water, sediment, or energy being delivered downstream that may affect fish, debris jam or dam See debrisjam or dam under , or capital improvements. landslide. delta Flat plane of alluvial deposits between the debris loading The quantity of debris located branches at the mouth of a river, stream, or creek. within a specific reach of stream channel due to See . natural processes or human activities. delta bar See delta bar under bar. debris pool See debris poolunder slowwater, dammed pool under channel unit. delta kame Deposit with the form of a steep, flat- debris slide See debris slide under landslide. topped hill located at the front of a retreating continental . debris torrent See debris torrent under landslide. delta lake See delta lakeunder lake. deck Walking or work surface on an impound- dendritic channel See dendritic channel under ment, dock, or boat. . deep-seated creep See deep-seatedcreepunder landslide. density (1) Number of individuals per unit of surface area or volume. (2) Mass per unit volume. deep-seated failures See deep-seatedfailures under landslide. density current A flow of water maintained by gravity through a large , such as a deepwater habitat Permanently flooded lands reservoir or lake, that retains its unmixed identity lying below the deepwater boundary of wet- because of density differences. c c diffusivity ... 29

c density stratification Seestratification. desiccation Process of dehydration or drying up.

C deposit An accumulation of organic or inorganic design high water level Elevation of the envel- material resulting from naturally occurring oped profile of the 50-year flood, or flood series, L: biological, chemical, or physical processes. routed through the reservoir with a full conserva- tion pool after 50 years of sediment, or the [: depositing substrate Bottom areas where solids elevation of the top of the flood control pond, are being actively deposited, often in the vicinity whichever is higher. t: of discharges. destratification See destratification under t: deposition Settling of material from the water stratification. column and accumulation on the streambank or [: bed. Occurs when the energy of flowing water is detention reservoir An ungated reservoir for unable to support the load of suspended temporary storage of flood water. L: material. detention storage Volume of water, other than [: deposition zone Location along an erosion depression storage, flowing on the land surface transport network where materials are deposited and that has not yet reached the channel. L: because water velocity and volume are insuffi- cient to retain the materials in suspension. detrital sedimentation Deposition of organic [: sediments. depression Any relatively sunken part of the L: earth's surface, especially low-lying areas sur- detritus A nondissolved product of disintegration rounded by higher ground, that may be natural or wearing away. Pertains to small organic or constructed. particles like leaves and twigs. Detritus may [: pertain to material produced by erosion, such as depression storage Volume of water contained in soil, sand, clay, gravel, and rock, carried down a [: natural depressions on the land surface (e.g., , and deposited on an outwash fan or L: ). floodplain. dewatering Removal of water from a site. L: depth See depthunder dimensions. depth: area ratio Seedepth: area ratio under diadromous Life history strategy, that includes [: dimensions. movement between fresh- and saltwater, where organisms exhibit two migrations to spend [: depth integration See depth integration under various life stages in different ecosystems. sediment load. Compare with anadromous, catadromous, c oceandromous, potamodromous. depth of scour A relationship of the depth of c scouring to the bed load transport rate: diagonal bar See diagonal bar under bar. diamond bar See diamond bar under bar. Qb . c ds = u w: b ps (1 p)' diamond-braided bar Seediamond-braided bar C under bar. ds = depth of scour; L ub = average bed load velocity; diatom Microscopic algae with a silaceous skeleton Qb =bed load transport rate; that occurs as plankton or attaches to substrate. C W = width of stream; p =particle size. diel Pertaining to a 24-hour period or a regular C occurrence in every 24-hour period. See diurnal. deranged channel See derangedchannel under diffuser A structure at or near the end of an C channel pattern. outfall designed to improve the initial dilution, desalinization Removal of salts from brackish or dispersal, or mixing of discharged effluent. C marine waters. diffusivity Rate at which a substance or tempera- C desert river Seedesert river under river. ture change will be transmitted through the water. L. C r l 30 ~ digger log digger log See digger log under habitat enhance- of flow. Multiple channel widths are summed ments. Compare with digger log under large to represent total channel width. organic debris. cross-sectional area Area formed by the width digital classification See digital classificationunder and depth of a stream, channel, or , remote sensing. measured perpendicular to the center line of flow. digital enhancement See digital enhancement depth Dimension of a water body measured under remote sensing. --' vertically from the surface to the bottom. digital terrain model See digital terrain model depth: area ratio Area of a lake, by depth under remote sensing. classification,expressed as a ratio to the total lake area. digitizing Seedigitizingunder remote sensing. drainage basin shape (Rf) Ratio of a basin's dike An embankment for controlling water. Also area (A) to the square of its maximum used for any impoundment structure that length (L): ---< completely spans a navigable water. Compare R =A/U. with berm under habitat enhancements. f ------.J dilution Reduction in the concentration, or hydraulic depth (D) Ratio of the cross-sectional area (A) divided by the width (W): strength, of a substance by increasing the propor- J tion of water in the mixture. D=A/W. ------J dimensions The linear, areal, and volumetric hydraulic radius (R) Ratio of the cross- -, features of an aquatic habitat as measured on sectional area (A) divided by the wetted -J both the horizontal and vertical scale. perimeter (P): R =A/P. :J acre-foot A unit for measuring the volume of water, equal to the quantity of water required lake volume An estimation of the total volume -.J to cover a surface area of one acre (0.4047 ha) of a lake: to a depth of one foot (0.3048 m) and equal to -.J 43,560 cubic feet, 325,851 gallons, or 1,233 v = (h/3) (AI + Az + [AIAz]\O); cubic meters. -, h =vertical depth; -J area Quantitative measurement of the surface Al =area of the upper surface; ~ -J of a body of water or drainage basin. Az = Area of lower surface. ----- average depth Total of all depth measurements lake width Distance on the lake surface from -J divided by the number of measurements taken shore to shore at right angles to the length. at a site on a water body. ~ length Distance along the thalweg of a stream average width Total of all width measurements channel or the longest straight axis between divided by the number of measurements taken the of a lake. at a site on a water body. maximum bank height Maximum vertical bank depth Vertical distance between the water distance from the water surface to the top of surface and the floodplain. the highest bank. bank width See channel width under maximum depth Greatest depth of the body of dimensions. water. In streams, the greatest water depth at the sample location. basin slope Change in depth per unit of horizontal distance. maximum elevation Highest point in the sample breadth See width under dimensions. area, or the highest point in a watershed. maximum lake length Single line distance on channel width Horizontal distance along a the lake surface between the most distant transect line from bank to bank at the bankful points on the lake shore. stage, measured at right angles to the direction c c dimensions:volumedevelopment ~ 31

maximum width Greatest measurement from 88.6 X Z c Z=- m shore to shore along a line perpendicular to r A\O c the thalweg of a stream or the greatest mea- surement across other bodies ofwater. (Rr) Ratio of a basin's length and [J altitude change in the basin: mean lake depth (Z) Volume (V) divided by t:J the surface area (A): Rr = h/L ; ~ Z=VjA. h = difference in elevation between the and the highest point in Compare with averagedepthunder dimensions. c; the drainage mean lake width Quotient of the lake area L =maximum length of a basin divided by the maximum length. c; shoreline: area ratio Ratio of lake shoreline mean stream length Length of a stream seg- length to area of lake surface. c; ment along a line extending from the point of origin in a stream along the center of the shoreline development (DL) Ratio of a lake's c; channel to the point where the measurement is shoreline length (L) to the circumference of a terminated. circle having the same area (A) as the lake: c; L median depth Midpoint elevation between the L: maximum depth and the surface on a line DL = 2(1TA)\O' from shore to shore. I: shoreline length Length of the perimeter of a median width Midpoint width between the lake. start of measurements and the maximum I: measurements. sinuosity An index (K) of a stream's meander I: as a function of stream length or valley profile. minimum bank height Minimum vertical L S distance from the water surface to the top of K - ---E.- -1!.. I: the lowest bank. - Lv - Sc '

I: pool: riffle ratio Ratio of the surface area or Lc= channel length; length of pools to the surface area or length of Lv = valley length; [:; riffles in a given stream reach, frequently Sv = valley slope; expressed as the relative percentage of each Sc = channel gradient. [:; category. stream width Distance between the two [:; pressure head Relative pressure (excess over margins of flowing water in a stream at right atmospheric pressure) divided by the unit angles to the flow. [:; weight of water, expressed in units of height. top width Width of a stream at the water radius of curvature (r) Radius of the curve that surface that varies with changes in flow. L: describes the symmetrical meander of a stream or river. Is often used to evaluate channel valley floor width index (VFWI) Measure, in channel widths, of the variation in the width [:; resistance to erosion or the migration rates of bends and . of a valley floor. t: (w + W ) L K-1.5 VFWI= ac fp. r m = . Wac' ' [:; c 13 (K -1) \0 ' Wac= width of active channel; [:; Lm= meander wavelength; K = sinuosity. Wfp=floodplain width; Wac*= average width of active channel for t: all reaches at each site. relative depth (Zr) Maximum depth (Zm)as a percentage of the mean diameter of a lake. c; volume development Comparison of the shape With diameter expressed in terms of lake area of a lake to the shape of an inverted cone equal t: (A), the formula is: to the lake's surface area. t: t:

~ =:J 32 ... dimensions: wetted cross section :J

wetted cross section Total cross-sectional area annual minimum daily discharge Lowest :J through which a river flows above the bed at a discharge recorded for any single day during a specific discharge. one-year period. :J Length of the wetted contact daily discharge Totaldischarge from midnight :J between a stream of flowing water and the to midnight for a continuous recording. stream bottom in a vertical plane at right hydraulic discharge An estimate of water :J angles to the direction of flow. volume (Q) passing by a point on a stream or wetted width Width of a water surface mea- river: ::J sured perpendicular to the direction of flow at Q=WDu; :J a specific discharge. Widths of multiple W = width; -, channels are summed to represent the total J wetted width. D = depth; u = velocity of flow. width Measure of the cross section shape of a :J stream channel or across the narrow dimen- Seestreamdischargeunder dischargefor an -,J sion of a lake, pond, or reservoir. alternate meaning of Q. width: depth ratio An index of the cross instantaneous discharge Discharge at a par- :J section shape of a stream channel, at bankful ticular point in time. level. mean monthly discharge Average volume of :J dimictic Seedimicticunder mixing. water discharged per month during the given ::J year. Expressed as hectares per meter. dip A hollow or depression in a land form. monthly mean discharge Average volume of :::J dipslope Conformation of land surface features water discharged per day during the given month. with the shape of underlying bedded materials. :::J stream discharge An estimate of water volume direct solar radiation See direct solar radiation :::J (Q) passing a point on a stream or river: under solar radiation. Q=AVn; :J direct toxicity Toxicity that has a direct-rather A = cross section area of stream channel; than indirect-effect on organisms, for example, :::J V =velocity of water; chronic exposure to toxicants from contaminated n = Manning's bed roughness constant. food organisms. :::J See hydraulic dischargeunder discharge for an discharge (1) Rate at which a volume of water alternative meaning of Q. ::J flows past a point per unit of time, usually expressed as cubic meters per second or cubic discharge area An area where water is released :J feet per second. (2) Intentional or unintentional into surface water, groundwater, or the release of substances into a waterway or water atmosphere. :J body that can occur from spilling, leaking, pumping, pouring, or dumping. (3) Any addition disclimax Term applied to a situation where :J of dredged or fill material into a waterway or recurring disturbances, such as grazing or water body. periodic burning, exert a predominant influence :J in maintaining the species composition and annual maximum daily discharge Highest density of vegetation. :::J total daily discharge during the year. discontinuity layer See discontinuity layerunder :J annual maximum instantaneous discharge stratification. Highest discharge recorded in a year. discontinuous gully Seediscontinuousgully under :J annual mean discharge Sum of total daily gully. discharges for a year divided by the number of :J days in a year. Also, the total annual discharge dished out bank Streambanks that have a bank divided by the number of seconds in a year. angle greater than 90°. See streambank. :J =:J L L ~ 33

L dispersal Multi-directional spread, at any time that occur every day. (2) May be applied to scale, of plants or animals from any point of organisms that are active during the day. See diel. L origin to another, resulting in occupancy of other areas in their geographic range. Differs from diversion An artificial structure, such as a canal, L: emigration or immigration where movements are embankment, channel, pipe, or other conduit, for one-way from or into an area, respectively. taking water from a stream or other body of L: water to another location. dispersion (1) Separation or scattering of particles L: in water. (2) Active movement of individual diversity Variation that occurs in plant and animal organisms into adjoining areas. taxa (i.e., species composition), habitats, or t: ecosystems within a given geographic location. Quantity of material dissolved in a t: specified volume of liquid. diversity index Any of several numerical mea- sures of animal or plant diversity in a given area. t: dissolved organic matter See dissolved organic Often, the relationship of the number of taxa matter (DOM) or dissolved organiccarbon (DOC) (richness) to the relative number of individuals t: under organic particles. per taxon (evenness) for a given community or area. See diversity index under biological indices. dissolved oxygen Concentration of oxygen Also, see habitat quality indices. t: dissolved in water, where saturation is the t: maximum amount of oxygen that can theoreti- divide Topographical boundary in a catchment cally be dissolved in water at a given altitude and area that is related to the highest elevation t: temperature. Expressed as milligrams per liter or surrounding the area. The hydrological divide as percent saturation. would include subsurface as well as . See drainage divide. t: dissolved solids Total of disintegrated organic and inorganic material that is dissolved in water. t: See total dissolved solids. dock A narrow walk or platform supported on posts or floats extending from the shore into a t: distorted meander See distorted meander under water body for the purpose of anchoring, dock- meander. ing, and landing boats, and for loading equip- t: ment and people into boats. Seedistributaryunder stream. t: doline lake See doline lakeunder lake. distribution Occurrence, frequency of occurrence, c: position, or arrangement of animals or plants domain Region or area that is characterized by a within an area. May also be applied to a rate such specific feature, such as the type of vegetation, c: as the number per unit of area or unit of time. aquatic system, or wildlife. c: distrophic (dystrophic) See distrophicunder domestic water supply Water from wells, streams, trophic. , or used for human consumption c: and other uses in homes. disturbance A force that causes changes in habitat c: or community structure and composition dominance and taxa (OAT) See dominance and taxa through (a) natural events such as fire, flood, (DAT) under biological indices. c: wind, or earthquake; (b) mortality due to insect or disease outbreaks; or (c) human activities such dominant discharge Stream discharge level(s), c: as agriculture, grazing, logging, mining, road usually the bank-full flow, that in aggregate is construction, etc. sustained over a long enough time period to form and maintain a relative equilibrium in a c: ditch A long, narrow excavation in the ground natural channel by dislodging, transporting, and (usually an open and unpaved channel, trench, or distributing bed materials. Also referred to as a t: waterway smaller than a canal) for conveying formative discharge. water to or from a specific location for purposes c: such as drainage or irrigation. downcutting Water erosion that deepens an existing channel or forms a new channel where C diurnal (1) Refers to events, processes, or changes one did not exist previously. L C r --. -.J 34 ~ down log --. -.J

--' down log See down log under large organic debris. culverts, open-faced culverts, bridges, and ditches. downstream link See downstream link under link. -..J drainage system Natural or artificial channels that draft tube See draft tube under control structure. transport water out of a basin.

dragline Equipment used to excavate and remove drainage texture Expression of the space between -J bottom materials from a water body. The materi- stream channels above a reference point in a als are removed with a bucket that is pulled stream. Determined by dividing the number of toward the piece of equipment with cables. stream crossings by the length of a contour.

drain (1) To remove and carry away surface or drained A condition where ground or surface subsurface water. (2) An artificial channel or pipe water has been removed by artificial means to used to transport surface or subsurface water. See the point that an area no longer meets the canal; ditch. hydrological criterion of a wetland.

drainage (1) A watershed that contains all tribu- draw A long, wide topographic feature formed by tary rivers, streams, sloughs, , and lakes perennial or intermittent surface runoff, without that drain a given area. (2) The process of down- reference to the presence or absence of water. ward removal of surface and subsurface runoff --' water from soil either by gravity or artificial drawdown (1) Lowering of water levels stored means. behind a dam or other water control structure. -... (2) Change in reservoir elevation during a -J drainage area Total land area, measured in a specified time interval. (3) Local decline of a horizontal plane, enclosed by a topographic water table due to water withdrawal. divide, from which direct surface runoff from :J precipitation normally drains by gravity into a dredge (1) Act of sampling or excavating material wetland, lake, or river. Also referred to as a from the bottom of a water body. (2) Equipment :J catchment area, watershed, and basin. In the case used for sampling or excavation material from of transbasin diversions, the drainage area would the bottom of a water body. :J include water from all diverted streams. See catchment area. drift (1) Dislodgement of aquatic invertebrates -J and fish from a stream bottom into the water drainage basin The total surface land area drained column where they move or float with the :J by a stream or river from its headwater divides to current. (2) Any detrital material transported by I its mouth. See catchment basin. water current. (3) Materials deposited ashore by ~ wind or water currents in a pond, lake, or --, drainage basin density (Dd) Ratio of total drain- reservoir. (4) Woody debris that has been modi- -.J age channel length (miles or kilometers, L) to fied by abrasion in a stream. Sometimes, this total drainage basin area (square miles or square term refers to floating materials or surface water -..J kilometers, A): set in motion by the wind.

Dd= LlA. drift line A visible elongated collection of floating Synonymous with stream density. debris, detritus, or organic matter that results when opposing forces such as wind and current drainage basin shape See drainage basin shape meet along a bank contour (Le., parallel to the under dimensions. shoreline of a lake or the flow of a stream) that marks the height of an inundation event or drainage divide The boundary formed along a streamflow. topographic ridge or along a subsurface forma- tion that separates two adjacent drainage basins. drift organism Benthic organisms temporarily suspended in water and carried by the current of drainage lake See drainage lakeunder lake. streams.

drainage structure A structure to remove runoff drop, See checkdamunder habitat water composed of metal, concrete, or wooden enhancements.

-,< E= ebullition

L drop inlet See drop inletunder control structure. when water fills most of the interspaces between soil particles. L drop-off A vertical or steepdescentin the bottom of a water body. duty of water In irrigation, the quantity of water C required to satisfy the irrigation water require- drowned valley Valley carved in land by a stream ments of land. It is expressed as the rate of flow C and later flooded by a rise in sea level. required per unit area of land, the area which can be served by a unit rate of flow, or the total C drum gate Seedrumgateunder control structure. volumetric quantity of water in terms of depth, required during the entire or portion of the drumlin A tear-drop shaped landform that results C irrigation season. In stating the duty, the crop, the from the deposit of glacial till or other drift with location of the land in question, and the soil type the tapered end pointing in the direction of the C are usually specified. glacial movement. [: dy Soft, fine-grained sediment (composed almost dry dam A dam designed for flood control that entirely of organic matter) in lakes, , does not provide permanent water storage. [: , or . Yellow-brown, flocculent, dry ravel See dry ravel under landslide. fibrous, undecomposed plant material with a low [: pH that is derived to a great extent from peat in a dry wash An intermittent streambed in an sedge mat or from other allochthonous C or that contains rainwater for a very short sources. time. C dynamic equilibrium (1) Condition of a system Duboy's equation An equation that calculates the where there is balanced inflow and outflow of t: force per unit of area exerted on the streambed at material. (2) A migrating channel that is in different flows or used to predict the capability of equilibrium in terms of shape,pattern, and C a system to move bed load material. geometry. C dug pond Seedugpondunder pond. dystrophiclake Seedystrophiclakeunder lake. C (1) Summit and sloping sides of a mound, hill, or ridge of loose, unconsolidated, granular C windblown deposits. (2) In streams, bedforms ..e that are generally transverse to the direction of C flow with a triangular profile that advances early succession stage See early successionstage downstream due to net deposition of particles under succession. C from the gentle upstream slope to the steeper downstream slope. move down the stream earth (1) Soft surface materials composed of soil at velocities that are small relative to streamflow. and weathered rock. See ground, soil. (2) Name C for the Planet Earth. dune bar See dune barunder bar. C earth dam A barrier formed by the accumulation C dune lake See dune lakeunder lake. of earth that impedes the flow of water. C dune pond See dune pondunder pond. earthflow Seeearthflow under landslide. duration curve A graphical representation (a earth islands See earth islands under habitat C curve) of the numberof times given quantities enhancements. such as streamflow occurred or a percentage of C eventswithin a time period. The event or quan- earthquake lake See earthquakelake under lake. tity is arranged in order of magnitude along the C ordinate with the time period expressed as a earth slump See earth slump under landslide. percentage along the abscissa. L ebullition Bubbling up of gasesproduced duration of inundation or saturation Length of through the decay of organic matter in the l.. time that water remains above the soil surface substrate. L C ~. :J 36 ~ ecoclimate :J ecoclimate Climate (temperature, humidity, ing habitats or communities with different :J precipitation, winds, and solar radiation) that vegetation, climate, flow, or other features that occurs in a particular habitat or ecosystem. contain an increased biological diversity and :J density of organisms. ecocline Gradual, continuous change in an :J environmental condition of an ecosystem or a edgewater Water that occurs at the interface community. between land and a water body. See also :J edgewaterunder slowwaterunder the main ecosystem Any complex of living organisms heading channel unit. :J interacting with nonliving chemical and physical components that form and function as a natural effluent (1) Discharge of liquid into a water body :J environmental unit. or emission of a gas into the environment. Usually composed of waste material. For ex- :J ecosystem function Any performance attribute or ample, emission of combustion gases into the rate function with some level of biological atmosphere from industry or manufacturing. :J organization (e.g., energy flow, detritus process- (2) Also, may be used to describe a ing, or nutrient spiralling). streamflowing out of a lake or reservoir. :J ecotone Transition zone between two or more effluent flow See effluentflow under flow. :J ecosystems or communities. effluent seepage Diffuse discharge of ectogenic meromixis See ectogenicmeromixis into groundwater or surface water. :J under mixing. Ekman dredge Device for sampling macro- :J invertebrates in bottoms of water bodies with edaphic Pertaining to or affected by geology or soil rather than climate or water. soft substrates. :J Ekman spiral (1) Current drift that is deflected 45° :J from the direction of the wind by geostrophic deflection. (2) Sequence of direction shifts of :J current that is generated by wind, usually downward from a lake surface. Ekman spirals :J are progressively more clockwise in the Northern Hemisphere. :J Ekman transport Refers to drifting currents or eddy (from Helm 1985) organisms in an Ekman spiral. :J eddy Circular current of water, sometimes quite elevation Height above or below sea level at a :J strong, diverging from and initially flowing given point on the earth's surface. Surface water against the main current in streams. Eddies are level in lake or reservoir. ::J usually formed where water flows past some obstruction or on the inside of river bends. eluvial Of, related to, or composed of eluvium or ::J Eddies often form backwater pools, alcove pools, fine weathered rock. or pocket water in rapids and cascades. See eddy :J under slow water,pool,scourpoolunder the main eluvium (1) Deposit of soil, dust, etc., formed by heading channel unit. the decomposition of rock that is found at its ::J place of origin. (2) Soil from which dissolved or eddy flow Pattern of water movement created suspended material has been removed by :J within an eddy. percolating water through the process of eluviation. :J eddy flux Continuous change and movement of water in an eddy. embankment An artificial deposit of natural material, such as a bank, mound, or dike, raised :J eddy return channel See eddyreturnchannel under above the natural surface of the land, and erected ::J channel pattern. along or across a wetted area to divert or hold back water, support a roadway, store water, or for edge effect Ecotone or zone between two adjoin- other similar purposes. See dike and streambank. :J ::J ::J c c enhancement"" 37

c embayment (1) An area of water that is enclosed shear stress Ability of water to mobilize C by the topography of the adjoining land. materials from the bed and banks in streams. (2) Portion of a stream flooded seasonally or Y= pRS; permanently by a reservoir. See arm; backwater I: under slow water, dammed pool under the main p = density of water; heading channel unit; bay; cove. R = hydraulic radius; I: 5 = channel slope. embeddedness Degree that gravel and larger sizes t:: of particles (boulders, cobble, or rubble) are stream power (SP) Stream power at a given surrounded or covered by fine sediment (e.g., location, expressed as joules per second per t: less than 2 mm). meter. t: emergency spillway Wide outlet in the dam of a Sp =pgQS ; reservoir that allows excess water to be passed or t; spilled during periods of high runoff. Often P =fluid density; intended to protect the structural integrity of the g =acceleration due to gravity; t;; dam when storage capacity is high. Q =discharge; 5 = average gradient of the channel. t:; emergent macrophyte Seeemergentmacrophyte under macrophyte. total stream power Availability of energy at a given location along a stream in relation to t: emergent vegetation Rooted aquatic plants with temporal loss of potential energy: some herbaceous vegetative parts that project m/1h t: above the water surface. Also referred to as p=_. /1t ' t: emersed vegetation. emergent wetland See emergent wetlandunder m = mass of water; t: wetlands. Lih = change in elevation above sea level; Lit =change in time. t: emulsion Mechanical mixture of two liquids that do not readily mix, such as oil and water. unit stream power Time-rate loss of potential t: energy per unit mass of water. endemic Species that is unique or confined to a t: specific locality or drainage. U>= pgvs; end moraine See end moraine under moraine. p = fluid density; t: g = acceleration due to gravity; endorheic Interior drainage from which no or s =energy slope of flowing water (usually I; little surface water reaches the sea. assumed to be similar to channel gradient); ~ energy Capacity for work or available power. In v =velocity gradient. streams, the capacity of the water to mobilize and r; move materials. energy dissipation See energy dissipation under energy. t:; energy dissipation Loss of kinetic energy in moving water due to bottom friction, pools, energy efficiency Measure of work accomplished t: large rocks, debris, and similar obstacles that in comparison to energy expended. impede flow. t: enhancement (1) An improvement of ecological potential energy (PE) Amount of energy in conditions over existing conditions for aquatic, t: precipitated water that will be dissipated terrestrial, or recreational resources. (2) Any during its transit to sea level: change that is made for the improvement of a I: structural or functional attribute for a species or PE =mgh ; habitat. Some enhancement activities that result L:: m =mass of water; in a positive impact on a single species or specific g = acceleration due to gravity; component of an ecosystem may negatively L h =elevation above sea level. impact others. C r: t-. :J 38 ~ enhancement flow -J--.. --.. enhancement flow See enhancementflow under flow. epilittoral See epilittoral under littoral. -J --, enrichment Process where discharge or runoff epineuston (1) Microscopic organisms living on -oJ carries nutrients into a water body, enhancing the the upper surface of the air-water interface. growth potential for bacteria, algae, and aquatic (2) See epineuston under neuston. :J plants. epipelic Occurring on the surface of fine sedi- :J entrainment (1)Accumulation or drawing in of ment. See also epipelicunder periphyton. organisms by a current, such as at a power plant -.JI intake. (2) Progressive erosion of the lower layers epiphyte Plant that lives on another plant but is --, in the that results in a corresponding not parasitic. -.J lowering of the thermocline in a stratified lake. --, epiphytic See epiphytic under periphyton. -J entrenched channel See entrenched channel under epipleuston Seeepipleustonunder neuston and confinement. pleuston. :J entrenched stream See entrenched stream under --, stream. epipotamon See epipotamon under potamon. -J entrenchment Stream channel incision from epipsammic See epipsammic under periphyton. :J . epirhithron See epirhithron under rhithron. :J entrenchment ratio Computed index used to epizooic Refers to materials or organisms that live describe the degree of vertical containment of a or dwell on the bodies of animals. :J river. It is the channel width of a flood prone area at an elevation twice the maximum bank-full equilibrium drawdown Ultimate, constant :J depth/bank-full width. draw down that results in a steady rate of pumped discharge. :J environment Combination of physical, chemical, climatic, and biotic conditions that influence the equitability Measure of the distribution of :J development, growth, structure, and vigor of an individuals among the species component in a organism, population, or community. diversity index. Also referred to as evenness. :J eolian See eolianunder streambank material. erosion (1) Process of weathering or wearing :J away of streambanks and adjacent land slopes by epeirogenesis Wide-ranging tectonic events that water, ice, wind, or other factors. (2) Removal of :J can raise large crustal blocks in the earth's rock and soil from the land surface by a variety surface and sometimes create large basins where of processes including gravitation stress, mass :J lakes can form. Similar to orogeny (Le., mountain wasting, or movement in a medium. building) but slower. :J accelerated erosion Rate of erosion that is ephemeral Short-lived or transitory. much more rapid than normal, natural or :J geologic erosion, due primarily to human ephemeral flooding See ephemeralfloodingunder activities. :J flooding. flow erosion Rapid downhill movement of :J ephemeral flow See ephemeralflow under flow. solum (Le., soil above the A and B horizons of the parent soil), along with some parent soil :J ephemeral lake See ephemerallakeunder lake. material, in a highly saturated condition. epibenthos Organisms living at the water- fluvial erosion Erosion caused by flowing :J water. substrate interface. :J geologic erosion Normal or natural erosion epilimnion Seeepilimnionunder stratification. from geologic processes through time. :J epilithic Refers to periphyton assemblages on gully erosion (1) Rapid erosion, usually in brief stones. See epilithic under periphyton. time periods, that creates a narrow channel :J .::J ~ I J L L eurysaline

L which may exceed 30 m in depth. (2) Forma- erosion remnant Material remaining after erosion tion of in surficial materials or bedrock of the surrounding landform. L by a variety of processes including erosion by running water, weathering and the impact of erosion surface Land face that is being eroded. C falling rock, debris slides, debris flows, and other types of mass movement; erosion by escape ladder See escapeladder under habitat C snow avalanches. enhancements. C interill erosion Uniform removal of soil from a escapement Number of fish that survive natural small area by the impact of raindrops or by and human-caused mortality to spawn. sheet flow. r: escape ramp See escaperampunder habitat natural erosion Wearing away of the earth's enhancements. L surface by ice, water, wind, or other agents under natural environmental conditions. C escarpment (1) Relatively continuous cliff or steep normal erosion Gradual erosion of land used slope, produced by erosion or faulting, between two relatively level surfaces. Most commonly, a C by people that does not greatly accelerate natural erosion. cliff produced by differential erosion. (2) A long, precipitous, cliff-like ridge of rock and other C erosion Erosion resulting from movement material, commonly formed by faulting or of soil by a network of small, shallow chan- fracturing. See scarp. L nels. essential elements Collection of habitat elements, C erosion Bouncing of small soil or such as water, food, and shelter, that are essential mineral particles from the action of wind, to the continued existence of a plant or animal C water, or gravity. species; used to describe critical habitat for endangered species. C sheet erosion Erosion of soil from across a surface by nearly uniform action of or estuarine See estuarine under valley segments. flowing water. Sometimes includes rill and C interill erosion. estuarine zone Environmental system consisting C splash erosion Dislodgement and transport of of an and the transitional area that are soil particles as a result of the impacts of consistently influenced or affected by water from sources such as, but not limited to, salt marshes, C raindrops. coastal and intertidal areas, bays, , C surface creep erosion Dislodgement and , inshore waters, and rivers. movement of small particles of soil or minerals C as a result of wind or gravity. estuary That part of a river or stream or other body of water having unimpaired connection C surface erosion Detachment and transport of with the open sea, where the sea water is measur- surface soil particles by running water, waves, ably diluted with freshwater derived from land currents, moving ice, wind, or gravity. Surface drainage. C erosion can occur as the loss of soil, in a uniform layer, in , or by dry ravel (broken eulittoral See eulittoral under littoral. C or crumbled rock). euphotic zone Lighted region in a body of water C suspension erosion Movement of dislodged that extends vertically from the surface to the soil or mineral particles by moving water or depth at which light is insufficient to enable C above the ground by air movement. photosynthesis to exceed respiration of phy- L erosion cycle Pattern of erosion in a given location toplankton. that moves and deposits materials over time. eupotamon Lotic side arms of a river connected at both ends. L erosion feature Physical feature or geological landmark created from differential erosion of L adjoining materials. euryhaline See euryhaline under . L erosion lake See erosion lakeunder lake. eurysaline Seeeurysalineunder salinity. L L.. t- 40 ~ eutrophic

eutrophic See eutrophic under trophic. stream without an obvious route of surface flow. These areas drain either by subsurface flow, eutrophication (1) Natural process of maturing shallow surface runoff without channels, or very (aging) in a body of water. (2) Natural and small ephemeral streams. human-influenced process of enrichment with nutrients, especially nitrogen (total nitrogen faceted gully side See facetedgully sideunder greater than 600 mg/m3) and phosphorus (total gully side form. phosphorus greater than 25 mg/m3), leading to an increased production of organic matter. See facultative wetland plants Plant species that also cultural eutrophication. usually occur in wetlands (estimated probability 67-99%), but occasionally found in uplands. eutrophy State of the nutrient condition (espe- cially nitrogen and phosphorus) in a water body. facultative wetland species Seefacultativewetland See trophic. speciesunder wetland status. evaporation Loss of liquid water by transition to failing bank Seefailing bank under bank stability. the gaseous phase. fall A free, precipitous descent of water. The See evaporationpond under pond. plural (falls) may apply to a single or to a series of waterfalls. See falls under fast water- evaporite Remains of a solution after most of the turbulent under the main heading channel unit. solvent (usually water) has evaporated. - , fall overturn Seefall overturn under stratification. evapotranspiration Movement of moisture from the earth to the atmosphere as water vapor by the false color Seefalse colorunder remote sensing. evaporation of surface water and the transpira- ~p" tion of water from plants. false karst lake Seefalse karst lakeunder lake. . , evorsion lake See evorsion lakeunder lake. fan See alluvial fan, delta. exorheic An area of open basins whose rivers fan apron Accumulation of relatively recent alluvial ultimately reach the sea. material covering an older fan or piedmont. . , extinction coefficient (11) (1) Degree of light fan terrace An older, inactive alluvial fan that has . " attenuation in water. (2) Availability of light with partially eroded, with more recent accumulations increasing depth as a negative exponential: of alluvial materials at the lower elevation. log I -log I 11= es ez; farm pond See farm pondunder pond. Z fast water-nonturbulent Seefast water - also given as: non turbulent under channel unit.

11Z= log.!s - log.!z ; fast water-turbulent Seefast water-turbulent under channel unit. Is = light at the water surface; Iz = light at depth z; fathom A unit of measure equal to 1.83m (6ft). z = depth. fault A plane or zone of fracture in a geographic extinct lake Seeextinct lakeunder lake. feature (usually rock) that marks where perma- nent displacement or shifting has occurred. ~f fault Seefault sagpond under pond. feature Any component of a community or fabric blanket Seefabric blanket under habitat ecosystem, obstruction, sample location, or other enhancements. item plotted during aquatic biophysical mapping of streams and digitizing processes. face Slope that drains directly into the length of a L flat bank'" 41 L

L feeder Term that is applied to a stream. bed measured at the tip of the fish's snout. See focal point. L fen Seefen under wetlands. fish habitat Aquatic and riparian habitats that L fence barrier Seefence barrierunder habitat provide the necessary biological, chemical, and enhancements. physical (Le.,environmental) requirements of C fish species at various life stages. fetch (1) An area where waves are generated by C wind. (2) The distance waves travel in open fish habitat indices Seehabitat quality indices. water from their point of origin to the point of L: breaking. (3) The distance along open water or Inclined waterway, commonly an land over which wind blows without appreciable artificial channel with stepped pools, installed at L: impedance or change in direction. (4) The a dam or waterfall to allow passage of migratory distance across a lake from a given point to the fish over or around an obstruction. May also be L: upwind shore. referred to as a fishway, fish passageway, or fish pass. L: fill (1) Localized deposition of material eroded and transported by a stream from other areas, fish sanctuary Resting, rearing, or spawning area C resulting in a change in bed elevation. Compare for fish where they are protected by barriers or with scour. (2) Deliberate placement of (gener- regulation from exploitation by sport or commer- L: ally) inorganic material on submerged land or cial fishers. low shoreline of a stream or other body of water to increase the surface elevation. [: fish screen Screen placed at the entrance of a water diversion for irrigation or power genera- film water Layer of water surrounding soil tion to prevent entry of fish. r: particles and varying in thickness from 1 to 100 or more molecular layers. c fish velocity See fish velocity under velocity. Also fine benthic organic matter Seefinebenthic organic referred to as focal point velocity. [: matter under benthic organic maHer. fixed logs Seefixed logs under large organic debris. [: fine load Seefine loadunder sediment load. Long, narrow inlet or arm along a sea coast r: fine particulate organic matter Seefine particulate bordered by steep cliffs or slopes that are usually organic matter under organic particles. formed through glacial erosion and typified by the presence of a partially obstructing rise in r: fines Particulate material, less than 2 mm in bathymetry at the seaward opening. c diameter, including sand, , clay, and fine organic material. flap gate See flap gate under gateand main head- ing control structure. c fine sediment Fine-grained particles (2 mm or less in diameter) in streambanks and substrate. See flashboard Temporary barrier (usually con- r: substrate particle-size table. structed of wood), of relatively low height that is placed along the crest of a spillway on a dam to r: fine woody debris Parts of woody vegetation, adjust the water surface in the reservoir. usually branches, twigs, leaves, roots, and Flashboards are constructed so that they can be L smaller limbs. readily added to increase water storage during low water years or removed to decrease water C finger lake Seefinger lakeunder lake. storage during high water years.

C Long, narrow indentations of a coastline. Rapid increase in streamflow due to C fish attractors Seefish attractors under habitat surface runoff, usually caused by torrential enhancements. upstream rainfall. L fish depth Seefish elevation. flash flow Seeflashflow under flow. L fish elevation Elevation of a fish above a stream- flat bank Seeflat bank under streambank. L (. ~ --, '-' 42 .. flatlandreservoir flatland reservoir Impoundment built in rela- damage. Extreme water level fluctuations usually tively level terrain or in a wide floodplain and characterize such reservoirs. See reservoir. -..I characterized by large shallow areas, often where a meandering river channel remains with its flood control storage Water stored in reservoirs to -oJ associated oxbows and sloughs. abate flood damage. See flood control pool. flat meander Seeflat meander under meander. flood frequency See recurrence interval. ---' flats Level landform composed of unconsolidated flooding Condition where the surface of soil that sediments, usually mud or sand, that may be is generally dry is temporarily covered with elongated or irregularly shaped and continuous flowing water from any source including inflow with the shore, that is covered with shallow from streams during high water years, runoff water or may be periodically exposed. May also from adjacent slopes, or any combination of be called a or . See wetlands, shoal. sources. Seeflood. floater Tree or piece of timber that remains afloat dam-break flooding Downstream surge of in water. water caused by the sudden breaching of a dam on an impoundment in a stream channel, floating aquatic vegetation Rooted or free aquatic that may be caused by a landslide, the deposit --' plants that wholly or partially float on the water of a debris flow, or a debris jam. surface. ephemeral flooding Inundation of the flood- floating macrophyte Seefloating macrophyte under plain that is short-lived or transitory. macrophyte. headwater flooding Situation where an area floating meadow floodplain Seefloating meadow becomes inundated directly by surface runoff floodplain under floodplain. from upland areas. floats Seefloats under large organic debris. long-duration flooding Inundation from a single event ranges from seven days to one floc Tuftlike mass of floating material formed by month. flocculation or the aggregation of a number of .-.I periodically flooded Soils that are regularly or fine suspended particles. irregularly inundated from of ' flocculation Coalescence of colloidal particles into groundwater, precipitation, overland flow, a larger mass that precipitates in the water stream flooding, or tidal influences that occur ~ at intervals of hours, days, or longer. column. --, J permanently flooded Water regime where flood (1) Rising and overflowing of a water body standing water covers a land surface during onto normally dry land. (2) Any flow that the entire year, except during extreme ~ exceeds the bank-full capacity of a stream or droughts. channel and flows onto the floodplain. (3) May J also refer to an exceptionally high in marine flood level Elevation or stage of water surface in a waters. See flooding. stream during a particular event when the stream ...... exceeds bank-full capacity. flood basin Largest floodplain possible occurring - -4 within one drainage. floodplain (1)Area adjoining a water body that becomes inundated during periods of overbank ~ flood channels Channels that contain water only flooding and that is given rigorous legal defini- during high water conditions or flood events. Also referred to as overflow channels. tion in regulatory programs. (2) Land beyond a -.-J stream channel that forms the perimeter for the flood control pool Maximum storage capacity of a maximum probability flood. (3) Strip of land flood control reservoir. bordering a stream that is formed by substrate deposition. (4) Deposit of alluvium that covers a flood control reservoir Reservoirs built to store valley flat from lateral erosion of meandering water during high water years to abate flood streams and rivers. --

:.J\ C L flow:channel maintenanceor preservationflow"" 43

C Nutrients, phytoplankton, and zooplankton ./ IfIlWV,p.r;e:TIPN _/ , produced in the floodplain provide a "flood C I pulse" when connectivity between the floodplain / " and river occurs. / L " / The pulse of river discharge ./ /' C ". due to flooding. See flood pulse. C flood recurrence interval See recurrence interval. C flood river Seeflood river under river. t: floodway (1) Part of a floodplain that is contained floodplain (from Firehock and Doherty 1995) by and is intended for emergency diver- t: sion of water during . (2) Part of a flood- coastal delta floodplain Terminal lateral plain that is kept clear of obstructions to facilitate t: expansion of the alluvial plain where the river the passage of floodwater. divides into numerous distributary channels flood zone Land bordering a stream that is subject as it enters an estuary or ocean. c:: to floods of about equal frequency. C floating meadow floodplain Flooded grass- land forming vast floating mats of vegetation flotation load Total organic debris that enters water. C that may occur seasonally. May also apply to land areas that are semi-aquatic. See wetlands. flotsam Floating debris of natural or human C fringing floodplain Relatively narrow strip of origin that is transported downstream but often floodplain between the walls of a river valley. collects in eddies. C internal delta floodplain Floodplains created flow (1) Movement of water and other mobile C by geologic features that result from lateral substances from one location to another. spreading where the main channel divides and (2) Volume of water passing a given point per C sheet flooding is common. unit of time. Synonymous with discharge. nonflooding floodplain Floodplain where average annual discharge Product of the C overbank flooding occurs very rarely. average water velocity of an aquatic system C occasionally flooded Floodplain that is covered times the cross-sectional area of that system. infrequently by standing water. average annual inflow Sum of the mean C permanently flooded floodplain Floodplain annual discharge for all streams entering a that is permanently covered by water and that water body. C. may contain floating, submerged, or rooted base flow Portion of the stream discharge that vegetation. See terms and definitions under L wetlands. is derived from natural storage (i.e., outflow from groundwater, large lakes or swamps), or L seasonally flooded floodplain Floodplain that sources other than rainfall that creates surface floods annually or seasonally. runoff; discharge sustained in a stream chan- L nel, not a result of direct runoff and without floodplain processes Seefloodplain processesunder regulation, diversion, or other human effects. L active valley wall processes. Also called sustaining, normal, dry weather, ordinary, or groundwater flow. floodplain width Distance between the edge of L the main stream channel and the land-water broken flow Nonlaminar flow with numerous interface at maximum flood stage where flooding standing waves. L occurs an average of every two years. channel maintenance or preservation flow L flood pulse Periodic increase in riverine productiv- Range of flows within a stream from normal peak runoff and may include, but is not L ity that occurs when rivers inundate floodplains. L L t- :J 44 ~ flOw:creepingflow --, -.J -J limited to, flushing flows or flows required to intermittent flow Flows that occur at certain maintain the existing natural stream channel times of the year only when groundwater --.. ...J and adjacent riparian vegetation. levels are adequate but may cease entirely in low water years or be reduced to a series of creeping flow Increased flow that spreads later- ::J separated pools. Compare with ephemeralflow ally across a low-relief, depositional floodplain. underflow. -, duration flow See duration curve. -.J interstitial flow See intergravelflow under flow. ----. -oJ effluent flow Streamflow generated from laminar flow Uniform streamflow with no groundwater. ---, mixing or turbulence. ...J enhancement flow Increased streamflow from least flow Lowest flow established by agree- ---, reservoir releases that improves natural ...J streamflow conditions for aquatic, terrestrial, ment in a regulated stream that will sustain an recreational, and other resources. aquatic population at agreed upon levels. This flow may vary seasonally. Compare with ::JI ephemeral flow in channels that minimum flow under flow. are short-lived or transitory and occur from -J precipitation, snow melt, or short-term water low flow Seeminimumflow under flow. --.. releases. ...J maximumflow Seepeakflowunderflow. flash flow Sharp peaks in streamflows on a mean annual flow Average annual streamflow, :J . usually expressed as cubic meters per second :J flushing flow Artificial or natural discharge of (m3/s). sufficient magnitude and duration to scour mean annual runoff Mean annual flow divided and remove fine sediments from the stream ::J by the catchment area (e.g, meters per hectare). bottom that helps to maintain the integrity of ::J substrate composition and the form of the mean flow Average discharge at a given natural channel. stream location, usually expressed in cubic :J generation flow Flow that results from water meters per second or cubic feet per second. The discharge is computed for the period of releases for power generation. :J record by dividing the total volume of flow improvement flow Discharge that provides by the number of days, months, or years in :J additional water for various uses, corrects the the specified period. Also referred to as deterioration of water quality and utilization average discharge, mean discharge, average :J pressures, and results in increases in popula- daily flow (AD F), or average annual flow tions of aquatic organisms. (QAA). ::J index flow Standard measure of discharge minimum flow (1) The lowest discharge used to compare other streamflows. recorded over a specified period of time. (2) ::J Lowest flow established by agreement in a influent flow Groundwater flows that recharge regulated stream that will sustain an aquatic :J . population to agreed upon levels. instantaneous flow Discharge measured at any :J instant in time. modified flow Discharge at a given point in a stream resulting from the combined effects of :J instream flow Discharge regime for a stream all upstream and on-site operations, diver- channel. sions, return flows, and consumptive uses. :J instream flow requirements Streamflow natural flow Stream discharge that occurs :J regime required to satisfy the water demand naturally through climate and geomorphology for instream uses. without regulation, diversion, or other modifi- :J cation by humans. intergravel flow Portion of surface water that infiltrates a streambed and moves through the optimum flow Discharge regime that provides :J gravel substrate. Also referred to as interstitial the maximum flow for any specified use in a flow. stream. :J ::J --"I flowduration curve'" 45

peak flow Highest discharge recorded within a that may be accompanied by additional water specified period of time that is often related to from increased snow melt. spring , summer, fall, or winter flows. Also called maximum flow. ,streamflow Flow of water, generally with its , in a well-defined channel or perennial flow Flows that are continuous water course. throughout the year. streamline flow Tranquil flow slower than placid flow Flow that is slow,tranquil, and shooting flow.Seetranquilflow under flow. sluggish. subsurface flow Portion of streamflow moving regulated flow Streamflows that have been horizontally through and below the streambed affected by regulated releases, diversions, or from groundwater seepage. It mayor may not other anthropogenic perturbations. become part of the visible streamflow at some point downstream. return flow Water,previously diverted from a stream, that is not consumed and returned to a surface flow Visible portion of streamflow that stream or to another associated body of occurs above the substrate within a channel. surface or groundwater. survival flow Discharge required to prevent rolling flow Streamflows with numerous death of aquatic organis~ in a stream during unbroken waves. specified periods of time (e.g., seven days) when streamflows are extremely low. seasonal flow Streamflows that exist only at certain times of the year, that may be derived swirling flow Streamflows characterized by from springs or surface sources, but usually eddies, boils, and swirls. are associated with seasonal precipitation patterns. tranquil flow Slow streamflow with low energy that results in little erosion to seven day low flow (Q7L) Lowest discharge streambanks and the stream bottom. Also that occurs for a seven consecutive day period referred to as subcritical flow. Compare with during the water year. shootingflow under flow. seven day/QI0 (Q7/10) Lowest flow (i.e., a transition flow Interface where laminar and specific critical low flow) that occurs or is turbulent flows meet. predicted to occur for seven consecutive days within a ten-year period. transverse flow Stream currents that operate at right angles to the main flow of the current. sheet flow Fast, nonturbulent flow over a level These currents are important in pool forma- streambed that approaches laminar flow. tion along the banks ofmeandering streams. shooting flow Swift, high energy streamflow tumbling flow Flow characterized by cascades, with great erosive potential. Also referred to as usually over large boulders or rocky outcrops. supercritical flow. Compare with tranquil flow. turbulent flow Streamflow characterized by an irregular, chaotic path, with violent mixing. sluggish flow Slow streamflow that occurs uniform flow Flow where water velocities are when runoff is spread over a period of time. the same in both magnitude and direction stable flow Streamflow with a constant from point to point in a cross section. Uniform discharge. flow is possible only in a channel where the cross section and gradient are constant. steady flow Little fluctuation in discharge Compare with laminarflow under flow. during a specified period of time. unsteady flow Flow in an open channel where stem flow Precipitation that is intercepted by the depth changes with time. plants and flows down a plant stem or tree trunk to the ground. flow duration curve Graphical representation of the number of times or frequency that a flow of a storm flow Sudden and temporary increase in given magnitude occurs. streamflow, resulting during a heavy rainfall

~ . ~.- J I ---"'I i 46 .. flow erosion flow erosion Seeflow erosionunder erosion. flux Variation of substances, such as nutrients, per unit of time. flow slides Seeflow slidesunder landslide. foam Collection of minute bubbles on the surface flow stability A description of flow consistency at of a liquid formed by agitation or fermentation. a given stream location. focal point Location, and the conditions at that flow till Seeflow till under landslide. location, occupied by an organism. Focal point flume A chute constructed to transport materials measurements help to define microhabitat. See microhabitat. with flowing water. See also flume falls under fast water-turbulent,falls under the main heading channel unit. fog Accumulation of minute water particles in a layer at or just above the ground surface that flush (1) Rapid release of water from a storage often occurs in river bottoms, depressions, or low structure, such as a reservoir, that has a sufficient lying areas. quantity of water to transport suspended and foliar cover Percentage of ground or water floating materials. (2) Sudden rush of water covered by shade from the aerial portion of down a stream that occurs during a freshet (flash plants. Small openings in the canopy are ex- flood). (3) Action of periodic high flow to keep a cluded; foliar cover is always less than the site at a spring or wetland wet or moist. (4) canopy cover and is never greater than 100%. Rinsing or cleansing of beaches by a flush of Synonymous with shading effect as measured water at high tide. with a vertical light source. See canopy cover. flushing flow Seeflushing flow under flow. foliar shading Seefoliar shading under stream flushing period Period of time required for the surface shading. total volume of water to be flushed through a system. ford Low-water stream crossing with bank access to allow wading or vehicular passage by people flushing rate Time required for a volume of water and crossing by livestock. The streambed must be equivalent to the reservoir volume to be dis- composed of materials that are resistant to charged. The flushing rate is calculated by erosion. Streamflows must either be low enough dividing the volume of the reservoir by the daily to allow shallow crossings or the "ford" cannot discharge. be used during high-water periods. fluvial Pertaining to or living in streams or rivers, forebay (1) A reservoir or canal from which water or produced by the action of flowing water. See is taken to operate equipment such as a also fluvial under streambank material. waterwheel or turbine. (2) The entry chamber of a dam through which water flows into an outlet sediment production zone Area of active works. (3) The area of a reservoir immediately erosion where sediments are derived and upstream and adjacent to the structure that forms moved downstream. Also referred to as a reservoir. drainage basin. foreshore (1) Land along the edge of a water body. sink zone Area with low gradient and water (2) Portion of land between the high water mark velocity where substrates are deposited. Also and the low water mark. referred to as the zone of deposition. transportation zone Area where the erosion forested wetland Seeforested wetlandunder wetlands. and deposition are generally in equilibrium so that the total eroded material does not increase or decrease but is transported downstream. fork The point at which a stream branches into two Also referred to as the transfer zone. channels that may be of similar size and flow. fluvial erosion See fluvial erosionunder erosion. form Shape of a streambank that results from fluvial processes. fluvial sedimentation Sediment created, trans- ported, and deposited by flowing water. formative discharge See dominant discharge. L-

i Froude number"" 47 L

L fossil water Water accumulated in an aquifer free-flowing Stream or stream reach that flows during a previous geologic time that has an unconfined and naturally without impoundment, L extremely long recharge period. diversion, straightening, rip-rapping, or other modification of the waterway. C foul Refers to materials or organisms that cling to a substrate so as to encumber it (Le., to entangle free-living Plants or animals not attached to or C or clog or render unsuitable for use). parasitic on other plants or animals (Le., capable of living and moving independently). C fracture Rock mass that is separated into distinct fragments or masses. In streams, fractures create free log Seefree logunder largeorganicdebris. C discontinuous surfaces, often with distinct boundaries. C free meander Seefreemeanderunder meander. fragipan Natural subsurface soil horizon with a free-swimming Organisms that are actively C high bulk density relative to the soil above that is moving or capable of moving in water. brittle and appears cemented when dry but less C so when moist. Generally such soils are mottled free water Water that drains freely by gravity. in color, only slowly permeable to water, and C commonly exhibit bleached cracks that form french drain Blind drain composed of piping with polygons in horizontal section. holes that allows water to into the piping L and drain from the site. framework riffle Riffle composed of coarse substrates, often resistant to hydraulic erosion, frequency of inundation or saturation Period that L that does not accumulate much sediment. an area is covered by surface water or soil is L saturated. It is usually expressed as the number frazil ice Fine spicules of ice formed in water (Le., of years the area is inundated or the soil is slush) too turbulent to allow the formation of L sheet ice or anchor ice. saturated during the portion of the growing season with prevalent vegetation. L Fredle index An index of the quality of frequently confined channel Seefrequently r salmonid spawning gravel, obtained by dividing '- geometric mean diameter of particle size by the confined channel under confinement. sorting coefficient: L frequently flooded channel A channel that floods d often (e.g., in most years). L f= S; 0 freshet Rapid temporary rise in stream discharge L and level caused by heavy or rapid melting dg = geometric mean particle diameter (see of snow and ice. geometric mean particle diameter); So = sorting coefficient, (d7/ d25)'h.;d75is the freshwater Seefreshwater under salinity. particle diameter at the 75th percentile of cumulative particle weight (weight is freshwater marsh Seefreshwater marsh under cumulated from small to large particles), wetlands. and d25is the diameter at the 25th weight percentile). fringe marsh Seefringe marsh under wetlands. freeboard (1) Vertical distance between the level fringing floodplain Seefringing floodplain under of the surface of the liquid in a conduit, reservoir, floodplain. tank, or canal, and the top of an open conduit, or that prevents waves or other movements by Froude number (Fr> Dimensionless number the liquid to overtop the confining structure. (2) expressing the ratio of inertial to gravitational Height of the sides in a boat above the water forces in a fluid: surface. V free-floating macrophyte Seefree-floating macro- phyteunder macrophyte. Fr= (gd)'h.

gross primaryproduction 49 glacial lake Seeglacial lake under lake. ward as a result of crustal activity to create an area that is lower than the adjoining landform. glacier Body of ice formed by the compaction and recrystalization of snow that has definite lateral graben lake Seegrabenlakeunder lake. limits and exhibits motion in a definite direction. graded bed Streambed with a series of sorted rock glacier Tongue of rock fragments held layers where the larger sizes of particles occur on together by interstitial ice that moves the bottom and finer sizes on the surface. downslope, similar to a glacier. graded stream Seegraded stream under stream. valley glacier Glacier that is smaller than a continental glacier or an ice cap that flows grade-stabilization or control structure See check mainly along well-defined valleys, often with dam under habitat enhancements. many . gradient (1) General slope, or the change in glaciofluvial Pertains to channelized flow of vertical elevation per unit of horizontal distance, glacier meltwater as well as deposits and land- of the water surface in a flowing stream. (2) Rate forms formed by glacial streams. of change of any characteristic per unit of length. Seeprofile. glaciofluvial materials Materials such as sedi- ments deposited by glacial streams either directly gravel Substrate particle size between 2 and 64 in front of, or in contact with, glacial ice. mm (0.1 and 2.5 in) in diameter. Compare with other substrate sizes under substrate size. glaciolacustrine materials Range of particles resulting from glacial action, deposited along the gravel bed (1) Natural accumulation or deposition margins of glacial lakes or released into the lakes of gravel-size particles in areas of low water by melt water. velocity, decreased gradient, or channel obstruc- tion. (2) Gravel artificially placed in a water body glaze Homogeneous, transparent ice layers that for fish habitat, primarily for spawning. are formed from rain or drizzle when the precipi- tation comes in contact with surfaces at tempera- gravel pit lake Seegravelpit lakeunder lake. tures of DoC(32°F) or lower. gravel restoration Seegravel restoration under gleization Process in saturated or nearly saturated habitat enhancements. soils that involves the reduction of iron, its segregation into mottles and concretions, or its gravity flow Seegravity flow under landslide. removal by leaching. Gleizated soils tend to be grey in color when the iron has been reduced and gravity waves Seegravity wavesunder wave. reddish when the iron is oxidized. graywater Drainage of dishwater, shower, laun- dry, bath, and washbasin effluents that contrast glide See glide under slow water under the main heading channel unit. with "blackwater" such as toilet drainage. greenway Protected linear open-space area that is global positioning system (GPS) System of either landscaped or left in a natural condition. satellites in permanent orbit above the earth that May follow a natural feature or landscape, such allow a receiver to triangulate their position on or above the earth's surface. as river or stream, or other types of right-of- ways. gorge (1) Small, narrow canyon with steep, rocky grit Fine, abrasive particles, usually composed of walls, especially one through which a coarse-grained siliceous rock (the size of sand or streamflows. (2) Portion of the water drainage smaller) with a sharp, angular form and depos- system situated between the catchment area and the outwash fan. ited as dust from the air or from impurities in water. graben Portion of the earth's crust bounded on at gross primary production Seegross primary least two sides by faults that have moved down- production under production. ~ 50 ~ ground ground Term applied to the solid surfaces of soil, porosity Porosity,n, is estimated by: weathered rock, and detritus on the earth. See n=5 +5 . earth, soil. y r' 5 = specific yield of groundwater; ground cover Seegroundcover under remote s: =specific retention (the volume of sensing. groundwater that does not drain under influence of gravity. ground moraine See ground moraine under moraine. groundwater budget Summation of water move- ground truthing Seegroundtruthingunder remote ment into and out of the groundwater during a sensing. specified period of time. groundwater dam Underground obstruction groundwater (1) Water located interstitially in hindering the movement of groundwater. the substrate of the earth that is recharged by and enters streams through seepage groundwater discharge Seepage or flow of water and springs. (2) Subsurface water in a zone of from groundwater to surface waters. saturation, standing in or passing though (groundwater flow) the soil and the underlying groundwater interchange Pattern of recharge and strata. discharge between groundwater and surface water. average linear velocity The average linear veloc- ity (V) of groundwater flow is estimated by: groundwater level Elevation of water in ground- water in relation to the surface or another fixed point. v = K (d/d,) n ' e groundwater recharge Flow of water from the surface into groundwater. K = hydraulic conductivity (m/ d); d/d, =hydraulic head; groundwater runoff Flow of groundwater along a ne = effective porosity, the volume of geologic gradient by gravity that is comparable interconnected pore space relative to to surface runoff. the total volume. groundwater table Surface below which rock, coefficient of storage The coefficient of storage, gravel, sand, or other substrates are saturated by 5, is estimated by: a body of unconfined groundwater. 5 = pgh(ex+ nl3); (groin) See groyne under habitat p =density of fluid; enhancement. g = gravitational constant; h =saturated thickness of aquifer; Small, narrow, often steep-sided stream ex=compressibility of the aquifer valley that results from a secondary incision into skeleton; a broader alluvial valley. See . n =porosity; Portion of an ocean or sea that is partly 13=compressibility of the fluid. enclosed by land. Darcy's law Darcy's law describes the liquid gully Small valley, ravine, or an ephemeral transporting properties of porous materials: stream channel that carries water during and Q =KA(d/ d,) ; immediately after rain that is generally longer than wide. Q = flow rate (m3/ d); K =hydraulic conductivity (m/ d); continuous gully Gully with many finger-like A =cross-sectional area through which extensions into its headwaters area that gains flow occurs (m2); depth rapidly downstream and maintains the did, = fluid head. depth to the mouth of the gully. L habitat enhancements: channel constrictor

discontinuous gully Gully that begins as an habitat diversity Number of different types of abrupt headcut and may occur singly or as a habitat within a given area. chain of gullies following one another in a downslope direction. habitat enhancements Actions taken to modify or enhance habitats to benefit one or more species. gully erosion See gully erosionunder erosion. a-jacks Structure with three arms fastened gully plug See gully plug and checkdam under together, resembling a child's toy jack, made habitat enhancements. of concrete or metal and placed along a bank or shoreline to prevent erosion from waves, gully side form Shape or profile of gully sides breakers, or current. compared to right angles in the direction of flow. articulated concrete mattress Collection of benched Sides having a horizontal section (less concrete slabs wired together to form a large than 5% or at least 30 cm wide) in an other- mattress that is used to stabilize a bank. wise vertical wall. artificial channels Short channels designed for faceted Sides with various combinations of spawning or rearing fish that are located near vertical and sloping segments. but separate from stream channels. sloping Sides with a general slope less than artificial holes Cavities of tile, pipe, hollow 65% from horizontal. logs, and similar structures of appropriate size vertical Sides with the general slope greater that are plugged at one end and are for fish than 65% from horizontal. spawning. artifical meander A human-constructed stream guzzler Water entrapment and containment channel that resembles a natural meander. structure used primarily to provide water for wildlife and livestock in arid regions. Structure of concrete, tires, or other solid material constructed to create cover gyrals (gyres) Surface currents in very large lakes - for aquatic organisms in marine or large or that circulate in very large swirls. freshwater environments.

gyttja Sediment mixture of particulate organic artificial riffle Stream reach where rocks are matter, often zooplankton fecal pellets, inorganic added to create a shallow area with turbulent L precipitates, and deposited matter that is less flow. than 50% inorganic by dry weight. Consists of a L- mixture of humus material, fine plant fragments, baffle Any device that changes the direction algal remains, quartz grains, diatom fistulas, and distribution of flow or velocity of water. exoskeleton fragments, spores of pollen relics, bank stabilization Placement of materials such and plankton. L as , logs, , and planting of vegetation to prevent bank erosion. L berm Natural or artificial levee, dike, shelf, ~h ledge, groyne, or bench along a streambank L that may extend laterally along the channel or habitat Specific type of place within an ecosystem parallel to the flow to contain the flow within l- occupied by an organism, population, or commu- the streambank. Also referred to as bund. See nity that contains both living and nonliving dike, levee. L components with specific biological, chemical, and physical characteristics including the basic brushpile Trees, brush, or other vegetation tied L life requirements of food, water, and cover or into bundles and placed in a water body as shelter. supplemental structure or cover. L bulkhead Wall of wood, metal, rock, or con- habitat component Single element (such as crete used to support a slumping bank. L velocity, depth, or cover) of the habitat or area where an organism lives or occurs. Component is channel constrictor Type of structure, such as a I L synonymous with attribute. notched drop structure or a double-wing L L L

52 ~ habitat enhancements:checkdam

current deflector, that forces the main flow of mid water, in a water body to create habitat for water through a narrow gap. spawning or nursery areas. crib Cubical structure constructed of logs, Overhead View metal posts, boulders, or other materials that Riprap Wings Prevent Bank is filled with rocks to protect streambanks and enhance cover in streams, lakes, or reservoirs. I Scouring See under habitat enhancements.

'~"~Y"'.~:'~:;~"~:'.~",'i.'~ crib well Log crib that is anchored to the bank that is usually filled with rocks or dirt and planted with woody vegetation such as willows.

Current deflector Single or double wing dam or Pattern constructed from boulders, logs, or gabions that is used to force the current in a different Orginal direction. See gabion and jetty under habitat Front View enhancements.

>;""""" I~~~~el digger log Type of current deflector that ~~~I~ ~~Iff consists of a log anchored to a streambank ,~,'i:;1.'f,',% ,,~,~lfN/f:' that protrudes into or across the channel to deflect the flow and excavate a depression in ;~~%; tM~ss; WI: :~~M?l~1; ?l/i ~t ~ *~ ~ ~*~ f:.~~~ ~~~~i the substrate.

drop, drop structure See checkdamunder habitat enhancements. Longitudinal Cross Section earth islands Islands of earth constructed in FollowingConstruction lakes, ponds, reservoirs, or other water bodies that provide habitat for birds or terrestrial animals and shallow-dwelling aquatic " :'""""!r:Jf!R.,w, "',' "'-iX!;">;", ";',' ,',' "':!:::~fJ.f~DN~:~!i~{:f:,'~':;"!':'~';,: "';!;:j {0' organisms. escape ladder Ladder-like structure of wood or Following Some Stream Flooding mesh that provides animal access to devel- oped water sources. '~ escape ramp Structures (ramps) of rock, concrete, or wood that are placed along steep ~::;~~l:;<~!\!"¥'f«<"'&'WI:*J,~"';Uit.W""I;iIPools sides of ponds, , or conduits to permit Formed animals access to water or to escape if trapped. fabric blanket Flexible, mesh-like material check (from Meehan 1991) (usually synthetic), that reduces erosion and through which vegetation can grow. Some- check dam Small dam of logs, rock, gabions, times placed under channel structures or rip rap to hold materials. concrete, or other materials that completely spans the stream channel, slowing swift fence barrier Fence-like arrangement of logs, current and creating a plunge pool down- pilings, gabions, or other materials placed stream from the sudden drop in channel along a streambank. elevation, Used to control , headcutting in streams, and retard the flow of fish attractors Brush, tires, plastic, stake beds, water and sediment in a channel. clay pipes, standing timber, or other structures used to create habitat for fish or other cover Logs, boulders, brush, or other materials organisms. placed along the banks, on the bottom, or gabion Wire cage or basket filled with rocks or habitat enhancements: low-headdam <411 53 L L stone used to stabilize banks and to enhance aquatic habitat. L "",;,'!""",'WJ"!:{,v,\1.'-/"J:":{,v,\>.,,,.. grade-stabilization or control structure See L- check dam under habitat enhancements. " <:," ~ gravel restoration Placement of gravel in a Smal / " C stream or other water body as spawning Logs "" " habitat for fish. \,,'

L- \O". groyne (groin) (1) Structure of wood, stone, or suea~ \"" " \,,' L- concrete projecting into water to prevent sand, ~ pebbles, gravel, or other substrates or materi- Large L- als from being washed away by the current. Log (2) Structure usually constructed of logs or L- rocks and placed on a streambank to control the soil erosion or direction of water current. ~,;;d§W;:'I,'1"!" ({ ""°, >:'-;.'N!.' ({ N,':-;~Jl!.:f~ ;fl:}, Top View L- gully plug (1) Refers to the construction of check dams in gullies. See checkdamunder L- habitat enhancements. (2) Also refers L- to filling of gullies with soil and planting vegetation. ~ Substrate'I <::--- '" - , C half-log Log split lengthwise and anchored to Surface the substrate (split side down) so that there is Side View C a gap between the log and the substrate that serves as cover for fish. C log sill (from Meehan 1991) Hewitt ramp Type of check dam made of logs, wood planks, or rocks that creates a gradual L incline downstream so that water can excavate a plunge pool in a stream with little gradient. L- See checkdamunder habitat enhancements.

L hurdles Smaller branches woven together and pegged against a bank on a moderate slope to L control bank erosion and promote growth of vegetation. L sim~eobllqueIogsil, key.llenched jack See a-jacks under habitat enhancements. intoeachbonkand'einlC>tt:edwilhrock L jetty Structure of rock, logs, pilings, gabions, or , other materials that projects part way across a L - channel to direct the stream current.

IaIefaJ.scour pool cut-awayIongilL.dnalsectionofasil1; l . k-dam Log structure with a "K" shape con- logsareoff.selabouI45' structed in a stream channel as habitat for fish 10allowbackwash""'ant l and other aquatic organisms. leg-type structure Concrete structure, sup- ported by either two legs along one side or four legs at the comers, or a "+" in the middle, placed in a stream channel.

log sill See checkdamunder habitat enhancements. low-head dam See checkdamunder habitat enhancements. oblique log sill (fromKohlerand Hubert 1993) :J' 54 .. habitat enhancements:junkerstructure

:JI lunker structure Plank and log, free-standing, spawning platform A floating or suspended :J' box-like structure with open sides that is wooden platform placed in a lake or reservoir installed just below the water at the toe of a as spawning habitat for fish. :JI bank to stabilize the bank and create habitat. spawning reef An artificial reef of gravel, rock, :JI mudsill Logs placed perpendicular to the bank or other material to serve as a spawning area i of a stream to prevent erosion. for fish. :J' off-channel pools Pools or ponds created in the spiling Term applied to control soil erosion riparian area adjoining a stream channel and using stakes that are driven into the ground :J connected with the channel, creating a pro- with branches woven between the stakes, or -, tected area for rearing fish or other aquatic two rows of staggered posts with brush -..J organisms. between them to help reduce soil erosion and ---, promote growth of vegetation. -..J retard Seefence barrierunder habitat ---, enhancements. stake bed Artificial fish habitat created either --.J by driving narrow wooden stakes vertically ---, A facing or structure made of large, into a lake bottom before impoundment (or durable material, such as earth-filled sacks, -..J when the water level is low) or by attaching trees, logs, stumps, gabions, or rocks placed on a streambank to deflect current. Term also similar wooden stakes to a weighted frame refers to the materials used to construct the that is lowered into place after impoundment. revetment. Similar to riprap under habitat structure Durable materials, such as large enhancements. organic debris, boulders, rock, or concrete placed in a stream, lake, reservoir, or other riprap Hard materials, such as logs, rock, or water body to create habitat. boulders (often fastened together) used to protect a bank or another important feature of Structure made from four legs of pre- a stream, lake, reservoir, or other water body. cast concrete joined at a central point, all at Similar to revetment under habitat angles of 109.50to each other, that functions enhancements. similar to an a-jack. See a-jack under habitat enhancements. roller dam See checkdam under habitat enhancements. timber crib Crib constructed of timber or planks in or along the margin of a water body scour structure Structure of rocks, logs, ga- to create habitat for aquatic organisms or to bions, or other materials placed along a stabilize a bank. streambank or in a stream channel to cause scouring and deposition of substrates. tire reef Artificial structure made of discarded vehicle tires that are generally attached sediment trap Artificial pool that is generally together and weighted to keep the reef on the excavated or constructed for collecting or bottom of a water body. Used to create fish trapping sand, silt, or other substrates that are habitat in fresh or saltwater. A type of artificial transported as the streambed load. reefdescribedunderhabitat sill Low horizontal barrier of rock or other enhancements. durable material in a stream. More particu- wall A low dam, that is normally larly, a low barrier that is generally con- constructed parallel or at an angle to a structed of masomy across a gorge to control streambank, to divert flow in a specific streambed erosion. Compare with gully plug direction. and checkdamunder habitat enhancements. trash collector Fence-like structure of heavy spawning box Boxes filled with gravel that are wire fastened to metal stakes or logs and placed in shallow water of a lake or reservoir placed across a stream to intercept and hold as artificial spawning habitat for fish. debris flowing downstream that creates a dam spawning marsh Artificial marshes constructed and a plunge pool. Used to protect bridge along a stream channel or margin of a lake or crossings, create pools as habitat for fish, and reservoir as spawning habitat for fish. collect gravel for spawning habitat. Synony- L heat budget ~ 55 c..

C mous with debris catcher, grizzly, or trash (mg/L) of calcium carbonate. Synonymous with catcher. total hardness. L: tree retards Trees placed along a streambank to hardpan A layer of earth that has become rela- reduce current and accumulate debris. L: tively hard and impermeable, usually through wedge dam Dam or weir constructed with the mineral deposits. A chemically hardened layer L: apex facing upstream. where the soil particles are cemented together with organic matter of SiOz' sesquioxides, or L: weir See checkdamunder habitat enhancements. CaCO3. t: wing dam See jetty under habitat enhancements. hardwater Water with a large concentration of Wisconsin bank cover Artificial ledge of wood alkaline cations derived from carbonates, chlo- L that is supported by rock on the margin of a rides, and sulfates of calcium and magnesium stream channel as cover for fish. that is generally found in areas of limestone L substrate. Compare with softwater. habitat fragmentation Division of existing L: habitats into separate discrete units from modifi- head Energy per unit weight of a fluid such as cation or conversion of the habitat by anthropo- that resulting from a difference in depth at two L: genic or natural activities. points in a body of water. Includes pressure head, velocity head, and elevation head. See hydraulic habitat quality indices Numerical indices have head. L: been devised to give an overall rating of the quality or quantity of an aquatic or terrestrial head cut Upstream migration or deepening of a C habitat. In aquatic habitats, these indices often stream channel that results from cutting (i.e., integrate many habitat elements such as erosion) of the streambank by high water C streamflow regime, substrate, cover, and water velocities. quality and are frequently used in stream condi- C tion assessments or evaluations and to predict headland Point of land, usually high and with a environmental impacts. sheer drop, extending out into a water body, C especially a sea. habitat type Aggregation of land or aquatic units C having equivalent structure, function, and head race Channel that delivers water to a water responses to disturbance and capable of main- wheel and causes the wheel to turn. C taining similar animal or plant communities. headscarp Seeheadscarpunder landslide. C half-log See half-logunder habitat enhancements. headwall Steep slopes at the upper end of a C haline See haline under salinity. valley, water course, or the cliff faces around a cirque. C haline marsh See haline marsh under wetlands. headwater flooding See headwaterflooding under L halocline See haloclineunder salinity. flooding. hanging garden Community of plants and headwaters (1) Upper reaches of tributaries in a L animals that develops on steep slopes or cliffs drainage basin. (2) The point on a nontidal where groundwater seeps onto the surface to stream above which the average annual flow is L form a confined ecosystem. less than five cubic feet per second. For streams that remain dry for long periods of the year, the L- hanging valley (1) Valley formed by a tributary headwaters may be established as the point on stream that has a noticeably higher elevation the stream where a flow of five cubic feet per L- than the main channel at their confluence. second is equaled or exceeded 50% of the time. (2) Valley that is high above a shore to a water '-. body and was formed from rapid erosion of the headwater stream See headwater stream under land or displacement by a fault. stream.

hardness Total concentration of calcium and heat budget (1) Amount of heat per unit of surface magnesium ions expressed as milligrams per liter area necessary to raise a body of water from the ---, ---' 56 ~ heat budget:summer heat income

minimum temperature ofwinter to the maximum hummock Rounded, undefined or chaotic pattern temperature of summer. (2)Totalamount of heat of steep-sided low hills and hollows. between the lowest and highest heat content. hummocky moraine See hummocky moraine under summer heat income Amount of heat needed moraine. to raise a body of water from isothermal winter conditions of 4°C to maximum summer humus General term for the dark organic material levels. of soils that is produced by the decomposition of vegetable or animal matter. The more or less winter heat income Amount of heat needed to -4 stable fraction of soil from decomposed organic raise a body of water from its minimum levels material, generally amorphous, colloidal, and to isothermal conditions at 4°c. --" dark-colored. Nonhumus organic material is height See height under wave. generally of low molecular weight, easily de- -J graded by microbes, and has a short retention time. Henry's law At a constant temperature, the -.J amount of gas absorbed by a given volume of hurdles See hurdles under habitat enhancements. liquid is proportional to the atmospheric pressure .--4 of the gas. hydraulic control point Top of an obstruction in a --' heterotrophic See heterotrophicunder trophic. stream or a point in a stream where streamflow is constricted by any large, relatively immobile ---, I Hewitt ramp See Hewitt ramp under habitat object (e.g., boulder, bedrock) that stabilizes the enhancements. stream geometry and maintains long-term channelcharacteL - J high gradient riffle See high gradient riffle under fast water-turbulent, riffles under the main hydraulic depth Seehydraulicdepth(D) under heading channel unit. dimensions. highland reservoir Impoundment built on steep hydraulic discharge See hydraulic dischargeunder terrain with a narrow floodplain. Most of the discharge. shoreline is characterized by steep, rocky, or clifflike formations. hydraulic drop Point where the streamflow changes from subcritical to supercritical in a high moor See high moor under wetlands. reach with rapid changes in flow. high tube overflow See high tube overflow under control structure. hydraulic flushing rate Rate at which an entire volume of lake water is replaced. Seeflushing rate. holding pond See holding pond under pond. hole Part of a water body or channel unit that is hydraulic gradient (1) Slope of water in a stream. distinctly deeper than the surrounding area. (2) Drop in pressure head per unit length in the direction of the streamflow. hollow Valley or landscape depression. hydraulic head Height of the free surface in a holomictic Seeholomicticunder mixing. water body above a given point beneath the surface, or the height of the water level at an homogeneous Refers to a water body that has a upstream point compared to the height of the uniform chemical composition throughout. water surface at a given downstream location. homoiohaline See homoiohalineunder salinity. hydraulic jump Transition form of supercritical flow that usually results from a change in chan- homothermous Refers to a water body that has nel elevation, geometry, or gradient. It may be the same temperature throughout. confined to a very short reach where the depth hot brine Saline water exceeding 37°C (98°P). increases dramatically in a turbulent wavelike feature or in a more gradual or undulating See hot spring under spring. increase. L L hygroscopicwater ~ 57

L hydraulic radius Ratio of the area of flow divided channels, seepage zones, springs, and soil by the wetted perimeter of a cross section: moisture including soil moisture characteristics L as deduced from vegetation characteristics. R=A/P; L A = area; hydrologic regime Water movement in a given area that is a function of the input from precipita- P = wetted perimeter of a cross section. C tion, surface, and groundwater and the output Refers to the motion and action of from evaporation into the atmosphere or transpi- L. water and other liquids. ration from plants.

L hydraulic slope Change in elevation of water hydrologic zone Area that is inundated by water surface between two cross sections divided by or has saturated soils within a specified range of L the distance between them. Compare with frequency and the duration of inundation or soil saturation. L gradient. hydric Moist. hydrometabolism Metabolism that occurs in free L. waters that is essentially all aerobic. hydric soils Soils that are saturated, flooded, or L ponded long enough during the growing season hydromorphic soil Soils that develop in the to develop anaerobic conditions in the upper presence of water sufficient to create anaerobic C layers. conditions in the soil. hydrograph Graph that illustrates the relation of hydrophobic soils Soils that can repel water due L discharge, stage velocity, or other water compo- to the presence of materials, usually of plant or nent with time, for a given point on a stream. animal origin, or condensed hydrophobic L. substances. hydrographic maps Maps of lakes with contour L lines delineating depth. hydrophyte (1) Plants that grow in water or saturated soils. (2) Any macrophyte that grows in L hydrohaline See hydrohalineunder salinity. wetlands or aquatic habitats on a substrate that is at least periodically deficient in oxygen because L hydrologic balance Relationship between the of excessive water content. quality and quantity of water inflow to, water L outflow from, and water storage in hydrologic hydropower reservoir Artificial water storage units such as an aquifer, drainage basin, lake, impoundments designed to retain water and L reservoir, or soil zone. It encompasses the dy- redirect it through turbines to generate electricity. namic relationships of precipitation, runoff, L evaporation, and changes in surface and ground- hydrosaline See hydrosalineunder salinity. water storage. hydrothermal Refers to water on or within the L hydrologic budget Compilation of the total water earth that is heated from within the earth. input to and output from a lake, drainage, or L watershed. hydrothermal alteration Process where heated L groundwater passes through cracks or pores in hydrologic control Natural or artificial structures rock that may alter the water, mineral, and rock. or conditions that manage or control the move- L ment of surface or subsurface flow. hydrothermal vein A cluster of minerals in a rock cavity that were precipitated by hydrothermal hydrologic cycle Cycle of water movement from L activity. the atmosphere to the earth via precipitation Ir "-- through surface and groundwater to the hygric See hydric. and return to the atmosphere via evaporation L from water bodies and transpiration by plants. hygrophyte Plants restricted to growing in or on See . moist sites. See hydrophyte. L hydrologic feature Refers to water-related fea- hygroscopic water Water adsorbed by dry soil L tures visible at the land surface, such as stream from an atmosphere of high relative humidity.

L

I \ :J~ 58 ~ hypereutrophic -."j-, hypereutrophic See hypereutrophicunder trophic. ice Sections of ice that form and float :J downstream when ice covering a river breaks up. hypertrophic See hypertrophic under trophic. :J ice scouring Abrasion or erosion of stream hypoeutrophic See hypoeutrophicunder trophic. bottoms by ice that normally occurs from ice :J jams. hypolimnion See hypolimnion under stratification. :J ice wedge Accumulation or piling of ice that is ---. hypopleuston See hypopleuston under pleuston. pushed forward by the flow of water or pressure ..J from ice and gravity. hypopotamon See hypopotamon under potamon. -J---. IFIM Abbreviation for instream flow incremental hyporheic zone Latticework of underground methodology. A method for relating changes in ---, habitats through the alluvium of the channel and --J the physical characteristics of a stream to changes floodplain associated with streamflows that in flows. extend as deep as the interstitial water in the i substrate. illumination Amount of light radiation impinging -4 on a surface, expressed as lux, watts per square hyporhithron See hyporhithron under rhithron. centimeter, foot-candles or lumens per square --4 meter. hypothermal Refers to water on or within the ---. earth that is lukewarm or tepid. illuviation Transport and deposition of soil --~ hypotrophic See hypotrophic under trophic. components from a higher to a lower level by percolating water. --< hypsographic curve Depth-area curve that describes the relationship of the cross-sectional image See image under remote sensing. area of a lake at a specific depth. A depth-volume imbrication Shingled or downstream overlapping curve is closely related and describes the volume of bed material due to water flow, most com- of the lake at a specific depth. monly as plate-shaped large gravel or cobble substrate materials.

~I. impermeable Refers to a layer of material of sufficient composition, density, and thickness ice See ice under streambank material. that it does not permit passage of a liquid or a gas. iceberg Large floating mass of ice. impervious Refers to material through which icecap Ice covering an area that slopes in all water cannot pass or passes with great difficulty. directions from the center unless confined between steep slopes. impoundment Natural or artificial body of water that is confined by a structure such as a dam to ice dam Dam created in the spring when broken retain water, sediment, or wastes. sections of ice create a structure that blocks or retards the movement of water. improvement flow See improvementflow under flow. ice-disintegration moraine See ice-disintegration moraine under moraine. impurity A foreign, objectionable material that contaminates water. ice jam Large blocks and pieces of ice that are jammed by a channel constriction or obstruction, incidental drift Casual or random drift of aquatic usually occurring during spring breakup. If organisms. water cannot penetrate freely through the ice, a incident light See incident light under solar dam can form that may cause flooding, damage radiation. to human-built structures, or loss of human lives. See ice dam. incised channel See incised channel under channel geometry. L ... 59 L interception

L incised stream See incised stream under stream. initial breaching Seeinitialbreachingunder breaching. L index Measurement of feature of an organism, community, or habitat that is used as a reference initial dilution zone Area receiving water adja- L for determining or monitoring change over time. cent to a point source discharge, extending from the point of discharge 100 m in all directions L index flow Standard discharge that is used to from the water surface to the bottom. State and compare with other discharges in a specific federal water quality objectives do not apply L stream. See also indexflow under flow. within an initial dilution zone. L index of biotic integrity UBI) See index of biotic inlet Long and narrow indentation of a shoreline integrity (IBI)under biological indices. or a narrow passage between two islands. L inner gorge Stream reach bounded by steep valley index of refraction (1) Number indicating the walls. Common in areas of stream downcutting speed of light in a given medium versus the L or geologic uplift. speed in water or other specified medium. L (2) Measure of the degree to which light is bent inshore On or very close to the shore. Also or scattered when passing through water or other referred to as onshore. L substances. insolation Exposure to sunlight. Solar radiation is L indicator organisms (1) Organisms that respond measured as the rate of delivery or intensity per predictably to various environmental changes, unit area on the horizontal surface of an object. L and whose presence, absence, and abundance are used as indicators of environmental conditions. instanteous discharge See instanteous discharge L (2) Any plant or animal that, by its presence, its under discharge. frequency, or its vigor, indicates any particular L property of a site. instanteous flow See instanteousflow under flow. instream Within the wetted perimeter of the L indigenous A fish or other aquatic organism stream channel. native to a particular water body, basin, or L region. instream cover Areas with structure (e.g., boul- ders, rocks, logs, etc.) in a stream channel that L indirect toxicity Toxicity that affects organisms by provide aquatic organisms with shelter or interfering with their food supply or modifying protection from predators or competitors. Also a L their habitat instead of acting directly on the place with low water velocity where organisms organisms. can rest and conserve energy. L infiltration Process by which water moves from instream flow See instreamflowunder flow. the earth or surface water into the groundwater L system. instream flow requirements See instreamflow requirements under flow. L infiltration rate Rate at which standing water percolates downward into the substrate. insular Of or pertaining to an island or islands. L Also applied to dwelling on an island, forming L inflow Location where water from one source an island, or occurring alone. enters another water body. Also, the movement insulated stream See insulated stream under of water from one source into another water stream. L body. r intensity See irradiance. L influent flow See influent flow under flow. , interbasin transfer Transport of water from one L influent seepage Water movement from the watershed or river basin to another. surface of the ground toward the water table. Also, refers to seepage of water into the stre- interception Physical interference of precipitation ambed from a stream above the water table. by vegetation. L..-

L- r -4-, 60 .. intercratonicbasin --J intercratonic basin Basin formed in a relatively volume of flow per unit of time through a unit .4 rigid and immobile area of the earth's crust. area composed of solids and voids. Also referred to as apparent or intragravel velocity: 0- 4 interface Surface that forms a boundary between adjacent areas, bodies, or spaces. May also refer Va=KS; 0--J to the point of interaction between two indepen- K = permeability (cm/h); --, dent systems. oj S =hydraulic gradient. --, interflow (1) Precipitation that infiltrates the ---4 soil and moves laterally until it resurfaces or is It can also be approximated from surface velocities by the equation: intercepted by an underground body of water. 0_-4 (2) Movement or inflow of water in a reservoir or (VYn2K lake between layers of water of different (higher Va= 2.22R4/3 ; . -, or lower) density. See also interflow under mixing.

0- J interfluve Elevated region that divides watersheds. Vs = mean velocity of surface water; n = roughness coefficient; ..J intergravel flow See intergravelflow under flow. K = permeability; R = hydraulic radius. interill erosion See interill erosionunder erosion. ow4 intertidal Zone between high and low tides. --, ... intermediate breaching See intermediate breaching under breaching. intrusive body Igneous rocks which, while fluid, penetrated into or between other rocks but intermittent (1) Alternately starting and stopping. solidified before reaching the surface; includes J (2) Water that flows or exists sporadically or very hard, coarse-grained rocks like granite, periodically. diorite, and gabbro. intermittent flow Seeintermittentflow under flow. inundation To be covered with standing or --, moving water. J intermittent lake Seeintermittentlakeunder lake. inverse estuary Type of estuary where evapora- tion exceeds the freshwater inflow plus intermittently exposed See intermittently exposed under water regime. precipitation. intermittently flooded Seeintermittentlyflooded inverse stratification See inverse stratification under stratification. under water regime. invert (1) Refers to the upstream end of a culvert. internal delta floodplain See internal deltaflood- (2) The bottom inside surface of a pipe or con- plain under floodplain. duit. Occasionally the term refers to the bottom or base elevation of a structure. internal progressive wave See internal progressive wave under wave. iones Relic riverbeds. internal seiche See internal seicheunder wave. irradiance Amount of electromagnetic energy received at a unit surface area per unit time, interrupted stream See interrupted stream under stream. usually measured for the visible and near-visible portion of the light spectrum. Light passing through a water surface is progressively ab- interstitial flow See intergravelflow under flow. sorbed with increasing depth; light intensity at depth z (I) is: interstitial space Spaces or openings in substrates

that provide habitat and cover for . 1=1e-T/ZZ 0 interstitial velocity Rate of subsurface water flow 10= light intensity at the water surface; through the substrate (Va)' expressed as the 11=extinction coefficientof light in water.

62 ~ lake: alkali lake

alkali lake Lake where alkaline salts have doline lake Lake, usually with circular and accumulated from evaporation (i.e., closed conically shaped sinks, that is developed from basin) or in situations where freshwater inflow the solution of soluble rock that gradually is insufficient to dilute the alkaline salts. erodes the rock stratum.

bitter lake Water body formed for salt extrac- drainage lake Lake that loses water through tion from or other water body that flows from an outlet. Sometimes separated contains a high concentration of salts in into further categories by whether the lake has solution. an inlet and outlet or is spring-fed with no inlet but an outlet. blind lake Lake that has neither an inflowing stream nor an outlet. Compare with seepage dune lake Lake formed by deposition of sand lakeunder lake. or other material that is moved, primarily or brine lake Lake with water that is saturated or partially, by wind. with high salt concentrations. dystrophic lake Lake with a high concentration of humic acid in the water that colors it brown, caldera lake Lake formed by subsidence in the low pH, and peat-filled margins that develop roof of a partially emptied magmatic chamber. See crater lakeand volcanic lakeunder lake. into peat bogs. See bog under wetlands. earthquake lake Lake formed in a depression cave-in lake Seekettlelake,sinklake,thawlake, themokarst lakeunder lake. created by an earthquake. ephemeral lake Lake that contains water for cirque lake Lake that occurs where valleys are short and irregular periods of time and shaped into structures resembling amphithe- usually contains water after a period of heavy aters by the action of freezing and thawing ice. precipitation. Usually found in the upper portion of a glaciated area or in mountains. erosion lake Lake formed in a depression by the removal or deposition of rock fragments or closed lake Lake that loses water only through other organic material. evaporation. evorsion lake Type of formed by coastal lake Lake formed by the enclosure of streambed abrasion. A category of fluvial lakes lagoons by wave action or an embayment associated with torrential flow and cataracts formed by bars deposited by currents along a shoreline. where rocks cut a pothole into the stream bedrock through erosion by a swirling action coldwater lake Lake with a fish community generated through hydraulic pressure. composed primarily of coldwater fishes. extinct lake A former lake as evidenced by crater lake See calderalakeand volcaniclake fossil remains or stratigraphy, that no longer under lake. holds water due to climatic changes or changes in hydraulic processes. cryogenic lake Lake formed inside an ice- wedge polygon that develops in permafrost false karst lake Lake in a depression caused by from water seepage through cracks in the geologic piping that results in turbulent surface of the ground. subsurface drainage channels in insoluble clastic rock. cutoff lake Artificial created by river channelization or levee construction that finger lake Lake that is narrow and elongate in isolates the lake from the river. A cutoff lake shape. may contain a water control structure to glacial lake Lake formed by glacial action such facilitate drainage into the river. as scouring or damming. dead lake Body of standing water that cannot graben lake Lake formed by geologic faulting support plants or animals because of adverse processes where depressions occur between chemical or physical features. masses of either a single fault displacement or delta lake Lake formed upstream of an alluvial in multiple downward displacements result- deposition. ing in troughs. See also tectonic lake. L L lake: thermokarst lake <0lIl63

L gravel pit lake Lake formed by water accumu- plunge lake An excavated lake at the foot of a lated in a pit from which gravel was excavated waterfall. L below the groundwater level. pluvial lake A former lake that existed under a C intermittent lake Lake that has surface water different climate in areas that are now dry. only part of the time at different recurring intervals and durations. pothole lake Ponds, pools, lakes, and wetlands C found in depressions (potholes) that were C lake Lake formed in a depression by formed by glacial activity. melting ice blocks deposited in glacial drift or public lake Lake legally open to the public for C in the . recreational activities that may include boat- landslide lake Lake formed by dams or ing, fishing, and swimming. C depressions created by the mass movement of relict lake A remnant lake or a larger pluvial soil, rock, and debris. C lake occupying a closed basin in arid regions. levee lake Shallow, often elongated body of reservoir A lake formed by impounding water C water that lies parallel to a stream and is behind a natural or constructed dam. separated from it by a strip of higher land. rift lake Lake formed along a geologic fault or c: maar lake Lake occupying a small depression fault zone. with a diameter less than 2 km, resulting from t: lava in contact with groundwater or from saline lake Lake with a high concentration of salts such as carbonates, chlorides, or sulfates. degassing of magma. t: saltern lake Lake with a high concentration of marl lake Lake with a high deposition or sodium chloride. C content of calcareous materials in the littoral zone. salt karst lake Lake formed by the dissolution C montane freshwater lake Circumneutrallake of evaporites. found in mountains below timberline. seepage lake Lake without an outlet drained by r: seepage into groundwater. Compare with blind moraine lake Lake formed by the damming lakeunder lake. c action of rock debris deposited by retreating . sink lake Lake that forms in a depression created by underground solution of limestone. c open lake Lake with outflow from an outlet or from seepage. small mountain lake A small lake (8 ha [20 L acres]) formed in a natural topographic oxbow lake Lake occupying a former meander depression on a mountain. L of a river isolated by a shift in the stream channel. soda lake Lake with a high concentration of L NaHCO3 and Na2CO3. paternoster lake A chain of small lakes in a glaciated valley formed by ice erosion. solution lake Lake formed by soluble rock L slowly dissolved by percolating groundwater. r pay lake Lake where the public pays a fee for stratified lake Lake with distinctive strata L swimming, fishing, and other recreational caused by density differences (e.g., tempera- r uses. L ture, salinity). perched lake Lake formed by surface water tectonic lake Lake formed in depressions from a perched groundwater table. created by movement or damming action of perennial lake Lake that always contains water. surface plates. playa lake An internally drained lake found in thaw lake Lake formed in shallow depressions ~- a sandy, salty, or muddy flat floor of an arid from unequal thawing of permafrost in arctic basin, usually occupied by shallow water only regions. Also termed thermokarst. after periods of prolonged heavy precipitation. thermokarst lake Lake formed by coalescing of Sometimes refers to an ephemeral lake that many cryogenic lakes, or by melting of large forms a "playa" upon drying up. amounts of ice deep in permafrost. ::J 64 ~ lake:two-story lake :J :J two-story lake Lake with an upper layer of bedrock landslide Infrequent landslides of warm water supporting warmwater fishes and rock whose strength is much higher than the :J a lower (i.e., deeper) layer of cold water strength of their boundaries. These landslides supporting coldwater fishes. usually occur as frequent small slides that produce irregular hillslopes with steep toes :J vemallake A shallow lake resulting from and head scarps. seasonal precipitation and runoff that is dry :J for part of the year. :J volcanic lake Lake formed by depressions in lava or volcanic cones or dams formed by lava :J that impounds water. See calderalakeand crater lakeunder lake. :J warmwater lake Lake with a fish community Bedrock composed primarily of warmwater fishes. :J --, lake volume See lakevolume under dimensions. J --, lake width See lakewidth under dimensions. -..J laminar flow See laminarflow under flow. debris avalanche (from Meehan 1991) J --, land Any part of the earth not covered by water. debris avalanche Rapid, shallow, downslope -J mass movement of saturated soil or surficial landform Any physical, recognizable form or --- feature of the earth's surfac~ that is produced by material (commonly including vegetation -J natural processes and has a characteristic or debris) that occurs on steep hillsides. --, unique shape. debris fall Fall or rolling soil or surficial -i material mass. --, landsat See landsat under remote sensing. -J debris flow Rapid mass movement of material --, landsat multispectral scanner (MSS) See landsat including vegetation, soil, mud, boulders, and _.4 multispectral scanner (MSS) under remote sensing. weathered rock (Le., a debris torrent) down a --, steep (greater than 5°) mountain slope or -J landsat thematic mapper (TM) See landsat stream channel. See debris torrent. -, thematic mapper (TM) under remote sensing. j debris flow tracks Erosion marks made by --- landscape Contiguous heterogeneous natural or debris flows characterized by the lack of _.. constructed land area with similar conditions vegetation or young plants, deposits of soil, over a larger geographic area. boulders, and rock, levees, or gullies. landslide Fall or slide of soil, debris, or rock on or debris jam or dam Accumulation of debris in a from a slope. Any downslope mass movement of channel that may cause ponding of water or soil, rock, or debris on a landform. See also alluvial deposition upstream from the accu- landslidepool under slow water,pool, dammed pool mulation, and block fish movements. under the main heading channel unit. debris slide Downslope sliding of a mass of soil or surface material that may be trans- avalanche Large mass of snow or ice, some- formed into a debris flow. times with rockS and vegetative debris that moves rapidly downslope. debris torrent Rapid, turbulent movement of water, soil, alluvium, and organic matter avalanche cone Accumulated material, similar to down a stream channel during storms or a talus cone, deposited by a snow avalanche. floods. Torrents generally occur in small avalanche track Channel-like pathway of an streams with scouring of the streambed and avalanche, marked by eroded surfaces and deposition of a large quantity of material at bent or broken trees. the lower end of the torrent. See debris flow. L L landslide: slump'" 65

L deep-seated creep Slow, gradual, more or less aggregate material from weathering and continuous and permanent deformation of soil erosion that reduces the steepness of slopes L caused by gravity. and deposits the material in lower areas. C deep-seated failures Landslides involving mud slide Horizontal and vertical movement deep regolith, weathered rock, or bedrock, as of mud caused by natural water saturation of C well as surface soil that may form large the soil or from anthropogenic disturbance. geologic features. C periglacial landslide Active valley wall dry ravel Downslope movement of dry, processes characteristic of very cold regions t: noncohesive soil or rock particles by gravity in such as next to active glaciers or alpine terrain. a form of soil creep. rock avalanche Rapid, downslope flow of large C earthflow Mass downslope movement of soil masses of rock by rock falls and slides from and particles of weathered rock smaller than bedrock areas. C sand that results when soils become saturated and unstable. rock creep Slow, gradual downslope progres- C sion of rock fragments. earth slump Downslope movement of a L: relatively intact mass of soil, colluvium, and rock fall Relatively free-falling and precipitous vegetation along a clearly defined, concave movement of newly detached fragments of C surface that is parallel to the slope. bedrock (any size) from a cliff or other very steep slope. flow slides Rapid downslope movement of a C cohesive soil mass that results from liquefac- rock slide Downslope movement of rock on or tion of a bank in saturated silty and sandy from a steep slope. C soils. rotational failure Horizontal downslope L flow till Debris flow resulting from melting ice movement of hillside material that results in that causes saturation of glacial debris and an upward turn on the toe of the slide. See L accumulates on a lower gradient, more stable slump. surface. L shallow-rapid landslide Shallow (1-2 m) gravity flow Downslope flow of a mixture of landslide on a steep slope produced by L water and sediment caused by slumping. failure (slipping, sliding) of the soil mantle headscarp Steep, upper portion of a landslide including glacial till and some weathered scar. bedrock that leaves an elongate, spoon- L shaped scar. lahar Flash floods or avalanche consisting of L semiliquid mud, rock, and ice that surge slab failure Broad, flat, somewhat thick rock L rapidly downslope from higher altitudes, and that breaks off or falls as a single unit. usually occur on the slopes of volcanoes. slide Mass movement of soil and rock where L landslide scar Part of a slope (commonly steep) slope failure occurs along one or more slip surfaces. May become a debris flow or torrent r that is exposed or visibly modified from L downslope movement of soils and rock flow if enough water is present in the mass. accompanying a landslide. slip erosion Downslope slide of a whole L large persistent deep-seated failure Slump- mantle rock. The large, spectacular forms are earthflows involving large areas of hillside on termed landslips, landslides, or debris '- that remain recognizable for a long avalanches. period of time. slope failure Rupture and collapse or flow of mass movement General term for a large surface materials, soil, or bedrock due to shear downslope movement of soil and rock or for stress exceeding the strength of the material. avalanches that result from natural or anthro- pogenic causes. slump Deep, rotational landslide, generally producing coherent lateral and downward mass wasting Downslope movement, flow, or movement (back-rotation) of a mass of soil, slumping of a large amount of coherent or rock, or other material that slips as a coherent 66 ~ landslide:slump-earthflow

Synonymous with large woody debris (LWD), a term that is commonly used in the Pacific North- west where organic debris generally is a log or tree.

aggregate Two or more large woody pieces at one location.

biological legacies Large trees, logs, snags, and other components of a forest that remain after logging for reseeding and that provide terres- trial or aquatic ecological structure. slump (from Meehan 1991) blowdown Trees that have fallen from high wind. mass. Also, a land area that sunk to create a bole Term referring to the trunk of a tree. boggy, marshy place. clump Irregular accumulation of debris along a slump-earthflow Landslide exhibiting charac- stream channel that does not form major teristics of slumps and earthflows in which the impediments to streamflow. upper part moves by slumping while the lower portion moves by flow. deadhead Log submerged and close to the water surface that is not embedded, lodged, or small sporadic deep-seated failures Com- rooted in the stream channel. monly smaller slumps that can result from storms or earth movement at irregular time digger log Log anchored to a streambank or intervals and can crumble or decay so that channel bottom to form a scour pool. they are indiscernible. down log Portion of a tree that has fallen or snow avalanche See avalanche under landslide. been cut and left on the forest floor.

landslide lake See landslide lake under lake. fixed logs Log (or group of logs) that is firmly embedded, lodged, or rooted in a stream landslide pool See landslidepool under slow water, channel. pool, under the main heading channel unit. floats Accumulations of logs floating on the landslide scar See landslidescar under landslide. surface but prevented from moving down- stream by an obstruction. landtype Unit on the earth's surface of a characteritistic geomorphic surface type and a free log Log (or group of logs) that is not particular lithological composition, indentifiable embedded, lodged, or rooted in the stream channel. on a spatial scale of hectares or acres. jam Wholly or partially submerged accumula- langmuir circulation See langmuir circulation under wave. tion of woody debris from winds, water currents, or logging activities that partially or completely blocks a stream channel and large benthic organic matter See largebenthic obstructs streamflow. organicmatter under benthic organic matter. large bole Bole 60 cm (24 in) or more in large bole See largeboleunder large organic diameter. debris. log In general, a tree trunk, bole, or large limb, large impoundment An impoundment larger with or without the roots attached. than 227 hectares (500 acres) in surface area. log dam Dam formed by the deposition of large organic debris Large woody material (e.g., woody debris and stream sediments at an log or tree) with a diameter greater than 10 cm obstruction caused by a log or several logs in (4 in) and a length greater than 1 m (39 in). the stream channel.

Ie c C Liebig'slawofthe minimum 67

L root wad Root mass from a tree. Synonymous leak Escape or entry of water. with butt ends. L leakage The amount of water that leaks into or scattered Singlepieces of debris distributed at out of a storage area. [J irregular intervals along a stream channel. small bole Bole less than 60 cm (24 in) in leaking Movement of water into or out of a [J diameter. storage area or stream.

0 snag Generally applies to a standing dead tree. least flow See leastflow under flow. Sometimes applied to a submerged fallen tree C in a large stream with the top exposed or only leave strips Bands of trees or other vegetation left slightly submerged. along stream, rivers, and roads as buffers from adjacent forest management and other human C stable debris Large woody debris, usually activities. See also buffer. 0 anchored or embedded in the stream bottom or bank that is not dislodged during periods of ledge Reef, ridge, shelf, or line of rock longer than C high flows. wide found in the sea, lakes, or other bodies of sweeper log Fallen tree with branches that water. 0 accumulates floating logs and other debris and projects into the channel, creating a hazard for lee The downwind side of an object being affected L navigation. by some physical process. volume Volume (V) of a piece of large woody lee bar See lee barunder bar. L debris can be calculated as: leeshore The shore protected from direct wind or L 1I"(V 2 + V 2)L V = 1 2 . a shore receiving wind only from the land. 8 ' L leg-type structure See leg-type structure under V1 = diameter of debris at one end; habitat enhancements. L V2 =diameter of debris at other end; L L = length. length See length under dimensions and wave. woody debris Collection of materials in the lentic An aquatic system with standing or slow water or substrate on the bank or shoreline L flowing water (e.g., lake, pond, reservoir, , I that is primarily composed of wood. marsh, and wetland). Such systems have a L large persistent deep-seated failure See large nondirectional net flow of water. See standing water. persistent deep-seatedfailure under landslide. lateral channel movement Movement of a stream levee (1) Naturally formed elongate ridge or channel laterally across a valley floor either embankment of fluvial sediments deposited gradually through meandering or suddenly along a stream channel. (2) Artificial embank- through avulsions. ment along a water course or an arm of the sea to prevent flooding or restrict movement of water lateral moraine See lateralmoraineunder moraine. into or through an area. Compare with berm under habitat enhancements, dike. lateral scour pool See lateralscour pool under slow water, pool, scour pool under the main heading levee lake See levee lakeunder lake. channel unit. level Surface elevation of a body of water relative late succession stage See late succession stage to mean sea level. under succession.

leachate Soluble substance that has been removed Liebig's law of the minimum Growth and from other material by water percolation. reproduction of an organism is hindered when a minimum quantity of an element or substance leaching Removal of soluble material in the such as oxygen, carbon dioxide, or calcium is ground by percolating water. available. 68 ~ limitingfactor limiting factor (1) Any condition that approaches middle infralittoral Zone of floating leaf or exceeds the limits of tolerance by an organism. vegetation. (2) A habitat component (biological, chemical, or sublittoral Portion of a shore from the lowest physical) whose quantity constraints or limits the .. " size of a population. water level to the lower boundary of plant growth. _.J limnetic (1) Open-water zone of a water body too supralittoral Shore area above the water line deep to support rooted aquatic vegetation. (2) that is subjected to spraying by waves. ~ Zone of deep water between the surface and compensation depth. upper infralittoral Zone of rooted vegetation. limnic material Soils made up of inorganic or littoral drift Material floating in the littoral zone of a lake. organic compounds that are deposited in water _. J by precipitation, aquatic organisms, underwater littoral sediment Sediment deposited along the or floating aquatic plants, or aquatic animals. shore of a lake. limnocrene A spring pool (generally large) with or without outlet. littoroprofundal See littoroprofundal under littoral. linear extent of structure Percentage of sides in a water body that are cliffs or . loading Addition of specific quantities of sub- stances or heat to a water body. link In drainage networks, stream reach of a particular order, or a stream at its origin. loess Fine, loamy soil or sand deposited by the wind. downstream link Magnitude of a link at the next downstream confluence. log See log under large organic debris.

link magnitude In drainage networks, the log dam See log dam under large organic debris. number of links upstream from a given point in the network. See logpond under pond. lithology Physical character of a rock or deposit log sill Seecheckdamunder habitat enhancements. that is defined by rock type or distribution of particle sizes. long-duration flooding See long-durationflooding under flooding. lithorheophilic See lithorheophilicunder benthos. longitudinal profile A plot of elevations with litter Leaves, needles, twigs and branches, and distances to depict stream channel characteristics. other small organic matter entering a water body. Also referred to as litter fall. Movement of sediment along a beach from wash and backwash of waves that littoral Shallow shore area (less than 6 m [-20 ft] make oblique contact with the shore. deep) of a water body where light can usually penetrate to the bottom and that is often occu- long wave See long wave under wave. pied by rooted macrophytes. losing stream See losing stream under stream. epilittoral Shore area entirely above the water line that is unaffected by spray. lotic Aquatic system with rapidly flowing water such as a brook, stream, or river where the net eulittoral Shoreline between the highest and flow of water is unidirectional from the headwa- lowest seasonal water levels. ters to the mouth. littoroprofundal Zone below the lower edge of the macrophyte boundary. lotic (riparian) wetland See lotic (riparian) wetland under wetlands. lower infralittoral Zone of submerged vegetation. lower bank Seelowerbankunder streambank. L- swamp"" 69

lower infralittoral See lower infralittoral under macroinvertebrate community indicators See littoral. water quality indicators.

lower valley wall tributary Seelowervalleywall macrophyte A plant that can be seen without the L tributary under tributary. aid of optics.

( L low flow Seelowflow underflow. emergent macrophyte Aquatic plants growing from submerged soils in water between 0.5 L- low gradient riffle Seelow gradientriffle under fast and 1.5 m (1.5-5 it) deep. water-turbulent, rifflesunder the main heading I L channel unit. floating macrophyte Floating aquatic vegeta- tion growing from submerged substrates in L low-head dam A low barrier that is placed in a water between 0.5 and 3.0 m (1.5-10 ft) deep. waterway to retain or redirect flows. See also checkdam under habitat enhancements. free-floating macrophyte Aquatic vegetation at L or near the surface not rooted in the substrate. i L lowland Land that is level and only slightly above nonpersistent emergent Emergent hydro- the elevation of the water surface and that is phytes whose leaves and stems die and r periodically subject to flooding. L decompose annually so that most portions of the plant above ground are easily transported lowland reservoir Impoundment constructed in L by currents, waves, or ice. rolling hill country or on a stream with a moder- ate floodplain. rheophyte A plant associated with fast-flowing ~ water. lowland stream See lowland stream under stream. L submerged macrophyte General term for low moor See low moor under wetlands. aquatic vegetation in the . lunker structure See lunker structure under habitat macroplankton See macroplankton under plankton. enhancements. madicolous habitat Thin sheets of water flowing over rock faces, found at the edge of rocky streams, at the sides of waterfalls, and on rocky ~m chutes. main channel Seemainchannelunder channel maar lake See maar lakeunder lake. pattern. Also referred to as main stem channel macroinvertebrate An invertebrate animal under channel pattern. (without backbone) large enough to be seen without magnification and retainedby a 0.595 main channel pool See main channelpoolunder mm (U.S. #30) screen. See benthos. pool,scourpoolunder the main heading channel unit. collectors Macroinvertebrates that feed on living algae, fine particulate matter, or decom- main-lake point A peninsula that juts into the main body of a lake or reservoir and continues posing particulate organic matter collected by underwater. filtering water or the surface of sediments. predators Macroinvertebrates that feed on flesh main stem Principal, largest, or dominating or fluids of other animals. stream or channel in any given area or drainage system. scrapers Macroinvertebrates that feed on algae or microflora attached to the substrate or to major waterway Any river, stream, or lake that is plants. extensively used by commercial or private watercraft. shredders Macroinvertebrate herbivores and detritivores that feed on living and decompos- mangrove swamp See mangrove swamp under ing vascular plant tissue. wetlands. 'I ' 70 ~ Manning'sn

Manning's n An empirical coefficient for comput- maximum depth Seemaximumdepthunder ing stream bottom roughness. Used in determin- dimensions. ing water velocity in stream discharge ---' calculations. In English units, maximum elevation Seemaximumelevationunder dimensions. 1.486R2/3Sl/2A Q= n maximum flow Seemaximumflow under flow. -..J

maximum lake length See maximum lake length _J Q = discharge; under dimensions. R = hydraulic radius; -.-J S = energy gradient (parallel to water slope); maximum likelihood Seemaximumlikelihood A = cross-sectional area. under remote sensing. ---' Because Q =water velocity, (V) times area (A), maximum wavelength Seemaximumwavelength 1.486R2/3S1/2 under wave. V= n maximum width Seemaximumwidthunder J dimensions. In metric units, the coefficient 1.486 becomes 1.0. mean annual flow See mean annual flow under marginal habitat Habitats that approach the limits flow. to which a species is adapted. More generally, habitats with physical or biological factors that mean annual runoff See mean annual runoff under support only limited species or populations. flow. marina Area to dock boats and provide other services for small watercraft. mean catchment slope Can be calculated by: (elevation at O.85L)- (elevation at 0.10L) marine Of, or pertaining to, the ocean and associ- ated seas. See also marine under streambank ~= Q~ ; material. L =maximum length of the catchment basin. marl Light gray, calcareous, generally friable, clay or clay-loam composed principally of carbonate mean column velocity See mean column velocity derived from photosynthetic activity of algae and under velocity. mollusk shells. mean cross section velocity See mean crosssection marl lake See marl lakeunder lake. velocity under velocity. marsh See marsh under wetlands. mean density of structural units Density of structures per unit of shoreline or bottom. mass movement See mass movement under landslide. meander Sinuous course of a river having specific geometric dimensions that describe the degree of mass wasting See mass wasting under landslide. curvature. More particularly, one curved portion of a sinuous or winding stream channel, consist- mat (1) Collection of floating debris, macrophytes, ing of two consecutive loops, one turning clock- or algae. (2) Submerged artificial fish structure, wise and the other counterclockwise. See particularly one made of brush and tree sinuosity. branches. acute meander Meander with sharp, hairpin mature river See mature river under river. turns. mature stream See graded stream under stream. amplitude Breadth or width of the meander. maximum bank height See maximum bank height belt of meander The approximate width of a under dimensions. stream valley. c c mean stream length ... 71

c compound meander Irregular meander pattern sinuous meander Meander with slight curva- developed on streams with more than one ture within a stream reach of less than ap- C dominant discharge. proximately two channel widths. I: confined meander Meander scrolls within a straight meander Meander with very little confined floodplain. curvature. I: distorted meander Meanders where obstruc- tortuous meander Meander that has a more or I: tions limit lateral movement and development less repeated pattern characterized by angles of sinuosity. greater than 90°. I: flat meander An irregular meander in a stream truncated meander Meander where confine- with a flat streambed. ment limits lateral movement and sinuosity I: free meander Meander in unconsolidated with undeveloped loops. /' I: alluvium that migrates freely to develop unconfined meander Meander that migrates waveforms without constraint from valley unrestricted across a floodplain. walls, adjacent terrain, or distortion from I: meander belt-width See meander belt-width under heterogeneous alluvium. meander. [: irregular acute meander Meander with an irregular pattern of sharp hairpin turns. meander length See meander length under c: meander. irregular meander Deformed or irregular meanders of variable size within a meander [: meander line A survey line that represents the belt. location of the actual shoreline of a permanent c: irregular meander with oxbow Irregular natural body of water, without showing all the t: meander that retained a remnant loop. details of its windings and irregularities. meander belt-width Normal width or distance See meander scarunder meander. I: between tangents drawn on the convex sides of successive belts. meander scrolls channel See meander scrolls channel under channel pattern. I: meander length Wave length of the meander. C meander scar Evidence of old channel locations mean flow See meanflow under flow. from the lateral migration of a meander. C mean high water Average height of the high paleopotamon A large, deep former river water over 19 years. C meander that is disconnected from the current river channel except at the highest flood flow. mean lake depth See mean lakedepth under dimensions. L parapotamon Dead arms that are permanently connected to a river channel at the down- mean lake width See mean lake width under L stream end. dimensions. plesiopotamon A former braided channel l- mean low water Average height of the low water connected only during high flows. ( over 19 years. L- point of inflection Location where the thalweg crosses from one bank to the other. mean monthly discharge See mean monthly L- dischargeunder discharge. r radius of curvature Degree of curvature of the L meander loop. mean sea level Average elevation of the surface of the sea for all tidal levels over 19 years. Altitudes regular meander Meander with regular inter- L or elevations are expressed as elevations above vals and a consistent pattern of sinuosity and mean sea level. loops. L~ simple meander Meander with one dominant mean stream length See mean stream length under meander belt-width and wavelength. dimensions. -., J 72 ~ mean stream slope mean stream slope The mean gradient or drop in mesohaline See mesohalineunder salinity. j stream surface elevation per unit length of stream. mesolimnion See mesolimnion under stratification. j

elevation at source - elevation at mouth mesophytic Plant species that grow in locations ~] 5 = where soil moisture and aeration conditions lie c length of stream between extremes (Le., occurring in habitats with -l medial moraine See medial moraine under moraine. average moisture conditions). median depth See median depth under dimensions. mesosaline See mesosalineunder salinity. mesotrophic See mesotrophicunder trophic. median lethal dose (LD50 or LDso) Dose (internal amount) of a substance that is lethal to 50% of a metalimnion See metalimnion under stratification. ~ group of organisms within a specified time -., period. metaphyton Algae aggregated in the littoral zone, -4 median lethal concentration (LC50 or LC50) The neither attached to substrate nor planktonic. --. . .;; concentration of a substance that kills half of the metapotamon See metapotamon under potamon. test organisms in a specified period of exposure. Called the median tolerance limit in older metarhithron See metarhithron under rhithron. literature. meteoric water Term applied to rainwater, snow, median line Line that is equidistant from the hail, and sleet. nearest points on opposite shores that forms the center line of the channel. microclimate The climatic factors operating in a ~ , terrestrial microenvironment (Le., small or median moraine See median moraine under restricted area). moraine. microenvironment All the external environmental median tolerance limit (TLm or TLm) See median conditions that may influence an organism's lethal concentration. physiology or energetics in a small or restricted area. median width Seemedianwidthunder dimensions. microhabitat Specific locations where organisms melt Action by which a solid becomes a liquid. live that contain combinations of habitat charac- meltout till Seemeltouttill under moraine. teristics that directly influence the organisms at any life stage. See niche. meltwater Water that originates from the melting of snow or ice. microplankton See microplankton under plankton. mid-channel bar See mid-channel barunder bar. meltwater channel See meltwater channel under channel pattern. mid-channel pool See mid-channel pool under pool, meltwater stream See meltwaterstreamunder stream. scour pool with the main heading of channel unit. middle infralittoral See middle infralittoral under merge See merge under remote sensing. littoral.

meromictic Seemeromicticunder mixing. middle stream See middle stream under stream. mesa High, nearly flat-topped and usually mid-successional stage See mid-successionalstage isolated area bounded by steep slopes. under succession. mesic Pertaining to or adapted to an area that has milk White or chalky-colored appearance of a balanced supply of water (Le., moderately wet). suspended mineral particles in water.

mesocline See mesoclineunder stratification. Seemillpondunder pond. L

L mine discharge Water that is drained, pumped, or ectogenic meromixis Lakes that do not mix siphoned from a mine. because of density differences. See meromictic L. under mixing. Spring with water containing a L: significant amount of dissolved minerals. holomictic Lakes that are mixed throughout the water column by wind. L: mineral turbidity Turbidity resulting from the interflow Flow of water into a lake that is presence of fine mineral particles such as clay. greater in density than the epilimnion or L: hypolimnion and remains as a plume at mineral water Water containing a significant intermediate depths. amount of dissolved minerals. t: meromictic Lake in which dissolved substances t: minimum bank height Seeminimumbankheight create a density gradient with depth that under dimensions. prevents complete (top to bottom) mixing or t: circulation of water. Periodic circulation occurs minimum flow Seeminimumflow under flow. only in waters above the chemocline. L: minor discharge Any discharge of less than 50,000 mixing characteristics Frequency with which L: gallons per day or a discharge that does not all or some part of water is mixed. adversely affect the receiving waters. mixing depth Depth of body of water where mixing occurs. L: mire Refers to slimy soil or deep mud but also may be applied to swampy ground, bogs, or mixing zone Area or location of a water body C marshes. where individual masses of water are mixed. monomictic Lake with one regular period of L mitigation (1) Action taken to alleviate or com- circulation per year. pensate for potentially adverse effects on aquatic L habitat that have been modified through anthro- oligomictic Lake with temperatures always pogenic actions. (2) In-kind mitigation may be greater than 4°C that exhibit only irregular L substituted for compensation to replace a re- circulation. L source that has been negatively impacted with overflow The inflow of water at the surface of a a similar resource (e.g., a stream for a stream). lake that is less dense than the lake water. (3) Out-of-kind mitigation refers to replacement L of one resource with another (e.g., a lake for a partial meromixis A normally dimictic lake stream). that skips a turnover, usually in spring, from L dynamic processes such as decomposition. mixing Internal circulation in a water body. L polymictic Lake with frequent or continuous amictic Lakes that do not mix because they are circulation. L perennially sealed off by ice from most of the turnover ratio Volume of water (as a percent- annual variation in temperature. L age) that is affected by turnover in meromictic biogenic meromixis Lakes that do not mix lakes. L because of salt accumulation in the hypolim- underflow Flow of water into a lake that has a nion from decomposition of organic matter in greater density than the water in the lake. l the sediment. warm monomictic Waters that do not drop cold monomictic Lakes with water temperature below 4°C and circulate freely in winter but l. never greater than 4°C that circulate only one stratify in summer. time in summer at or below 4°c. L warm polymictic Waters that circulate freely at crenogenic meromixis Lakes that do not mix temperatures well above 4°c. [ because of high salinity from saline springs at mixing characteristics See mixing characteristics r deep pockets in the basin. l under mixing. dimictic Lakes with two periods of mixing- one in the spring and one in the fall. mixing depth See mixingdepthunder mixing. 1\ 74 ~ mixingzone J mixing zone See mixing zoneunder mixing. end moraine A ridge of glacial till that remains ~ in equilibrium at the terminus of a valley I mixohaline Seemixohalineunder salinity. glacier or at the margin of an ice sheet. ---I mixolimnion Seemixolimnionunder ground moraine Thin deposits left underneath =:J stratification. a retreating glacier that may have a gently rolling or hummock-like appearance. =:J mixosaline Seemixosalineunder salinity. hummocky moraine Moraine composed of ---, -.J modified flow See modifiedflow under flow. generally random knobs, ridges, hummocks, and depressions. -.J modified universal soil loss equation An esti- ice-disintegration moraine Moraine formed by mate of sediment yield for an individual storm accumulation of till and other materials on toe event can be calculated from: I of stagnant ice. Y = 95(Qq)o.56KLSCP ; lateral moraine Geologic deposits formed --, Y =single storm sediment yield, in tons; along the sides of a retreating glacier. Q = storm runoff in acre-feet; medial moraine A long strip of rock debris q =peak discharge in cubic feet per second; carried on or within a glacier from the conver- K = soil erodibility factor; gence of lateral moraines where two glaciers L =slope length factor; join. S =slope steepness factor; C =cover management factor; median moraine Geologic deposits along the P = supportive practices factor. central path of a glacier. --' monimolimnion See monimolimnion under meltout till Material that collects on or under glacier ice of a stationary or stagnant glacier. ---, stratification. J neoglacial moraine Term applied to a moraine monomictic See monomictic under mixing. , that formed during the Neoglacial period and --' monsoon (1) Wind that affects the climate of a the more recent Little Ice Age. ---, J large area when it changes direction with the recessional moraine Moraine created by seasons. (2) Specifically applies to the seasonal accumulation of materials deposited by a ~ wind in southern Asia that blows from southwest melting glacier that marks a temporary halt in in summer and northeast in winter and is associ- its general retreat. ated with episodes of heavy rainfall separated by ~ periods of little or no rain. terminal moraine Geologic deposits at the front lobe or foot of a glacier that marks the furthest ~ montane Pertaining to mountains or mountainous point reached by a glacier. areas. moraine lake See moraine lakeunder lake. montane freshwater lake See montanefreshwater morass See morass under wetlands. lakeunder lake. morphoedaphic index (ME!) An index of the monthly mean discharge See monthly mean trophic state of a water body: dischargeunder discharge. moor See moor under wetlands. MEI = [(TDS)/a]1> ; TDS =total dissolved solids; morainal See morainalunder streambank material. d =mean depth. moraine Irregular, surficial geologic deposit of morphology Physical attributes of a water body sand, rock, and debris left by a retreating glacier. and the methods for measuring those attributes.

ablation moraine Moraine formed by melting morphometry The physical shape of a water body, ice that has a typically hummock form. such as a stream, lake, or reservoir. c c.. negative heterograde ... 75 c mosaic See mosaic under remote sensing. ..n c moss-lichen wetland See moss-lichenwetland c under wetlands. nadir Seenadir under remote sensing. nannoplankton Planktonic organisms that are mountain processes See mountain processesunder [: active valley wall processes. small enough to pass through a 0.03 mm mesh net. See also nannoplankton under plankton. mouth Downstream terminus of a stream as it I: ultranannoplankton Plankton that are less than enters another water body. [: 0.2f.Lm. moveable bed A streambed composed of materi- nannoseston See nannoseston under seston. L: als that are readily transported by streamflow. nasmode A spring complex or an area where a L: muck Soft fine-grained soil composed of silt, clay, number of nearby springs originate from the or organic substrate material, typically dark in same groundwater source. t: color, that consists of 20-50% highly decomposed organic matter with intermingled silt and clay. native species Plant and animal species that occur naturally in aquatic and terrestrial habitats. t: mud (1) Wet, sticky earth composed of silt inter- mingled with clay that may contain organic natural erosion See natural erosionunder erosion. t: material. (2) Term that is often applied to firm t: streambeds composed of soil. natural flow See naturalflow under flow. mudbank Lateral sides of a streambank created natural levee Sediment deposited on a \" t: by mud deposition. streambank as floodwaters subside that creates natural banks or ridges slightly above the [: mud cracks Cracks formed in mud as it dries and floodplain. shrinks. [: natural spillway See natural spillway under mud flats Shallow areas of a stream composed of control structure. c silt and other fine particles that are periodically exposed at relatively even elevations. navigable Waterways used by humans for trans- c portation or transport of goods. Legally applied mudflow Lateral flow of mud that has been to interstate waters: intrastate lakes, rivers, and c wetted by precipitation. streams that are used by interstate travelers for recreational or other purposes; intrastate lakes, L- mudsill See mudsill under habitat enhancements. rivers, and streams from which fish or shellfish are taken and sold in interstate commerce; and mud slide See mud slide under landslide. L intrastate lakes, rivers, and streams that are used multipurpose reservoir Artificial impoundment for industrial purposes by industries involved in interstate commerce. L used for water storage where water releases are regulated for various uses including domestic nearshore Zone extending from a shore to a L water supply, irrigated agriculture, power distance where the water column is no longer generation, and navigation. influenced by conditions on or drainage from L land. multispectral classification See multispectral classification under remote sensing. L neck Narrow strip of land, such as an isthmus, , or . L multispectral imagery See multispectral imagery under remote sensing. L needle ice Thin ice crystals formed on soil and multispectral scanner (MSS) See multispectral rocks from frost-heaving. scanner (MSS) under remote sensing. LH negative heterograde See negative heterograde muskeg Seemuskegunder wetlands. under stratification. L~ , I J 76 .. nekton nekton Actively swimming organisms able to nonfoliar shading See nonfoliar shading under I move independent of water current. stream surface shading. , -.J neoglacial moraine See neoglacialmoraine under nonhydric Soils that develop under predomi- , moraine. nantly aerobic soil conditions. -.J, neritic zone Relatively shallow water zone in nonmarine sediment Sediment that accumulates :JI oceans or seas that extends from the high-tide in rivers or freshwater lakes. mark to the edge of the continental shelf. :J, nonpersistent emergent See nonpersistent emergent , net primary production See net primary production under macrophyte. -I under production. nonpersistent wetland See nonpersistent wetland :J net seston See net seston under seston. under wetlands. ---. ...J neuston Microscopic organisms associated with habitats at the interface of air and water. See nonpoint source Usually applied to pollutants entering a water body in a diffuse pattern rather ...... pleuston. than from a specific, single location that includes land runoff, precipitation, atmospheric deposi- epineuston Neuston living on the upper :J surface of water. tion, or percolation...... hyponeuston Neuston living on the underside nonsaturated zone Zone where the actual amount of the surface water film. of oxygen or other material dissolved in water is -~ less than saturation. neutral estuary Type of estuary where neither the ...... freshwater inflow nor evaporation predominates nonsensitive reservoir Reservoir where overall (Le., total freshwater inflow and precipitation productivity is not decreased by low reservoir . , equals evaporation). production rates. -J niche (1) Ecological position of an organism nonwetland Area that is sufficiently dry so that within its community or ecosystem that results hydrophytic vegetation, hydric soils, and wet- . , from the organism's structural adaptations, land hydrology do not occur; includes uplands as physiological responses, and specific behavior. well as former wetlands that are drained. An analogy is, the habitat is an organism's .. "address," while its niche is its "profession." nonwoody benthic organic matter See nonwoody . , (2) Ecological and functional role of an organism benthic organic matter under benthic organic in a community, especially with regard to its food matter. consumption. See microhabitat. normal erosion See normal erosionunder erosion. nick point () (1) Narrowing of a channel causing an increase in current velocity normal high water High water mark that occurs that results in an upstream accumulation of annually in a water body. In streams, it occurs at water and deposition. (2) Abrupt changes in bank-full flows and is also called the peak annual slope at the confluence of streams or associated flow (QFP). with geologic features. nose velocity Water velocity immediately in front nodal point See nodalpointunder wave. of a fish that is positioned into the current. node Refers to the ending points of a line that is nuisance organism Term applied to an organism used in GIS systems as a reference point along a that is capable of interfering with the use or stream. treatment of water. nonelastic Crystalline chemical precipitates nutrient Element or compound essential for forming sedimentary deposits. growth, development, and life for living organ- nonflooding floodplain See nonflooding floodplain isms such as oxygen, nitrogen, phosphorus, and under floodplain. potassium. L organicdebris

C nutrient budget Gain and loss of all nutrients in a offshore Away from, moving away from, or at a [: specific water body. distance from the shore. nutrient cycling Circulation of nutrient elements offshore wind Wind blowing away from the shore. L and compounds in and among the atmosphere, soil, parent rock, flora, and fauna in a given area ogee Seeogeeundercontrolstructure. such as a water body. I: old river See old river under river. ~ nutrient depletion Situation where the export of nutrients is greater than the import and where oligohaline See oligohalineunder salinity. the reduction in the total amount of nutrients and L oligomictic See oligomictic under mixing. their rate of uptake, release, movement, transfor- L mation, or export negatively affects organisms oligopelic Bottom deposit containing very little clay. that inhabit a particular area. oligosaline Seeoligosalineunder salinity. L nutrient loading Addition of nutrients into the L water column via runoff, discharge, internal oligosaprobic zone Seeoligosaprobiczoneunder recirculation, groundwater, or atmosphere. saprobein system.

t: nutrient spiraling Cycling and downstream oligotrophic See oligotrophicunder trophic. transport of nutrients from physical and biologi- I: cal activities in a stream. onshore In water, refers to a location on, moving onto, close to, or parallel to the shore. On land, t: refers to a location adjacent to a water body.

L: ~O onshore wind Wind blowing toward the shore. L: oasis Isolated, fertile area with vegetation in an ooze (1) Soft, fine-textured bottom mud. (2) A arid region that is supplied with water from a condition where a substance flows, or is ex- L: well or spring. truded, very slowly through openings. L: obligate wetland species See obligate wetland opacity Degree of obstruction to light passage. speciesunder wetland status. open basin Basin with a surface outlet. C obsequent stream See obsequent stream under stream. C open lake Seeopenlakeunder lake. obstruction Object or formation that partially or open water (1) Water free of vegetation, stumps, C wholly blocks or hinders water flow and move- or artificial obstructions that is away from the ment of organisms or that restricts, endangers, shoreline. (2) Water in a pond, lake, or reservoir L or interferes with navigation. Examples in that remains unfrozen or is not covered by ice aquatic habitats include geologic features, falls, during winter. L cascades, chutes, beaver dams, and dams 011 impoundments. operating pool Amount of water retained in a L reservoir for limited periods and released to occasionally flooded floodplain See occasionally operate turbines. L floodedfloodplainunder floodplain. optimum flow Seeoptimumflow under flow. L oceanadromous Life cycle strategy of fish includ- ing migrations, reproduction, and feeding that optimum level The most suitable degree of any L occur entirely in saltwater. Compare with environmental factor for the well-being, health, anadromous, catadromous, diadromous, and and productivity of a given organism. potamodromous. L organic See organicunder streambank material. off-channel pond See off-channelpondunder pond. l organic debris Material of organic origin that off-channelpools Seeoff-channelpoolsunder ranges in size from fine particulate matter to l habitat enhancements. large trees. 78 ~ organicparticles

organic particles Particles that are ofbiological outslope Face of a fill or embankment that slopes origin. downward from the highest elevation to the toe.

coarse particulate organic matter (CPOM) outsloping Sloping a road surface to direct water Living or dead organic material ranging in away from the cut side of the road. size from I mm (0.04 in) to 10 cm (4 in) that is often referred to as detritus. outwash Material, chiefly sand or gravel, that is dislodged (i.e., washed) from a glacier by melt dissolved organic matter (DOM) or dissolved water. organic carbon (DOC) Organic material that is smaller than 0.45 !Lm(i.e., passes through a outwash fan Detritus mass deposited at the foot 0.45 !Lmfilter). of a glacier or mouth of a gorge by free-flowing water that is heavily loaded with sediment where fine particulate organic matter (FPOM) Organic velocity is suddenly reduced as a result of lower material ranging in size from 0.45 !Lmto lateral constrictions. lmm.

ultrafine particulate matter Matter smaller outwash plain Flat area formed gradually by than 0.45 !Lm. sediment carried to the site from a glacier and deposited by changes in carrying capacity of organism Any living thing composed of one or glacier meltwater. more cells. overbank flooding Any situation where inunda- orientation Position of an object or organism tion occurs when the water level of a river or relative to the direction of streamflow or current stream rises above the bank. in a lake, reservoir, or ocean. overbank storage Flood water from overbank orthograde See orthogradeunder stratification. flooding of a stream that remains in floodplain depressions where it is temporarily "stored" until orthophotos See orthophotosunder remote sensing. it percolates into the stream or evaporates into the atmosphere. oscillation Repeated, regular fluctuation above and below some mean value, or a single fluctua- overflow See overflow under mixing. tion between the maximum and minimum levels of such a periodic fluctuation. See also oscillation overflow channel Abandoned channel in a under wave. floodplain that carries water during periods of high runoff. outer beach Zone of a beach that is ordinarily dry and wetted only by waves during violent storms. overhang Organic or inorganic materials that project over or into a water body. outfall Outlet of a water body, drain, culvert, or other structure. overhead cover Plant foliage or overhanging material that provides protection to fish or other outflow Water flowing out of a water body, drain, aquatic animals. sewer, or other structure. overlay See overlay under remote sensing. outlet (1) Opening or passage that allows water to flow from one place to another. (2) River or oversaturation Concentrations of dissolved gases stream flowing from a water body. (3) Terminus or other dissolved materials that exceed the or mouth of a stream where it flows into a larger predicted saturation level in water based on water body such as a lake, reservoir, or sea. temperature and pressure. outlet depth Midline depth of principal outlet. overturn Seeoverturnunder stratification. outlet drain Drain that collects and transports the oxbow Bend or meander in a stream that becomes discharge of side drains. detached from the stream channel either from natural fluvial processes or anthropogenic outlet tower See outlet towerunder control structure. disturbance. C L pelagic ... 79

L oxbow lake See oxbow lakeunder lake. passage An avenue or corridor for fish migration either up or down a river system. C oxygen deficit Difference between the observed oxygen concentration and the amount that would patch More homogeneous ecological islands that C theoretically be present at 100% saturation for are recognizeably different from parts of an existing conditions of temperature and pressure. ecosystem that surround them but interact with E: the rest of the ecosytem.

[J paternoster lake Seepaternosterlakeunder lake. ~p I: pattern Configuration of a channel reach described paleopotamon Seepaleopotamonunder meander. in terms of its relative meander characteristics. I: palustrine (1) Nontidal wetlands that are domi- pavement Surface layer of resistant material in a I: nated by trees, shrubs, persistent or nonpersis- streambed, such as stones and rocks, exposed tent emergents, mosses, or lichens. (2) May also after finer materials have been eroded away. I: include wetlands (smaller than 8 ha) without vegetation, wetlands with water depths less than pay lake Seepaylakeunder lake. L: 2 m, and wetlands with salinity of less than 0.5 ppt. See also palustrine under wetlands. peak flow Seepeakflow under flow.

L parallel stream See parallelstream under stream. peat Unconsolidated, partially decomposed organic-mainly plant-material, deposited C parameter Any quantitative characteristic that under waterlogged, oxygen-poor conditions. describes an individual, population, or commu- A layer of organic material containing plant C nity or that describes the biological, chemical, residues that have accumulated in a very wet environment. C and physical components of an ecosystem. parapotamon Seeparapotamon under meander. peat bog See peat bog under wetlands. C parent material Unconsolidated (more or less) peatland General term for any land covered with L weathered mineral or organic matter from which a soil layer that contains a higher percentage of soil is developed. peat than adjoining areas. L partial meromixis Seepartial meromixis under pebble Small (2-64 mID), gravel-sized stone with L mixing. rounded edges, especially one smoothed by the action of water. Compare with other substrate particle Individual fragment of organic or mineral sizes under substrate size. L material. L pebble beach Beach area dominated by small, particle cluster Cluster of small particles that are gravel-sized, rounded stones. grouped around one or more large particles and L do not move until the large particle moves. pebble count Method of measuring the composi- tion of streambed material by manual collection L particle size Linear dimension, usually designated while wading a stream. as "diameter," that characterizes the size of a L particle. pediment Gradually sloping rock surface at the base of a steep slope, usually covered by thin L- particle size distribution Frequency distribution alluvium. Also applied to a gentle sloping rock (expressed as dn)of the relative amounts of surface in front of an abrupt and receding l_.- particles in a sample that are within a specified hillslope, mountain slope, plateau, or mesa in an size range, or a cumulative frequency distribu- arid or semi-arid environment. l tion of the relative amounts of particles that are

r coarser or finer than a specified size. pelagic (1) Open water areas of lakes, reservoirs, L or seas away from the shore. (2) Refers to organ- particulates Any finely divided solid substance isms at or near the surface in water away from L suspended in the water. the shore. Compare with limnetic. --' 80 ~ pelephilic _.J

pelephilic See pelephilic under benthos. perilithon Organisms (microscropicalgae, proto- zoans, fungi, and bacteria) growing on the pellicle Refers to a thin film or skim of material submerged portion of coarse rock substrates. on the surface of water. period Seeperiod under wave. -I pelometabolism Metabolism in benthic sedi- ments, primarily bacterial metabolism in anaero- periodic drift Drift of bottom organisms that J bic conditions. occur regularly or at predictable time periods such as diurnal or seasonal. --I pelorheophilic See pelorheophilicunder benthos. periodically flooded Seeperiodicallyfloodedunder _.J peneplain Low, large, nearly featureless land flooding. surface deposited by erosional processes operat- --./ ing over a long period of time. periodicity Tendency to recur at regular intervals.

peninsula Arm of land almost completely sur- period of uninodal surface oscillation Seeperiod rounded by water. ofuninodalsurfaceoscillationunder wave. penstock Seepenstockunder control structure. periphyton Attached microfIora growing on the bottom, or on other submerged substrates, peraquic moisture regime Soilcondition where including higher plants. -.. reducing conditions always occur due to the presence of groundwater at or near the soil epilithic Flora growing on the surface of rock surface. or stones. epipelic Flora living on fine sediment. percent fines Percentage of fine sediments, by _-.1 weight or volume, that are less than 2 mm epiphytic Flora growing on the surface of (0.08 in) in diameter in substrate samples. See macrophytes. fine sediment. epipsammic Flora growing on or moving perched groundwater Groundwater that is through sand. separated from the main groundwater body by permanently flooded Water regime where unsaturated, impermeable material. standing water covers the land surface during the entire year, except during extreme droughts. perched lake Seeperchedlake under lake. See various types of aquatic habitats in such areas under wetlands. Seealso permanently perched stream Seeperchedstreamunder stream. floodedunder flooding, floodplain, and water percolation Downward movement of water regime. through soil, sand, gravel,or rock. permeability Measure of the rate at which water , lake, or other water body with can penetrate and pass through a medium such water present continuously during a normal as soil or other substrate. The rate depends on the composition and degree of compaction of the water year. substrate. perennial astatic See perennial astaticunder astatic. persistent emergent hydrophytes Hydrophytes perennial flow See perennialflow under flow. that normally remain standing, at least until the beginning of the next growing season. perennial lake Seeperenniallakeunder lake. pesticide Any chemical used to control popula- periglacial Pertains to active valley wall processes tions of organisms that are undesirable to hu- characteristic of very cold regions such as found mans. The term "pesticide" is a generic term that next to active glaciers or in alpine terrain. is applied to chemicals used to control animals. More specific terms include "herbicide" (to periglacial landslide Seeperiglacial landslide under control plants), "insecticide" (to control insects), landslide. and "lampricide" (to control sea lampreys). L L plankton:zooplankton

C pH Measure of the acidity and alkalinity of a pinnate stream See pinnate stream under stream. solution, expressed as the negative loglo of the C hydrogen-ion concentration on a scale of 0 piping Bank erosion caused by seepage of (highly acidic) to 14 (highly basic). A pH of 7 is groundwater, with subsurface erosion that C neutral. creates underground conduits, sometimes causing collapse of the surface. C PHABSIM Abbreviation for "physical habitat simulation method" that is used to translate piping depression pond See piping depressionpond c changes in streamflow to changes in quantity and under pond. quality of habitat. For a range of measured and pitch See pitch under remote sensing. r: simulated flows, the distribution of depths, velocity, substrates, and cover types across a pixel See pixel under remote sensing. c: channel are converted to an index of physical habitat as preference curves for a given species placer Shallow deposits of gravel or similar L: and life stage. substrate containing precious metals such as gold. The term is also applied to the site or form C photic zone Seeeuphotic zone. of mining.

C photogrammetry Seephotogrammetryunder placid Term refers to surface water that is quiet remote sensing. with no eddies or waves and that is usually C associated with very slowly moving waters. photophobic Term applied to an organism that C avoids light. placid flow See placidflow under flow. C phototrophism Movement of organisms in plain Any flat or gently sloping (elevation differ- response to light. ences of less than 150 m [500 it]) area formed from C deposition of eroded substrates at low elevations phreatophyte Deeply rooted plant that obtains its and that may be forested or bare of trees. water supply from a more or less permanent L subsurface zone of saturation. plane bed Bed of fine sediments.

L physicochemical Term applied to the physical and plankton Small plants and animals, generally chemical characteristics of an ecosystem. smaller than 2 mm and without strong locomo- L tive ability, that are suspended in the water phytophilic See phytophilic under benthos. column and carried by currents or waves that L may make daily or seasonal movements in the phytoplankton See phytoplankton under plankton. water column. L picoplankton See picoplankton under plankton. macroplankton Planktonic organisms that are L larger than 500 J..Lm. piedmont Deposit that is located or formed near L the base of a mountain. Also applies to a physi- microplankton Planktonic organisms that ographic province located between mountains range in size from 50 to 500 J..Lm. and a coastal plain. L nannoplankton Planktonic organisms that range in size from 10 to 50 J..Lm. L Structure constructed on pilings or that floats and that is used as a moorage for boats. See phytoplankton Planktonic plants that are L pilings. composed primarily of diatoms and algae. piezometer Small diameter, nonpumping tube, picoplankton Planktonic organisms that are L pipe, or well used to measure the elevation of smaller than 1 J..Lm. r water table or potentiometric surface. L ultraplankton Planktonic organisms that range pilings Vertical columns, usually of timber, steel, in size from 0.5 to 10 J..Lm. or reinforced concrete, that are driven into the L zooplankton Planktonic animals that are bottom of a water body to support a structure composed primarily of protozoans and small L- such as a pier or bridge. crustaceans. 82 ~ plateau plateau Flat areas that are elevated over the point of inflection Seepointofinflectionunder surrounding terrain. meander. playa lake See playalakeunder lake. point source Material, usually pollutants, flowing into a water body from a single well-defined plesiopotamon See plesiopotamonunder meander. source such as a pipe or ditch. pleuston Organisms adapted for life in the pollute To contamina:t~ land, water, air, plants, interface between air and water. animals, or microorgamsms with substances considered objectionable or harmful to the health epipleuston Organisms living on the surface of of living organisms. the air-water interface. pollution Presence of matter or energy, usually of hypopleuston Organisms living on the under- human origin, whose nature, location, or quan- side of the air-water interface. tity, produces undesired environmental effects on plug A piece of material or an accumulation of natural systems. material that prevents the movement of water or other fluids. polygon See polygon under remote sensing. polyhaline Seepolyhalineunder salinity. plume (1) Flow of dissolved or suspended mate- rial into a larger water body. (2) Mass of water polymictic Seepolymicticunder mixing. discharged by a river, outfall, or some other source into a water body that is not completely polysaline Seepolysalineunder salinity. mixed and retains measurably different charac- teristics from the rest of a water body. polysaprobic zone. See polysaprobiczone under saprobien system. plunge lake See plunge lakeunder lake. pond Natural or artificial body of standing water plunge pool See plunge pool under pool, scour pool that is typically smaller than a lake (less than 8 ha under the main heading channel unit. [20 acre]), characterized by a high ratio of littoral zone relative to open water. plunging breaker See plunging breakerunder wave. aerated pond or Natural or artificial basin where mechanical equipment is used to pluvial Refers to rain or the action of falling rain. increase the supply of oxygen to decompose organic waste, increase aquaculture produc- pluvial lake See pluvial lakeunder lake. tion, or improve aesthetics. pocket water See pocket water under pool, scour pool aestival pond Pond that exists only in summer. under the main heading channel unit. Mostly small, irregular water exposures in barren lava with a surface level at poco sin See pocosin under wetlands. the marine water table so the water is poikilohaline See poikilohalineunder salinity. mixohaline from dilution by groundwater and salinity is usually 1-10%0. poincare wave See poincarewave under wave. beaver pond Pond containing water im- pounded behind a dam built by beaver. point Peninsula or land that projects from the shore into a water body. A stationary location borrowpit pond Pond formed by the accumula- used for reference such as the single source of a tion of water in an area excavated by mining pollutant. for sand, gravel, or boulders used in construction. See point barunder bar. charco Small pond formed by a soil dam that is point of diversion Location where water is usually round with a basin shaped like an diverted for some use. inverted cone that is filled by groundwater. u u pool feature ... 83

(J Often found in the desert of southwestern some instances) and generally supplied with 0 . groundwater. cooling pond Pond with water used to cool sag pond Small body of water occupying a [J equipment in a power plant or other industrial depression or sag formed by active or recent u facility. geologic fault movements. dug pond Pond formed by excavation, without salt chuck pond A log pond in seawater. [J a dam, and supplied with water from runoff Compare with salt chuck. or seepage. sedimentation pond Impoundment created to G dune pond Pond in a basin formed from the trap suspended sediments. Seesettlingpond blockage of a stream mouth by sand dunes and stillingpondunderpond. t: that move along a shoreline of an ocean. settling pond Impoundment used to precipi- tate materials that accumulate on the bottom [: evaporation pond Shallow ponds filled with water that are allowed to evaporate to recover and are removed periodically. See sedimenta- 1: suspended or dissolved materials such as salts tion pond and stilling pond under pond. or other minerals. stilling pond Deep depression constructed in a (: streambed on the outwash fan that is used to farm pond Pond created for agricultural catch detritus and sediments. See sedimentation purposes (i.e., irrigation or water for live- t: stock), culture of commercial fishes, or for pond and settling pond under pond. L: recreation (including sportfishing, swimming, tank Artificial pond to hold water for livestock, and boating). wildlife (sometimes including fish) and other uses. C fault sag pond Pond in a small depression along an active or recent geologic fault that is vernal pond Small (usually less than 1 ha), C supplied by groundwater. temporary pond that forms from melting snow and rainfall in late winter or early C holding pond Pond or reservoir constructed for spring. settling and storage of sediments, for aerating c:.. or aging water for a fish hatchery, or for wall-based pond See off-channelpond under storing wastes or polluted runoff. pond. L lagoon See lagoon. pondage Term applied to storage capacity or water that is held for later release above the dam C log pond Pond used for storing logs, generally of a hydroelectric plant to equalize daily or attached to saw or veneer mills. See mill pond. L weekly fluctuations of streamflow or to permit mill pond Impoundment created by damming irregular releases of water through turbines to L a stream to produce a head of water for accommodate the demand for electricity. operating a mill or for storage of logs. Synony- ponded Water that is impounded from anthropo- mous with log pond. L genic or natural blockage or obstruction. Also off-channel pond Pond that is not part of the referred to as ponding. L active channel but is supplied with water from overbank flooding or through a connection pool Small depression with standing water such L with the main stream by a short channel. as found in a marsh or on a floodplain. Also see These ponds are generally located on flood poolunder slow water under the main heading L terraces and are called wall-based channel channel unit. ponds when located near the base of a valley L wall. pool digger Rock or log structure designed to scour a plunge pool on its downstream side or a r L- piping depression pond Pond that forms in a lateral scour pool. small depression resulting from subsurface c I pooled channel See pooledchannelunder stream. L piping. quarry Pond formed in the depression created pool feature Condition or object that causes the L by excavation of rock or coal (as well as clay in formation of a pool including logs, trees, roots, .- J 84 ~ pool margin . .

. '" stumps, brush, debris, channel meanders, hypopotamon Bottom layer of the potamon sediment deposition, beaver dams, culverts, region. -.., . . bridges, or other artificial or natural structures. metapotamon Intermediate layer of the pool margin Outer edge of a pool as identified by potamon region. -.4 bed topography. potamon plankton Plankton living in freshwater . oJ lotic habitats. pool quality Estimate of the ability of a pool to . support target fish species, based on measure- potential energy See potential energy under energy. . ments such as length, width, depth, velocity, and --, cover. pothole lake See potholelake under lake. pool: riffle ratio See pool: riffle ratiounder power pool See operating pool. _.. dimensions. prairie pothole Ponds, pools, lakes, and wetlands poorly drained Condition where water is re- found in depressions (potholes) that were formed moved from the soil so slowly that the soil is by glacial activity. A local term used in the Great saturated periodically during the growing season Plains of central United States and . See and remains wet for long periods (e.g.,more potholelakeunder lake. than 7 d). precipitate Solid that settles from water through pore space Unoccupied interstices in the substrate. physical or chemical changes. porosity (1) Existence of interstices or "pores" in precipitation Water, hail, sleet, and snow that falls soil or rock, and the ratio of the volume of pores to earth from its origin as atmospheric moisture. to the total volume of solids plus voids. (2)Also refers to the ease or speed that water can move predators See predatorsunder macroinvertebrate. into or through the substrate. See also porosity under groundwater. preservation Protection and maintenance of intact and functional natural areas and ecosystems. positive estuary Coastal indentures where there is Compare with restoration. a measurable dilution of seawater by land drainage so that freshwater inflow plus precipita- pressure A force per unit of area. tion is greater than evaporation. pressure head See pressureheadunder dimensions. positive heterograde See positive heterogradeunder stratification. pristine Term used to describe a natural location or habitat unaffected by anthropogenic disturbances. potable Water that is suitable or safe for drinking problem area wetland See problemareawetland according to established health standards. under wetlands. potamodromous Life-cycle strategy of a fish that includes migrations, spawning, and feeding process water Water used in manufacturing or entirely in freshwater. Compare with anadro- processing including the production or use of mous, catadromous, diadromous, any raw material, intermediate product, finished oceanadromous. product, by-product, or waste product. See effluent. potamology Study of the biological, chemical, geological,and physical aspects of rivers. production (1) Process of producing organic material. (2) Increase in biomass by individuals, potamon Portion of a stream that includes the species, or communities with time (e.g., the total thalweg (or deepest part of the channel) and is amount of fish tissue produced by a population nearly always defined as lotic. Also applied to of fish within a specified period of time). that portion of a stream that contains water even if discharge becomes intermittent. gross primary production Total rate of photo- synthesis including the organic matter used up epipotamon Upper layer of the potamon region. in respiration during the measurement period. L L

L net primary production Rate of storage of greatest dimension), shallow (usually a few organic matter in plant tissues in excess of the inches in depth) pool of water that is ephemeral L respiratory use by the plants during the and often dirty or muddy. measurement period. L. pump chance Water body, usually small, that is secondary production Total energy storage at accessible to equipment collecting water for fire r:: the consumer and decomposer trophic levels. control. Consumers and decomposers utilize food C materials that have already been produced pumped storage reservoir Reservoir used to store and convert this matter in different tissues water for use during peak periods of electricity t: with energy loss to respiration. Efficiency of production. During periods of low demand for conversion in secondary production decreases electricity, water is pumped into the storage t: with trophic levels. reservoir for later release through turbines to generate electricity during periods of peak C productivity (1) Rate of formation of new tissue or demand. energy use by one or more organisms. (2) Capac- ity or ability of an environmental unit to produce pycnocline See pycnocline under stratification. C organic material. (3) Recruitment ability of a L population from natural reproduction. profile Graphical or other representation of shape ~q L or relationship. Compare with stream profile. quaking bog See quaking bog under wetlands. L profundal Deep, bottom-water area beyond the depth of effective light penetration including all quarry See quarry under pond. L. of the lake or sea floor beneath the upper margin of the hypolimnion. quick sand Soft or loose sand, sometimes of meas- L urable depth, saturated with spring or stream progressive wave See progressivewave under wave. L water that yields when weight is placed on it. prolonged speed See prolongedspeedunder C swimming speed. ~r C promontory High point of land or rock overlook- ing or projecting into a water body. radial See radialunder stream.

L protected area Area administratively set aside as a radial gate See radialgate under gate and main L buffered or structured area that is shielded from heading of control structure. damage from anthropogenic disturbances. radio telemetry See radio telemetry under remote L psammon Refers to the beach zone along an ocean sensing. or an organism growing in or moving through L sand on the beach. radius of curvature See radius of curvature under dimensions as well as under meander. L psammorheophilic See psammorheophilicunder benthos. raft (1) Collection of timbers or bamboo, tied L together or enclosed within a boom, for transport public lake See public lakeunder lake. by floating. (2) Also, a large number of closely L spaced timbers that can free float on water. public water Water that is navigable by federal rain-on-snowevent Event that occurs in late Ld. test or court decree, legally accessible over public lands, or impressed with prescriptive rights winter, spring, and early summer when snow- '-.r vested in the public. packs are partially or completely melted during rainstorms causing flooding. I L public water system System providing piped water for public consumption. rain shadow Area of reduced precipitation on the leeward side of mountains that results from the L Small (several inches to several feet in its interception of storms by the mountains.

>.. 86 ~ raisedbog ......

-..J raised bog See raised bogunder wetlands. larval and juvenile fish find food and shelter to live and grow. Also referred to as nursery habitat. --, rapids See rapids under fast water-turbulent with J the main heading of channel unit. reattachment bar See reattachment barunder bar. , ; raster See raster under remote sensing. receiving site Water collection sites where water is , collected by subsurface flow from higher eleva- ~ raster data See raster data under remote sensing. tions and precipitation. --, J ravine Narrow, steep-sided valley that is com- receiving waters Any body of water into which -, monly eroded by running water. untreated or treated wastes, or polluted waters, --,< are discharged. raw water Untreated surface or groundwater that is -J available for use but mayor may not be potable. recessional moraine See recessionalmoraineunder moraine. reach (1) Any specified length of stream. (2) Relatively homogeneous stretch of a stream recharge Process by which water is added to an , having a repetitious sequence of physical charac- aquifer. teristics and habitat types. (3) Length of channel - ,-/ where a single gage affords a satisfactory mea- recharge area Area where water infiltrates into the sure of the stage and discharge. (4) Portion of a ground and joins the aquifer through hydraulic stream that extends downstream from the head. confluence of two streams or rivers to the next - -, encountered confluence. (5)According to the recharge zone Area through which water is added Environmental Protection Agency, that portion of to an aquifer. -' a river reach extending downstream from the confluence of two rivers (or from the uppermost reclamation (1) Most recently defined as any -l --.J end of a river) to the next encountered action that results in a stable, self-sustaining confluence. ecosystem that mayor may not include intro- , duced species. (2) Traditionally defined as the ..J archival reach Reach whose boundaries and process of adapting natural resources to serve a properties have been modified by natural or utilitarian human purpose. Historically this term 0' I other events since an original survey was included the conversion of riparian or wetland conducted. Original data is compared with ecosystems to agricultural, industrial, or urban _4 new data to evalute changes. uses.

critical reach Stream segment that is essential recovery Ability of a disturbed system to re- for development and survival of a particular establish habitats and plant or animal communi- / aquatic organism, or a particular life stage of ties that were present prior to the disturbance. an aquatic organism. recreational pool The "normal" surface elevation representative reach Stream segment that of a reservoir with fluctuating water levels that is represents a larger segment of the stream generally a stable level established by the water with respect to area, depth, discharge, slope, controlling agency to maximize recreational uses or other physiochemical or biotic characteristics. during spring, summer, and fall (i.e., open water period). Compare with summer pool. specific reach Stream segment that is uniform with respect to selected habitat characteristics rectangular drainage See rectangular stream under or elements (discharge, depth, area, slope, stream. population of hydraulic units), species compo- sition, water quality, and condition of bank rectangular stream See rectangular stream under cover. stream. reaeration Supply of oxygen to oxygen-depleted rectification See rectification under remote sensing. water. recurrence interval Expected or observed time rearing habitat Areas in a body of water where intervals between hydrological events of a C L remote sensing: aerial photography'" 87

L particular magnitude described by stochastic or regular meander See regularmeanderunder meander. probabilistic modes (log-log plots). The average C. interval of time within which a given event, such regular meander channel See regular meander C as a flood, will be equalled or exceeded one time. channel under channel pattern. redd Nest excavated in the substrate by fish for regulated flow See regulatedflow under flow. L: spawning where fertilized eggs are deposited and develop until the eggs hatch and larvae regulated zone Area in a reservoir between c: emerge from the substrate. conservation pool and flood control pool. t: reducers Organisms, usually bacteria or fungi, regulation Control of the volume and timing of that break down comple~ organic materials into streamflow at a specific location. c: simpler compounds. rehabilitation (1) Action taken to return a land- t: reef Ridge of rocks, sand, soil or coral projecting form, vegetation, or water body to as near its from the bottom to or near the surface of the water. original condition as practical. (2) Term implies C making land and water resources useful again reference wetland See referencewetland under (primarily for humans) after natural or anthropo- wetlands. genic disturbances. This term differs from C restoration that implies a return to predisturb- reflectance See reflectanceunder remote sensing. ance conditions and functions in natural aquatic C or terrestrial systems. See restoration. reflected solar radiation See reflectedsolar radiation t: under solar radiation. rejuvenated river See rejuvenated river under river.

C refracted solar radiation See refractedsolar radia- relative depth See relative depth under dimensions. tion under solar radiation. C relative thermal resistance Ratio of the density refraction See refractionunder wave. difference between water at the top and bottom L of a water column with a definite thickness, to refugium (1) Habitats that support sustainable the density difference between water at soC and C populations of organisms that are limited to 4°c. "Thermal resistance" also refers to mixing, fragments of their previous historic and geo- or the amount of work done by meteorological or L graphic range. (2) Habitats that sustain organ- anthropogenic events to mix a water column. isms during periods when ecological conditions C. are not suitable elsewhere. For example, trout in relict Remnant of a biotic community or popula- alpine areas use the deeper pools in a stream tion that was formerly widespread. L during winter or fish use a lake with high dissolved oxygen levels to escape adjacent relict lake See relict lakeunder lake. L hypoxic swamps and marshes. (3) Waters where threatened or endangered fishes are placed for relief (1) Change in elevation of a land surface l- safe-keeping or where a portion of the popula- between two points. (2) Configuration of the tion is maintained to prevent extinction. earth's surface including such features as hills L and valleys. regime (1) Seasonal pattern of streamflow during L. a year. (2) Balance or equilibrium of erosion and relief ratio See relief ratiounder dimensions. deposition in a channel with time so that the stream channel maintains its overall remote sensing (1) Acquisition of information L characteristics. from a distance, generally by transmissions that r involve electromagnetic energy and sometimes ~" regimen Characteristics of a stream with respect by gravity and . (2) Measurement or L to velocity and volume changes in a channel acquisition of data on an object by satellite, aerial capacity to transport sediment and the amount of photography, and radar that are some distance sediment transported with time. from the object.

regolith Unconsolidated mantle of weathered rock, aerial photography Images on film or in digital soil, and surficial materials overlying solid rock. format taken above the surface of a planet. ~t-- -J 88 ~ remote sensing:attribute I...... ---. attribute Nongraphic information associated digitizing Process that converts nondigital data with a point, line, or polygon. into numerical data that is usually stored in a -.., computer. J AVHRR Advanced very high resolution (1.1 X 1.1 km or 4 X 4 km) radiometer data false color Use of one color to represent a :J with small-scale imagery produced by a characteristic or feature or a color substituted NOAA polar orbiting satellite. for the true color on an image. :J r, azimuth Principal plane in a clockwise angle on geometric registration Process of aligning data -, J a tilted photograph. resolution scales so that information can be visually or digitally superimposed. ~ band Set of values for a specific portion of the -J ground cover (1) Vegetation and litter on or electromagnetic spectrum of reflected light, ~ emitted heat, or some other user-defined slightly above the ground surface. (2) The -4 percentage of area bearing such cover. information, created by combining or enhanc- ~ ing the original bands. ground truthing Field verification of data J band ratio Method in which ratios of different gathered away from the site by remote sensing -.J spectral bands from the same image or from or by some other method. ~

two registered images are used to reduce image Picture or representation of an object or ,J certain effects such as topography or to scene on paper or computer display screen. enhance subtle differences of certain features. ---... Remotely sensed images are digital represen- .-J tations of the earth. cartesian Coordinate system in which data are ---... organized on a grid and points on the ground landsat Satellite system that provides imagery - J are referenced by their x- and y-coordinates. used for remote sensing inventory and analy- ---... sis. Also refers to a series of earth-orbiting -..,J cell Pixel or grid cell with a 10 X 10area of satellites gathering multispectral scanner or ---, coverage. thematic mapper imagery. ~ cell size Area represented by one pixel, mea- landsat multispectral scanner (MSS) Satellite- --4 sured in map units. borne sensor capable of recording reflectance class Set of pixels in a GIS file that represents energy from the surface of the earth in four -I areas that share some condition. wavelength bands for a 180 X 180 km scene. - .. clump Contiguous group of pixels in one class landsat thematic mapper (TM) Satellite sensor that is also called a raster region. capable of recording reflected and emitted energy from the surface of the earth in seven cluster Natural groupings of pixels when bands or divisions of the visible and infrared plotted in a spectral space. spectrum. conjugate points (conjugate principal points) maximum likelihood Classification decision Positions on an aerial photograph that are rule based on the probability that a pixel principal points on adjacent photos of the belongs to a particular class. The basic equa- same flight line. Conjugate points are used to tion assumes that the probabilities are equal justify or align photographs for creation of a for all classes, and that the input bands have larger photographic mosaic. normal distribution. digital classification Process for using algo- merge The process of combining information rithms to group pixels with similar spectral from one or more sources or the restructuring signatures. of an existing database to create a new data- base that retains the original data. digital enhancement Manipulating digital information to increase or improve features of mosaic (1) Pattern of vegetation across a interest for interpretation. landscape. (2) Composite image created by joining smaller images, usually aerial photo- digital terrain model Analysis of pixel or graphs, into a single composite. topographic information to produce a three- dimensional representation of the landform. multispectral classification Process of sorting Also called digital elevation model. pixels into a finite number of individual L L remote sensing: SPOT'" 89

L classes or categories of data that are based on in physical contact with the object under data files in multiple bands. study. More precisely, recording of environ- C mental images using electromagnetic radiation multispectral imagery Satellite imagery with C data recorded in two or more bands. sensors and their interpretation. resolution (1) Spatial: Ability to reproduce an multispectral scanner (MSS) Landsat sensor isolated object or to separate closely spaced C system that generates spectral data from objects or lines that are usually measured in reflected light in the visible light spectrum. C lines per millimeter. (2) Temporal: How often a nadir Point where a vertical line from the center sensor records imagery of a specific geo- C of the camera lens intersects the plane of the graphcal area. (3) Spectral: The number and photograph. dimension of wavelength intervals in the C electromagnetic spectrum recorded by the orthophotos Images based on aerial photo- sensor. (4) Radiometric: Sensitivity of a C graphs that are true to scale and free of detector to differences in signal strength. distortion. Orthophotos resemble aerial C photographs but are really accurate maps. satellite imagery Passive images of natural radia- tion detected in visual or infrared wavelengths. overlay Process in which data from different C themes or plots are placed over a base map or scan line Strip of land within the view of a C in a series to show spatial interactions. remote sensor as it passes over a surface. photogrammetry Gathering of information on scanning Transfer of analog data, such as C physical objects and the environment by photographs, maps, or other viewable images recording and interpreting images and into a digital (raster) format. L phenomena. sensor Device that gathers energy, converts it to L pitch Rotation of a camera around the y- or a digital value, and presents it in a form exterior x-axis. suitable for obtaining information about the environment. L pixel Abbreviation for "picture element" that is the smallest division of an image. signature Set of statistics that define a training L polygon Closed figure usually with three or sample or cluster that is used in a classification more sides. Also refers to a set of closed lines process. Each signature corresponds to a GIS class that is created with a classification L defining an area. decision rule. L radio telemetry Use of transmitters attached to an animal to send signals to a remote receiver SLAR Abbreviation for "Sideways Looking L that is used to track the animal. Airborne Radar." A form of remote sensing where an aircraft sends out and receives long L raster Pattern of scanning lines that cover an wavelength radiation, and interference in the area where images are projected. return pattern is analyzed for physical features L raster data Data that are organized in a grid of of the area surveyed. An antenna is fixed columns and rows and usually represent a below an aircraft and pointed to one side to L planar graph or geographic area. transmit and receive the radar signal. L rectification Transformation of an image to a sonar Method using echolocation to detect and horizontal plane to correct tilt and to convert locate objects, including living organisms, L to a desired scale. below the surface of water. reflectance Measure of the ability of a surface spectral signature (spectral reflectance curve) L to reflect energy as a ratio of reflected and Characteristic wavelength patterns associated incident light. Reflectance is influenced by the with vegetation, structures, water, or other L nature of the reflected surface and the pattern features. of light. L SPOT Series of earth-orbiting satellites oper- remote survey Measurement or acquisition of ated by the Centre National d'Etude Spatiales r of France. L information by a recording device that is not 90 ~ remote sensing:supervisedclassification

supervised classification Computer- In a remote sensing database, only verticals of implemented classification based on pattern vector data are stored (rather than every point recognition of assigned class signatures. that makes up the element). vector format A GIS database file where supervised training Any method of generating J signatures for classification in which the information is used to code lines and polygons analyst is directly involved in a pattern to express size, direction, and degree of recognition process. Supervised training connection between data points. usually requires an analyst to select training samples from the data that represent patterns remote survey See remotesurvey under remote to be classified. sensing.

swath width Total width of the area on the repose bank See reposebank under streambank. ground covered by the scanner in a satellite ---I system. representative reach See representative reachunder reach. synthetic aperture radar (SAR) Use of a side- looking, fixed antenna sensor to create a reregulating reservoir Reservoir for reducing synthetic aperture. The sensor transmits and diurnal fluctuations in volume from the opera- receives as it is moving, and the signals that tion of an upstream reservoir for power are received during a time interval are com- production. bined to create an image. SAR sensors are mounted on satellites and the NASA space reservoir (1) Generally, natural or artificial im- shuttle. poundment where water is collected, stored, regulated, and released for human use. (2) An thematic data Raster data that are qualitative underground porous, permeable substrate that and categorical. Thematic layers often contain contains accumulated water. See reservoirunder classes of related information, such as land lake and small impoundment. cover, soil type, slope, and hydrology that can be displayed on maps illustrating the class reservoir river See reservoirriver under river. characteristics. residence time Amount of time that some mate- thematic mapper Advanced satellite sensor system in Landsat 4 and 5 that incorporates rial, such as large woody debris, pesticide, or radiometric and geographic design improve- sedimentary material, remains in one location. ments relative to the older MSS system. resident fish Fish species that remain in one water theme Data set used for mapping information body (i.e., nonmigratory species). on a particular subject. Individual theme information can be displayed and related to resident species Organisms normally found in a other themes. single habitat, ecosystem, or area.

training Process of defining the criteria by residual depression storage Depression storage which patterns in image data are recognized that exists at the end of a period of heavy rainfall. for classification. residual depth Term corresponding to a minimum unsupervised classification Computer- streamflow that just barely flows through pools automated method of pattern recognition that is calculated by subtracting water depth at a where some parameters are specified by the riffle crest from water depth in the upstream user to define statistical patterns that are inherent in the data. pool.

vector A line in space characterized by direction residual detention storage Detention storage and magnitude. In GIS systems, vectors are existing at the end of a period of heavy rainfall. used to create a file of points that can be connected from point to point to create line residual pool See residual poolunder slowwater, segments. pool, scour pool under the main heading channel unit. vector data Data that represent physical elements such as points, lines, and polygons. residual volume of fine sediment Fraction of a c.. riffles ~ 91 c.

c scour pool volume (V*) occupied by fine revetment A facing or structure made of hard sediment. material such as boulders or logs along a c streambank or shoreline that reduces erosion. See Vf . riprap under habitat enhancements. c V* = (Vf+ Vr) , Reynolds number (R) Dimensionless value c v = fine sediment volume; expressing the ratio of inertial to viscous forces c v: =residual pool volume. acting on a fluid or a particle in the fluid: resilience Capacity of species or ecosystems to R = VD c recover after a natural disturbance or anthropo- e -' V ' genic perturbation. r: v = velocity of the fluid or particle (m/ s); resistance Capacity of an ecosystem to maintain D a relevant dimension (pipe diameter, natural function and structure after a natural = c particle length, etc.) (m); c disturbance or anthropogenic perturbation. v = kinetic viscosity (1~ m2/s). response segment Reach or segment of a stream rheocrenes Perennial seeps and springs that flow c channel where localized inputs of wood, water, only a short distance over a rock surface or in energy, and sediments causes changes in form to indistinct channels. c that reach of the stream channel. rheophilus Current-loving organisms. c resolution See resolution under remote sensing. rheophyte See rheophyteunder macrophyte. restoration (1) Reestablishment of predisturbance c riparian or stream functions and related biologi- rhithron Reach of stream that extends from the cal, chemical, and physical processes in an headwaters downstream to where the mean C ecosystem. (2) Actions taken to return a habitat, monthly summer temperature reaches 20°C, an ecosystem, or a community to its original dissolved oxygen levels are always high, flow is L condition after damage resulting from a natural fast and turbulent, and the bed is composed of disturbance or an anthropogenic perturbation. rocks or gravel with occasional sandy or silty C (3) Sometimes used to describe reestablishment patches. The rhithron is subdivided into three of fish stocks or populations that were eliminated zones covering a range of water courses. L or reduced from anthropogenic actions. See rehabilitation. epirhithron Upper reaches of the rhithron C region that are characterized by rapids, restrictive layer Soil layer that restricts the waterfalls, and cascades. L movement of water because of its density or composition. hyporhithron Lower reaches of the rhithron L region that are characterized by an increase in resurgent water Water that resurfaces or reappears. backwaters with mud and debris bottoms. L retard Seefence barrierunder habitat enhancements. metarhithron Middle reaches of the rhithron L region that are characterized by a more gentle retarding reservoir See detention reservoir. gradient and higher percentage of pools. '---r retention Portion of the gross storm rainfall that is ribbon falls See ribbonfalls under fast water- intercepted, stored, or delayed, and thus fails to turbulent,falls under the main heading channel L. reach a concentration point by either surface or unit. subsurface routes during the time period under L. consideration. riffle crest Shallowest continuous line (usually not straight) across the channel close to where a L retention time Length of time that water is stored water surface becomes continuously riffled. within a drainage system or water body. L riffles See rifflesunder fast water-turbulent under return flow Seereturnflow under flow. the main heading channel units. L

I 92 ~ rifflestability index riffle stability index An index to determine the riprap See riprap under habitat enhancements. size class percentage of riffle material moved Compare with revetment under habitat during channel forming flows. Determined by enhancements. comparing the largest, commonly occurring size rithron Seerhithron. of particles moved by the force of a frequent flood event to the cumulative particle size distribution of bed materials in a riffle river Large, natural or human-modified stream that flows in a defined course or channel, or a rift lake Seerift lakeunder lake. series of diverging and converging channels. desert river River in an arid area that is charac- rift valley Long, narrow valley resulting from terized by flash floods and no tributaries. subsidence (Le., settling) of strata between more Desert rivers increase in alkalinity and con- or less parallel geologic faults. . ductivity as they flow downstream and may . rill One of the first and smallest channels formed terminate in salt marshes or lakes. -" by surface runoff. flood river River with extremes of annual fluctuation in streamflow. . , rill erosion Mild water erosion caused by over- land flow producing very small and numerous mature river River system where erosion and -" J channels. See also rill erosionunder erosion. deposition are in balance. rilling Removal of soil by water from very small old river River where depositional processes - 4 but well-defined, visible channels or streamlets dominate. where there is substantial overland flow. --J rejuvenated river An old or mature river where gradient changes result in a temporary rever- -..J riparian area (1) Of, pertaining to, situated or sal of normal succession processes. dwelling on the margin of a river or other water body. (2)Also applies to banks on water bodies reservoir river River with an extensive area of --.4 where sufficient soil moisture supports the lakes, swamps, and floodplain depressions growth of mesic vegetation that requires a that stores or holds water. moderate amount of moisture. Also referred to as sandbank river River that conveys floodwaters , riparian management area, or but frequently ceases to flow or even dry out riparian habitat. seasonally. , J riparian ecosystem Ecosystem located between savanna river Floodbank or sandbank river ecocline of aquatic and terrestrial environments. characterized by high silt loads and low pH See ecocline. and conductivity. riparian rights Entitlement to water on or border- tropical river River in the tropics that functions ing a landowner's property including the right to similar to a reservoir river and is characterized prevent diversion of water upstream. by black water with low pH, low conductivity, low silt load, and high humus load. riparian vegetation Vegetation growing on or tundra river River in an arctic or subarctic near the banks of a stream or other water body region with streamflows that fluctuate with that is more dependent on water than vegetation that is found further upslope. the freezing cycle. young river Generally used in reference to the riparian vegetation rating System headwaters where erosional processes are for ranking the relative effectiveness of riparian most active. vegetation to control bank erosion. riverbank Elevated edges of a channel that control ripping The process of breaking up or loosening lateral movement of water. compacted soil to improve aeration and assure development of root systems from seeds or river channel Natural or artificial open conduits planted seedlings. that continuously or periodically contain moving water. Also applied to a connection between two ripple See ripple under wave. water bodies. L L salinity ~ 93

L river continuum Ecological succession that occurs boulders) that obstructs streamflow in a channel from the headwaters to the mouth in a river and and influences the pattern of bed load transport L that is associated with an increase in nutrients and deposition in a stream reach. and organic matter. L rubble Stream substrate particles between 128 and riverine (riverain) (1) Habitats that are formed by 256 mm (5-10 in) in diameter. Compare with L or associated with a river or stream. (2) Wetlands other substrate sizes under substrate size. and deeper water habitats within a channel that L are influenced strongly by the energy of flowing run See run under fast water-nonturbulent under the main heading channel unit. L. water. (3) Also applied to vegetation growing in a floodplain, in close proximity to water courses runoff (1) Natural drainage of water away from L with flowing water, or on islands in a river. an area. (2) Precipitation that flows overland riverine wetland See riverine wetland under before entering a defined stream channel. L wetlands. (3) Total discharge of stream within a specified time from a specific area that includes both L rivulet Refers to a small stream. surface and subsurface discharge and is generally measured in cubic feet (cubic meters) or acre feet L rock Mass of stone of any size, consolidated or (hectare meters) of water. unconsolidated, of various mineral composition. runoff curve Graphic estimator of runoff potential L rock avalanche See rock avalancheunder landslide. in a drainage basin based on precipitation, soils, vegetation, and land use. L. rock creep See rockcreepunder landslide. run-of-the-river flow Flow through a dam that is L rock fall See rockfall under landslide. minimally regulated by the dam and approxi- mates the flow that would occur in the absence of L rock-fill dam (1) Dam composed of large, broken, a dam. and loosely placed rocks that allows water to run-of-the-river reservoir Narrow reservoir that is L percolate and continue to flow downstream. (2) Dam with an impervious core of composted held to the width of the natural river channel in L rock and soil with large rocks (Le.,riprap) on the which short-term water input approximates upstream face or surface. equal short-term outflow. L rock glacier See rock glacierunder glacier.

L rock slide See rock slide under landslide. ~S

L roller dam See rollerdam under habitat saddle Narrow, submerged isthmus of land enhancements. surrounded by deeper water which may connect L a point and an island, hummock, or another land roller gate See rollergate under gate and main mass. L heading control structure. sag pond See sag pond under pond. L rolling flow Seerollingflow under flow. salinas Inland desert basins that are light-colored L root wad See rootwad under large organic debris. from salt. L rotational failure See rotationalfailure under saline (1) Soil or water containing sufficient landslide. soluble salts to interfere with the growth of most L plants. (2) See saline under salinity. roughness Pertains to the irregularity of a sub- L strate surface. saline marsh See saline marsh under wetlands. L roughness coefficient See Manning's n. saline lake See saline lakeunder lake. roughness element Any object or structure ( e.g., salinity Relative concentration of salts, mainly L bedrock outcrops, large woody debris, and sodium chloride, in a given water, expressed as L L r --J 94 ... salinity:euryhaline

the weight per volume or weight per weight. The oligosaline (1) Waters with salinity between terms "haline" and "saline" are often used 0.5 and 5.0%0from land-derived salts. ---' interchangeably, but differ based on the origin of (2) Organisms that are able to live in waters the salts. Haline refers to ocean-derived salts and with a low range of from land- saline refers to land-derived salts. derived salts. ~J -" euryhaline (1) Waters with a salinity between poikilohaline Salt concentrations that fluctuate -, 30.1 and 40%0(parts per thousand) from widely. -..J ocean-derived salts. (2) Organisms that are polyhaline Waters with salinity between 18.1 able to live in waters with a wide range of and 30%0from ocean-derived salts. ocean-derived salts. polysaline Waters with salinity between 18.1 eurysaline (1) Waters with a salinity between and 30%0from land-derived salts. 30.1 and 40%0from land-derived salts. (2) Organisms that are able to live in waters saline Waters with salinity that is greater than with a wide range of land-derived salts. 30%0. freshwater Water with salinity of less than seawater Waters with salinity of about 35%0 0.5%0dissolved salts. dissolved salts. - .1 haline Refers to saline conditions from ocean- stenohaline Organisms that are able to live in derived salts. waters with a narrow range of ocean-derived salts. haloc1ine Well-defined vertical salinity cleav- age or boundary in a water body. stenosaline Organisms that are able to live in waters with a narrow range of land-derived homoiohaline Refers to saline conditions in salts. oceans that are either stable or with narrow fluctuations. saltation erosion See saltation erosionunder erosion. hydrohaline Waters with a salinity greater than 400/00from ocean-derived salts. Also referred to salt chuck General term for the estuarine areas at as hyperhaline. the mouth of rivers. Compare with salt chuck hydrosaline Waters with salinity greater than under pond. 40%0from land-derived salts. Also referred to saltern lake See Saltern Lake under lake. as hypersaline. mesohaline (1) Waters with salinity between salt flat Land area with little or no elevational 5.1 and 18%0from ocean-derived salts. Also changes and with a surface layer of salts that referred to as metahaline. (2) Saltwater organ- remains after prolonged flooding and desicca- isms that are able to live in waters with tion. medium salinities. salt karst lake See salt karst lakeunder lake. mesosaline (1) Waters with salinity between 5.1 and 18%0from land-derived salts. Also See salt marsh under wetlands. referred to as metasaline. (2) Organisms that are able to live in waters with a medium range salt water intrusion Invasion of saltwater into of salinities from land-derived salts. fresh surface or groundwater systems, usually as a result of freshwater depletion that provides mixohaline Waters with salinity between access for saltwater. 0.5 and 30%0from ocean-derived salts. sand Substrate particles between 0.062 and 2 mm mixosaline Water with salinity between 0.5 and 30%0from land-derived salts. (0.00003-0.01 in) in diameter. Compare with other substrate sizes under substrate size. oligohaline (1) Waters with salinity between 0.5 and 5.0%0from ocean-derived salts. sandbank river See sandbank river under river. (2) Saltwater organisms that are able to live in waters with low salinities. sand dune Seesand wave. [J secchidisk ~ 95 [J

c sand splay Deposits of flood debris that are during the growing season. See also saturated usually composed of coarse organic matter and under water regime. c sand particles in the form of splays or scattered debris. saturated zone (1)Area of land that is completely [J soaked by water where the substrate is saturated sand wave Series of generally sinusoidal waves to the surface for extended periods during the [:; that form on the sandy bottom of a river from the growing season. (2) Zone of water with the interaction of flowing water and the substrate maximum concentration of dissolved gases, L when the Froude number is close to or greater elements, or other materials. than one. Sand waves are often transitory, vary in savanna river See savanna river under river. t: height, and may migrate along the river bottom. Also referred to as an or sand dune. t: scan line See scan line under remote sensing. saprobic Term applied to living on dead or scanning See scanning under remote sensing. t: decaying organic matter. scarp (1) Line of cliffs formed by the faulting or L saprobicity Sum of all metabolic processes that fracturing of the earth's crust or by erosion. (2) To can be measured either by the dynamics of form or cut into a steep slope. See escarpment. t: metabolism or analysis of community structure. scattered See scatteredunder large organic debris. [: saprobien system System of classifying organisms according to their response to organic pollution scour Localized erosion of substrate from the L: in slow moving streams. streambed by flowing water when water veloci- ties are high. [: alpha-mesosaprobic zone Zone of active decomposition, that is partly aerobic and scour chain Steel chains implanted in the stre- [: partly anaerobic, in a stream that is heavily ambed to measure scour and sediment deposi- polluted with organic wastes. tion within a period of time. c: beta-mesosaprobic zone Zone of a stream that scour pool See scour pool under slowwater,pool is moderately polluted with organic wastes. c under the main heading channel unit. oligosaprobic zone Stream reach that is slightly scour structure See scour structure under habitat polluted with organic wastes and contains the c enhancements. mineralized products of self-purification from organic pollution with none of the organic c scrapers See scrapersunder macroinvertebrate. pollution remaining. C. scrub-shrub wetland See scrub-shrub wetland polysaprobic zone Zone of a grossly polluted under wetlands. L stream containing complex organic wastes that are decomposing primarily by anaerobic seasonal astatic See seasonalastatic under astatic. L processes. seasonal flow See seasonalflow under flow. L saprolite See saproliteunder streambank material. sapropel Neutral humus or a thick layer of old, seasonally flooded See seasonallyflooded under L stratified and saturated organic matter that is floodplain and water regime. nearly completely mineralized. L seasonally flooded floodplain See seasonally satellite imagery See satellite imagery under remote floodedfloodplain under floodplain. L sensing. seawater See seawaterunder salinity. L saturated Condition where all easily drained secchi disk A disk 20 or 50 cm (-8 or 20 in) in voids (Le., interstices or pores) between soil diameter with alternating white and black L particles are temporarily or permanently filled quarters that is lowered into a water column with with water. This condition results in significant saturation if it continues for one week or more a calibrated chain or rope used to visually L measure the depth of light transparency in water. : L

'-- r 96 ~ secondarilyconfinedchannel

The depth is determined directly from the frequently in contact with a streambed by calibrations on the chain or rope. rolling, sliding, and sometimes bouncing with the flow. Bedload sediments are composed of secondarily confined channel See secondarily particles greater than or equal to 0.062 mm confined channel under confinement. (-0.01 in) in diameter. - J secondary channel See secondary channel under Portion of the stream sedi- channel pattern and slow water, pool,dammed pool ment load that is composed of particle sizes under the main heading channel unit. present in appreciable quantities in the streambed. - , secondary current cells Generally applied to . ; coarse load Portion of the bed load that is more stream currents that move at right angles to the main current, primarily in meandering streams, difficult to move by flowing water than and are responsible for the formation of concave sediment because it requires higher water banks and point bar deposition. Also referred to velocities with enough power to move larger as helical flow or transverse flow. substrate materials. dsoor Dso Size of particle diameters that con- secondary production See secondaryproduction tains 50% fine sediments. The percentage of under production. fines can be set from 1 to 100%. sediment Fragmented material from weathered depth integration Method of sampling at all rocks and organic material that is suspended in, points throughout the sample depth so that a transported by and eventually deposited by water-sediment mixture is collected propor- water or air. tional to the stream velocity at each point. This procedure yields a discharge weighted sedimentary Substrate that is formed by the sample. deposition of water-borne mineral fragments, organic debris, or mineral precipitates that fine load Portion of the total sediment load that become cemented and pressed into a solid form is composed of particles smaller than the (Le., rocks). particles present in appreciable quantities in the bed material. Similar to washloadunder sedimentation (1) Action or process of forming sediment load. and depositing sediments. (2) Deposition of suspended matter by gravity when water veloc- suspended load Portion of the total sediment ity cannot transport the bed load. load that moves in suspension, free from contact with the streambed, and made up of sedimentation pond See sedimentation pondunder small sediment particles. The density and pond. grain size of the sediment particles are dependent upon the amount of turbulence sediment budget An account of the sediment and water velocity. Only unusually swift types, amounts, sources, movement, routes to streams are turbulent enough or have water specific locations, storage, and disposition of velocities high enough to lift particles larger sediment in a basin. than medium-sized sand from their beds. See also bed load and washloadunder sediment sediment discharge Mass or volume of sediment load. (usually mass) passing a stream transect in a unit of time, and that is generally expressed as tons washload Portion of the sediment load that can per day of suspended sediment discharge, bed be carried in large quantities and is limited load discharge, or total sediment discharge. only by availability in the watershed. The washload contains sediments that are finer sediment load General term that refers to sedi- than the smallest 10% of the bed load and ment moved by a stream in suspension (sus- usually less than 0.062 mm (-0.002 in) in pended load) or at the bottom (bed load). diameter. Compare with fine loadunder Sediment load is not synonymous with either sediment load. discharge or concentration. sediment production zone See sediment production bed load Sediment that moves on or near and zoneunder fluvial. E C shapeindex ~ 97

C. sediment rating curve A graph that illustrates the sensor See sensorunder remote sensing. relationship between sediment discharge and L stream discharge at a specificstream cross separation bar See separation barunder bar. section. C seral stages See seralstages under succession. sediment storage Mineral and organic matter that L is transported by a stream or river and deposited serial discontinuity Concept where dams shift at locations where it remains in a relatively stable biological and physical characteristics of streams L state. and rivers from the predicted pattern related to the . C sediment transport Process by which individual particles of bed material are lifted from the serpentine channel See serpentine channel under t: streambed and transported by water velocity. channel pattern. c: sediment transport rate Mass or volume of sessile Organisms that are attached to a substrate sediment (usually mass) that passes a stream but do not penetrate it and are unable to move c: cross section in a specific unit of time. about freely. sediment trap Seesedimenttrapunder habitat seston All organic and inorganic material greater c enhancements. than 60 j.Lmin size that is suspended in the water column. c sediment yield Quantity of sediment produced from a specific area in a specified period of time. nannoseston Seston that passes through a c plankton net. seep Small groundwater discharge that slowly net seston Seston that does not pass through a c oozes to the surface of the ground or into a plankton net. stream. A seep oozes water slowly and differs C from a spring that visibly flows from the settleable solids Matter in the water column that ground. does not stay in suspension when the water is L immobile and sinks to the bottom or floats to the seepage (1) Movement of water through the surface. L substrate without the formation of a definite channel. (2) Loss of water by infiltration from a settling pond Seesettlingpondunder pond. L canal, reservoir, other water body, or field. seven day low flow (Q7L) See seven daylowflow L seepage lake See seepagelakeunder lake. (Q7L) underflow. L seiche See seicheunder wave. seven day/QI0 See seven day/QlO under flow. L self-maintaining system An Refuse liquids including human body that can perform all of the natural ecological wastes or wastes carried off by sewers. L functions without human intervention or a dependence on engineered structures. shade density Inverse of the percentage of direct L light passing through crowns such that complete semi permanently flooded See semipermanently shading yields a value of 100%. flooded under water regime. L shallow Term applied to water that is usually sensitive reservoir Reservoir where high produc- less than 2 m (less than 6.5 ft) in depth. See shoal. L tion rates decrease restoration or recovery. See eutrophic under trophic. shallow-rapid landslide Seeshallow-rapidlandslide L under landslide. sensitive slope Any slope that is prone to mass L erosion or wasting. shape index An index of the width and depth of a stream habitat. Values less than 9 generally L sensitivity Susceptibility of a watershed, stream, indicate pools, greater than 9, riffles: or lake to damage from natural processes or l human activities. shape index = (w/d)Wdm1J.X);

( L -"I -.-i 98 ~ shear stress ---, -.J

--' w =width; shoreline: acreage ratio See shoreline: acreageratio d =mean depth; under dimensions. dmax= maximum depth along a cross section. shoreline development See shorelinedevelopment """I shear stress Force per unit area that is parallel to a (0) under dimensions. I surface. Seealso shearstressunderenergy. I, shoreline length See shoreline length under I sheen An iridescent appearance on a water dimensions. surface. --' shredders See shreddersunder macroinvertebrate. sheet Migrating accumulations of bed load one or --J two grain-diameters thick that alternate between side bar Seesidebar under bar. fine and coarse particles. See also sheetunder fast side channel See side channel under channel -.J water-non turbulentunder the main heading channel unit. pattern. Also, see side channel under slow water, pool, dammed pool with the main heading of sheet erosion Erosion of soil from sloping land in channel unit. thin layers or sheets that may be imperceptible, signature See signature under remote sensing. particularly when caused by wind, or denoted by J numerous fine rills. See also sheet erosion under erosion. significant wave height See significant wave height under wave. -..J sheet flow Flow of water over the ground in a siliceous Term applied to material containing --' more or less continuous sheet. If the flow is large, silica or silica dioxide. it is termed a sheet flood. See also sheetflow --.J under flow. sill (1) Elevated area of the bottom at the mouth of sheetwash Flow of rainwater that covers the a or , or at the outlet of a water body such as a lake or estuary. (2) Bottom of a stop-log entire ground surface with a thin film and is not concentrated in streams. gate structure or dam crest that controls water level with flash boards. Compare with sill under habitat enhancements. shelf Sandbank or submerged area of rock in a water body or bedrock underlying an alluvial silt (1) Fine soil that is between 0.004 and 0.062 deposit. mm (0.00002 - 0.0003 in) in diameter. (2) Also Shelford law of tolerance When one environmen- applied to a soil or substrate containing a very tal factor or condition is near the limits of toler- high proportion of silt particles. Compare with ance at either a minimum or maximum level or other substrate sizes under substrate size. state, that one factor or condition will determine siltation Settling of fine suspended sediments in whether or not a species will be able to maintain water where water velocity is reduced. itself under those specific environmental conditions. silting Process of depositing silt when water velocities and transport capabilities of a stream shoal Shallow area that is usually a sandbank, are reduced. Also applied to conditions that sandbar, or a rocky, swift section of stream. See shallow. accompany the deposition of excessive amounts of silt. shoal water substrate Composition of the bed in a silt load Quantity of silt being transported in a shallow (shoal) area of a river, sea, or other water specified quantity of water. body. simple meander See simple meanderunder meander. shooting flow See shootingflow under flow. sink (1) Depression or low-lying, poorly drained shore Land along the edge of a water body. area or hole formed where the underlying rock shoreline Interface between land and water or the dissolves and waters collect in the depression or intersection of land and permanent water. where water disappears through evaporation. C L 99

L (2) Area where the input of mass or energy pool, dammed pool under the main heading exceeds the output or production. (3) Location channel unit. L where streamflow disappears into the bed material of the stream. (4) To move downward in SLAR See SLAR under remote sensing. L: the water column. slick (1) Glassy smooth flow of water that is I: sinker Term applied to logs or large limbs that do sometimes used interchangeably with glide. See not remain afloat in water either because of glide under slowwaterin channel unit. (2)A thin, c:: intrinsic density or through water-logging. shiny layer of material on the surface of the water usually referring to oil or other petroleum-based C sinkhole Depression, often steep-sided, that is product. created by subsidence where subterranean t: minerals or substrate dissolves and results in the slide See slide under landslide. collapse of an underground passage or piping. t: sliding beads Procedure used to measure sub- sinking current Downward movement of sea or strate movement in a streambed that involves I: lake water that has become denser through burying numbered beads on a cable. The beads cooling or increased salinity, or moves down- slide to the end of the cable when substrate is c:. ward as the result of an onshore wind. dislodged from high water velocities associated with peak flows that scour the streambed. The c:: sink lake See sink lakeunder lake. number of beads that are dislodged provide a measure of the depth of streambed scour. See L: sink zone Seesinkzoneunder fluvial. scour. C sinter General term applied to chemical sediments sliding gate See sliding gate under gateand main deposited by mineral springs. heading of control structure.

C sinuosity (1) Ratio of channel length between two slip erosion See slip erosionunder landslide. points in a channel to the straight line distance c:. between the same two points. (2) Ratio of chan- slope Incline of any part of the earth's surface. nellength to valley length. Channels with Land with an incline or oblique direction in c:: of 1.5 or more are called "meander- reference to the vertical or horizontal plane. See ing," while those close to 1.0 are called "straight." also gradient. c (3) See also sinuosity under dimensions. slope break Pattern on a slope where gradient c sinuous channel See sinuous channel under changes abruptly. channel pattern. C slope failure See slopefailure under landslide. sinuous meander See sinuous meander under L meander. slope processes Mass movement by debris slides and surface wash that results in transport of fine L site Area described or defined by biotic, climatic, sediments downslope by overland flow. water, and soil conditions that forms the smallest L planning unit with a defined boundary. slope stability Measure of slope resistance to erosion, slumping, sliding, or other unstable L skid road In forestry practices, any road or trail conditions. used for hauling logs from the logging site to a r slope wash Motion of water and sediments down L landing where logs are loaded on trucks or other conveyances for transport. a slope caused by sheet flow. r L ski jump See ski jump under control structure. sloping gully side See sloping gully side under gully side form. '~ slab failure See slabfailure under landslide. slough (1) Low swamp or swamp-like area in a '- slack water Quiet, still pool-like area of water in a marshy or reedy pool, pond, inlet, or backwater stream usually on the side of a bend where water with marsh characteristics such as abundant current is low. See slackwater under slow water, vegetation. (2) Channel where water flows 100 ~ slowwater

sluggishly or slowly through low swampy soil drainage Pattern of water drainage from soils, ground on a delta or floodplain. (3) Marshy tract generally applied to saturated soil. located in a shallow, undrained depression or a sluggish creek in a bottomland. (4) Tidal channel soil erosion Removal of soil through erosion by in a salt marsh. (5) Lower reach of a tributary that wind, precipitation, surface water, or other has been ponded by sediment and debris at the natural processes. confluence with the main channel. soil pore Area, interstice, or space within soil that slow water See slow water under channel unit. is occupied by either air or water where the degree of porosity is dependent upon the ar- sludge Deposit of a semifluid mass such as mud, rangement of individual soil particles. ooze, sediment, or organic matter in the bottom of a water body. soil water potential Amount of work required to transport a given quantity of water from the sluggish flow See sluggishflow under flow. surface into groundwater. slump See slump under landslide. solar arc See solar arc under solar radiation. slump-earthflow See slump-earthflow under solar radiation Electromagnetic energy from the landslide. sun at all wavelengths. More particularly, radia- tion with wavelengths between 0.2 and 4.5 /-Lm small bole See small boleunder large organic that emanate from the sun and can be measured debris. by instruments (e.g., actinometer, pyranometer, radiometer, or solimeter). The fraction of incident small impoundment Small reservoir (generally 8 ha [20 acres] or less in surface area) used for light or electromagnetic radiation that is reflected by a surface or body is known as albedo. Net water storage and control on a stream. See reservoir. radiation is the algebraic sum of the upward and downward vertical components of long- and small mountain lake See small mountain lake short-wave radiation. under lake. arc of the sun Change in the angle of the sun small-sporadic deep-seated failures See small- on a given day in degrees from when sunlight first strikes water. The arc of the sun on sporadicdeep-seatedfailures under landslide. August 1st at the same location is used as a snag (1) Standing dead tree. (2) Submerged fallen standard. tree in a stream, sometimes with an exposed or direct solar radiation Radiation that reaches a only slightly submerged tree top. (3) See also snag water surface in an unobstructed straight line. under large organic debris. incident light Visible light reaching a water snagging Removing or cutting snags on land or in surface. water. reflected solar radiation Radiation that does soda lake See sodalakeunder lake. not penetrate a water surface but is reflected from the surface. softwater Freshwater with low alkalinity, conduc- tivity, or salinity that is generally found in areas refracted solar radiation Radiation that pen- with sandstone substrate or headwater streams. etrates a water surface and is either bent or Compare with hardwater. deflected from its original path. soil Portion of the earth's surface that consists of solar arc Measure of canopy angle in degrees earth, disintegrated rock, and humus and that is that is based on the measurement of the angles capable of supporting vegetation. See earth, formed from the line of sight to the visible ground. horizon. total solar radiation Sum of direct, reflected, soil creep Gradual downslope movement of soil by gravity. and refracted radiation reaching a given point. c 101 c spring breakup

stable flow See stableflow under flow. standing wave See standing wave under wave. static head Distance from a standard datum stage (1) Elevation of a water surface above or below an established reference point. (2) Quanti- (artificially defined reference point) of the water ---, surface on a column of water that can be sup- fication of a discharge expressed as a percent of -4 I mean annual discharge or some other reference ported by the static pressure at a given time. - -. .. flow. (3) Depth of water at any point in a stream station (1) Exact place of occurrence of an that is generally calibrated so that discharge can be estimated with a weir. individual or species within a given habitat. (2) Permanent or semi-permanent sample area. stage class See stageclassunder succession. (3) A circumscribed area that contains all the environmental conditions required by an indi- stagnant Layer of inert water with little or no vidual or group of individuals. circulation of water and low dissolved oxygen. status See status under trophic. stagnation point Point at the leading edge of an object where the water velocity of the oncoming steady flow See steadyflow under flow. flow is zero where the water collides with the object. steep bank Seesteepbank under streambank. L stratification: destratification 103 L ....

L stem flow See stemflow under flow. storage ratio Net available water storage divided by the mean annual flow for a basin within a L stenobathic Refers to an organism that is re- period of one year. stricted to living at a certain depth in a water L column. storage reservoir Reservoir designed to retain water during peak water periods for release and L stenohaline See stenohaline under salinity. use downstream at another time when streamflows are low. See reservoir, storage. L stenosaline See stenosaline under salinity. storm event Major episode of atmospheric distur- stenotherm Organisms that have a narrow L bance that is often associated with heavy precipi- temperature tolerance. tation, lighting, and thunder. L stenotypic organism An organism with a narrow storm flow See stormflow under flow. range of tolerance to a particular environmental L factor. story One of several distinct layers of plant L step run See steprununderfastwater-turbulent growth such as tall trees, large shrubs, low shrubs, and ground cover. L under the main heading channel unit. still Water is considered to be still when it is straight See straight under slow water, scour pool L motionless, free from turbulence, without waves under channel unit. or perceptible current. L straight channel See straight channel under stilling basin Deep pool located in or below the channel pattern. L spillway of a dam that dissipates the energy of the water in the spillway. straight meander See straight meander under L meander. stilling pond See stilling pondunder pond. L strait Narrow passage of water connecting two stocking Release of bird, fish, or wildlife species larger water bodies. L into a given habitat that were obtained through captive propagation or were captured from the terrace Terrace composed of ancient alluvial wild elsewhere. material that is deposited as a mantle over a base of bedrock. stone Naturally formed hard substance consisting of mineral or earth materials such as rock forma- stratification Arrangement of water masses into tions, weathered rock in the form of boulders, or distinct, horizontal layers that are separated by gravel (pieces of rock that have become rounded differences in density associated with water from scouring in a streambed). Compare with temperature and dissolved or suspended matter. other substrate sizes under substrate size. bathylimnion Deepest part of a lake that is stop log See stop logunder control structure. located below the clinolimnion.

storage (1) Water that is artificially impounded in chemoc1ine Density gradient, or pycnocline, from differences in salt concentration. surface or underground reservoirs for future use. (2) Water that is naturally detained in a drainage c1inograde Oxygen profile in which the hy- basin as groundwater, channel storage, and polimnion has less dissolved oxygen than the depression storage. The term "drainage basin epilimnion. storage" or simply "basin storage" is sometimes used in reference to the total amount of naturally c1inolimnion Layer or region of a water body stored water in a drainage basin. where the rate of heating decreases exponentially. storage coefficient Coefficient that expresses the relation of storage capacity in a reservoir to the destratification Process that interrupts the mean annual flow of a single stream or all boundary between water strata and induces streams that are direct tributaries to the reservoir. mixing between strata. 104 ~ stratification:discontinuitylayer

Limnetic (Pelagic) Zone

Epilimnion Littoral ( Zone (------

stratification layers (adapted from Thorp and Covich 1991)

discontinuity layer See thermoclineunder and hypolimnion that exhibits a marked stratification. thermal discontinuity with a temperature gradient equal to or exceeding 1°C per meter. epilimnion Uppermost layer of water in a lake See mesocline, thermocline. characterized by an essentially uniform temperature where relatively thorough mixing mixolimnion Upper strata of a lake that occurs from wind and wave action to produce exhibits periodic circulation. See epilimnion a less dense but oxygen-rich layer of water. In under stratification. a thermally stratified lake the epilimnion extends from the water surface down to the monimolimnion Deeper stratum or layer of a metalimnion. lake that remains perennially stagnant and rarely circulates, especially the layer below the fall overturn Physical phenomenon that chemocline in a meromictic lake. involves the thorough mixing of water that negative heterograde Term applied to a vertical occurs in temperate-zone water bodies during profile of water with minimum oxygen levels. the fall season. The sequence of events leading to the fall overturn includes: (a) cooling and orthograde Oxygen profile where the oxygen increased density of surface waters producing level below the epilimnion remains at or near convection currents from top to bottom; saturation. (b) circulation of the total water volume by wind actions and density differences resulting overturn Period of mixing or circulation of in a uniform water temperature that allows water in a previously thermally stratified complete mixing of nutrients and chemicals water body. Seefall overturn under throughout the entire water mass. stratification. hypolimnion Poorly oxygenated and illumi- positive heterograde Profile where an oxygen nated lower layer or region in a stratified lake profile remains well above saturation. that extends from the metalimnion to the pycnocline Layer or region in saltwater where bottom and is essentially removed from major a marked change occurs in the density of a surface influences. Water in the hypolimnion water column that acts as a partial barrier to is denser and colder than strata higher in the exchange between the upper and lower water water column. columns.

inverse stratification Water body with colder spring overturn Physical phenomenon that water in a stratum over warmer water. may involve the thorough mixing of water in mesoc1ine See thermocline under stratification. temperate-zone water bodies during the early spring. The sequence of events leading to mesolimnion Term used in place of ther- spring overturn includes: (a) melting ice cover; mocline. See thermocline under stratification. (b) warming surface waters; (c) changing densities in surface waters that produce metalimnion Stratum between the epilimnion convection currents from top to bottom; and LJ stream:insulatedstream ... 105 L

C (d) circulation of the entire water volume by animals within the channel and the riparian wind action, resulting in a uniform water vegetation zone. C temperature that allows complete mixing of alluvial stream Stream where the form of the nutrients and chemicals throughout the entire C water mass. streambed is composed of appreciable quanti- ties of sediments that are transported and L: sprungschicht Term that is synonymous with deposited in concert with changes in thermocline or metalimnion. streamflow. L: thermal stratification Vertical temperature beaded stream Stream connecting a series of stratification in north temperate lakes result- small ponds or lakes. C ing in: (a) virtually uniform water temperature in the epilimnion; (b) rapid and marked beheaded stream Stream that has been sepa- C gradient change in temperature with depth in rated from a portion of its headwater tributar- C the metalimnion; and (c) cold and nearly ies. See stream piracy. uniform water temperature in the hypolim- centripetal stream Streams that converge in the nion, from the bottom of the metalimnion to central part of a basin. C the bottom of a water body. consequent stream Stream that flows in the C thermocline Stratum between the epilimnion same direction as local geologic strata. and hypolimnion that exhibits a marked C temperature gradient equal to or exceeding continuous stream Stream where the flow 1°C per meter. Synonomous with mesolimnion along its course is not interrupted in space or C or metalimnion. time. L turnover Refers to the thorough mixing of distributary Division of stream channels, as on water in a lake by wind action that occurs a delta or alluvial fan, that flow away from the L when density differences of a thermally main channel, usually into a larger stream, stratified water column disappear and tem- lake, or other receiving water body. Distribu- C peratures become uniform. See fall turnover tary streams form where deposition exceeds and spring turnover. erosion. C stratified Refers to a series of water layers that entrenched stream Stream that has eroded into form from density differences of water tempera- the substrate and is confined by walls resistant C tures. See thermocline under stratification. to erosion.

C stratified flow Layered flow that results from a gaining stream Stream or stream reach that receives water from the zone of saturation. difference in density due to temperature, dis- L solved, or suspended materials between the graded stream Stream that has achieved a state inflowing and receiving water. of equilibrium between the rate of sediment L supply, transport, and deposition throughout stratified lake See stratified lakeunder lake. l- long reaches. stratified stream segment Portion of a stream that headwater stream Stream that has few or no L is relatively homogeneous based on geomorphol- tributaries, and has steep, incised channels ogy, streamflow, geology, and sinuosity. This that are often associated with active erosion, L term also refers to a series of short reaches with a seeps, and springs. Headwater streams are common morphology. referred to as first order streams. See seep, L spring, stream order. streaks Surface areas parallel to direction of the L wind that coincide with lines of surface conver- incised stream Stream that has, through gence and downward movement of water. See degradation, cut its channel into the bed of a L also langmuir circulation under wave. valley. insulated stream Stream or stream reach that r stream Natural water course containing flowing L~ neither contributes to nor receives water from water, at least part of the year, together with , dissolved and suspended materials, that nor- the zone of saturation because it is separated L~ mally supports communities of plants and by an impermeable bed. -, -.J 106 ~ stream:interrupted stream ..J

=:J interrupted stream Stream without a continu- trellis stream Stream pattern in which tributary ous flow where reaches with water may be streams join the main stream at or near right --J perennial, intermittent, or ephemeral. angles and are fed by elongated secondary tributaries parallel to the main stream so that losing stream Stream or stream reach that the whole system resembles a vine on a trellis. :J contributes water to the zone of saturation. -, lowland stream Stream that flows across low streambank Ground bordering a channel above --I the streambed and below the level of rooted gradient terrain, has a bed composed of fine substrate materials, and is located in the lower vegetation that often has a gradient steeper than :J 45° and exhibits a distinct break in slope from the part of a drainage network downstream from mountains. stream bottom. The portion of the channel cross :J section that restricts lateral movement of water --, mature stream Seegradedstreamunderstream. during normal streamflow. Right and left banks -J are determined while looking downstream. meltwater stream Channelized flow of glacial --J melt water. concave bank Bank that is indented such that middle stream Refers to a stream reach that is the top and bottom of the bank are higher and --J located in the center of a stream course is often characterized by bank erosion. Gener- between headwaters and the mouth, has beds ally, a concave bank is located on the outside ---- of diverse substrates, variable habitat patterns, of a river curve or bend of a meandering stream. and usually has equilibrium or balance _-4 between scouring and deposition. See deposi- convex bank Bank that is inverted such that the -- , tion, scour. top and bottom of the bank are lower and is obsequent stream Stream that flows in a often characterized by sediment deposition at direction opposite of the general trend in local a point bar. Generally, a convex bank is located geologic strata. on the inside bank on a river curve or bend, especially on a meandering stream. parallel stream Stream that flows in close proximity to and in the same direction as cut bank Streambank that is actively eroding another stream but separated by a divide. and has a steep face. perched stream Stream that may be classified flat bank Streambank where the riverbed as either "losing" or "isolated" and is sepa- slopes gently to the level of rooted vegetation. rated from the underlying groundwater by a lower bank Bank that is periodically sub- zone of aeration. See losing stream and isolated stream under stream. merged between the normal high water line to the water's edge during the summer low flow pinnate stream Stream pattern characterized by period. a series of small tributaries distributed along repose bank Bank with an angle of repose the stream gradient of the main stem. (usually 34-37°) in unconsolidated material. pooled channel An intermittent stream with steep bank Bank that is nearly vertical and is significant surface pool area and without consolidated by the cement action of minerals, flowing surface water that is supplied by compaction, and roots from riparian groundwater. vegetation. radial Pattern of stream channels flowing out undercut bank Bank with a cavity below the from a central point such as a volcanic cone. water line that is maintained by scour from rectangular stream A system of streams in substrates and high water velocities. See scour. which each straight segment of stream takes unstable bank Streambank boundary of the one of two characteristic perpendicular channel that is actively failing through erosion directions that follow perpendicular land- forms. or slumping, that is recognized by clumps of sod and earth along the base of the bank, and superimposed stream A stream whose course, that is expressed as a percentage of the total once established, is maintained by erosion length of both banks for the reach. See erosion cutting deeper into the landform. and earthslumpunder landslide. L stream corridor .... 107 L

L upper bank Portion of a bank in the topo- in situ, principally by chemical and weather- graphic cross section of the channel from the ing processes. L break in the general slope of the surrounding undifferentiated Multiple layers of different land to the normal high water line. L types of material. streambank material Substrates that compose volcanic Unconsolidated volcanic or igneous banks along stream courses. The following terms L (pyroclastic) sediments that accumulate from classify bank material according to composition, volcanic eruptions or fine volcanic dust carried origin, and method of formation. r::; by winds and deposited some distance from the volcano. r: anthropogenic Materials created or modified by humans, including those associated with streambank stability Index of firmness or resis- r: mining of minerals, waste disposal, and tance to disintegration of a bank based on the erosion control. See revetment, riprap. percentage of the bank showing active erosion r: bedrock Rock outcrop or rock covered by a thin and the presence of protective vegetation, woody mantle (less than 10 cm) of consolidated material, or rock. See stableand unstableunder L material. bank stability, and cut bank and unstable bank under streambank. L colluvial Product of massmovement of materi- als (usually angular and poorly sorted) that streambed Substrate plane, bounded by banks, of L reachedtheir present position by direct a stream bottom. Also referred to as the stream influence of gravity such asslides or talus bottom. C slopes.Seelandslide. stream capacity (1) Total volume of water that a C eolian Materials (usually silt or fine sand) that stream can transport within the high water are transported and deposited by wind. channel. (2) Maximum sediment load a stream L fluvial Materials (usually rounded, sorted into can transport at a given velocity and discharge. horizontal layers, and poorly compacted) that L are transported and deposited by streams and stream capture Upstream connection of one rivers. stream by erosion into the drainage basin of C another stream that results in changes of drain- ice Frozen water from seeps or glaciers, or age patterns. See stream piracy. C atmospheric conditions. See glacier, seep. lacustrine Fine-textured sediments that have stream channel (1) Long, narrow depression shaped by the concentrated flow of a stream and settled to the bottom from suspension in L covered continuously or periodically by water. bodies of standing freshwater or that have (2) Bed and banks formed by fluvial processes L accumulated at the margins of lakes or reser- where a natural stream of water runs continually voirs through wave action. May be fine or intermittently. See channel. L textured with repetitive layers. L marine Sediments that have settled from stream classification Systems used to group or suspension in brackish or saltwater of estuar- identify streams possessing similar features ies or oceans. I using geomorphic structure (e.g., gradient and L- confinement), water source (e.g., spring creek), morainal Poorly sorted (angular to subangular) associated biota (e.g., trout zone), or other material transported in front of, beneath, characteristics. A hierarchical classification. Two beside, or within a glacier and deposited approaches are commonly used: a management- directly by the glacier. May be highly com- related classification that is based almost entirely pacted and have significant clay content. on value to fish populations, and a geomorphic- organic Materials resulting from vegetative habitat classification system. growth, decay, and accumulation in closed basins or on gentle slopes where the rate of stream corridor Perennial, intermittent, or ephem- accumulation exceeds that of decay. eral stream and riparian vegetative fringe that L occupies the continuous low profile of the stream saprolite Weathered bedrock that decomposed valley. L 108 ~ stream density stream density Abundance of streams that is Two first-order streams flow together to form a expressed as kilometers of stream per square second-order stream, two second orders combine kilometer of landscape or terrain. Synonymous to make a third-order stream, etc. with . See landscape, terrain. stream pattern Seechannel type. ' stream discharge See stream dischargeunder i discharge. stream piracy Transfer of a stream from one basin .J to another as a result of geomorphic changes, stream-estuary ecotone Transitional area from a usually by erosion through a common divide. See . -4, stream mouth and lower limit of marsh vegeta- stream capture. tion that extends to the upper limit of tidal -.,j influence. See ecotone. stream power Energy or ability of a stream to move substrates and scour streambanks that is . . ~ streamflow See streamflow under flow. See also based on gravity, slope, discharge, and water discharge. velocity.Seealso streampowerunder energy. stream-forest ecotone Area of a stream that is stream profile Graphical presentation of elevation . . directly influenced by riparian vegetation, versus distance of a stream channel or shape of a including the streambank and upland area cross section. In open channel hydraulics, it is a adjacent to the stream. Its size depends on stream plot of water surface elevation against channel width, type of vegetation, and physical character- distance. istics of the adjoining uplands. See ecotone, streamside management zone. stream reach See reach. stream frequency The number of streams per stream shore water depth Water depth at a stream square kilometer of area. shoreline or at the edge of a bank overhanging a ,j shoreline. streamline Direction of water movement at a ..,j given instant. streamside management zone The land, together with the riparian vegetation, that is in immediate - , streamline flow See streamlineflow under flow. contact with a stream and sufficiently close to have a major influence on the total ecological character and function of the stream. See stream- forest ecotone.

stream surface shading Percentage of the stream surface area that is shaded.

foliar shading Shading attributable to riparian vegetation. nonfoliar shading Shading from debris, undercut banks, and surrounding terrain. stream transport capability Ability of a stream to move sedimentary materials and organic mate- rial during periods of peak flow. This ability is influenced by water volume (Le., discharge), water velocities, channel slope, timing of the peak flows, and the presence or absence of obstructions in the channel.

stream width See wettedwidth under dimensions. stream order (from Helm 1985) structure (1) Any object, usually large, in a chan- stream order Hierarchical ordering of streams nel that influences streamflow. (2) Features that based on the degree of branching. A first-order create a diversity of physical habitat within a stream is an unforked or unbranched stream. stream, lake, or reservoir. (3) Organization of taxa c c summerkill

c into various functional or trophic groupings in a subsurface outflow Water moving horizontally biological community. Compare with structure through the upper soil layers away from a water c under habitat enhancements. body.

c stump field Area in the bottom of an impound- subsurface runoff Term for the portion of runoff ment where stumps remain after trees were cut that percolates through the soil by gravity as c and removed before impoundment. groundwater before emerging to the surface as seepage or springs. c subbasin Surface area of a watershed drained by a tributary to a larger stream that is bounded by subterranean stream Part of a stream reach that c ridges or other hydrologic divides and is located flows underground. within the larger watershed drained by the larger c stream. Also referred to as subdrainage. succession Changes in species composition of plants and animals in an ecosystem with time, c subdrainage See subbasin. often in a predictable order. More specifically, the gradual and natural progression of physical and c sublittoral See sublittoral under littoral. biological changes, especially in trophic structure of an ecosystem, toward a climax condition or c submerged Refers to under a water surface. stage. submerged macrophyte See submerged macrophyte climax succession stage Culminating stage in c under macrophyte. plant succession for a given site where the vegetation has reached a highly stable C subsidence Lowering of surface elevations caused condition. by loss of support and subsequent settling or L caving of substrate strata. early succession stage Stage in forest or other plant community that includes species that L substrate (1) Mineral and organic material form- colonize early, or a stage of young growth ing the bottom of a waterway or water body. including seedlings, saplings, and pole-sized L (2) The base or substance upon which an organ- trees. ism is growing. Also referred to as substratum. L late succession stage Plant community that has substrate size The following table includes the developed mature characteristics. Also re- average diameter of various substrates in milli- ferred to as the climax stage. L meters and inches. mid-successional stage Succession in a plant L Diameter of particle community between the early colonizers and transition to a mature community. L Name of particle Millimeters Inches seral stages Series of relatively transitory plant Large boulders >1,024 40-160 L Small boulders 256-1,024 10-40 communities that develop with ecological Stone 256-600 10-24 succession from bare ground to the climax L Rubble (large cobble) 128-256 5-10 stage. Cobble (small cobble) 64-128 2.5-5 Pebble 2-M 0.08-2.5 stage class Any distinguishable phase of L growth or development of a population or Coarse gravel 32-64 1.3--2.5 L Fine gravel 2-32 0.08-1.3 community. Sand 0.062-2.0 summer heat income See summer heat income Silt 0.004-0.062 L under heat budget. Clay <0.004 L summerkill Complete or partial dieoff of a fish subsurface flow Water that moves horizontally population during summer when extended cloud L below the earth's surface. See also subsurfaceflow cover prevents sunlight from allowing photosyn- underflow. thesis of plants. The death of rooted aquatic L subsurface inflow Water moving horizontally plants depletes dissolved oxygen in warm water through the upper soil layers into a water body. and fish die by suffocation or from toxins pro- L duced by certain species of decaying algae.

L- r 110 .. summer pool summer pool Water level in a reservoir, usually surface and includes all perennial and ephemeral maintained at a stable level during the summer water bodies. months. Compare with recreational pool. surface water inflow Water flowing into a water sump A pit, well, or depression where water or body from one or more stream channels. other liquid is collected. surface water outflow Water flowing out of a superimposed stream See superimposed stream water body in one or more stream channels. under stream. surface wave See surfacewave under wave. supervised classification See supervised classifica- tion under remote sensing. surfactant Chemical agent that improves the emulsifying, dispersing, spreading, or wetting supervised training See supervised training under abilities of other chemicals such as herbicides and remote sensing. pesticides.

supralittoral See supralittoral under littoral. surge An episode of uneven flow and strong momentum such as a swell due to a sudden surf Waves or swells that break upon the shore of change in pressure or a rapid destabilizing a water body. Generally this term applies to physical event. See swell. ocean environments.

surface Interface between water and the survival flow See survival flow under flow. atmosphere. suspended load See suspended loadunder sedi- ment load. Compare with bed load and washload surface area Area of a water body at the interface under sediment load. between water and the atmosphere. suspended sediment discharge Quantity, usually surface creep erosion See surface creeperosion under erosion. expressed as mass or volume, of suspended sediment passing a stream cross section in a surface elevation Height of the surface above given unit of time. mean sea level. suspended sediments Sediments that are carried surface erosion See surface erosionunder erosion. in suspension in the water column by turbulence and water velocity or by Brownian movement so surface film Surface tension of water due to air- that they are transported for a long time without water (molecular) interactions that provides settling to the bottom. See suspended load. support for certain plants and animals so they can live at the air-water interface. suspended solids Particles of unfiltered, undis- solved solid matter such as wood fibers or soil surface flow See surfaceflow under flow. that are present in water. See total dissolved solids (IDS). surface impoundment Natural topographic depression, artificial excavation, or dike arrange- suspension erosion See suspension erosionunder ment containing water that is constructed above, erosion. below, or partially in the ground (or in navigable waters) and mayor may not have a permeable suspenso ids Colloidal particles that remain in bottom and sides. suspension under most conditions and combine or react with liquid only to a limited extent. surface runoff Portion of the runoff that flows over the surface without infiltrating into the sustained (cruising) speed See sustained (cruising) groundwater. speed under swimming speed.

surface seiche See surface seicheunder wave. swale A moist or marshy depression or topo- graphic low area, particularly in prairies. surface water Standing water above the substrate or water that flows exclusively across a land swamp See swamp under wetlands. C 111 L telluric water ...

C swash Landmark rush of water from a breaking system Regularly interacting or interdependent wave up the slope of a beach. group of items or things forming a unified whole. L In stream applications, it includes a watershed or swath width See swath width under remote sensing. basin. For examples, see basin, drainage, ecosys- L tem, watershed. sweeper log See sweeper log under large organic L debris. C swell Seeswellunder wave. ~t

C swimming speed Speed that fish or other aquatic taiga Northern, subarctic coniferous forest (com- organisms travel when swimming that varies from posed of sparse stands of small spruces and firs) C essentially zero to over six m/s (19.7 ft/s), de- in Asia, Europe, and North America that is pending upon species, size, and activity. Swim- typically open or interspersed with bogs and C ming speed of fish is often expressed as body forms a transition zone between denser forest to length per second. Three categories of swimming the south and tundra to the north. C performance are generally recognized: tail Transition between habitat types that is burst (darting) speed Speed that a fish can C usually shallow where the water velocity in- maintain for a very short time, generally 5-10 creases (e.g., the downstream section of a pool, seconds, without fatigue. Burst speeds are C glide, or other habitat type). Synonymous with used by fish in feeding, escape from predators, tailout or flat. C or to pass barriers such as cascades or falls during migration, and represent the maximum Mining waste from screening or process- C swimming speed for a species. ing mineral ore. Tailings may contain suspended prolonged speed Speed that a fish can maintain solids, heavy metals, radioactive materials, acids, and other contaminants that can leach into a L for a prolonged period of time (minutes but water course. usually less than 1 ill) that ultimately results L in fatigue. A fish is under some degree of stress when it swims at its prolonged speed. tailrace (1) Channel with highly turbulent water, L Prolonged speeds in fish typically involve usually confined by concrete or riprap, in the anaerobic metabolism. tailwater of a reservoir. (2) Channel that carries L water from a water wheel. sustained (cruising) speed Speed that a fish L can maintain for an extended period of time tailwater Flowing water below a dam that is (hours) without fatigue or stress during released from an upstream impoundment. Often L normal movements between two sites. Cruis- releases from the hypolimnion in the reservoir ing speeds in fish typically involve aerobic provides clear, cold water in the tailwater that L metabolism. can support coldwater sport . L swimming velocity See swimming speed. talus (1) Slope with numerous, loosely aggregated rocks. (2) The sloping accumulation of rock swirling flow See swirlingflow underflow. L fragments at the base of a cliff. synergism Interaction of two or more substances L (e.g., chemicals) such that the action of anyone of tank See tank under pond. them on living cells or tissues is increased. taxon Any formal taxonomic unit or category of Compare with antagonism. L organisms (e.g., species, genus, family, order). L synthetic aperture radar (SAR) See synthetic The plural of taxon is taxa. aperture radar(SAR) under remote sensing. tectonic lake See tectonic lakeunder lake. L synusia Any component of a community that is telluric water Surface water derived from sources L composed of one or more species, belonging to the same life-form, having similar environmental other than direct precipitation on a site (e.g. seep L requirements, and occurring in similar habitats. or spring). See seep, spring. L

r'- I 112 .. temporarily flooded _.J temporarily flooded See temporarily flooded under thermal Related to or caused by heating or warm ~.-' water regime. temperatures. tenaja Pools in seasonal streams that may support thermal bar Narrow transition zone of nearly 4°C a flora similar to vernal pools upon desiccation. in the vertical isotherm between an open water -.J mass and the stratified area of a water body. terminal moraine See terminal moraine under moraine. thermal refuge Zone in a water body that main- tains oxygenated water and temperatures -.4 terrace Relatively level or gently inclined land adequate for fish survival. surface that is elevated above an active stream -.i channel in a steplike arrangement of a slope or thermal stratification Seethermalstratification lake bed. Terraces are remnants of floodplains or under stratification. -.. perched shorelines at low water levels. See bench. thermocline See thermocline under stratification. .... terrace tributary See terrace tributary under tributary. thermokarst Depression created in permafrost by ---, melting of ground ice with a subsequent settling -.J of the soil. terracing Dikes constructed along the contour of --' agricultural land to contain runoff and sediment, thermokarst lake See thermokarst lake under lake. thereby reducing erosion. See dike. -, terrain Comprehensive term describing the throughfall All the precipitation that eventually landscape with respect to its features. See reaches a forest floor including direct precipita- -, tion and drip from foliage but minus stem flow. landscape. --' terrestrial Belonging to, or living on, the ground tidal flat Level land that is regularly inundated by or earth. ocean tides, often with muddy substrate. _.4 terrigenous sediments Sediments produced from tidal inlet An opening along the shoreline where -, soil, ground, earth, or weathered rock that are water extends at high tide. derived directly from the neighboring land. _. . tidal marsh See tidal marsh under wetlands. tetrapod See tetrapod under habitat enhancements. tide Alternate rising and falling of the surface of texture Size, shape, and arrangement of particles an ocean (including bays and gulfs connected to in a substrate. an ocean) that generally occurs twice daily from the gravitational pull of the moon and sun on the thalweg Path of a stream that follows the deepest earth. part of the channel. till Unmodified substrate material deposited by thalweg depth Vertical distance from the water glaciers and ice sheets. surface to the deepest point of a channel cross section. timber crib Seetimbercrib under habitat enhancements. thalweg velocity Seethalwegvelocityunder velocity. tin whistle See tin whistle under control structure. thaw lake See thaw lakeunder lake. tire reef See tire reefunder habitat enhancements. thematic data See thematic data under remote toe The base of a slope along a bank or other sensing. geographic feature where a gentle incline changes abruptly to a steeper gradient. thematic mapper Seethematicmapper under remote sensing. toe of the bank The point at the base of a streambank where the bank becomes more level theme See theme under remote sensing. as it forms the channel bed. L L transitionflow'" 113

L toe undercutting Erosionby a stream at the toe of total dissolved solids (TDS) Measure of inorganic an underwater slope that may result in bank and organic materials dissolved in water that L failure. pass through a 0.45 J.Lmfilter, expressed as mg/L. Sometimes used as an indicator of potential L toe width The width of the exposed toe along a production in habitat quality indices. Also slope. referred to as filterable residue (FR). See conduc- C tivity; compare to suspended solids. tolerance Relativecapability of an organism to L endure or adapt to unfavorable environmental total sediment discharge Total quantity of sedi- conditions. ment passing a stream crosssection during a C. prescribed unit of time. tolerance association Association of organisms c.. capable of withstanding adverse environmental total solar radiation See total solar radiation under conditions within a habitat. This association is solar radiation. L often characterized by a reduction in the number of species and, in the case of organic pollution, an total storage Volume of water in a reservoir at any L increase in individuals representing certain stage from full pool to dead storage. species. C total stream power See total stream power under tolerance limit Concentration of a substance that energy. L can be endured by an organism for a specified total suspended solids (TSS) Organic and inor- period of time. C ganic material left on a standard glass filter of 0.45 J.Lmafter a water sample is passed through tolerance quotient (TQ) See tolerance quotient (TQ) the filter. Also referred to as filterable under biological indices. L residue (FR). tolerance range Range of one or more environ- L toxicant (1)A substance that, through its chemical mental conditions (i.e., the highest and lowest or physical action, kills, injures, or impairs an L values) in which an organism can function and survive. organism. (2)Any environmental condition that L results in a harmful biological effect. top of the bank Point on a bank that corresponds toxicity Quality, state, or degree of a harmful L to the high water mark for normal streamflows. effect in organisms that results from alteration of natural environmental conditions. L topography Configuration of a surface including its relief and the position of its natural and training See training under remote sensing. L artificial features. training wall Seetrainingwallunder habitat L top set bed Horizontal sedimentary bed formed at enhancements. the top of a delta over the existing streambed. tranquil flow See tranquilflow under flow. L top width Seetopwidthunder dimensions. transect (1) A line on the ground along which L torrent Refers to a violent high streamflow observations are made or data are collected at L condition that is created by heavy rainfall or fixed intervals. (2) A line across a region selected rapid snowmelt and is characterized by a near to show spatial relationships of landforms, L bank-full discharge or greater, increased velocity, vegetation, or other features. (3) A straight line standing waves, and high sediment load in across a stream channel, perpendicular to the L alluvial or meltwater streams. See alluvial stream flow, along which habitat features such as depth and meltwater stream under stream. or substrate are measured at pre-determined r intervals. L tortuous meander See tortuous meander under meander. transitional habitat Habitat serving as a bound- L ary between two dissimilar habitat types. r tortuous meander channel See tortuous meander L channel under channel pattern. transition flow Seetransitionflow under flow. 114 ~ transitionregion transition region Stream reach where the flow trellis stream See trellis stream under stream. changes from laminar to turbulent. trench See trench under slow water, pool, scour pool transition zone Narrow or broad zone where a under the main heading channel unit. change occurs from wetlands to nonwetlands. tributary Stream that flows into or joins a larger translation See translation under wave. stream. Synonymous with feeder stream or side stream. Tributary types are based on watershed transmissivity Rate at which water is transmitted geomorphology. through a unit width of an aquifer under a unit hydraulic gradient. Transmissivity values can be lower valley wall tributary Characterized by expressed as square meters per day (m2/ d) or moderately steep gradients that occur at the square meters per second (m2/s). slope break between valley wall and valley floor. transparency Ability of water to transmit visible light. terrace tributary Stream flowing across terraces to the main stem, originating from springs or transpiration Process in plants where water is from tributaries draining valley slopes. released as vapor (primarily through the stomata, upper valley wall tributary Possess very steep or pores, in leaves) into the atmosphere. gradients, high water velocities, and flow in a transportation zone See transportation zoneunder stepwise profile of alternating pools and cascades. fluvial. wall-based tributary Flow along the base of a transport capacity Ability of a stream to transport valley wall and into the main stem channel. a suspended sediment load that is expressed as May flow parallel to the main stem for a short the total weight of sediment. distance. - . transport velocity Velocity required to move tripton Nonliving, nondetritus fragments in sediment of different sizes in a stream. water.

Transport velocities for various trophic Related to the processes of energy and sizes of streambed materials nutrient transfer (i.e., productivity) from one Diameter Transport velocity level of organisms to another in an ecosystem. mm in cmls ft/s autotrophic Water body where all organic 0.005-0.5 0.00002-0.002 15-20 0.49-0.66 compounds are produced through photosyn- 0.25-2.5 0.01-0.10 30-65 0.98-2.13 thesis rather than imported from external 5.0-15 0.2-0.6 80-120 2.62-3.94 sources. 25-75 1.0-3.0 140-240 4.59-7.87 dystrophic Shallow lake with colored water, 100-200 4.0-7.8 270-390 8.86--12.80 high humic and total organic matter content, low nutrient availability, high oxygen de- transverse bar See transverse barunder bar. mand, and limited bottom fauna. Oxygen is continually depleted and pH is usually low. transverse flow See transverseflow under flow. The stage between a eutrophic lake and a wetland in lake succession. transverse rib Lines of large clasts across a channel that are usually one or two diameters eutrophic Water body that is rich in nutrients, wide. organic materials, and productivity. During trash collector See trash collectorunder habitat the growing season, chlorophyll concentra- enhancements. tions are typically 10-100 mg/m3. heterotrophic Water body where all organic trash rack See trash rack under control structure. compounds are derived from sources that are external to the water body. tree retards See treeretards under habitat enhancements. hypereutrophic Water body receiving very L L ultranannoplankton .... 11S L high nutrient enrichment, usually from human than 8° C, and variable flows that are supplied L activities such as agricultural runoff and from snow and ice melt. sewage effluent. Specifically, phosphorus C levels are greater than 100 mg/m3, and tundra river See tundra river under river. chlorophyll levels are greater than 40 mg/m3. turbidity (1) Refers to the relative clarity of a C. hypertrophic See hypereutrophic. water body. (2) Measure of the extent to which light penetration in water is reduced from hypoeutrophic Water body with less than the C suspended materials such as clay, mud, organic desired nutrients and productivity. matter, color, or plankton. Measured by several C hypotrophic See hypoeutrophic. nonequivalent standards such as nephelometric turbidity units (NTU), formazin turbidity units c:. mesotrophic Water body with productivity (FTU), and Jackson turbidity units OTU). intermediate between oligotrophic and C eutrophic with chlorophyll levels typically at A mass of mixed water and 4-11 mg/m3 during the growing season. sediment that flows downward (sometimes C oligotrophic Water body characterized by low rapidly) along the bottom of an ocean or lake because it is denser than the surrounding water. C dissolved nutrients and organic matter, dissolved oxygen near saturation, and chloro- turbine See turbine under control structure. L phyllieveis typically at less than 4 mg/m3 during the growing season. turbulence Streamflows in which the velocity at a L status Position of an organism with respect to given point varies erratically in magnitude and energy flow within an aquatic ecosystem. direction and disrupts reaches with laminar flow. L Turbulence causes disturbance of the water trophogenic region Area of a water body where surface and produces uneven surface levels L organic production from mineral substances which results in poor visibility because air takes place on the basis of light energy and bubbles are entrained in the water. L photosynthetic activity. turbulent flow See turbulent flow under flow. tropholytic region Deep area of a water body where L decomposition of organic matter predominates. turnover (1) Complete mixing of nutrients and oxygen in a lake that occurs when stratification L tropical river See tropicalriver under river. breaks down due to changes in water tempera- ture, water density, and wind action. (2) Time L trough (1) A long depression or hollow. (2) Small interval between the use and replacement of one human-built structure of metal, wood, or con- or more nutrients in a nutrient pool. See fall L crete used to hold water (e.g., watering trough turnover, spring turnover, turnover, and thermal for livestock).Seetrenchunder poolunder the stratification under the main heading of L main heading channel unit. stratification.

L true color Color of water resulting from dissolved turnover ratio See turnover ratio under mixing. substances rather than from colloidal or sus- L pended matter. tussock Clumps or thick tufts of vegetation forming a more solid surface in a wetland. L truncated meander See truncatedmeanderunder meander. two-story lake See two-story lakeunder lake. L tumbling flow See tumblingflow underflow. L tundra Zone of low vegetation found above the u L tree line in the arctic or in mountainous areas but below zones of perpetual ice and snow (Le., ultrafine particulate matter See ultrafine particu- r snowbanks or glaciers). L late matter under organic particles. tundra brook Narrow, shallow stream with low ultranannoplankton See ultranannoplankton under L dissolved solids, water temperature usually less nannoplankton. ( L 116 .. ultraplankton - ultraplankton See uItraplankton under plankton. predicts the amount of soil lost in an average . year: unchanneled colluvium See unchanneled colluvium _.

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