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River Terminology

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River Terminology L L channel unit: fast water-turbulent, rapids .... 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 sediment. 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 floodplain of streams large substrates, and a well-defined stepped C in a drainage basin or river reach. longitudinal profile that exceeds 50% in supercritical flow. C channel type A system for characterizing channels based on features such as channel and valley 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 channel types. 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 stream uninterupted face. channel. C flume 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 whitewater. 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 Sediment transport Slope-valley interface L C Precipitation runoff Sediment deposition 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, riffles :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 riffle. embayment An off-channel, pond-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 waters. - 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 dam, 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 stream gradient. deposition at the confluence of a tribu- ~~ i , I L 0 channel unit ~ 19 0 0 TABLE2.-Channel Types of Rosgen (1996) 0 Type Description Slope Landform Aa Very steep, deeply entrenched with >10% High relief, deeply entrenched and erosional. 0 debris transport. Vertical steps with deep scour pools and waterfalls. 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 bar-, 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 alluvium [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 sinuosity, and an expansive well- bars that are laterally stable and a broad wetland [J vegetated floodplain and associated floodplain. wetlands. [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 bank erosion. [J G Entrenched" gully" 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 bank erosion rates. c Flood-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 bedform 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 bedforms 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 main stem 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.
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