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F-1 Aerial photograph A vertical or oblique photograph taken from an airplane. Aggradation General and progressive buildup of the longi- tudinal profile of a channel bed because of sediment deposition. Alluvial channel Channel wholly in alluvium; no bedrock is exposed in channel at low flow or likely to be exposed by erosion. Alluvial stream A stream that has formed its channel in cohesive or noncohesive materials that have been and can be transported by the stream. Alluvium Unconsolidated material deposited by a stream in a channel, floodplain, alluvial fan, or delta. Alternate bars Elongated deposits found alternately near the right and left banks of a channel. Amplitude The distance between points of maximum curva- ture of successive meanders of opposite phase in a direction normal to the general course of the meander belt, measured between centerlines of channels. Anabranch Individual channel of a braided or anastomosing stream. Anastomosing stream A stream whose flow is divided at most stages by vegetated islands that have elevations equiv- alent to the floodplain. Individual islands are wider than about three times water width, and the channels are more widely and distinctly separated than in a braided stream. Apex (of a bend) The tip, point, or location of maximum outward extension of a meander bend. ArcView A GIS and software package developed by Envi- ronmental Systems Research Institute, Inc. (ESRI). Avenue A programming language and development envi- ronment used to create specialized graphical user interfaces and to run scripts that customize the functionality of ArcView. Avulsion A sudden change in the channel course that usu- ally occurs when a stream breaks through its banks; it is usu- ally associated with a flood or a catastrophic event. Bank The sides of a channel between which the flow is normally confined. Bankline A line defining the top edge of a bank along a channel. Bank protection Engineering works for the purpose of protecting streambanks from erosion. Bank revetment Erosion-resistant materials placed directly on a streambank to protect the bank from erosion. Bar An alluvial deposit forming a topographically distinct feature on the channel bed, not permanently vegetated. Bed The bottom of a channel bounded by banks. Bed form A recognizable relief feature on the bed of a channel, such as a ripple, dune, plane bed, antidune, or bar. Bed forms are a consequence of the interaction between hydraulic forces (boundary shear stress) and the bed sediment. Bed material Material found in and on the bed of a stream (may be transported as bed load or in suspension). Bedrock The solid rock exposed at the surface of the earth or overlaid with soils and unconsolidated material. Bend apex The point on the outer bank of a meander bend as defined by the intersection of the bank and a line that passes through the bend centroid and bisects the bend. Bend centroid The center point of a best-fit circle used to define a meander bend. Braided stream A stream whose flow is divided at normal stage by small mid-channel bars; the width of the individual bars is less than about three times water width. A braided stream has the aspect of a single large channel within which there are subordinate channels (anabranches). Channel The bed and banks that confine the surface flow of a stream. Channel pattern The aspect of a stream channel in plan view, with particular reference to the degree of sinuosity, braiding, and anabranching. Clay (mineral) A particle whose diameter is in the range of 0.00024 to 0.004 mm. Clay plug An abandoned meander bend filled with fine- grained cohesive sediments. Cobble A fragment of rock whose diameter is in the range of 64 to 250 mm. Confluence The junction of two or more streams. Countermeasure A measure intended to prevent, delay, or reduce the severity of hydraulic problems. Crossing The relatively short and shallow reach of a stream between bends where the main thread of flow shifts from one side of the channel to the other, also called a crossover or riffle. Cross section A section normal to the trend of a channel or flow. Cutbank The concave wall of a meandering stream, often found along the outer bank of a meander bend, formed as a result of erosion at the base of the bank. Cutoff (1) A direct channel, either natural or artificial, con- necting two points on a stream, thereby shortening the orig- inal length of the channel and increasing its slope, and (2) a natural or artificial channel that develops across the neck of a meander loop (neck cutoff) or across a point bar (chute cutoff). APPENDIX F GLOSSARY
Debris Floating or submerged material, such as logs, veg- etation, or trash, transported by a stream. Degradation (bed) A general and progressive (long-term) lowering of the channel bed because of erosion over a relatively long channel length. Discharge Volume of water passing through a channel during a given time. Drainage basin An area confined by drainage divides, often having only one outlet for discharge (also catchment, water- shed). Erosion Displacement of soil particles because of water or wind action. Floodplain A nearly flat, alluvial lowland bordering a stream that is subject to frequent inundation by floods. Fluvial geomorphology The science dealing with the mor- phology (form) and dynamics of streams and rivers. Fluvial system The natural river system consisting of (1) the drainage basin, watershed, or sediment source area; (2) the tributary and mainstem river channels or sediment transfer zone; and (3) alluvial fans, valley fills and deltas, or the sediment deposition zone. Geographic information system (GIS) A computer-based system that enables storing, integrating, manipulating, ana- lyzing, and displaying spatially related information. Geomorphology/morphology That science that deals with the form of the earth, the general configuration of its surface, and the changes that take place because of erosion and deposition. Georeference Aligned with north and east in a ground co- ordinate system. Gravel A rock fragment whose diameter ranges from 2 to 64 mm. Hard point A streambank protection structure whereby âsoftâ or erodible materials are removed from a bank and replaced by stone or compacted clay. Some hard points pro- trude a short distance into the channel to direct erosive cur- rents away from the bank. Hard points also occur naturally along streambanks as passing currents remove erodible materials, leaving nonerodible materials exposed. Helicoidal (helical) flow Three-dimensional movement of water particles along a spiral path in the general direction of flow. These secondary-type currents are of most signifi- cance as flow passes through a bend; their net effect is to remove soil particles from the cutbank and deposit this material on a point bar. Hydraulics The applied science concerned with the behav- ior and flow of liquids, especially in pipes, channels, struc- tures, and the ground. Hydrology The science concerned with the occurrence, distribution, and circulation of water on the earth. Incised stream A stream that has deepened its channel through the bottom of the valley floor, so that the floodplain is left as a terrace. F-2 Island A permanently vegetated area, emergent at normal stage, which divides the flow of a stream. Islands originate by establishment of vegetation on a bar, by channel avulsion or flow splits, or at the junction of a minor tributary with a larger stream. Lateral erosion Erosion in which the removal of material is extended horizontally, as contrasted with degradation and scour in which erosion occurs in a vertical direction. Levee An embankment, generally landward of the top bank, which confines flow during high-water periods, thus preventing overflow into adjoining lowlands. Meander A meander in a river consists of two consecutive loopsâone flowing clockwise relative to the meanderbelt alignment and the other flowing counterclockwise. Meanderbelt The distance between lines drawn tangent to the extreme limits of successive, fully developed meanders. Meander loop An individual loop of a meandering or sin- uous stream lying between inflection points with adjoining loops. Meander width The amplitude of a fully developed mean- der measured from midstream to midstream. Meandering stream A stream having a sinuosity greater than some arbitrary value. The term also implies a moder- ate degree of pattern symmetry, imparted by regularity of size and repetition of meander loops. The channel gener- ally exhibits a characteristic process of bank erosion and point bar deposition associated with systematically shifting meanders. Migration The change in position of a channel by lateral erosion of one bank and simultaneous accretion of the oppo- site bank. Outcrop The exposure of bedrock projecting through the overlying soil. Overbank flow Water movement that overtops the bank either because of stream stage or overland surface water runoff. Oxbow The abandoned former meander loop that remains after a stream cuts a new, shorter channel across the narrow neck of a meander (often bow-shaped or horseshoe-shaped). Photogrammetry The art, science, and technology of obtaining reliable information about physical objects and the environment through processes of recording, measur- ing, and interpreting photographic images and patterns phenomena. Point bar An alluvial deposit of sand or gravel lacking per- manent vegetal cover occurring in a channel at the inside of a meander loop, usually somewhat downstream from the apex of the loop. Radius of curvature The radius of a circle inscribed on the centerline or outer bankline of a meander loop that best defines the meander bend. Reach A segment of stream length that is arbitrarily bounded for purposes of study.
Rectify The removal of the effects of tilt or edge distortion from an aerial photograph. Revetment Rigid or flexible armor placed to inhibit scour and lateral erosion (see bank revetment). Riffle A natural, shallow flow area extending across a streambed in which the surface of flowing water is broken by waves or ripples. Typically, riffles alternate with pools along the length of a stream channel. Riparian Pertaining to anything connected with or adjacent to the banks of a stream (corridor, vegetation, zone, etc.). Runoff That part of precipitation that appears in surface streams of either perennial or intermittent form. Sand A rock fragment whose diameter is in the range of 0.062 to 2.0 mm. Scour Erosion of streambed or bank material because of flowing water, often considered as being localized (see local scour, contraction scour, and total scour). Script In an ArcView project, the component that con- tains the Avenue code used to automate tasks and add new capabilities to ArcView. Sediment/fluvial sediment Fragmental material transported, suspended, or deposited by water. Shear stress The force or drag developed at the channel bed by flowing water. For uniform flow, this force is equal to a component of the gravity force acting in a direction parallel to the channel bed on a unit wetted area (usually in units of stress, Pa [N/m2] or [lb/ft2]). Shoal A relatively shallow submerged bank or bar in a body of water. Silt A particle whose diameter is in the range of 0.004 to 0.062 mm. Sinuosity The ratio between the channel centerline length and the length of the valley as measured between two points on the channel or valley floor. Slope (or gradient) Fall per unit length along the channel centerline or thalweg. Stability A condition of a channel when, though it may change slightly at different times of the year as the result of varying conditions of flow and sediment charge, there is no F-3 appreciable change from year to year; that is, accretion bal- ances erosion over the years. Stream A body of water that may range in size from a large river to a small rill flowing in a channel. By extension, the term is sometimes applied to a natural channel or drainage course formed by flowing water whether it is occupied by water or not. Streambank erosion Removal of soil particles or a mass of particles from a bank surface primarily because of water action. Other factors, such as weathering, ice and debris abrasion, chemical reactions, and land use changes, may also directly or indirectly lead to bank erosion. Streambank failure Sudden collapse of a bank because of an unstable condition, such as removal of material at the toe of the bank by scour. Streambank protection Any technique used to prevent ero- sion or failure of a streambank. Terrace An abandoned floodplain that was formed when the channel flowed at a higher level. Thalweg The line joining the deepest points of a stream channel. Theme In an ArcView project, a set of geographic features in a view. Upper bank The portion of a streambank having an eleva- tion greater than the average water level of the stream. View In an ArcView project, an interactive map that allows the user to display, explore, query, and analyze geographic data. Wandering channel A channel exhibiting a more or less nonsystematic process of channel shifting, erosion, and deposition with no definite meanders or braided pattern. Watershed See drainage basin. Wavelength The straight-line distance between corre- sponding points of successive meanders. World File An ASCII file containing coordinate informa- tion about an image that is needed by ArcView to perform an âimage-to-worldâ transformation.
