Definitions A – C

Active Construction Area.  The area where the contractor intends to be actively involved in soil disturbing work during the ensuing 20 day period during the winter season.  This may include areas where soils have been disturbed as well as areas where soil disturbance has not  yet occurred.

Aggradation.    General and progressive raising of a stream bed by deposition of sediment. Modification of the earth's surface in the direction of uniformity of grade, or slope, by deposition as in a river bed.

Aggressive.  Refers to the corrosive properties of soil and water.

Alluvial.  Referring to deposits of silts, sands, gravels and similar detrital material which have been transported by running water.

Alluvium.  Stream-borne materials deposited in and along a channel.

Apron.  A lining of the bed of the channel upstream or downstream from a  lined  or  restricted waterway.  A floor or lining of concrete, rock, etc., to protect a surface from erosion such as the pavement below chutes, spillways, at the toes of dams, or along the toe of bank protection.

Aqueduct.  (1) A major conduit.  (2) The entire transmission main for a municipal water supply that may consist of a succession of canals, pipes, tunnels, etc.  (3) Any conduit for water; especially one for a large quantity of flowing water.  (4) A structure for conveying a canal over a river or hollow.

Aquifer.  Water-bearing geologic formations that permit the movement of ground water.

Arid Area.  Area receiving less than 10 inches of rainfall per year.

Armor.  Artificial surfacing of bed, banks, shore or embankment to resist erosion or scour.

Arroyo.  Waterway of an ephemeral stream deeply carved in rock or ancient alluvium.

Artesian  Waters.    Percolating  waters confined below impermeable formations with sufficient pressure to spring or well up to the surface.

Articulated.  Made flexible by hinging particularly of small rigid slabs adapted to revetment.

Avulsion.  (1) A forcible separation; also, a part torn off.  (2) The sudden removal of land from the estate of one person to that of another, as by a sudden change in a river, the property thus separated continuing in the original owner.  (3) A sudden shift in location of channel.

Backfill.  Earth used to fill a trench or excavation.

Backing Layer.  A layer of graded rock between rock riprap and underlying engineering fabric or filter layer to prevent extrusion of the soil or filter layer material through the riprap.

Backshore.  The zone of the shore or beach lying between the foreshore and the coastline and acted upon by waves only during severe storms, especially when combined with exceptionally high water.

Backwater.  An unnaturally high stage in stream caused by obstruction or confinement of flow, as by a dam, a bridge, or a levee.  Its measure is the excess of unnatural over natural stage, not the difference in stage upstream and downstream from its cause.

Baffle.  A pier, vane, sill, fence, wall or mound built on the bed of a stream to parry,  deflect, check or disturb the flow or to float on the surface to deflect or dampen cross currents or waves.

Bank.  The lateral boundary of a stream confining water flow.  The bank on the left side of a channel looking downstream is called the left bank, etc.

Bank  Protection.    Revetment,  or other armor  protecting a bank of a stream from erosion, includes devices used to deflect the forces of erosion away from the bank.

Bar.  An elongated deposit of alluvium within a channel or across its mouth.

Barrier.  A low dam or rack built to control flow of debris.

Base Flood.  The flood or tide having a 1 percent chance of being exceeded in any given year (100-year flood).  The 'base flood' is commonly used as the 'standard flood'  in Federal  flood insurance studies.  (see Regulatory Flood).

Base Floodplain.  The area subject to flooding by the base flood.

Base Flow.  The flow contribution to a creek by groundwater.  During dry periods, base flow constitutes the majority of stream flow.

Basin.  (1) The surface of the area tributary to a stream or lake.  (2) Space above or below ground capable of retaining or detaining water or debris.

Bay.  An indentation of bank or shore, including erosional cuts and slipouts, not necessarily large.

Beach.  The zone of sedimentary material that extends landward from the low water line to the place where there is marked change in material or form, or to the line of permanent vegetation (usually  the  effective limit  of  storm waves).  The seaward limit of a beach, unless otherwise specified, is the mean low water line.  A beach includes foreshore and backshore.

Bed.   The earth below any body of water, limited laterally by bank or shore.

Bed Load.  Sediment that moves by rolling, sliding, or skipping along the bed and is essentially in contact with the stream bed.

Bedding.  The foundation under a drainage structure.

Beneficial Uses.   As  referred  to  in  the  State  Water  Quality  Standards,  beneficial  uses  are activities that range from recreational to agricultural uses, depending on the source of the water.

Berm.   (1) A bench or terrace between two slopes.  (2) A nearly horizontal part of the beach or backshore formed at the high water line by waves depositing material.  Some beaches have no berms, other have one or several.

Best Management Practice (BMP).  (1)A measure that is implemented to protect water quality and  reduce  the  potential  for  pollution associated with storm water runoff.  (2) Any program, technology, process, siting criteria, operating method, measure, or device that controls, prevents,removes, or reduces pollution.

Block.  Precast prismatic unit for riprap structure.

Bluff.  A high, steep bank composed of erodible materials.

Boil.  Turbulent break in a water surface by upwelling.

Boom.  Floating log or similar element designed  to  dampen  surface  waves  or  control  the movement of drift.

Bore.    A  transient solitary wave in a narrow or converging channel advancing with a steep turbulent front; product of flash floods or in-coming tides.

Boulder.  Largest rock transported by a stream or rolled in the surf; arbitrarily heavier than 12 kg and larger than 200 mm.

Braided Stream.  A stream in which flow is divided at normal stage by small islands.  This type of stream has the aspect of a single large channel with which there are subordinate channels.

Breaker.  A wave meeting a shore, reef, sandbar, or rock and collapsing.

Breakwater.  A fixed or floating structure that protects a shore area, harbor, anchorage, or basin by intercepting waves.

Bulkhead.   A steep or vertical structure placed on a bank, bluff, or embankment to retain or prevent sliding of the land and protect the inland area against damage.

Bulking.  The increase in volume of flow due to air entrainment, debris, bedload, or sediment in suspension.

Buoyancy.   Uplift force on a submerged body equal to the mass of water displaced times the acceleration of gravity.

Camber.   An upward adjustment of the profile of a drainage facility under a heavy  loading (usually a high embankment) and poor soil conditions, so that as the drainage facility settles it approaches the design profile.

Canal.  An artificial open channel.

Canyon.  A large deep valley; also the sub-marine counterpart.

Cap.  Top layer of stone protective works.

Capacity.  The  effective  carrying  ability  of  a  drainage  structure. Generally measured in cubic meters per second.

Capillarity.  The attraction between water and soil particles which cause water to move in any direction through the soil mass regardless of gravitational forces.

Capillary  Water.    Water  which  clings  to  soil  particles  by  capillary  action.    It  is  normally associated with fine sand, silt, or clay, but not normally with coarse sand and gravel.

Catch Basin.  A drainage structure which collects water.  May be either a structure where water enters from the side or through a grating.

Causeway.  A raised embankment or trestle over swamp or overflow areas.

Cavitation.  Erosion by suction, especially in the partial vacuum of a diverging jet.

Celerity.  Velocity of a moving wave, as distinguished from velocity of particles oscillating in the wave.

Channel.  The space above the bed and between banks occupied by a stream.

Channelization.  The process of making a channel or channels.  A channel is the bed of a stream or river, or the hollow or course in which a stream flows.

Check.  A sill or weir in a channel to control stage or velocity.

Check Dam.   A  small dam generally placed in steep ditches for the purpose of reducing the velocity in the ditch.

Cienega.  A swamp formed by water rising to the surface at a fault.

Clean Water Act (CWA).  The Federal Water Pollution Control Act enacted in 1972 by Public Law 92-500 and amended by the Water Quality Act of 1987.  The Clean Water Act prohibits the discharge of pollutants to Waters of the United States unless said discharge is in accordance with an NPDES permit.  The 1987 amendments include guidelines for  regulating  municipal, industrial, and construction storm water discharges under the NPDES program.

Cleanout.    An access opening to a roadway drainage system.  Usually consists of a manhole shaft, a special chamber or opening into a shallow culvert or drain.

Cliff.  A high, steep face of rock; a precipice.

Cloudburst.  Rain storm of great intensity usually over a small area for a short duration.

Coast.  (1) The strip of land, of indefinite width (up to several kilometers), that extends from the shoreline inland to the first major change in terrain features. (2) As a combining form, upcoast is northerly and downcoast is southerly.

Cobble.   Rock smaller than a boulder and larger than gravel; arbitrarily 0.5 to 12 kg, or 75 to 200 mm in diameter.

Coefficient of Runoff.  Percentage of gross rainfall which appears as runoff.

Composite Hydrograph.  A plot of mean daily discharges for a number of years of record on a single year time base for the purpose of showing the occurrence of high and low flows.

Concentrated Flow.  Flowing water that has been accumulated into a single fairly narrow stream.

Concentration.  In addition to its general sense, means the unnatural collection or convergence of waters so as to discharge in a narrower width, and at greater depth or velocity.

Conduit.  Any pipe, arch, box or drain tile through which water is conveyed.

Cone.  Physiographic form of sediment deposit washed from a gorge channel onto an open plain;a debris cone, also called an alluvial fan.

Confluence.  A junction of streams.

Constriction.  An obstruction narrowing a waterway.

Construction  Activity.    Includes  clearing,  grading,  or  excavation  and  contractor  activities  that result in soil disturbance.

Construction Site.  The area involved in a construction project as a whole.

Contraction.  The reduction in cross sectional area of flow.

Contractor.  Party responsible for carrying out the contract per plans and specifications.

Control.  (1) A section or reach of an open conduit or stream channel which maintains a stable relationship between stage and discharge.  (2) For flood, erosion, debris, etc., remedial means or procedure restricting damage to a tolerable level.

Conveyance.   (1) A measure  of  the  water carrying capacity of a stream or channel.  (2)  Any natural or man-made channel or pipe in which concentrated water flows.

Core.  Central zone of dike, levee, rock groin, jetty, etc.

Corrasion.  Erosion or scour by abrasion in flowing water.

Corrosion.  Erosion by chemical action.

Cradle.  A concrete base generally constructed to fit the shape of a structure that is to be forced through earthen material by a jacking operation.  The  cradle  is  constructed  to  line  and  grade. Then  the  pipe  rides  on  the  cradle  as  it is worked through the given material by jacking and tunneling methods.  Also serves as bedding for pipes in trenches in special conditions.

Creek.  A small stream, usually active.

Crest.  (1) Peak of a wave or a flood.  (2) Top  of  a  levee,  dam,  weir,  spillway  or  other  water barrier or control.

Crib.  An open-frame structure loaded with earth or stone ballast  to  act  as  a  baffle  in  bank protection.

Critical Depth.  (Depth at which specific energy is a minimum) - The depth of water in a conduit at which under certain other conditions the maximum flow will occur.  These other conditions are the conduit is on the critical slope with the water flowing at its critical velocity and there is an adequate supply of water.  The depth of water flowing in an open channel or a conduit partially filled, for which the velocity head equals one-half the hydraulic mean depth.

Critical  Flow.  That  flow in open channels at which the energy content of the fluid is at a minimum.  Also, that flow which has a Froude number of one.

Critical Slope.  That slope at which the maximum flow will occur at the minimum velocity.  The slope or grade that is exactly equal to the loss of head per meter resulting from flow at a depth that will give uniform flow at critical depth; the slope of a conduit which will produce  critical flow.

Critical Velocity.  Mean velocity of flow when flow is at critical depth.

Culvert.  A closed conduit, other than a bridge, which allows water to pass under a highway.  A culvert has a span of less than 6.1 m, or if multispan, the individual spans are 3.0 m or less.

Current.  Flow of water, both as a phenomenon and as a vector. Usually qualified by adjectives like downward, littoral, tidal, etc. to show relation to a pattern of movement.

Current Meter.  An instrument for measuring the velocity of a current.  It is usually operated by a wheel equipped with vanes or cups which is rotated by the action of the impinging current.  An indicating or recording device is provided to indicate the speed of rotation, which is correlated with the velocity of the current.

Cutoff Wall.  A wall at the end of a drainage structure, the top of which is an integral part of the drainage structure.  This wall is usually buried, and its function is to prevent undermining of the drainage  structure  if  the  natural  material  at  the  outlet  of  the  structure  is  scoured  by  the  water discharging from the end of the structure.  Cutoff walls are sometimes used at the upstream end of a structure when there is a possibility of erosion at this point.