Definitions Q – S

Rainfall.    Point  Precipitation: That which registers at a single gauge.  Area Precipitation: Adjusted point rainfall for area size.

Rainwash.  The creep of soil lubricated by rain.

Range.  Difference between extremes, as for stream or tide stage.

Rapidly Varied Flow.  In this type of flow, changes in depth and velocity take place over short distances, acceleration forces dominate, and energy loss due to friction is minor.

Rapids.  Swift turbulent flow in a rough steep reach.

Ravine.  A valley larger than a gulch, smaller than a canyon, and less bold in relief than a gulch or arroyo.

Reach.  The length of a channel uniform with respect to discharge, depth, area, and slope.  More generally, any length of a river or drainage course.

Recession.  Retreat of shore or bank by progressive erosion.

Reef.  Generally, any solid projection from the bed of a stream or other body of water.

Regime.  The system or order characteristic of a stream; its behavior with respect to velocity and volume, form of and changes in channel, capacity to transport  sediment,  amount  of  material supplied for transportation, etc.

Regimen.  The characteristic behavior of a stream during ordinary cycles of flow.

Regulatory Floodway.  The open floodplain area that is reserved in by Federal, State, or local requirements, i.e., unconfined or unobstructed either horizontally or vertically, to provide for the discharge of the base flood so that the cumulative increase in water surface elevation is no more than a designated amount (not to exceed 0.3048  m  as  established  by  the  Federal  Emergency Management Agency (FEMA) for administering the National Flood Insurance Program (NFIP)).

Regulatory  Framework.  A particular set of laws, rules, procedures, and agencies designed to govern a particular type of activity or solve a particular program.

Reliction.   Pertaining to being left behind.  For example: that area of  land  is  left  behind  by reliction when the water surface of a lake is lowered.

Repose.    The stable slope of a bank or embankment, expressed as an angle or the ratio of horizontal to vertical projection.

Restore.   To  reestablish  a  setting  or  environment  in  which  the  functions  of  the  natural  and beneficial floodplain values adversely impacted by a development can continue to operate.

Restriction.  Artificial or natural control against widening of  a  channel,  with  or  without construction.

Retard.  Bank-protection structure designed to check the riparian velocity and induce silting or accretion.

Retarding Basin.  Either a natural or man made basin with the specific function of delaying the flow of water from one point to another.  This tends to increase the time that it takes all the water falling on the extremities of the drainage basin to reach a common point, resulting in a reduced peak flow at that point.

Retention.  The holding of runoff in a basin without release except by means of  evaporation, infiltration, or emergency bypass.

Retention Storage.  Water that accumulates and ponds in natural or excavated depressions in the soil surface with no possibility for escape as runoff.  (See Detention Storage)

Retrogression.  Reversal of stream grading; i.e., aggradation after degradation, or vice versa.

Revegetation.     Planting of indigenous plants to replace natural vegetation that is damaged or removed as a result of construction projects or permit requirements.

Revetment.  Bank protection to prevent erosion.

Rill Erosion. The formation of numerous, closely spaced streamlets due to uneven detachment of surface soils by runoff on slopes.

Riparian.  Pertaining to the banks of a stream.

Ripple.  (1) The light fretting or ruffling of a water caused by a breeze.  (2) Undulating ridges and furrows, or crests and troughs formed by action of the flow.

Riprap.  A layer, facing, or protective mound of broken concrete, sacked concrete, rock, rubble, or stones randomly placed to prevent erosion, scour, or sloughing of a structure or embankment; also, the stone used for this purpose.

Riser.   In  mountainous  terrain where much debris is encountered, the entrance to a culvert sometimes becomes easily clogged.  Therefore, a corrugated metal pipe or a structure made of timber or concrete with small perforations, called a riser, is installed vertically to permit entry of water and prohibit the entry of mud and debris.  The riser may be increased in height as the need occurs.

Risk.    The consequences associated with the probability of flooding attributable  to  an encroachment.  It includes the potential for property loss and hazard to life during the service life of the structure or project.

Risk  Analysis.    An economic comparison of design alternatives using expected total costs (construction costs plus risk costs) to determine the alternative with the least expected cost to the public.

River.  A large stream, usually active when any streams are flowing in the region.

Rock.  (1) Cobble, boulder or quarry stone as a construction material. (2) Hard natural mineral, in formation as in piles of talus.

Rounded Inlet.   The edges of a culvert entrance that are rounded for smooth transition which reduces turbulence and increases capacity.

RSP Fabric.  (See Filter Fabric).

Rubble.  Rough, irregular fragments of rock or concrete.

Runoff.  (1) The surface waters that exceed the soil.s infiltration rate and depression storage.  (2) The portion of precipitation that appears as flow in streams.  Drainage or flood discharge which leaves an area as surface flow or a pipeline flow, having reached a channel or pipeline by either surface or subsurface routes.

Runup.  The rush of water up a beach or structure, associated with the breaking of a wave. The amount of runup is measured according to the vertical height above still water level that the rush of water reaches.

Sag Culvert (or Sag Pipe).  A pipeline with a dip in its grade line crossing over a depression or under a highway, railroad, canal, etc.  The term inverted siphon is common but inappropriate as no siphonic action is involved.  The term 'sag pipe' is suggested as a substitute.

Sand.  Granular soil coarser than silt and finer than gravel, ranging in diameter from 0.05 to 5 mm.

Scour.    The result of erosive action of running water, primarily in streams,  excavating  and carrying away material from the bed and banks.  Wearing away by abrasive action.

Scour, General.  The removal of material from the bed and banks across all or most of the width of a channel, as a result of a  flow contraction  which  causes  increased  velocities  and bed shear stress.

Scour, Local.  Removal of material from the channel bed or banks which is restricted to a minor part of the width of a channel.  This scour occurs around piers and embankments and is caused by the actions of vortex systems induced by the obstruction to the flow.

Scour, Natural.  Removal of material from the channel bed or banks which occurs in streams with the migration of bed forms, shifting of the thalweg and at bends and natural contractions.

Sea.  Ocean or other body of water larger than a lake; state of agitation of any large  body  of water.

Seawall.  A structure separating land and water areas, primarily designed to prevent erosion and other damage due to wave action. (See bulkhead).

Sediment.  Fragmentary material that originates from weathering of rocks and is transported by, suspended in, or deposited by water.

Sedimentation.  Gravitational deposit of transported material in flowing or standing water.

Seepage.  Percolation of underground water through the banks and into a stream or other body of water.

Seiche.  A standing wave oscillation of an enclosed waterbody that continues, pendulum fashion, after the cessation of the originating force, which may have been either seismic or atmospheric.

Seismic Wave.  A gravity wave caused by an earthquake.

Semi-Arid Area.  Area receiving between 10 and 20 inches of rainfall per year.

Sheet Erosion.  Erosion of thin layers of soil by sheets of flowing water.

Sheet Flow.  Any flow spread out and not confined; i.e., flow across a flat open field.

Sheet Pile.  A pile with a generally slender, flat cross-section that is driven into ground or bottom of a water body and meshed or interlocked with like members to form a wall or bulkhead.

Shoal.  A shallow region in flowing or standing water, especially if made shallow by deposition.

Shoaling.  Deposition of alluvial material resulting in areas with relatively shallow depth.

Shore.  The narrow strip of land in immediate contact with the water, including the zone between high and low water lines. See backshore, foreshore, onshore, offshore, longshore, and nearshore.

Silt.  (1) Water-Borne Sediment.  Detritus carried in suspension or deposited by flowing water, ranging in diameter from 0.005 to 0.05 mm.  The term is generally confined to fine earth, sand, or mud, but is sometimes both suspended and bedload.  (2) Deposits of Water-Borne Material. As in a reservoir, on a delta, or on floodplains.

Sinuosity.  The ratio of the length of the river thalweg to the length of the valley proper.

Skew.  When a drainage structure is not normal (perpendicular) to the longitudinal axis  of  the highway, it is said to be on a skew.  The  skew  angle  is  the  smallest  angle  between  the perpendicular and the axis of the structure.

Slide.  Gravitational movement of an unstable mass of earth from its natural position.

Slipout.    Gravitational  movement  of  an unstable mass of earth from its constructed position. Applied to embankments and other man-made earthworks.

Slope.  (1) Gradient of a stream.  (2) Inclination of the face of an embankment, expressed as the ratio of horizontal to vertical projection; or (3) The face of an inclined embankment or cut slope. In hydraulics it is expressed as percent or in decimal form.

Slough.  (1) Pronounced SLU.  A side or overflow channel in which water is continually present. It is stagnant or slack; also a waterway in a tidal marsh.  (2) Pronounced SLUFF.  Slide or slipout of a thin mantle of earth, especially in a series of small movements.

Slugflow.    Flow  in  culvert  or  drainage  structure  that  alternates  between  full  and  partly  full. Pulsating flow -- mixed water and air.

Soffit.  The bottom of the top -- (1) With reference to a bridge, the low point on the underside of the suspended portion of the structure.  (2) In a culvert, the uppermost point on the inside of the structure.

Source  Control  BMP.    An  effort  to  prevent  or  limit  the  exposure  of  significant  materials  to storm water at the source.

Specific Energy.  The energy contained in a stream of water, expressed in terms of head, referred to the bed of a stream.  It is equal to the mean depth of water plus the velocity head of the mean velocity.

Spur Dike.  A structure or embankment projecting a short distance into a stream from the bank and at an angle to deflect flowing water away from critical areas.

Stage.  The elevation of a water surface above its minimum; also above or below an established 'low water' plane; hence above or below any datum of reference; gage height.

Standing Wave.  (1) The motion of swiftly flowing stream water, that resembles a wave, but is formed by decelerating or diverging flow that does not quite produce a hydraulic jump.    (2) A term which when used to describe the upper flow regime in alluvial channels, means a vertical oscillation of the water surface between fixed nodes without appreciable progression in either an upstream or downstream direction.  To maintain the fixed position, the wave must have a celerity (velocity) equal to the approach velocity in the channel, but in the opposite direction.

Steady Flow.  A flow in which the flow rate or quantity of fluid passing a given point per unit of time remains constant.

Stone.    Rock  or  rock-like material;  a  particle  of  such material,  in  any  size  from pebble  to  the largest quarried blocks.

Storage.  Detention, or retention of water for future flow, naturally in channel and marginal soils or artificially in reservoirs.

Storage Basin.  Space for detention or retention of water for future flow, naturally in channel and marginal soils, or artificially in reservoirs.

Storm.    A  disturbance  of  the  ordinary,  average conditions of the atmosphere which, unless specifically qualified, may include any or all meteorological disturbances, such  as  wind,  rain, snow, hail, or thunder.

Storm Drain.  That portion of a drainage system expressly for collecting and conveying former surface water in an enclosed conduit.  Often referred to as a 'storm sewer', storm drains include inlet structures, conduit, junctions, manholes, outfalls and other appurtenances.

Storm Water.  Storm water runoff, snow melt runoff, and surface runoff and drainage.

Storm Water Management.  The recognition of adverse drainage resulting from altered runoff and the solutions resulting from the cooperative efforts of public agencies and the private sector to mitigate, abate, or reverse those adverse results.

Storm Water Pollution Prevention Plan (SWPPP).  A plan required by storm water regulations or  permits  that  includes  site map(s),  an  identification  of  construction/contractor  activities  that could cause pollutants in the storm water, and a description of measures or practices to control these pollutants.

Strand.   (1) To lodge on bars, banks, or overflow plain, as for drift. (2) Bar of sediment connecting two regions of higher ground.

Stream.  Water flowing in a channel or conduit, ranging in size from small creeks to large rivers.

Stream  Power.    An expression used in predicting bed forms and hence bed load transport  in alluvial  channels.    It  is  the  product of the mean velocity, the specific weight of the water- sediment mixture, the normal depth of flow and the slope.

Stream Response.  Changes in the dynamic equilibrium of a stream by any one, or combination of various causes.

Stream  Waters.    Former surface waters which have entered and now flow in  a  well  defined natural watercourse, together with other waters reaching the stream by direct  precipitation  or rising from springs in bed or banks of the watercourse.  They continue as stream waters as long as they flow in the watercourse, including overflow and multiple channels as well as the ordinary or low-water channel.

Strutting.  Elongation of the vertical axis of pipe prior to installing in a trench.  After the backfill has been placed around the pipe and compacted, the wires or rods holding the pipe in its distorted shape are removed.  Greater side support from the earth is developed when  the  pipe  tends  to return to its original shape.  Generally used on pipes which, because of size or thinness of the metal, would tend to deform during construction operations.  Arches are strutted diagonally per standard or special plan.

Subcritical Flow.  In this state, gravity forces are dominant, so that the flow has a low velocity and is often described as tranquil and streaming.  Also defined as flow that has a Froude number less than one.

Subdrain.  A conduit for collecting and disposing of underground water.  It generally consists of a pipe, with perforations in the bottom through which water can enter.

Subsidence.   A general lowering of the land surface by consolidation or removal of underlying soil.

Substrate.  The layer of earth or rock that lies immediately below the surface soil.

Sump.  In drainage, any low area that does not permit the escape of water by gravity flow.

Supercritical Flow.  In this state, inertia forces are dominant, so that flow has a high velocity and is usually described as rapid, shooting and torrential.  Also defined as flow that has  a  Froude number greater than one.

Support Base Floodplain  Development.    To  encourage,  allow,  serve,  or  otherwise  facilitate additional base floodplain development.  Direct support  results  from  an  encroachment,  while indirect support results from an action out of the base floodplain.

Surcharge.  A condition where the hydraulic capacity of the storm drain system is temporarily exceeded (e.g., during a storm event), and the amount of water that enters the system exceeds the conveyance capacity.

Surf.  The breaking of waves and swells on the foreshore and offshore shoals.

Surface  Runoff.    The movement  of  water  on  earth's surface, whether flow is over surface of ground or in channels.

Surface Waters.  Surface waters are those which have been precipitated on the land from the sky or forced to the surface in springs, and which have then spread over the surface of the ground without  being collected into a definite body or channel.  They appear as puddles, sheet or overland flow, and rills, and continue to be surface waters until they disappear from the surface by  infiltration  or  evaporation,  or  until  by overland or vagrant flow they reach well-defined watercourses or standing bodies of water like lakes or seas.

Surge.  (1) A sudden swelling of discharge in unsteady flow.  (2) A large mass of moving water, such as a wave or swell.  Also a heavy, violent swelling motion, such as a surge of water through a storm drain during a heavy rain.

Suspended Load.  Sediment that is supported by the upward components of turbulent currents in a stream and that stay in suspension for appreciable amount of time.

Suspended  Solids.    Organic or inorganic particles which are suspended in  and  carried  by  the water.  The term includes sand, mud and clay particles as well as solids in wastewater.