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145 Cards in this Set

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Wearing away by friction


The course along which the cetner line of a roadway or channel is located

Angle of repose

The angle which the sloping face of a bank of loose earth or gravel or other material makes with the horizontal

Antecedent precipitation

Rainfall that has recently preceded the storm event being analyzed

Area drain

A structure for collecting runoff from relatively small paved areas


Earth or other materials used to replace material removed during construction, such as in pipeline and culvert trenches and behind retaining walls

Base (course)

A layer of specified or selected material of planned thickness, constructed on the subbase or on the natural subgrade to distribute the load and provide drainage, or on which a wearing surface or a drainage structure is placed.

Bearing capacity (soil)

The load-supporting capacity of a soil


Planing or smoothing the ground surface

Borrow area

A source of earth fill materials used in the construction of embankments or other earth fill structures.

Catch basin

A receptacle, with a sediment bowl or sump, for diverting surface water to a subsurface pipe.

Center line

The survey line in the center of a road, ditch, or similar project.


A natural stream, or a ditch or swale constructed to convey water.


The densification of a soil by a mechanical process.

Continuity equation

A formula expressing the principle of conservation of mass as applied to the flow of water (or other fluids of constant density), which states that the product of cross section of flow and velocity at any point in a channel is a constant.

Contour line

An imaginary line, or its representation on a map, following all points at the same elevation above or below a given datum

Critical depth

The depth of flow in an open channel at which critical flow occurs. For a given flow rate, depths greater than critical result in subcritical, or tranquil, flow. Those smaller than critical result in supercritical, or rapid flow.

Critical flow

An unstable flow condition in open channel which occurs at critical depth

Critical velocity

The velocity of flow in an open channel which occurs at critical depth


The rise or difference in elevation between the edge and the center line of a roadway


Any structure not classified as a bridge which provides a waterway or other opening under a road

Cut section (or cut)

That part of the ground surface which, when graded, is lower than the original ground.


A horizontal reference plane used as a basis for computing elevations.

Detention basin (dry pond)

An impoundment, normally dry, for temporarily storing storm runoff from a drainage area to reduce the peak rate of flow.

Discharge q

Flow rate in a culvert, pipe, or channel.


A channel, with or without a supporting ridge on the lower side, constructed across a slope to intercept surface runoff.


Interception and removal of groundwater or surface water by artificial or natural means.

Drainage area

The area drained by a channel or a subsurface drain


The study of the soil from the standpoint of higher plants and crop production


(a) the altitude relative to a given datum

(b) a scale drawing of the facade of a structure


A bank of earth, rock, and other material constructed above the natural ground surface

Emergency spillway

A channel for safely conveying flood discharges exceeding the capacity of the principal spillway of a detention or retention pond


The susceptibility of soil material to detachment and transportation by running water or wind


Detachment and movement of soil or rock fragments by water, wind, ice, and gravity


(a) the act of taking out materials

(b) the hollow or depression after the materials have been removed

Fill section (or fill)

That part of the ground surface which, when graded, is higher than the original ground

Filter Strip

A vegetated buffer zone for removing sediments and pollutants before runoff reaches ponds, waterways, or other drainage facilities

Fine grade

Preparation of the subgrade preceding placement of surfacing materials


The portion of a structure (usually below ground level) that distributes the pressure to the soil or to artificial supports

Free Water

Soil water that moves by gravity, in contrast to capillary and hydroscopic water

French drain

A trench filled with coarse aggregate (with or without a pipe) for intercepting and conveying ground water


A compartment-ed rectangular container, made of steel wire mesh and filled with stone; used for erosion control and retaining wall purposes.

Finished grade

The completed surfaces of lawns, walks, and roads brought to grades as designed

Natural grade

The undisturbed natural surface of the ground


The grade established in preparation for top surfacing of roads, lawns, etc.


The degree of inclination of a surface, road, or pipe, usually expressed as a percentage


Modification of the ground surface by cuts and/or fills. Fine or finish grading is light or thin grading to finish a prepared earth surface

Grassed waterway

A natural or constructed channel, usually broad and shallow and covered with erosion-resistant vegetation, used to conduct surface runoff.


Aggregate composed of hard and durable stones or pebbles, crushed or uncrushed, often mixed with sand.


Free subsurface water, the top of which is the water table.


An artificially surfaced and generally shallow waterway, usually provided at the sides of a roadway for carrying surface drainage


A vertical wall at the end of a culvert to support the pipe and prevent earth from spilling into the channel

Hydraulic radius

The cross-sectional area flow of a pipe or channel divided by the wetted perimeter


A graph showing, for a given point on a channel, the discharge, stage, velocity, or other property of water with respect to time

Hydrologic condition

Vegetative cover, residue, and surface roughness of a soil as they may affect potential runoff

Hydrologic cycle

The concept of a closed system, involving the transformation of water from the vapor phase to the liquid (and solid) phase and back to the vapor phase, and the movement of that water

Hydrologic soil group (HSG)

A soil classification system based on infiltration and potential runoff characteristics


The property of a material through which water will not flow under ordinary hydrostatic pressure


The downward entry of water into the surface of a soil or other material, as contrasted with percolation, which is the movement of water through soil layers or materials

Infiltration basin

An open surface storage area with no outlet, except an emergency spillway, which permits runoff to infiltrate the soil

Initial abstraction (I.)

Losses before runoff begins, including infiltration, evaporation, interception by vegetation, and water retention in surface depressions


An arrangement for conveying surface water to an underdrain

Intercepting ditch

An open drain to prevent surface water from flowing down a slope by conducting it around the slope (see also diversion)

Interpolation (topographic)

The process of determining the location of elevations from the plotted locations of known elevations


The lowest point of the internal cross section of a pipe or of a channel.

Low-flow channel

A small ditch, constructed in flat bottoms of larger ditches or detention basins, to facilitate their drainage during periods of low flow


A structure, covered with a lid, which allows a person to enter a space below ground level

Manning's equation

A formula for calculating the velocity of flow in a channel as a function of relative roughness, cross sectional configuration, and gradient

Maximum potential retention (S)

The greatest proportion of precipitation that could possibly be retained by a specific soil and land use combination

Modified Rational method (MRM)

An extension of the Rational method for calculating the rate of runoff from a drainage area, including provisions for antecedent precipitation and for development of hydrographs

Moisture content

The percentage, by weight, of water contained in soil or other material, usually based on dry weight


A boundary stone or other permanent marker locating a property line or corner


Point of water disposal from a stream, river, lake, tidewater, or artificial drain

Peak discharge

The maximum instantaneous flow rate resulting from a given storm condition at a specific location


Movement of soil water towards the water table


An exterior platform at a building entrance, usually with steps leading up to it


The property of a material which permits movement of water through it under ordinary hydrostatic pressure


A measure of alkalinity or acidity; pH 7 is neutral and pH 6.5 presents a desirable degree of soil acidity


Having many small openings through which liquids may pass

Porous pavement

A pavement constructed from a material that permits percolation of storm water to the subgrade

Principal spillway

A component of retention or detention ponds, generally constructed of permanent materials. It is designed to regulate the normal water levels, provide flood protection, and/or reduce the frequency of operation of the emergency spillway


The study of soil as a natural body, including its origin, characteristics, classification, and description

Rainfall intensity (i)

The rate at which rain falls. In the US usually measured in inches per hour (iph).


An inclined plane serving as a way between two different levels

Rational method

A formula for calculating the peak runoff rate from a drainage area based on land use, soils, land slope, rainfall intensity, and drainage area

Recession or receding limb (of a hydrograph)

The portion of a hydrograph that occurs after the peak when the flow rate decreases

Retention basin (wet pond)

A reservoir, containing a permanent pool, for temporarily storing storm runoff and reducing the storm runoff rate from a drainage area

Retaining wall

A wall built to support a bank of earth

Right of way

The entire strip of land dedicated for highway purposes


Stones or other material placed on a slope to prevent erosion by water

Rising limb (of a hydrograph)

The portion of a hydrograph preceding the peak when the flow rate increases.

Rough grade

Stage of grading operation in which the desired landform is approximately attained

Roughness coefficient (n)

A factor in the Manning formula representing the effect of channel or conduit roughness on energy losses in the flowing water


The part of precipitation carried off from the area on which it falls. Also, the rate of surface discharge of the above. (The ration of runoff to precipitation is a coefficient, expressed as a decimal)

Runoff curve number (CN)

A parameter used in SCS hydrological techniques, based on soil characteristics and land use


Soil Conservation Service, a federal agency in the Department of Agriculture, dealing with erosion and flood control


Soil material, both mineral and organic, in suspension, being transported, or having been moved from its original site, by air, water, gravity, or ice

Sediment basin

A reservoir formed by the construction of a barrier or dam built at a suitable location to permit the settling out of sediments (rock, sand, gravel, silt, or other material) before releasing the water

Shallow concentrated flow

flow in shallow rills

Sheer stress (channel)

Force per unit area exerted on the wetted area of a channel, acting in the direction of flow

Sheet flow

Flow over plane, sloped surfaces in a thin layer


The portion of roadway between the edge of the hardened wearing course and the ditch or embankment

Sight distance

The distance between approaching vehicles when first visible to one another along a horizontal or vertical curve


Movement of soil on a slope resulting in a reduced angle of repose usually occurring as a result of rainfall, high water, or thaw.


The face of an embankment or cut section; any ground whose surface makes an angle with the horizontal plane

Splash block

A masonry block with its top close to the ground surface, which receives roof drainage and prevents erosion below the spout

Storage (runoff)

Runoff that is being temporarily impounded to permit controlling the runoff rate and/or improving water quality

Storm sewer

A conduit used for conveyance of rain water


Anything constructed that requires a permanent location on the ground or is attached to something that has a permanent location on the ground


A pervious backfilled trench containing a pipe with perforations or open joints for the purpose of intercepting groundwater or seepage


The rise of the outer edge of the pavement relative to the inner edge at a curve in the highway, expressed in feet per foot, intended to overcome the tendency of speeding vehicles to overturn when rounding a curve


A constructed or natural vegetated waterway


A straight road segment connecting two curves


An essentially level and defined area, usually raised, either paved or planted, forming part of a garden or building setting

Time of concentration

The time for water to flow from the hydraulically most remote point in a drainage area to a point of interest

Time of recession

The period of time from the peak of a hydrograph until it again reaches the beginning flow rate

Time of rise (of a hydrograph)

The period of time from the beginning flow rate until the peak flow rate is reached

Travel time

The time of runoff to flow from one point in a drainage area to another

Trench drain

A linear structure that collects runoff from a paved area

water quality basin

A reservoir which has a provision for removing pollutants from storm runoff by retaining the runoff from high-frequency storms (i.e. those with 1 or 2 year frequencies) for prolonged periods (i.e. from 18 to 36 hours)


Region or area contributing to the supply of a stream or lake (also drainage basin or catchment area)

Water table

The level below which the ground is saturated


A natural course, or a constructed channel, for the flow of water


A small hole, as in a retaining wall, to drain water to the outside


An opening in the crest of a dam or embankment to discharge excess water; also used for measuring the rate of discharge

Wetter perimeter

The length of the wetted contact between the water and the containing conduit, measure along a plane that is perpendicular to the conduit

Basis of Bearing

A line between two points on the ground and indicated on a survey map, referenced to true North, which is the basis for property boundaries or other information on a survey showing horizontal relationships of objects to each other


A fixed point on the ground who's location and relative elevation is known, marked by temporary or permanent markers, and usually shown on a topographic survey. Benchmarks are set by the USGS, sate or local governments, or surveyors

Concave Slope

A slope where the angle of the surface gets flatter as one gets closer to the bottom of the hill. People, vehicles and runoff tend to decelerate on concave slopes, whether going up or down


An imaginary line of equal elevation on the earth's surface. A line depicting topographic information on a plan. Usually each contour is depicted in increments of one foot or more

Convex Slope

A slope where the angle of the surface gets steeper as one gets closer to the bottom of the hill. People, vehicles and runoff tend to accelerate on convex slopes, whether going up or down.

Detention Basin

A basin (with or without a permanent pool) which is intended to temporarily hold surface runoff for the purpose of controlling the discharge rate leaving the site or watershed. Usually this is accomplished by providing a temporary storage area and by undersizing the outlet from the basin to restrict outflow to some predetermined maximum discharge


A branch of engineering science concerned with the flow of liquids, usually in channels, pipes, or porous media (such as soil)


The study of water. The study of rainfall/runoff relationships during storm events as affected by factors of climate, event probability, and local topographic, soil characteristics and land use conditions


A method of determining elevations between two known spot elevations or contours. It is possible to determine either the elevation of a known location, or the location of a known elevation.


A graphical device used to solve mathematical or scientific equations with multiple variables. A nomograph is a mathematical equation that has been transformed into a graphical representation.

Retention Basin

A basin (with or without a permanent pool) which is intended to hold surface runoff for the purpose of controlling both the discharge rate and the runoff volume leaving the site or watershed. There is usually some minimum storage component where the water can only leave the basin via infiltration or evaporation


A line of elevations which are higher than elevations on either side. These often define the boundaries of watersheds.

Slope formula

The basic equation for determining horizontal distance, vertical distance, or gradient when the other two variables are known. Extremely useful in all grading applications.

Spot Elevation

A point on the ground or plan showing its exact elevation relative to some datum.


The art or practice of graphical delineation to show the physical features of a place in relation to each other in position and elevation.


A line of elevations which are lower than elevations on either side. These often define stream channels or flow lines for watersheds.


An area bounded by ridges having a single outlet from which water can flow. All water flowing or landing as rainfall within the watershed will eventually exit at that outlet.

Water Gathering (Slope)

A landform which tends to push surface runoff to the center of the landform. Example: A valley or a bowl.

Water Spreading (Slope)

A landform which tends to push surface runoff to the edges of the landform. Example: a ridge or dome.