Lare Section 4 Vocabulary

Front 1

Abrasion

Back 1

Wearing away by friction

Front 2

Alignment

Back 2

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

Front 3

Angle of repose

Back 3

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

Front 4

Antecedent precipitation

Back 4

Rainfall that has recently preceded the storm event being analyzed

Front 5

Area drain

Back 5

A structure for collecting runoff from relatively small paved areas

Front 6

Backfill

Back 6

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

Front 7

Base (course)

Back 7

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.

Front 8

Bearing capacity (soil)

Back 8

The load-supporting capacity of a soil

Front 9

Blading

Back 9

Planing or smoothing the ground surface

Front 10

Borrow area

Back 10

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

Front 11

Catch basin

Back 11

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

Front 12

Center line

Back 12

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

Front 13

Channel

Back 13

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

Front 14

Compaction

Back 14

The densification of a soil by a mechanical process.

Front 15

Continuity equation

Back 15

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.

Front 16

Contour line

Back 16

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

Front 17

Critical depth

Back 17

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.

Front 18

Critical flow

Back 18

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

Front 19

Critical velocity

Back 19

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

Front 20

Crown

Back 20

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

Front 21

Culvert

Back 21

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

Front 22

Cut section (or cut)

Back 22

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

Front 23

Datum

Back 23

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

Front 24

Detention basin (dry pond)

Back 24

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

Front 25

Discharge q

Back 25

Flow rate in a culvert, pipe, or channel.

Front 26

Diversion

Back 26

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

Front 27

Drainage

Back 27

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

Front 28

Drainage area

Back 28

The area drained by a channel or a subsurface drain

Front 29

Edaphology

Back 29

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

Front 30

Elevation

Back 30

(a) the altitude relative to a given datum

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

Front 31

Embankment

Back 31

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

Front 32

Emergency spillway

Back 32

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

Front 33

Erodability

Back 33

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

Front 34

Erosion

Back 34

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

Front 35

Excavation

Back 35

(a) the act of taking out materials

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

Front 36

Fill section (or fill)

Back 36

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

Front 37

Filter Strip

Back 37

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

Front 38

Fine grade

Back 38

Preparation of the subgrade preceding placement of surfacing materials

Front 39

Foundation

Back 39

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

Front 40

Free Water

Back 40

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

Front 41

French drain

Back 41

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

Front 42

Gabion

Back 42

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

Front 43

Finished grade

Back 43

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

Front 44

Natural grade

Back 44

The undisturbed natural surface of the ground

Front 45

Subgrade

Back 45

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

Front 46

Gradient

Back 46

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

Front 47

Grading

Back 47

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

Front 48

Grassed waterway

Back 48

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

Front 49

Gravel

Back 49

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

Front 50

Groundwater

Back 50

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

Front 51

Gutter

Back 51

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

Front 52

Headwall

Back 52

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

Front 53

Hydraulic radius

Back 53

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

Front 54

Hydrograph

Back 54

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

Front 55

Hydrologic condition

Back 55

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

Front 56

Hydrologic cycle

Back 56

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

Front 57

Hydrologic soil group (HSG)

Back 57

A soil classification system based on infiltration and potential runoff characteristics

Front 58

Imperviousness

Back 58

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

Front 59

Infiltration

Back 59

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

Front 60

Infiltration basin

Back 60

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

Front 61

Initial abstraction (I.)

Back 61

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

Front 62

Inlet

Back 62

An arrangement for conveying surface water to an underdrain

Front 63

Intercepting ditch

Back 63

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

Front 64

Interpolation (topographic)

Back 64

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

Front 65

Invert

Back 65

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

Front 66

Low-flow channel

Back 66

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

Front 67

Manhole

Back 67

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

Front 68

Manning's equation

Back 68

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

Front 69

Maximum potential retention (S)

Back 69

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

Front 70

Modified Rational method (MRM)

Back 70

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

Front 71

Moisture content

Back 71

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

Front 72

Monument

Back 72

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

Front 73

Outlet

Back 73

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

Front 74

Peak discharge

Back 74

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

Front 75

Percolation

Back 75

Movement of soil water towards the water table

Front 76

Perron

Back 76

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

Front 77

Pervious

Back 77

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

Front 78

pH

Back 78

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

Front 79

Porous

Back 79

Having many small openings through which liquids may pass

Front 80

Porous pavement

Back 80

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

Front 81

Principal spillway

Back 81

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

Front 82

Pedology

Back 82

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

Front 83

Rainfall intensity (i)

Back 83

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

Front 84

Ramp

Back 84

An inclined plane serving as a way between two different levels

Front 85

Rational method

Back 85

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

Front 86

Recession or receding limb (of a hydrograph)

Back 86

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

Front 87

Retention basin (wet pond)

Back 87

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

Front 88

Retaining wall

Back 88

A wall built to support a bank of earth

Front 89

Right of way

Back 89

The entire strip of land dedicated for highway purposes

Front 90

Riprap

Back 90

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

Front 91

Rising limb (of a hydrograph)

Back 91

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

Front 92

Rough grade

Back 92

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

Front 93

Roughness coefficient (n)

Back 93

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

Front 94

Runoff

Back 94

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)

Front 95

Runoff curve number (CN)

Back 95

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

Front 96

SCS

Back 96

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

Front 97

Sediment

Back 97

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

Front 98

Sediment basin

Back 98

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

Front 99

Shallow concentrated flow

Back 99

flow in shallow rills

Front 100

Sheer stress (channel)

Back 100

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

Front 101

Sheet flow

Back 101

Flow over plane, sloped surfaces in a thin layer

Front 102

Shoulder

Back 102

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

Front 103

Sight distance

Back 103

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

Front 104

Slide

Back 104

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

Front 105

Slope

Back 105

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

Front 106

Splash block

Back 106

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

Front 107

Storage (runoff)

Back 107

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

Front 108

Storm sewer

Back 108

A conduit used for conveyance of rain water

Front 109

Structure

Back 109

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

Front 110

Subdrain

Back 110

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

Front 111

Superelevation

Back 111

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

Front 112

Swale

Back 112

A constructed or natural vegetated waterway

Front 113

Tangent

Back 113

A straight road segment connecting two curves

Front 114

Terrace

Back 114

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

Front 115

Time of concentration

Back 115

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

Front 116

Time of recession

Back 116

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

Front 117

Time of rise (of a hydrograph)

Back 117

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

Front 118

Travel time

Back 118

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

Front 119

Trench drain

Back 119

A linear structure that collects runoff from a paved area

Front 120

water quality basin

Back 120

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)

Front 121

Watershed

Back 121

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

Front 122

Water table

Back 122

The level below which the ground is saturated

Front 123

Waterway

Back 123

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

Front 124

Weephole

Back 124

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

Front 125

Weir

Back 125

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

Front 126

Wetter perimeter

Back 126

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

Front 127

Basis of Bearing

Back 127

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

Front 128

Benchmark

Back 128

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

Front 129

Concave Slope

Back 129

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

Front 130

Contour

Back 130

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

Front 131

Convex Slope

Back 131

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.

Front 132

Detention Basin

Back 132

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

Front 133

Hydraulics

Back 133

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

Front 134

Hydrology

Back 134

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

Front 135

Interpolation

Back 135

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.

Front 136

Nomograph

Back 136

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.

Front 137

Retention Basin

Back 137

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

Front 138

Ridge

Back 138

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

Front 139

Slope formula

Back 139

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

Front 140

Spot Elevation

Back 140

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

Front 141

Topography

Back 141

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

Front 142

Valley

Back 142

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

Front 143

Watershed

Back 143

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.

Front 144

Water Gathering (Slope)

Back 144

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

Front 145

Water Spreading (Slope)

Back 145

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