User Guide 030

20 Appendix J: Glossary

A

Abrasion: The mechanical wearing away by rock material transported by wind or water Active Bed: The portion of the bed sediment that is being transported.

Active Layer: The top surface layer of sediment in which sediments are subject to exchange with those moving with the flow (entrainment or deposition). Accretion: The accumulation of (beach) sediment, deposited by natural fluid flow processes.

Advection: Physical process by means which a substance (i.e. sediment, salinity) or conserved property (energy or enthalpy) is transported by a fluids bulk motion. Aggradation: The geologic process by which various parts of the surface of the earth are raised in elevation or built up by the deposition of material transported by water or wind.

Amplitude: Half of the peak-to-trough range (or height) of a wave. Angle of Repose: Angle between the horizontal and the maximum slope that a soil assumes through natural processes.

Armoring: The formation of a resistant layer of relatively large particles resulting from removal of finer particles by erosion.

B

Bathymetry: The measurement of depths of water in oceans, seas and lakes; also the information derived from such measurements.

Bay: A recess or inlet in the shore of a sea or lake between two capes or headlands, not as large as a gulf but larger than a cove.

Bed: The bottom of a watercourse, or any body of water.

Bed load: Sediment transport mode in which individual particles either roll or slide along the bed as a shallow, mobile layer a few particles in height above the bed.

Bedform: Any deviation from a flat bed that is readily detectable by eye and higher than the largest sediment size present in the parent bed mate-rial; generated on the bed of an alluvial channel by the flow.

Breaker Index: Maximum ratio of wave height to water depth in the surf zone, typically 0.78 for spilling waves, ranging from about 0.6 to 1.5.

Bulk Density: Bed density equal to the total mass sand and water per unit volume of the bed.

Bypasssing Sand: Hydraulic or mechanical movement of sand from the accreting updrift side to the eroding downdrift side of an inlet or harbor entrance. The hydraulic movement may include natural as well as move-ment caused by man.

C

Channel: (1) A natural or artificial waterway of perceptible extent which either periodically or continuously contains moving water, or which forms a connecting link between two bodies of water. (2) The part of a body of water deep enough to be used for navigation through an area otherwise too shallow for navigation. (3) The deepest portion of a stream, bay, or strait through which the main volume of current of water flows. (4) An open conduit for water either naturally or artificially created, but does not include artificially created irrigation, return flow or stockwatering channels.

Chart Datum: The plane or level to which soundings, tidal levels or wa-ter depths are referenced, usually low water datum. See also Datum.

Constituent Tide: See Tidal Constituent.

Convection: Physical process by means which a substance (i.e. sediment, salinity) or conserved property (energy or enthalpy) is transported by advection and diffusion.

Conveyance: A measure of the flow carrying capacity of a channel sec-tion. Flow is directly proportional to conveyance for steady flow. From Manning’s equation, the proportionality factor is the square root of the energy slope.

Coordinate System: A set of rules for specifying how coordinates are to be assigned to points.

Coriolis Force: Force or Pseudo-force due to the Earth's rotationwhich causes moving bodies to be deflected to the right in the Northern Hemi-sphere and to the left in the Southern Hemisphere. The force is propor-tional to the speed and latitude of the moving object. It is zero at the equator and maximum at the poles.

Cross-shore: Perpendicular to the shoreline.

D

Datum: A datum is a point, line or surface used as a reference as in sur-veying, mapping, geology or numerical modeling.

Depth: Vertical distance from still-water level (or datum as specified) to the bottom.

Dry Density: Bed density equal to the mass of (dry) sand per unit volume of the bed.

E

Ebb: Period when tide level is falling; often taken to mean the ebb current which occurs during this period.

Elevation: The distance of a point above a specified surface of constant potential; the distance is measured along the direction of gravity between the point and the surface.

Equilibrium Argument: The theoretical phase of the equilibrium tide. It is usually represented by the expression (V + u), in which V is a uniformly changing angular quantity involving multiples of the hour angle of the mean Sun, the mean longitudes of the Moon and Sun, and the mean longitude of lunar or solar perigee; and u is a slowly changing angle de-pending upon the longitude of the Moon's node. When pertaining to an initial instant of time, such as the beginning of a series of observations, it is expressed by (V0 + u).

Equilibrium Tide: Hypothetical tide due to the tide-producing forces under the equilibrium theory. Also known as gravitational tide.

F

Fetch length: (1) The horizontal distance (in the direction of the wind) over which a wind generates waves or creates wind setup. (2) The horizontal distance along open water over which the wind blows and generates waves.

G

Gradation: (ASTM D 653) The proportions by mass of a soil or frag-mented rock distributed in specified particle-size ranges.

Graded Bed: An arrangement of particle sizes within a single bed, with coarse grains at the bottom of the bed and progressively finer grains toward the top of the bed.

Grain Density: See Sediment Density.

Greenwich Mean Time or GMT: Mean solar time at the meridian of Greenwich, England. It has been used as a basis for standard time throughout the world. Also called Zulu time. (See also Coordinated Uni-versal Time or UTC).

Grid: Network of points covering the space or time-space domain of a numerical model. The points may be regularly or irregularly spaced.

H

Harmonic Analysis: The mathematical process by which the observed tide or tidal current at any place is separated into basic harmonic constituents.

Hydrodynamic: Relates to the specific scientific principles that deal with the motion of fluids and the forces acting on solid bodies immersed in fluids, and in motion relative to them.

I

Infragravity wave: Long waves with periods of 30 seconds to several minutes. Initial Conditions: The values of water levels, velocities, concentrations, etc., that are specified everywhere in the grid or mesh at the beginning of a model run. For iterative solutions, the initial conditions represent the first estimate of the variables the model is trying to compute.

Interpolation: Estimation of an intermediate value of one variable (de-pendent) as a function of a second variable (independent) when values of the dependent variable corresponding to several discrete values of the independent variable are known.

J

Jetty: (1) On open seacoasts, a structure extending into a body of water, and designed to prevent shoaling of a channel by littoral materials, and to direct and confine the stream or tidal flow. Jetties are built at the mouth of a river or tidal inlet to help deepen and stabilize a channel. (2) A shore-perpendicular structure built to stabilize an inlet and prevent the inlet channel from filling with sediment.

K

Kinematic Viscosity: The dynamic viscosity divided by the fluid density.

L

Longshore: Parallel to and near the shoreline; Alongshore.

LHW: Lower High Water.

LLW: Lower Low water

M

MHHW: Mean Higher High Water. The average of the higher high water height of each tidal day observed over the National Tidal Datum Epoch.

MHW: Mean High Water. The average of all the high water heights ob-served over the National Tidal Datum Epoch.

MSL: Mean Sea Level. The arithmetic mean of hourly heights observed over the National Tidal Datum Epoch.

MLW: Mean Low Water. The average of all the low water heights ob-served over the National Tidal Datum Epoch.

MLLW: Mean Lower Low Water. The average of the lower low water height of each tidal day observed over the National Tidal Datum Epoch

N

National Geodetic Vertical Datum: The vertical-control datum used by the National Geodetic Survey since 1980. This definition is considered to be misleading because it implies the adoption of an NGVD as adjusted in 1980. Accordingly, this expression should be disregarded. Consultation with the National Geodetic Survey (N/CG172, NOAA/NOS) resulted in the confirmation that NGVD of 1929 still applies. (See also National Geodetic Vertical Datum of 1929.)

Nodal Factor: A factor depending upon the longitude of the Moon's node which, when applied to the mean coefficient of a tidal constituent, will adapt the same to a particular year for which predictions are to be made.

O

Overdepth: (1) (EM 1110-2-1003) Additional depth below the required section (or template) specified in a dredging contract. This additional depth is permitted (but not required) because of inaccuracies in the dredging process. (2) The distance between the theoretical maintenance depth and the actual dredging depth. (3) The amount of extra dredging depth that is allowed and paid for, if dredged, in excess of prescribed contract depth

P

Particle Size: A linear dimension, usually designated as "diameter," used to characterize the size of a particle. The dimension may be determined by any of several different techniques, including sedimentation sieving, micrometric measurement, or direct measurement.

Phi Grade Scale: A logarithmic transformation of the Wentworth grade scale for size classifications of sediment grains based on the negative logarithm to the base 2 of the particle diameter: = -log2d.

Porosity: Percentage of the total volume of a soil sample not occupied by solid particles but by air and water, n = Vv/VT × 100. (ASTM D 653) the ratio, usually expressed as a percentage, of (1) the volume of voids of a given soil or rock mass, to (2) the total volume of the soil or rock mass.

Progradation: The building forward or outward toward the sea of a shoreline or coastline (as with a beach, delta, or fan) by nearshore deposition of river-borne sediments or by continuous accumulation of beach material thrown up by waves or moved by longshore drifting.

Q

Quality Assurance or QA: The total integrated program for assuring the reliability of data. A system for integrating the quality planning, quality control, quality assessment, and quality improvement efforts to meet user requirements and defined standards of quality with a stated level of confidence.

Quality Control or QA: The overall system of technical activities for ob-taining prescribed standards of performance in the monitoring and meas-urement process to meet user requirements.

R

Rectification: The process of producing, from a tilted or oblique photograph, a photograph from which displacement caused by tilt has been removed.

Reconnaissance Survey: (EM 1110-2-1003) A general minimum-effort survey performed to determine the general project or channel conditions. The surveys may be controlled or uncontrolled. The survey may serve as a before dredging survey. Reflection of Water Waves: The process by which the energy of the wave is returned seaward.

Refraction of Water Waves: (1) The process by which the direction of a wave moving in shallow water at an angle to the contours is changed. The part of the wave advancing in shallower water moves more slowly than that part still advancing in deeper water, causing the wave crest to bend toward alignment with the underwater contours. (2) The bending of wave crests by currents.

S

Salinity: Number of grams of salt per thousand grams of sea water, usually expressed in parts per thousand (symbol: ‰) or in Practical Salinity Units (PSU).

Scatter Plot: A two-dimensional plot showing the joint distribution of two variables within a data sample.

Sediment Density: Density of the sediment grains or solids per unit volume of the solids. Also known as grain density.

Sediment Transport Formula: A formula or algorithm for calculating sediment transport rate given the hydraulics and bed material characteristics at a point or cross section.

Sediment Transport Paths: The routes along which net sediment movement occurs.

Spinup Period: The time it takes for the simulation errors due to the initial condition to disappear.

T

Tidal Datum: A tidal datum is a standard elevation defined by a certain phase of the tide. Tidal datums are used as references to measure local water levels.

Tidal Constituent: a harmonic element consisting of an amplitude, fre-quency, and phase, representing a periodic variation in the corresponding tide or tidal currents due to the relative positions of the Earth, Moon, and Sun. Also known as Constituent Tide.

U

Universal Time Coordinated (UTC): Coordinates time scale main-tained by the Bureau International des Poids et Measures (BIPM). Generally equivalent to Greenwich Mean Time (GMT). Also referred to simply as Universal Time, Z Time, or Zulu Time.

Universal Transverse Mercator (UTM): A worldwide metric military coordinate system rarely used for civil works applications (EM 1110-2-1003).

V

Validation: In computer modeling and simulation, validation is the pro-cess of determining the degree or accuracy to which a model or simulation is an accurate representation of a real world process from the perspective of the intended uses of the model or simulation.

Verification: In computer modeling and simulation, verification is the process of determining the accuracy of which the governing equations of a specific model or simulation are being solved.

W

Wash Load: Part of the suspended load with particle sizes smaller than found in the bed; it is in near-permanent suspension and transported without deposition; the amount of wash load transported through a reach does not depend on the transport capacity of the flow; the load is ex-pressed in mass or volume per unit of time.

Water Surface Elevation: A measure of the free water surface with re-spect to a given datum. See also - Water Elevation.

Weir Jetty: An updrift jetty with a low section or weir over which littoral drift moves into a predredged deposition basin which is then dredged pe-riodically.

Winnow: Natural removal of sediments through suspension and erosion of fine particles by water flow.

X

Y

Z