Glossary

a b c d e f g h i j k l m n o p q r s t u v w x y z

abrasion

frictional erosion by material transported by wind and waves

abrasion platform

rock or clay platform which has been worn by the processes of abrasion

abutment

the part of a valley side against which a dam is constructed, or the approach embankment in case of bridges which may intrude some distance into the waterway

accretion

accumulation of (beach) sediment, deposited by natural fluid flow processes

aggradation

build-up or raising of a river or sea bed due to sediment deposition

alluvial plane

plain bordering a river, formed by the deposition of material eroded from areas of higher elevation

alongshore

parallel and close to the coastline

angle of repose

the maximum slope at which soils and loose materials on the banks of canals, rivers or embankments stay stable

anisotropic

having properties that change with changing directions

apron

layer of stone, concrete or other material to protect the toe of a seawall

armour layer

protective layer on a breakwater or seawall composed or armour units

armour unit

large quarried stone or specially shaped concrete block used as primary protection against wave action

artificial nourishment

the process of supplementing the natural supply of beach material to a beach, using imported material

asperities

three-dimensional irregularities forming the surface of an irregular stone (or rock) subject to wear and rounding during attraction

astronomical tide

tidal levels and character which result from gravitational effects, e.g. of the Earth, Sun and Moon, without any atmospheric influences

backrush

seaward return of water following the uprush of a wave

backshore

the upper part of the active beach above the normal reach of the tides (high water), but affected by large waves occurring during a high tide

backwater curve

longitudinal profile of the water surface in an open channel where the depth of flow has been increased by an obstruction as a weir or a dam across the channel, by increase in channel roughness, by decrease in channel width or by a decrease of the bed gradient

barrier beach

sand or shingle bar above high tide, parallel to the coastline and separated from it by a lagoon

bathymetry

spatial variability in the bottom of a body of water

beach crest

the point representing the limit of high tide storm wave run-up

beach cusp

one of a series of low mounds of beach material separated by crescent-shaped troughs spaced at more or less regular intervals along the beach face

beach face

the part of the beach from the beach crest owl to the limit of sediment movement

beach feeding

the process of supplementing the natural supply of beach material to a beach, using imported material

beach head

cliff, dune or sea wall looming the landward limit of the active beach

beach material

granular sediments, usually sand or shingle moved by the sea

beach nourishment

the process of replenishing or enlarging a beach, which may be brought about naturally by longshore transport or artificially by the deposition of dredged materials

beach plan shape

shape of the beach in plan; usually shown as a contour line, combination of contour lines or recognizably features such as beach crest and still water line

beach profile

cross-section taken perpendicular to a given beach contour; the profile may include the face of a dune or sea wall, extend over the backshore, across the foreshore, and seaward underwater into the nearshore zone

beach recharge

the process of replenishing or enlarging a beach, which may be brought about naturally by longshore transport or artificially by the deposition of dredged materials

beach replenishment

the process of supplementing the natural supply of beach material to a beach, using imported material

Beach Wizard

a model for estimating the nearshore bathymetry through assimilation of remotely sensed data and numerical model computations.

bed forms

features on a seabed resulting from the movement of sediment over it

bed load

sediment transport mode in which individual particles either roll or slide along the bed as a shallow, mobile layer a few particle diameters deep

bed protection

structure on the bed in order to protect the underlying bed against erosion due to current and wave action

bed shear stress

force acting parallel at the sea bed face induced by the tangential component of waves or currents

berm breakwater

rubble mound with horizontal berm of armour stones at about seaside water level, which is allowed to be shaped by the waves

boulder

rounded rock larger than 250 mm in diameter

bound long wave

long wave directly due to the variation in set-down at the breaker line due to wave groups

bounded coast

a stretch of coast along which wave currents, tidal currents and sediment transport is interrupted by either natural or man-made features, causing a rapid change in coastline orientation

braided river

river type with multiple channels separated by shoals, bars and islands

breaker

wave breaking on a shore or over a structure

breaker depth

depth of water, relative to still water level at which waves break; also known as breaking depth or limiting depth

breaker index

maximum ratio of wave height to water depth in the surf zone

breaker zone

the zone within which waves approaching the coastline commence breaking, typically in water depths of between 5 and 10 meter

breakwater

structure constructed on a coast as part of coastal defense or to protect an anchorage from the effects of weather and longshore drift

breastwork

vertically-faced or steeply inclined structure usually built with timber and parallel to the shoreline, at or near the beach crest, to resist erosion or mitigate against flooding

bull nose

substantial lip or protuberance at the top of the seaward face of a wall, to deflect waves seaward

caisson

concrete box-type structure

catchment

the area which drains naturally to a particular point on a river, thus contributing to its natural discharge

chart datum

the level to which both tidal levels and water depths are reduced - on most Nautical charts, this level is that of the predicted lowest astronomical tide level (LAT)

clay

fine grained, plastic, sediment with a typical grain size less than 0.004 mm; clay possesses electromagnetic properties which bind the grains together to give a bulk strength or cohesion

closure depth

depth at the offshore limit of discernible bathymetric change between surveys

cobble

rounded rock with diameter ranging from about 75 to 250 mm

cofferdam

temporary structure enclosing all or part of the construction area sot that construction can proceed in the dry

cohesive sediment

sediment containing significant proportion of clays, the electromagnetic properties of which cause the sediment to bind together

collapsing breaker

breaker in which breaking occurs over lower half of the wave, with minimal air pocket and usually no splash-up; bubbles and foam are also present

Coriolis force

force due to the Earth's rotation, capable of generating currents

cove

small, sheltered recess in a coast, often inside a larger embayment

crenulate

indented or wavy shoreline beach form, with the regular seaward-pointing parts rounded rather than sharp, as in the cuspate type

crescentic sandbar

crescentic (or lunate) shaped, rhythmically interspaced sandbar feature with shoreward pointing ends; typical longshore wavelengths are of order O(100 m)

cross-shore

perpendicular to the shoreline

crown wall

concrete superstructure on a rubble mound

current refraction

process by which wave velocity is affected by a current

cuspate

form of beach shoreline involving sharp seaward-pointing cusps (normally at regular intervals) between which the shoreline follows a smooth arc

deep water

water too deep for waves to be affected by the seabed; typically taken as half the wavelength, or greater

deflation

erosion of dunes by wind action

degradation

the wearing away of material by the action of natural forces

density

mass per unit of volume of a substance

for pure water the density is 1000 kg/m³
for seawater the density is usually more; the density increases with increasing salinity, and decreases with increasing temperature
for stone and sand, usually a density of 2600 kg/m³ is assumed; concrete is less dense, in the order of 2400 kg/m³; some types of basalt may reach up to 2800 kg/m³
for sand, including the voids, one may use 1600 kg/m³, while mud often has a density of 1100 - 1200 kg/m³

density current

phenomenon of relative flow within water due to difference in density; the salt-water wedge is a density current when stratification occurs between identifiable flow masses

detached breakwater

breakwater without any constructed connection to the shore

DGPS

Differential Global Positioning System

diffraction

process affecting wave propagation, by which wave energy is radiated normal to the direction of wave propagation into the lee of an island or breakwater

diffraction coefficient

ratio of diffracted wave height to deep water wave height

dike

earth structure along sea or river in order to protect littoral lands from flooding by high water; dikes along rivers are sometimes called levees

discharge

volume of water per unit of time flowing along a pipe or channel

ditch

long and small channel to convey water for irrigation or drainage

diurnal

literally "of the day", but here meaning having a period or a "tidal day", i.e. about 24.8 hours

diversion channel

waterway used to divert water from its natural course; the term is generally applied to a temporary arrangement e.g. to by-pass water around a dam site during construction

downdrift

in the direction of the longshore transport of beach material

drowned flow

flow for which the Froude number is less than unity; surface disturbances can travel upstream

drying beach

the part of the beach which is uncovered by water (e.g. at low tide)

dyke

earth structure along sea or river in order to protect littoral lands from flooding by high water; dykes along rivers are sometimes called levees

dynamic viscosity

ratio between the shear stress acting along any plane between neighbouring fluid elements and the rate of deformation of the velocity gradient perpendicular to this plane

ebb current

seaward movement of water along a tidal channel

eddy

vortex type motion of water flowing partly opposite to the main current

edge wave

wave which mainly exists shoreward of the breaker line, and propagates along the shore; egde waves are generated by the incident waves, their amplitude is a maximum at the shoreline and diminishes rapidly in a seaward direction

epifauna

animals living in the sediment surface or on the surface of other plants or animals

erosion

the wearing away of material by the action of natural forces

estuary

funnel-shaped river mouth, affected by tidal circulation

fetch-limited

situation in which wave energy (or wave height) is limited by the size of the wave generation area (fetch)

flood gate

gravity outlet fitted with vertically-hinged doors, opening if the inner water level is higher than the outer water level, so that drainage takes place during low water

flood mark

proof of any kind on the shoreline used to determine the highest level attained by the water surface during the flood (note: the height of the flood mark usually includes the wave run-up)

flood plain

the area within the flood embankments or within the flood dikes (in Europe often called winterbed)

flood routing

attenuating effect of storage on a river-flood passing through a valley by reason of a feature acting as control (e.g. a reservoir with a spillway capacity less than the flood inflow, or the widening or narrowing of a valley)

flood wall

wall retired from the seaward edge of the seawall crest, to prevent water from flowing onto the land behind

flow regime

combinations of river discharge and corresponding water levels and their respective (yearly or seasonally) averaged values and characteristic fluctuations around these values

foreshore

the intertidal area below highest tide level and above lowest tide level

free flow

flow through a canal or over a structure which is not affected by the level of the tail water

freeboard

height of the crest of a structure above the still water level

friction factor

factor used to represent the roughness of the sea bed

frontager

person owning, and often living in, property immediately land ward of the beach

Froude number

dimensionless number representing the ratio of inertia forces and gravity forces acting upon water and making it possible to distinguish between sub-critical and super-critical flow (Fr² = v²/gh)

fully-arisen sea

wave conditions which cannot grow further without an increase in wind speed

fully-developed sea

wave conditions which cannot grow further without an increase in wind speed

gabion

steel wire-mesh basket to hold stones or crushed rock to protect a bank or bottom from erosion

gauge

device for measuring the water level relative to a datum

geotextile

synthetic fabric which may be woven or non-woven used as a filter

GIS

Geographical Information System

gravel

rounded rock between 2 and 4 mm, coarser than sand but finer than pebbles

group velocity

the speed of wave energy propagation; half the wave phase velocity in deep water, but virtually equal to the phase velocity in shallow water

groyne

narrow roughly shore-normal structure built to reduce longshore currents, and to trap and retain beach material; most groynes are of timber or rock, and extend from a sea wall, or the backshore, well onto the foreshore

groyne bay

beach compartment between two groynes

hard defences

impermeable coastal defense structures of concrete, timber, steel, masonry, etc, which reflect a high proportion of incident wave energy

headwater level

water level in a reservoir

hindcasting

retrospective forecasting using observed information; usually applied for model validation

hydraulic radius

quotient of the wetted cross-sectional area and the wetted perimeter

hydrodynamics

the description of liquids in motion

incident wave

wave moving landward

inclination

angle of dip of a rock stratum, fault or mineral vein
angle between the plane of the orbit of a body and the ecliptic; the inclination of a moon's orbit is the angle between the plane of its orbit and the plane of its primary's equator; for example, the moon does not rotate around the earth’s equator, but follows an orbit that is inclined in relation to the earth’s axis, which has an important effect on tides

infauna

animals living in the sediment

infragravity wave

wave with periods above about 30 seconds generated by wave groups breaking in the surf zone

inlet sandwave

rhythmic bedform pattern that can be found on the bed of channels in tidal inlets; their crests are perpendicular to the direction of the principal tidal current, and typical wavelengths are four to ten times the local water depth

inshore

areas where waves are transformed by interaction with the sea bed

internal erosion

formation of voids within soil or soft rock caused by the mechanical or chemical removal of material by seepage

intertidal

between the high and low water marks

irregular waves

series of waves with random wave periods (and in practice, also heights); irregular waves are typical for natural wind-induced waves

isobath

line connecting points of equal depth, a seabed contour

isopachyte

line connecting points on the seabed with an equal depth of sediment

kinematic viscosity

dynamic viscosity divided by the fluid density

lee side

side of a slope that is opposite to the direction of flow of ice, wind, or water

levee

river dike

littoral drift

movement of beach material in the littoral zone by waves and currents; includes movement parallel (longshore drift) and sometimes also perpendicular (cross-shore transport) to the shore

littoral transport

movement of beach material in the littoral zone by waves and currents. Includes movement parallel (longshore drift) and sometimes also perpendicular (cross-shore transport) to the shore

littoral zone

beach plus surf zone

locally generated wave

wave generated within the immediate vicinity of the point of interest

long wave

shallow water wave which is non-dispersive: its wave speed is independent of its period and depends only on the water depth

long-crested random waves

series of random waves with variable heights and periods, but a single direction

longshore

parallel and close to the coastline

longshore bar

submerged ridge of sandy material, located in the surf zone and oriented more or less parallel to the coast; a longshore bar often contains (quasi-) rhythmic alongshore variations, such as rip channels or crescentic plan shapes

longshore drift

movement of sediments approximately parallel to the coastline

mach-stem wave

higher-than-normal wave generated when waves strike a structure at an oblique angle

macro-tidal

tidal range greater than 4 m

mean wave height

mean of all individual waves in an observation interval; in case of a Rayleigh distribution 63% of the significant wave height

meandering

single channel having a pattern of successive deviations in alignment which results in a more or less sinusoidal course

mega ripple

sandy bedform that can most often be found in the shoreward trough of a longshore bar in the surf zone; its height is about one-fifth of the water depth and its length may be up to a few meters

meso-tidal

tidal range between 2 m and 4 m

micro-tidal

tidal range less than 2 m

monochromatic waves

series of waves, each of which has the same wave period

morphodynamics

the change of spatial variability in the bottom of a body of water

morphologically averaged

single wave condition producing the same next longshore wave condition drift as a given proportion of the annual wave climate

morphology

spatial variability in the bottom of a body of water

mud flat

area of fine silt usually exposed at low tide but covered at high tide, occurring in sheltered estuaries or behind shingle bars or sand spits

neap tide

tide occurring near the time of quadrature of the moon with the sun; the neap tide range is usually 10 to 30 percent less than the mean tidal range

NWO

Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Netherlands Organisation for Scientific Research)

oblique bar

sandbar oriented at an oblique angle to the shoreline (that is, neither perpendicular nor parallel to the shoreline)

offshore

zone beyond the nearshore zone where sediment motion induced by waves alone effectively ceases and where the influence of the sea bed on wave action is small in comparison with the effect of wind

offshore breakwater

breakwater built towards the seaward limit of the littoral zone, parallel (or nearly parallel) to the shore

offshore sandwave

rhythmic bedform pattern that can be found on the seabed of shelf seas with strong tidal currents; typical wavelengths are ten times the local water depth; its crest is perpendicular to the direction of the principal tidal current

overtopping

water carried over the top of a coastal defense due to wave run-up exceeding the crest height

overwash

the effect of waves overtopping a coastal defense, often carrying sediment land wards which is then lost to the beach system

parapet

solid wall at crest of seawall projecting above deck level

pebble

rounded rock between about 4 mm to 75 mm diameter

perennial stream

stream that flows continuously throughout the year

permeability

property of bulk material (sand, crushed rock, soft rock) which permits movement of water through its pores

phase velocity

velocity at which a wave crest propagates

phreatic level

upper surface of an unconfined aquifer (e.g. the top sand layer in a dike) at which the pressure in the groundwater is equal to atmospheric pressure

piezometric surface

level within (or above) a soil stratum at which the pore-pressure is zero

pitching

squared masonry, precast blocks or block-shaped natural stones (e.g. basaltic columns) laid in a regular fashion with dry or filled joints on the river or sea side of an embankment, dike, or dam as a protection against wave and ice action

plunging breaker

breaker in which the crest curls over an air pocket; breaking is usually with a crash; smooth splash-up usually follows

pocket beach

small beach between two headlands

polder

tract of low land, reclaimed from marshland, the sea or an other body of water, by endiking it; in a polder, runoff is controlled by sluicing or pumping, and the watertable is controlled and independent of the watertable in the adjacent areas

pore pressure

interstitial pressure of water within a mass of soil or rock

porosity

percentage of the total volume of a soil not occupied by solid particles by air and water

quarry

site where natural rock stone is mined

quarry run

waste of generally small material, in a quarry, left after selection of larger grading

Rayleigh distribution

model probability distribution, commonly used in analysis of waves

reef breakwater

rubble mound of single-sized stones with a crest at or below sea level which is allowed to be (re)shaped by the waves

reflected wave

the part of an incident wave that is returned (reflected) seaward when a wave impinges on a beach, seawall or other reflecting surface

refraction

process by which the direction of a wave moving in shallow water at an angle to the contours is changed so that the wave crests tend to become more aligned with those contours

refraction coefficient

ratio of refracted wave height to deep water wave height

revetment

sloping surface of stone, concrete or other material used to protect an embankment, natural coast or shoreline against erosion

Reynolds number

dimensionless number, ratio between the inertia and the viscous forces for pipes Re = vD/þ, for open channels Re = vR/þ (D = Diameter, R = hydraulic radius)

RIKZ

Rijksinstituut voor Kust en Zee (National Institute for Coastal and Marine Management)

rip channel

channel through a longshore bar, or between transverse or oblique bars, containing a rip current

rip current

strong seaward flowing current, that forms part of the horizontal nearshore circulation and can be considered as the return movement of water moved onshore by incoming waves and wind

rip-rap

wide-graded quarry stone normally used as a protective layer to prevent erosion

river training structure

a configuration constructed in a stream or placed on, adjacent to or in the vicinity of a stream bank that is intended to deflect currents, induce sediment deposition, induce scour, or in some other way alter the flow and sediment regimes of the river

rock weathering

physical and mineralogical decay processes in rock brought about by exposure to climatic conditions either at the present time or in the geological past

rubble mound

mound of random-shaped and random-placed stones

run-down

lower level reached by a wave on a beach or coastal structure, relative to still-water level

run-up

upper level reached by a wave on a beach or coastal structure, relative to still-water level

runnel

channel on a beach, usually running approximately shore-parallel and separated by beach ridges

s-slope breakwater

rubble mound with gentle slope around still-water level and steeper slopes above and below

salinity

content of totally dissolved solids in water

sandbar

sandwave

regular patterns in marine non-cohesive bottoms caused by tidal currents, characterised by a wavelength of the order of few hundreds meters and a height of up to ten meters

scarp

almost vertical slope along the beach caused by erosion by wave action; it may vary in height from a few cm to several meters, depending on wave action and the nature and composition of the beach

seawall

solid coastal defence structure built parallel to the coastline

sediment

particulate matter derived from rock, minerals or bioclastic debris

sediment cell

a length of coastline in which interruptions to the movement of sand or shingle along the beaches or near shore sea bed do not significantly affect beaches in the adjacent lengths of coastline

sediment sink

area at which beach material is irretrievably lost from a coastal cell, such as an estuary, or a deep channel in the seabed

sediment source

area on a coast from which beach material arises, such as an eroding cliff, or river mouth

seiche

standing wave oscillation in an effectively closed body of water

semi-diurnal

having a period of half a tidal day, i.e. 12.4 hours

shallow water

water depth at which surface waves are noticeably attested by bottom topography; typically this implies a water depth equivalent to less than half the wavelength

shingle

loose term for coarse beach material, a mixture of gravel, pebbles and larger material, often well-rounded and of hard rock, e.g. chert, flint etc

shoaling

the transformation of wave profile as it propagates inshore

shoaling coefficient

ratio of shoaled wave height to deep water wave height

shoreface

region between the nearshore region and the inner continental shelf

shoreface connected ridge

elongated sand bank found in the inner part of some continental shelves in horizontal patterns with a length scale of order O(10 km); it starts at the offshore end of the shoreface and extends seaward forming an angle of 20° - 35° with respect to the coastline

shoreline sandwave

longshore undulation in the shoreline, often with a rhythmic spacing of order O(0.1 - 1 km)

significant wave height

average height of the highest one third of the waves in a given sea state

spilling breaker

breaker in which bubbles and turbulent water spill down front face of wave; the upper 25 percent of the front face may become vertical before breaking; breaking generally occurs over quite a distance

splash wall

wall retired from the seaward edge of the seawall crest, to prevent water from flowing onto the land behind

spring tide

tide that occurs at or near the time of new or full moon and that rises highest and falls lowest from the mean sea level

spur-dike

narrow roughly shore-normal structure built to reduce longshore currents, and to trap and retain beach material; most spur-dikes are of timber or rock, and extend from a sea wall, or the backshore, well onto the foreshore

still-water level

water level that would exist in the absence of waves

subaerial beach

the part of the beach which is uncovered by water (e.g. at low tide)

subcritical flow

flow for which the Froude number is less than unity; surface disturbances can travel upstream

subtidal beach

part or the beach which extends from low water out lo the approximate limit of storm erosion; the latter is typically located at a maximum water depth of 8 to 10 meters and is often identifiable on surveys by a break in the slope of the bed

surf beat

independent long wave caused by reflection of bound long wave

surf zone

zone of wave action extending from the water line out to the most seaward point of the breaker zone

surging breaker

breaker in which the wave peaks up, but bottom rushes forward from under wave, and wave slides up beach face with little or no bubble production; the water surface remains almost plane except where ripples may be produced on the beachface during runback

suspended load

mode of sediment transport in which the particles are supported, and carried along by the fluid

swell

long series of waves, generally produced by wind, and lasting after the wind has ceased

SWL

still-water level, water level that would exist in the absence of waves

tailwater level

water downstream of a dam or sill

thalweg

locus of the deepest points in a valley at successive cross-sections

tidal current

movement of water associated with the rise and fall of the tides

tidal inlet

natural inlet between two barrier islands (or spits), maintained by tidal flow reversals and connecting the open sea with the tidal flats or lagoons lying between the barrier islands or spits and the mainland

tidal prism

volume of water that flows into a tidal channel and out again during a complete tide, excluding any upland discharges

tidal range

vertical difference in high and low water level once decoupled from the water level residuals

tidal river

the part of a river where the water level is influenced by the tide

tidal wave

rise and fall in water level due to the passage of the tide

tombolo

coastal formation of beach material developed by refraction, diffraction and longshore drift to form a 'neck' connecting a coast to an offshore island or breakwater

training wall

wall built to confine or guide the flow over the downstream face of an overflow dam or in a channel

transverse bar

sandbar that is often attached to the shore and extends for some distance into the surf zone; typical longshore spacing (bar-to-bar distance) is of order O(10-100 m)

tsunami

series of waves of extremely long wave length and long period generated in a body of water by an impulsive disturbance that vertically displaces the water

updrift

direction opposite to that of the predominant longshore movement of beach material

uprush

landward return of water following the backrush of a wave

wave celerity

speed of wave propagation

wave climate

temporal distribution of wave height, period and direction

wave climate atlas

series of maps showing the variability of wave conditions over a long coastline

wave directional spectrum

distribution of wave energy as a function of wave frequency and direction

wave frequency spectrum

distribution of wave energy as a function of frequency

wave generation

growth of wave energy by wind

wave rose

rose diagram showing the long-term distribution of wave height and direction

wave set-up

elevation of the water level at the coastline caused by radiation stress gradients in the surf zone

wave steepness

ratio of wave height to wavelength

weir

low dam or wall across a stream to raise the upstream water level

wind rose

rose diagram showing the long-term distribution of wind speed and direction

wind sea

wave conditions directly attributable to recent winds, as opposed to swell

wind set-up

elevation of the water level over an area directly caused by wind stress on the water surface

Xbeach

a public-domain two-dimensional model for wave propagation, long waves and mean flow, sediment transport and morphological changes of the nearshore area during storms.

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