D
Datum (vertical) For marine applications, a base elevation used as a reference from
which to reckon heights or depths. It is called a tidal datum when
defined in terms of tidal phenomena and is based on a 19-year tide
cycle (in the USA)- the datum is referenced to a fixed point typically
known as a bench mark.
Decision maker The person or organizational unit that decides on a course of action in
relation to the safety of a dam on the basis of a range of
considerations which may include a risk assessment.
Deflation A lowering of the beach profile.
Delphi method A technique for obtaining subjective judgmental values through iterative estimations by a group of experts
DeltaWhere a river reaches
the sea and splits up into many channels, depositing large quantities of mud
over a wide area. These areas are usually very wet or swampy.
DepositionWhen mud, sand or
pebbles are dropped by the sea.
Detached Breakwater A breakwater without any coastal connection to the shore.
DetritusThe particulate, organic remains and waste of organisms. It constitutes a major food source in marine ecosystems
Dikes and Levees Dikes are typically earth structures (dams) that keep elevated water levels from flooding interior lowlands.
Disaster A serious disruption of the functioning of a community or a society
causing widespread human, material, economic or environmental losses
which exceed the ability of the affected community or society to cope
using its own resources.
Dissolved Oxygen (DO) The quantity of oxygen dissolved in a unit volume of water; expressed
as milligrams per liter (mg/L) or parts per million (ppm).
DocksA stretch of coast with specially built sea walls and
deep water so that ships can come in to load and unload.
DomeOval or circular mounds that generally lack a slipface. Dome
dunes are rare and occur at the far upwind margins of sand seas.
DowndriftFlow in the direction of net long shore sediment transport
Dredging The excavation of sediments and other material from aquatic areas for
the purpose of maintaining adequate depths in navigation channels and
berthing areas, as well as for other purposes.
DumpingAny deliberate disposal at sea of wastes or other matter, or any deliberate disposal of vessels or other man-made structures
DuneA bank of sand piled
up by the wind. The sand usually blows off a beach so dunes are often found
behind a beach.
Dune RestorationThe technique of rebuilding an eroded or degraded dune through one or more various methods (sand fill, drift fencing, revegetation, etc.).
Dune face The seaward face of a dune system where coastal processes may cause erosion or accretion.
Dunes Accumulations of sand in ridges or mounds landward of
the beach berm formed by natural processes and usually parallel to the
shoreline.
DynamicSomething that is
changing with time. The sea slowly wears away the coast and so the coast
changes - it is dynamic.