Oblique wave approach

Waves that approach the beach at an angle (e.g., not straight-on) and generate longshore currents.


The study of the sea embracing and indicating all knowledge pertaining to the sea's physical boundaries, the chemistry and physics of the seawater, marine biology, and marine geology.

Offshore breakwater

Structure parallel to the shore, usually positioned in the sea, that protects the shore from waves.


An aquatic environment typified by a low amount of nutrient; the opposite of “eutrophic”.

Opportunity cost

A term from multiple use economics that means the value of options that is lost (excluded) because of choosing one particular mode of use.

Organic detritusSuspended small organic particles, usually of vegetative origin



Typically used in relation to the Outputs of a project or programme and linked to measurable indicators of project/programme impact, such as agricultural yields, number of visits by health workers, area of land brought under irrigation, number of teachers trained, legislation revised, trade agreements implemented etc. Outputs are an important element in the Logical Framework.


Overlay mapping

Superimposition of several theme maps to spatially analyze environmental resources and development modes, particularly useful in studying the interactions between various components of land use.



 The water that splashes over the top of a breakwater, seawall or other coastal defence structure.


 Transport of the sediment landward of the active beach by coastal flooding during a tsunami, hurricane, or other event with extreme waves. The part of the up rush that runs over the crest of a berm of a structure and does not flow directly back to the ocean or lake. The effects of waves overtopping a coastal defence, often carrying sediment landwards which is then lost to the beach system

Oxidation pond

A man-made lake or body of water in which wastes are treated, mostly by bacterial consumption; a sewage treatment lagoon.