Flood, levee, and erosion control glossary - O
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Ocean Discharge Waiver
A variance from Clean Water Act
requirements for discharges into marine waters.
Off-Site
Any area lying upstream of the site that drains
onto the site and, any area lying downstream of the site to which the site
drains.
Offshore
1. In beach terminology, the comparatively flat zone of variable width, extending from the shoreface to the edge of the continental shelf. It is continually submerged. 2. The direction seaward from the shore. 3. The 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. 4. The breaker zone directly seaward of the low tide line.
Offshore Breakwater
A breakwater built towards the seaward limit of the littoral zone, parallel (or nearly parallel) to the shore.
Offshore Current
1. (NAVFAC DM-26.3) Any current in the offshore zone. 2. Any current flowing away from shore.
Oligohaline Waters
Waters having salinity less than 5 ppt.
Oligotrophic
Clear waters with little organic matter or
sediment and minimum biological activity.
One-Percent Annual Chance Flood
A flood of the magnitude
that has a one-percent chance of being equaled or exceeded in any given year.
Often referred to as the "100-year" flood or base flood, the
one-percent annual chance flood is the standard most commonly used for
floodplain management and regulatory purposes in the United States.
Onshore
(NAVFAC DM-26.3) A direction landward from the sea.
OPA
Abbreviation for Otherwise Protected Area.
Operation and Management Plan (O&M)
A written course
of action to ensure that BMPs are incorporated into any silvicultural practice
to maintain water quality.
Organic Compounds
Natural or synthetic substances based on
carbon.
Organic Matter
Decomposition products of plant and animal
materials such as litter, leaves, and manure.
Organic Soil
A soil that contains a high percentage, 20%
to 30%, of organic matter throughout the soil mixture.
Orifice
An opening with closed perimeter, usually
sharp-edged, and of regular form in a plate, wall, or partition through which
water may flow, generally used for the purpose of measurement or control of
flow.
Ornamentals
Plants or shrubs grown for their decorative
effect.
Outfall
The point where a storm drain discharges from a pipe, channel, ditch, or
other conveyance to a waterway.
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Photo of an Outfall. |
Outlet Channel
A waterway constructed or altered primarily
to carry water from man-made structures, such as terraces, tile lines, and
diversions.
Outlet Structure
A structure at the outlet of a canal, conduit, or tunnel for the purpose of discharging water from the reservoir.
Overbank
In a river reach, the area between the bank of the main channel and the limits of the floodplain.
Overbank Drainage
Water flow over top bank and down the
slope.
Overbank Flooding
The increase in volume of water within a
river channel and the overflow of water from the channel onto the adjacent
floodplain.
Overbank Levee
A levee with a cross section larger than that required to meet all engineering considerations.
Overfalls
Breaking waves caused by the meeting of currents or by waves moving against the current.
Overflow
A pipeline or conduit device, together with an
outlet pipe, that provides for the discharge of portions of combined sewer
flows into receiving waters or other points of disposal, after a regular device
has allowed the portion of the flow which can be handled by interceptor sewer
lines and pumping and treatment facilities to be carried by and to such water
pollution control structures.
Overflow Section
That portion of a dam, usually occupied by a spillway, which allows the overflow of water. Also referred to as spillway section.
Overgrowth
Foliage that has grown and spread out so as to
obstruct or block any natural watercourse, improved drainage device, or
structure.
Overland Flow
A land application technique that cleanses
waste water by allowing it to flow over a sloped surface. As the water flows
over the surface, contaminants are absorbed and the water is collected at the
bottom of the slope for reuse.
Overland Runoff
That portion of precipitation which is not
intercepted by vegetation, absorbed by the land surface or evaporated, and thus
flows overland into a depression, stream, lake or ocean (runoff called
"immediate subsurface runoff" also takes place in the upper layers of
the soil).
Overpacking
Process used to isolate waste by jacketing or
encapsulating waste to prevent further spread or leakage of contaminating
materials.
Overseeding
Seeding into a dormant turf with cool season
turfgrass in order to provide a playable surface (on a golf course) during
winter months in the South, or for aesthetics.
Oversplash
The water that splashes over the top of a breakwater, seawall, etc.
Overtopping
The passing of water over the top of a natural or artificial structure as a
result of wave runup or surge. To flow over the limits of a containment or conveyance
element.
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Photo of Overtopping. |
Overtopping Breach
A levee breach whose cause is known to be a result of overtopping (system exceeded). The levee has been compromised after overtopping and must be repaired to function prior to the next event.
Overwash
1. The part of the uprush that runs over the crest of a berm or structure and does not flow directly back to the ocean or lake. 2. the effect of waves overtopping a coastal defense, often carrying sediment landwards which is then lost to the beach system. 3. A process in which waves penetrate inland of the beach. Particularly common on low barriers. 4. Storm waves that wash across the beach and onto
adjacent land areas.
Overwithdrawal
Withdrawal of ground water over a period of
time that exceeds the recharge rate of the supply aquifer.
Owner
Owner shall mean any person who has dominion over,
control of, or title to land and improvements.
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