Water — page 21 of 31

Water terms

2001. Nonutility power producer A corporation, person, agency, authority, or other legal entity or instrumentality that owns electric generating capacity and is not an electric utility.
2002. Normal depth The depth of flow that would exist for a steady-uniform flow condition.
2003. Normal loading conditions Loading conditions that occur or are anticipated to occur with some degree of regularity or frequency, as constrasted to unusual loading conditions such…
2004. Normal Water Level (Normal Pool Level) For a reservoir with a fixed overflow, the lowest crest level of that overflow.
2005. Normal water surface The highest elevation at which water is normally stored, or that elevation which the reservoir should be operated for conservation purposes.
2006. Normal Water Surface Elevation (Normal Pool Level) The lowest crest level of overflow on a reservoir with a fixed overflow level (spillway crest elevation).
2007. Normal Year A year during which the precipitation or stream flow approximates the average for a long period of record.
2008. North American Electric Reliability Council (NERC) (NERC) A council formed in 1968 by the electric utility industry to promote the reliability and adequacy of bulk power supply in the electric utility systems of…
2009. Notification The third of five Early Warning System components consisting of communicating alerts and warnings about an emergency condition at a dam to appropriate…
2010. Nutrients Animal, vegetable, or mineral substance which sustains individual organisms and ecosystems.
2011. NWSRFS V5.0, or Version 5 (National Weather Service River Forecast Model Version 5) The system of data entry, data preprocessing, and forecast programs which are used by RFCs. To make river forecasts, RFCs run NWSRFS V5.
2012. O-ring A rubber seal used around stems of some valves to prevent water from leaking past.
2013. Oakum Loosely woven hemp rope that has been treated with oil or other waterproofing agent; it is used to caulk joints in a bell and spigot pipe and fittings.
2014. Obligate riparian species A species that depends completely upon habitat along a body of water.
2015. Observation Well A hole used to observe the ground-water surface at atmospheric pressure within soil or rock.
2016. Occupational Safety and Health Act of 1970 (OSHA) The Williams-Steiger Occupational Safety and Health Act of 1970 (OSHA) is a law designed to protect the health and safety of industrial workers and also…
2017. Off-peak energy Electric energy supplied during periods of relatively low system demand.
2018. Offstream uses Water withdrawn from surface or ground water sources for use at another place.
2019. Ogee A reverse curve, shaped like an elongated letter S. The downstream faces of overflow dams are often made to this shape. (From the French word Ogive).
2020. Ogee crest The shape of the concrete spillway crest that represents the lower profile of the undernappe of a jet of water flowing over a sharp-crested weir at a…
2021. OH The Office of Hydrology, located in Silver Springs, MD.
2022. Ohm The unit of electrical resistance to current flow. The resistance in a conductor in which one volt of potential difference produces a current of one…
2023. Oil Defined as oil of any kind or in any form including, but not limited to, petroleum, fuel oil, sludge, oil refuse, and oil mixed with wastes.
2024. Oil spill contingency fund A revolving fund for spill control efforts has been authorized in cases where the Federal government has taken over containment and cleanup operations.
2025. Oligotrophic Lake classification used to describe young bodies of water characterized by deep, clear, cold, weedless water that can support fish, such as trout.
2026. OML An Operations Manual Letter. These serve as updates to policy and procedure for the NWService Operations Manual (WSOM).
2027. Omnivore Animal that eats both vegetable and animal substances.
2028. On-district storage Small water storage facilities located within the boundaries of an irrigation entity, including reregulating reservoirs, holding ponds, or other new…
2029. On-farm Activities (especially growing crops and applying irrigation water) that occur within the legal boundaries of private property.
2030. On-farm irrigation efficiency The ratio of the volume of water used for consumptive use and leaching requirements in cropped areas to the volume of water delivered to a farm (applied…
2031. On-Peak Energy Energy supplied during periods of relatively high system demands as specified by the supplier.
2032. On-scene coordinator (OSC) The Federal official predesignated by the EPA or Coast Guard to coordinate and direct Federal removal efforts at the scene of an oil or hazardous…
2033. One Percent Chance Flood (One Hundred Year Flood) Flood magnitude that has one chance in 100 of being exceeded in any future 1-year period.
2034. Ongoing Visual Inspection (OVI) The Ongoing Visual Inspection Checklist identifies specific visual inspection items that should regularly receive special attention.
2035. Onsite Coordinator (OSC) For Reclamation-operated facilities, the OSC is any employee discovering hazardous or suspected hazardous waste on Reclamation lands.
2036. Open access same-time information system (OASIS) An electronic information system that allows users to instantly receive data on the current operating status and transmission capacity of a transmission…
2037. Open transmission access Enables all participants in the wholesale market equal access to transmission service, as long as capacity is available, with the objective of creating a…
2038. Open-cut A method of excavation in which the working area is kept open to the sky. Used to distinguish from cut-and-cover and underground work.
2039. Open-work materials Poorly-graded (uniform or gap-graded gradation) gravels, cobbles and boulders with few fines in the matrix, resulting in a deposit containing a large…
2040. Operating basis earthquake (OBE) The earthquake that the structure must safely withstand with no damage. All systems and components necessary to the uninterrupted functioning of the…
2041. Operating log. See logbook.
2042. Operating reserve Generation capacity dedicated to maintaining adequate and reliable system operation during sudden reduction in system capacity.
2043. Operational losses Losses of water resulting from evaporation, seepage, and spills.
2044. Operational waste Water that is lost or otherwise discarded from an irrigation system after having been diverted into it as part of normal operations.
2045. Operations and Maintenance (O&M) (O&M) Operations and maintenance (O&M) activities protect the integrity of the selected cleanup plan for a Superfund site.
2046. Operations and maintenance costs The ongoing, repetitive costs of operating and maintaining a water system.
2047. Optimum moisture content, or Optimum water content The one water content (percent of dry weight of the total material) of a given soil and a given compactive effort that will result in a maximum dry…
2048. Option value Value associated with people who know they can visit an area in the future if they so desire.
2049. Ore Rock or earth containing workable quantities of a mineral or minerals of commercial value.
2050. Organic Derived from living organisms.
2051. organism A living thing, such as an animal, a plant, a bacterium, or a fungus.
2052. Orifice An opening with a closed perimeter and a regular form through which water flows.
2053. Original ground (surface) The surface of the earth as it exists in an unaltered state (i.e. prior to any earthwork). See existing ground.
2054. Orographic Precipitation Precipitation which is caused by hills or mountain ranges deflecting the moisture-laden air masses upward, causing them to cool and precipitate their…
2055. Outage A discontinuance of electric power supply.
2056. Outburst Flood See Jokulhlaup.
2057. Outflow The volume of growing cells that is removed from a bioreactor during a continuous fermentation process.
2058. Outflow Channel A natural stream channel which transports reservoir releases.
2059. Outlet An opening through which water can be freely discharged from a reservoir to the river for a particular purpose.
2060. Outlet capacity The amount of water that can be safely released through the outlet works.
2061. Outlet channel (exit channel) Channel downstream from terminal structure that conveys releases back to the "natural" stream or river.
2062. Outlet Discharge Structure Protects the downstream end of the outlet pipe from erosion and is often designed to slow down the velocity of released water to prevent erosion of the…
2063. Outlet Gate A gate controlling the flow of water through a reservoir outlet.
2064. Outlet Works A combination of structures and equipment required for the safe operation and control of water released from a reservoir to serve various purposes, i.e.
2065. Outlet works tower A tower within a reservoir that contains the mechanisms to open the entrance to the outlet works.
2066. Overall safety of dams classification One of the following classifications is assigned to a dam following an onsite examination and subsequent analyses using available data and…
2067. Overamping Exceeding the rated capacity of a system.
2068. Overbreak Moving or loosening of rock as a result of a blast, beyond the intended line of cut.
2069. Overburden Soil or rock lying on top of a pay formation.
2070. Overdraft When the amount of money withdrawn from a bank account is greater than the amount actually available in the account, the excess is known as an overdraft…
2071. Overexcavation Excavation beyond specified or directed excavation. Removing unsuitable foundation material.
2072. Overflow dam A dam designed to be overtopped.
2073. Overflow spillway (ogee spillway) A spillway that has a control weir that is ogee-shaped (S-shaped) in profile. A spillway on a dam that functions like a dam, but allows water to safely…
2074. Overhang See: extension.
2075. Overhaul Movement of (earth) material far enough so that payment, in addition to excavation pay, is made for haulage.
2076. Overland Flow The flow of rainwater or snowmelt over the land surface toward stream channels. After it enters a watercourse it becomes runoff.
2077. Overtopping Flow of water over the top of a dam or embankment.
2078. Overturn The almost spontaneous mixing of all layers of water in a reservoir or lake when the water temperature becomes similar from top to bottom.
2079. Overwinding A rope or cable wound and attached so that it stretches from the top of a drum to the load.
2080. Oxbow channel A natural U-shaped channel in a river as viewed from above.
2081. Ozonation The application of ozone to water for disinfection or for taste and odor control.
2082. Ozone Tropospheric ozone (ground-level ozone), or smog, is formed when volatile organic compounds, oxygen and nitrogen oxides react in the presence of sunlight.
2083. P.T Pipe thread.
2084. Pacific flyway An established air route of migratory birds along the west coast of the United States.
2085. Paleo- Refers to the studies of the geolgic past.
2086. Paleoflood Paleoflood peak discharges are estimated using geology, fluvial, geomorphology, and stratigraphic records.
2087. Paleoflood data Paleoflood data include two broad categories: fluvial geomorphic evidence and botanical evidence.
2088. Paleoflood hydrology The study of past or ancient floods which occurred prior to the time of human observation or direct measurement by modern hydrologic procedures.
2089. Palmer Drought Severity Index An index whereby excesses or deficiencies of precipitation are determined in relation to average climate values.
2090. Palustrine habitat Marsh habitat.
2091. Pan evaporation A measurement that combines or integrates the effects of several climate elements: temperature, humidity, solar radiation, and wind.
2092. Pancake Ice Circular flat pieces of ice with a raised rim; the shape and rim are due to repeated collisions.
2093. Paradox gate Similar to a ring follower gate except the gate leaf is supported along either side by endless trains of rollers.
2094. Parallel path flow As defined by the North American Electric Reliability Council, this refers to the flow of electric power on an electric system's transmission facilities…
2095. Parametric Data Data such as rating curves, unit hydrographs, and rainfall/runoff curves which define hydrologic variables in models.
2096. Parapet Wall A solid wall built along the top of a dam (upstream and/or downstream edge) used for ornamentation, for safety of vehicles and pedestrians, or to prevent…
2097. Parshall Flume (Improved Venturi Flume) A flume with a specially shaped open-channel flow section that may be installed in a drainage lateral or ditch to measure the rate of flow of water.
2098. Partial-Duration Flood Series A list of all flood peaks that exceed a chosen base stage or discharge, regardless of the number of peaks occurring in a year.
2099. Particle acceleration The time rate of change of particle velocity.
2100. Particle displacement The difference between the initial position of a soil particle and any later temporary position during shaking.