NPDP Dam Dictionary

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Term AKA Definition
Phreatophyte Water plant.
Physiography Description of nature or natural phenomenon in general.
Phytophagous Plant eating.
Piezometer An instrument which measures pressure head or hydraulic pressures in a conduit or hydraulic pressures within the fill of an earth dam or the abutment; at the foundation because of seepage or soil compression; or on a flow surface of a spillway, gate, or valve.
Pipe A circular conduit constructed of any one of a number of materials that conveys water by gravity or under pressure. See crown, flexible pipe, haunches, invert, rigid pipe, and springline.
Pipe trench A temporary excavation in which pipe is placed and eventually covered with soil material.
Piping The action of water passing through or under an embankment dam and carrying with it to the surface at the downstream face some of the finer material. The progressive removal of soil particles from a mass by percolating water leading to the development of channels. The progressive development of internal erosion by seepage, appearing downstream as a hole discharging water.
Pit run gravel Natural gravelly material taken from excavation. Gravelly material which is not processed.
Pitching Squared masonry, precast blocks, or embedded stones laid in regular fashion with dry or filled joints on the upstream slope of an embankment dam or on a reservoir shore or on the sides of a channel as a protection against wave and ice action.
Placed To put in a particular place or in a particular state.
Plankton Plants (phytoplankton) and animals (zooplankton) with limited powers of locomotion usually living free in the water away from substrates.
Plant Station where mechanical, chemical, and/or nuclear energy is converted into electric energy.
Plant factor Ratio of average load on the plant for period of time considered to be the aggregate rating of all the generating equipment installed in the plant.
Plastic limit The water content corresponding to an arbitrary limit between the plastic and the semisolid states of consistency of a soil; water content at which a soil will just begin to crumble when rolled into a thread approximately 1/8 inches in diameter.
Plasticity The property of a soil which allows it to be deformed beyond the point of recovery without cracking.
Plasticity index Numerical difference between the liquid limit and the plastic limit.
Playa An intermittent shallow lake formed at the bottom of an undrained desert basin after heavy rains.
Plot Area of land that is studied or used for an experimental purpose, in which sample areas are often located.
Point source Any discernible, confined, or discrete conveyance from which pollutants are or may be discharged, including, but not limited to, any pipe, ditch, channel, tunnel, conduit, well, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft.
Ponding Flooding A method for compacting soil using water added after the soil is in place until free water stands on the surface
Population Total of individuals occupying an area.
Population density Number per unit area of individuals of any given species at a given time.
Pore pressure The interstitial pressure of fluid (air or water) within a mass of soil, rock, or concrete.
Pore-water pressure Internal hydrostatic pressure in an embankment caused by the level of water in the reservoir acting through pressure-transmitting paths between soil particles in the fill.
Porosity The ratio of the volume of void space to the total volume of an undisturbed sample.
Pounds per square inch psi or lb/in2 A pressure designation for pounds per square inch.
Powder factor Explosives factor A term expressing the amount of explosives used to break a quantity of rock. Normal units for the powder factor are lb/yd3 or kg/m3; however, lb/ton and kg/ton are also used as well as the reciprocals of all of these terms.
Power Electrical energy generated, transferred, or used; usually expressed in kilowatts.
Power demand Rate at which electric energy is required and delivered to or by a system over any designated period of time.
Power pool Two or more interconnected electric systems which operate as a single system to supply power to meet combined load requirements.