NPDP Dam Dictionary

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Term AKA Definition
Pacific flyway An established air route of migratory birds along the west coast of the United States.
Paleo Refers to the studies of the geolgic past.
Palustrine habitat Marsh habitat.
Parapet wall A solid wall built along the upstream or downstream edge of the top of dam designed for ornamentation, to reflect waves, and/or for the safety of vehicles and pedestrians.
Parshall 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. A calibrated device developed to measure the flow of liquid in an open channel. See short-throated flume.
Particle size Diameter of the various particles comprising a particular soil.
Pass A working trip or passage of an excavating, grading, or compaction machine. See compaction.
Pattern cracking Fine cracks in the form of a pattern on a concrete surface.
Payline Lines of excavation, backfill, compacted backfill or embankment which are described in the specifications or shown on the drawings which describe or show the limits to which earthwork is paid for.
Pea gravel A uniformly graded gravel with a particle size of approximately 3/16. "
Peak demand or load (energy) Maximum demand occurring within a specified period. See energy.
Peak flow Maximum instantaneous flow in a specified period of time.
Peak ground acceleration PGA That acceleration representing the peak acceleration of ground motion.
Peak load plant Powerplant that normally is operated to provide power during maximum load periods.
Peaking capacity Power generating equipment operated only during highest daily, weekly, or seasonal loads. See capacity.
Peat A fibrous mass of organic matter in various stages of decomposition, generally dark brown to black in color and of spongy consistency. See humus.
Penstock A pipeline or conduit designed to withstand pressure surges leading from a forebay or reservoir to power-producing turbines, or pump units. Conduit used to convey water under pressure to the turbines of a hydroelectric plant.
Percolation See seepage.
Perennial stream A stream that flows continually throughout the year.
Permeability The measure of the flow of water through soil. Ease with which gasses, liquids, or plant roots penetrate or pass through a layer of soil.
Permeable Having pores or openings that permit liquids or gasses to pass through.
Pervious Permeable, having openings that allow water to pass through.
Pervious zone A part of the cross section of an embankment dam comprising material of high permeability.
pH Indicator of acidity.
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.