Water — page 22 of 31

Water terms

2101. Particle size Diameter of the various particles comprising a particular soil.
2102. Particle velocity The time rate of change of particle displacement.
2103. Parts per billion (ppb) A measurement of concentration on a weight or volume basis. Equivalent to micrograms per liter.
2104. Parts per million (ppm) A measurement of concentration on a weight or volume basis. Equivalent to milligrams per liter (mg/l).
2105. Pascal (Pa) The pressure or stress of one newton per square meter. 1 psi = 6895 Pa.
2106. PASS A working trip or passage of an excavating, grading, or compaction machine. See compaction.
2107. Passive earth pressure The maximum value of earth pressure. This condition exists when a soil mass is compressed sufficiently to cause its internal shearing resistance along a…
2108. Pattern cracking Fine cracks in the form of a pattern on a concrete surface.
2109. Pay formation A layer or deposit of soil or rock whose value is sufficient to justify excavation.
2110. Payline Lines of excavation, backfill, compacted backfill or embankment which are described in the specifications or shown on the drawings which describe or show…
2111. Pea gravel A uniformly graded gravel with a particle size of approximately 3/16".
2112. Peak demand Maximum electrical demand occurring within a specified period of time. Maximum power used in a specific time period. See energy.
2113. Peak Discharge Highest rate of discharge of a volume of water passing a given location during a given period of time (during the year, or a flood event, etc..).
2114. Peak flow The highest flow of water attained during a particular flood for a given stream or river.
2115. Peak ground acceleration (PGA) That acceleration representing the peak acceleration of ground motion.
2116. Peak load The maximum power load in a stated period of time.
2117. Peak load plant Powerplant that normally is operated to provide power during maximum load periods.
2118. Peaking capacity Power generation equipment or system capacity to meet peak power demands.
2119. Peaking power Powerplant capacity typically used to meet the highest levels of demand in a utility's load or demand profile.
2120. Peat A fibrous mass of organic matter in various stages of decomposition, generally dark brown to black in color and of spongy consistency.
2121. Pegmatite Very coarse-grained intrusive igneous rock of granitic composition that typically fills fractures to form veins.
2122. Pelagic Pertaining to the open ocean and organisms living within it, including highly migratory fishes such as swordfish, tuna, and many species of shark.
2123. Penstock A component of a hydropower plant; a pipe that delivers water to the turbine.
2124. Per capita use The average amount of water used per person during a standard time period, generally per day.
2125. Perched Groundwater Local saturated zones above the water table which exist above an impervious layer of limited extent.
2126. Perched Water Table Underground water lying over dry soil, and sealed from it by an impervious layer.
2127. Percolation The filtering of a liquid passed through a medium with many fine spaces.
2128. Percolation Deep In irrigation or farming practice, the amount of water that passes below the root zone of the crop or vegetation.
2129. Percolation Path The course followed by water moving or percolating through any other permeable material, or under a dam which rests upon a permeable foundation.
2130. Percolation Rate The rate at which water moves through porous media, such as soil. The intake rate used for designing wastewater absorption systems.
2131. Perennial Stream A stream that flows continually throughout the year.
2132. Perennial yield Maximum quantity of water that can be annually withdrawn from a ground water basin over a long period of time (during which water supply condditions…
2133. Perforated pipe Pipe designed to discharge water through small, multiple, closely spaced orifices or nozzles, placed in a segment of its circumference for irrigation…
2134. Periodic Facility Review (PFR) A field review performed on a high- or significant-hazard dam every 6 years that entails a thorough examination from both operation and maintenance and…
2135. Periphyton Microscopic plants and animals that are firmly attached to solid surfaces under water such as rocks, logs, pilings and other structures.
2136. Permafrost Perennially frozen soil.
2137. Permanence of Protection For the Marine Protected Areas Inventory, in order for sites to be considered for inclusion in the database, they must provide year round (12-month)…
2138. Permanent Control A stream gaging control which is substantially unchanging and is not appreciably affected by scour, fill, or backwater.
2139. Permanent Monument Fixed monuments placed away from the dam which allow movements in horizontal and vertical control points on the dam to be monitored by using accurate…
2140. Permanent wilting point (permanent wilting percentage) Soil water content below which plants cannot readily obtain water and permanently wilt. See wilting point.
2141. Permeability The rate at which liquids pass through soil or other materials in a specified direction.
2142. Permeability Coefficient The rate of flow of a fluid through a cross section of a porous mass under a unit hydraulic gradient, at a temperature of 60 degrees Fahrenheit.
2143. Permeable Referring to a membrane, cell or cell system through which small molecules can diffuse.
2144. Permeameter Device for containing the soil sample and subjecting it to fluid flow in order to measure permeability or hydraulic conductivity.
2145. Permeate To penetrate and pass through, as water penetrates and passes through soil and other porous materials.
2146. Pervious Permeable, having openings that allow water to pass through.
2147. Pervious Zone A part of the cross section of an embankment dam comprising material of high permeability.
2148. Petcock A small drain valve. A small ground key type valve used with soft copper tubing.
2149. pH A measurement for liquids to determine acidity or alkalinity. On a scale of one to 14, seven is considered neutral.
2150. Philadelphia rod A leveling rod in which the hundredths of feet, or eights of inches, are marked by alternate bars of color the width of the measurement.
2151. Photogrammetry Techniques of obtaining precise measurements from images. This process can derive elevation from specially created stereo pairs of aerial photos.
2152. Photosynthesis A chemical process by which green plants synthesize organic compounds from carbon dioxide and water in the presence of sunlight.
2153. Phreatic surface The free surface of water seeping at atmospheric pressure through soil or rock.
2154. Phreatic water Water within the earth that supplies wells and springs; water in the zone of saturation where all openings in rocks and soil are filled, the upper surface…
2155. Phreatic Zone The locus of points below the water table where soil pores are filled with water. This is also called the zone of saturation.
2156. Phreatophyte Water-loving plant. Vegetation that consumes much water.
2157. Physiography The physical geography of an area or the description of its physical features.
2158. Phytophagous Plant eating.
2159. Phytoplankton Small, often single-celled plants that live suspended in bodies of water.
2160. Pico A prefix meaning "one trillionth".
2161. Piezometer A nonpumping well, generally of small diameter, for measuring the elevation of a water table.
2162. Piezometric Level (or Surface) Confined groundwater is usually under pressure because of the weight of the overburden and the hydrostatic head.
2163. Piezometric surface The surface at which water will stand in a series of piezometers.
2164. Pig An air manifold having a number of pipes which distribute compressed air coming through a single large line.
2165. Pile Relatively slender structural element which is driven, or otherwise introduced, into the soil, usually for the purpose of providing vertical or lateral…
2166. Pioneering The first working over of rough or overgrown areas.
2167. pipe A circular conduit constructed of any one of a number of materials that conveys water by gravity or under pressure.
2168. Pipe trench A temporary excavation in which pipe is placed and eventually covered with soil material.
2169. Piping The erosion of embankment or foundation material (soil) due to leakage. The action of water passing through or under an embankment dam and carrying with…
2170. Pit An area consisting of a number of gaming tables.
2171. Pit run gravel Natural gravelly material taken from excavation. Gravelly material which is not processed.
2172. Pitching Fishing technique in which worms or jigs are dropped into cover at close range with an underhand pendulum motion using a long bait-casting rod, and…
2173. Pitot Tube A device for measuring the velocity of flowing water using the velocity head of the stream as an index of velocity.
2174. Place-Based Management A conservation or management regime that includes a legally-defined area with greater conservation regulation or statutory law applying inside its…
2175. Placed To put in a particular place or in a particular state.
2176. Planimeter A device that measures area.
2177. Plankton Collectively, all organisms (plants and animals) suspended in the water which are not independent of water movements.
2178. Planning basis Guidance concerning: (1) size of planning area (distance); (2) time dependence of releases; and (3) flood characteristics of releases.
2179. Planning standard(s) Standards which emergency plans of the dam operating organization and local authorities should conform to.
2180. Plant Station where mechanical, chemical, and/or nuclear energy is converted into electric energy.
2181. Plant factor The capacity factor of an entire generating facility including all available generating units. (See also capacity factor)
2182. Plant-use electricity The electric energy used in the operation of a plant. This energy total is subtracted from the gross energy production of the plant; for reporting…
2183. Plastic limit The water content corresponding to an arbitrary limit between the plastic and the semisolid state of consistency of a soil; water content at which a soil…
2184. Plastic soil A soil that exhibits plasticity.
2185. Plasticity A phenomenon used to describe a cell that is capable of becoming a specialized cell type of different tissue.
2186. Plasticity index Numerical difference between the liquid limit and the plastic limit.
2187. Playa Flat areas that contain seasonal or year-to-year shallow lakes that often evaporate, leaving minerals behind.
2188. Plot A forest area defined by its condition.
2189. Plumb Exactly vertical; at right angles to the horizontal.
2190. Plumb Bob A pointed weight hung from a string. Used for vertical alignment.
2191. Plunge pool A natural or artifically created pool that dissipates the energy of free-falling water.
2192. Pluvial In hydrology, anything that is brought about directly by precipitation.
2193. Ply One of several layers of fabric or of other strength-contributing material.
2194. Pneumatic Powered or inflated by compressed air.
2195. Pneumatic Gate (Rubber Gate or Bladder Gate) A tubular flexible gate anchored to a foundation or inside a pipe that is operated by filling with air under pressure.
2196. Point Discharge Instantaneous rate of discharge, in contrast to the mean rate for an interval of time.
2197. Point Precipitation Precipitation at a particular site, in contrast to the mean precipitation over an area.
2198. 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…
2199. Pollutant Any inorganic or organic substance that contaminates air, water or soil. Generally, any substance introduced into the environment that adversely affects…
2200. Pollution A resource that is out of place. Generally, the presence of matter or energy whose nature, location or quantity produces undesired environmental effects.