NPDP Dam Dictionary

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Term AKA Definition
Return flow Drainage water from irrigated farmlands that re-enters the water system to be used further downstream. May contain dissolved salts or other materials that have been leached out of the upper layers of the soil. Portion of water previously diverted from a stream and subsequently returned to that stream or to another body of groundwater or surface water.
Revetment An embankment or wall of sandbags, earth, etc., constructed to restrain material from being transported away. A facing of stone, cement, sandbags, etc., to protect a wall or embankment.
Rewind Act of putting new copper insulated wire in the armature windings of a generator.
Richter scale A scale of numerical values, proposed by C. F. Richter, to describe the magnitude of an earthquake, ranging from 1 to 9, by measurements made in well-defined conditions and with a given type of seismograph. The zero of the scale is fixed arbitrarily to fit the smallest recorded earthquake. The largest recorded earthquake magnitudes are near 8.7 This is the result of observations and not an arbitrary upper limit like that of the intensity scale. For more information about the Richter Scale visit the U.S. Geological Survey National Earthquake Information Center.
Riffle A stretch of choppy water caused by an underlying rock shoal or sandbar. A run is a long riffle.
Riffle and pool complex A water habitat composed of riffles (characterized by water flowing rapidly over a coarse substrate) and pools (deeper areas of water associated with riffles).
Right abutment See abutment.
Rigid pipe Pipe designed to transmit the backfill load to the foundation beneath the pipe. Rigid pipe must be supported on the bottom portion of the pipe.
Ring gate A ring- or annular-shaped steel drum operating in a recess or gate chamber in a spillway crest and controlled in a manner similar to a drum gate. See gate.
Ring-follower gate A gate consisting of a rectangular leaf and an opening equal in diameter to that of the conduit that forms an unobstructed passageway when the leaf is in the raised or open position.
Riparian Living on or adjacent to a water supply such as a riverbank, lake, or pond. Of, on, or pertaining to the bank of a river, pond, or lake.
Ripple In a streambed, a ripple is a small triangle-shaped elements having gentle upstream slopes and steep downstream slopes.
Riprap A layer of large uncoursed stones, broken rock, boulders, or precast blocks placed in random fashion on the upstream and downstream faces of embankment dams, stream banks, on a reservoir shore, on the sides of a channel, or other land surfaces to protect them from erosion caused by current, wind, wave, and/or ice action. Aprotective blanket of large loose stones, which are usually placed by machine to achieve a desired configuration. Very large riprap is sometimes referred to as armoring." "
River Stream The river or stream designation may be entered in one of two ways. For the convenience of some organizations, an alternative field entry is provided which is consistent with the tributary and offstream" designations used in the 1995-96 NID. If the alternative form is used TEC will convert it to the standard form prior to inclusion in the national inventory. River or Stream Standard Entry: The official name of the river or stream on which the dam is built. If the stream is unnamed identify it as a tributary to a named river. e.g. Snake-TR. If the river or stream is located offstream the name will be the name of the river or stream plus the word "OFFSTREAM" e.g. Snake-OFFSTREAM.
River mile RM A unit of measurement (in miles) used on rivers.
River trash wall Walls constructed to deflect heavy floating debris away from the upper ends of a fishway.
Riverine Riparian; pertaining to a riverbank.
Rock The hard, firm and stable parts of the earth's crust. A sound and solid mass, layer, or ledge of mineral matter inplace, and of such hardness and texture that it cannot be effectively loosened or broken down by a 6-pound drifting pick or by ripping in a single pass. Natural solid mineral matter occurring in large masses or fragments.
Rock excavation Hard and firm parts of the earth's crust which is dug out and removed from a particular site or area, see rock. Boulders or detached pieces of solid rock more than 1 cubic yard in volume are classified as rock excavation. See excavation.
Rock fragment Detached pieces of rock which generally are not rounded.
Rockfill dam An embankment dam in which more than 50 percent of the total volume comprises compacted or dumped cobbles, boulders, rock fragments, or quarried rock.
Rolled fill dam An embankment dam of earth or rock in which the material is placed in layers and compacted by the use of rollers or rolling equipment.
Roller compacted concrete RCC A mixture of cement, water, and aggregate compacted by rolling.
Roller gate A gate rolled up or down inclined supporting rails by a hoist through sprocket chains around the ends of a cylinder.
Rolling A method of compacting soil using a sheepsfoot roller or a smooth drum roller.
Root zone The area where a low- angle thrust fault steepens and descends into the crust.
Rough fish A nonsport fish.
Rubble dam A masonry dam in which the stones are unshaped or uncoursed. See dam.
Run Seasonal upstream migration of anadromous fish.
Saddle dam A subsidiary dam of any type constructed across a saddle or low point on the perimeter of a reservoir.