NPDP Dam Dictionary

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Term AKA Definition
Mill Monetary cost and billing unit used by utilities; equal to 1/1000 of U.S. dollar (equivalent to 1/10 of one cent).
Million acre-feet maf The volume of water that would cover 1 million acres to a depth of 1 foot
Millisecond delay A type of delay cap with a definite but extremely short interval between initiation and explosion
Minimum flow Negotiated lowest flow in a regulated stream that will sustain an aquatic population of agreed-upon levels. Flow may vary seasonally.
Mitigation Action taken to avoid, reduce the severity of, or eliminate an adverse impact.
Modification/Repair Type A data field used to summarize the type of modification (change to a dam) or repair (work performed to remedy damage that occurred to a dam or its apputenances) that was implemented.
Modified homogeneous earthfill dam A homogeneous earthfill dam that uses pervious material specially placed in the embankment to control seepage. See embankment dam. Modified Mercalli scale. An earthquake intensity scale which has twelve divisions
Modified Mercalli scale An earthquake intensity scale which has twelve divisions ranging from I (not felt by people) to XII (nearly total damage). For more information on the modified Mercalli scale, visit the U.S. Geological Survey National Earthquake Information Center.
Moisture content water content The ratio of the weight of water in a soil sample to the weight of the dry soil, expressed as a percentage. See optimum moisture content.
Monomictic lakes Warm- water lakes which turn over annually, usually in winter, and where the temperature never falls below 4 degrees C.
Morning glory spillway A circular or glory hole form of a drop inlet spillway. Usually free standing in the reservoir and so called because of its resemblance to the morning glory flower.
MS connectors Surface delays for use when shooting with detonating cord.
Multiple arch dam A buttress dam, the upstream part of which comprises a series of arches.
Multiple-purpose reservoir A reservoir planned to operate for more than one purpose.
Multipurpose dam A dam constructed for two or more purposes (e.g. storage, flood control, navigation, power generation, or recreation.)
Nameplate Power generation capacity of a generator that can be guaranteed under continuous operation.
NATDAM ID Identification number assigned to a dam in the U.S. National Inventory of Dams.
National Weather Service Please visit the website:
Natural frequency The natural frequencies of a structure are the frequencies of free vibration. Free vibration is vibration that occurs in the absence of forced vibration. In a structure undergoing vibration, a mode of vibration is a characteristic pattern (shape) assumed by the structure in which the motion of every particle is simple harmonic motion with the same frequency. The fundamental mode of vibration of a structure is the mode having the lowest natural frequency
Natural period of vibration T The period of vibration of a a structure is the time required for one cycle of the simple harmonic motion in one of these characteristic patterns (shapes). T = 1/f.
Naturalness Area which generally appears to have been affected primarily by the forces of nature, with the imprint of man's work substantially unnoticeable.
Neatlines (of structure) A line which defines the limits of work, such as an excavation, cut stone, etc. Also, the true face line of a building regardless of the projections of the stones; a line back of, or inside of, incidental projections. Any material removed beyond the neat line is overbreak.
Neotropic migrant A bird that migrates to tropical regions during the winter.
Net economic benefits Economic benefits less economic costs.
NID Core Type The watertight or impermeable part of a dam. Types include: Bituminous Concrete, Concrete, Earth, Metal, Plastic, Unlisted/unknown. Core positions include: Upstream Facing, Homogenous Dam, Core, Unlisted/unknown. Core certainty is listed as Known or Estimated.
Non-reimbursable Cost of constructing, operating, or maintaining a Reclamation project that is borne by the Federal taxpayer and is not reimbursed by any other individual, entity, or organization.
Non-uniform flow The velocity varies with position.
Non-utility generators NUG's Facilities for generating electricity that are not owned exclusively by an electric utility and which operate connected to an electric utility system.
Nonconsumptive water uses Water uses that do not substantially deplete water supplies, including swimming, boating, waterskiing, fishing, maintenance of stream related fish and wildlife habitat, and hydropower generation.
Nonfirm power Power that is not available continuously and may be interruptible. This power may be marketed on a short-term basis.