NPDP Dam Dictionary

Browse by Letter:
All  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z  


Term AKA Definition
Nonpoint source A contributing factor to water pollution that cannot be traced to a specific spot. Man-made or man-induced alteration of the chemical, physical, biological, or radiological integrity of water, originating from any source other than a point source.
Normal depth The depth of flow that would exist for a steady-uniform flow condition.
Normal Storage The normal storage in acre-feet. It is defined as the total storage space in a reservoir below the normal retention level, including dead and inactive storage and excluding and flood control or surcharge storage.
Normal water surface The highest elevation that water is normally stored, or that elevation which the reservoir should be operated for conservation purposes. Usually the elevation at the top of the active conservation capacity. The maximum elevation to which the reservoir may rise under normal operating conditions exclusive of flood control capacity.
NPDP Dams Directory The NPDP Dams Directory is a comprehensive database of dams in the U.S. It is being developed to include: 1. All dams in the U.S. regulated by state regulatory agencies. 2. Dams in the U.S. that state dam safety programs maintain a record of (whether regulated or not). 3. All dams in the current U.S. National Inventory of Dams (NID). 4. Dams the NPDP has information on that pre-date the National Inventory of Dams or state dam safety programs (i.e., Teton Dam failed in 1976 and pre-dates the NID). Unlike the NID, which maintains data on dams currently in operation, the NPDP Dams Directory retains all dams?historic, currently operating, and recently removed or retired. Features of the Dams Directory are: 1. All dams remain in the database, including those that have been removed, failed and not re-built or repaired, etc. 2. The capability to maintain a history of changes to a dam (e.g., changes to the spillway capacity, raising of the dam crest, removal of dam gates, etc.) 3. Data on structures, systems and components at a dam can be included in the database (as such information becomes available). 4. Dams no longer in service are retained. 5. The Dams Directory is linked to the NPDP dam incident database, consequence, database, etc.
NPDP ID Unique identification number assigned to each dam in the NPDP Dams Directory. The NPDP ID is equivalent to the U.S. National Inventory of Dams ID (NATDAM ID) for dams that have been assigned a NATDAM ID. For dams that pre-date the National Inventory of Dams (i.e., failed or were retired prior to the creation of the national inventory) or are not included in the current inventory (i.e., do not satisfy the NID size criteria), the NPDP staff assigns an identificaiton number. Format: AAnnnnn, where AA is the abbreviation for the state or territory where the dam is located, and nnnnn is a sequentially assigned index number. For NPDP assigned IDs, the format is AASnnnnn.
NPDP Remarks (Non-Public) Use this field to provide notes about the consequences, things that should be verified, etc.
Nutrients Animal, vegetable, or mineral substance which sustains individual organisms and ecosystems.
Obligate riparian species A species that depends completely upon habitat along a body of water.
Off-peak energy Electric energy supplied during periods of relatively low system demand.
Ogee crest The shape of the concrete spillway crest that represents the lower profile of the undernappe of a jet of water flowing over a sharp-crested weir at a design depth.
Ohm The unit of resistance. The value of resistance through which a potential difference of one volt will maintain a current of one ampere.
Omnivore Animal that eats both vegetable and animal substances.
On-peak energy Electric energy supplied during periods of relatively high system demand.
Onfarm Activities (especially growing crops and applying irrigation water) that occur within the legal boundaries of private property.
Operating basis earthquake OBE The earthquake that the structure must safely withstand with no damage. All systems and components necessary to the uninterrupted functioning of the project are designed to remain operable during the ground motions associated with the OBE. This includes the dam, appurtenant structures, electrical and mechanical equipment, relays, spillway gates, and valves. For most usage in Reclamation, the OBE is specified to have a 90% probability of nonoccurrence in a 25-year-exposure period. This is equivalent to a recurrence interval of 237 years. Economic considerations for specific projects may lead to consideration of other values.
Operating log See logbook.
Operational losses Losses of water resulting from evaporation and seepage.
Optimum moisture content Optimum water content The one water content (percent of dry weight of the total material) of a given soil and a given compactive effort that will result in a maximum dry density of the soil.
Option value Option value Value associated with people who know they can visit an area in the future if they so desire. Also a reversible decision or an option to develop at some time in the future have option value.
Original ground (surface) The surface of the earth as it exists in an unaltered state (i.e. prior to any earthwork). See existing ground.
Outage Period during which a generating unit, transmission line, or other facility is out of service.
Outflow The amount of water passing a given point downstream of a structure, expressed in acre-feet per day or cubic feet per second. Water flowing out of a body of water
Outlet An opening through which water can be freely discharged from a reservoir to the river for a particular purpose.
Outlet capacity The amount of water that can be safely released through the outlet works.
Outlet channel Exit channel Channel downstream from terminal structure that conveys releases back to the natural" stream or river. Channel can be excavated in rock or soil with or without riprap soil cement or other types of erosion protection."
Outlet works A combination of structures and equipment required for the safe operation and control of water released from a reservoir to serve various purposes, i.e., regulate stream flow and quality; release floodwater; and provide irrigation, municipal, and/or industrial water. Included in the outlet works are the intake structure, conduit, control house-gates, regulating gate or valve, gate chamber, and stilling basin. A series of components located in a dam through which normal releases from the reservoir are made.
Outlet works tower A tower within a reservoir that contains the mechanisms to open the entrance to the outlet works
Overamping Exceeding the rated capacity of a system.
Overexcavation Excavation beyond specified or directed excavation. Removing unsuitable foundation material.