Water terms starting with U

49 terms

U.S. Army Corps of Engineers (USACE) As part of the Department of the Army, the Corps has responsibilities in civil and military areas.
U.S. Bureau of Reclamation (USBR) The Federal agency whose mandate was to reclaim the arid west of the United States.
U.S. Geological Survey (USGS) The USGS serves the Nation by providing reliable scientific information to describe and understand the earth; minimize loss of life and property from…
Ultimate bearing capacity The load per unit of area required to produce failure by rupture of a supporting soil or rock mass.
Unbalanced head. See differential head.
Unbundling (functional unbundling) Electric service is traditionally provided on a bundled basis, meaning that generation, transmission, and distribution services are provided as a single…
Uncertainty Describes situations where potential outcomes cannot be estimated based on historical events.
Unclassified excavation Excavation paid for at a fixed price per yard, regardless of whether it is common or rock excavation.
Uncompacted backfill Material used in refilling an excavation without the material being compacted. See backfill.
Unconfined aquifer See Aquifer-unconfined
Unconformity A break or gap in the geologic record where rock layers were eroded or never deposited.
Undercurrent A current below the upper currents or surface of a fluid body.
Underflow The movement of groundwater through the soil or a subsurface stratum, or under a structure; specifically, the water flowing beneath the bed of a stream…
Understory The trees and other woody species growing under a relatively continuous cover of branches and foliage formed by the overstory trees.
Undertaking Any project, activity, or program that could change the character or use of historic properties.
Undisturbed sample A soil sample that has been obtained by methods in which every precaution has been taken to minimize disturbance to the sample.
Unified Soil Classification System A method of grouping and describing soils according to their engineering properties.
Uniform flow Open channel flow where the depth and discharge remain constant with respect to space. Also, the velocity at a given depth is the same everywhere.
Unit Hydrograph The direct runoff hydrograph resulting from a unit depth of excess rainfall produced by a storm of uniform intensity and specified duration.
Unit Hydrograph (or Unitgraph) The discharge hydrograph from one inch of surface runoff distributed uniformly over the entire basin for a given time period.
Unit Hydrograph Duration The time over which one inch of surface runoff is distributed for unit hydrograph theory.
Unit Hydrograph Theory Unit Hydrograph Theory states that surface runoff hydrographs for storm events of the same duration will have the same shape, and the ordinates of the…
Unit weight Weight per unit volume. See density, dry unit weight, maximum unit weight, saturated unit weight, unit weight of water, wet unit weight.
Unit weight of water The weight per unit volume of water. See unit weight.
United States Includes the several States, the District of Columbia, the Commonwealth of Puerto Rico, the Virgin Islands of the United States, American Samoa, Guam, and…
United States Army Corps of Engineers (USACE, Corps) The United States Army Corps of Engineers provides quality, responsive engineering services to the nation which includes planning, designing, building and…
Universal Type Weighting and Recording Gage A gage which collects precipitation and then converts the weight onto an inked pen movement which traces on graph paper fixed to a clock driven drum.
Unlisted items Line item used in an appraisal estimate for design changes and to estimate pay items that have little influence on the total cost.
Unload-reload cycle A loading sequence resulting in rebound and recompression.
Unpaid Federal investment A year-end amount owned to the Treasury which remains to be repaid and is synonymous to "balance to be repaid."
Unsaturated zone The subsurface zone, usually starting at the land surface and ending at the water table, that includes both water and air in spaces between rocks.
Unsteady flow The velocity at a point varies with time.
Unsuitable material Those soils that cannot be compacted in embankment or backfill or where excavated to finished grade result in unstable material.
Unwatering As opposed to dewatering, unwatering is the interception and removal of ground water outside of excavations and the removal of ponded or flowing surface…
Uplift Charges from an RTO/ISO collected outside of the market-clearing commodity price; these charges can include payments to reliability must run (RMR) units…
Uplift pressure See pore-water pressure.
Uprate An increase of greater than 15 percent in powerplant unit output at an existing facility through modifications or replacement of equipment.
Upstream Blanket An impervious blanket placed on the reservoir floor and abutments upstream of a dam.
Upstream face The inclined surface of the dam that is in contact with the reservoir. See face.
Upstream Slope The part of the dam which is in contact with the reservoir water. On earthen dams, this slope must be protected from the erosive action of waves by rock…
Urban area Predominantly cities, towns or developed areas where the population is significant.
Urban Flash Flood Guidance A specific type of flash flood guidance which estimates the average amount of rain needed over an urban area during a specified period of time to initiate…
Urban Flooding Flooding of streets, underpasses, low lying areas, or storm drains. This type of flooding is mainly an inconvenience and is generally not life threatening.
Urbanization To become urban in nature or character; residential, commercial, and industrial development.
Usable storage capacity The quantity of ground water of acceptable quality that can be economically withdrawn from storage.
Use value The economic benefit associated with the physical use of a resource, usually measured by the consumer surplus or net economic value associated with such…
User day The participation in a recreation activity at a given resource during a 24-hour period by one person.
User fee A fee which is collected only from those persons who use a particular service, as opposed to one collected from the public in general.
Utility See Useful.