U.S. Environmental Protection AgencyThe independent federal agency, established in 1970, that regulates federal environmental matters and oversees the implementation of federal environmental…
Ultimate AnalysisA procedure for determining the primary elements in a substance (carbon, hydrogen, oxygen, nitrogen, sulfur, and ash).
Unconsolidated shore wetlandsIncludes all wetland habitats having three characteristics: (1) unconsolidated substrates with less than 75% areal cover of stones, boulders, or bedrock…
UnderflowThe movement of groundwater through the soil or a subsurface stratum, or under a structure; specifically, the water flowing beneath the bed of a stream…
UnderstoryThe trees and other woody species growing under a relatively continuous cover of branches and foliage formed by the overstory trees.
Uniform Building Code (UBC)A building code published by the International Conference of Building Officials, adopted and amended by Oregon Department of Commerce.
Uniform Mechanical Code (UMC)A code sponsored by the International Association of Plumbing and Mechanical Officials and the International Conference of Building Officials, adopted and…
Unit (fuel or pulp)A bulk measure of hog fuel or pulp chips containing 200 cubic feet. A unit contains varying amounts of solid material depending on the amount of…
Unit (timber)A timber harvest area with defined boundaries. The area is managed as a unit for harvest and subsequent management activities.
United States Code (USC)A compilation of the general and permanent federal laws of the United States. It is divided into 51 titles that represent broad areas subject to federal…
Unmerchantable woodMaterial which is unsuitable for conversion to wood products due to poor size, form, or quality.
Unrest (episode)Usually non-eruptive volcanic activity (e.g., ground deformation, steam plumes, degassing) that may be interpreted as a precursor to an eruption.
Unstable slopesSlopes considered unstable due to their incline (or critical angle of repose), applied to slopes made of unconsolidated material.
Unsuitable areasAreas not appropriate for timber harvest due to fragile or shallow soils, scenic values, special wildlife habitat areas, and riparian or wetland values…
UplandThe portion of the landscape above the valley floor or stream.
UplightingLight directed upward at greater than 90° above nadir, generally upward into the sky.
Upper-air soundingAn upper-air observation of the vertical profile of an atmospheric variable such as temperature or wind.
UpwarpA broad anticline with gently sloping limbs formed as a result of differential uplift.
Urban Growth BoundaryA line drawn around a city that prohibits development outside that boundary. Designed to slow or prevent sprawl, UGBs are designed to accommodate growth…
uronic acidA simple sugar whose terminal -CH2OH group has been oxidized to an acid, COOH group.
Utility scale facilitiesFacilities that generate large amounts of electricity that is delivered to many users through transmission and distribution systems.