R655-10-4. Definitions

ABUTMENT is the part of the valley side against which the dam is constructed. Right and left abutments are those on respective sides of an observer when viewed looking downstream.

ACRE-FOOT (AC-FT) of water is the volume of water required to cover one acre, one foot deep. This is the term commonly associated with reservoir storage. It is equal to 43,560 cubic feet.

ACTIVE FAULT is a fault that has exhibited one or more of the following characteristics:

(a) movement at or near the ground surface at least once in the last 35,000 years;

(b) instrumentally determined seismicity that demonstrates a causal relationship with the fault;

(c) structural relationship to an active fault such that movement on one fault could be expected to cause movement on the other.

ACTIVE STORAGE CAPACITY is the amount of storage that can be released and utilized.

ANISOTROPY means having physical characteristics which vary in different directions.

APPURTENANT STRUCTURE means the outlet works, spillways, access structures, bridges, and other related structure to a dam.

AXIS OF DAM is the plane or curved surface, arbitrarily chosen by a designer, appearing as a line, in plan or in cross section, to which the horizontal dimensions of the dam can be referred.

BENCHMARK is a permanent physical mark of known horizontal coordinates and elevation.

BREACH is an opening or a breakthrough in a dam.

CALIBRATED WATERSHEDS are watersheds with sufficient precipitation and streamflow measuring devices and records to allow for computations of the relationships between precipitation and streamflow.

CAMBER is additional material placed on the dam crest to protect design freeboard from anticipated settlement.

CAPACITY is the maximum volume that can be stored in a reservoir below the primary spillway level.

CAVITATION is wear on a hydraulic structure where a high hydraulic gradient is present.

CHANGE ORDER is a document used to modify approved plans or make adjustments in pay quantities.

COLLECTION PIPE is a conduit used to collect seepage waters from drainage blankets and drains and convey the water to a point downstream of the dam.

CONDUIT is a closed channel to convey water through, under, or around a dam.

CONDUIT FILTER DRAIN is a pervious filter drain around a conduit for the purpose of seepage control.

CONTROL SECTION is the section where flow passes through critical depth.

CONTOUR LINE is a line of constant elevation on a map or drawing.

CREST LENGTH is the developed length of the top of a dam.

CREST WIDTH is the developed width of the top of a dam.

CUBIC FEET PER SECOND (CFS) is a unit expressing rates of discharge. One cubic foot per second is equal to the discharge through a rectangular cross-section, one foot wide and one foot deep, flowing at an average velocity of one foot per second.

CUTOFF COLLAR is a projecting collar, usually of concrete, built around the outside of a pipe, tunnel, or conduit, to lengthen the seepage path along the outer surface of the conduit.

DAM is any artificial barrier or obstruction, together with appurtenant works, if any, which impounds or diverts water.

DEAD STORAGE is the storage that lies below the invert of the lowest outlet and that cannot be withdrawn from the reservoir without pumping.

DEFORMATION ANALYSIS is a study of how a dam will permanently deform as a result of strains caused by seismic loads.

DENTAL CONCRETE is concrete used to level discontinuities in dam foundations and abutments.

DESICCATION is the process of cracking of soils due to shrinkage during drying.

DIFFERENTIAL SETTLEMENT is unequal settlement of a structure or soil mass, often leading to excessive stresses or unacceptable strains.

DISPERSIVE CLAYS are clays whose particles detach in the presence of water and may be transported by the water, leading to a piping failure.

DRAINAGE AREA or watershed is the area that drains naturally to a particular point on a river, stream or creek.

DRAINAGE BLANKET is a drainage layer placed directly over the foundation material.

DRAINAGE WELLS or pressure relief wells are wells or boreholes usually downstream of impervious cores, grout curtains, or cutoffs, designed to collect and control seepage through or under a dam, so as to reduce uplift pressures under or within a dam. A line of wells forms a drainage curtain.

DRAWDOWN is the lowering of a reservoir's water surface level due to releases.

DRAWINGS are graphical details of proposed construction.

DROP STRUCTURES are permanent structures used to facilitate the vertical downward movement of water without causing erosion.

DYNAMIC ANALYSIS is an analysis which predicts the stability and/or deformation of a dam due to seismic loads.

EARLY WARNING SYSTEM is an automatic device used to alert downstream interests of existing or impending high flows caused by storms or dam failures.

EMERGENCY ACTION PLAN is a predetermined plan of action to be taken to reduce the potential for loss of life and property damage in an area affected by a dam break.

EMERGENCY SPILLWAY, or secondary spillway, is the spillway designed to convey excess water generated by unusual hydrological events through, over or around a dam.

ENLARGEMENT is any change or addition to an existing dam or its appurtenant works which increases, or may increase, the maximum quantity of water which can be stored therein.

EPICENTER is the point on the earth's surface directly above the site of initial movement on the fault.

EXIT CHANNEL is an open channel, located downstream from any conduit or spillway, which conducts the flow to a point where it may be released without jeopardizing the dam.

FACE, in reference to a structure, is the external surface that limits the structure.

FILTER or filter zone is a band or zone that is incorporated in a dam and is graded, either naturally or by selection, so as to allow seepage to flow across or down the filter without allowing the migration of material from zones adjacent to the filter.

FLASHBOARDS are lengths of timber, concrete, or steel placed on the crest of a spillway to raise the water level but that may be quickly removed in the event of a flood, either by a tripping device or by a deliberately designed failure of the flashboards or their supports.

FLOOD ROUTING is a computation of the changes in the rise and fall in stream flow or reservoir levels as a flood moves downstream. The results provide hydrographs of flow or elevation versus time at given points on the stream or in a reservoir.

FLOOD STAGE is the stage or elevation in which overflow of the natural banks of a stream or body of water begins.

FLOWLINE or invert is the lowest point in a water conveyance structure where water can flow.

FOUNDATION OF DAM is the natural material on which the dam structure is placed.

GALLERY is a permanent accessible structure within the interior of a dam used for seepage collection, monitoring, and remedial work.

GEOLOGIST is a person with a degree in geology or a related field from an accredited college or university with at least three years of experience in engineering geology.

GEOMEMBRANE is a term for a geosynthetic which is designed to be an impermeable barrier.

GEOSYNTHETICS is a broad term used to describe manmade fabrics used in geotechnical applications.

GEOTEXTILE is a term for a geosynthetic which is designed to be a filter, a drain, act as reinforcement, or for separation.

GROIN is that area along the contact or intersection of the face of a dam with the abutments.

GROUT CURTAIN is a barrier to reduce seepage under a dam, produced by injecting grout into a vertical zone in the foundation.

HYDRAULIC FRACTURING is the fracturing of soil materials due to excessive fluid pressures.

HYDRAULIC HEIGHT is the vertical dimension of a dam as measured from the natural streambed at the downstream toe to the elevation of the water surface at the crest of the primary spillway.

HYDRAULICS is the science of the static and dynamic behavior of fluids.

HYDROGRAPH is a graphical representation of discharge, stage, volume, or other hydraulic property, with respect to time, for a particular point.

HYDROLOGY is the study of the properties, distribution and movement of water on the earth's surface, in the soil and underlying rocks.

INCREMENTAL DAMAGE ASSESSMENT (IDA) is an analysis showing the influence of a dam failure when superimposed upon an extreme hydrologic event.

INDEPENDENT CONSULTANT is a consultant used, in addition to the owner's engineer, to assess the design, construction, investigation or operation of a dam.

INFILTRATION RATE is the rate at which a given soil can accept surface water.

INFLOW DESIGN FLOOD (IDF) means the flood hydrograph which is used to size a dam's spillway.

INITIAL FILLING PLAN is a written procedure used during the first filling of a reservoir.

INLET CHANNEL is an open channel upstream from a spillway or conduit.

INTERNAL EROSION is piping.

INUNDATION MAPS show areas that would be subject to flooding due to storm conditions or failure of a dam.

LIQUEFACTION is the sudden loss of strength or stiffness of a soil resulting from dynamic loading as from earthquakes.

LOG BOOM is a floating device intended to prevent large floating debris from being carried into a spillway.

LOW-LEVEL OUTLET is a conduit from a reservoir, generally used for lowering the reservoir or for providing downstream releases.

MAGNITUDE of an earthquake is a quantity characteristic of the total energy released by an earthquake.

MAXIMUM CAPACITY is the maximum volume of water that can be stored in a reservoir when filled to the crest of the dam.

MAXIMUM CREDIBLE EARTHQUAKE (MCE) -- All active sources of seismicity with the potential to impact the stability of a dam should be assigned a maximum credible seismic event. The event which has the greatest potential to cause damage at the site will be defined as the Maximum Credible Earthquake.

NAPPE is the free-falling stream from a weir.

NORMAL FREEBOARD is the vertical distance between the primary spillway overflow crest and the top of the dam.

ONE HUNDRED YEAR FLOOD means the flood having a one percent probability of being equalled or exceeded in any given year.

ONE HUNDRED YEAR PRECIPITATION means the precipitation having a one percent probability of being equalled or exceeded in any given year.

OPERATING BASIS EARTHQUAKE (OBE) -- All active sources of seismicity with the potential to impact the stability of a dam should be assigned an operating basis seismic event. This event is considered to have a return interval of at least 200 years. The event which has the greatest potential to cause damage at the site will be defined as the Operating Basis Earthquake.

OWNER includes all who own, control, operate, maintain, manage, or propose to construct a dam; also, their agents, lessees, trustees, and receivers.

OWNER'S ENGINEER is a professional engineer, licensed in Utah, retained to design, construct, monitor, operate, or evaluate a dam.

PEAK FLOW is the maximum instantaneous discharge that occurs during a flood. It is coincident with the peak of a flood hydrograph.

PERVIOUS ZONE is a part of the cross section of an embankment dam comprising material of high permeability.

PHREATIC SURFACE is the free surface of ground water at atmospheric pressure.

PIEZOMETER is an instrument for measuring pore water pressure within soil, rock, or concrete.

PIPING is the progressive development of internal erosion by seepage, appearing downstream as a hole or seam, discharging water that contains soil particles.

PLANS are engineering drawings, specifications, and design reports supporting the design of a dam and detailing the construction of the dam.

POROUS INTERVAL is the portion of a piezometer where infiltrating water is allowed to act on the device.

PRINCIPAL SPILLWAY is the main spillway for normal operating conditions.

PROBABLE MAXIMUM FLOOD (PMF) is the flood that may be reasonably expected from the most severe combination of critical meteorologic and hydrologic conditions that are possible in the region.

PROBABLE MAXIMUM PRECIPITATION (PMP) is the maximum amount of precipitation that could be expected to fall on a drainage under the most severe meteorologic condition.

PSEUDO STATIC ANALYSIS is an approximate method for predicting the dynamic stability of a structure using static loads.

RESERVOIR AREA is the surface area of a reservoir when filled to a given water elevation.

RESERVOIR RIM is a term used to describe the land forms around the perimeter of a reservoir which could have an adverse impact on the dam or reservoir due to movement.

RESERVOIR STAGE is the measure of the depth or elevation of water in a reservoir relative to an established datum.

RESIDUAL FREEBOARD means the vertical distance between the maximum water surface during a given hydrologic event and the top of the dam.

RESPONSE SPECTRUM is a graphical representation of actual motions, including displacement, velocity, and acceleration, caused by seismic events.

RIPRAP is a layer of large stones, broken rock, or precast blocks placed on the upstream slope of an embankment dam, on a reservoir shore, or on the sides of a channel, as a protection against waves, ice, and scour.

SEDIMENT POOL is the portion of the reservoir allotted to the accumulation of submerged sediment during the design life of the dam.

SEISMIC means pertaining to an earthquake or earth vibration.

SLOPE PROTECTION is the protection of an embankment slope against wave action or erosion.

SPECIFICATIONS are written descriptions of the proposed construction.

SPILLWAY is an open or closed channel, conduit or drop structure used to convey excess water through a reservoir. It may contain gates, either manually or automatically controlled, to regulate the discharge of the water.

SPILLWAY EVALUATION FLOOD (SEF) is the flood that may be expected at the dam from applying the SEP to a given watershed.

SPILLWAY EVALUATION PRECIPITATION (SEP) is the lowest, site specific, precipitation estimate allowed by the State Engineer, used in the analysis of new, existing, high or moderate hazard dams.

STAFF GAGE is a permanent instrument or device used to read reservoir stage.

STANDARD OPERATING PLAN is a written procedure outlining the operation and maintenance of a dam and its appurtenant structures and equipment.

STATE ENGINEER is the Director of the Utah Division of Water Rights.

STILLING BASIN is a basin constructed to dissipate excess energy of waters emerging from a spillway or outlet.

STOPLOGS are beams placed on top of each other with their ends held in guides on each side of a channel or conduit.

STORAGE CAPACITY is the volume of water which can be stored at the elevation of the primary spillway, including both active and dead storage.

STRUCTURAL HEIGHT means the vertical dimension of a dam as measured from the natural streambed at the downstream toe of a dam to the top of a dam.

SURVEY MARKER is a permanent physical mark on a dam or appurtenant structure used to measure changes in horizontal and vertical movement.

TECTONICS is a study of the broader features of the earth's crust and the causes of its deformation.

TEST BORINGS are holes drilled to determine the type and physical properties of subsurface materials.

TEST PIT is an excavation used to evaluate and observe subsurface materials.

TOE OF DAM is the junction of a dam face with the foundation. For an embankment dam, the junction of the upstream face with ground surface is called the upstream toe, and the junction of the downstream face with the ground surface is referred to as the downstream toe.

TRANSITION ZONE is a zone of material used to provide filter requirements between two zones of material which do not meet filter requirements.

TRASH RACK is a screen located at an intake to prevent the entry of floating or submerged debris.

UNGATED OUTLET is an outlet that allows uncontrolled flow through or around a dam.

UNIT HYDROGRAPH is a hydrograph which shows the rates at which runoff occurs for one inch of storm runoff from a drainage area.

UPLIFT is the upward water pressure in the pores of a material or on the base of a structure.

WATER STOPS are strips of material used to prevent leakage through joints between adjacent sections of concrete.

WEIR is a device used to measure or control water.