R655. Natural Resources, Water Rights.
R655-10. Dam Safety Classifications, Approval
Procedures and Independent Reviews.
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.
KEY: dam safety, dams, reservoirs
November 29, 2001
Notice of
Continuation July 12, 2001
73-5a