That part of the valley wall against which the dam
is constructed. The part of a dam that contacts the riverbank.
A structure that supports the ends of a dam or bridge. An artificial
abutment is sometimes constructed, as a concrete gravity section,
to take the thrust of an arch
dam where there is no suitable natural abutment. Action or
place of abutting; the part of a structure that is the terminal
point or receives thrust or pressure. Defined in terms of left
and right as looking away from the reservoir,
looking downstream (i.e., left abutment, right abutment). "The
Tropics climbing area at Soldier Canyon Dam was located
on the northern abutment of that dam.
A horizontal strip or shelf built into an embankment
or cut to break the
continuity of the slope,
usually for the purpose of reducing erosion
or to increase the thickness of the embankment at a point of change
in a slope or defined water
surface elevation. A horizontal step in the sloping profile
of an embankment
dam. A shelf that breaks the continuity of a slope, or artificial
ridge of earth. A ledge or shoulder, as along the edge of a road
or canal. An artificial
ridge of earth. A "stability berm will be added
to all four Horsetooth Dams for compliance with new Bureau of
Reclamation earthquake requirements.
To loosen or move rock
or soil by means
of explosives or an explosion.
areas: Generally, surface areas, that contain borrow pits.
The area from which material for an embankment
is excavated. The contractor is blasting the overhangs off
the northern or left (looking down from the dam) abutment
at Soldier Canyon Dam.
Material excavated from one area to be used as fill
material in another area. The constractor will use borrow material
for the stability berms at all four dams.
pits: Specific site(s) within a borrow area from which material
is excavated for use. The contractor will reopen old borrow
pits, or borrow areas, to access borrow material.
A rock fragment,
usually rounded by weathering or abrasion,
with an average dimension of 12 inches or more: will not pass
a 12-inch screen. A particle of rock
that will not pass a 12-inch (300-mm) square opening. A rock which
is too heavy to be lifted readily by hand. Some riprap boulders
exist on the face and to the sides of the dams.
A one-piece fabricated steel unit which is lowered into guides
and seals against a frame to close a water passage in a dam,
etc. An object used to isolate a portion of a waterway for examination,
maintenance, or repair. A wall or partition erected to resist
ground or water pressure. When water levels were lowered to
dead storage at Horsetooth Dam in the fall of 2001, regular maintenance
work was performed on the intake structures "bulkhead
of Reclamation (USBR, Reclamation, BOR): The mission of the
Bureau of Reclamation
is to manage, develop, and protect water and related resources
in an environmentally and economically sound manner in the interest
of the American public. The USBR built and owns Horsetooth
Reservoir, its four dams, one dike, and adjacent land.
A channel, usually
open, that conveys water by gravity to farms, municipalities,
etc. The Hansen Supply Canal carries water from Horsetooth
Dam and Reservoir to water users along the Poudre River.
headworks: The beginning of a canal.
The headworks for the Hansen Supply Canal are located at Horsetooth
Fine-grained soil or the fine-grained portion of soil
that can be made to exhibit plasticity
(putty-like properties) within a range of moisture
contents, and that exhibits considerable strength when air-dry.
which passes a No. 200 (0.075 mm) United States Standard sieve.
Reclamation geologists have identified some clays in the various
foundations of the Horsetooth dams.
gravel protection: Gravel
generally placed in a layer upon a finished surface to protect
the finished surface from deterioration or erosion.
All four dams at Horsetooth have a gravel protection layer.
(impervious core or impervious zone): A zone of low permeability
material in an embankment
dam. Sometimes referred to as central core, inclined
core, puddle clay core, and rolled clay
core. A cylindrical piece of an underground formation
cut and raised by a rotary drill with a hollow bit. All four
dams at Horsetooth have an impervious core.
feet per second (cfs or ft3/s): A unit of discharge
for measurement of a flowing liguid equal to a flow
of 1 cubic foot per second (448.8 gallons per minute (gpm), 7.48
gallons per second, or 1.98 acre-feet
per day). A rate of streamflow; the volume, in cubic feet, of
water passing a reference point in 1 second. Water in and out
of Horsetooth Reservoir is recorded in cfs.
An impervious construction by means of which water is prevented
from passing through foundation
trench (keyway): An excavation
in the foundation
of an embankment
dam, usually located upstream of the dam
axis or centerline crest
which extends to bedrock
or to an impervious stratum. The excavation is backfilled
material to form a cutoff
and reduce percolation
under the dam. See foundation
wall. A wall of impervious
material (e.g., concrete, asphaltic concrete, timber, steel
sheet piling, or impervious grout curtain) located in the foundation
beneath a dam and
which forms a water barrier and reduces seepage
under a dam or spillway. A cutoff wall or trench is being designed
to stop the seepage underneath Horsetooth Dam.
A barrier built across a watercourse to impound or divert water.
A barrier that obstructs, directs, retards, or stores the flow
of water. Usually built across a stream. A structure built to
hold back a flow of water. Horsetooth Reservoir has four dams:
Spring, Dixon and Soldier Canyon Dams and Horsetooth Dam.
foundation: The excavated surface or undisturbed material
upon which a dam
is placed. A limestone section of the dam foundation at Horsetooth
Dam is seeping.
safety issue: Dam safety related issues and concerns are those
which, if not adequately addressed could/would:
to a failure or malfunction resulting in an uncontrolled release
of stored water that would place the downstream population potentially
at risk or;
the agency's ability to detect developing adverse dam performance
and prudently respond to that performance.
foundation seepage at Horsetooth Dam and the modernization upgrades
of filter buttresses and stability berms at all four dams are
considered Dam Safety issues; they are, therefore, financed in
part by Reclamations Safety of Dams Program (see the In
Depth Funding Report under "Data and Reports)
DataWeb is an electronic
presentation of the Bureau
of Reclamation's Project Data book and contains historical,
statistical, and technical information on the projects of the
Bureau of Reclamation. More information on the Colorado-Big
Thompson Project, of which Horsetooth Reservoir is a part, can
be found on Dataweb.
capacity (dead storage): The reservoir
capacity from which stored water cannot be evacuated by gravity.
Horsetooth Reservoir was lowered to dead storage at Horsetooth
Dam once in fall 2000 in order to fill the sinkhole and again
in fall 2001 for general maintenance work.
of cutoff: The vertical distance that the cutoff
penetrates into the dam
foundation. The depth of the cutoff wall at Horsetooth
Dam is still under design.
basis earthquake (DBE): The earthquake
a structure is required to safely withstand with repairable damage.
Those systems and components important to safety must remain functional
and/or operable. For design purposes, the intended use of this
earthquake loading is for economic design of structures or components
whose damage or failure
would not lead to catastrophic loss. For most usage in Reclamation,
the DBE is defined to have a 90% probability of nonoccurrence
in a 50-year-exposure period, which is equivalent to a recurrence
interval of 474 years. Economic considerations for specific projects
may lead to consideration of other values. Reclamations
new earthquake compliances are based on DBEs.
As opposed to unwatering,
dewatering is the removal and control of ground
water from pores or other open spaces in soil
or rock formations
to the extent that allows construction activities to proceed as
intended, including the relief of ground water pressure. Removing
water by pumping, drainage,
The removal of ground water and seepage
from below the surface of the ground or other surfaces through
the use of deep wells and wellpoints.
All four dams at Horsetooth Reservoir must be dewatered before
they can be excavated. Dams are monitored 24-7 when they are being
A low embankment,
usually constructed to close up low areas of the reservoir rim
and thus limit the extent of the reservoir.
Embankment for restraining a river or a stream.
Embankments which contain water within a given course. Usually
applied to dams built to protect land from flooding.
See saddle dam.
There is one dike at Horsetooth Reservoir. Satanka Dike abuts
Horsetooth Dam on its western side.
An entity that has a contract with the Bureau
of Reclamation for the delivery of irrigation water. Such
entities include, but are not limited to: canal companies, conservancy
districts, ditch companies, irrigation and drainage districts,
irrigation companies, irrigation districts, reclamation districts,
service districts, storage districts, water districts, and water
users associations. The Northern Colorado Water Conservancy
District is the contracting entity on the Colorado-Big Thompson
Project of which Horsetooth Reservoir is a part.
face: The inclined surface of a dam
away from the reservoir.
See face. The
downstream faces of Spring, Dixon, and Soldier Canyon Dams are
all visible from the city of Ft. Collins.
Lowering of a reservoir's water level; process of depleting a
storage. Vertical distance the free water
surface elevation is lowered or the reduction of the pressure
head due to the removal of free water. The difference between
a water level and a lower water level in a reservoir within a
particular time. The amount of water used from a reservoir. The
water at Horsetooth Reservoir draws down every summer by irrigators
and other water users. Horsetooth has also been drawn down to
a temporary water level restriction for the duration of the construction.
dam (earthfill dam): An embankment
dam in which more than 50 percent of the total volume is formed
of compacted earth material generally smaller than 3-inch size.
Seepage through the dam is controlled by the designed use of upstream
blankets and/or internal cores constructed using compacted soil
of very low permeability. All four dams at Horsetooth are earthen,
earthfill, embankment dams.
Any one or combination of the operations involved in altering
or movement of earth. Construction on the Horsetooth Dams will
involve a lot of earthwork.
The right to use land owned by another for some specific purpose.
Reclamation and the District have secured the proper easements
to access all four Horsetooth Dams.
analysis: A procedure that includes both tangible and intangible
factors to evaluate various alternatives. Reclamation had to
prepare an economic analysis as part of its justification of work
at the Horsetooth Dams.
assessment (EA): A NEPA
compliance document used to determine if an action would have
a significant effect on the human environment. If not, a finding
of no significant impact (FONSI) is written. If so, an environmental
impact statement (EIS) is written. An Environmental Assessment
was drafted and finalized prior to the final design and construction
at the Horsetooth Dams.
A gradual wearing away of soil
or rock by running
water, waves, or wind. Concrete surface disturbance caused by
moving particles in water, impact of pedestrian or vehicular traffic,
or impact of ice floes. Surface displacement of soil caused by
weathering, dissolution, abrasion, or other transporting. The
gradual wearing away of material as a result of abrasive action.
Excessive recreation along the faces of the dams has caused
unnecessary erosion along the abutments.
Exposed surface of dam materials (earth, rockfill, or concrete),
upstream and downstream. The downstream faces of the dams at
Horsetooth will be excavated so the filter can be placed.
Structures associated with Reclamation
irrigation projects, municipal and industrial water systems, power
generation facilities, including all storage, conveyance, distribution,
systems. Horsetooth Reservoir and its four dams are facilities
on the Colorado-Big Thompson Project.
(filter zone): One or more layers of granular material incorporated
in an embankment
dam and is graded (either naturally or by selection) to allow
or within the layers while preventing the migration of material
from adjacent zones. A layer or combination of layers of pervious
materials designed and installed in such a manner as to provide
drainage, yet prevent the movement of soil particles due to flowing
water. A filter buttress is being added to all four Horsetooth
Lower part of a structure that transmits loads directly to the
soil. The excavated
surface upon which a dam is placed. The foundation at Horsetooth
Dam includes a layer of limestone that has been channeling water
from the reservoir, under the dam, to the valley downstream of
drains: Tile or pipe
for collecting seepage
within a foundation.
All four of the Horsetooth Dams have foundation drains. The
foundation drains at Horsetooth Dam were what first indicated
there was a seepage problem.
A machine with a centrally located blade that can be angled to
cast to either side, with independent hoist control on each side.
An example of some of the heavy construction equipment the
contractor is using at the Horsetooth Dams.
The contact between the upstream or downstream
face of a dam
and the abutments.
The area along the contact (or intersection) of the face of a
dam with the abutments. Recreation trails have caused erosion
along the groin of Soldier Canyon and Dixon Canyon Dams.
cap: A concrete pad or wall constructed to facilitate subsequent
pressure grouting of the grout curtain beneath the grout cap.
A grout cap was placed atop the sinkhole at Horsetooth Dam
once the sinkhole was filled.
curtain (grout cutoff): A vertical zone, usually thin, in
into which grout
is injected to reduce seepage
beneath a dam. The
cutoff wall at Horsetooth Dam will be a form of grout curtain.
Filling cracks and crevices with a cement mixture.
hazard: A downstream hazard
classification for dams
in which more than 6 lives would be in jeopardy and excessive
economic loss (urban area including extensive community, industry,
agriculture, or outstanding natural resources) would occur as
a direct result of dam failure. This classification also applies
to structures other than dams. All four dams at Horsetooth
Reservoir are considered "High Hazard" under this
environment: Natural and physical environment and the relationship
of people with that environment,
including all combinations of physical, biological, cultural,
social, and economic factors in a given area. The human environment
will be impacted by the construction at Horsetooth Reservoir.
Consequently, under NEPA, Reclamation prepared an EA.
Any device used to monitor the performance of the structure during
its construction and throughout its useful life. An arrangement
of devices installed into or near dams (i.e., piezometers, inclinometer,
strain gages, measurement points, etc.) and used to evaluate the
structural behavior and performance parameters of the structure.
Reclamation has utilized a variety of instrumentation, most
often piezometers, to evaluate the situations and conditions of
all four Horsetooth Dams.
Any structure through which water can be drawn into a waterway.
Any structure in a reservoir, dam, or river into which water can
be drawn and then discharged. Both Horsetooth and Soldier Canyon
Dams have an intake structure to take water out of the reservoir.
structure: Concrete portion of an outlet
works, including trashracks and/or fish screens, upstream
from the tunnel
or conduit portions.
The entrance to an outlet works.
reservoir (multipurpose reservoir): A reservoir
planned to operate for more than one purpose. Horsetooth is
a multi-purpose reservoir.
dam: A dam constructed
for two or more purposes (e.g. storage, flood control, navigation,
power generation, recreation, or fish and wildlife enhancement.)
Horsetooth Dam is a multipurpose dam.
project: A project designed for irrigation,
power, flood control, municipal and industrial, recreation, and
fish and wildlife benefits, in any combinations of two or more
(contrasted to single-purpose projects serving only one need).
The Colorado-Big Thompson Project, of which Horsetooth is a
part, is a multipurpose project.
Environmental Policy Act (NEPA): An act requiring analysis,
public comment, and reporting for environmental impacts of Federal
actions. See National
Environmental Policy Act of 1969. An EA was prepared under
NEPA for the Horsetooth Dams Modernization Project.
and maintenance (O&M): Operation, maintenance, repairs,
replacements, and testing of Reclamation facilities. O&M
responsibilities for Horsetooth Reservoir and the four dams was
transferred to the Northern Colorado Water Conservancy District
in the late 1980s.
An opening through which water can be freely discharged from a
the river for a particular purpose. Horsetooth Reservoir has
two outlets, one at Horsetooth Dam and one at Soldier Canyon Dam.
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,
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. A device
to provide controlled releases from a reservoir. A pipe that lets
water out of a reservoir, mainly to supply downstream demands.
The outlets at Horsetooth and Soldier Canyon Dams have associated
Projecting parts of a face or bank. Overhangs have been blasted
off the left abutment at Soldier Canyon Dam.
The measure of the flow
of water through soil.
The ease (or measurable rate) with which gasses, liquids, or plant
roots penetrate or pass through a layer of soil or porous media.
The capacity or ability of a porous rock, sediment, or soil to
allow the movement of water through its pores.
Having pores or openings that permit liquids or gasses to pass
zone: A part of the cross section of an embankment
dam comprising material of high permeability.
All four earthen dams at Horsetooth Reservoir are partly permeable.
An instrument which measures pressure head or hydraulic pressures
in a conduit
or hydraulic pressures within the fill
of an earth dam
or the abutment;
at the foundation
because of seepage
or soil compression; or on a flow surface of a spillway, gate,
or valve. Piezometers are used regularly for monitoring of all
four dams at Horsetooth Reservoir.
The erosion of
embankment or foundation material (soil) due to leakage. The action
of water passing through or under an embankment
dam and carrying with it to the surface at the downstream
face some of the finer material. The progressive removal of
soil particles from a mass by percolating water leading to the
development of channels.
The progressive development of internal
erosion by seepage,
appearing downstream as a hole discharging water. The process
of conveying erodible embankment or foundation materials through
a continuous, open "pipe" which is able to maintain a self-supported
roof. The pipe normally begins at an unprotected exit and works
it's way upstream (up gradient) along an erodible flow path until
the reservoir is reached. The filter buttresses will be installed
at all four dams as an improvement for preventing piping.
The likelihood of an event occurring. Reclamation had to tally
probabilities in its Safety of Dams Modification Report that was
presented to Congress in December 2000 as justification for the
Horsetooth Dams work.
maximum flood (PMF) (maximum probable flood, MPF): The largest
flood that may
reasonably be expected to occur at a given point on a stream
from the most severe combination of critical meteorologic and
hydrologic conditions that are reasonably possible on a particular
watershed. This term identifies estimates of hypothetical flood
characteristics (peak discharge, volume, and hydrograph shape)
that are considered to be the most severe "reasonably possible"
at a particular location, based on relatively comprehensive hydrometeorological
analyses of critical runoff-producing precipitation (and snowmelt,
if pertinent) and hydrologic factors favorable for maximum flood
runoff. The maximum
runoff condition resulting from the most severe combination of
hydrologic and meteorologic conditions that are considered reasonably
possible for the drainage basin under study. All four dams
at Horsetooth Reservoir were raised in the late 1980s based on
Recreational opportunities at more than 1,900 federal recreation
sites managed by the Bureau
of Reclamation and other federal agencies can be found at
the interagency Recreation.Gov
website (www.recreation.gov). Recreation is one of the
many uses of Horsetooth Reservoir.
office: Five Reclamation
offices in the 17 Western States that supervise Area, Field, and
Project Offices in their respective geographic locations. See
Great Plains, Lower
Colorado, Mid Pacific,
and Upper Colorado.
Horsetooth Reservoir, the Colorado-Big Thompson Project and
the Eastern Colorado Area Office are all under the Great Plains
Region of the U.S. Bureau of Reclamation.
A body of water impounded by a dam and in which water can be stored.
Artificially impounded body of water. Any natural or artificial
holding area used to store, regulate, or control water. Body of
water, such as a natural or constructed lake, in which water is
collected and stored for use. Dam design and reservoir operation
capacity and water
surface elevation data. To ensure uniformity in the establishment,
use, and publication of these data, the following standard definitions
of water surface elevations shall be used.
capacity: The capacity of the reservoir,
usually in acre-feet.
Dam design and reservoir operation utilize reservoir capacity
surface elevation data. The water level restriction in
place at Horsetooth Reservoir for the duration of the construction
was based, in part, on reservoir capacity.
inflow: The amount of water entering a reservoir expressed
per day or cubic feet per second. Inflow to Horsetooth Reservoir
is near Inlet Bay.
regulation (or operating) procedure: Operating procedures
that govern reservoir storage and releases. The Bureau of Reclamation
writes and updates the reservoir operating procedures for Horsetooth
Reservoir. These are also known as Standard Operating Procedures.
surface area: The area covered by a reservoir
when filled to a specified level. Reservoir surface area is
often used to determine how many boats can utilize the reservoir
at one time. With the water level restriction in place, Horsetooths
surface area is greatly reduced.
A layer of large uncoursed stones, broken rock,
blocks, bags of cement, or other suitable material generally placed
in random fashion on the upstream and downstream
faces of embankment
dams, stream banks, on a reservoir shore, on the sides of
a channel, or
other land surfaces to protect them from erosion
or scour caused
by current, wind, wave, and/or ice action. A protective blanket
of large loose stones, which are usually placed by machine to
achieve a desired configuration. Riprap is usually placed by dumping
or other mechanical methods but, in some cases, is hand placed.
It consist of relatively large pieces as distinguished from a
Very large riprap is sometimes referred to as "armoring." All
four dams at Horsetooth are covered with riprap. The riprap will
be removed and eventually replaced as part of the construction.
The relationship between the consequences resulting from an adverse
event and its probability of occurrence. The potential for losing
credibility, failing to solve a problem, or getting hurt. The
ability to describe potential outcomes using historic probability.
The likelihood or chance of an unacceptable event occurring.
assessment: As applied to dam safety, the process of identifying
the likelihood and consequences of dam
failure to provide the basis for informed decisions. Reclamation
had to provide a risk assessment as part of its justification
for the work at the Horsetooth Dams.
dam: A subsidiary dam
of any type constructed across a saddle or low point on the perimeter
of a reservoir.
See dike. All
four dams at Horsetooth Reservoir are also saddle dams.
A spot where ground
water oozes slowly to the surface, usually forming a pool.
Seeps were located downstream of Horsetooth Dam near Bellvue.
The slow movement or percolation
of water through soil
or rock. Movement
of water through soil without formation of definite channels.
The movement of water into and through the soil from unlined canals,
ditches, and water
storage facilities. The slow movement or percolation of water
through small cracks, pores, interstices,
etc., from an embankment, abutment, or foundation. Seepage
was detected through the foundation of Horsetooth Dam.
A steep-sided depression formed when removal of subsurface embankment
material causes overlying material to collapse into the resulting
void. Seepage through the limestone foundation at Horsetooth
Reservoir has caused sinkholes at the south end of the reservoir
near the Swim Beach and also one sinkhole near the upstream face
of Horsetooth Dam. All sinkholes have been filled and capped.
A storage pile of materials. Dam face material stripped from
the dams at Horsetooth will be stored in stockpiles near each
of the dams.
(toe of dam): The point of intersection between the bottom
of a slope or the upstream
face of a dam
and the natural ground, for example, the upstream or downstream
toe of a dam or the downstream toe of a landslide or debris fan.
The junction of the face of a dam with the ground surface. During
construction, a lot of activity will be going on at the toe of
the dams. As a result, all recreation trails and access will be
closed in those areas.
drain(s): Open-jointed tile or perforated
pipe located at the toe of the dam used in conjunction with
blankets to collect seepage
from the embankment
and conveys the seepage to a location downstream from the dam.
A system of pipe and/or pervious material along the downstream
toe of a dam used to collect seepage from the foundation and embankment
and convey it to a free outlet. Tile or pipe used to collect external
seepage along the downstream toe of an embankment. Spring Creek
starts at the toe drain of Spring Canyon Dam.
A metal or reinforced concrete structure placed at the intake
of a conduit,
pipe, or tunnel
that prevents entrance of debris over a certain size. A device
or structure located at an intake to prevent floating or submerged
debris from entering the intake. The intake structure at Horsetooth
Dam, visible at dead storage, has a large trashrack section.
Measure of extent to which light passing through water is reduced
due to suspended materials (see nephelometric).
The optical property of water based on the amount of light reflected
by suspended particles. Cloudiness of water, measured by how deeply
light can penetrate into the water from the surface. The cloudy
appearance of water caused by the presence of suspended and colloidal
matter. The scattering and absorption
of light that makes the water look murky. Caused by the content
and shape of matter suspended in the water. The state of having
sediment or foreign particles suspended
or stirred up in water. Reclamation partnered with the City
of Ft. Collins to provide additional water quality monitoring
equipment needed, in part, to better detect turbidity at low water
levels, particularly during construction.
user: Any individual, district,
association, government agency, or other entity that uses water
supplied from a Reclamation
project. The Northern Colorado Water Conservancy District represents
the majority of Horsetooths water users.
year (WY): Period of time beginning October 1 of one year
and ending September 30 of the following year and designated by
the calendar year in which it ends. A calendar year used for water
calculations. Horsetooth Reservoir is traditionally at its
lowest water level elevation at the end of each water year.
Lands including swamps, marshes, bogs, and similar areas such
as wet meadows, river overflows, mudflats,
and natural ponds. An area characterized by periodic inundation
or saturation, hydric soils, and vegetation adapted for life in
saturated soil conditions. A jurisdictional wetland is subject
to regulation under the Clean
Water Act. A nonjurisdictional is subject to consideration
under the Fish
and Wildlife Coordination Act. There are a few wetlands
near Horsetooth Reservoir. Construction impacts to wetlands are
covered in the EA.