LAKE ESTES

2001 SURVEY

U.S. Department of the Interior

Bureau of Reclamation
REPORT DOCUMENTATION PAGE Form Approved

0MB No. 0704-0 188

1. AGENCY USE ONLY (Leave Blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

February 2003 Final ___________________________________

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Lake Estes PR

2001 Survey

6. AUThOR(S)

Ronald L. Ferrari ___________________________

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

Bureau of Reclamation, Technical Service Center, Denver CO 80225-0007 REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING

Bureau of Reclamation, Denver Federal Center, P0 Box 25007, AGENCY REPORT NUMBER

Denver CO 80225-0007 DIBR

II. SUPPLEMENTARY NOTES

Hard copy available at Bureau of Reclamation Technical Service Center, Denver, Colorado

12a. DISTRIBUTION/A VAILABILITY STATEMENT I2b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The Bureau of Reclamation (Reclamation) surveyed Lake Estes in August of 2001 to develop a topographic map and compute a

present storage-elevation relationship (area-capacity tables). The data were used to calculate reservoir capacity lost due to

sediment accumulation since dam closure in November of 1948. The underwater survey was conducted between lake elevation

7,471.4 and 7,473.0 feet (project datum). The underwater survey used sonic depth recording equipment interfaced with a global

positioning system (GPS) that gave continuous sounding positions throughout the underwater portions of the reservoir covered by

the survey vessel. The above-water topography was determined by digitizing the developed contour lines from the U.S. Geological

Survey quadrangle (USGS quad) maps of the reservoir area. The new topographic map of Lake Estes was developed from the

combined digitized USGS quad contours and August 2001 underwater measured topography. This study assumed no change from

elevation 7470.0 (feet) and above.

As of August 2001, at maximum water surface elevation 7,475.0, the surface area was 185 acres with a total capacity of 2,783 acrefeet. Since initial operation in November of 1948, about 284 acre-feet of sediment have accumulated in Lake Estes below elevation

7,470.0, resulting in a 12.8 percent loss in reservoir volume. Since 1948, the estimated average annual rate of reservoir capacity

lost to sediment accumulation is 5.4 acre-feet.

14. SUBJECT TERMS 15. NUMBER OF PAGES

reservoir area and capacity! sedimentation! reservoir surveys! sonar! sediment distribution! _______________________

contour area! reservoir area! sedimentation survey! global positioning system! lake 16. PRICE CODE

17. SECURITY 18. SECURITY 19. SECURITY CLASSIFICATION 20. LIMITATION OF

CLASSIFICATION CLASSIFICATION ABSTRACT

OF REPORT OF ABSTRACT

OF ThIS PAGE

UL UL UL

UL

______________________ ___________________

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescnbed by ANSI SIxI. 239-18

298-102
Lake Estes

2001 Survey

by

Ronald L. Ferrari

Sedimentation and River Hydraulics Group

Water Resources Services

Technical Service Center

Denver, Colorado

February 2003
ACKNOWLEDGMENTS

The Bureau of Reclamation's (Reclamation) Sedimentation and River

Hydraulics Group of the Technical Service Center (TSC) prepared and

published this report. Kent Collins and Ronald Ferrari of the TSC

conducted the hydrographic survey. Ron Ferrari of the TSC completed the

data processing needed to generate the new topographic map and areacapacity tables. Sharon Nuanes of the TSC completed the final map

development. Kent Collins of the TSC performed the technical peer review

of this documentation.

Mission Statements

The mission of the Department of the Interior is to protect and provide

access to our Nation's natural and cultural heritage and honor our trust

responsibilities to Indian Tribes and our commitments to island

communities.

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 information contained in this report regarding commercial products or

firms may not be used for advertising or promotional purposes and is not to

be construed as an endorsement of any product or firm by Reclamation.

The information contained in this report was developed for the Bureau of

Reclamation; no warranty as to the accuracy, usefulness, or completeness is

expressed or implied.

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CONTENTS

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Page

Introduction 1

Summary and Conclusions 2

Reservoir Operations 3

Hydrographic Survey Equipment and Method 3

GPS Technology and Equipment 3

Survey Method and Equipment 5

Lake Estes Datum 6

Reservoir Area and Capacity 6

Topography Development 6

Development of 2001 Contour Areas 7

2001 Storage Capacity 7

Reservoir Sediment Analyses 8

References 10

TABLES

Table

I Reservoir sediment data summary (page 1 of 2) 11

I Reservoir sediment data summary (page 2 of 2) 12

2 Summary of 2001 survey results 13

FIGURES

Figure

1 Lake Estes location map 14

2 Olympus Dam, plan and sections 15

3 Lake Estes topographic map 17

4 2001 area and capacity curves 19

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INTRODUCTION

Lake Estes, formed by Olympus Dam, is located in Larimer County on the Big Thompson River

approximately 2 miles east of the city of Estes Park in Colorado (fig. 1). Colorado State

Highway 36 divides the lake with the smaller portion to the south on the Fish Creek arm and the

larger portion being north on the Big Thompson River arm. Six 5-foot diameter culverts located

under the highway connect the two lakes. The dam and lake are features of the Colorado-Big

Thompson Project that provides water from Colorado River diversions from the western slope of

the Continental Divide to lands on the eastern slope. Lake Estes, located on the eastern slope, is

used as an afterbay for the Estes Powerplant and provides water for irrigation, recreation and

forebay storage for the Pole Hill Powerplant.

Olympus Dam, completed in 1948, is a composite structure consisting of a zoned earth

embankment whose dimensions are (fig. 2):

Hydraulic height1 45 feet

Top width 30 feet

Crest elevation 7,481.0 feet2

Structural height 70 feet

Crest length 1,951 feet

The spiliway is located in the center of the concrete gravity section of the dam with a crest

elevation of 7,460.0. The spillway flows are controlled by five 17- by 20-foot radial gates, with

a top elevation of 7,475.0, over an ogee-shaped overflow into a 120-foot wide stilling basin. The

spillway provides a maximum discharge of 21,200 cubic feet per second (cfs) at maximum

reservoir elevation 7,475.0.

A river outlet with a crest elevation of 7,450.25 is located in the concrete dam left of the

spiliway. The release from the river outlet is about 60 cfs through an 18-inch diameter pipe

controlled by a 2.5-foot square cast iron slidegate. A canal outlet work, with a crest elevation of

7,456.0, is located in the right side of the concrete dam. The canal outlet consists of a trashrack

with a fish screen protection intake structure that discharges up to 575 cfs into the 10.75-foot

diameter Olympus Siphon.

The drainage area above Olympus Dam is 158 square miles and for this study all is considered

sediment contributing. The lake is around 1.2 miles in length and around 0.2 miles in width.

1The definition of such terms as "hydraulic height," "structural height," etc. may be found in manuals such as

Reclamation's Design of Small Dams and Guide for Preparation of Standing Operating Procedures for Dams and

Reservoirs, or ASCE's Nomenclature for Hydraulics.

2Elevation levels are shown in feet. All elevations shown in this report are based on the original project datum

established by U.S. Bureau of Reclamation that is tied to the National Geodetic Vertical Datum of 1929.

1
SUMMARY AND CONCLUSIONS

This Reclamation report presents the 2001 results of the survey of Lake Estes. The primary

objectives of the survey were to gather data needed to:

• develop reservoir topography

• compute area-capacity relationships

• estimate storage depletion caused by sediment deposition since dam closure

A Real-time Kinematic (RTK) GPS control survey was conducted to establish a temporary

horizontal and vertical control point near the marina used for this reservoir survey. The

horizontal control was established in the Colorado north state plane coordinate zone in the North

American Datum of 1983 (NAD83). The RTK GPS control survey was conducted with the base

set on the National Geoldetic Survey (NGS) datum point "Collinson Az Mark" located near the

lake. All elevations in this report are referenced to the Reclamation project datum that is

assumed to be tied to the National Geodetic Vertical Datum of 1929 (NGVD29).

The underwater survey was conducted in August of 2001 between reservoir water surface

elevations 7,471.4 to 7,473.0. The bathymetric survey was run using sonic depth recording

equipment interfaced with a differential global positioning system (DGPS) capable of

determining sounding locations within the reservoir. The system continuously recorded depth

and horizontal coordinates of the survey boat as it was navigated along grid lines covering Lake

Estes. The positioning system provided information to allow the boat operator to maintain a

course along these grid lines. Water surface elevations recorded by the reservoir gauge (tied to

the Reclamation vertical datum) during the time of collection were used to convert the sonic

depth measurements to true reservoir bottom elevations. The above-water topography was

determined by digitizing the developed contour lines from the U.S. Geological Survey

quadrangle (USGS quad) maps of the reservoir area. The RTK GPS was used to collect water

surface data during the underwater collection along with a limited amount of above water

topography points. Due to the limited amount of above water data collected, the 2001 study

assumed no change since the original survey from elevation 7,470.0 and above.

The 2001 Lake Estes topographic map is a combination of the USGS quad contours and the

underwater and above water survey data. The 2001 reservoir surface areas at predetermined

contour intervals were generated by a computer graphics program using the collected reservoir

data. The 2001 area and capacity tables were produced by a computer program that uses

measured contour surface areas and a curve-fitting technique to compute area and capacity at

prescribed elevation increments (Bureau of Reclamation, 1985).

Tables 1 and 2 contain summaries of the Lake Estes sedimentation and watershed characteristics

for the 2001 survey. The 2001 survey determined that the reservoir has a total storage capacity of

2,783 acre-feet and a surface area of 185 acres at maximum reservoir elevation 7,475.0. Since

closure in November of 1948, the reservoir had an estimated volume change of 284 acre-feet

below reservoir elevation 7,470.0. This volume represents a 12.8 percent loss in total capacity

and an average annual loss of 5.4 acre-feet per year.
RESERVOIR OPERATIONS

Lake Estes is part of the Colorado-Big Thompson Project and operates as an afterbay for the

Estes Powerplant, along with providing water for irrigation, recreation, and forebay storage for

the Pole Hill Powerplant. The August 2001 capacity table shows 2,783 acre-feet of total storage

below the maximum water surface elevation 7,475.0. The 2001 survey measured a minimum

lake bottom elevation of 7,432.0. The following values are from the August 2001 capacity table:

• 2,470 acre-feet of conservation use between elevation 7,450.25 and 7,475.0.

• 313 acre-feet of inactive storage between elevation 7,432.0 and 7,450.25.

The Lake Estes inflow and end-of-month stage records in table 1, operation period 1977 through

2001, show the inflow and annual fluctuation for several readily available years of operation.

The estimated historical average inflow into the reservoir from the natural drainage basin was

92,480 acre-feet per year. For recreational purposes the normal operation of Lake Estes has

annual fluctuations between 7,469.5 and 7,474, but lower operations do occur as needed. The

maximum-recorded elevation was 7,474.6 on June 19, 1965.

HYDROGRAPHIC SURVEY EQUIPMENT AND METHOD

The hydrographic survey equipment, mounted on an 18-foot pontoon raft with an outboard

motor, consisted of a GPS receiver with a built-in radio and an omnidirectional antenna, a depth

sounder, a helmsman display for navigation, a computer, and hydrographic system software for

collecting underwater data. On-board batteries supplied power to the equipment.

The shore equipment included a second GPS receiver with an external radio and an

omnidirectional antenna. The GPS receiver and antenna were mounted on a survey tripod over a

known datum point. To obtain the maximum radio transmission range, known datum points with

clear line-of-sight to the survey boat were selected. A 12-volt battery provided the power for the

shore unit.

GPS Technology and Equipment

The hydrographic positioning system used at Lake Estes was Navigation Satellite Timing and

Ranging (NAVSTAR) GPS, an all-weather, radio-based, satellite navigation system that enables

users to accurately determine three-dimensional position. The NAVSTAR system's primary

mission is to provide passive global positioning and navigation for land-, air-, and sea-based

strategic and tactical forces and is operated and maintained by the Department of Defense

(DOD). The GPS receiver measures the distances between the satellites and itself and

determines the receiver's position from intersections of the multiple-range vectors. Distances are

determined by accurately measuring the time a signal pulse takes to travel from the satellite to the

receiver.

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The NAVSTAR system consists of three segments:

• The space segment is a network of 24 satellites maintained in a precise orbit about 10,900

nautical miles above the earth, each completing an orbit every 12 hours.

• The ground control segment tracks the satellites, determining their precise orbits.

Periodically, the ground control segment transmits correction and other system data to all

the satellites, and the data are then retransmitted to the user segment.

• The user segment includes the GPS receivers that measure the broadcasts from the

satellites and calculate the position of the receivers.

The GPS receivers use the satellites as reference points for triangulating their position on earth.

The position is calculated from distance measurements to the satellites that are determined by

how long a radio signal takes to reach the receiver from the satellite. To calculate the receiver's

position on earth, the satellite distance and the satellite's position in space are needed. The

satellites transmit signals to the GPS receivers for distance measurements along with the data

messages about their exact orbital location and operational status. The satellites transmit two "L"

band frequencies (called Li and L2) for the distance measurement signal. At least four satellite

observations are required to mathematically solve for the four unknown receiver parameters

(latitude, longitude, altitude, and time); the time unknown is caused by the clock error between

the expensive satellite atomic clocks and the imperfect clocks in the GPS receivers.

The GPS receiver's absolute position is not as accurate as it appears in theory because of the

function of range measurement precision and the geometric position of the satellites. Precision is

affected by several factors--time, because of the clock differences, and atmospheric delays caused

by the effect of the ionosphere on the radio signal. Geometric dilution of precision (GDOP)

describes the geometrical uncertainty and is a function of the relative geometry of the satellites

and the user. Generally, the closer together in angle two satellites are from the receiver, the

greater the GDOP. GDOP is broken into components: position dilution of precision (x,y,z)

(PDOP), and horizontal dilution of precision (x,y) (HDOP). The components are based only on

the geometry of the satellites. The PDOP and HDOP were monitored at the survey vessel's GPS

receiver during the Lake Estes Survey, and for the majority of the time they were less than 3,

which is within the acceptable limits of horizontal accuracy for Class 1 and 2 level surveys

(Corps of Engineers, 1994).

An additional and larger error source in GPS collection is caused by false signal projection called

selective availability (S/A). The DOD implements S/A to discourage the use of the satellite

system as a guidance tool by hostile forces. Positions determined by a single receiver when S/A

is active can have errors of up to 100 meters. in May of 2000 the use of S/A was discontinued,

but the errors of a single receiver are still around ±10 meters.

A method of collection to resolve or cancel the inherent errors of GPS is called differential GPS

(DGPS). DGPS is used during the reservoir survey to determine positions of the moving survey

vessel in real time. DGPS determines the position of one receiver in reference to another and is a

method of increasing position accuracies by eliminating or minimizing the uncertainties.

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Differential positioning is not concerned with the absolute position of each unit but with the

relative difference between the positions of two units, which are simultaneously observing the

same satellites. The inherent errors are mostly canceled because the satellite transmission is

essentially the same at both receivers.

At a known geographical benchmark, one GPS receiver is programmed with the known

coordinates and stationed over the geographical benchmark. This receiver, known as the master

or reference unit, remains over the known benchmark, monitors the movement of the satellites,

and calculates its apparent geographical position by direct reception from the satellites. The

inherent errors in the satellite position are determined relative to the master receiver's

programmed position and the necessary corrections or differences are transmitted to the mobile

GPS receiver on the survey vessel.

For the Lake Estes survey, position corrections were determined by the master receiver and

transmitted via an ultra-high frequency (UHF) radio link every second to the survey vessel

mobile receiver. The survey vessel's GPS receiver used the corrections along with the satellite

information it received to determine the vessel's differential location. Using DGPS can result in

sub-meter positional accuracies for the survey vessel.

The Sedimentation and River Hydraulics Group conducts their bathymetric surveys using RTK

GPS. The system employs two receivers, like with DGPS, and collects additional satellite data

that allows on-the-fly centimeter accuracy measurements. The major benefit of RTK versus

DGPS is that precise heights can be measured in real time for monitoring water surface elevation

changes. The basic outputs from an RTK receiver are precise 3D coordinates in latitude,

longitude, and height with accuracies on the order of 2 centimeters horizontally and 3 centimeters

vertically. The output is on the GPS datum of WGS-84, which the hydrographic collection

software converted into Colorado's NAD83 state plane north coordinate zone.

Survey Method and Equipment

The Lake Estes hydrographic survey collection was conducted from August 9 through August 12

of 2001 between water surface elevations 7,471.4 and 7,473.0 (Reclamation project datum). The

bathymetric survey was run using sonic depth recording equipment, interfaced with an RTK

GPS, capable of determining sounding locations within the reservoir. The survey system

software continuously recorded reservoir depths and horizontal coordinates as the survey boat

moved across closely-spaced grid lines covering the reservoir area. Most of the transects (grid

lines) were run somewhat in a north or south direction of the reservoir at a 100-foot spacing or

less. Data was also collected along the shore as the boat traversed between transects. The

survey vessel's guidance system gave directions to the boat operator to assist in maintaining the

course along these predetermined lines. During each run, the depth and position data were

recorded on the notebook computer hard drive for subsequent processing.

The 2001 underwater data were collected by a depth sounder that was calibrated by lowering a

weighted cable below the boat with beads marking known depths. The depth sounder was

calibrated by adjusting the speed of sound, which can vary with density, salinity, temperature,

turbidity, and other conditions. The collected data were digitally transmitted to the computer

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collection system via a RS-232 port. The depth sounder also produces an analog hard-copy chart

of the measured depths. These graphed analog charts were printed for all survey lines as the data

were collected and recorded by the computer. The charts were analyzed during post-processing,

and when the analog charted depths indicated a difference from the recorded computer bottom

depths, the computer data files were modified. The water surface elevations at the dam, recorded

by a Reclamation gauge, were used to convert the sonic depth measurements to true lake-bottom

elevations.

Lake Estes Datum

Prior to the underwater survey, a RTK GPS survey was conducted to establish a horizontal and

vertical control point near the marina of Lake Estes. The NGS control point "Collinson Az Mk"

located south of the dam was used as the base station for the control survey. This datum was

readily available and provided a first order horizontal accuracy that was needed for the boat

survey. There was no stated vertical accuracy on this NGS datum, but all vertical information for

this study is referenced to the reservoir water surface gauge measurements. The gauge is

referenced to the Reclamation project datum that is reported as tied to NGVD29. The RTK GPS

survey equipment was also used to collect a limited amount of above water data along the shore

of the lake, along the highway, and on top of the dam.

RESERVOIR AREA AND CAPACITY

Topography Development

The topography of Lake Estes was developed from the 2001 collected underwater and above

water data combined with digitized contours from the USGS quad maps. The digitized USGS

contour lines included the Lake Estes water surface labeled elevation 7468 and 7475 along with

contour lines 7480 and 7520 that surrounded the reservoir area. The USGS quad maps were

developed from aerial photography dated 1958 and photorevised from aerial photographs taken

in 1978. This study found several areas that had to be adjusted to enclose the 2001 underwater

data. ARC/INFO V7.0.2 geographic information system software was used to digitize the USGS

quad contours. The digitized contours were transformed to Colorado's NAD 1983 state plane

north zone coordinates using the ARC/INFO PROJECT command.

The elevation 7468 and 7475 contour lines that were digitized from USGS quad maps were used

to perform a clip of the Lake Estes triangular irregular network (TIN) such that interpolation was

not allowed to occur outside the enclosed polygon. The complete 7475 contour was selected

since it was the closest complete elevation to represent the reservoir water surface at the time the

survey was conducted, which was near reservoir elevation 7473. This clip was performed using

the hardc lip option of the ARC/INFO CREATET1N command. Using ARCEDIT, the

underwater collected data and digitized contours from the quad maps were plotted. The plot

showed that the underwater data did not lie completely within this clip, which required

modifications to include the entire underwater data set. Modified areas included the shoreline

near the marina towards the dam and the majority of the shoreline of the reservoir located south

of the highway. It is assumed these changes were due to construction around the marina and boat

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launch area and from shoreline erosion that has occurred since the 1950's. Using select and

move commands within ARCEDIT, the vertices of the clip were shifted to fit all the collected

underwater data. The clip was assigned an elevation of 7,471.0 to reflect the original area of the

developed polygons.

Contours for the reservoir below elevation 7,471.0 were computed from the underwater data set

using the triangular irregular network (TIN) surface-modeling package within ARC/INFO. A

TIN is a set of adjacent non-overlapping triangles computed from irregularly spaced points with

x,y coordinates and z values. TiN was designed to deal with continuous data such as elevations.

The TIN software uses a method known as Delaunay's criteria for triangulation where triangles

are formed among all data points within the polygon clip. The method requires that a circle

drawn through the three nodes of a triangle will contain no other point, meaning that sample

points are connected to their nearest neighbors to form triangles using all collected data. This

method preserves all collected survey points. Elevation contours are then interpolated along the

triangle elements. The TIN method is discussed in greater detail in the ARC/INFO V7.0.2 Users

Documentation, (ESRI, 1992).

The linear interpolation option of the ARC/INFO TINCONTOUR command was used to

interpolate contours from the Lake Estes TIN. In addition, the contours were generalized by

filtering out vertices along the contours. This generalization process improved the presentability

of the resulting contours by removing very small variations in the contour lines. This

generalization had no bearing on the computation of surface areas and volumes for Lake Estes

since the areas were calculated from the developed TIN. The areas of the enclosed contour

polygons at one-foot increments were developed from the survey data elevations 7,432.0 through

elevation 7,468.0. The 2001 study assumed no change in area since the original survey for

elevation 7,470.0 and above. The contour topography at 1-foot intervals is presented on figure 3.

Development of 2001 Contour Areas

The 2001 contour surface areas for Lake Estes were computed at 1-foot increments from

elevation 7,432.0 to 7,468.0. The 2001 underwater survey measured a minimum reservoir

bottom elevation of 7,432.0. These calculations were performed using the ARC/INFO

VOLUME command. This command computes areas at user-specified elevations directly from

the TIN and takes into consideration all regions of equal elevation. As indicated above, the 2001

underwater survey data was collected near reservoir elevation 7,473 and included limited amount

of above water data points. For the purpose of this study the measured 2001 survey areas at 1-

foot increments from elevation 7,432.0 through 7,468.0 were used to compute the new area and

capacity tables. Due to the limited amount of above water data, this study assumed no change in

original area from elevation 7,470.0 and above. The area and capacity program computed the

areas between elevation 7,468.0 and 7,470.0 by assuming a straight-line interpolation.

2001 Storage Capacity

The storage-elevation relationships based on the measured surface areas were developed using

the area-capacity computer program ACAP85 (Bureau of Reclamation, 1985). The 2001

surveyed surface areas at 1-foot contour intervals from reservoir elevation 7,432.0 to elevation

7
7,468.0 were used as the control parameters for computing the 2001 Lake Estes capacity. Since

this study did not collect adequate above water data, the original 1-foot surface areas from

elevation 7,470.0 to 7,475.0 were used to complete the area and capacity table. The program can

compute an area and capacity at elevation increments 0.01- to 1.0-foot by linear interpolation

between the given contour surface areas. The program begins by testing the initial capacity

equation over successive intervals to ensure that the equation fits within an allowable error limit.

The error limit was set at 0.00000 1 for Lake Estes. The capacity equation is then used over the

full range of intervals fitting within this allowable error limit. For the first interval at which the

initial allowable error limit is exceeded, a new capacity equation (integrated from basic area

curve over that interval) is utilized until it exceeds the error limit. Thus, the capacity curve is

defined by a series of curves, each fitting a certain region of data. Differentiating the capacity

equations, which are of second order polynomial form, derives final area equations:

y = a1 + a2x + a3x2

where: y = capacity

x = elevation above a reference base

a1 = intercept

a2 and a3 coefficients

Results of the 2001 Lake Estes area and capacity computations are listed in table 1 and columns

4 and 5 of table 2. On table 2, columns 2 and 3 list the original surface areas and recomputed

original capacities. A separate set of 2001 area and capacity tables has been published for the

0.01, 0.1 and 1-foot elevation increments (Bureau of Reclamation 2001). A description of the

computations and coefficients output from the ACAP85 program is included with these tables.

Both the original and 2001 area-capacity curves are plotted on figure 4. As of August 2001, at

elevation 7,475.0, the surface area was 185 acres with a total capacity of 2,783 acre-feet.

RESERVOIR SEDIMENT ANALYSES

Figure 4 is a plot of Lake Estes original surface area and capacity versus the 2001 measured

surface area and capacity that illustrates the differences between the two. Since Olympus Dam

closure in 1948, the measured total volume change at reservoir elevation 7,470.0 was estimated

to be 284 acre-feet. The estimated average annual rate of capacity lost for this time period (52.8

years) was 5.4 acre-feet per year. The storage loss in terms of percent of original storage capacity

was 12.8 percent at elevation 7,470.0. All sediment computations are based on elevation 7,470.0

due to the lack of 2001 survey data above this elevation. Tables 1 and 2 contain the Lake Estes

sediment accumulation and water storage data based on the 2001 resurvey. Section 26 of table 1

shows that 66.2 percent of the measured sediment has deposited between the conservation

storage elevations of 7,450.25 to 7,470.0 and 33.8 percent has deposited in the inactive zone

below elevation 7,450.25.

The original estimated sediment inflow used during the design of Lake Estes was an annual

contribution of 15.5 acre-feet that would result in around 50 percent of reservoir storage space

bemg depleted after the first 100 years of operation. The 2001 study determined an annual rate

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of 5.4 acre-feet or a total capacity lost of 284 acre-feet after the first 52.8 years of reservoir

operation. It must be noted that the 2001 area and capacity tables were generated assuming no

change in original area and capacity from elevation 7,470.0 and above which in all probability is

not the case. It must also be noted that the original estimate was generated with the best

information available at the time of the design with a reservoir survey being the best means to

determine actual sediment inflow.

Since the closure of Olympus Dam in November of 1948 there have been several events that

have affected the sediment inflows into Lake Estes. On May 25 of 1951 the Lily Lake dike broke

which was located on the headwaters of Fish Creek about 5.5 miles upstream of Lake Estes. The

dike was only around 5 to 6 feet high, but from investigation memorandums it appears a large

amount of debris was carried downstream that eventually emptied into Lake Estes. During the

Big Thompson Flood of 1976 no major sediment inflow into the lake was noted since the

majority of the rain fell downstream in Big Thompson Canyon between Estes Park and Loveland.

During this 1976 flood event there was a large amount of debris, cobbles, and boulders

deposited in the spiliway-stilling basin below the dam as a result of a large flood flow from Dry

Creek. On July 15, 1982 Lawn Lake and Cascade Lake Dams, located on the Falls River, failed

causing extensive damage as the flood flowed through Estes Park and eventually into Lake Estes

(USGS 1986). There were no accurate measurements of the sediment and debris deposited in

Lake Estes from this flood, but following the flood Reclamation did conduct debris and sediment

removal operations from the Lake Estes area. It was also reported that a large volume of

sediment was deposited the following year during a 1983 high spring snowmelt flood with the

main source of the sediment material being exposed riverbanks from the 1982 flood.

A resurvey of Lake Estes should be considered in the future if major sediment inflow events are

observed or if the average annual rate of sediment accumulation requires further clarification.

An above water survey should be conducted if better information is needed for elevation 7,470.0

and above.

9
REFERENCES

American Society of Civil Engineers, 1962. Nomenclature for Hydraulics, ASCE Headquarters,

New York.

Bureau of Reclamation, 1981. Project Data, Denver Office, Denver CO.

Bureau of Reclamation, 1985. Surface Water Branch, ACAP85 User's Manual, Technical

Service Center, Denver CO.

Bureau of Reclamation, 1987(a). Guide for Preparation of Standing Operating Procedures for

Bureau of Reclamation Dams and Reservoirs, U.S. Government Printing Office, Denver, CO.

Bureau of Reclamation, 1987(b). Design of Small Dams, U.S. Government Printing Office,

Denver CO.

Bureau of Reclamation, August 2001. Denver Office, Lake Estes Area and Capacity Tables,

Colorado - Big Thompson Project, Great Plains Region, Billings, MT.

Corps of Engineers, January 2002. Engineer and Design - Hydrographic Surveying,

EM 1110-2-1003, Department of the Amiy, Washington DC,

(www.usace.army.millinetlusace-docs/eng-manuals/em 1110-2-1 003/toc.htm).

Environmental Systems Research Institute , Inc. (ESRI), 1992. ARC Command Referen ces.

U.S. Geological Survey, 1986, Professional Paper 1,369, Hydrology, Geomorphology, and

Dam-Break Modeling of the July 15, 1982 Lawn Lake Dam and Cascade Lake Dam Failures,

Larimer County, Colorado, U.S. Government Printing Office, Washington.

10
RESERVOIR SEDIMENT

Lake Estes

1

DATA SMY

MANE OF RESERVOIR

DATA SHEET NO.

D 1. OWNER Bureau of ReclamatiOn 2. STREAM Big Thompson River 3. STATE Colorado

A 4. SEC. 29 TWP. 5 N RANGE 72 W 5. NEAREST P.O. Estee 6. COUNTY Lancer

M 7. LAT 40 22' 31" LONG l05 29' 19" 8. TOP OF DAM ELEVATION 7481.0 9. SPILLWAY CREST EL 7,460,0'

R 10. STORAGE 11. ELEVATION 12. ORIGINAL 13. ORIGINAL 14. GROSS STORAGE 15. DATE

E ALLOCATION TOP OF POOL SURFACE AREA, AC CAPACITY, AR ACRE- FEET STORAGE

S BEGAN

E

R a. SURCHARGE

V b. FLOOD CONTROL

________________ _________________ 11/48 0

I

C POWER

R d JOINT USE 16. DATE

a. CONSERVATION 7475.0 185 2,659 3,068 NORMAL

OPERATION

f. INACTIVE 7450.25 409 409 BEGAN

g. DEAD 11/48

-

17. LENGTH OF RESERVOIR 1.2 MILES AVG. WIDTH OF RESERVOIR 0.2 MILES

B 18. TOTAL DRAINAGE AREA 158 SQUARE MILES 22. MEAN ANNUAL PRECIPITATION 152 INCHES

19. NET SEDIMENT CONTRIBUTING AREA 158 SQUARE 23. MEAN ANNUAL RUNOFF il.04 INCHES

20. LENGTH MILES AV . WIDTH MILES 24. MEAN ANNUAL RUNOFF 92,480 ACRE-FEET

N 21. MAX. ELEVATION MIN. ELEVATION 25. ANNUAL TEMP. MEAN 48F RANGE -41F to l02F'

S 26. DATE OF 27. 28. 29. TYPE OF 30. NO. OF 31. SURFACE 32. CAPACITY 33. C/I

U SURVEY PER. ACCL. SURVEY RANGES OR AREA, AC. ACRE-FEET RATIO AF/AF

R YRS. YES. INTERVAL

V 11/48 Contour (D) 5-ft 1850 3,068' .02

E

Y

D 8/01 52.8 52.8 Contour (D) 1-ft 185 2,783 .02

A

26. DATE OF 34. PERIOD 35. PERIOD MATER INFLOW, ACRE FEET WATER INFLOW TO DATE, AF

T

SURVEY ANNUAL _______________________________ A PRECIP. a. MEAN ANN. b. MAX. ANN. . TOTAL a. MEAN ANN. b. TOTAL

8/01 92,480 136,300 92,480

26. DATE OF 37. PERIOD CAPACITY LOSS, ACRE-FEET 38. TOTAL SEDIMENT DEPOSITS TO DATE, AF

SURVEY __________________________________________________

a. TOTAL b. AV. ANN. C. /MI.'-YR. a. TOTAL b. AV. ANNUAL C. /MI.'-YR.

8/01 284 5.4 0.034 284 5.4 0.034

26. DATE OF 39. AV. DRY 40. SED. DEP. TONS/MI.'-YR. 41. STORAGE LOSS, PUT. 42. SEDIMENT

SURVEY MT. (#/FT') _______________ _____________________________________________

a. PERIOD

______________

b. TOTAL TO a. AV. b. TOTAL TO a. b.

8/01 0.2410 12.810

26.

DATE

43. DEPTH DESIGNATION RANGE BY RESERVOIR ELEVATION

OF

SURVEY

7525-

7435

7435-

7445

7445-

7450.2

7450.2

-7455

7455-

7460

7460-

7465

7465-

7470

PERCENT OF TOTAL SEDIMENT LOCATED WITHIN DEPTH DESIGNATION

11.3 10.9 11.6 11.6 18.3 19.8 16.5

26. 44. REACH DESIGNATION PERCENT OF TOTAL ORIGINAL LENGTH OF RESERVOIR

DATE

SURVEY

0-10 10-

20

20-

30

30-

40

40-

50

50-

60

60-

70

70-

80

80-

90

90-

100

100-

105

105-

110

110-

115

115-

120

120-

125

PERCENT OF TOTAL SEDIMENT LOCATED WITHIN REACH DESIGNATION

Table 1. - Reservoir sediment data summary (page 1 of 2).

11
45. RANGE IN RESERVOIR OPERATION8

YEAR MAX. ELEV. MIN. ELEV. INFLOW, AF YEAR MAX. ELEV. MIN. ELEV. INFLOW, AF

1977 7,473.8 7,467.9

1978 7,474.1 7,468.2 114,200 1979 7,474.1 7,468.0 114,100

1980 7,474.0 7,469.4 121,900 1981 7,474.0 7,469.7 56,000

1982 7,473.9 7,464.9 89,900 1983 7,473.9 7,469.7 133,600

1984 7,474.1 7,468.4 112,600 1985 7,474.2 7,470.6 87,700

1986 7,474.4 7,469.8 113,200 1987 7,473.9 7,469.7 73,100

1988 7,473.9 7,470.3 72,300 1989 7,474.0 7,470.1 61,400

1990 7,473.9 7459.8 88,700 1991 7,474.0 7,470.2 80700

1992 7,473.8 7,463.3 71,600 1993 7,474.0 7,469.5 101,500

1994 7,474.2 7,469.9 76,400 1995 7,473.7 7,469.7 133,300

1996 7,473.6 7,470.0 108,200 1997 7,473.4 7,460.1 136,300

1998 7,473.8 7,460.1 107,400 1999 7,473.5 7,461.2 120,100

7000 ______________ 77.200 7001 7.000

46. ELEVATION - AREA - CAPACITY DATA FOR 2001 CAPACITY1'

ELEVATION AREA CAPACITY ELEVATION AREA CAPACITY ELEVATION AREA CAPACITY

7,432 0 0 7,435 7 11 7,440 14 65

7,445 22 155 7,450 38 304 7,450.25 39 313

7,455 58 546 7,460 73 874 7,465 102 1,313

7,470 156 1,936 7,475 185 2,783

47. REMARKS AND REFERENCES

1

Controlled by five radial gates with top elevation of 7,475.0 .

2

Bureau of Reclarsaton Project Data Book, 1981. Values for Co lorado Big Thompson Project.

Natural drainage area above the dam is 158 square miles. Val ue does not include diversions from Colorado River

and sediment control by upstream darns.

Calculated using mean annual runoff value of 92,480 AR, item 24, 1936-2001.

Historical annual average for natural drainage above dam for water years 1936 through 20001 . Does not include

Colorado River diverted flows.

Original surface area and capacity at elevation 7,475.0. For sediment computation purposes the original capacity

was recomputed by the Reclamation ACAP program using the ori ginal surface areas.

Surface area & capacity at elevation 7,475.0 computed by ACAP program.

Inflow values in acre-feet and maximum and minimum elevations in feet by water year for read ily available years,

1978 through 2001. The historical inflow average for water years 1936 through 2001 is 92,480 AF. Normal

operation of the reservoir is between elevation 7469.5 through 7 474. Maximum pool elevation was 7,474.6 on

June 19, 1965. Inflow values does not include diverted Colorado River flows.

Computed sediment volume at elevation 7,470.0. 2001 study assumed no change from elevation 7,470.0 and above due

to lack of above water survey data.

10 Storage losses at elevation 7,470.0.

Capacities computed by Reclamation's ACAP computer program.

48. AGENCY MAKING SURVEY Bureau of Reclamation

49. AGENCY SUPPLYING DATA Bureau of Reclamation DATE January 2003

Table 1. - Reservoir sediment data summary (page 2 of 2).

12
1 2 3 4 5 6 7 8

- t

- -

4 - -

2001 2001 Percent of

Elevations Original

-______ _____ -

Original 2001 2001 Sediment Percent of Reservoir

Survey Capacity Survey Survey Volume Sediment Depth

(feet) (acres)

- - 1

(acre-feet) (acres) (acre-feet)

- -__

(acre-feet)

__

7,475.0 l85 3068 1852783 1O0.o

7,474.0 177k 2887 177k 2602 98.0

7,473.0 l72 2712 172 2428 96.0

7,472.0 166 2543 166 , 2259 94.0

7 471 0 l62 2379 162 L

209 920

7,470.0

-

7,465.0

7,460.0

156

t

112

-

86

2220 156

-

1550 102

105 73

f l936

-

1313

- 874

284 100.0

+

________

237[ 83.5

L

i81 637

90.0

80.0

L70•°

7,45S.0 66 675j

-

546 129 45.4 9

7,450.2J

7,450.0

46

45

409 39

398

3l3

-.

304

_____

96 33.8

.. ----- -

1

94 33.1

50.5

___

50.0

7,44S. 27 221 155 63 22.2 40.0

7,440.Oj ______ 16 110 14 __________ 65 4 15.8 30.0

7,435.0 11 43 7 11 32 11.3 20.0

1

1

_ _

-

------H __ __

_

_

__

1 J

-

2

!levationof reservoir water surface.

Original reservoir surface area. j

-

I ----- -

3

4

Original reservoir_capacity recomputed using ACAP

Reservoir surface area from 2001 survey.

.

_____ -

5 Reservoir capacity computed using ACAP.

- ________ -

6 Measured sediment volume column (3) - column (5 ).

7 Measured sediment expressed in percentage of total sediment 284.

8 Depth of reservoir expressed in percentage of total depth of 50 feet.

Table 2. - Summary of 2001 survey results

13
-NORTI4 POUORE

SUPPLY CANAL

i7

LA

TsIoNoAM T/D50R TENS ION

POUDHE SUPPLY CANAL

CHARLES HANSEN

CANAL

SOLDIER CANYON DAM

HORSETOOTH

AM------ Fort

Collins SATANKA-IE

-----

i

(S

rn

(A

CD

(A

0

Krem

0..

POWER

PLANT

UNIVtL POLE HILL TUNNEL

US5I±ON /J FLATIRON

OLYMPUS dAM)T AFTER8AY1

LAKE ESTES

POWERPLANT

COH

\O,E5TES/

ILL

__.. RE5SU8( TUNNEL I'\ \

\\ EAST

RESERVOIR ) Grand

0J\ 1'

MARYS LAKE

MARYS LAKE

L- CREEK \

POWERPLANT,-'1---

SHADOW MOUNTAIN

LAKE Lake S?4V RAMS HORN JPOLE

CANAL '-'

TUNNE>,_

\c GRAN8Y PUMP *

'Lonqs

\ CANALSHADOW MOU

J NorM St Vr

GRANBY PUMPING-' DAM RATTLESNAKE

PLANT TUNNEL

WILLOW WILtOW CREEK A

DAM CREEK RESERVOIR GRA N8Y WILLOW CREEK

PUMPING PLANT

'\GRANBY'?

- .1

BOULDER CREEK

UPPLY CANALGranby DAM

DAM

GREEN MOUN AIN

RESERVOIR

\ ) MOUNTAIN

SOUL DER

RESER VOIR

Boulder

EXPLANATION

._.._-.-- CANAL

TUNNEL

S.- ( SIPHON

• P04-ER PLANT

o PUMPINU PLANT

DI'X N CANYON DAM

SPRING -

CANYON T.

DAM '

'HOROE TOOTH

RESERVOIR BIG THOMPSON

CHARLES HANSEN POWERPLANT

FEEDER CANAL

BIG THOMPSON SIPH N

BIG THOMPSON 0/VERSION STRUCTURE AND

7'4

Loveland TUNNEL No.1 Greeley

LFLATIRON POWER AND

PIJNIINGPL ANT

PRESSURE TUNNEL

CARTER LAKE

BALD MOUNTAIN CT'-

PRESSUREr NELTTL

sCARTER LAKE ST. VRAIN

SUPPLY CANAL

RATTLESNAKE DAM AND 5-

PINE WOOD LAKE

0Longmont

CTee1 4,

SOUTH PLATTE

SUPPLY CANAL

'-4-

COAL RIDGE trestone WASTE LAKE

CrCt

Erie

S 0 5 0

SCALE OF MILES

OEN
Space intentionally left blank due to security concerns 
17
Area-Capacity Curves for Lake Estes

Area (acre)

200 180 160 140 120 100 80

7,475.0

7,465.0

1 _

.!7,455.0

C)

7,445.0

7,435.0

0

7 A7 (

60 40 20

7,425.0

0

Area

H

2001 Survey

Original Survey

(,' u._)

7,465.0

7,455.0

7,445.0

7,435.0

7,425.0

320 640 960 1280 1600 1920 2240 2560 2880 3200

Capacity (acre-feet)