PILOT BUTTE RESERVOIR

1995 SEDIMENTATION SURVEY

1fr FOR THE p

U.S. Department of the Interior

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

July 1996 Final

____________________________

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Pilot Butte Reservoir

1995 Sedimentation Survey PR

6. AUTHOR(S)

Ronald L. Ferrari

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

Bureau of Reclamation REPORT NUMBER

Technical Service Center

Denver CO 80225

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

Bureau of Reclamation AGENCY REPORT NUMBER

Denver Federal Center DIBR

P0 Box 25007

Denver CO 80225-0007

11. SUPPLEMENTARY NOTES

Hard copy available at the Technical Service Center, Denver, Colorado

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Available from the National Technical Information Service,

Operations Division, 5285 Port Royal Road, Springfield, Virginia 22161

13. ABSTRACT (Maximum 200 words)

The Bureau of Reclamation surveyed the underwater area of Pilot Butte Reservoir on June 29, 1995, to compile

field data for developing a topographic map and computing a present storage-elevation relationship (areacapacity tables). The data were also used to calculate the volume of reservoir capacity lost because of sediment

accumulation since dam closure in December 1926. The bathymetric survey used sonic depth recording

equipment interfaced with a GPS (global positioning system) that gave continuous sounding positions throughout

the reservoir. The underwater topography was developed by a computer graphics program using the collected

data. The above-water topography was determined by digitizing contour lines from the USGS quad (United

States Geological Survey quadrangle) map of the reservoir area. The USGS quad was developed from aerial

photography obtained in 1948 and photorevised in 1978. The new topographic map of Pilot Butte Reservoir is a

combination of the digitized contours and the 1995 underwater measured topography.

As of June 29, 1995, at top of active conservation elevation (ft) 5,460.0, the surface area was 901 acres with a

total capacity of 33,721 acre-feet and an active capacity of 29,918 acre-feet. Since initial filling in December

1926, about 3,853 acre-feet of sediment have accumulated in Pilot Butte Reservoir, resulting in a 10.2-percent

loss in reservoir volume. Since 1926, the average annual rate of reservoir capacity lost because of sediment

accumulation is 56.2 acre-feet.

14. SUBJECT TERMS- -reservoir area and capacity! sedimentation! reservoir surveys! 15. NUMBER OF PAGES

sonar! sediment distribution! contour area! reservoir area! sedimentation survey! 17

16. PRICE CODE

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

OF REPORT OF THIS PAGE OF ABSTRACT

UL UL UL UL

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

Prescribed by ANSI Std. 239-18

298-102
PILOT BUTTE RESERVOIR

1995 SEDIMENTATION SURVEY

by

Ronald L. Ferrari

Sedimentation and River Hydraulics Group

Water Resources Services

Technical Service Center

Denver, Colorado

July 1996
ACKNOWLEDGMENTS

The Bureau of Reclamation's Sedimentation and River Hydraulics

Group of the TSC (Technical Service Center) prepared and

published this report. Ronald Ferrari and James Melena of the

TSC conducted the hydrographic survey. Ronald Ferrari

completed the data processing needed to generate the new

topographic map and area-capacity tables. Paul Weghorst of the

TSC developed the procedures for generating the new topographic

maps and computing the surface areas. Sharon Nuanes of the

TSC completed the USGS contour digitizing and was consulted

during the map development. James Melena performed the

technical peer review of this documentation.

U.S. Department of the Interior

Mission Statement

As the Nation's principal conservation agency, the Department of the

Interior has responsibility for most of our nationally-owned public lands

and natural resources. This includes fostering sound use of our land

and water resources; protecting our fish, wildlife, and biological

diversity; preserving the environmental and cultural values of our

national parks and historical places; and providing for the enjoyment of

life through outdoor recreation. The Department assesses our energy

and mineral resources and works to ensure that their development is in

the best interests of all our people by encouraging stewardship and

citizen participation in their care. The Department also has a major

responsibility for American Indian reservation communities and for

people who live in island territories under U.S. administration.

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 the Bureau of 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.

11
CONTENTS

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Page

Introduction 1

Summary and conclusions 2

Reservoir operations 2

Hydrographic survey equipment and method 3

GPS technology and equipment 3

Survey method and equipment 5

Reservoir area and capacity 6

Topography development 6

Development of 1995 contour areas 7

1995 storage capacity 7

Reservoir sediment analyses 8

References 8

Table

TABLES

1 Reservoir sediment data summary (page 1 of 2) 9

1 Reservoir sediment data summary (page 2 of 2) 10

2 Summary of 1995 survey results 11

Figure

FIGURES

1 Pilot Butte Reservoir location map 12

2 Pilot Butte Dam, plan and section 13

3 Pilot Butte Reservoir topographic map 15

4 1995 area and capacity curves 17

in
INTRODUCTION

Pilot Butte Dam, Reservoir, and Powerplant are features of the Riverton Unit of the Pick-Sloan

Missouri Basin Program. Additional major Riverton Unit features are Bull Lake Dam, Pilot

Butte Powerplant, and the Wind River Diversion Dam. Pilot Butte Dam, located in Fremont

County of west-central Wyoming, is located near the town of Morton in the Wind River Valley

about 22 miles northwest of Riverton, Wyoming (fig. 1).

Pilot Butte is an off-channel reservoir and obtains Wind River water through the Wyoming

Canal diverted by the Wind River Diversion Dam. The drainage area above the dam is 8.5

square miles ranging from elevation (ft) 5,410, top of inactive pool, to elevation 5,988 at one

point along the northeast boundary. The Wyoming Canal traverses the basin, crossing just

above the reservoir and separating the drainage into two areas. The larger area, above the

canal, is 5.8 square miles; and the smaller area, surrounding the reservoir, is 2.7 square miles,

1.4 square miles of which is covered by the reservoir. The reservoir's original total capacity

was reported as 36,900 acre-feet at reservoir elevation 5460.0 (Bureau of Reclamation, 1981).

Pilot Butte Dam was constructed between 1922 through 1926, and storage began in December

1926. The reservoir is formed by three zoned earthfill dike embankments (fig. 2) whose

dimensions are:

Embankments

No.1 No.2 No.3

Hydraulic height* offstream offstream offstream

Structural height (ft) 51 25 12

Top width(ft) 19.4 26 12

Crest length (ft) 1,300 1,200 3,400

Crest elevation(ft) 5469.5 5469.5 5467.0

Pilot Butte Dam is equipped with an uncontrolled, concrete-lined, open channel spiliway which

has a capacity of 500 cubic feet per second at maximum water surface elevation 5,461.3. The

spiliway, located in the right abutment of the main embankment, has a crest length of 100 feet

with a crest elevation of 5,460.0. The outlet works is a concrete conduit through the foundation

near the center of the main embankment controlled by three 4.8- by 6-foot slide gates. The

capacity is 1,000 cubic feet per second at elevation 5,460.0.

Pilot Butte Powerplant is located at the drop from the Wyoming Canal into Pilot Butte

Reservoir. The capacity is 1,600 kilowatts developed by two 800-kilowatt units operating at

a maximum head of 105 feet.

* The definition of terms such as structural height," "hydraulic 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.
SUMMARY AND CONCLUSIONS

This Reclamation (Bureau of Reclamation) report presents the 1995 results of the first

extensive survey of Pilot Butte Reservoir. The primary objectives of the survey were to gather

data needed to:

• develop underwater topography

• compute area-capacity relationships

• estimate storage depletion caused by sediment deposition since closure of Pilot Butte Dam.

The bathymetric survey was run using sonic depth recording equipment interfaced with a

DGPS (differential global positioning system) capable of determining sounding locations within

the reservoir. The system continuously recorded depth and horizontal coordinates as the

survey boat was navigated along close spaced grid lines covering the reservoir area. The

positioning system provided information to allow the boat operator to maintain course along

these grid lines. Water surface elevations recorded by a Reclamation gage during the time of

collection were used to convert the sonic depth measurements to true reservoir bottom

elevations.

The 1995 underwater surface areas at predetermined 2-foot contour intervals were generated

by a computer program using the collected data. The above-water reservoir areas were

measured from the digitized USGS quad (U.S. Geological Survey 7.5-minute quadrangle) map

of Pilot Butte Reservoir. The new topographic map of Pilot Butte Reservoir is a combination

of the digitized and underwater measured topography (fig. 3). The area and capacity tables

were produced by a computer program that uses measured contour surface areas and a curvefitting technique to compute area and capacity at prescribed elevation increments.

Table 1 contains a summary of the Pilot Butte Reservoir watershed characteristics for the 1995

survey. The 1995 survey determined that the reservoir has a storage capacity of 33,721 acrefeet and a surface area of 901 acres at reservoir elevation (ft) 5,460.0. Since closure in 1926,

the reservoir has accumulated a sediment volume of 3,853 acre-feet below reservoir elevation

5,460.0. This volume represents a 10.2-percent loss in capacity and an average annual loss of

56.2 acre-feet.

RESERVOIR OPERATIONS

The reservoir is primarily an irrigation facility with surcharge storage (the following valueS

from June 1995 area-capacity tables):

• 1,271 acre-feet of surcharge storage between elevations 5,460.0 and 5,461.4.

• 29,918 acre-feet of active conservation storage between elevations 5,410.0 and 5,460.0.

• 665 acre-feet of inactive storage between elevations 5,407.5 and 5,410.0.

• 3,138 acre-feet of dead storage below elevation 5,407.5.

Pilot Butte Reservoir is an off-channel reservoir that receives its inflow from Wind River

diversions into the Wyoming Canal. A structure in the Wyoming Canal permits flow to

continue down the Wyoming Canal to an open channel into Pilot Butte Reservoir or into the

2
penstock of the Pilot Butte Powerplant. Available records for years 1950 through June 1995

show that the average inflow into the reservoir was 212,761 acre-feet per year. The inflow and

end-of-month stage records in table 1 show the extreme annual fluctuation of the reservoir.

The available records show Pilot Butte Reservoir operation ranging from elevation 5,410.0 in

1965 to maximum elevation of 5,459.4 in 1977 and 1989.

HYDROGRAPHIC SURVEY EQUIPMENT AND METHOD

The hydrographic survey equipment was mounted in the cabin of a 24-foot tn-hull aluminum

vessel equipped with twin in-board motors. The hydrographic system contained on the survey

vessel consisted of a GPS (global positioning system) receiver with a built-in radio and

omnidirectional antenna, a dual frequency depth sounder, a helmsman display for navigation,

a plotter, a computer, and hydrographic system software for collecting the underwater data.

Power to the equipment was supplied by an on-board generator.

The shore equipment included a second GPS receiver with a built-in radio and an

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

over a known datum point. The power for the shore units was provided by a 12-volt battery.

GPS Technology and Equipment

The positioning system used at Pilot Butte Reservoir was NAVSTAR (NAVigation Satellite

Timing and Ranging) 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 DOD (Department

of Defense). 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.

The NAVSTAR system consists of three segments:

• The space segment is a network of 24 satellites that is maintained in precise orbits, 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, which are then retransmitted to the user segment.

The user segment is the GPS receivers, which 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 for the distance measurement signal

3
called Li and L2. 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. For hydrographic surveying the altitude, Pilot Butte's

water surface elevation parameter was known, which realistically meant only three satellite

observations were needed to track the survey vessel. During the Pilot Butte Reservoir survey,

the best six available satellites were used for position calculations.

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

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

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

caused by the effect on the radio signal by the ionosphere. GDOP (geometric dilution of

precision) describes the geometric 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: PDOP is position dilution

of precision (x,y,z), and HDOP is horizontal dilution of precision (x,y). The components are

based only on the geometry of the satellites. The PDOP and HDOP were monitored during the

Pilot Butte Reservoir Survey, and for the majority of the time they were less than 3, which is

within the acceptable limits of horizontal accuracy for Class i and 2 level surveys.

An additional and larger error source of GPS collection is caused by false signal projection,

called S/A (selective availability). 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 iOO meters.

A method of collection to resolve or cancel the inherent errors of GPS (satellite position or S/A,

clock differences, atmospheric delay, etc.) is called DGPS (differential GPS). DGPS was used

during the Pilot Butte 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.

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 Pilot Butte Reservoir, position

corrections were determined by the master receiver and transmitted via a UHF (ultra-high

frequency) radio link every 3 seconds 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 resulted in positional accuracies of 1 to 2 meters

for the moving vessel compared to positional accuracies of 100 meters with a single receiver.

The TSC (Technical Service Center) mobile and reference GPS units are identical in

construction and consist of a 6-channel Li C/A code continuous parallel tracking receiver, an
internal modem, and a UHF radio transceiver. The differential corrections from the reference

station to the mobile station are transmitted using the industry standard RTCM (Radio

Technical Commission for Maritime Services) message protocol via the UHF radio link. The

programming to the mobile or reference GPS unit is accomplished by entering necessary

information via a notebook computer. The TSC's GPS system has the capability of establishing

or confirming the land base control points by using notebook computers for logging data and

post-processing software. The GPS collection system has the capability of collecting the data

in 1927 or 1983 NAD (North American Datums) in the surveyed area's state plane coordinate

system zone. For Pilot Butte Reservoir, the collected data were in Wyoming's 1927 NAD west

central state plane zone.

Survey Method and Equipment

The Pilot Butte Reservoir hydrographic survey collection took 1 day and was conducted on

June 29, 1995, at water surface elevation 5,454.0. The bathymetric survey was run using sonic

depth recording equipment interfaced with a DGPS 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 close-spaced grid lines covering the

reservoir area. The majority of the transects were run in a mostly north-south direction. Data

were also collected along the shore as the boat traversed to the next transect. Transects were

also run in a mostly east-west direction to provide additional data for complete contour

development. The survey vessel's guidance system gave directions to the boat operator to

assist in maintaining course along these predetermined grid lines. During each run, the depth

and position data were recorded on the notebook computer hard drive for subsequent

processing by TSC personnel. The underwater data set includes about 8,661 data points. A

graph plotter was used in the field to track the boat and ensure adequate coverage during the

eollection process. The water surface elevation recorded by a Reclamation gage during the time

of collection was used to convert the sonic depth measurements to true lake bottom elevations.

The hydrographic survey crew used a benchmark as the control point for the shore station site

that was previously verified by personnel from Reclamation's Cody Office. The shore unit was

set over a Reclamation 4-inch brass cap marked CSSA, which is located at the north shore of

the reservoir. This point was selected because it had known coordinates, was accessible, was

located near the reservoir, and was on a hill overlooking the reservoir. The location allowed

fpr good radio transmission from the known reference survey point to the mobile survey vessel

throughout the reservoir. During post processing of the collected data, all points without

differential correction were removed.

Prior to data collection, the depth sounder was calibrated by lowering a deflector plate below

the boat by cables with known depths marked by beads. The depth sounder was calibrated by

adjusting the speed ofsound, which can vary with density, salinity, temperature, turbidity, and

other conditions. The collected data were digitally transmitted to the computer collection

system via an 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.

5
RESERVOIR AREA AND CAPACITY

Topography Development

The topography of Pilot Butte Reservoir was developed from collected underwater data and

from a USGS quad (USGS 7.5-minute quadrangle map). The upper contours of Pilot Butte

Reservoir were developed by digitizing the reservoir water surface contour line from the USGS

quad map that covered the Pilot Butte Reservoir area. The measured surface area of this

contour was 836 acres. This measured surface area compares to the original reservoir water

surface elevation of 5,454.0 feet. In the 1995 study, the USGS Pilot Butte Reservoir water

surface contour was assumed to be elevation 5,454.0. The USGS quad map was dated 1959

and was photorevised in 1978. ARC/INFO V7.0.2 geographic information system software was

used to digitize the USGS quad contours. The digitized contours were transformed to

Wyoming's NAD 1927 west central state plane coordinates using the ARC/INFO PROJECT

command.

Contours for elevations below 5,454.0 feet were computed from collected underwater data using

the TIN (triangular irregular network) surface modeling package within ARC/INFO. The

underwater survey data were collected in the Wyoming west central zone state plane

coordinates in NAD 1927. The collected underwater data ranged in elevation from 5,386.6 to

5,450.6 feet. 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 know as Delaunay's criteria for triangulation. Triangles are

formed between all data points including all boundary points. This method preserves all

collected survey points. The method requires that a circle d.rawn through the three nodes of

a triangle will contain no other point. This requirement means that sample points are

connected to their nearest neighbors to form triangles. Elevation contours are then

interpolated along the triangle elements. The TIN method is discussed in great detail in the

ARC/INFO V7.0.2 user documentation.

The elevation 5,454.0-foot contour that was digitized from the USGS quad map was used to

perform a clip of the Pilot Butte Reservoir TIN such that interpolation was not allowed to occur

outside of the 5,454.0-foot contour. This clip was performed using the hardclip option of the

ARC/INFO CREATETIN command. In creating the TIN, points that fell within a set distance

of each other were weeded out to eliminate flat triangular elements. Flat triangles occur where

all three points making up a triangle have the same elevation. Elimination of redundant

points helped to improve the performance of the contouring process as well as helped to create

more continuous contours in the lower elevations of the reservoir.

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

interpolate contours from tle Pilot Butte Reservoir TIN. In addition, the contours were

generalized by weeding 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 little bearing on the computation of surface areas and volumes

for Pilot Butte Reservoir. The contour topography at 5-foot intervals is presented on figure 3.

6
Development of 1995 Contour Areas

The 1995 contour surface areas for Pilot Butte Reservoir were computed in 2-foot intervals

from elevation 5,388.0 to 5,454.0 using the Pilot Butte Reservoir TIN discussed above. The

1995 survey measured the minimum reservoir elevation as 5,386.4 feet. 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.

1995 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). Surface areas

at 2-foot contour intervals from minimum reservoir elevation 5,386.5 to elevation 5,554.0 were

used as the control parameters for computing the Pilot Butte Reservoir capacity. The original

surface area of 901 acres at maximum conservation storage elevation 5,460.0 was used as the

maximum control parameter. The program can compute an area and capacity at elevation

increments of 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, which was set at 0.00000 1 for Pilot Butte

Reservoir. This 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) tests

the fit until it also exceeds the error limit. Thus, the capacity curve is defined by a series of

curves, each fitting a certain region of data. Final area equations are derived by differentiating

The capacity equations, which are of second order polynomial form:

y = a1 + a2x + a3x2

where:

y = capacity

x = elevation above a reference base

a1 = intercept

a2 and a3 = coefficients

Results of the 1995 Pilot Butte Reservoir area and capacity computations are listed in table

1 and columns (4) and (5) of table 2. Listed in columns (2) and (3) of table 2 are the original

surface areas and recomputed capacity values. A separate set of 1995 area and capacity tables

has been published for the 0.01-, 0.1-, and 1-foot elevation increments (Bureau of Reclamation,

1995). A description of the computations and coefficients output from the ACAP85 program

is included with these tables. Both the original and 1995 area-capacity curves are plotted on

figure 4. As of June 1995, at elevation 5,460.0, the surface area was 901 acres with a total

capacity of 33,721 acre-feet and an active capacity of 29,918 acre-feet.
RESERVOIR SEDIMENT ANALYSES

Sediments have accumulated in Pilot Butte Reservoir to a total volume of 3,853 acre-feet since

dam closure in December 1926. This volume is calculated at spiflway crest elevation 5,460.0.

It must be noted that the 1995 underwater survey was conducted at water surface elevation

5,454.0 and the final product relied on a USGS quad map for the above water topography and

the original surface areas above elevation 5,454.0 for computing the 1995 reservoir capacity.

Column (6) of table 2 gives the measured sediment volume by elevation and illustrates that the

majority of the deposit is located in the lower elevations of the reservoir.

Of the total deposited sediment of 3,853 acre-feet, 2,235 acre-feet was deposited in the inactive

pool storage areas and 1,618 acre-feet in the active pooi storage areas. The average annual

rate of sediment deposition between closure and June 1995 (68.5 years) was 56.2 acre-feet per

year. The storage loss in terms of percent of original storage capacity was 10.2 percent. Tables

1 and 2 contain the Pilot Butte Reservoir sediment accumulation and water storage data based

on the 1995 resurvey.

REFERENCES

American Society of Civil Engineers, Nomenclature for Hydraulics, ASCE Headquarters, New

York, 1962.

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

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

Center, Denver, Colorado, 1985.

Bureau of Reclamation, Guide for Preparation of Standing Operating Procedures for Bureau

ofReclamation Dams and Reservoirs, U.S. Government Printing Office, Denver, CO, 1987a.

Bureau of Reclamation, Design of Small Dams, U.S. Government Printing Office, Denver, CO,

1987b.

Bureau of Reclamation, Denver Office, Pilot Butte Reservoir Area and Capacity Tables,

Riverton Unit, Great Plains Region, Denver, CO, June 1995.

Environmental Systems Research Institute, Inc., ARC Command References, 1992.

8
Table 1. - Reservoir sediment data summary (page 1 of 2).

RESERVOIR SEDIMENT

DATA SUMMARY Pilot Butte Reservoir

NEWS OF RESERVOIR 1

DATA SHEET NO,

O 1. OWNER Bureau of Reclamation 2. STREAN offatreas,' 3. STATE Wyoming

A 4. SEC. 33 'DSP. 3H RANGE 1E 5. NEAREST P.O. Riverton 6. COUNTY Fremont

N 7, LAT 43° 11' 39' LONG 108° 45' 20' 8. TOP OF DAN ELEVATION 5,467 9. SPILLWAY CREST EL 5,460

B 10 , STORAGE 11, ELEVATION TOP 12, ORIGINAL SURFACE 13. ORIGINAL 14. GROSS STORAGE 15 DATE

E ALLOCATION OF POOL AREA, Ac CAPACITY, AF ACRE-FEET STORAGE BEGAN

S ________________________________

E

____

a,

________________________

SURCHARGE

____ ____________________

5,461.4

_________ ______________

915

________________ ____________________________

1,271' 38,845'

R

V

____

b.

_____________________

FLOOD CONTROL

____ ___________________________ ____________________________ _________________________ _____________________________

O 12/1926

C, POWER

R

d. WATER SUPPLY 16, DATE

NORMAL

P. IRRIGATION OPERATION

6. CONSERVATION 5,460 901 31,536' 37574 BEGAN

g. INACTIVE 5.410 345 6,038' 6,038'

17 . LENGTH OF RESERVOIR 2.3 WILES AVG. WIDTH OF RESERVOIR 0.6 WILES

B 18 . TOTAL DRAINAGE AREA 8.5 SQUARE WILES 22, MEAN ANNUAL PRECIPITATION 9' INCHES

A _________________________________________________________________________________

S 19 . NET SEDIMENT CONTRIBUTING AREA 8.5 SQUARE MILES

____________________________

33. MEAN ANNUAL RUNOFF

_____________________________________________

" INCHES

20 . LENGTH MILES AV. WIDTH MILES , 24, MEAN ANNUAL INFLOW 212,761 ACRE-FEET

21, MAX. ELEVATION 5,988 WIN. ELEVATION 5,410 55-WIN. 25. ANNUAL TEMP. MEAN 44°F' RANGE 101°F to -42°F' 103°F,"

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

U PER. ACCL. SURVEY RANGES OR AREA, AC. ACRE-FEE'S RATIO AF/AF

R YRS. YES, INTERVAL

E

12/1926 Contour (0) 5-ft 901' 37,574' 0,18

6/29/95 68 . 5 68 . 5 Contour (D( 2-ft 901" 33 , 721' 0 . 16

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

ANNUAL PRECIF.

a, MEAN ANN. H. MAX. ANN. c, TOTAL a. MEAN ANN. H. TOTAL

6/29/85 9 212,761' 296,698' 9,733,840' 212,761' 9,733,840'

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

a. TOTAL H. AV. ANN. c. /MI.'-YR. a, TOTAL b. AV. ANNUAL C, /NI.'-YE.

6/29/95 3,853 56.2 6 .6 3,853 56.2 6.6

26. DATE IF SURVEY 39. AV. DRY NT. 40. SED, DSP, TONS/MI.'-YR. 41. STORAGE LOSS, PCT. 42. SEDIMENT

(*/FT'( INFLOW, PPM

a. PERIOD H. TOTAL TO a. AV. ANNUAL H. TOTAL TO DATE a. b.

DATE PER, TOT.

6/29/95 O.150 10.2

26.

DATE OF

VEY

43. DEPTH DESIGNATION RANGE IN FEET BELOW, AND ASOVE, CREST ELEVATION

-

95.0-

80.0

80.0-

70.0

75.0-

60.0

60.0-

50.0

50.0-

40.0

40.0-

20.0

20.0-

Crest

PERCENT OF TOTAL SEDIMENT LOCATED WITHIN DEPTH DESIGNATION

6/95 3.2 24.0 14.4 16.4 20,7 19,4 1.9

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

DATE OF

SURVEY I I I I I I I I

PERCENT OF TOTAL SEDIMENT LOCATED WITHIN REACH DESIGNATION
Table 1. - Reservoir sediment data summary (page 2 of 2).

45. RANGE IN RESERVOIR OPERATION

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

1950 5451,2 5418.2 221529 1951 5450 .7 5411 .0 228253

1952 5445,3 5410.4 268114 1953 5457 .6 5419 .6 259754

1954 5453.0 5421.0 285,891 1955 5457 .6 5417 .0 247,317

1956 5455.2 5410.4 257,733 1957 5455 .7 5418 .5 234,447

1958 5456.3 5420.7 263,253 1959 5451 .9 5418 .6 234,480

1860 5453.6 5417.9 255,289 1961 5456. 6 5421 ,1 210,069

1962 5456.8 5421.9 268,238 1963 5458. 5 5422 .5 259,207

1964 5459.2 5410.1 249,139 1965 5459. 2 5410 .0 224,190

1966 5458.2 5425,5 264,469 1967 5457. 5 5412 .0 247,640

2968 5487.1 5421.6 267,078 1969 5457. 6 5424 .4 273,838

1970 5457.9 5432.5 239,394 1971 5451. 8 5417 .3 186,319

1972 5453.5 5426.0 296,698 1973 5457. 4 5438 .2 188,848

1974 5456.9 5429.6 195,918 1975 5455, 3 5438 .9 168,730

1976 5451.9 5429.3 192,766 1977 5459. 4 5424 .9 120,770

1978 5458.5 5423.4 187,679 1979 5452. 8 5428 .5 171,997

1980 5457.0 5425.7 201372 1981 5458. 2 5422 ,8 183,545

1982 5457.5 5431.6 195,417 1983 5458. 6 5447 .6 166,026

1984 5457.3 5445,0 203,391 1985 5457. 6 5436 ,1 183,500

1986 5458,5 5441.0 204,085 1987 5459. 3 5420 ,5 170,196

1988 5458.3 5426.2 183,205 1989 5459, 4 5445 .4 185,614

1990 5455.6 5439,1 184,192 1991 5457. 9 5436 ,2 160,312

1992 5457.9 ' 5435.1 160,956 1993 5458, 0 5438 .5 169,881

1994 5455.8 5427.9 151,325 1995 5455. 9 5453 .3 62,772

46. ELEVATION - AREA - CAPACITY DATA FOR 1995 CAPAL,EY

ELEVATION AREA CAPACITY ELEVATION AREA CAPACITY ELEVATION AREA CAPACITY

5386 0 0 5388 41 24 5392 101.2 317

5396 145.2 812 5400 187.7 1,479 5404 223,5 2,303

5408 258.8 3,267 5410 277.9 3,803 5412 297,2 4,379

5416 341,1 5,652 5420 394.8 7,120 5424 455.2 8,819

5428 513.9 10,756 5432 573,2 12,931 5436 625.0 15,329

5440 671.8 17,922 5444 721,3 20,704 5448 770,8 23.691

5452 814.0 26,860 5454 836.0 28,510 5460 901 33,721

47. REMARKS AND REFERENCES

Wind River diverted via Wyoming Canal.

Original capacity recomputed by Bureau of Recl amation program ACAP.

Reclamation Project Data Book, 1981.

Off-channel reservoir, inflows regulated from Wind River diversions.

Calculated, unregulated, monthly inflows for available records, water years 1950 through June 1 995.

Surface area and capacity at elevation 5460.0, spillway crest. Area and capacity calcula ted by Bureau of Reclamation program RCA?.

1995 survey determined surface areas from unde r-water collected depths and digitized USOS contours. From measured surface area of 836

acres, USD0 digitized contour was assumed to be elevation 5454.0, 901 acres at elevation 54 60.0 from original measured values, which

assumed no area change. -

Average annual and total sediment deposits div ided by 37,574 acre-feet, original capacity at elevation 5460.0.

Maximum and minimum end-of-month water surface elevations.

For water year 1995, from October 1994 through June 1995.

48. AGENCY WAXING SURVEY Bureau of Reclamation

49. AGENCY SUPPLYING DATA Bureau of Reclamation DATE March 1996

10
Table 2. - Summary of 1995 survey results.

(1) (2) (3) (4) (5) (6) (7) (8)

Measured

Original Original 1995 1995 sediment Measured Reservoir

Elevation Area Capacity Area Capacity Volume Sediment Depth

(ft) (acres) (acre-ft) (acres) (acre-ft) (acre-ft) (%) (%)

5460.0 901.0 37,574 901 33,721 3,853 100.0 100.0

5456.0 858.0 34,055 (858) 30,204 3,851 99.9 95.3

5454.0 836.0 32,361 836.0 28,510 3,851 99.9 92.9

5452.0 815.0 30,710 814.0 26,860 3,850 99.9 90.6

5448.0 772.0 27,537 770.8 23,691 3,846 99.8 85.9

5444.0 728.0 24,540 721.3 20,704 3,836 99.6 81.2

5440.0 686.0 21,703 671.8 17,922 3,781 98.1 76.5

5436.0 643.0 19,056 625.0 15,329 3,727 96.7 71.8

5432.0 599.0 16,572 573.2 12,931 3,641 94.5 67.0

5428.0 556.0 14,261 513.9 10,756 3,505 91.0 62.3

5424.0 514.0 12,121 455.2 8,819 3,302 85.7 57.6

5420.0 470.0 10,153 394.8 7,120 3,033 78.7 52.9

5416.0 426.0 8,361 341.1 5,652 2,709 70.3 48.2

5412.0 375.0 6,758 297.2 4,378 2,380 61.8 43.5

5410.0 345.0 6,038 277.9 3,803 2,235 58.0 41.2

5408.0 (325) 5,367 258.8 3,267 2,100 54.5 38.8

5407.5 (320) 5,206 (254) 3,138 2,068 53.7 37.6

5404.0 (286) 4,145 223.5 2,303 1,842 47.8 34.1

5400.0 (246) 3,080 187.7 1,479 1,601 41.6 29.4

5396.0 (207) 2,174 145.2 812 1,362 35.3 24.7

5392.0 (168) 1,262 101.2 317 945 24.5 20.0

5388.0 (128) 833 41.0 24 809 21.0 15.3

5386.0 (108) 596 0.0 0 596 15.5 12.9

5384.0 (89) 399 - - 399 10.4 10.6

5380.0 (49) 123 - 123 3.2 5.9

5376.0 (10) 5 - - 5 0.1 1.2

5375.0 0 0 - - 0 0.0 0.0

(1) Elevation of reservoir water surface.

(2) Original reservoir surface area.

(3) Original calculated reservoir cap acity computed using Reclamation's computer program ACAP from

original measured surface areas.

(4) Reservoir surface area from 1995 survey.

(5) 1995 calculated reservoir capacity computed using ACAP.

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

(7) Measured sediment expressed in percentage of total sediment of 3, 853 acre-feet at elevation 5460.0.

(8) Depth of reservoir expressed in percentage of total depth (85 ft).

11
-

it.

_

r RRIGA1EO AREA + OR

0

Figure 1. - Pilot Butte Reservoir location map.

IOrS(R

0 ES
Space intentionally left blank due to security concerns 
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/ / // 1 I / /Y \

/

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0

me

tt

m

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/

1i17

1/Yl 1/

K K / ,/ -

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'T:/

I K -- --

-- 1,

7i //

-+ 499000

-/

1499000 1499000 1499000

/

/

I

/ /

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//

C)1
V

0

PILOT BUTTE AREA - CAPACITY CURVES

Area (acre)

960 840 720 600 480 360 240 120

5460

5450

5440

5430

5420

0

-1

-

5410

w

5400

5390

5380

5370

Capacity -

-________ _______ __________

Area

__ __

:n::ey

__

5460

5450

5440

5430

5420

5410

5400

5390

5380

5370

0 5000 10000 15000 20000 25000 30000 35000 40000

Capacity (acre-feet)

Figure 4. - Area and capacity curves-Pilot Butte Reservoir.
Mission

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.