ENDERS RESERVOIR

1997 SEDIMENTATION SURVEY

M

FOR THE 102.

U.S. Department of the Interior

Bureau of Reclamation
REPORT DOCUMENTATION PAGE I oo% iaa

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

August_1998 Final

4. TITLE AND SUBTITLE

___________________________

5. FUNDING NUMBERS

Enders Reservoir PR

1997 Sedimentation Survey

6. AUTHOR(S)

Ronald L. Ferrari

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

REPORT NUMBER

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

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

____________________________

10. SPONSORINGJMONrrORING

AGENCY REPORT NUMBER

Bureau of Reclamation, Denver Federal Center, PC Box 25007,

Denver CO 80225-0007 DIBR

11. SUPPLEMENTARY NOTES

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

12a. DISTRIBUTION/AVAILABILiTY STATEMENT 12b. DISTRIBU11ON CODE

Available from the National Technical Information Service,

Operations Division, 5285 Port Royal Road, Springfield VA 22161 ___________________________

13. ABSTRACT (Maximum 200 words)

The Bureau of Reclamation (Reclamation) surveyed the underwater area of Enders Reservoir in May 1997 to develop

a topographic map and compute a present storage-elevation relationship (area-capacity tables). The data were also

used to calculate reservoir capacity lost due to sediment accumulation since dam closure on October 23, 1950. The

survey used sonic depth recording equipment interfaced with a global positioning system (GPS) that gave continuous

sounding positions throughout the underwater portion of the reservoir. Reservoir topography was developed by a

computer program using collected underwater data along with above-water topography determined from digitized

contour lines from the U.S. Geological Survey quadrangle (USGS quad) maps. The USGS quads of the reservoir

area were developed from aerial photography obtained in 1973. The new topographic map of Enders Reservoir is a

combination of digitized contours and 1997 underwater measured topography.

As of May 1997, at top of active conservation elevation 3,112.3 (feet), the surface area was 1,707 acres, the total

capacity was 42,910 acre-feet, and the active capacity was 33,962 acre-feet. Since initial filling in October 1950 ,

about 1,572 acre-feet of sediment has accumulated in Enders Reservoir below elevation 3105.0, resulting in a

1.95-percent loss in reservoir volume. Since 1950, the estimated average annual rate of reservoir capacity lost to

sediment accumulation is 33.7 acre-feet.

14. SUBJECT TERMS 15. NUMBER OF PAGE5

reservoir area and capacity/ sedimentation! reservoir surveysl sonar/ sediment 19

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

17. SECURITY CLASSIFICATION

OF REPORT

18. SECURITY CLASSIFICATION

OF ThIS PAGE 19. SECURITY CLASSIFICATION

OF ABSTRACT

20. LiMITATION OF ABSTRACT

UL UL UL UL

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

Prcrtb.d by ANSI Std. 239-1!

298-102
ENDERS RESERVOIR

1997 SEDIMENTATION SURVEY

by

Ronald L. Ferrari

Sedimentation and River Hydraulics Group

Water Resources Services

Technical Service Center

Denver, Colorado

August 1998
ACKNOWLEDGMENTS

The Bureau of Reclamation's (Reclamation) Sedimentation and

River Hydraulics Group of the Technical Service Center (TSC)

prepared and published this report. Ronald Ferrari conducted

the hydrographic survey. Special thanks to Mr. David Moomey,

the Great Plains Regional Superintendent at Enders Reservoir,

for the field assistance during the hydrographic survey. Ronald

Ferrari completed the data processing needed to generate the

new topographic map and area-capacity tables. Sharon Nuanes

of the TSC completed the USGS contour digitizing and was

consulted during the map development. Cassie Klumpp of the

TSC performed the technical peer review of this documentation.

U.S. Department of the Interior

Mission Statement

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.

11
CONTENTS

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Introduction 1

Summary and conclusions 1

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 1997 contour areas 7

1997 storage capacity 7

Sediment analyses 8

References 8

Table

TABLES

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

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

2 Summary of 1997 survey results 12

Figure

FIGURES

1 Enders Reservoir location map 13

2 Enders Dam, plan and section 14

3 Enders Reservoir underwater data points 15

4 Enders Reservoir topographic map 17

5 Area and capacity curves - Enders Reservoir 19

In
INTRODUCTION

Enders Dam and Reservoir are principal features of the Frenchman-Cambridge Division of

the Pick-Sloan Missouri Basin Program. Additional storage features are Harry Strunk Lake,

Hugh Butler Lake, and Swanson Lake. Enders Dam and Reservoir, on Frenchman Creek, are

located in Chase County in southwestern Nebraska about 2 miles southeast of Enders, 9 miles

east of Imperial, and 26 miles north of Benkelman (fig. 1).

Enders Dam was constructed between January 1947 and January 1951 with first storage on

October 23, 1950. The dam is a rolled earthfill structure with riprap on the upstream face,

whose dimensions are (fig. 2):

• Hydraulic height' 93 feet

• Structural height 134 feet

• Top width 30 feet

• Crest length 2,603 feet

• Crest elevation 3,137.5 feet

Enders Dam's spiliway, located in the right abutment, consists of an approach channel, 10-foot

uncontrolled overflow crest, six 5- by 30-foot radial gates, and a stilling basin. The crest of the

10-foot overflow notch is at elevation 3,112.32 and the crest of the radial gates is at elevation

3,097.0. The discharge capacity is 200,000 cubic feet per second (ft3/s) at reservoir elevation

3,129.5 (Bureau of Reclamation 1981).

The outlet in the right center of the dam, consists of an 84-inch steel conduit with an

emergency 6.0- by 7.5-foot hydraulic slide gate. There are two 60-inch hollow-jet regulating

valves for releases to the river. The discharge capacity is 1,448 ft3/s at reservoir elevation

3,129.5.

Enders Reservoir stores water from Frenchman Creek with an above-dam drainage area of

950 square miles. The drainage area ranges from elevation 3,082.4, top of inactive pool, to

greater than elevation 4,500 at its headwaters. The reservoir length, at elevation 3,129.5, is

around 4.5 miles with an average width of 0.3 mile.

SUMMARY AND CONCLUSIONS

This Reclamation report presents the 1997 results of the first extensive survey of Enders

Reservoir. The primary objectives of the survey were to gather data needed to:

• develop reservoir topography

• compute area-capacity relationships

'The 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

Reseivoirs, or ASCE's Nomenclature for Hydraulics.

2Elevation levels are shown In feet.
. estimate storage depletion caused by sediment deposition since Enders Dam closure

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 Enders Reservoir. The

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

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

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

elevations.

The 1997 underwater surface areas at predetermined contour intervals were generated by a

computer graphics program using the underwater collected data. The above-water reservoir

contours were digitized from U.S. Geological Survey 7.5 minute quadrangle (USGS quad)

maps of Enders Reservoir. The new topographic map of Enders Reservoir is a combination of

the digitized and underwater measured topography. The 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. The 1997 area

and capacity tables were generated using the 1997 measured areas at elevation 3,100.0 and

less and the original measured areas for elevation 3,105.0 and greater.

Table 1 contains a summary of Enders Reservoir's watershed characteristics for the 1997

survey. The 1997 survey determined that the reservoir has a current storage capacity of

79,161 acre-feet and a surface area of 2,557 acres at reservoir elevation 3,129.5. Since closure

in 1950, the reservoir has accumulated a sediment volume of 1,572 acre-feet below reservoir

elevation 3,105.0. This volume represents a 1.95 percent loss in capacity and an average

annual loss of 33.7 acre-feet.

RESERVOIR OPERATIONS

Enders Reservoir is primarily an irrigation and flood protection facility (the following values

are from May 1997 area-capacity tables):

• 6,203 acre-feet of surcharge storage between elevations 3,127.0 and 3,129.5

• 30,048 acre-feet of flood control between elevations 3,112.3 and 3,127.0

• 33,962 acre-feet of active conservation storage between elevations 3,082.4 and 3,112.3

• 1,432 acre-feet of inactive storage between elevations 3,080.0 and 3,082.4

• 7,516 acre-feet of dead storage below elevation 3,080.0

The Enders Reservoir inflow and end-of-month stage records in table 1 show the annual

(January through December) inflow and fluctuation for the operation period January 1951

through May 1997. The average annual reservoir inflow for this operation period was

42,052 acre-feet. The records show the annual elevation fluctuation of the reservoir water

surface varied from a maximum elevation of 3,118.2, occurring March 25, 1960, to a minimum

elevation of 3,080.7, occurring August 28, 1978, since normal reservoir operations began.

2
HYDROGRAPHIC SURVEY EQUIPMENT AND METHOD

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

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

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

omnidirectional antenna, a depth sounder, a helmsman display for navigation, a plotter, a

computer, and hydrographic system software for collecting 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 unit was provided by a 12-volt battery.

GPS Technology and Equipment

The positioning system used at Enders Reservoir 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 seabased 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.

The NAVSTAR system consists of three segments:

The space segment is a network of 24 satellites maintained in 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 which measure the broadcasts from the

satellites and calculate the positions 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

3
unknown is caused by the clock error between the expensive satellite atomic clocks and the

imperfect clocks in the GPS receivers. For hydrographic surveying of the altitude, Enders'

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

observations were needed to track the survey vessel. During the Enders 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 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 on the radio signal of the ionosphere. 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 during

the Enders 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 1 and 2 level surveys (Corps of

Engineers 1991).

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.

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 differential GPS (DGPS). DGPS was used

during the Enders 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 that 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 Enders Reservoir survey, position

corrections were determined by the master receiver and transmitted via an ultra-high

frequency (UHF) 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

4
1 to 2 meters for the moving vessel compared to positional accuracies of 100 meters with a

single receiver.

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

construction and consist of a six-channel Li coarse acquisition (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 Radio Technical Commission for Maritime Services (RTCM) 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 postprocessing software. The GPS collection system has the

capability of collecting the data in 1927 or 1983 North American Datums (NAD) in the

surveyed area's state plane coordinate system's zone. For Enders Reservoir, the data were

collected in the Nebraska's 1983 NAD south state plane zone.

Survey Method and Equipment

The Enders Reservoir hydrographic survey was conducted May 27 through May 29, 1997

between reservoir water surface elevations 3,104.1 and 3,104.2. 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. Most of the transects (grid lines) were run primarily in a

nOrth-south direction. Data were also collected along the shore as the boat traversed to the

next transect and as it maneuvered in the open areas between the vegetation. Vegetation

growth and shallow conditions in some of the coves and upper reservoir prevented the boat

from surveying some areas. Figure 3 illustrates the reservoir area covered by the 1997

underwater survey versus the contours digitized from the USGS quad maps. The survey

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

along these predetermined 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 39,788 data points. The water surface elevation recorded by a

Reclamation gauge during the time of collection was used to convert the sonic depth

measurements to true lake bottom elevations.

For stationing the master GPS unit there were no known benchmarks or datums that

overlooked the reservoir that had the needed control information. For the underwater

collection, the hydrographic survey crew established a datum at a USBR brass cap marked

R7R/RSRIR4OL using a precision lightweight GPS receiver (PLGR). The PLGR unit utilizes

the precise positioning service of the DOD GPS that is available to federal users only and has

a horizontal accuracy of ±4 meters. This method calculated 1983 NAD state plane coordinates

of North 221,402.25 and East 1,209,342.60 at this location. The shore-based master GPS unit,

which transmits the correction information to the mobile GPS unit on the survey vessel, was

stationed at this new datum site throughout the survey. This location was chosen because it

was accessible and overlooked the reservoir. The location allowed for good radio transmission

5
of the differential corrections to the mobile survey vessel throughout the reservoir survey.

This precision met the accuracy for producing the 1997 reservoir contour map since no abovewater aerial data were collected requiring using the USGS quad contour, with an accuracy of

1 inch equals 2,000 feet, for above water map development. During postprocessing of the

collected underwater data, the few collected points without differential correction were

removed.

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

deflector plate below the boat by cables with known depths marked by heads. 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 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 postprocessing, and when the analog charted depths indicated a difference

from the recorded computer bottom depths, the computer data files were modified.

RESERVOIR AREA AND CAPACITY

Topography Development

The topography of Enders Reservoir was developed from the 1997 collected underwater data

and from the USGS quad maps. The upper contours of Enders Reservoir were developed by

digitizing the contour lines of elevation 3,112.0 and 3,137.5, from the USGS quad maps that

covered the Enders Reservoir area. The USGS quad maps were developed from aerial

photography dated 1973. ARC/INFO V7.0.2 geographic information system software was used

to digitize the USGS quad contours. The digitized contours were transformed to Nebraska's

NAD 1983 south state plane coordinates using the ARC/INFO PROJECT command.

The elevation 3,112.0 contour digitized from USGS quad maps was used to perform a clip of

the Enders Reservoir triangular irregular network (TIN) such that interpolation was not

allowed to occur outside the 3,112.0 contour. This complete contour was selected since it was

the elevation that most nearly enclosed the 1997 underwater data collected below reservoir

elevation 3,104. This clip was performed using the hardclip option of the ARC/INFO

CREATETIN command. Using ARCEDIT, the underwater collected data and the digitized

3,112.0 contour from the USGS quad maps were plotted (fig. 3). The plot found that the

majority of the underwater data occurred completely within the elevation 3,112.0 clip and

required only minor adjustments to enclose all collected data.

Contours for elevations 3,100.0 and below were computed from the developed underwater data

using the TIN surface modeling package within ARC/INFO. The underwater survey data were

collected in the Nebraska south zone state plane coordinates in NAD 1983 (a TIN is a set of

adjacent, nonoverlapping 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. Triangles

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

6
collected survey points. 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. Elevation contours are then

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

ARC/INFO V7.0.2 ARC Command References (ESRI 1992).

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

interpolate contours from the Enders 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 Enders Reservoir. The contour topography at 5-foot intervals is presented on figure 4,

drawing number 328-D-2339.

Development of 1997 Contour Areas

The 1997 contour surface areas for Enders Reservoir were computed at 2-foot increments, from

elevation 3,050.0 to 3,100.0, using the Enders Reservoir TIN discussed above. The 1997

survey measured the minimum reservoir elevation at 3,049.8 feet. These calculations were

performed using the ARC/INFO VOLUME command. This command computes areas at userspecified elevations directly from the TIN and takes into consideration all regions of equal

elevation. Due to the lack of 1997 survey data above water surface elevation 3.104, the final

1997 area computations assumed no change in surface area from elevation 3,105 and above.

1997 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 3,049.8 to elevation 3,100.0 and

the original surface areas at 5-foot contour intervals from elevation 3,105.0 to 3,125.0 and

elevations 3,127.0 and 3,129.5 were used as the control parameters for computing the Enders

Reservoir capacity. 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 0.000001 for Enders

Reservoir. 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. Final area equations are derived by

differentiating the capacity equations, which are of second order polynomial form:

y = a1 + a2x + a3x2

7
where:

y = capacity

x = elevation above a reference base

a1 = intercept

a2 and a3 = coefficients

Results of the 1997 Enders 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 1997 area and capacity tables has

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

1997). A description of the computations and coefficients output from the ACAP85 program

is included with these tables. Both the original and 1997 area-capacity curves are plotted on

figure 5. As of May 1997, at active conservation elevation 3,112.3, the surface area was

1,707 acres with a total capacity of 42,910 acre-feet and an active capacity of 33,962 acre-feet.

SEDIMENT ANALYSES

Sediments have accumulated in Enders Reservoir to a total volume of 1,572 acre-feet since

dam closure in October 1950. This volume was calculated at reservoir water surface elevation

3,105.0. It must be noted that the 1997 underwater survey was conducted at water surface

elevation 3,104.2, and the final product relied on the original measured surface areas at

elevation 3,105.0 and greater for computing the 1997 reservoir area and capacity tables.

Column 6 of table 2 gives the measured sediment volume by elevation, and the area curve on

figure 5 illustrates the resulting measured surface areas and calculated capacities. This table

and figure illustrate that the majority of the sediment deposition is in the lower elevations of

the reservoir with 84 percent of the sediment found below elevation 3,090. The average

annual rate of sediment deposition between closure and May 1997 (46.6 years) was 33.7 acrefeet. The storage loss in terms of percent of original storage capacity was 1.95 percent.

Tables 1 and 2 contain the Enders Reservoir sediment accumulation and water storage data

based on the 1997 resurvey.

Reclamation's original 100-year sediment deposition prediction was 4,000 acre-feet or an

average annual loss of 40 acre-feet. Of the predicted 4,000 acre-feet, 1,757 acre-feet or

44 percent was projected to settle above elevation 3,082.4. This compares to the 1997 study

that measured an average annual loss of 33.7 acre-feet with 561 acre-feet or 36 percent above

elevation 3,082.4. The annual maximum and minimum reservoir elevations in table 1 show

that during several years the reservoir has operated as low as a few feet above the inactive

pool elevation of 3,082.4. This provided the condition for portions of the upper reservoir

sediment delta to be flushed into the lower portion of the reservoir.

REFERENCES

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

York, 1962.

8
Bureau of Reclamation, Project Data, Denver Office, Denver, Colorado, 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, Colorado,

1987(a).

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

Colorado, 1987(b).

Bureau of Reclamation, Denver Office, Enders Reservoir Area and Capacity Tables,

Frenchman-Cambridge Division, Great Plains Region, Denver, Colorado, May 1997.

Corps of Engineers, March 1991. Application of Differential Global Positioning System for

Hydrographk Survey and Dredge Positioning, ETL 1110-7-5 (FR), Department of the

Army, Washington DC.

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

9
RESERVOIR SEDINENT

DATA StJM!1ARY Enders Reservoir

NAME OF RESERVOIR :1.

DATA SHEET NO.

D 1. OWNER Bureau of Reclamation 2. STREAM North Fork Frenchman Ck 3. STATE Nebraska

A 4. SEC. 9 TWP. 5W RANGE 37W 5. NEAREST P.O. Enders 6. COUNTY Chase

M 7. LAT 400 25 05' LONG 1010 30' 55' 8. TOP OF DAM ELEVATION 3,137.5 9. SPILLWAY CREST EL.3,097.0

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

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

S BEGAN

E _____________________ ___________________

R

____________________

a. SURCHARGE

_ ______________

3,129.5

______

2,557 6,210 80,680

b. FLOOD CONTROL 3,127.0 2,405 30,000 74,470

10/23/50

I C. PO

R

d. WATER SUPPLY 3,112.3 1,707 34,500 44,470 16. DATE

e. IRRIGATION ________________ OPERATION

f. INACTIVE

____________

3,082.4

_____ __________________

658 1,500 9,970 BEGAN

g. DEAD 3,080.0 586 8,470 8,470 10/50

-

17. LENGTH OF RESERVOIR 4.5 MILES AVG. WIDTH OF RESERVOIR 0.3 MILES

B 18. TOTAL DRAINAGE AREA 950 SQUARE MILES 22. MEAN ANNUAL PRECIPITATION 20' INCHES

19. NET SEDIMENT CONTRIBUTING AREA 950 SQUARE MILES 23. MEAN ANNUAL RUNOFF 0.83' INCHES

I 20. LENGTH MILES AV. WIDTH MILES 24. MEAN ANNUAL RUNOFF 42,0520 ACRE-FEET

N

21. MAX. ELEVATI84 4,500 MIN. ELEVATION 3,080 25. ANNUAL TEMP. MEAN 52'F RANGE -220F to 110F'

5 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, kC. ACRE-FEET RATIO AF/AF

R YRS. YRS. INTERVAL

V

E

y 10/50 Contour (0) 5-ft 2,557 80,732 1.92

5/97 46 6 46 6

5576 Contour (0) 2-ft . .2 , 79,1616 1.88

T 26. DATE OF 34. PERIOD 35. PERIOD WATER INFLOW, ACRE FEET WATER INFLOW TO DATE, AX

A SURVEY ANNUAL ___________________________

PRECIP.

a. MEAN ANN. b. MAX. ANN. c. TOTAL a. MEAN ANN. b. TOTAL

5/97 202 42,052 15,500 1,959,600 42,052 1,959,600

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

SURVEY ________________

a. TOTAL b. AV. ANN. C. /MI.2-YR. a. TOTAL b. AV. ANNUAL C. /MI.2-YR.

5/97 1,572 33.7 0.04 1,572 33.7 0.04

26. DATE OF 39. AV. DRY 40. SED. DEP. TONS/MI.2-YR. 41. STORAGE LOSS, POT. 42. SEDIMENT

SURVEY NT. (*/FT3) INFLOW, PPM

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

DATE ANNUAL DATE PER. TOT.

5/97 0.O42 1.958

26.

DATE

43. DEPTH DESIGNATION RANGE IN FEET BETWEEN ELEVATION

OF

SURVEY

________

3042-

3050

_________

3050-

3055

_________

3055-

3060

________

3060-

3070

_________

3070-

3080

_________

3080-

3085

_________

3085-

3090

________

3090-

3095

3095-

3105

PERCENT OF TOTAL SEDThT LOCATED WITHIN DEPTH DESIGNATION

5/97 14.3 18.3 11.3 8.1 8.5 .4 14.1 11.2 4.8

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

0-10 10-

20

20- I

30 I

30-

40

40-

50

50-

60

60-

70

70-

80

80-

90

90- I

100 I

100-

105

105-

110

110-

115

115-

120

120-

125

SURVEY

PERCENT OF TOTAL SEDIMENT LOCATED WITHIN REACH DESIGNATION

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

10
45. RANGE IN RESERVOIR OPERATION'

YEAR MAX. EI,EV. MIN. ELEV. INPLOW, AF YEAR MAX. ELEV. MIN. ELEV. INFLOW, AR

1951 3,111.2 3,085.1 75,500 1952 3,112.8 3,101.0 66,000

1953 3,106.1 3,099.9 62,200 1954 3,112.0 3,104.0 60,500

1955 3,112.4 3,105.0 62,100 1956 3,112.3 3,104.4 61,000

1957 3,112.1 3,107.9 63,700 1958 3,113.7 3,109.9 65.600

1959 3,113.2 3,105.0 59,900 1960 3,116.5 3,106.0 73,100

1961 3,112.8 3,095.5 55,700 1962 3,113.2 3,096.1 64,200

1963 3,111.9 3,088.6 54,500 1964 3,112.6 3,090.9 54,000

1965 3,112.9 3,098.2 59,400 1966 3,113.6 3,096.0 58.700

1967 3,112.8 3,096.4 63,100 1968 3,112.9 3,086.6 52,600

1969 3,112.2 3,087.2 51,300 1970 3,108.9 3,082.4 47,600

1971 3,109.2 3,082.3 49,700 1972 3,108.2 3,084.4 44,000

1973 3,109.0 3,081.4 43,100 1974 3,108.2 3,085.9 38,100

1975 3,109.5 3,085.4 38,300 1976 3,107.0 3,082.8 33,700

1977 3,105.7 3,083.4 32,300 1978 3,103.9 3,081.0 30,300

1979 3,101.0 3,085.4 26,600 1980 3,102.9 3,083.9 26,600

1981 3,102.3 3,089.4 27,300 1982 . 3,105.5 3,094.0 30,100

1983 3,107.9 3,090.5 30,100 1984 3,106.5 3,089.9 29,200

1985 3,103.5 3,086.7 25,500 1986 3,101.5 3,088.0 23,900

1987 3,102.2 3,087.5 25,900 1988 3,102.2 3,088.5 21,600

1989 3,100.4 3,086.3 19,500 1990 3,099.6 3,082.7 19,400

1991 3,097.6 3,086.7 18,300 1992 3,097.8 3,090.7 19,500

1993 3,101.2 3,094.6 21,000 1994 3,104.1 3,094.4 18,300

1995 3,104.5 3,092.7 18,800 1996 3,103.4 3,095.8 20,100

1997 3104.2 3.101 c 6.600'

46. ELEVATION - AREA - CAPACITY DATA FOR 1997 CAPACI

_____________

_________

ELEVATION AREA CAPACITY ELEVATION AREA

_________

CAPACITY ELEVATION

_________

AREA

_________

CAPACITY

3049.8 0 0 3052 23.2 17 3054 57.1 97

3056 93.3 247 3058 114.9 455 3060 136.6 707

3062 177.6 1,021 3064 219.8 1,419 3066 250.6 1,889

3068 289.0 2,429 3070 337.6 3,055 3072 380.5 3,773

3074 420.8 4,575 3076 465.5 5,461 3078 511.1 6,437

3080 567.1 7,516 3082 616.5 8,699 3084 670.6 9,986

3086 726.4 11,383 3088 777.4 12,887 3090 846.0 14,511

3092 926.8 16,283 3094 1,010.1 18,220 3096 1,102.2 20,333

3078 1,169.8 22,605 3100 1,227.3 25,002 3105 1,398 31,565

3110 1,613 39,092 3112.3 1,707 42,910 3115 1,818 47,669

3120 2,069 57,387 3125 2,284 68,269 3127 2,405 72,958

3129.5 2,557 79,161 ____________

47. R6ARXS AND REFERINCES

Top of spillway gates elevation 3,127.0. 10-ft wide uncontr olled overflow section in center, crest el. 3112.3.

2 Bureau of Reclamation Proj ect Data Book, 1981.

Calculated using mean annual runoff value of 42,052 AR, item 24.

Computed annual inflows from 10/50 through 5/97 by calendar year.

Original surface area and capacity at elevation 3,129.5, top of surcharge. Original capacity recomputed by

Reclamation' s ACAP program using original surface areas.

6 Surface area and capacity at elevation 3,129.5 computed by ACAP program using 1997 and original surface areas.

1997 surveyed only underwater portion of reservoir below elevation 3104.7. Elevation 3,105.0 and above from

original measured areas.

Computed sediment volume at reservoir elevation 3,105.0.

Capacity loss by comparing original recomputed capacity and 1997 capacity at reservoir elevation 3,129. 5.

Maximum and minimum elevations and inflow values in acre-feet by calendar year, from 1950 through 5/97.

10 Capacities computed by ACAP computer program. Areas at elevation 3105 and above from original survey.

48. AGENCY MAKING SURVEY Bureau of Reclamation

49. AGENCY SUPPLYING DATA Bureau of Reclamation DATE April 1998

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

11
1 2 3 4 5 6 7 8

Computed

Original Original 1997 1997 Sediment Percent of Percent

Elevation Area Capacity Area Capacity Volume Measured Reservoir

(feet) (acres) (acre-feet) (acres) (acre-feet) (acre-feet) Sediment Depth

3129.5 2557 80732 2557 79161 100.0

3127.0 2405 74530 2405 72958 97.1

3125.0 2284 69841 2284 68269 94.9

3120.0 2069 58958 2069 57387 89.1

3115.0 1818 49241 1818 47669 83.4

3112.3 1707 44482 1707 42910 80.3

3110.0 1613 40664 1613 39092 77.7

3105.0 1398 33137 1398 31565 1572 100.0 72.0

3100.0 1240 26542 1227 25002 1540 98.0 66.3

3097.0 1142 22969 1136 21452 1517 96.5 62.9

3095.0 1077 20750 1056 19253 1497 95.2 60.6

3090.0 890 15832 846 14511 1321 84.0 54.9

3085.0 735 11770 699 10671 1099 69.9 49.1

3082.4 658 9959 627 8948 1011 64.3 46.2

3080.0 586 8467 567 7516 951 60.5 43.4

3075.0 460 5852 443 5007 845 53.8 37.7

3070.0 332 3872 338 3055 817 52.0 32.0

3065.0 244 2432 235 1646 786 50.0 26.3

3060.0 170 1397 137 707 690 43.9 20.6

3055.0 119 675 75 163 512 32.6 14.9

3050.0 61 225 0 0 225 14.3 9.1

3045.0 18 27 0 0 27 1.7 3.4

3042.0 0 0 0 0 0 0.0 0.0

1 Elevation of reservoir water surface.

2 Original reservoir surface area.

3 Original calculated reservoir capacity computed using ACAP.

4 Reservoir surface area from 1997 survey for elevations 3100 and below. Areas

for elevation 3105 and greater are original measured areas.

5 1997 calculated reservoir capacity computed using ACAP from 1997 surface areas.

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

7 Meau red sediment expressed in percentage of total sediment 1572 acre-feet at

elevation 3105.

8 Depth of reservoir expressed in percentage of total depth (87.5 feet).

12
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Figure 1. - Enders Reservoir location map.
Space intentionally left blank due to security concerns 
______ rtawic ovz_______

L'E2Z 81 __________

, 4_'

Figure 3. - Enders Reservoir underwater data points.

1c

S

- AE&l

ENO5 /?E5ERVO/

/897 !rn!'ril9r 80/9

TaXNML 

I - - 

- *,-&Iwrsk M26 w 

- 

Figure 3. - Enders ~essvoir underwater data points. 

- - 
ENDES

ooo4 ooo± 2OOO

Th

N 1

w Tr

215000± 215000± 215000-1-- 215000+ 215000-4-

fw atv w

*cI,r f:/4tt'

Horizontal datum based on Nebraskas

State Plane Coordinate System,

South Zone (N4383)

7

/

&VDLF'S RE5t?VO/,V

raozoor

Di1hW8Y_______ Tfa/IcAL I/PROVA!

I27 8K 14ft7fr_______________

Pivi, C'/arud' 4/bZ fi, flb'8 J28-%2JJ.9

Figure 4. - Enders Reservoir topographic map. 17
Area-Capacity Curves for Enders Reservoir

Area (acres)

2600 2340 2080 1820 1560 1300 1040 780 520 260

3130

3120

3110

3100

3090

3080

3070

3060

3050

3040

0

Capacity Area

___ ___

1 iU

3120

3110

3100

3090

3080

3070

3060

3050

3040

0 8320 16640 24960 33280 41600 49920 58240 66560 74880 83200

Capacity (acre-feet)

Figure 5. - Area and capacity curves -Enders 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.