ARROWROCK RESERVOIR

1997 SEDIMENTATION SURVEY

NT

U.S. Department of the Interior

Bureau of Reclamation
REPORT DOCUMENTATION PAGE I

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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

Arrowrock 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. SPONSORINGIMONITORING AGENCY NAME(S) AND ADDRESS(ES)

___________________________

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

Bureau of Reclamation, Denver Federal Center, P0 Box 25007,

Denver CO 80225-0007 DIBR

11. SUPPLEMENTARY NOTES

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

12a. DISTRIBU11ONJAVAILABILFrY STATEMENT 12b. DISTRIBUTION 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 Arrowrock Reservoir in October of 1987 and June 1997 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 1915. The 1987

aerial data were collected near reservoir elevation 3,028 feet. The 1997 underwater survey was conducted to

complete topography of the reservoir and to measure changes that had occurred, due to sediment deposition, since

1987. The underwater 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. The new

topographic map of Arrowrock Reservoir was developed from the combined 1987 aerial and 1997 underwater

measured topography.

As of June 1997, at top of active conservation elevation (feet) 3,216.0, the surface area was 3,141 acres with a total

capacity of 272,224 acre-feet. Since initial filling in 1915, about 19,376 acre-feet of sediment have accumulated in

Arrowrock Reservoir below elevation 3,216.0, resulting in a 6.64 percent loss in reservoir volume. Since 1915, the

estimated average annual rate of reservoir capacity lost to sediment accumulation is 235.4 acre-feet

14. SUBJECT TERMS 15. NUMBER OF PAGES

reservoir area and capacity/ sedimentation! reservoir surveys! sonar/ sediment 33

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)

Pr..crf bed by ANSI Std. 239-18

298-102
ARROWROCK 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 of the TSC

conducted the hydrographic survey with assistance from Mr.

Charlie (Pete) Swan and Mr. James Dean of the Pacific

Northwest Region. Ronald Ferrari completed the data processing

needed to generate the new topographic map and area-capacity

tables. Sharon Nuanes of the TSC completed the final 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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Page

Introduction 1

Summary and conclusions 2

Reservoir operations 3

Hydrographic survey equipment and method 3

GPS technology and equipment 4

Survey method and equipment 6

Reservoir area and capacity 7

Topography development 7

Development of 1997 contour areas 9

1997 storage capacity 9

Sediment analyses 9

References 11

Table

TABLES

1 Reservoir sediment data summary (page 1 of 2) 13

1 Reservoir sediment data summary (page 2 of 2) 14

Figure

FIGURES

1 Arrowrock Reservoir location map 15

2 Arrowrock dam, plan and section 16

3 Arrowrock 1997 underwater data points 17

4 Arrowrock Reservoir topographic map, No. 3-D-2227 19

5 Arrowrock Reservoir topographic map, No. 3-D-2228 21

6 Arrowrock Reservoir topographic map, No. 3-D-2229 23

7 Arrowrock Reservoir topographic map, No. 3-D-2230 25

8 Arrowrock Reservoir topographic map, No. 3-D-2231 27

9 Arrowrock Reservoir topographic map, No. 3-D-2232 29

10 Arrowrock Reservoir topographic map, No. 3-D-2233 31

11 1997 area and capacity curves 33

in
INTRODUCTION

Arrowrock Dam, one of five principal features of the Boise Project, is located in Elmore County

about 15 miles east of Boise, Idaho and about 4 miles below the confluence of the North and

South Forks of the Boise River (fig. 1). Additional principal features are Anderson Ranch

Dam, Black Canyon Dam, Boise River Diversion Dam, Cascade Dam, and Deadwood Dam.

Lucky Peak Dam, built by the Corps of Engineers, is located about 1 mile upstream from the

Boise River Diversion Dam and backs water up to Arrowrock Dam. Arrowrock Dam and

Reservoir are owned and operated by Reclamation with the principal purpose to furnish

irrigation water.

Arrowrock Dam construction was completed in 1916 with first storage in February 1915. The

dam was repaired and raised an additional 5 feet from 1935 through 1937. The dam is a thick

arch concrete structure whose dimensions are (fig. 2):

• Hydraulic height1 257 feet

• Top width 16 feet

• Crest elevation 3,216.0 feet

• Structural height 350 feet

• Crest length 1,150 feet

• Top of parapet wall 3,219.75 feet

The drainage area above Arrowrock Dam is 2,210 square miles, of which a calculated

1,597 square miles contributed sediment inflow during the study period. Sediments from the

remaining drainage area are trapped by Anderson Ranch Reservoir and Dam that have a

drainage area of 980 square miles and began water storage in December 1945. The basin

ranges from elevation (feet)2 3,216, top of dam, to about 10,000 feet. Arrowrock Reservoir has

an average width of 0.2 miles with a length, at elevation 3,216, of around 23.5 miles that

includes the North and South Forks of the Boise River.

Arrowrock Dam's spillway, located in a granite cut at the right side of the dam, is a sidechannel type structure controlled by 6 structural steel drum gates that are 62 feet long and

6 feet high, and separated by 6-foot piers. The spillway chute channel, about 800 feet long, is

a concrete lined trapezoidal section that discharges into the tailwater formed by Luck Peak

Reservoir. The spillway crest is at elevation 3,210.0 with top of gates at elevation 3,216.0.

The spillway provides a maximum discharge of 40,000 cubic feet per second (ft3/s) at maximum

reservoir water surface elevation 3,219.75.

The outlet works consists of 25 outlets through the dam that are located in 3 tiers. These

outlets have an original maximum discharge of 28,600 ft3Is at reservoir water surface elevation

3,210.0. However, operation restrictions, as described in the current Arrowrock Dam standard

operating procedures, have been placed on the outlets, have reduced the maximum discharge

capacity allowed. The lower tier consists of five sluice outlets with a centerline elevation of

2,967.0. Each sluice outlet is 60 inches in diameter and controlled by 5- by 5-foot highpressure gates. The middle tier consists of 10 outlets with a centerline elevation of 3,018.0.

1The definitions 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

Reser.'oirs, or ASCE's Nomenclature for Hydraulics.

2Elevation levels are shown in feet.
Seven of these outlets are 52-inches in diameter with the other 3 tapering from 52- to 72-inch

diameter. The upper tier consists often 52-inch diameter outlets with a centerline elevation

of 3,105.0. The upper and middle outlets are primarily for irrigation and river releases

controlled by 58-inch Ensign balanced valves installed at the upstream face of the dam.

SUMMARY AND CONCLUSIONS

This Reclamation report presents the 1997 results of the survey of Arrowrock Reservoir. 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

Standard land surveying methods were used to establish the horizontal and vertical control

points for the aerial survey that was flown in October 1987 around reservoir water surface

elevation 3028. The aerial survey analysis was conducted by Reclamation's Mid-Pacific Region

with the purpose of developing an area-capacity table of Arrowrock Reservoir. The average

end area method was used to calculate the reservoir area and resulting volume by

interpolating cross sections at 200-foot spacing throughout the reservoir. The survey

measured a surface area of 3, 138 acres and a storage capacity of 280,526 acre-feet at reservoir

elevation 3,216.0. The study assumed a reservoir capacity of 5,430 acre-feet at elevation

3,028.0. This capacity came from the 1949 Arrowrock capacity tables and assumed no volume

change due to sediment inflow.

The 1997 underwater survey was conducted to complete the reservoir topography below

elevation 3,028 and to measure changes due to sediment deposition, above elevation 3,028,

since the 1987 aerial survey. The horizontal control established for the aerial survey was also

used for the June 1997 hydrographic survey. 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 Arrowrock Reservoir. The positioning system provided information to allow the

boat operator to maintain course along these grid lines. The grid lines were set up and run

to concentrate the data collection in the channel sections of the 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.

1997 Arrowrock Reservoir surface areas at predetermined contour intervals were generated

by a computer graphics program using the collected reservoir data. The new reservoir

topographic map is a combination of the 1987 aerial and 1997 underwater-measured

topography, but was predominantly developed by the 1987 aerial data. The 1997 underwater

collection provided data not covered by the aerial survey and in the river channel sections of

the reservoir that had changed due to sediment deposition since 1987. The 1997 area and

capacity tables were produced by a computer program that uses measured contour surface

2
areas and a curve-fitting technique to compute area and capacity at prescribed elevation

increments (Bureau of Reclamation 1985).

Table I contains a summary of the Arrowrock Reservoir's watershed characteristics for the

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

272,224 acre-feet and a surface area of 3,141 acres at reservoir elevation 3,216.0 feet. Since

closure in 1915, the reservoir had an estimated volume change of 19,376 acre-feet below

reservoir elevation 3,216.0. This volume represents a 6.6 percent loss in capacity and an

average annual loss of 235.4 acre-feet per year.

RESERVOIR OPERATIONS

Arrowrock Reservoir is primarily an irrigation facility, but operates in conjunction with

Anderson Ranch and Lucky Peak Reservoirs to provide flood control. The July 1997 areacapacity tables show 272,224 acre-feet of total storage below elevation 3,216.0. The 1997

survey measured a minimum elevation of 2,987.4 which is around 20 feet above the five sluice

outlets of the dam.

The Arrowrock Reservoir inflow and end-of-month stage records in table 1, operation period

October 1947 through June 1997, show the inflow and annual fluctuation since the last

reservoir survey in 1947. The average inflow into the reservoir for this operation period was

1,799,300 acre-feet per year. Extreme storage fluctuations of Arrowrock Reservoir ranged

from an elevation of 2,969.0 in 1987, when there was no usable content, to the maximum

recorded elevation of 3,219.1 in 1948 (table 1). The records show that in most years the

reservoir fills to the near-full reservoir elevation of 3,216 and annually, while supplying

irrigation water downstream, drops 100 to 200 feet in elevation. Records also show that, prior

to the 1954 construction of Lucky Peak Reservoir, 50 percent of the years the sluice gates were

operated wide open from a few days to a few months at a time. This allowed the natural flow

to pass through the reservoir flushing a portion of the accumulated sediment downstream

toward the dam and through the sluice gates. The 1947 sedimentation study estimated

1,300 acre-feet of the reservoir sediment was removed by sluicing from 1915 through 1947.

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. To obtain the maximum radio transmission range, known datum

points with clear line-of-sight to the survey boat were selected. The power for the shore unit

was provided by a 12-volt battery.

3
GPS Technology and Equipment

The hydrographic positioning system used at Arrowrock Reservoir was Navigation Satellite

Timmg 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.

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 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 (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. For hydrographic surveying of the altitude, Arrowrock's

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

observations were needed to track the survey vessel. During the Arrowrock 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

4
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 Arrowrock 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 Arrowrock 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 Arrowrock 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

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 6-channel Li coarse acquisition (CIA) code continuous paralleltracking receiver, an internal modem, and a UHF radio transceiver. The differential

correctious 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 to collect data in 1927 or 1983 North American Datums (NAB) in the surveyed

5
area's state plane coordinate system's zone. For Arrowrock Reservoir, the data were collected

in Idaho's 1927 NAD west state plane zone. The 1997 developed contours had to be shifted

slightly to match the digitized U.S. Geological Survey (USGS) quad features.

Survey Method and Equipment

The Arrowrock Reservoir hydrographic survey collection was conducted June 16 through

June 19, 1997. The water surface, collected in 15-minute increments, varied between

elevations 3,211.4 and 3,214.9, where at the time, the reservoir was spilling. 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 closely spaced grid lines covering the reservoir area. Most of the transects (grid lines)

were run in a perpendicular direction to the original river thaiweg at 300-foot spacing. 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. A graphic plotter

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

process.

The topography of the Boise River drainage area above Arrowrock Dam is rugged and

mountainous with the reservoir having very steep slopes and the upper area very narrow with

steep bank conditions. These conditions make it difficult for surveying mainly when you

consider the original survey was conducted by standard land survey techniques. The 1987

aerial survey needed extensive horizontal and vertical control requiring a helicopter to gain

access to many of the control points. The 1987 aerial collection was conducted when the

reservoir was nearly empty, about elevation 3028, which allowed mapping of the majority of

the reservoir area. The 1947 sedimentation study (Reclamation 1948) observed a

redistribution of sediment during the course of the survey where the channel sediments in the

upper arms of the reservoir were flushed downstream into the lower reservoir. Due to these

conditions the 1997 survey focused the underwater collection in the channel portions of the

reservoir using the aerial data to map the steep side slopes of the reservoir. This assumed no

change of the steep side slopes of the reservoir since 1987. The 1997 hydrographic survey ran

transects of the channel portions of the reservoir from Arrowrock Dam upstream into the

North and South Forks of the Boise River. The collection ended in the upstream area of the

north and south forks of the reservoir when a comparison of the 1997 collected depths with the

1987 depths found no significant change.

To keep the 1997 control work to a minimum the hydrographic survey started with three 1987

established control points that were accessible and located in the lower portions of the

reservoir. Three temporary points were established in June of 1997, using the 1987 control,

to provide the needed shore datums to survey the channel areas of the north and south forks

of the river. A listing of the 1987 control points used during the 1997 hydrographic survey

control is shown below.

6
Point number North East Elevation

101 701095.50

103 706226.60

104 703082.73

456656.78

459852.96

465451.93

3255.94

3228.70

3245.63

The 1997 underwater data were collected by a depth sounder that 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 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 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 postprocessing, and when the analog charted depths indicated a difference

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

charts were also used to determine the steep side slopes of the data files which were removed

from the underwater data set. The water surface elevations at the dam, recorded by a

Reclamation gauge at 15-minute intervals, were used to convert the sonic depth measurements

to true lake-bottom elevations.

RESERVOIR AREA AND CAPACITY

Topography Development

Using ARC/INFO the topography of Arrowrock Reservoir was developed from the combined

1987 aerial and 1997 underwater data. ARC/INFO is a software package for development and

analysis of geographic information system (GIS) layers and development of interactive GIS

applications (ESRI 1992). GIS technology provides a means of organizing and interpreting

large data sets. The new topography was predominantly developed by the 1987 aerial data.

The 1997 underwater collection provided data in the channel sections of the reservoir not

covered by the aerial collection and in the reservoir areas that changed due to sediment

deposition since 1987.

Using ARCEDIT the underwater and aerial data layers were plotted. Using the select and

delete commands the 1987 aerial data points of the reservoir channel sections that were

overlapped by the 1997 underwater channel section data were removed. Removal of the

overlapping 1987 channel data generated present reservoir condition topography. This data

set was used to compute present reservoir capacity.

During contour development, interpolated data points wre used because there were inadequate

aerial data points for developing complete upper contours at Arrowrock Dam and at the

vertical wall of Lambing Creek. The 1987 aerial analysis measured cross sections at 200-foot

spacings starting at the upstream face of the dam. This was adequate for area computations,

but lacked necessary data points to cause complete upper contour closure. At elevation

3,216.0, the 1987 cross section aerial analysis measured a surface area of 3,140 acres and the

1997 study measured a surface area of 3,141 acres with the interpolated data points. The

7
interpolated data points resulted in a complete contour that was closer with an insignificant

change to the area computation. Appending the edited aerial and underwater data sets gave

a total of 16,191 coordinate points for contour development as illustrated on figure 3. The

combined collected data ranged from elevation 2,987.3 to elevation 3,490.8. The data were

collected in the Idaho west zone state plane coordinates in NAD 1927. A slight shift in the

contour data was required to match with the USGS quad map features.

The contours of the reservoir were developed by digitizing a boundary around the edge of the

combined data set that covered the reservoir area. The digitized polygon enclosing the data

set was assigned an elevation of no data and was used to perform a clip of Arrowrock Reservoir

such that interpolation was not allowed to occur outside of this boundary. This clip was

performed using the hardclip option of the ARC/INFO CREATETIN command.

Contours for the reservoir were computed from the combined 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 between 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

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 Arrowrock 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 no bearing on the computation of surface areas and volumes

for Arrowrock Reservoir since the areas were calculated from the developed TIN.

ARC/INFO V7.O.2 GIS software was used to digitize the USGS quad features such as the dam,

roads and portions of reservoir contour elevation 3,216.0. The digitized features were

transformed to Idaho's NAI) 1927 west state plane coordinates using the ARC/INFO

PROJECT command. Using ARCEDIT, the 1997 developed contours and the digitized USGS

feature layers were plotted. The resulting plot found that the 1997 developed contours did not

line up with the USGS digitized features. To match the USGS quad layer with the 1997

contour layers required shifting the 1997 contours about 90 feet to the west and 195 feet to the

south. This shift to line up the features did not affect the computed surface areas and

resulting reservoir volume since the 1987 aerial and 1997 underwater data were collected with

the same control system. The contour topography at 10-foot intervals is presented on

figures 4 through 10 (drawing numbers 3-D-2227 through 3-D-2233). The contour topography

on these maps was drawn as developed without any shifting of the 1987 and 1997 collected

data. The USGS features on the maps were shifted about 90 feet to the east and 195 feet to

the north to line up with the 1997 Arrowrock Reservoir contours.

8
Development of 1997 Contour Areas

The 1997 contour surface areas for Arrowrock Reservoir were computed at 5-foot increments,

from elevations 2,988.0 to 3,225.0, using the Arrowrock Reservoir TIN discussed above. The

1997 survey measured the minimum reservoir elevation at 2,987.3 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.

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 5-foot contour intervals from minimum reservoir elevation 2,987.3 to elevation 3,225.0 were

used as the control parameters for computing the Arrowrock Reservoir capacity. 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. The error limit was set at 0.000001 for Arrowrock 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

where:

y = capacity

x = elevation above a reference base

a1 = intercept

a2 and a3 = coefficients

Results of the 1997 Arrowrock Reservoir area and capacity computations are listed in table 1.

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 June 1997, at elevation

3,216.0, the surface area was 3,141 acres with a total capacity of 272,224 acre-feet.

SEDIMENT ANALYSES

Figure 11 is a plot of Arrowrock Reservoir's original area data versus the 1997 measured

areas. This illustrates the difference between the original and the 1997 measured surface

9
areas. At elevation 3,216.0, the 1997 survey measured a 1.6 percent larger surface area of

3,141 acres compared to the original measured surface area of 3,089 acres. This difference

could be attributed to shore line erosion, but the area plots are a near-mirror image of each

other possibly indicating an elevation datum difference between the surveys. Review of

available literature did not find any reference to either of these conditions.

The topography of the drainage area above Arrowrock Dam is rugged and mountainous with

the slopes of the valley sides of the reservoir being very steep. These types of conditions make

it very difficult for surveying. It is assumed that the 1915 surface areas were measured by

standard plane table survey techniques. For the 1987 aerial survey a helicopter was used to

gain access to many of the control points. It is the general conclusion by this study that the

resulting surface area difference of the two surveys was mainly attributed to the accuracy

difference between the two methods of collection.

One of the purposes of the 1997 survey was to measure the reservoir volume lost due to

sediment contribution since dam closure in 1915 and since the last reservoir sedimentation

survey in 1947. The 1947 sedimentation survey of Arrowrock Reservoir indicated that the

original, 1915, measured capacity at elevation 3,216.0 was 279,250 acre-feet with the 1947

measured capacity being 271,550 acre-feet. The 1947 operation capacity at elevation 3,216.0

was reported as 286,500 acre-feet which was calculated from inflow-outflow records. The

14,950 acre-feet difference between the 1947 measured and operating capacity was attributed

to significant bank storage. For the purpose of the 1997 study it was assumed the capacity

difference is more due to the method and accuracy of the different surveys than bank storage.

From the 1915 inflow and outflow records the original operation capacity at elevation 3,211.0

was reported as 276,500 acre-feet. In 1935, the dam was raised to elevation 3,216.0. For the

purpose of calculating 1997 sediment deposition the original capacity was projected to be

291,600 acre-feet at elevation 3,216.0.

Since Arrowrock Dam closure in February 1915, the measured total volume change at

reservoir elevation 3,216.0 was estimated to be 19,376 acre-feet. The estimated average

annual rate of capacity lost for this time period (82.3 years) was 235.4 acre-feet per year. The

storage loss in terms of percent of original storage capacity was 6.64 percent. Table 1 contains

the Arrowrock Reservoir sediment accumulation and water storage data based on the 1997

resurvey.

The sediment computation values must be questioned due to all the interpolation of reservoir

capacity and sluicing of reservoir sediments, but the resulting value of 235.4 acre-feet per year

appears reasonable when compared to previous studies and other reservoirs in the region. It

must be noted that all the annual sediment accumulation values in table 1 do not account for

reservoir sediment that has been removed due to sluicing operations. The 1947 sediment

survey of Arrowrock Reservoir gave a conservative estimate of 1,300 acre-feet of sediment that

had been sluiced from the reservoir. If this value was considered in the 1947 study then the

estimated average annual rate of sediment inflow would have been 276.1 acre-feet. The

sediment trapping affect of Anderson Ranch reduced this annual value to 230.2 acre-feet, but

as stated previously all the interpolations affect the actual sediment computation values. A

resurvey of Arrowrock Reservoir should be considered in the future if major sediment inflow

10
events are observed, or if the average annual rate of sediment accumulation requires further

clarification.

REFERENCES

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

York, 1962.

Bureau of Reclamation, Sedimentation Survey of Arrowrock Reservoir, Boise Project,

Hydrology Division, Denver, Colorado, March 1948.

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

of Reclamation 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, Arrowrock Reservoir Area and Capacity Tables, Boise

Project, Pacific Northwest Region, Denver, Colorado, June 1997.

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

Hydrographic Survey and Dredge Positioning, EU 1110-7-5 (FR), Department of the

Army, Washington DC.

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

Goodson & Associates, Inc., Technical Data Workbook Abstract Report for Arrowrock Dam,

Sun River Project, Montana, Upper Missouri Region, May 22, 1981.

11
I

I

t

RESERVOIR SEDIMENT

DATA SUMMARY Arrowrock Reservoir

NAME OF RESERVOIR 1

DATA SHEET NO.

D 1. OWNER Bureau of Rec1anation 2. STREAM Boise River 3. STATE Idaho

A 4. SEC. 13 TWP. 3 N RANGE 4 E 5. NEAREST P.O. Boise

1

6. COUNTY Elmore

H 7. LAT 43' 35' 39 LONG 115' 55' 20'

.

8. TOP OF DAM ELEVATION 3219.75 9. SPILLWAY CREST EL 3210.0'

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

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

S BEGAN

E _______________________ _____________________ ______________________

R a. SURCHARGE

_____________________ ______________________

V

0

b. FLOOD CONTROL

2

I C. POWER /15

H d. WATER SUPPLY 16. DATE

e. IRRIGATION

________________ ________________ OPERATION

f. CONSERVATION 3216.0 3089

________________

286,500

_________________

286,500 BEGAN

g. DEAD 2/15

-

17. LENGTH OF RESERVOIR 23.5 MILES AVG. WIDTH OF RESERVOIR 0.2 MILES

B 1$. TOTAL DRAINAGE AREA 2,210 SQUARE MILES 22. MEAN ANNUAL PRECIPITATION 11.7 INCHES

19. NET SEDIMENT CONTRIBUTING AREA 1,597' SQUARE MILES 23. MEAN ANNUAL RUNOFF 14.6' INCHES

I 20. LENGTH 66 MILES AV. WIDTH 33 MILES 24. MEAN ANNUAL RUNOFF 1,717,100' ACRE-FEET

N

21. MAX. ELEVATION 10000 MIW. ELEVATION 3216 25. ANNUAL TDP. MEAN 52'F RANGE -23'F to 108'F'

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, AC. ACRE-FEET RATIO AR/AR

R YRS. YRS. INTERVAL

V

E

2/15 Contour 20-ft 3.089 291,600 .17

Y 10/47 32.6 32.6 Range 71 3,089 286,500 .17

6/97 497 82.3 Contour (D) 10-ft 3,141 272,22410 .16

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

A STJRVEY ANNUAL

PRECIP. a. MEAN ANN. b. MAX. ANN. C. TOTAL a. MEAN ANN. b. TOTAL

10/47 18.53 1,572,509 3,006,000 51,892,823 1,572,509 51,892,823

6/97 11.7 1,799,30011 3,107,800 89,423,890 1.717,100 141,316,713

26. DATE OF 37. PERIOD CAPACITY 1.055, ACRE-FEET 38. TOTAL SEDIMENT DEPOSITS TO DATE, AR

SURVEY

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

10/47 7,700" 235.9 .11 7,700 235.9 .11

6/97 14,27613 230.2 .14 19,37614 235.4 .15

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

SURVEY MT. (#/r13) INFLOW, PPM

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

DATE ANNUAL DATE PER. TOT.

10/47 73 173.3 173.3 0.0869 2.84 174 174

6/97 0.080714 6.6414

26.

DATE

43. DEPTH DESIGNATION RANGE BY RESERVOIR ELEVATION

1';RVEY I I

PERCENT OF TOTAL SEDIMENT LOCATED WITHIN DEPTH DESIGNATION

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).

13
45. RANGE IN RESERVOIR OPERATION

YEAR MAX. ELEV. MIN. ELEV. INFLOW, AR YEAR MAX. EL,EV. WIN. ELEV. INFLOW, AR

1948 3,219.1 3,089 1,572,900 1949 3,219 3,056 1,492,850

1950 3,219 3,057 1,816,940 1951 3,218 3,048 1,797,780

1952 3,216 3,071 2,553,240 1953 3,216 3,087 1,898,980

1954 3,219 3,058 1,907,430 1955 3,217 3,068 1,166,880

1956 3,217 3,045 2,213,570 1957 3,217 3,070 1,976,870

1958 3,217 3,068 2,204,260 1959 3,214 3,030 1,382,600

1960 3,217.0 2,993.0 1,591,300 1961 3,217.0 2,993.0 1,235,080

1962 3,211.5 3,031.0 1,447,110 1963 3,217.8 3,035.9 1,606,100

1964 3,216.4 3,060.2 1,606,200 1965 3,216.8 3,108.7 3,107,800

1966 3,214.9 3,021.9 1,300,700 1967 3,206.4 3,019.7 1,378,500

1968 3,214.2 3,006.0 1,336,100 1969 3,215.6 3,023.8 2,163,500

1970 3,216.0 3,067.8 2,053,600 1971 3,216.8 3,009.1 2,904,800

1972 3,216.2 3,063.4 2,659,500 1973 3,214.7 3,024.5 1,331,400

1974 3,213.4 3,106.0 2,714800 1975 3,213.7 3,101.5 2,257,200

1976 3,213.3 3,061.1 1,871,600 1977 3,185.0 2,994.0 912,600

1978 3,213.1 3,071.8 1,672,200 1979 3,213.7 3,181.0 1,080,600

1980 3,215.8 3,120.6 1,731,100 1981 3,216.4 3,085.2 1,254,800

1982 3,217.2 3,108.5 2,714,900 1983 3,215.3 3,094.8 2,796,900

1984 3,216.7 3,112.8 2,582,670 1985 3,205.7 3,085.5 1,492,680

1986 3,216.0 3,148.4 2,462,560 1987 3,199.7 2,969.0 1,129,570

1988 3,181.8 3,000.0 994,330 1989 3,188.2 3,025.4 1,444,930

1990 3,172.7 3,068.0 1,160,000' 1991 3,198.9 3,055.7 1,079,460

1992 3,160.4 3,040.6 777,570 1993 3,213.2 3,103.2 1,470,800

1994 3,198.7 3,044.1 1,007,870 1995 3,215.6 3,077.8 l,848,00O

1996 321'3 2.39.9t1 1997 -.21S 3111 2.7l4.R30

46. ELEVATION - AREA - CAPACITY DATA FOR 1,9'? CAPACITf' __________ __________ __________ __________

ELEVATION AREA CAPACITY ELEVATION AREA CAPACITY ELEVATION AREA CAPACITY

2987.3 0 0 3000 7.7 21 3010 40.1 263

3020 70.9 814 3030 156.3 1,957 3040 202.0 3,740

3050 265.8 6,071 3060 402.6 9,464 3070 554.5 14,149

3080 702.5 20,472 3090 869.6 28,339 3100 1,045.1 37,912

3110 1,204.0 49,160 3120 1,358.8 61,962 3130 1,531.9 76,383

3140 1,694.8 92,540 3150 1,853.0 110,295 3160 2,022.6 129,683

3170 2,195.7 150,750 3180 2,374.7 173,605 3190 2,561.2 198,282

3200 2,775.2 224,962 3210 2,998.1 253,815 3216 3,141 272,224

3220 3,248.0 285,003

7. REMARKS AND REFERENCES

2

Top parapet wall is elevation 3219.75. Roadway elevation is 3216.0. Dam raised 5-feet in 1935.

Top of gates elevation is 3216.0. Spillway sill elevation is 3210.0.

Length main arm = 12.8 miles, length of South Fork arm = 10.7 miles.

Bureau of Reclamation Project Data Book, 1981. Reported value for all of Boise Project. 2

Represents loss of contributing rea since am closure2 12/45, at Anderson Ranch with tot al drainage of 980 mi

6

Net contributing area of 1597 mi = 2210 ml - 980 ml (51.5 yrs/82.3 yrs) .

Calculated using mean annual runoff value of 1,717,100 AR, item 24, 1915-1997.

Computed annual inflows from 1915 through 6/97.

The original calculated volume at el. 3216 was 279,550 AR which did not include bank stor age. Based on 1915

inflow-outflow records the original operating capacity, at el. 3211, was reported as 276. 500 AR. Dam raised 5-ft

in 1935. For sediment computations, the original operating capacity, at el. 3216, was projected to be 291,600 AR.

1947 survey measured capacity reported as 271,550 AR at El. 3216. The operation capacity reported as 286,500 AK,

10 based on 1935 inflow - outflow records. The difference attributed to significant bank st orage.

Surface area & capacity at el. 3216.0 computed by ACAP program using 1987 aerial and 1997 underwater survey data.

Inflow values in acre-feet and maximum and minimum elevations in feet by water year from 2/15 through 6/97.

Inflow estimated for 1990 and 1995 due to missing monthly records. Years with whole elevation values in item 45

12 were estimated from reservoir content reCords. 1960 through 1996 from USGS water records.

The 1947 sediment survey assume a original capacity of 279,250 AR and 1947 capacity of 27 1,550 AR at El. 3216.0.

Volume does not include 1,300 AR of sediment estimated to have been remov ed by sluicing. 13

14 Difference of capacity 1935 (286,500 AR) & 1997 (272,224 AK). Average value for 62 years of operation.

Question as to true original capacity. 1915 inflow - outflow records measured capacity as 276,500 AR at el. 3211.

Projected 1915 reservoir capacity as 291,600 AR, at el. 3216.0. ASsume portion of capaci ty difference due to

1ccuracy difference of two surveys.

Capacities computed by Reclamation's ACAP computer program.

48. AGENCY MAKING SURVEY Bureau of Reclamation

49. AGENCY SUPPLYING DATA Bureau of Reclamation } DATE May 1998

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

14
McCall

I

cowcii f: IRRIGABLE AREA

C.4XADE

(J RE$ERVOIR

• CRANE J / / DEADWOOD

RESE OIR, R&ERV()!R

/

WASH JNGTON

__

. CU'TR

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- / .

P A Y E]/T E Lowman

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I

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Murphy 6

SCALE OF MILES

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S. (1 RESERVOIR,T

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AWWRK

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OtSE RJVZZ .. -

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Home

Figure 1. - Arrowrock Reservoir location map.

15
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OOOO9

006r +- ooos f

°° -F

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Figure 4. - Arrowrock Reservoir topographic map, No. 14
about

atch

dd

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.'f#i hVntr 8E5EA'VO/R

ac*,,r_____ ff1W/t(1 AMf(

gure 5. - rrowroci IIeSOIVOII iopograpnic map, NO.

--'''

21
B

115000+

770000+

zootol datum by US Bureau of

amatsorl survey, Must be shifted about

eet sest 51171 195 feet south to match

os State Plane Zone West (NA027)

Icel OStum is National Geodetic

ical Datum of 1929 (LevelS pr'ovaded

5 Bureau of Geclamatlon(

755055+ 755050+

,cwacr #reqva,n'

Ta7

ae*'ar______ mwitt 4qh

P Ir_____ __________

aFIgure 6. - Anowmck Reservoir topographic maps No. 3-D-2229. 23
ou Of

8flft8d 8bOUt

outh to .atch

'St (N0027)

Geode t C

tis provided

'VOl,?

Figure 7. - Arrowrock Reservoir topographic map, No. 25
700000+ 000004

695000+

N

w

665000-

E

S

rift7 LV Itfll ha'

.*..f,: 1lif

6.0000-f000*00+

10,'OZorOtOi Saturn by US Bureau of

Seci000tion suroey. Huet be Ohoftad about

90 feet west and 190 feet south to natch

109506 State piase Zone West (NAD27)

VertIcal Saturn Is NatIor00l ue000toc

fertocal Saturn Of 1929 L00010 000voded

y US Bureau of Reclomatfoni

awtxr h'ESEk'VO/R

_______ JTW/t 04'flf

z' ar_____ __________

a-

_________ Av.w, t4/icth uvrjo, uN

FIgure 8. - Arrowrock Reservoir topographic map, No. 3-D-2231.

27
N

w E

S

6500 Tiff

L, $i* IVt ff.X

$.vI: IV

S

HorIzontal datue by US Buresu of

Reclamation survey, Must be shafted about

90 feet west and 195 feet south to metch

Idahos State Plane Zone West (NA027

Vertical datum is Natlonel Geodetic

Vertical Oatait üf 1929 (Levels provided

by US Bureau of Reclamatloul

S

0

B

555000+

w.me

wcr #rs'roi#

_______ /Ta*/t41 4MKH

if_____ _________

Agure 9. - Arrowrock Resevofr topographic map, No. 3-D-2232. 29
WHE

__

e00000+

12 v iw 15X °°°°°+

te/,z f:**B

-

South Fork Boise River

sono- 6GouHorizontal datum by US Bureau of

PeciemaUun survey. Bust be shifted about

90 feet meet and 195 feet south to edhub

Idahos State Plane Zone West NA027)

Verticel datoc is fiatl000l GeodetIc

Vertical batum of 1929 LeuelS irovided

by US Bureau of Peclamatlon

,fEs&WO/R

ratxar

1WY______ iraWIAt 4

aw iv _________

iw, t4/#(M' I

Figure 10. - Arrowrock Reservoir topographic map, No. 3-0-2233.
Area-Capacity Curves for Arrowrock Reservoir

Area (acres)

3300 3025 2750 2475 2200 1925 1650 1375 1100 825 550 275 0

3220

3200

3180

3160

3140

3120

3100

3080

3060

3040

3020

3000

2980

2960

_/iI Capacf y - ________ ---- _______ ________ ________ ________ ________ ________ ________

________

3200

3180

3160

3140

3120

3100

3080

3060

3040

3020

3000

2980

2960

0 25000 50000 75000 100000 125000 150000 175000 200000 225000 250000 275000 300000

CapacIty (acre-feet)

Figure 11. - 1997 area and capacity curves.
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.