NELSON RESERVOIR

1999 RESERVOIR SURVEY

r,..FORTFIp.

U.S. Department of the Interior

Bureau of Reclamation
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July2001 Final

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4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Nelson Reservoir PR

1999 Reservoir Survey

6. AUTHOR(S)

Ronald L. Ferrari

_______________________

7. PERFORMING ORGANTZA11ON NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

REPORT NUMBER

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

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AGENCY REPORT NUMBER

Bureau ofReclamation Denver Federal Center P0 Box 25007

Denver CO 80225-0007 DIBR

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13. ABSTRACT (Maximum 200 words)

The Bureau of Reclamation (Reclamation) surveyed Nelson Reservoir in May 1999 to develop a topographic map and compute a

present storage-elevation relationship (area-capacity tables). The underwater survey was conducted near reservoir elevation 2,218

feet (project datum). The underwater survey used sonic depth recording equipment interfaced with a global positioning system

(GPS) that gave continuous sounding positions throughout the underwater portions of the reservoir covered by the survey vessel.

The above-water topography was determined by digitizing the water surface contour line from the U.S. Geological Survey

quadrangle (USGS quad) maps of the reservoir area. The new topographic map of Nelson Reservoir was developed from the

combined 1999 underwater measured topography and the digitized water surface contour. As of May 1999, at maximum

conservation water surface elevation (feet) 2,221.6, the surface area was 4,331 acres with a total capacity of 78,950 acre-feet.

14. SUBJECT TERMS 15. NUMBER OF PAGES

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

contour area] reservoir area! sedimentation survey! global positioning system

_____________________

16. PRICE CODE

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

CLASSIFICATION CLASSIFICATION OF ABSTRACT ABSTRACT

OF REPORT OF THIS PAGE

UL

UL UL UL

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

Prescribed by ANSI Std. 239-18

298-102
NELSON RESERVOIR

1999 RESERVOIR SURVEY

by

Ronald L. Ferrari

Sedimentation and River Hydraulics Group

Water Resources Services

Technical Service Center

Denver, Colorado

July 2001
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 and James Melena of the TSC

conducted the hydrographic survey. Ronald Ferrari completed the data

processing needed to generate the new topographic map and area-capacity

tables. Sharon Nuanes of the TSC completed the final map development.

James Melena 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, useflulness, or completeness

is expressed or implied.

11
CONTENTS

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Page

Introduction 1

Summary and Conclusions 1

Reservoir Operations 2

Hydrographic Survey Equipment and Method 2

GPS Technology and Equipment 3

Survey Method and Equipment 5

Nelson Reservoir Datum 5

Reservoir Area and Capacity 6

Topography Development 6

Development of 2000 Contour Areas 8

2000 Storage Capacity 9

Analyses of Results 9

References 10

TABLES

Table

1 1999 Nelson Reservoir Static GPS control survey 7

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

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

3 Summary of 1999 survey results 13

FIGURES

Figure

1 Nelson Reservoir location map 14

2 Nelson Reservoir underwater data collection 15

3 Nelson Reservoir topology map, No. 15-D-282 17

4 Nelson Reservoir topology map, No. 15-D-283 19

5 Nelson Reservoir topology map, No. 15-D-284 21

6 Nelson Reservoir topology map, No. 15-D-285 23

7 Nelson Reservoir topology map, No. 15-D-286 25

8 Nelson Reservoir topology map, No. 15-D-287 27

9 1999 area and capacity curves 29

111
INTRODUCTION

Nelson Reservoir is an offstream storage facility of the Milk River Project located about 19 miles

northeast of Malta, Montana (figure 1). The reservoir is formed by five dikes designated as Nelson

Dikes A, B, C, D, and DA, with DA being the largest with a structural height of 28 feet and a

hydraulic height of 21.6 feet. Dikes C and DA were originally constructed in 1915 by the U.S.

Reclamation Service. In 1922, Dikes C and DA were raised around 11 feet and Dikes A, B, and D

were constructed to enlarge the reservoir. The five dikes are homogeneous earth embankments with

structural heights varying from 5 to 28 feet. The dikes have crest width that vary from 18 to 26 feet

and a crest length of 9,900 feet at elevation 2,228.0 (feet)'. Numerous surveys have been conducted

over the years indicating settlement at some dike locations with measured elevations below the

design crest elevation 2,228.0. The reservoir had an original total storage capacity of 79,224 acrefeet at elevation 2221.6 with a dead storage capacity of 18,650 acre-feet at elevation 2200.0. The

reservoir has a maximum design capacity at elevation 2223.0, but it has never operated above

elevation 2221.6.

Nelson is an offstream storage reservoir with no designed spiliway. All reservoir releases are

through the outlet works requiring the dam tender to prevent dike overtopping while preventing

discharges from overtopping the canal banks. The reservoir has two outlet works, one through Dike

C with discharges up to 550 cubic feet per second (cfs) to the Nelson North Canal that discharges

into the Milk River and through Dike DA with discharges up to 250 cfs to the Nelson South Canal

used for project irrigation.

The drainage area above the Nelson Reservoir dikes is around 35.2 square miles with normal base

inflow from the drainage area being essentially zero. Nelson Reservoir has an average width of 0.7

miles and a length of 9 miles at elevation 2221.6.

SUMMARY AND CONCLUSIONS

This Reclamation report presents the 1999 results of the survey of Nelson Reservoir. The primary

objectives of the survey were to gather data needed to develop reservoir topography and compute

present area-capacity relationships. Prior to the underwater survey in May of 1999, a static global

positioning system (GPS) control survey was conducted by a private contractor to establish

horizontal and vertical control points around the reservoir (see table 1). The horizontal control was

established in Montana State plane coordinates in the North American Datum of 1983 (NAD83).

The vertical control for the established points was in the National Geodetic Vertical Datum of 1929

(NGVD29) and the North American Vertical Datum of 1988 (NAVD88). The survey determined

that for these established points the average elevations in NGVD29 were around 2.46 feet lower than

in NAVD88. During the May 1999 underwater survey, the average reservoir water surface recorded

by the Reclamation gauge was elevation 2218 which was around 1.7 feet lower than the NGVD29

GPS measured water surfaces at the same time. All computations in this report are based on the

Reclamation gauge project datum which is 1.70 feet lower than NGVD29.

1Elevation levets are shown in feet. All elevations in this report are based on the original project datum

established by U.S. Bureau of Reclamation which is 1.70 feet lower than National Geodetic Vertical Datum of 1929.

1
The bathymetric survey was run using sonic depth recording equipment interfaced with a differential

global positioning system 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 Nelson Reservoir. The positioning system provided information

to allow the boat operator to maintain a 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.

Since an above water survey wasn't conducted for this study, the Nelson Reservoir water surface

contour (labeled elevation 2,222.0) was digitized from the U.S. Geological Survey 7.5 minute

quadrangle (USGS quad) maps. To match the Reclamation project datum this contour elevation was

reduced 1.7 feet and assigned an elevation of 2,220.3. The new topographic map of Nelson

Reservoir is a combination of the digitized and underwater-measured topography. The 1999

reservoir surface areas at predetermined contour intervals were generated by a computer graphics

program using this combined reservoir data. The 1999 area and capacity tables were produced by

a computer program that uses measured contour surface areas and a curve-fitting technique to

compute area and capacity at prescribed elevation increments (Bureau of Reclamation, 1985).

Tables 2 and 3 contains a summary of the 1999 Nelson Reservoir survey. The 1999 survey

determined that the reservoir has a total storage capacity of 78,950 acre-feet and a surface area of

4,331 acres at reservoir elevation 2,221.6.

RESERVOIR OPERATIONS

Nelson Reservoir operates in conjunction with several other reservoirs of the Milk River Project to

provide irrigation water. The May 1999 area-capacity tables show 78,950 acre-feet of total storage

below elevation 2,221.6. The 1999 survey measured a minimum reservoir bottom elevation of

2,174.8. The dead storage below elevation 2,220.0 was measured as 18,140 acre-feet.

The Nelson Reservoir inflow and end-of-month stage records are listed on the second page of table

1 for water year 1947 through May 1999. These records were the only ones readily available of the

reservoir operation that actually began in 1916. The estimated average inflow into the reservoir for

this available recorded period was 39,600 acre-feet per year. Since 1947, the recorded storage

fluctuations of Nelson Reservoir ranged from an end of month elevation 2,200.5 in 1984 to a

maximum end-of-month elevation 2,221.4 in 1960.

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 GPS receiver with a built-in radio and an omnidirectional antenna, a depth sounder,

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

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

was also mounted in a smaller flat bottom boat for the shallow water areas, but the rainy and breezy

2
conditions during the time of the survey did not safety allow much use of the small boat setup during

the time of this survey.

The shore equipment included an identical second GPS receiver with 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.

GPS Technology and Equipment

The hydrographic positioning system used at Nelson 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 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

L 1 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, the altitude, Nelson's

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

observations were needed to track the survey vessel. During the Nelson Reservoir survey, the best

available satellites were used for position calculations which usually consisted of 5 or more.

3
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 at the survey vessel's GPS receiver during the

Nelson 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, 1994).

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

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

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

can have errors of up to 100 meters.

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 are used during

the reservoir survey to determine positions of the moving survey vessel in real time. DGPS

determines the position of one receiver in reference to another and is a method of increasing position

accuracies by eliminating or minimizing the uncertainties. Differential positioning is not concerned

with the absolute position of each unit but with the relative difference between the positions of two

units, which are simultaneously observing the same satellites. The inherent errors are mostly

canceled because the satellite transmission is essentially the same at both receivers.

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

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

unit, remains over the known benchmark, monitors the movement of the satellites, and calculates

its apparent geographical position by direct reception from the satellites. The inherent errors in the

satellite position are determined relative to the master receiver's programmed position, and the

necessary corrections or differences are transmitted to the mobile GPS receiver on the survey vessel.

For the Nelson Reservoir, position corrections were determined by the master receiver and

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

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

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

positional accuracies for the survey vessel compared to positional accuracies of 100 meters with a

single receiver.

The Sedimentation and River Hydraulics Group began using Real-time Kinematic (RTK) GPS in

the spring of 1999. The major benefits of RTK versus DGPS are that precise heights can be

measured in real time for monitoring water surface elevation changes along with the precise

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

and height with accuracies in the order of 2 centimeters horizontally and 3 centimeters vertically.

This output is on the GPS datum of WGS-84 which the hydrographic collection software converted

4
into Montana's NAD83 state plane coordinate system. RTK GP S system employs two receivers that

track the same satellites simultaneously just like with DGPS. The receivers track the Li C/A code

and full cycle Li and L2 carrier phases. The additional data logged from the second frequency

allows the on-the-fly centimeter level measurements.

Survey Method and Equipment

The Nelson Reservoir hydrographic survey collection was conducted on May 8 through May 13,

1999 near water surface elevation 2,218 (Reclamation project datum). The bathymetric survey was

run using sonic depth recording equipment interfaced with an RTK GPS capable of determining

sounding locations within the reservoir. The survey system 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 somewhat in a perpendicular direction

to the center line of the reservoir at 300-foot spacing (figure 2). Data was also collected along the

shore as the boat traversed to the next transects. The figure shows that the western portion of the

reservoir was not as densely collected. This was due to the weather and shallow conditions of the

reservoir during the time of collection. A small boat set up was used to collect shoreline data in this

portion of the reservoirs prior to rain returning to the area. The equipment was transferred back to

the larger boat to complete the collection of the interior portion of this portion of the reservoir prior

to the heavy rains and winds. To access the western area the boat maneuvered through the narrow

portion of the reservoir plowing through the soft reservoir bottom conditions. Once in the larger

western body of the reservoir, visual cross sections were run about 1000 feet apart. The collected

data found the bottom to be very vegetated and fairly flat from bank to bank. Due to these

conditions and deterioration of the weather conditions a decision was made that adequate underwater

data was collected. The survey vessel's guidance system gave directions to the boat operator to assist

in maintaining the course along these predetermined lines. During each run, the depth and position

data were recorded on the notebook computer hard drive for subsequent processing.

The 1999 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 an RS-232 port. The depth sounder also produces an analog hard-copy chart

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

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

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

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

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

lake-bottom elevations.

Nelson Reservoir Datums

Prior to the underwater survey in May of 1999, a static global positioning system (GPS) control

survey was conducted to establish horizontal and vertical control points around the reservoir by a

private contractor. The horizontal control was established in Montana State plane coordinates in

5
NAD83. The vertical control for the established points was in NGVD29 and NAVD88. The survey

found that for the established points the average elevations in NGVD29 were around 2.46 feet lower

than in NAVD88. The results from the static survey are listed on table 1.

This control network was used during the May 1999 underwater survey for measuring horizontal and

vertical data using R1'K GPS measuring techniques. This included periodic water surface

measurements. A comparison of the reservoir water surface recorded by the Reclamation gauge 4

every 15 minutes found it was around 1.7 feet lower than the NGVD29 GPS measured water surface

at the same time. It must be noted that all computations in this report are based on the Reclamation

gauge project datum.

The Montana Area Office of the Bureau of Reclamation performed additional surveys to verify the

datum shifts. These surveys determined the original construction datum for Nelson Dikes are 1.7

feet lower then NGVD29 and all USGS quadrangle elevations should be reduced 1.7 feet to match

the original construction datum. These surveys also checked the hydromet instrumentation that is

located on the Nelson South Control Structure. The hydromet measures the reservoir elevations that

are tied to the top of the Nelson South Control Structure whose original construction elevation was

2228.0 (Reclamation datum). The survey measured the top elevation to be within 0.05 feet of the

original control datum, confirming it should continue to be used to check the hydromet

measurements.

RESERVOIR AREA AND CAPACITY

Topography Development

Using ARC/INFO the topography of Nelson Reservoir was developed from the 1999 collected

underwater data and USGS quad maps. 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 upper contours of Nelson Reservoir were developed by digitizing the water surface contour line

from the USGS quad maps that covered the Nelson Reservoir area. These contour lines were

compiled from aerial photographs taken in 1977. ARC/INFO V7. 0.2 geographic information system

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

Montana's NAD 1983 state plane coordinates using the ARC/INFO PROJECT command. The

quad's water surface contour was labeled elevation 2,222 in NGVD29. As noted previously, the

1999 GPS surveys estimated that the Nelson Reservoir Reclamation project datum was around 1.7

feet lower than NGVD29. For map development this digitized contour was assigned a vertical

elevation of 2,220.3 (elevation 2,222.0 - 1.7 feet).

6
U.S. BUREAU OF RECLAMATION I

NELSON RESERVOIR

1999 STATiC GPS CONTROL SURVEY I

CONTRACT #1 425-98-CA-60-00090

___________ ____________________

________________ ______ _______ _____________________

Montana State Plane

_______

_________

______

________

______

________

Point # Latitude

____________________

Longitude

________

Ellipsoid

_________

NAD83(1 992) NAVD 88 NGVD 29

___________ NAD83(1 992) NAD83(1 992) Height

________

Northing

____________

Easting Elevation

________

Elevation

___________ ___________________ Meters

________

Meters Meters Meters

________

Meters

NEL-1 48°" 29' 1 25705" N

___________________

107°" 35' 2 65157"W 664 121 472190 6320 741582 1942 680 839

________

680 091

NEL-2 48°" 29' 36.08509" N 107°" 39' 11.13578"W 670.309

_______

473143.3166 736457.1524 687.056

_______

686.304

NRD-NDA1 48°" 31' 49.92448" N 107°" 31' 6.26810"W 663.635

_______

477518.2664 746301.6713 680.421

_______

_______

679.677

NRD-NDA2 4800 31' 17 65837" N 107°" 31' 1268305"W 663 637

_______

476518 8441 746195 3220 680407 679664

US REC BM 4800 32' 23.37515" N 107°" 31' 4.26759"W 657.475

_______

478551.9740 746316.5512 674.278

_______

673.534

LAKESIDE 48°°25' 34.92034"N 107°°40'24.88469"W 678.555

_______

465662.7213 735117.4895 695.190

_______

694.442

NELSON 48°° 30' 48.80439" N 107°" 33' 18.18278" W 693.904

_______

475563.5849 743643.7325 710.669

_______

________

709.922

MORAINE 4800 30' 19.89407" N 10700 34' 13.65634"W 701.924

________

474642.9345 742527.9031 718.677 717.930

L439 48°°35' 2.81217"N 107°°44' 9.20971"W 666.310

_______

483089.5240 730113.4979 683.175

_______

682.414

M439 4800 33' 50.84596" N 107°" 45' 41.40358"W 677.701

_______

480825.3718 728274.2890 694.541

_______

693.775

P539 48°" 25' 55.89251" N 107°" 39' 34.05285"W 668.891

_______

466334.5995 736146.6671 685.533

_______

_______

684.788

R539 48°° 26' 17.04019" N 107°° 35' 42.02256"W 679.683

_______

467101.4268 740897.5050 696.318 _______

695.568

T539 4800 26' 16.82546" N 107°° 33' 3.07303"W 671.183

_______

467175.1427 744162.6299 687.799 687.051

W539 48°" 27' 1.94862" N 107°° 29' 24.96772"W 658.847

_______

468681.3083 748606.8826 675.451

_______

674.717

I

Notes:

The horizonta

_________ _________ ____ ____

l coordinates were established by GPS observat on and were adjusted t

_____ _____ ________

o NGS "B" order stations LAKESIDE and NELSON.

____

________

I I ________ ___ ___

Elevation values are based upon GPS observation.

___ ___ _____

________ ________ ___________ ________ ________ ________

NAVD 88 Elevations are based upon NGS Published values wnich were held at stations L439, M439, P539, R539, T539, and W539.

________

NGVD 29 Elevations are based upon the NGS "SUPERSEDED SURVEY CONTROL" value held at station MORAINE.

________ ________

I I I I I I ______

Table 1 - 1999 Nelson Reservoir Static GPS Control Survey
The elevation 2,220.3 contour digitized from USGS quad maps was used to perform a clip or boundary

around the edge of the underwater data set 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.

The underwater collected data and digitized 2,220.3 contour from the USGS quad maps are plotted on figure

2.

Contours for elevations 2,220.3 and below were computed from the underwater data set using the triangular

irregular network (TIN) surface modeling package within ARC/INFO. A TIN is a set of adjacent, 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

Delaunays criteria for triangulation where triangles are formed among all data points within a polygon or the

boundary clip. This 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 preserving all collected survey points. Elevation contours are then interpolated along the

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

Documentation, (E5'R] 1992).

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

from the Nelson 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 Nelson Reservoir since the areas were calculated from the developed TIN. The contour

topography at 2-foot intervals is presented on figure 3 through 8, drawing numbers 15 -D-282 through 1 5-D287.

Development of 1999 Contour Areas

The 1999 contour surface areas for Nelson Reservoir were computed at 1-foot increments, from elevation

2,175.0 to 2,220.0, using the Nelson Reservoir TIN discussed above. The 1999 survey measured the

minimum reservoir elevation at 2,174.8. These calculations were performed using the ARC/INFO VOLIJMIE

command. This command computes areas at user specified elevations directly from the TiN and takes into

consideration all regions of equal elevation. Due to the lack of 1999 survey data above elevation 2,215,

(survey conducted near water surface elevation 2,218), the final 1999 area computations assumed no change

in surface area from elevation 2,215 and above from the original measured areas.

As discussed in the previous section the USGS quad water surface contour was used as a clip to develop

contours from the underwater data collection in May 1999. To match the Reclamation project datum the

assigned water surface contour elevation of 2,222.0 was reduced 1.7 feet and assigned an elevation of 2,220.3.

The area of this digitized enclosed polygon, minus the areas of the islands that were located within, was found

to be around 4,127 acres, From the April 24, 1922-area-capacity tables, the original surface area for elevation

2,220.3 was listed as 4,124 acres.

8
1999 Storage Capacity

The storage-elevation relationships based on the measured surface areas were developed using the areacapacity computer program ACAP85 (Bureau of Reclamation, 1985). Starting from the 1999 minimum

elevation 2,174.8, the 1999 measured surface areas from elevation 2,176.0 to elevation 2,214.0 and the

original surface areas from elevation 2,215.0 to 2,223 were used as control parameters for computing the

1999 Nelson 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 Nelson 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 a 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 1999 Nelson Reservoir area and capacity computations are listed in table 2 and columns (4)

and (5) of table 3. Listed in columns (2) and (3) of table 2 are the original surface areas and recomputed

capacity values. A separate set of 1999 area and capacity tables has been published for the 0.01-, 0.1-, and

1-foot elevation increments (Bureau of Reclamation 1999). A description of the computations and

coefficients output from the ACAP85 program is included with these tables. Both the original and 1999 areacapacity curves are plotted on figure 9. As of May 1999, at active conservation elevation 2,221.6, the surface

area was 4,331 acres with a total capacity of 78,950 acre-feet and an active capacity of 60,810 acre-feet.

Analyses of Results

The Nelson Reservoir original and 1999 area and capacity values are illustrated on the figure 9 and the results

are listed on table 2 and 3. Since Nelson Reservoir operation began in 1916, the measured total volume

change at reservoir elevation 2,215.0 was estimated to be 446 acre-feet. These presentations illustrate the

little capacity difference that has occurred during the 83 years of reservoir operations. This is a very minimal

change for this length of operation, but is reasonable assuming minimum sediment inflow from the diverted

flows and due to the different methods used to survey and calculate the original and 1999 surface areas. It

must be noted that the 1999 measured surface areas for elevations 2,214.0 and below and the original surface

areas for elevation 2,215.0 and above were used to develop the 1999 capacity values. This was due to the

fact the reservoir water surface elevation was near 2,218 during time of underwater collection and no above

water data was collected in 1999. As indicated previously the digitized surface area of the USGS quad

contour labeled 2,222 (adjusted to elevation 2,220.3 to match the project datum) is nearly the same as the

9
original measure surface area at the same elevation. The original surface areas are from a 1921 topography

survey and the USGS quads were compiled from aerial photographs taken in 1977. The original capacity in

column 3 was recomputed using the original area values for comparison purposes. There were no original

area values available below elevation 2,200, but several publications indicated that the original capacity

below elevation 2,200 was 18,650 acre-feet.

The area comparison plot of figure 9 illustrates the large jump in surface areas for both the original and 1999

measured surface areas. Forthe original survey, thejump occurred between elevation 2,213 and 2,214. For

the 1999 survey the large jump in measured surface area occurred between elevation 2,211 and 2,212. A

datum shift between the surveys is possible, but the original and 1999 surface areas for elevations 2,208

through 2,211 were very close. As illustrated on figure 2 there was limited data collected in 1999 in the

western portion of the reservoir due to the shallow water and weather conditions during the survey. There

may be some high spots in this area that were not measured and contoured in 1999. Another theory is that

the original survey measured larger islands throughout the reservoir that have since been reduced in size,

above elevation 2,213 due to reservoir wave action. If this has occurred, the eroded material would have

settled in the lower elevations of the reservoir as the 1999 survey measured. This eroded material does not

affect the total capacity of the reservoir, just the distribution of the available storage. The best means to

resolve this dispute and to obtain more accurate reservoir topography would be to collect above water

topography when the reservoir elevation was at elevation 2,210 or below.

REFERENCES

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

New York.

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

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

Service Center, Denver CO.

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

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

Denver, CO.

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

Denver CO.

Bureau of Reclamation, May 1999. Denver Office, Nelson Reservoir Area and Capacity

Tables, Milk River Project, Great Plains Region, Billings MT.

Corps of Engineers, October 1994. EngineerandDesign - HydrographicSurveying, EM 1110-2-1003 (FR),

Department of the Army, Washington DC (www.usace. army.mil/inetlusace.docs/eng-manuals/em.htm).

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

10
RESERVOIR SEDIMENT

DATA SUMMARY Nelson Reservoir

NAME OF RESERVOIR

1

DATA SHEET NO.

0 1. OWNER Bureau of Reclamation 2. STREAM off stream 3. STATE Montana

A 4. SEC. 14 TWP. 32 N RANGE 32 E S. NEAREST P.O. Malta

1

6. COUNTY Phillips

H 7. LAT 48° 31' 42" LONG 107° 31' 00" 8. TOP OF DAM ELEVATION 2228 9. SPILLWAY CREST EL 2

R 10. STORAGE 11. ELEVATI ON 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 SURCHARGE

________________________ __________________________

V b. FLOOD CONTROL

o 9 6

c. POWER 1 1

R d. WATER SUPPLY 2225.6 4,496 4,410 83,634 16. DATE

e. IRRIGATION

__________________ ___________________

NORMAL

OPERATION

f. CONSERVATION 2221.6 4,320

_________________

60,574

___________________

79,224 BEGAN

g. DEAD 2200.0 1,667 18,650 18,650 1916

17. LENGTH OF RESERVOIR 9 MILES AVG. WIDTH OF RESERVOIR 0.7 MILES

B 18. TOTAL DRAINAGE AREA 35.2 SQUARE MILES 22. MEAN ANNUAL PRECIPITATION 13' INCHES

19. NET SEDIMENT CONTRIBUTING AREA 35.2 SQUARE MILES 23 . MEAN ANNUAL RUNOFF 21 . 1 INCHES

I 20. LENGTH MILES AV. WIDTH MILES 24. MEAN ANNUAL RUNOFF 39,600 ACRE-FEET

N 21. MAX. ELEVATION MIN. ELEVATION 25. ANNUAL TEMP. MEAN 42°F RANGE -56°F to 109°F'

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

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

R YRS. YRS. INTERVAL

V 1916 4,331' 79,396' 2.0 E

Y

D 5/99 83 83 Contour (D) 5-ft 4,331' 78,950' 2.0

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

SURVEY ANNUAL

,

A

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

5/99 13' 3P,6OO 75,800 2,047,200 39,600 2,047,200

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

SURVEY

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

5/99 446 5.4 - 446 5.4 -

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

SURVEY WT. (t/FT°)

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

5/99 O.01 O.56

26.

DATE

43. DEPTH DESIGNATION RANGE BY RESERVOIR ELEVATION.

_____________________________________________________________________________

SURVEY

_________________________________________________________________________________

_____________________________________

_______________________________________

PERCENT OF TOTAL SEDIMENT LOCATED WITHIN DEPTH DESIGNATION

5/99

26.

DATE

44. REACH DESIGNATION PERCENT OF TOTAL ORIGINAL LENGTH OF RESERVOIR

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

11
45. RANGE IN RESERVOIR OPERATION12

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

1947 2,217.7 2,212.4 35,100 1948 2,217.8 2,214.2 21,000

1949 2,216.5 2,203.5 (-(4,400 1950 2,209.3 2,202.7 30,200

1951 2,217.1 2,207.9 40,800 1952 2,218.1 2,215.1 15,400

1953 2,220.0 2,213.4 22,300 1954 2,220.3 2,215.9 27,000

1955 2,221.2 2,216.8 8,900 1956 2,218.2 2,214.8 39,800

1957 2,221.2 2,218.9 46,500 1958 2,220.6 2,216.7 28,900

1959 2,219.8 2,216.1 36,000 1960 2,221.4 2,216.8 36,800

1961 2,218.0 2,204.0 23,300 1962 2,220.8 2,207.7 64,000

1963 2,220.0 2,216.3 10,000 1964 2,217.5 2,212.4 47,900

1965 2,221.3 2,214.7 52,500 1966 2,221.0 2,218.3 43,300

1967 2,221.0 2,215.1 36,400 1968 2,219.3 2,215.3 59,300

1969 2,220.4 2,217.1 39,100 1970 2221.1 2,217.6 4,300

1971 2,220.0 2,211.8 37,700 1972 2,219.2 2,215.3 38,800

1973 2,219.8 2,210.2 20,000 1974 2,220.9 2,209.5 53,000

1975 2,220.8 2,217.9 24,200 1976 2,221.4 2,218.2 42,400

1977 2,219.7 2,203.6 (-(2,800 1978 2,219.4 2,203.4 71,900

1979 2,220.2 2,216.7 39,200 1980 2,218.7 2,209.4 26,300

1981 2,214.8 2,208.2 45,500 1982 2,221.0 2,213.1 65,900

1983 2,219.9 2,209.2 24,800 1984 2,211.2 2,200.5 12,900

1985 2,211.5 2,202.7 33,100 1986 2,221.4 2,213.5 75,800

1987 2,220.8 2,216.8 39,100 1988 2,218.8 2,203.1 (-(2,100

1989 2,215.6 2,201.7 72,200 1990 2,220.2 2,215.7 59,800

1991 2,217.4 2,214.7 72,400 1992 2,218.0 2,206.9 25,700

1993 2,221.3 2,206.4 74,300 1994 2,221.3 2,212.9 23,600

1995 2,216.8 2,209.8 51,000 1996 2,221.0 2,212.6 63,800

1997 2,219.1 2,213.9 56,400 1998 2,220.4 2,212.9 68,300

1999 2.218.1 2.215.2 30.400 7000

46. ELEVATION - AREA - CAPACITY DATA FOR 1999 CAP?.CXfl"

ELEVATION AREA CAPACITY ELEVATION AREA CAPACITY ELEVATION AREA CAPACITY

2174.8 0 0 2176 3 2 2178 116 121

2180 248 485 2182 388 1,121 2184 525 2,034

2186 670 3,229 2188 784 4,683 2190 879 6,346

2192 966 8,191 2194 1,052 10,209 2196 1,226 12,487

2198 1,415 15,128 2200 1,597 18,140 2202 1,763 21,500

2204 1,920 25,184 2206 2,096 29,194 2208 2,286 33,580

2210 2,469 38, 337 2212 2,928 43, 615 2214 3,312 49,865

2216 3,614 56,816 2218 3,855 64,291 2220 4,085 72,225

2221.6 4,331 78,950 2222 4,398 80,696 2223 4,560 85,175

47. REMARKS AND REFERENCES

Design elevation of five d ikes was 2228.0. Documented settlement of some di kes of 1.4 feet or greater.

2 Off stream reservoir, no s pillway.

Bureau o f Reclamation Proj ect Data Book, 1981.

Calculated using mean annu al runoff value of 39,600 AF, item 24, water years 1947-1999 . Offstream reservoir,

majority of inflows diverted.

Computed annual inflows fr om 1947 through 5/99.

6 Original surface area and capacity at elevation 2,221.6. Or iginal capacity recomputed by Reclamation's ACAP

program using original surface areas.

Surface area and capacity at elevation 2,221.6 computed by ACAP program usin g 1999 and original surface areas.

1999 surveyed only underwater portion of reservoir below ele vation 2214. El evation 2215 and above from original

survey.

Values f rom water years 19 47 through 5/99 (51.7 years).

Capacity loss calculated by comparing original recomputed capacity and 1999 capacity a t reservoir elevation

2221.6, top of conservation elevation. Portion of capacity difference due to accuracy of two surveys. Majority

of inflows from diverted i nflows accounting for the small di fference and lit tle sediment inflow over the life of

the reservoir.

Maximum and minimum eleva tions and inflow values in acre-feet by water year, from October 1946 through May 1999.

Capacit ies computed by ACAP computer program. Areas at elevation 2215 and above from original survey.

48. AGENCY MAKING SURVEY Bureau of Reclamation

49. AGENCY SUPPLYING DATA Bureau of Reclamation DATE March 2001

Table 2. - Reservoir sediment data sunxnary (page 2 of 2).

12
1 2 3 ____

4 5

j 6 7 8

___

Elevalions

_______

OriginaJ

__________

Original 1999 1999

Jçomputed

Sediment

Percent of

Computed

jPercent of

fReservoir

I Areas Capacity Areas4

Capacity Volume Sediment pepth

(feet) r

(acres) (acres)

-

(acre-feet)

2223 45 85621 45 85175 44

2222 1 4398 81142 4398 80696 446

__

1 100.0

__

97.9

2221.6f 4331 79396 4331 78950 446 100.0 97.1

222 4230 [ 768281 4230 76382 446J 100.0 95.9

2220 4085 r 72670f 4085 [ 72225 445 99.8 93.8

2219 39641 686 3964 68200 446 100.0 91.7

2218

2217

38

3740

64736

60939

3855

3740

64291

60493

1 445

L

446

99.8

100.0

89.6

87.6

2216 3614 57262 3614 56816 446 100.0 85.5

2215 1 3488 53711 3488 53265 446 100.0 83.4

2214 3349 50292 3312 49865 427 95.7 81.3

2213 1 2822 47207 3130 46644 563 126.2 79.3

22121 2670 44461 2928 43615 846 189.7 77.2

2211 1 2566 41843 2580 40861 982 220.2 75.1

2210 J 2473 39323 2469 38337 986 221.1 73.0

2209 2387 36893 2379 35913 980 219.7 71.0

2208 2312 34544 2286 33580 964 216.1 68.9

2207 2232 32272 2195 31340 932 209.0 66.8

2206 2150 30081 2096 29194 887 198.9 64.7

2205 2065 27973 2002 27145 828 185.7 62.7

2204 1986 25948 1920 25184 764 171.3 60.6

2203 1905 24002 1843 23303

____

699 156.7 58.5

2202 1824 22138 1763 21500 638 143.0 56.4

2201 i742 20355 1680 19778 577 129.4 54.4

2200 1667 18650 1597 18140 510 114.3 52.3

1415 15128 48.1

2196 0 0 1226 12487 44.0

0 0 1052 10209 39.8

0 0 966 8191

_______

35.7

2190

____2188j

T

OJ 0

____

0

0

879

784

6346

4683

______

31.5

27.4

21861 0 0

-

670 3229 23.2

2184E 0

2182k 0 0,

525

388

4

1121

2180 0 Th 2481 485

___

10.8

2178 01 iif

-

2174.8 O 0

f

Elevation of reservoir water surface in feet. j

•2 Original reservoir surface area.

_____ __

-

3 Recomputed_original reservoir capacity.

reservoir surface areas. j

t

-

5 1999 reservoir capacity.

-

-

6 Sediment vokime (col. 3 -col. 5).t ____

7 Percentage of total sediment (446AF

8 Percentage of total depth (48.2).

-

Table 3. - Summary of 1999 survey results

13
Figure 1. - Nelson Reservoir location map.
iS

Figure 2. - Nelson ReseTVOff

underWat& data co1leCt10'
I

j567,00+

Nelson

Dam

1e,oo--

w

ti.

I

I

14

p

E

S

F.,.'

LV LV

SaI. Ir

I

I

N

Vertical datum based on Bureau of

Reclamations project datum which

is 1.70 feet lower than the

National Vertical Datum of 1929.

Horizontal datum based on Montanas

State Plane Coordnate System.

North Zone (NADB3)

17

Figure 3. - Nelson Reservoir topology map, No. 1 5-D-282.
/wpJ

*557O

N

S

I

. ,..

ertical datum based on Bureau of

eclamations project datum which

s 1.70 feet lower than the

ational Vertical Datum of 1929.

orizontal datum based on Montanas

tate Plane Coordnate System.

orth Zone (NADB3)

19

Figure 4. - Nelson Reservoir topology map, No. 15-D-283.
Figure 5. - Nelson Reservoir topology map, No. 15-D-284.
g

8U of

which

929.

ntana '5

Figure 6. - Nelson Reservoir topology map, No. 15-D-285.
4

N

oo4 ,oo4 ioooo-

'-I

x aV rn*

Vertical datum based on Bureau of

Reclamation's project datum which

is 1.70 feet lower than the

ational Vertical Datum of 1929.

Horizontal datum based on Montana's

State Plane Coordinate System.

North Zone (NAD83I.

t5OOO+

A7.$' RfSEV/I

if_____ _________

'VftW, Oe/o,M .4'L 12, V1

Figure 7. - Nelson Reservoir topology map, No. 15-D
w

'if,

4V

5,k. Il&

N

Vertical datum based on Bureau of

Rec1amations project datum which

is 1.70 feet lower than the

National Vertical Datum of 1929.

Horizontal datum based on Montanas

State Plane Coordinate System.

North Zone (NAD83)

Figure 8. - Nelson Reservoir topology map, No. 15-D-287.
*

4600 4140

2225

2220

2215

2210

4-

! 2205

0

4-m

>w2200 _____

2195

2190

2185

2180

21Th

Area-Capacity Curves for Nelson Reservoir

Area (acres)

3680 3220 2760 2300 1840 1380 920 460 0

Capacity

- . Area

0 8600 17200 25800 34400 43000 51600 60200

Capacity (acre-feet)

Figure 9. - 1999 area and capacity curves

LJ

2220

2215

2210

2205

2200

2195

2190

2185

2180

68800 77400 86000

2175