LAKE COMO

1991 Reservoir Survey

U.S. Department of the Interior

Bureau of Reclamation
7-2090 (4-81)

Bureau of Reclamation TECHNICAL REPORT STANDARD TITLE PAGE

1. REPORT NO. 3. RECIPIENTS CATALOG NO.

4. TITLE AND SUBTITLE 5. REPORT DATE

September 1992

Lake Como 6. PERFORMING ORGANIZATION CODE

1991 Reservoir Survey

-

D-5753

7. AUTHOR(S) 8. PERFORMING ORGANIZATION

REPORT NO.

Ronald L. Ferrari

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. WORK UNIT NO.

Bureau of Reclamation 11 CONTRACT OR GRANT NO.

Denver Office

Denver CO 80225 13. TYPE OF REPORT AND PERIOD COVERED

12. SPONSORING AGENCY NAME AND ADDRESS

Same

14. SPONSORING AGENCY CODE

DIBR

15. SUPPLEMENTARY NOTES

Microfiche and hard copy available at the Denver Office, Denver, Colorado. Ed: TH

16. ABSTRACT

Lake Como was surveyed m 1991 to compile field data for developing a reservoir topographic

map and computing the present storage-elevation relationship. This was the first survey to

determine the natural lake capacity inundated because of construction of Como Dam. The

original active capacity was based on topography collected prior to construction and did not

include areas below the natural lake's water surface. The 1991 bathymetric survey used sonic

depth recording equipment interfaced with an automated microwave positioning system that

gave continuous depth and sounding positions. The above-water reservoir area was calculated

from close interval cross sections measured from aerial photography obtained in 1990. A new

reservoir contour map was developed by the computer graphics program SURFACE H using

the collected data.

Reclamation is conducting a dam safety investigation with options of raising the dam and

modifying the spillway. As of May 1991, at the present reservoir spiliway crest elevation (feet)

4236.0, the surface area was 883 acres with a total capacity of 36,271 acre-feet and an active

capacity of 29,439 acre-feet.

17. KEY WORDS AND DOCUMENT ANALYSIS

a. DESCRIPTORS-- *reservoir area and capacity/ reservoir surveys! sonar! reservoir areal

reservoir survey

b. IDENTIFIERS- Lake Como

C. COSATI Field/Group COWRR: SRIM:

18. DISTRIBUTION STATEMENT 19. SECURITY CLASS 21 NO. OF PAGES

(THIS REPORT) 13 UNCLASSIFIED

20. SECURITY CLASS 22. PRICE

(TS REPORT)

UNCLASSIFIED
LAKE COMO

1991 RESERVOIR SURVEY

by

RONALD L. FERRARI

BUREAU OF RECLAMATION

EARTH SCIENCES DIVISION

SURFACE WATER BRANCH

SEDIMENTATION SECTION

DENVER OFFICE

DENVER, COLORADO

September 1992
ACKNOWLEDGMENTS

The Bureau of Reclamation prepared and published this report

under the supervision of Robert I. Strand, Head, Sedimentation

Section, Earth Sciences Division. Ronald Ferrari arid Joseph

Lyons of the Denver Office conducted the hydrographic survey.

Personnel from the Columbia Basin Projects Office of the Pacific

Northwest Region assisted during the hydrographic survey and

performed the required land survey for the hydrographic and

aerial data collection. Special thanks to Jerry Harrod and

Chuck Woodruff of the Columbia Basin Projects Office for the

field assistance during the hydrographic survey and Gerald

Schultz of the Denver Office for the office assistance. Ronald

Ferrari completed the data processing needed to generate the

new topographic map and area-capacity tables. James 0.

Blanton, Steven Gavlick, Rebert I. Strand, and Dave Zimmer

consulted in the engineering computations, topographic map

development, and report preparation.

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.

The information contained in this report regarding commercial

products or firms may not be used for advertising or promotional

purposes and is not to be construed as an endorsement of any product

or firm by the Bureau of Reclamation.

The information contained in this report was developed for the Bureau

of Reclamation; no warranty as to the accuracy, usefujness, or

completeness is expressed or implied.
Photo by Joe Lyons of the Denver Office. Taken near dam 'ooking upstream.

This was the 'ast hydrographic survey using the Sedimentation Section's

MoriArk survey boat, nicknamed the African Queen.

Lake Como with MonArk survey boat
CONTENTS

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Page

Introduction 1

Summary and conclusions 2

Description of watershed 3

Reservoir operations 3

Survey method and equipment 3

Sediment analyses 4

Reservoir area and capacity 4

Development of 1991 contour areas 4

Revised 1991 storage capacity 4

References 6

TABLES

Table

1 Reservoir sediment data summary 7

FIGURES

Figure

1 Lake Como location map 9

2 Lake Como Dam, plan and section 10

3 Lake Como topographic map 11

4 1991 area and capacity curves 13
INTRODUCTION

Lake Como Dam and Reservoir, of the Bitter Root Project, is located on Rock Creek. The dam, located in

Ravalli County of west-central Montana, is about 5 miles northwest of Darby and 16 miles southwest of

Hamilton, Montana (fig 1).

Como Dam was originally constructed by the Bitter Root Valley Irrigation Company between 1908 and

1910. In 1920, the Bitter Root Irrigation District was formed, in accordance with Montana law, to

replace the irrigation company. In 1930, Congress authorized the Bureau of Reclamation (Reclamation)

to undertake measures for rehabilitation of the district's irrigation system and liquidation of its private

indebtedness. Additional rehabilitation was performed in 1936, 1948, 1956, and 1974. Reclamation is

conducting a dam safety investigation with options of raising the dam and modifying the spillway.

Como Dam (fig. 2) is an earth and gravel embankment constructed by the semi-hydraulic fill method.

Material hauled to the site by rail was dumped from both the upstream and downstream sides of the fill

where the finer materials washed to the lower and central part of the dam. At dam crest elevation

4249.0 (feet) the embankment has:

• a structural height* of 70 feet

• a top crest width of 25 feet

• a crest length of 2,550 feet

Closure of the dam and first reservoir storage occurred in 1909. The reservoir impounded by the dam

inundated a natural lake on Rock Creek. At elevation 4245.0 the reservoir extends 3.2 miles up Rock

Creek and has an average width of 0.4 mile.

The present spillway, located at the left abutment, was constructed in 1923 with a crest length of 75 feet

at elevation 4236.0. The current maximum capacity is 5,460 cubic feet per second at reservoir water

surface elevation 4245.9. The spiliway consists of:

• an excavated approach channel

• a concrete control and transition section

• flashboard bays

• a concrete chute

• a natural rock-formed stilling basin

• a downstream channel

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

Design of Small Dams and Guide for Preparation of Standing Operating Procedures for Dams and Reservoirs, or ASCE's

Nomenclature for Hydraulics.

1
The outlet works, located in the right one-third of the dam, consists of:

• a trashracked intake structure

• a 6-foot-diameter concrete conduit with redwood stave and steel plate lining

• two tandem 5.5-foot diameter gate valves

• a stilling basin

The outlet's hydraulic capacity is 450 cubic feet per second at reservoir elevation 4203.4.

Lake Como had an original calculated active capacity of 29,087 acre-feet at the present reservoir

spillway crest elevation 4236.0. The original capacity of the natural lake (dead storage) was unknown,

but was estimated to be 1,800 acre-feet.

SUMMARY AND CONCLUSIONS

This report presents the results of the first extensive survey of Lake Como by Reclamation since

construction of Como Dam. The primary objective of the 1991 survey was to gather necessary data for

computing the current total and active capacities of Lake Como. This was the first detailed survey to

determine the area and capacity of the natural lake inundated by the reservoir created by the dam.

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

aerial and hydrographic surveys. A local horizontal grid system was established for both surveys using

monumented control points located in the reservoir area. The bathymetric survey was run using sonic

depth recording equipment interfaced with an automated survey system consisting of a line-of-sight

microwave positioning unit capable of determining sounding locations within the reservoir. The system

continuously recorded reservoir depth and horizontal coordinates as the survey boat was steered across

close-spaced range lines covering the reservoir area. The positioning system provided information to

allow the boat operator to maintain course along these range lines. Water surface elevations measured

by the land surveyors at the time of data collection were used to convert the sonic depth measurements

to true reservoir bottom elevations.

The 1991 surface areas at predetermined 5-foot contour intervals were generated by a computer

graphics program that produced a new contour map of the reservoir (fig 3). The ACAP85 computer

program computed the reservoir capacity and surface area at prescribed increments of elevation by

using a curve-fitting technique from the generated contour surface areas (Reclamation, 1985).

Table 1 contains a comprehensive summary of the reservoir data and watershed characteristics for the

1991 survey. The 1991 survey determined that the reservoir has a surface area of 883 acres at the

present reservoir spiliway crest elevation 4236.0, providing a total capacity of 36,271 acre-feet, and an

active capacity of 29,439 acre-feet. The survey measured a reservoir dead storage of 6,832 acre-feet

between elevations 4122.1 and 4188.5. Lake Como had an original calculated active capacity of 29,087

acre-feet with an interpolated surface area of 880 acres at the same reservoir elevation. The original

capacity of the natural lake (dead storage) was unknown, but was estimated to be 1,800 acre-feet. The

2
1991 survey found that the natural lake area was much larger than originally estimated. A summary of

reservoir sediment data was not presented because this was the first survey to compute the total

reservoir capacity.

Because of low sediment production in the drainage area, a resurvey of Lake Como should not be

necessary unless major sediment inflow occurs in the future.

DESCRIPTION OF WATERSHED

The drarnage area of Lake Como basin (above the dam) is 54.6 square miles and is part of the Bitterroot

Mountain Range. The elevation of the basin ranges from elevation 4188.5 at the intake of the outlet

tower to elevations nearly 10,00C) feet at the mountain peaks. The minimum elevation of the natural

lake, which was inundated by the reservoir, was measured to be 4122.1 feet.

The Bitterroot Range is not a continuous mountain ridge, but is a complex of mountain masses

separated by low saddles or valleys. Within the mountain groups the higher peaks are not located on the

divide between the Bitterroot and Seiway (and Lochsa) River watersheds, but are situated within the

watersheds of the east slope streams, such as El Capitan Peak (9965 feet) and Como Peak (9552 feet) in

the Rock Creek watershed. Rock Creek watershed is steep and rocky, and aside from bare rock faces of

the higher peaks and its talus slopes, the basin is quite heavily forested.

RESERVOIR OPERATIONS

The records of monthly inflow and end-of-month stage for Lake Como are limited (see table 1). The

available records show an average unregulated inflow of 92,214 acre-feet per year with a calculated

mean annual runoff from the basin of 31.7 inches. The available end-of-month stage records show the

extreme annual fluctuations of Lake Como with a minimum elevation of 4188.0 occurring in several

years to a maximum elevation of 4244.7 in June 1945.

SURVEY METHOD AND EQUIPMENT

The Lake Como survey was completed using the contour method (Blanton, 1982). The procedure

involved collecting adequate coordinate data for developing a reliable contour map by photogrammetric

and bathymetric survey methods. Standard land surveying methods were used by Columbia Basin

Project Office personnel to establish horizontal and vertical control points for both survey methods. A

local horizontal grid system was established for both surveys using monuinented points located in the

reservoir area. The above-water data was collected by aerial photography obtained in 1991 at water

surface elevation 4205.2. The field survey work for the bathymetric survey involved establishing a

triangulation network around the reservoir to provide horizontal and vertical control for all required

range lines and shore station locations. No previously established range lines existed on the reservoir

and permanent range lines were not established during this survey. Because of the size and shape of the

reservoir, any future survey would also employ the contour method; therefore, permanent range line end

markers were not necessary.

3
The hydrographic survey took place May 5 and May 6, 1991, at reservoir water surface elevations

4222.85 and 4222.6, respectively. The bathymetric survey was run using sonic depth recording

equipment interfaced with an automated survey system consisting of a line-of-sight microwave

positioning unit capable of determining sounding locations within the reservoir. This positioning system

transmitted line-of-sight microwave signals to fixed shore stations and converted the reply time to range

distances, which were used by the system data logger to compute the coordinate position of the sounding

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

boat moved across close-spaced range lines covering the reservoir area. To produce adequate data for

developing contours of Lake Como, a grid spacing of 200 feet was selected for the main body; 300-foot

intervals were used in the upper portion of the reservoir. The system gave directions to the boat operator

to assist in maintaining course along the close-spaced range lines. During each run, the depth and

position data were recorded on a floppy disk for subsequent processing by Denver Office personnel. A

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

collection process. Water surface elevations surveyed at the time of collection were used in converting

the sonic depth measurements to true reservoir bottom elevations.

SEDIMENT ANALYSES

The total sediment accumulation in Lake Como cannot be computed because this was the first survey of

the natural lake area (dead storage) since the dam was constructed. Because of the large reservoir dead

storage measured in 1991 and the low sediment production of the drainage area, a resurvey of Lake

Como should not be necessary unless major sediment inflow occurs in the future.

RESERVOIR AREA AND CAPACITY

Development of 1991 Contour Areas

The 1991 contour surface areas for Lake Como were developed by generating a contour map from the

collected aerial and underwater coordinate data. Five-foot contour intervals of the reservoir area were

created by a computer graphics software program (Kansas Geological Survey, 1978). A modification of

this program by the Denver Office calculated surface areas of the closed contours of the generated map.

The generated contours and the calculated surface areas were done using a local horizontal grid system

that was established for the 1991 field collection. After completion of the 1991 sedimentation survey,

state plane coordinates were established on the control points. The final reservoir map with state plane

coordinates was generated and prepared by the Denver Office Computer Drafting Unit of the Drafting

Section. The map shown on figure 3 has a scale of 1 inch equals 500 feet with 5-foot contour intervals.

1991 Revised Storage Capacity

The storage-elevation relationships based on the 1991 aerial and underwater survey data were

developed using the area-capacity computer program ACAP85 (Reclamation, 1985). Surface areas at

5-foot contour intervals computed from the aerial and underwater survey data were used as the control

parameters for computing reservoir capacity. The program computes an area at elevation increments of

0.01- to 1.0-foot by linear interpolation between the 5-foot contour intervals. The program begins by

4
testing the initial capacity equation over successive intervals to ensure that the equation fits within an

allowable error limit, which was set at 0.000001 for Lake Como. Then the capacity equation is used over

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

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

that interval) tests the fit until it also exceeds the error limit. Thus, the capacity curve is defined by a

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

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

where:

y = a1 + azx +

a^

y = capacity,

x = elevation above a reference base,

a1 = intercept, and

a2 and a3 = coefficients

Results of the 1991 Lake Como area and capacity computations are listed in table 1 and plotted on

figure 4. A separate set of 1991 area and capacity tables has been published for the 0.01-, 0.1-, and 1-foot

elevation increments (Reclamation, 1991). The 1991 total capacity is 36,271 acre-feet with a surface area

of 883 acres at the present reservoir spiflway crest elevation 4236.0.

5
REFERENCES

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

1962.

Blanton, James 0. ifi, "Procedures for Monitoring Reservoir Sedimentation, Technical Guideline for

Bureau of Reclamation", Denver Office, Denver, Colorado, October 1982.

Bureau of Reclamation, Surface Water Branch, ACAP85 User's Manual, Denver Office, 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, CO, 1986.

Bureau of Reclamation, Design of Small Dams, U.S. Government Printing Office, Denver, CO, 1987.

Bureau of Reclamation, Denver Office, "Lake Como Area and Capacity Tables, Bitter Root Project,

Pacific Northwest Region", Denver, Colorado, May 1991.

Kansas Geological Survey, SURFACE II GRAPIIICS SYSTEM, Lawrence, Kansas, 1978.

6
RESERVOIR SEDIMENT

Lake Como

1

DATA SUMMARY

N OF RESERVOIR

DATA SHEET NO.

T' 1. OWNER Bitter Root Irrigation 2. STREAM Rock Creek 3. STATE Montana

A 4. SEC. 32 TWP. 4N RANGE 21W 5. NEAREST P.O. Derby 6. COUNTY Ravalli

N 7. LAT 46' 03' 40" LONG 114 14' 00' 8. TOP OF DAM ELEVATION 4249.0' 9. SPILLWAY CREST 4236.0'

10. STORAGE 11. ELEVATION 2. 19912 13. 19912 4. 1991 GROSS 15. DATE

E ALLOCATION TOP OF POOL SURFACE AREA. Ac CAPACITY, Al STORAGE ACRE- STORAGE

G

a. FLOOD CONTROL BE AN

R b. MULTIPLE USE 4236.0 883 29,439 36,271 1909

O c.POWER

I

R

d. WATER SUPPLY 16. DATE

e. I A NORMAL

_______________ ________________ OPERATION

f. CONSERVATION

______________

BEGAN

g. INACTIVE 4188.5 203 6,832 6,832 1910

' "

17. LENGTH OF RESERvOIR 3.2k MILES AVG. WIDTH OP RE RVOIR 0.4 MILES

T 18. TOTAL DRAINAGE AREA 54.6 SQUARE MILES 22. MEAN ANNUAL PRECIPITATION 13.2' INCHES

19. NET SEDIMENT CONTRIBUTING AREA 54.6 SQUARE MILES 23. MEAN ANNUAL RUNOFF 31,7S INCHES

I

N

20. LENGTH 12.2 MILES MI AV. WIDTH 4.5 MILES 24. MEAN ANNUAL RUNOFF 92,214' ACRE-FEET

21. MAX. ELEVATION 9965 MIN. ELEVATION 4188.5 25. ANNUAL TEMP. MEAN 46'F4 RANGE -38F to 103'F4

T 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

1909 2

Y

May 5,1991 82 82 Contour (D)' 5-ft. 883 36,271' 0.39

A

T

A

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

SURVEY ANNUAL

PRECIP .

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

May 5,1991 13.2 92,214' 170,500' ' 92,214'

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

SURVEY

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

May 5, 1991

2 2

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

SURVEY WT. (#/FT3) PPM

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

DATE ANNUAL DATE PER. TOT.

May 5,1991

2 2

26.

DATE

43. DEPTH DESIGNATION RANGE IN FEET BELOW AND ABOVE CREST ELEVATION

OF

SURVEY

PERCENT OF TOTAL SEDIMENT LOCATED WITHIN DEPTH DESIGNATION

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- 105-

100 105 110

11-

115

115-

120

120-

125

_______

PERCENT OF TOTAL SEDIMENT LOCATED WITHIN REACH DESIGNATION

Table 1. - Reservoir sediment data summary (page 1 of 2).
45. RANGE IN RESERVOIR OPERAT ION

WATER YEAR MAX. ELEV. NIH. ELEV. INFLOW, AF WATER YEAR MAX. ELEV. MIN. ELEV. INFLOW • AF

1940 4240.0 4188.0 1968 4244.5 4192.7 77,100

1941 4240.1 4197.2 1967 4243.3 4188.0 97,200

1942 4242.4 4188.0 1968 4243.4 4206.3 100,700

1943 4242.4 4198.1 1969 4244.2 4190.0 68,300

1944 4242.4 4188.0 1970 4243.4 4190.5 109,900

1945 4244.7 4188.0 1971 4243.0 4197.0 92,200

1946 4242.4 4188.0 1972 4242.6 4193.0 170,500

1947 4242.3 4213.2 1973 4232.6 4190.8 56,400

1948 4242.4 4205.3 1974 4242.4 4197.4 94,500

1949 4242.3 4195.3 1975 4244.0 4203.0 83,900

1950 4242.3 4198.5 1976 4243.0 4204.2 120,100

1951 4239.5 4209.4 1977 4227.2 4186.0 49,300

1952 4242.5 4192.4 1978 4242.8 4203.0 124,000

1953 4242.5 4191.6 1979 4242.7 4191.0 94,700

1954 4240.4 4198.1 1980 4242.2 4193.4 83,300

1955 4243.7 4188.0 1981 4242.6 4184.8

1956 4244.3 4194.1 1982 4242.2 4194.1 115,600

1957 4244.6 4192.6 1983 4242.7 4209.6 54,500

1958 4244.1 4191.1 1984 4242.7 4209.1

1959 4243.4 4190.7 1985 4240.0 4202.2

1960 4244.6 4188.0 1986 4243.0 4193.3

1961 4244.1 4192.4 1987 4238.6 4196.6 65,320

1962 4243.6 4193.0 1988 4241.0 4196.4

1963 4244.6 4190.4 81,500 1989 4243.0 4202.0 90,740

1964 4244,6 4191.4 93,500 1990 4243.0 4200.0 101,070

1965 4243,2 4193.5 96,600 1991 4240,5 4205,7

46. ELEVATIOr - AREA - CAPALITY DATA FOR 1991 Total Capacity9 ___________ ___________ __________

_____________

_ __________

ELEV. AREA CAP. ELEV. AREA CAP. ELEV. AREA CAP.

4122.1 0 0 4170 154 3,611 4220 792 22,826

4125 4 6 4175 164 4,407 4225 825 26,868

4130 22 70 4180 175 5,256 4230 853 31,063

4135 44 234 4185 184 6,154 4236 883 36,271

4140 60 494 4188.5 203 6,831 4240 902 39,840

4145 74 829 4195 240 8,267 4245 923 44,401

4150 85 1,227 4200 376 9,807 4249 938 48,124

4155 99 1,688 4205 563 12,155 4252 949 50,955

4160 119 2,232 4210 702 15,317

4165 140 2,878 4215 755 18,958

47. REMARKS AND REFERENCES

' Elevations from 1971 survey. Reclamation is conducting dam safety inves tigations with Options of rais ing dais and

modifying spillway.

2 Reservoir inundated a natural lake. The original area-capacity of natural lake was unknown. The 1991

survey was first to determine total reservoir area and capacity.

Measured from USGS topographic map at elevation 4245.

Project data book, USBR, 1981. Climate for years 1966-80.

Calculated from mean annual runoff value 92,214 acre-feet, item 24.

6 Unregulated inflow monthly records for water years 1963-19 90. Water years 1981. 84, 85, 86, and 89 have

missing records. Records unavailable prior to 1963.

Reservoir areas were measured using data from 1991 bathyme tric survey and aerial photography.

Total capacity of reservoir at present spillway crest El. 4236.0. Active capacity of 29,439 acre-feet from

El. 4188.5 to 4236.0.

Following table shows total capacity. A dead capacity (natural lake) of 6,832 acre-feet was computed from 1991

data. First survey o f natural lake area.

48. AGENCY MAKING SURVE Y Bureau of Reclamation

49. AGENCY SUPPLYING DATA Bureau of Reclamation DATE August 1992

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

Florence

L

N

L

- tevensyiFlee

N

Victor0 à

torva I

I.'

_____

______ IRRIGBLE AREA

LL Mi/I Pon LLHmjltfl

LL

,crantsdale

L

Ch"o'

051 N

rIo" Cr SCALE OF MILES

COMO DAM .

'CI' -ROCK CREEK

COMO LAKE

RESERvON -- DIVERSION DAM

Darby

Figure 1. - Lake Como location map - Bitter Root Project.

9
Space intentionally left blank due to security concerns 

AREA (ACRES)

1000 900 800 700 600 500 400

4260 __________ __________ __________

4250

4240 __________ __________

4230

4220 __________ ___________ __________

4210

Li

LU 4200 ________ _________ _____

z

D

4190

-I

4180 _________ _________ _________ >

Li

-J

U 4170

4150

C

6) 4150 _______________________________

0

f'I

z

4140

z ____________________________ -4

4130

z

6)

4120

(0

Ui

o

-'I

flfl ';iflfl inn n

_ N _ _

____ I__ ___ ___ ____

_ _ _ _

-

, /

-

/

CHPAC

__ __

A

____ __

- - REA ______ ______

________ LEGEND _______ /

/

1991 ACTIVE CAPACITY

_______ _______

1991 TOTAL CAPACITY

- - _ _ --- 0I I I

4001) RIlflfl lflflfl irnr-i,-

I I

0000 uuuu 'tuuu uuu uuu bUUU 10000 44000 48000

CAPACITY ACRE-rEET,1

Figure 4. - Area and capacity curves - Lake Como, 1991.