Wyoming State Water Plan, Wyoming Water Development Office
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Powder/Tongue River Basin Water Plan
Technical Memoranda

SUBJECT: Appendix J
Storage Operation and Description
TWIN LAKES

PREPARED BY: HKM Engineering Inc.

DATE: March 2002

KEY STORAGE FACILITIES

Reservoir: TWIN LAKES
The upstream face of Twin Lakes Dam
Date: 27 Feb. 2001
Location: NWSW 35,T54N,R87W
Owner: City of Sheridan
Year of Construction: 1937 – original expansion of existing Twin Lakes No. 1 with a dam to 1,180 acre-foot capacity
Enlargement History: 1971 – Twin Lakes No.1 expanded by 136.9 acre-feet, Twin Lakes No. 2 dam built to accommodate 202.9 acre-feet of capacity.

1998 – Expansion of Twin Lakes No. 1 of 1,856 acre-feet, conversion of Twin Lakes No. 2 into a wetland area.
Total Storage: 4,041 acre-feet
Active Storage: 3,403 acre-feet

Twin Lakes Reservoir's labyrinth spillway

Twin Lakes Reservoir's spillway channel
(downstream of spillway, left)
Dead Storage: 7.5 acre-feet
Area/Capacity Data: (Source: Permit on file with Safety of Dams Office, State Engineer's Office, Cheyenne)

Elevation Area Acre-Ft.
Increment
Acre-Ft.
Released
Acre-Ft.
Remaining
Ft. Below
Spillway

8595.3 94.1

4040.6 plus 7.2 F


27.4


L
8595 92.3

4013 plus 7.0 O


89.1


O
8594


3924 plus 6.0 D


88.5



8593


3836 plus 5.0


87.8


S
8592


3748 plus 4.0 T


87.2


O
8591


3661 plus 3.0 R


86.5


A
8590 83.1

3574 plus 2.0 G


82.3


E
8589


3492 plus 1.0


81.0



8588 80.5
0.0 3411 0.0 Pmt. 4129R
1180 Ac./Ft.


79.9


8587

78.6 3331 1


78.8


8586

157.2 3252 2


77.6


8585 76.7
235.8 3175 3


76.8


8584

311.4 3098 4


76.3


8583

387.0 3021 5


75.6


8582

462.6 2946 6


74.9


8581

538.2 2871 7


74.2


8580 74.5
613.8 2797 8


73.6


8579

686.0 2723 9


72.9


8578

758.2 2650 10


72.2


8577

830.4 2578 11


71.8


8576

902.6 2506 12


70.5


8575 70.0
974.8 2436 13


69.7


8574

1043.6 2366 14


68.9


8573

1112.4 2297 15


66.6


8572.018 67.7
1180.0 2230.5 15.982


68.7


Pmt. 6502R
202.9 Ac./Ft.
8571

1248.2 2162 17


66.4


8570 66.2
1315.2 2095 18


67.8


8568.962 64.2
1382.9 2027.6 19.038


61.3


Pmt. 6847R
136.9Ac./Ft.
8568

1443.9 1966 20


75.6


8566.803 62.5
1519.8 1890.7 21.197


49.7


Pmt. 10349R
1883.2 Ac./Ft.
Active Storage
8566

1569.7 1841 22


62.5


8565 62.0
1632.0 1779 23


61.6


8564

1692.0 1717 24


60.8


8563

1752.0 1656 25


60


8562

1812.0 1596 26


59.2


8561

1872.0 1537 27


58.4


8560 57.9
1932.0 1478 28


57.6


8559

1988.0 1421 29


56.8


8558

2044.0 1364 30


56.0


8557

2100.0 1308 31 Pmt. 10340R
1183.2 Ac./Ft.
Active Storage


55.2


8556

2156.0 1253 32


54.4


8555 54.1
2212.0 1199 33


53.5


8554

2263.9 1145 34


52.7


8553

2315.8 1092 35


51.9


8552

2367.7 1040 36


51.1


8551

2419.6 989 37


50.3


8550 49.7
2471.5 939 38


49.1


8549

2519.1 890 39


48.4


8548

2566.7 842 40


47.6


8547

2614.3 794 41


46.8


8546

2661.9 747 42


46.1


8545 45.6
2709.5 701 43


45.3


8544

2753.3 656 44


44.6


8543

2797.1 611 45


43.8


8542

2840.9 567 46


42.3


8541

2884.7 525 47


43.1


8540 42.0
2928.5 482 48


42.2


8539

2968.9 440 49


41.3


8538

3009.3 398 50


40.4


8537

3049.7 358 51


39.4


8536

3090.1 319 52


38.5


8535 38.8
3130.5 280 53


37.6


8534

3166.2 243 54


36.7


8533

3201.9 206 55


35.7


8532

3237.6 170 56


34.8


8531

3273.3 135 57


33.8


8530 32.6
3309.0 102 58


18.8


8529

3327.8 83 59


18.8


8528

3346.6 64 60


18.8


8527

3365.4 45 61


18.8


8526

3384.2 26 62


18.8


8525 5.0
3403 8 63 Pmt. 10349R
7.5 Ac./Ft.
Inactive storage


2.5


8524

3405.5 5 64


2.5


8523

3408 3 65


2.5


8522 0.0
3410.5 0 66

Note: Permit 10349R had not yet been transferred to the Div. II Tab Book by 15 Nov. 2001.
Dam Construction Type: Earth Fill
Outlet: Single 42-inch pipe with a discharge capacity of 888 cfs. Three valves, 6-inch, 16-inch, and 42-inch, discharge into the pipe.
Spillway: Labyrinth spillway with a flow capacity of more than 14,000 cfs. The spillway channel is cut into the granite adjacent to the dam.
End-of-Month Storage Records: Yes
Water Rights: (Source: Tabulation of Adjudicated Surface Water Rights of the State of Wyoming, Water Division Number Two, Oct. 1999)

Reservoir Permit Number Permitted Use Priority Date Volume (af) Headgate Location (S-T-R)
Twin Lakes No. 1 Res. 4129R Mun 11-21-1928 1180 35-54-087
Twin Lakes No. 2 Res. 6502R D,Ind 05-06-1955 202.9 35-54-087
Enl. Twin Lakes No. 1 Res 6847R Mun 01-23-1962 136.9 35-54-087

Note: Expansion in 1989 provided more capacity that is not recorded here. Permit 10349R had not been recorded in the Tab Book as of 15 Nov. 2001. 1,500 acre-feet.
Designated Use: Water supply
Recreational Use: Fishing, non-motorized boating, swimming
Associated Irrigation Diversions: None
Operational Discussion: Twin Lakes Reservoir is an on-channel facility for Snail and Coney creeks. The reservoir's permit requires the City of Sheridan to release 3.2 cfs or the inflow (whichever is less) of those two streams to the reservoir. During the winter, this flow averages 1 cfs. In spring, runoff allows the city to store water and release 3.2 cfs. In the latter part of July, when the Goose creeks go into regulation, the operator begins releases to the City of Sheridan intakes in the Big Goose Canyon. These releases are approximately 6 cfs (three each for city and the Sheridan County Joint Powers Board).

In addition, the operator is required to provide three days of 50 cfs flushing flow in May or June. The operation takes approximately 20 days to complete, given the gradual increases and decreases required to bracket the flushing flow.
References: Al Kinter, City of Sheridan water superintendent, interview, 28 Feb. 2001.

Active Dams, State Engineer's Office Safety of Dams Engineering Div. Database, transmitted by Larry Stockdale, Safety of Dams engineering consultant, 16 Feb. 2001.

Tabulation of Adjudicated Surface Water Rights of the State of Wyoming, Water Division Number Two, Oct. 1999, database transmitted by Rebecca Mathisen, SEO Technical Services Division administrator, 8 Sept. 2000.

Twin Lakes Dam Profile (Source: Permit on file in State Engineer's Office, Water Div. II):

Net Evaporative Loss from Twin Lakes Reservoir:

Tie Hack Reservoir End-of-Month Storage


Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Wet (1997) 2450 2450 2450 2450 2450 2450 2450 2450 2450 2450 2450 2450
Average (1999) 2450 2450 2450 2450 2450 2450 2450 2450 2450 2450 2450 2450
Dry (2001) 2450 2450 2450 2450 2450 2450 2447 2241 2014 2034 2079 2055
Historical Ave. Storage (acre-feet) 2450 2450 2450 2450 2450 2450 2449 2380 2305 2311 2326 2318
Corresponding Area (acres) 54.63 54.63 54.63 54.63 54.63 54.63 54.63 54.63 54.63 54.63 54.63 54.63

Calculations:
Monthly Lewis Evap. (inches) 1.296 1.2 1.872 3.84 5.52 6.288 8.208 7.488 5.52 3.648 1.872 1.248
Monthly Precipitation (inches) 0.75 0.75 0.75 1.75 2.75 2.25 1.25 0.75 1.75 1.25 0.75 0.75
Net Evaporation (inches) 0.546 0.45 1.122 2.09 2.77 4.038 6.958 6.738 3.77 2.398 1.122 0.498 TOTAL
Total Net Evaporation (acre-feet) 2 2 5 10 13 18 32 31 17 11 5 2 148

Note: Because Twin Lakes Dam was completed so recently, its records were culled for the wet, average, and dry years identified by Wyoming State Engineer's Office water commissioner-hydrographers. These were averaged to provide the basis for the evaporative loss