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