Powder/Tongue River Basin Water Plan
Technical Memoranda

SUBJECT:	Appendix J Storage Operation and Description BIG HORN
PREPARED BY:	HKM Engineering Inc.
DATE:	March 2002

KEY STORAGE FACILITIES

Reservoir:	BIG HORN
Date:	20 Feb. 2001
Location:	TRACT 38 27,T53N,R86W
Owner:	BIG HORN RESERVOIR COMPANY
Year of Construction:	1909
Enlargement History:	1965, 1985
Total Storage:	5,756 acre-feet
Active Storage:	4,624 acre-feet
Dead Storage:	Information not available
Area/Capacity Data:	(Source: Undated table on file with State Engineer's Office, Water Div. II)
	Feet Elevation Area Average Area Volume Released Volume Remaining 0.0 132.4 179.34 171.59 000.00 4627.20 1.0 131.4 179.34 171.59 171.59 4455.61 2.0 130.4 179.34 171.59 343.18 4284.02 3.0 129.4 179.34 171.59 514.77 4112.43 4.0 128.4 179.34 171.59 686.36 3940.84 5.0 127.4 163.85 159.47 857.95 3769.25 6.0 126.4 163.85 159.47 1017.42 3609.78 7.0 125.4 163.85 159.47 1176.89 3450.31 8.0 124.4 163.85 159.47 1336.36 3290.84 9.0 123.4 163.85 159.47 1495.83 3131.37 10.0 122.4 155.10 151.35 1655.30 2971.90 11.0 121.4 155.10 151.35 1806.65 2820.55 12.0 120.4 135.10 151.35 1958.00 2669.20 13.0 119.4 155.10 105.95 2109.35 2517.85 13.7 118.7 147.60 143.05 2215.30 2411.90 14.7 117.7 147.60 143.05 2358.35 2268.85 15.7 116.7 147.60 143.05 2501.40 2125.80 16.7 115.7 147.60 143.05 2644.45 1982.75 17.7 114.7 147.60 143.05 2787.50 1839.70 18.7 113.7 138.50 131.00 2930.55 1696.65 19.7 112.7 138.50 131.00 3061.55 1565.65 20.7 111 7 138.50 131.00 3192.55 1434.65 21.7 110.7 138.50 131.00 3323.55 1303.65 22.7 109.7 138.50 131.00 3454.55 1171.65 23.7 108.7 123.50 107.64 3585.55 1041.65 24.7 107.7 123.50 107.64 3693.19 934.01 25.7 106.7 123.50 107.64 3800.83 826.37 26.7 105.7 123.50 107.64 3908.47 718.73 27.7 104.7 123.50 107.64 4016.11 611.09 28.7 103.7 91.79 73.29 4123.75 503.45
Dam Construction Type:	Earth Fill
Outlet:	36-inch welded steel pipe with steel slide gate
Spillway:	Emergency spillway: 40' x 3' concrete slot in dike B
End-of-Month Storage Records:	No
Water Rights:	(Source: 1980 Reservoir Filing Agreement on file in State Engineer's Office, Water Div. II and 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) Bighorn Res. 1352R I 07-10-1908 2624.19 27-53-086 Colorado Colony 1453R I 2-3-1909 69.45 27-53-086 Colorado Colony 1454R I 2-3-1909 54.95 27-53-086 Enl. Bighorn Res 6946R I 02-08-1960 1652.5 T 38-53-086 Enl. Bighorn Res 6947R I 11-18-1960 223.3 T 38-53-086
Designated Use:	Irrigation
Recreational Use:	Because Bighorn Reservoir occupies deeded land, public access is limited to walk-in fishing.
Associated Irrigation Diversions:	(Source: Bill Knapp, Div. II water commissioner/hydrographer)
	Diversion Tributary Colorado Colony Ditch Little Goose
Associated Industrial Diversions:	None
Operational Discussion:	Cross Creek flows into Bighorn Reservoir once it has been released from Cross Creek Reservoir, upstream. Because of Bighorn's elevation, releases aren't possible until well into the irrigation season because the channels in the mountain must be clear.
	The first releases are scheduled in general based on the type of water year.
	First release timing, Bighorn Reservoir Wet Year Average Year Dry Year 1st week of August 2nd week of July Last week of June
	Diversions end as close to the end of the water year (Oct. 1) as operators can manage. The closure can happen a week early if the operator believes a snowstorm will close access to the reservoir.
References:	Bill Knapp, water commissioner, interview, State Engineer's Office, Sheridan, Wyoming, 13 Feb. 2001
	Sue Lowry, telephone conversation, 20 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.

Net Evaporation from Bighorn Reservoir:

Lewis Annual Evaporation (in.)	45
Total Storage (acre-feet)	5,756

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Average percent of total storage	56.72	57.55	57.87	60.80	71.16	72.71	68.17	64.03	57.62	57.03	58.79	60.84
Generated storage (acre-feet)	3265	3313	3331	3500	4096	4185	3924	3685	3317	3283	3384	3502
Corresponding area (acres)	163.85	163.85	163.85	163.85	179.34	179.34	163.85	163.85	163.85	163.85	163.85	163.85
Calculations:
Monthly Lewis Evap. (inches)	1.215	1.125	1.755	3.6	5.175	5.895	7.695	7.02	5.175	3.42	1.755	1.17
Monthly Precipitation (inches)	1.75	1.75	2.25	2.75	3.75	2.75	1.75	1.25	2.25	2.25	1.75	1.75
Net Evaporation (inches)	0	0	0	0.85	1.425	3.145	5.945	5.77	2.925	1.17	0.005	0	TOTAL
Total Net Evaporation (acre-feet)	0	0	0	12	21	47	81	79	40	16	0	0	296