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Gross Reservoir

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Coordinates: 39°56′31″N 105°22′22″W / 39.94194°N 105.37278°W / 39.94194; -105.37278
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Gross Reservoir
The reservoir in 2014.
Location of Gross Reservoir in Colorado, USA.
Location of Gross Reservoir in Colorado, USA.
Gross Reservoir
Location of Gross Reservoir in Colorado, USA.
Location of Gross Reservoir in Colorado, USA.
Gross Reservoir
LocationBoulder County, Colorado
Coordinates39°56′31″N 105°22′22″W / 39.94194°N 105.37278°W / 39.94194; -105.37278
Typereservoir
EtymologyNamed for Denver Water former Chief Engineer Dwight D. Gross.[1]
Primary outflowsSouth Boulder Creek
Basin countriesUnited States
Managing agencyDenver Water
Surface area440 acres (180 ha)
Water volume41,811 acre⋅ft (51,573,000 m3)
Surface elevation2,222 m (7,290 ft)[2]

Gross Reservoir, located in Boulder County, Colorado, is owned and operated by Denver Water. Completed in 1954, the reservoir has a surface area of 440 acres (180 ha), and the spillway sits at 7,225 feet (2,202 m) elevation.[1] The reservoir is undergoing an expansion project.

The reservoir receives water from the western side of the Continental Divide through the Moffat Tunnel. South Boulder Creek flows out of the 340-foot high dam (100 m).

Recreation

The reservoir provides opportunities for fishing (including ice fishing), hiking, canoeing, kayaking, and some camping. No water-contact activities such as swimming or wading are allowed. Only non-motorized boats are permitted.[1]

Expansion project

The proposed expansion of Gross Reservoir would allow Denver Water to store an additional 77,000 acre-feet (95,000,000 m3) of water, drawn mostly from the Fraser and Williams Fork Rivers.[3] Construction on the project, expected to be complete around 2027,[4] will raise the level of the dam by 131 feet (40 meters), resulting in an additional 77,000 acre-feet (95,000,000 cubic meters) of water storage capacity in the reservoir and making it the tallest dam in Colorado.[5]

Denver Water applied to the U.S. Army Corps of Engineers for a permit under section 404 of the Clean Water Act, required to construct the expansion, and that permit was granted in 2017.[6] In response, several environmental groups sued USACE on grounds that the agency's deliberations about granting the permit violated the Clean Water Act, Endangered Species Act, and National Environmental Policy Act.[7] In July 2020 the Federal Energy Regulatory Commission granted a required modification to the Federal Power Act license granted to Colorado Water for Gross Dam before it was built.[8]

A contract for design services was awarded to Stantec, an engineering consulting firm, in 2017.

Boulder County announced in spring 2019 that it would require Denver Water to obtain a land use permit under Colorado law before commencing the expansion project.[9] Denver Water submitted its application for that permit in September 2020.[10] Boulder County commissioners approved the expansion in 2021 and accepted a $12.5 million mitigation deal.[11][12]

Climate

According to the Köppen Climate Classification system, Gross Reservoir has an oceanic climate, abbreviated "Cfb" on climate maps. The hottest temperature recorded at Gross Reservoir was 94 °F (34.4 °C) on July 9, 2003, June 23, 2012, June 26, 2012, and June 22, 2016, while the coldest temperature recorded was −24 °F (−31.1 °C) on February 2, 2011.[13]

Climate data for Gross Reservoir, Colorado, 1991–2020 normals, extremes 1978–present
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Record high °F (°C) 67
(19) 		64
(18) 		72
(22) 		78
(26) 		89
(32) 		94
(34) 		94
(34) 		92
(33) 		91
(33) 		81
(27) 		70
(21) 		64
(18) 		94
(34)
Mean maximum °F (°C) 57.7
(14.3) 		58.1
(14.5) 		66.3
(19.1) 		72.3
(22.4) 		78.7
(25.9) 		88.0
(31.1) 		89.8
(32.1) 		87.7
(30.9) 		84.7
(29.3) 		75.5
(24.2) 		66.5
(19.2) 		58.1
(14.5) 		91.0
(32.8)
Mean daily maximum °F (°C) 39.3
(4.1) 		39.7
(4.3) 		47.2
(8.4) 		52.2
(11.2) 		60.8
(16.0) 		72.6
(22.6) 		79.3
(26.3) 		77.1
(25.1) 		69.7
(20.9) 		56.8
(13.8) 		47.0
(8.3) 		39.5
(4.2) 		56.8
(13.8)
Daily mean °F (°C) 28.1
(−2.2) 		28.2
(−2.1) 		34.7
(1.5) 		39.7
(4.3) 		48.1
(8.9) 		58.1
(14.5) 		64.5
(18.1) 		62.3
(16.8) 		55.2
(12.9) 		44.1
(6.7) 		35.3
(1.8) 		28.5
(−1.9) 		43.9
(6.6)
Mean daily minimum °F (°C) 16.9
(−8.4) 		16.7
(−8.5) 		22.1
(−5.5) 		27.1
(−2.7) 		35.4
(1.9) 		43.6
(6.4) 		49.6
(9.8) 		47.6
(8.7) 		40.6
(4.8) 		31.3
(−0.4) 		23.5
(−4.7) 		17.5
(−8.1) 		31.0
(−0.6)
Mean minimum °F (°C) −4.5
(−20.3) 		−6.1
(−21.2) 		5.4
(−14.8) 		13.7
(−10.2) 		23.3
(−4.8) 		35.7
(2.1) 		43.9
(6.6) 		40.0
(4.4) 		30.6
(−0.8) 		15.5
(−9.2) 		4.9
(−15.1) 		−5.2
(−20.7) 		−11.8
(−24.3)
Record low °F (°C) −13
(−25) 		−24
(−31) 		−14
(−26) 		0
(−18) 		11
(−12) 		28
(−2) 		35
(2) 		27
(−3) 		16
(−9) 		−1
(−18) 		−14
(−26) 		−19
(−28) 		−24
(−31)
Average precipitation inches (mm) 0.71
(18) 		0.90
(23) 		1.94
(49) 		2.73
(69) 		2.89
(73) 		1.87
(47) 		2.04
(52) 		2.12
(54) 		1.99
(51) 		1.35
(34) 		0.96
(24) 		0.78
(20) 		20.28
(514)
Average snowfall inches (cm) 9.4
(24) 		14.0
(36) 		21.0
(53) 		19.8
(50) 		3.9
(9.9) 		0.1
(0.25) 		0.0
(0.0) 		0.0
(0.0) 		0.9
(2.3) 		6.9
(18) 		12.0
(30) 		11.1
(28) 		99.1
(251.45)
Average extreme snow depth inches (cm) 7.7
(20) 		8.2
(21) 		11.3
(29) 		10.4
(26) 		3.4
(8.6) 		0.0
(0.0) 		0.0
(0.0) 		0.0
(0.0) 		0.9
(2.3) 		5.1
(13) 		7.3
(19) 		7.9
(20) 		18.4
(47)
Average precipitation days (≥ 0.01 in) 4.7 5.6 6.3 8.4 10.5 8.1 10.2 10.9 7.3 6.0 4.9 4.9 87.8
Average snowy days (≥ 0.1 in) 4.0 4.7 4.8 4.6 1.3 0.0 0.0 0.0 0.4 1.9 3.8 4.0 29.5
Source 1: NOAA[14]
Source 2: National Weather Service[13]

See also

References

  1. ^ a b c Denver Water. Gross Reservoir. Viewed 2014-09-22.
  2. ^ "Gross Reservoir". Geographic Names Information System. United States Geological Survey, United States Department of the Interior. Retrieved September 23, 2014.
  3. ^ Gardner-Smith, Brent (April 20, 2016). "Denver Water official says more West Slope water projects 'not on our radar'". Aspen Journalism. Retrieved November 25, 2020.
  4. ^ Ingram, Elizabeth (July 20, 2023). "Why Denver Water is raising Gross Dam". Hydro Review. Retrieved October 21, 2023.
  5. ^ Brennan, Charlie (January 2, 2018). "Denver firm awarded $13M design contract for expansion of Boulder County's Gross Reservoir". Boulder Daily Camera. Boulder, CO. Retrieved November 25, 2020.
  6. ^ Ingram, Elizabeth (July 12, 2017). "Denver Water approved to expand reservoir behind Gross Dam". Hydro Review. Retrieved November 25, 2020.
  7. ^ Brennan, Charlie (December 19, 2018). "Environmental groups sue to block expansion of Boulder County's Gross Reservoir". Boulder Daily Camera. Retrieved November 25, 2020.
  8. ^ Jones, Corey H. (July 17, 2020). "Boulder County's Gross Reservoir Can Proceed With Expansion Following Lawsuit". CPR News. Retrieved November 25, 2020.
  9. ^ Lacey, Hank (November 24, 2020). "Gross Reservoir Expansion Proposal Presents Water Demand, Environmental Concerns". Law Week Colorado. Retrieved November 25, 2020.
  10. ^ Swearingen, Deborah (October 5, 2020). "County's review of proposed Gross Reservoir expansion underway". Boulder Daily Camera. Retrieved November 25, 2020.
  11. ^ Booth, Michael (October 20, 2023). "Forest Service says Denver Water is taking down too many trees, rushing requests to change plan to raise Gross Dam". The Colorado Sun. Retrieved October 21, 2023.
  12. ^ "Gross Reservoir Impact Mitigation Fund". Boulder County. Retrieved October 21, 2023.
  13. ^ a b "NOAA Online Weather Data – NWS Boulder/Denver". National Weather Service. Retrieved February 7, 2023.
  14. ^ "U.S. Climate Normals Quick Access – Station: Gross RSVR, CO". National Oceanic and Atmospheric Administration. Retrieved February 7, 2023.
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