2021-07-07_REVISION - M1997058 (4)

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a '' COLORADO Division of Water Resources Department of Natural Resources Dam Safety Branch July 6th, 2021 Mr. Brad Hagen, P.E. When replying, please refer to: Civil Resources, LLC Walker Reservoir North Dam, DAMID 020697 8308 Colorado Blvd, Suite 200 Water Division 1, Water District 2 Firestone, Colorado 80504 via email: brad@civiLresources.com SUBJECT: Jurisdictional Determination for Walker North Reservoir Dam Dear Mr. Hagen, Thank you for submitting the Walker Reservoir hazard classification recommendation memo dated June 29th, 2021 for review and hazard classification determination. The above referenced structure is located approximately 2 miles north of the City of Brighton, Section 36, Township 1 N, and Range 67 West of the 6th P.M. in Weld County Colorado. The Walker Reservoir complex consists of two reclaimed gravel pit cells (North and South Cell). The pits have been lined with slurry walls and will come on line for water storage in the near future. Civil Resources, LLC has reviewed the available historic topographic information for this area and determined storage in the south cell is below grade and formal approval by the dam safety branch is not required. The majority of the water storage in the north cell is also below grade; however, overburden from mining operations were used to create an embankment that will result in storage of water approximately 5 foot above the pre-mined ground surface in the northeast corner of the reservoir. The reservoir will store water approximately 5-ft above the original (pre-mined) ground surface, which wilt result in 170.2 acre-feet of above grade storage. Due to this above grade storage volume, the North Cell is considered a jurisdictional dam. A critical section was evaluated in the northwest corner of the reservoir for a potential dam failure and it was determined the breach flood flows will travel northeast across undeveloped land for approximately 0.5 miles and into the South Platte River. Breach flows would inundate land within the South Platte River flood plain that will unlikely be developed. Based on this information, this office agrees with your findings the dam is No Public Hazard. We sincerely appreciate that you contacted this office for a ruling on the status of this project. Please keep me up-to-date as this storage complex is completed and brought on tine. Feel free to contact me at (970) 352-8712 x1251 if you have any questions or comments regarding the information presented herein or any dam safety related topics. Sincerely, V John Batka, P.E. Dam Safety Engineer of.C�10 1313 Sherman Street, Room 821, Denver, CO 80203 P 303.866.3581 www.cotorado.gov/water I Ne o� Jared S. Potis, Governor I Dan Gibbs, DNR Executive Director I Kevin G. Rein, Director/State Engineer ►1876 �,,.