HomeMy WebLinkAbout1.18 Inundation Analysis of Hopkins Dam Break
February 11, 2022
Martin Van Ardenne
The Seligman Group
600 Montgomery St, 40th floor
San Francisco, CA 94111
415-658-2889
RE: Review of the Hopkins Dam Inundation Mapping on Proposed Phase Development of Spring
Valley Ranch and the future development.
Dear Martin:
Garfield County has a requirement for a dam break analysis of Hopkins Dam and the impacts it
has on the proposed emergency access road and future phases of the development. This report is
intended to respond to Condition No. 8.0 of the Preliminary Plan Approval (Reception No.
747016), which states:
The dam break failure analysis for an enlarged Hopkins Reservoir must be incorporated into the
drainage plan and subdivision improvements agreement for phase 2 and incorporated into
subsequent phases as applicable in a manner adequate to prevent damage or potential loss of life
or structures within the subdivision.
Zancanella & Associates has reviewed the sunny day dam break as defined by Colorado Dam
Safety from the Dam Reconstruction Project that was recently completed including the inundation
flood boundaries from said break. This project consisted of removing the existing dam and
rebuilding it to current Dam Safety Standards.
The flood wave is confined to the Landis Creek drainage and currently does not severely impact
existing structures. It does impact the existing access road and County Road 115. With the
construction of the emergency access road (future High Grange Pass Rd) which involves
improving the existing road and raising the grades, the flood inundation wave will be affected as
will the impacts on the infrastructure.
After the flood wave impacts County Road 115, it diffuses and spreads out to have minimal
impacts on future development. The proposed improvements to the emergency access road is not
anticipated to change this. An attached map is included with this analysis that includes the flood
inundation wave boundaries, the proposed future phase lots, and other information pertinent to this
analysis.
The flood inundation wave is not anticipated to impact current structures significantly more than
current conditions, nor get to the point of potential for loss of life with the improvements, but the
emergency access road (High Grange Pass Rd) will be impacted to the point of possible failure.
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As there are alternative egress routes on the property, we do not anticipate this to be a deterrence
to the development of the property. Additionally, access to the site from Highway 82 can be
achieved by either using County Road 115 from the North or Spring Valley Road and County
Road 115 from the South.
With the construction of the emergency access road, the dam should still maintain the Significant
Hazard Classification which is defined from Colorado Dam Safety as potential for loss of property
but not loss of life.
No structure that is habitable should be located within the inundation boundary unless additional
review and analysis has taken place to ensure no loss of life or significant property damage will
occur during a sunny day dam break.
Included in this report is the full dam break and inundation study performed as part of the Hopkins
Reservoir approval documents. Additionally, the Hopkins Dam Certificate of Acceptance for the
recent dam reconstruction project is included for reference in this report.
Should you have any questions or need additional information, please feel free to contact us to
discuss the additional
Very truly yours,
Zancanella & Associates, Inc.
__________________________
Matthew V Weisbrod, PE
Attachments: Inundation Map.
Dam Break Analysis.
Hopkins Dam Reconstruction Certificate of Acceptance.
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Dam Safety Branch
1313 Sherman Street, Room 821, Denver, CO 80203 P 303.866.3581 https://dwr.colorado.gov/
Jared S. Polis, Governor | Dan Gibbs, DNR Executive Director | Kevin G. Rein, Director/State Engineer
January 18, 2022
SUBJECT:Final Acceptance of Construction
Dear Mr. Van Ardenne,
Our office performed a final construction inspection of the newly constructed Hopkins Dam on October
7, 2020. Rule 8 of the Rules and Regulations for Dam Safety and Dam Construction (the Rules) requires
that your design engineer, Zancanella & Associates, prepare as-constructed plans, a completion report
documenting all aspects of construction, and their professional certification stating that the project
was completed in accordance with the approved plans and specifications. Zancanella & Associates
submitted completion documents on April 2, 2021. Our office provided final comments on April 30,
2021 which were satisfactorily addressed on January 12, 2022.
This project involved construction of a new, Significant Hazard dam at the site of a previously
breached structure. Based on observations during construction inspections, oversight and certification
by your engineer, and our review of the construction completion documents, we believe the project
has been satisfactorily completed in general accordance with the approved plans and specifications.
Therefore the project is accepted for full storage when water is physically and legally available,
and in accordance with your engineer’s monitoring plan.
The structure has a dam height of 25 feet and crest length of 700 feet. The reservoir created by the
dam covers approximately 12 acres and has full storage capacity of 113 acre-feet at the emergency
spillway crest elevation.
The State Engineer, by providing this construction acceptance does not assume responsibility for any
unsafe condition of the subject dam. The sole responsibility for the safety of this dam rests with the
reservoir owner and operator, who should take every step necessary to prevent damages caused by
leakage or overflow of waters from the reservoir or floods resulting from a failure of the dam.
Therefore, it is in the owner’s best interest to operate and maintain the facility in a manner such that
the safety of the dam and the general public are not jeopardized.
We are enclosing a copy of Rules 11 and 13 of the Rules for your reference and use. These rules
pertain to general maintenance items and the owner’s responsibilities, respectively.
We would like to recognize the efforts of Seligman Group, Zancanella & Associates, and Mueller
Construction, and all other parties who worked to complete this dam construction project. Thanks to
all for minding the safety of those who live below this dam and the resiliency of those served by it.
If you have any questions, please contact me at 719.227.5294 or Dam Safety Engineer Jackie Blumberg
at 303.505.6469.
Mr. Martin Van Ardenne
Seligman Group
600 Montgomery St.
40th Floor
San Francisco, CA 94111
via email: mvanardenne@seligmangroup.com
When replying, please refer to:
HOPKINS DAM, DAMID 380113
Water Division 5, Water District 38
Construction File No. C-0090C
Mr. Van Ardenne
Hopkins Dam – Final Project acceptance Letter
DAMID 380113, C-0090C
January 18, 2022
Page 2 of 2
Sincerely,
John Hunyadi, P.E.
Chief, Colorado Dam Safety Branch
Enc. Copy of Rules 11 and 13 of the “Rules and Regulations for Dam Safety and Dam Construction”
ec: James Heath, Division Engineer, Water Division 5
Heather Ramsey, WD 38 Water Commissioner
Jackie Blumberg, Dam Safety Engineer
Jeremy Franz, Design Review Engineer
Jason Ward, Design Review Engineer
Matt Weisbrod, Zancanella & Associates,MWeisbrod@za-engineering.com