HomeMy WebLinkAbout810679.tiff STATE OF COLORADO
Deparimeni of Mililery Affairs - of Cob,
DIVISION OF DISASTER EMERGENCY SERVICES •
A��pp,jt�i$
Camp GeorgeWeil
Golden,Colorado 80401 4'
Phone (3031 279-2511 s 1gj6.
Richard D Lamm
_ A Governor
C .J)
`• ) t- Bug.Gen John l franc,
V the Adjwanl General
John P. Byrne
jD• Doeclor
CODES � .:'' November 10, 1981
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Mr. Chuck Carlson, Chairman .
Board of County Commissioners - -
Weld County - -
915 10thSt. , Box 459
Greeley, CO 80631
Dear Commissioner Carlson: .
Enclosed for your information and action is a copy of the letter
of transmittal that accompanied the Phase I Inspection Report on a
Reservoir Dam (Horse Creek Dam ) that is geographically located with-
in your county. This report has been provided by the State Division of
Water Resources to the dam owners and recommends that they develop a
plan in coordination with local authorities to deal with an emergency
situation should one arise, due to a partial or total failure of the
dam structure. This action is in addition to the recommendations for
work to be accomplished on the structure itself.
Because of the many implications a dam failure could have on local
government and its citizens, I recommend the county review the situa-
tion (locally) to determine the population and property at risk should
this dam fail. Based on this review, the county should then take those
actions necessary to prepare warning and evacuation plans and procedures
for a dam failure 'at this site. If more detailed information is required
concerning the Phase I report, it can be obtained by contacting the State
Engineer's Office at telephone 866-3581.
Due to the significance of this situation, it is requested that the
county notify this office in writing of those actions that are taken to
address this hazard.
Sincerely,
tilt-
Jahn 13, B •
Director
• JPB: pw 810679
cc: Div. of Water Resources,
State of Colorado
Emergency Preparedness Office Weld County
/ ,
i 11 y" lG�aLs
-i;LhARD D. LAMM / F��'�""'�9� JERIS A ANIELSO
Governor I o t/ ti ��� D State Engineer `�
DIS PA LCiCL } .„�r�" fr �`�
' ODES 1876 . jy
``C�CT 7" II iOfPItt OF THE STATE ENGINEER ��
DIVISION OF WATER RESOURCES
1313 Sherman Street-Room 818
Denver, Colorado 80203
(303) 866-3581
October 20, 1981
Mr. Roy Kaufman, President
Henrylynn Irrigation District
P. 0. Box 85
Hudson, CO 80642
Re: Horse Creek Dam, CO-12
W. Div. 1 W. Dist. 1
Dear Mr. Kaufman:0
. 04
Enclosed are two copies of the phase I dam inspection report for your
Horse Creek Dam. The report was prepared under U. S. Government Authority
in accordance with PL 92-367 for the Army Corps of Engineers and their National
Dam Safety Program (NDSP) . Please implement the recommendations made therein,
taking into account the previous requests by our office.
In addition to the recommendations in the report, you should establish a
written plan for dealing with any emergency situations that might arise due to
a partial or total failure of dam structures that you own. The plan should
include actions to be taken in case of impending or partial failure of the dam
(i.e. slides, excessive seepage, overtopping by flood waters, etc.) and actions
to contain outflows should a breach occur. Items that might be required include
engineering supervision, equipment, equipment operators and hand laborers, sand-
bags, riprap and fill material, transportation for equipment and materials, and
lighting for night work. Your local emergency preparedness coordinator can
assist you in locating the nearest sources available. The coordinator for your
area can be identified by contacting the Operations Section of Colorado's
Disaster Emergency Services Agency at (303) 279-2511 Ext. 240 or 241. A model
emergency preparedness plan is enclosed for your use.
Procedures to warn and evacuate downstream residents should be coordinated
with local law enforcement authorities. After your emergency plans have been
drafted, they should be thoroughly reviewed by all persons that will be expected
to assist in their implementation including local law enforcement, and civil
defense personnel. We will appreciate a copy of your plan for our review and file.
Please advise us of your plans to implement the recommendations by December
31, 1981.
Very truly you s,
AEP:mvf
Enclosures \ Q(. Y ` r
cc: John Monzingo, USCE Ala E. Pea so7'V:E.
Jim Clark, Div. Eng. Chief, Dam Safety Branch
DODES
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SUMMARY OF ASSESSMENT AND It P:CUMMP;NUA'L'LONS
WELD COUNTY , COLORADO
HORSE CREEK DAM
L. D. NO. CO 00012
HAZARD POTENTIAL CATEGORY: HIGH
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INSPECTED: 6 July, 1981
In general. , Horse Creek Dam is in very poor condition due to lack
of proper maintenance of the upstream slope and the recent distress
which occurred to the embankment . In April and May of 1981 , about 450
feet of the crest of the dam, near the midsection of the dam, settled
by about 3 .5 feet and cracks developed on the upstream and downstream
slopes. This incident caused utmost concern about the safety of the
darn. The State Engineer immediately ordered that the reservoir be
lowered to a level at least 4 feet below the spillway crest , at a
maximum discharge rate equal to the 4011 cfs capacity of the downstream
canal . Construction of an earthfill berm along the downstream toe, to
stabilize and strengthen the distressed area, was quickly initiated to
ensure the safety of the clam and to retain as much water as possible.
While work on the berm progressed , cl awdow❑ of the reservoir continued
al the maximum rate until a level approximately 4 .5 feet below the
cresC. of the spillway was attained . Construction of the berm was
completed in mid—June, approximately three weeks after work began. As
of the date of this report , work is continuing on other required
remedial measures and the reservoir is essentially at the dead storage
level . The Colorado State Engineer' s Office will assure that all
remedial work is completed and meets the National Dam Safety Guide-
lines before any significant level of storage is allowed in the
reservoir.
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From a hydrologic and hydraulic standpoint , the safety of Horse
1 Creek Dam is considered adequate in view of its ability to pass the
Probable Maximum Flood . This analysis is based on the dam crest being
uniformly restored to its design elevation 5078.44 feet (NGVD) , the
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existing, configuration of the Denver-Hudson Canal, and the water
1 surface of the reservoir being at the spillway crest at the inception
of the flood.
The following; actions should be implemented to improve the struc-
tural integrity and the operational adequacy of the dam:
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(1 ) The reservoir should not he refilled- to any substantial level
of storage until all remedial work is complete and approved, and all
reports and analysis have been submitted, and reviewed by the State
Engineer's Office.
(2) The crest of the darn should be repaired and uniformly re-
stored to its intended design elevation in accordance with i.nstruc
Lions issued by the State Engineer' s office.
' (3) The abandoned outlet conduit passing through the dam near the
• distressed area should be plugged at the upstream end in accordance
with instructions issued by the State Engineer.
(4) Stability analysis of the embankment , being performed by the
owner's engineer to determine the adegirar'y of the upstream and down-
stream slopes and the crest width, should be finalized and submitted
to the State Engineer for review. Included in Ibis study should be a
determination of the in-situ strengths of the embankment and founda-
tion soils. These test results should be used to carry out stability
analyses of the clam.
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(`i) The riprnlr nlrsng thi' np:;dream slope should be upgraded in
those areas where concrete rubble and other debris have been dumped.
(6) Seepage at the downstream toe of the darn and discharge from
the finger drains should be inspected periodically to note if any
embankment material is being washed out .
(7) A comprehensive monitoring program should be developed and
approved by the State Engineer and implemented by the owner. As part• of the program, dam instrumentation, i .e. , pi.ezometers, movement• markers, and inclinometers, should be read periodically and the data
should be recorded and immediately evaluated .
(8) The trees and brush on the embankment should be removed and
regrowth prevented. Removal of Large trees .should be done only under
the guidance of an engineer experienced in the design and construction
of earth dams. Indiscriminate clearing could jeopardize the safety of
the dam and therefore should not he allowed. The grass cover on the
downstream slope should be properly maintained.
(9) To insure that seepage paths do not develop through the
embankment as a result of the activities of burrowing animals, all
burrowing animals should be eliminated from the embankment and their
burrows properly bat-kfilled.
( Ill) Driftwood should be removed from the inlet area of the
spillway. Future accumulations of driftwood in the spillway inlet
.should be removed periodically.
( Ii ) The barbed wire fence across the spillway channel should be
either removed altogether or periodically inspected to detect any
accumulation of the debris that could obstruct the spillway.
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( 12) 'riI•I p,l ass cover in the ••pi. I lwav Marino should be per rodi.c:r
IIV mar nl :lined Io 0n:.in ,, lint III,' ',piilw:iv I • nut,h:•tiunIoil.
( 13) As-built drawings ul all repair works to Lhc embankment the
• outlet works , control gates , hoists , and hydraulic control piping
:should he prepared and flied with the St :ii Engineer ,
( 14) The condition of the gate). , hoi_:,Lt , intake structure , and
the and et. pipe should he thoroughly investigated while the reservoir
is low. Equipnent alu)uld be r epaIt ed ta. replaced as Iequi.r eel to
n;;ur tloilb10—tree: opelat. ion O1 the r_ontrul ate:; .
( 15) The condition or_ the outlet pipes , and the gates and hoists
of the outlet works should be thoroughly inspected periodically to
detect any (literiot al ton. Neceshary repairs or replacement, should he
dour promptly,
( 16) • b',' cracking and sparring of the concrete of the outlet
works should be repaired Lu on:;u, a the :tructur :ll htahilily ul the
structure.
( 17) The apparent undermining of the downstream end of the outlet
structure should be further investigated and repaired if deemed
( 18) A r np•n1ni prop') am of mai ill r,nnnrs shorlld be adopted tot the
dam and Ih„ appurtenant htructures . All maintenance and ropall :,
should he recorded. The outlet gate); and opelaling equipment_ shunter
b•• Ittipl in iu ,,pul opolat Iup, u uudll tun at :III fluky. .
( 19) Pet iodic i n:;;WC l lull of Lhc dnnl by a pi olcssiona1 eugiHeel
experienced in the design and construct ion o1 earth dams , such a;
I_huh 1):1 (wmed by Lire Si ate Engineer , :Would he cant inued and the
i n:.p,•t t i•iil I ••p,)1 I Iliad/. a m:Ii 101 of r ^t ill d.
( 21)) A contingency plan for emergencies in case of a possible dam
failure should be adopted . The plan should include a ;scheme in which
people downstream of the dam could be notified off
failure. Materials � an impending dam
and equipment which could ho used to prevent ;i
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possible dam failure should he stockpiled in no :accessible area.
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/il 7,r�Lt Ctr.:I .
Yin Au—Young
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Acting Chicf Engineer
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