September 13, 2013
Attention: Antonio Tebsherani, Kurt Carlson, & Rob Neuhauser
Recipient's Address
Dear All,
Reference: Post Event Scour Inspections – Adams County Fairgrounds
As requested, post high flow event and scour inspections were performed on 9-13-2013 by Stantec
inspectors at the two main vehicular bridge entrances to the Adams County Fair Grounds (structure
ADA127-09.5N193 and the unnamed structure on Park Blvd.). Brantner Gulch reached record flows during
rain events over the past few days, overtopping these structures and others along the course of the stream.
A summary of results from these inspections are as follows:
•
Park Blvd Structure:
o
Structure consists of a single span, precast double-T girder bridge on CIP wall abutments.
The channel through the structure is protected with a concrete lining.
o
The channel lining and slope protection immediately upstream and through the structure
appears to be intact with little evidence of deterioration (flows through the channel were
still high at the time of the inspection allowing limited access and inspection).
o
It appears that no channel lining was originally installed at the outlet of the structure (none
exists now). A 6 ft drop currently exists from the channel lining bottom slab to the channel
bottom immediately downstream from the structure exposing the downstream edge of the
slab and cutoff wall. The channel bottom is protected with riprap stone. Significant scour
deterioration was not observed but should be verified once channel flows diminish.
o
The southeast channel embankment, fill behind the southeast wingwall and the roadway
embankment up to the gutter and shoulder of Park Blvd is significantly scoured and eroded.
The approximate dimensions of the scoured area measure 50 ft along the channel, 30 ft
from the back of the wingwall and 15 ft deep throughout. The backfill beneath the south
approach gutter and shoulder is unstable with undermining up to 12 inches horizontally
beneath the gutter immediately behind the south abutment. The southeast wingwall is
free-standing with unknown pile embedment supporting the corrugated metal decking.
The scoured area is also responsible for the collapse of an irrigation water main (unbraced
pipe bridge over waterway) and exposure of several additional utilities. The foundation for
the steel gate used to close the roadway is completely exposed and could become unstable
should further loss of roadway embankment occur.
September 13, 2013
Antonio Tebsherani, Kurt Carlson, & Rob Neuhauser
Page 2 of 8
Reference: Post Event Scour Inspections – Adams County Fairgrounds
o
The east shoulder of the roadway at the south approach was closed at the conclusion of the
inspection per recommendation by Stantec inspectors.
o
The northeast channel embankment is near vertical and unstable with significant loss of
riprap channel protection. The northeast wingwall is providing sufficient reinforcement of
roadway embankment material at this location.
o
The bridge deck, superstructure and substructure appear sound with no significant
deficiencies which would require immediate action.
o
The bridge is suitable for vehicular use provided the east shoulder of the roadway remain
closed and no further sloughing of embankment material continues at the south approach.
It is recommended that the vertical walls of the scour depression be braced with driven
piles and lagging or compacted backfill to stabilize the embankment until the exposed
utilities can be shored and the entire area backfilled to original design.
Figure 1: Bridge elevation looking east
September 13, 2013
Antonio Tebsherani, Kurt Carlson, & Rob Neuhauser
Page 3 of 8
Reference: Post Event Scour Inspections – Adams County Fairgrounds
Figure 2: 6 ft drop in channel bottom elevation at outlet
Figure 3: View of scour at southeast
September 13, 2013
Antonio Tebsherani, Kurt Carlson, & Rob Neuhauser
Page 4 of 8
Reference: Post Event Scour Inspections – Adams County Fairgrounds
Figure 4: Undermining of approach gutter and gate foundation at southeast
•
Structure ADA127-09.5N193:
o
The structure consists of a single span, steel multi-girder bridge on driven steel H-pile
abutments. The channel beneath the structure is protected with a trapezoidal concrete
lining.
o
The sloped channel lining of the south channel bank has failed for a distance of 75 ft
upstream from the structure, the entire 24 ft width of the structure, and an additional 36 ft
downstream from the structure. Significant loss of soil embankment behind the failed
lining has occurred.
o
The channel lining bottom slab and north slope appear to be intact. Limited access and
visibility due to high channel flows at time of inspection.
o
Significant embankment scour has exposed the pile bent substructure of the south
abutment and removed a large portion of the backfilled soil approach. The scoured area
measured beyond the deck of the structure is 24 ft by 7 ft by 7 ft deep. Steel H-piles of the
south abutment are exposed vertically 44 inches, 47 inches, 41 inches, 35 inches, and 8
inches respectively starting at the westernmost pile and moving east. The piles exhibit light
surface corrosion (R1).
September 13, 2013
Antonio Tebsherani, Kurt Carlson, & Rob Neuhauser
Page 5 of 8
Reference: Post Event Scour Inspections – Adams County Fairgrounds
o
Localized scour at the north abutment has exposed the top 8 to 20 inches of the steel Hpiles at this location.
o
In order to re-open the bridge, it is recommended that the material scoured from the south
approach and embankments be backfilled and compacted around the south abutment and
that the concrete channel lining be reconstructed.
Figure 5: Structure ADA127-09.5N193 Elevation
September 13, 2013
Antonio Tebsherani, Kurt Carlson, & Rob Neuhauser
Page 6 of 8
Reference: Post Event Scour Inspections – Adams County Fairgrounds
Figure 6: Failed south bank concrete channel lining
Figure 7: Scour of south approach and abutment backfill
September 13, 2013
Antonio Tebsherani, Kurt Carlson, & Rob Neuhauser
Page 7 of 8
Reference: Post Event Scour Inspections – Adams County Fairgrounds
Figure 8: Exposed steel H-piles of the south abutment
•
Additional Pedestrian and Golf Course Structures:
o
In addition to the vehicular structures, pedestrian structures and golf course structures
were briefly observed for major structural deficiencies.
o
The two pedestrian structures between Structure ADA127-09.5N193 and the Park Blvd
structure have significant damage due to overtopping.
o

The structure immediately east of Structure ADA127-09.5N193 has been shifted off
its foundation (founded on the trapezoidal channel lining) approximately 6 ft at the
north abutment and 3 ft at the south abutment. It is recommended that the
structure be completely reconstructed; re-use of the steel girders should be
possible.

The second structure was completely removed from its foundation and has likely
washed downstream into the lake. Complete reconstruction will be needed for
replacement.
The golf course structures have problems at the abutments associated with scour beneath
the abutments and of embankment fill material. All structures will need to be backfilled
September 13, 2013
Antonio Tebsherani, Kurt Carlson, & Rob Neuhauser
Page 8 of 8
Reference: Post Event Scour Inspections – Adams County Fairgrounds
around their abutments. A few of the timber plank cart bridges will need to have their
abutments reconstructed and timbers reset. All bridges will need new railings.
Please contact our offices in Denver with any questions or comments regarding these structures or the scour
inspections performed. We appreciate the opportunity to provide our services to you.
Regards,
Frank J Block, PE
Bridge Inspector, Team Leader
Phone: 303.758.4058
Frank.block@stantec.com
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