July/August 2021 - 78

To evaluate appropriate and costeffective
means of remediating the dam,
a subsurface investigation consisting of
test holes and borings was performed
through the concrete cladding above the
spillway to identify the composition of
the dam and the underlying soils.
Although a clay core had reportedly
existed, this condition was not observed.
Substantial voids were encountered
within the upper zone of the dam. The
soils consisted of bedded river deposits
(gravelly sand and sandy gravel) with a
localized deep zone of clay-dominated
soils. Cobbles were noted at depth, and
numerous cobbles and boulders were
observed at the surface.
The state of the structure was thus
Water pouring through, below and downstream of the structure's damaged dry face
supported or rock-filled wood crib
structure to supply water to power
adjacent millworks located along the
Catatonk Creek in the Town of Candor,
Tioga County, New York.
The dam was later fully encapsulated
with a timber pile-supported
continuous concrete spillway, an upstream
concrete apron and a downstream
splash apron comprised of large
stone slabs. Prior to the storm, the Town
of Candor had occasionally noted small,
telltale whirlpools in the upstream
water surface and sporadic loss of
streambed in proximity to the crest. The
dam was last repaired in 1997 to patch
those precursor events and to replace
portions of the concrete that encapsulated
the older structure and served
as the spillway.
Restoring the dam's subsurface
stability would clearly promote downstream
safety, but so would removal of
the dam. Catatonk Creek has a very
shallow gradient of 5 ft/mi (0.95 m/km).
Uncontrolled loss (or elective decommissioning)
would have altered over
2
1,500 upstream meters (0.06 mi
2
[141,640 m ]) of river habitat that had
established over more than 100 years.
78 * DEEP FOUNDATIONS * JULY/AUG 2021
This habitat was already subject to
protective seasonal work limitations,
and New York State Department of
Environmental Conservation (NYSDEC)
further requested studies of three
species of freshwater mussels and the
inclusion of a fish passage. The Federal
Emergency Management Agency
(FEMA) ultimately declined to fund a
fish passage, so that element was
removed. With dam removal presenting
a broad, dramatic and adverse impact to
the area, preservation of the dam
structure and the environment upstream
became the principal goal.
Structural Investigation
A visual investigation was performed in
June 2012 to thoroughly document the
condition of the dam and assess the
degree to which the storm had destabilized
the structure. Boils were
observed within portions of the splash
apron, undermining the stones, and
significant seepage emanated from riprap
that lined the sides of the river bank
immediately downstream of the
spillway. Seepage was also documented
from cracks within the
concrete cladding of the spillway itself.
confirmed to be unpredictable, and
remediation was required. The storm
was declared a federal disaster in
September 2011, and the town applied
for funding through FEMA. FEMA
ultimately agreed the storm had
dramatically exacerbated the seepage
and destabilized the dam, but was only
willing to fund the repairs required to
mitigate seepage.
Remediation Approach
Since the internal structure of the dam
could not be reliably ascertained for
direct improvement, stabilizing the dam
indirectly through seepage control was
deemed the best approach. Tectonic
Engineering Consultants, Geologists &
Land Surveyors selected a sheet pile cutoff
wall as a cost-effective and environmentally
sensitive means of controlling
seepage from beneath, through and
around the dam. Aesthetically, this
approach also considered that the dam
is very visible to both the Village and
Town of Candor residents. The sheet
piling selected to control seepage would
not alter the exposed structure or
change the dam's observable profile.
Alternative methods, which commonly
consist of mineral and/or chemical
grouts, were eliminated as they can be
difficult to control and the materials can
become lost to the environment.
July/August 2021

Table of Contents for the Digital Edition of July/August 2021
