Colyer Lake is a 77-acre Commonwealth-owned impoundment located near State College in Potter Township,
Centre County, Pennsylvania. A dam located on Sinking Creek, a tributary of Penns Creek, creates
the lake. The impoundment is very popular with outdoor recreation enthusiasts in central Pennsylvania.
The Colyer Lake Dam consists of an earth embankment approximately 700 feet long
with a normal pool depth of 33 feet and a top of dam width of 15 feet. The flood discharge facilities
for the dam consist of a combined primary and emergency spillway located on the right abutment (looking
downstream). The spillway structure consists of a trapezoidal concrete-lined spillway discharge chute
that terminates with a concrete plunge pool at the toe level of the dam. Water flows over a 69-foot-long
trapezoidal concrete weir. The weir’s
elevation is approximately eight feet below the top of the dam’s
crest. The primary outlet works consist of a reinforced concrete box culvert and a control tower
located at the center of the embankment. The conduit is equipped with a trash rack device on the
upstream end and an endwall at the discharge end. Stop logs located in the control tower control
the flow through the conduit. The stop logs divide the control tower into inflow and outflow chambers.
The stop logs in the control tower extend from the bottom of the box culvert to the pool elevation.
The flow enters the intake chamber of the control tower through the upstream portion of the outlet
conduit. Then the flow rises to the top stop log and spills over into the outflow chamber, which
in turn discharges into the downstream portion of the outlet conduit.
Under normal pool conditions
the top stop log is set at the same elevation as the emergency spillway. The lake can be drawn down
below the normal pool elevation by removing the stop logs. The control tower is not equipped with
any mechanical device for removing the stop logs. This outlet system constitutes the emergency drawdown
facility for the dam. Colyer Lake's dam
spillway includes a 10 foot wide bypass channel. The bypass channel is used to divert incoming water
away from the lake during summer months.
Downstream from the dam, Sinking Creek generally flows east,
meandering for approximately 13 miles, and joins Penns Creek in Spring Mills. It is estimated that
failure of the dam would pose a serious public safety threat. Approximately 250 residents and 77
homes as well as Spring Mills Elementary School would be inundated if a failure were to occur.
The annual dam inspection for Colyer Lake Dam was conducted on August 23, 2002. The inspection
revealed several deficiencies in the emergency spillway. There are four areas where seepage (severe
leaking) is surfacing through the floor of the emergency spillway. The four areas are:
- Weep hole
closest to the weir (small amount).
- Weep hole and lateral crack in channel floor above the
stilling basin (moderate amount).
- Area where channel floor meets left training wall directly
in line with lateral crack in the channel floor (moderate amount).
- Three weep holes in the
stilling basin (significant amount).
PFBC engineering staff conducted dye tests on August 23,
2002, to determine the source of the seepage. Stop planks were installed at the diversion box
upstream of the lake to route the water into Colyer Lake instead of through the bypass channel.
Dye was then placed in the forebay (the flat area of the lake bed adjacent to the spillway) of
the lake to determine if the seepage was occurring through the emergency spillway weir. No dye
was evident in any of the seepage areas hours after the dye was placed in the forebay. Next,
dye was placed in a pool of the bypass channel approximately 75 feet upstream of the emergency
spillway. Within a half hour, the dye started surfacing through the seepage areas. There is evidence
that the bypass channel has undermined the floor of the emergency spillway and is the cause of
part of the seepage.
The temperature of each area of seepage was taken and has caused concern
beyond that of the bypass channel. The temperatures were: Area 1, 25°C; Area
Area 3, 22°C; and Area
4, 18°C. The temperature of the surface lake water was 22°C and the temperature of the water in the
bypass channel was 18°C. Seepage areas 2 and 3 match the temperature of the lake and the seepage area 4 matches
the bypass channel. It is unexplained why seepage area 1 had a higher temperature than the lake
Soundings of the spillway channel were taken to determine if any undermining had occurred.
There were several areas that produced hollow sounds indicating the presence of undermining.
Additionally, there is evidence of limestone aggregate flowing with the seepage in area 2. This
demonstrates drainage material beneath the spillway is eroding with the seeping water.
determined that the deficiencies within the emergency spillway at Colyer Lake could pose a
threat to the structural integrity of the dam, and a meeting was called with DEP Division of
Dam Safety personnel. Upon discussing the deficiencies found during the inspection, PFBC engineers
determined a drawdown of the lake was necessary to protect the downstream population. The slow
drawdown allowed the engineering staff to closely monitor the spillway for the potential areas
of seepage. The drawdown stopped at a level of 10 feet below normal pool when the seepage stopped.
Colyer Lake will remain at that level unless further seepage is discovered or corrective measures
HYDRAULIC AND HYDROLOGICAL ANALYSIS
The dam/spillway was constructed in 1966 to the
regulatory standards of the time. Due to an increase in the standard Spillway Design Flood (SDF)
the dam/spillway are not up to current regulations. In developing the Emergency Action Plan (EAP)
for Colyer Lake Dam, a hydraulic analysis of the spillway showed that the dam could only pass/store
24% of the SDF. Furthermore, Colyer Lake Dam will overtop the embankment at a depth of 3.5 feet.
TO THE DAM/SPILLWAY
Current dam safety regulations require embankment overtopping protection in addition
to the repairs to address the spillway seepage issues. Any repair plan without embankment overtopping
protection will not be permitted. The most cost-effective solution to remediate the dam would be
to rebuild/update the existing spillway along with armoring the embankment with Roller Compacted
Concrete (RCC). The Rebuilt spillway will correct the seepage problems and the RCC armoring will
allow the entire embankment to act as an emergency spillway during such a SDF event.
cost of this project is approximately $5.9 million. The Commission does not currently
have funding available or allocated for completing the repairs. If the Commission
secures the necessary funding it will take approximately two (2) years for design and permitting
and an additional two (2) years for construction. The PFBC anticipates the repairs will be functional
for 50 years.
PFBC DAM FUNDING NEEDS
Colyer Lake is one of five (5) PFBC lakes drawn down in recent
years to address dam safety concerns. The Commission continues to work to secure funding
for repairs on each of the dams. The Commission remains optimistic that a funding source outside
of the day-to-day operating revenues in the fish and boat funds will be found and will be available
for the substantial infrastructure improvement needs for the Commission has. The total need for dam
repairs alone is estimated at more than $83 million.