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.

DAM AND APPURTENANCES

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.

DRAWDOWN PROCEDURE

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:

1. Weep hole closest to the weir (small amount).
2. Weep hole and lateral crack in channel floor above the stilling basin (moderate amount).
3. Area where channel floor meets left training wall directly in line with lateral crack in the channel floor (moderate amount).
4. 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 2, 22°C; 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 water.

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.

It was 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 are taken.

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.

REPAIRS 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.

The estimated 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.

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