Leaser Lake is a 117-acre Commonwealth-owned impoundment located near Allentown in Lynn Township, Lehigh County, Pennsylvania. A dam located on Jacksonville Branch of the Ontelaunee Creek, a tributary of Maiden Creek, creates Leaser Lake. The impoundment is very popular with outdoor recreation enthusiasts in southeast Pennsylvania.

The PFBC leases the public use areas around the lake to Lehigh County and has done so since 1970. Lehigh County maintains park facilities and is responsible for maintenance of the areas used by lake visitors. The PFBC is responsible for the dam.

DAM AND APPURTENANCES

The Leaser Lake Dam consists of an earth embankment approximately 430 feet long by 53 feet high and a top of dam is 24 feet wide. 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 61-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 entering into the intake chamber of the control tower through the upstream portion of the outlet conduit 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.

Downstream from the dam, Sinking Creek generally flows east, meandering for approximately 4 miles, and joins Maiden Creek in the village of Kempton. It is estimated that failure of the dam would pose a serious public safety threat. Approximately 900 residents and 291 homes would be inundated if a dam failure were to occur.

DRAWDOWN PROCEDURE

The dam has a history of seepage problems dating back to the initial filling. Concern about the quantity of seepage discharge and the possible undermining or erosion of foundation materials beneath the concrete chute spillway on the right abutment led to the lake being drawn down in the summer of 1999 (July-Sept.).

The PFBC is responsible for dam inspection and other requirements associated with maintaining the dam. In 2000, the Commission contracted for a dam assessment with Schnabel Engineering at a cost of approximately $95,000. The assessment included videotaping the existing embankment drains. The videotapes show sediment and drainage aggregate in the pipes. This is an indication of piping and erosion within the embankment.

Leaser Lake was drawn down 21 feet to enable the dam to withstand a 100-year storm event (required by regulations) without activating the emergency spillway. Today the pool size is approximately 40 acres and 24 feet deep versus the normal pool of 117 acres and 45 feet deep.

HYDRAULIC AND HYDROLOGICAL ANALYSIS

The dam/spillway was constructed in 1970 at 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 Leaser Lake Dam, a hydraulic analysis showed that the dam/spillway could only pass/store 59% of the SDF.

REPAIRS TO THE DAM/SPILLWAY

The engineering assessment indicates the repairs/upgrades must address the embankment seepage issues as well as the inadequate spillway issue. The dam embankment may require a grout curtain to repair the embankment leakage. Further investigation is needed to determine the necessity of a grout curtain. The total estimated cost of the capital project is $3.7 to $5.3 million (depending on the necessity for a grout curtain). Once the Commission secures the necessary funding it will taken approximately two (2) years for design/permitting and an additional two (2) years for construction. The PFBC anticipates the repairs will be functional for 50 years.

PFBC DAM FUNDING NEEDS

Leaser 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 the Commission has. The total need for dam repairs alone is estimated at more than $83 million.

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