Flood Control

Origins of Blue Marsh Lake

In 1955, prior to the construction of dams along Delaware River tributaries, floods in eastern Pennsylvania claimed 90 lives and over $100 million in property damage. A subsequent Federal study of the Delaware River Basin included the Blue Marsh Lake project among its recommendations.

Blue Marsh Lake was authorized by the 87th Congress through the Flood Control Act of 1962 as a multi-purpose project, including flood control, water quality, water supply, and recreation.

Tropical Storm Agnes brought torrential rains to eastern Pennsylvania in June 1972. Berks County experienced heavy flooding and millions of dollars in property damage. The chances of another flood of that magnitude have been vastly reduced since completion of the Blue Marsh dam.

The Corps designed the reservoir to hold up to 11 billion gallons above the normal winter elevation, providing protection up to a 100-year flood. Reading, Pottstown, Norristown and parts of Philadelphia, all sites of prior flooding, directly benefit from the presence of Blue Marsh Lake.

The earthen dam was erected across Tulpehocken Creek, which drains a 175-square-mile area upstream. From its source near Lebanon, Pennsylvania, it flows eastward nearly 24 miles to the Schuylkill River at Reading.

This is a helpful way to understand how the Blue Marsh dam and reservoir operate:

• The "FAUCETS" are the creeks flowing into the lake, along with rain and snow.
• The "DRAINS" are gates controlled by the dam operator to regulate flow out of the lake. There are two near the bottom of the lake for flood control, and one about mid-level in the tower for water quality. Normally the flood control gates stay partly open, releasing water into the Tulpehocken Creek. Under flooding conditions they are lowered to hold back water from downstream areas, then raised to restore lake elevation once the flooding hazard subsides.
• The "OVERFLOW GUTTER" is the spillway, a chute-like channel located along the lake’s edge about a quarter-mile south of the dam and at a lower elevation. If impounding of water for flood protection exceeds the lake’s capacity, the overflow will go through the spillway and downstream without overtopping the dam.
• The "WATER LEVEL" is the normal seasonal elevation, somewhat lower in winter than in summer to allow for snow melt and early spring rainfall.

Water Supply

Located a half-mile downstream of the dam, the Authority draws water from the Tulpehocken Creek for water supply to local communities.

The flow of the Schuylkill River is augmented by water released from the lake. Communities along the Schuylkill downstream of Blue Marsh draw water for drinking and industrial uses.

During drought conditions the salt line in the Delaware River starts creeping up the Delaware River, threatening the Philadelphia region’s water supply.

Based on guidance from the Delaware River Basin Commission, the Dam Operator responds with "augmentation releases" into the Tulpehocken Creek. The increased flow ultimately reaches the Delaware River and helps push the salt line back to the bay. These releases also improve water quality and provide additional water for communities.

Water Quality

The quality of water is tested by both the District engineers and an independent firm.

• Philadelphia District personnel test Blue Marsh Lake water bi-weekly between May and November.
• An independent contractor also conducts periodic water quality tests.
• These tests check water temperature, dissolved oxygen, pH level and coliform bacteria levels.

Tulpehocken Creek is home to a variety of aquatic life, including trout. The District has a longstanding agreement with the Pennsylvania Fish and Boat Commission to maintain the downstream creek water temperature at 68 degrees Fahrenheit or lower during the summer, as the trout prefer cooler water.

Using the control tower’s "selective withdrawal system," the Dam Operator achieves the desired temperature by mixing warmer and cooler releases from the water quality and flood control gates, respectively.

These releases usually start by the end of June, leading to a 100 percent release out of the flood control gates by August for maximum cooling.

The mix goes back to 100 percent release out of the water quality gate on Jan. 1, staying there until the cycle repeats itself.

Recreation

While Blue Marsh Lake was built primarily for flood control, recreation is the purpose for which it is best known and most enjoyed.

Well over a million visitors a year take advantage of one or more of these opportunities (click on a topic for more information):

• Trail system (hiking, biking, horseback riding)
• Hunting
• Wildlife viewing
• Picnicking
• Swimming
• Boating (no horsepower limit) with three launch ramps
• Fishing
• Winter activities