Marquette Lake Dam at Ft. Indiantown Gap

Federal Government, National Guard Bureau, Lebanon County, PA

The Marquette Lake/Dam is located in Lebanon County Pennsylvania on property owned by the Commonwealth of Pennsylvania, Department of Veterans and Military Affairs. The dam (High Hazard) is part of the facilities leased to the Federal Government, National Guard Bureau and is located at the western side of the Fort Indiantown Gap. The dam is approximately 1180 feet long and 27 feet high

The Marquette Lake Drainage Basin consists of 5.8 square miles of land, primarily in the Training Corridor between Blue Mountain and Second Mountain. The pond surface covers approximately 15 acres with a storage capacity of approximately 253 acre‐ft of water. When full, the pond will hold approximately 95 million gallons of water.

As a result of Hurricane Ivan in September 2004, the PADEP performed a hydraulic analysis on the Marquette Lake Drainage Basin and concluded that the amount of runoff from the Probable Maximum Flood design storm would be 28,810 cfs, or approximately 3 times the capacity of the existing spillway. Subsequently, the flood water would overtop the entire 1180‐ft length of the dam. Additionally, the spillway channel has become unstable due to excessive flows.

The goal of the project is to design the most cost effective renovations to the Dam, Spillway, and downstream channel including effective protection system that will armor the dam breast and spillway during an overtopping condition. The design shall be completed to meet the requirements of Pennsylvania’s PADEP Chapter 105 Dam safety regulations and withstand the Probable Maximum Flood (PMF).

The overtopping protection is needed to prevent the failure of the dam embankment up to the PMF event. The downstream channel does not have to be enlarged to convey the PMF. It is recommended by DEP that the downstream channel be upgraded to convey the maximum spillway flow of 10,572 cfs. This maximum spillway capacity may be reevaluated based on actual field survey of existing conditions. For overtopping flows, the downstream conditions should be analyzed to assure that spillway channel improvements will not cause a hydraulic jump to occur relative to the overtopping protection. The level of tailwater and the location of a hydraulic jump should also be considered for a few flood magnitudes that are greater than the spillway capacity, but less that the PMF (for example, the 0.5PMF and .75PMF) events.