Reading Area Water Authority
Lake Ontelaunee Dam, built mid-1920, has stood for over 90 years supplying drinking water to the City of Reading and surrounding areas. Pennsylvania Code (Chapter 105) now requires most dam owners to upgrade to new flood standards or breach their dams.
SSM’s team of professional engineers (hydrologist, geotechnical and civil), geologists (geophysicist, structural and hydrogeological), surveyors, GIS technicians and construction specialists completed a Concept Design to fortify Lake Ontelaunee Dam to safely comply with design criteria for a Probable Maximum Flood (PMF). The Concept Design was prepared for the Reading Area Water Authority in response to the PADEP – Division of Dam Safety’s requirements to bring Lake Ontelaunee Dam into compliance.
The dam consists of a 544 foot uncontrolled ogee crest concrete spillway and a 2,890 foot earthen embankment section. Under the PMF criteria, the earthen embankment will perform as an emergency spillway. To fortify the embankment and prevent it from eroding away during a PMF event, its upstream face needs to be thickened and its downstream slope requires hardening with Roller Compacted Concrete (RCC). However, prior to RCC installation, subsurface soils need to be stabilized to support the proposed overtopping engineering controls and subjected PMF forces. In addition, the team addressed complications created by State Highway 73 which traverses the top of the dam with its guiderail system that raised the PMF.
In developing the most cost effective solution for the Authority, SSM evaluated several technologies and their subsequent costs or risks in addition to RCC including: articulated concrete block, 1,000 linear feet of culvert beneath Route 73, dam height reduction, a parapet wall option and a hardened artificial turf like system. Stability analysis, geotechnical investigations, environmental assessments, underwater dam inspections, and geophysical and hydrogeological studies were included with the Design Concept.