Introduction

The Ravine Lake dam Analysis performed by PS&S for the Somerset Lake and Game Club is an example of how an evaluation of an existing structure underscores effective safety management while improving the aesthetics and usability of a County asset.

THE OPPORTUNITY

The Ravine Lake dam, built in 1898-1899, is 276 feet long and is constructed of masonry materials. The dam is 35 feet high from the stream bed to the top of the dam and is classified as a NJDEP Class I, High Hazard with a total spillway capacity of 3,140 CFS and a 26.2 square mile contributory drainage area.

THE CHALLENGE

The Ravine Lake dam’s structural integrity was questioned in a US Army Corps of Engineers Phase I inspection report. The factor of safety associated with the dam structure during a maximum flood event needed to be confirmed as well as the risks associated with a catastrophic failure of the dam.

THE PS&S SOLUTION

PS&S performed a complete analysis in accordance with NJDEP Dam Safety Division guidelines. The analysis included evaluation of the general structural integrity and hydraulic adequacy, structural stability, structural deterioration (if any), recommended remedial action, and performance of a dam break analysis. PS&S also performed a seismic and geotechnical evaluation to address the concerns raised in the US Army Corps of Engineers Phase I inspection report.

The conclusion was that under unusual loading conditions the factor of safety was well within prescribed limits. The inundation stages for a 12 mile stretch of the channel downstream of the Ravine Lake Dam were calculated under the conditions of a catastrophic failure in the event of the probable maximum flood (PMF) event as well as for a sunny-day failure using the National Weather Service’s DAMBRK model.