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Project: Upper Shadow Lake Dam Classification & Design Storm Determination
Client: Shadow Lake Inc.
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GSE was retained by Shadow Lake Inc. to determine the Hazard Classification
and the Spillway Design Flood (“SDF”) of Upper Shadow Lake
Dam. This analysis was required by the NJDEP Bureau of Dam Safety in order
to classify the dam and to determine compliance requirements. The analysis
required GSE to perform an Incremental Damage Analyses (“IDA”).
Before performing any modeling, GSE undertook a bathymetric survey of
the lake bottom to allow for a much more accurate prediction of the discharged
lake water volume during a failure event allowing for a more accurate
hazard classification. The IDA consisted of breaching the dam in incremental
values of the Probable Maximum Flood (PMF) as well as the 100-year storm
and assessing the incremental downstream damage to determine the threat
to life and property. The results dictated the minimum allowable Hazard
Classification. The subject analysis determined the dam as a Class II,
Significant Hazard structure which required that GSE develop the Spillway
Design Flood (SDF) for the dam. The SDF is equal to the flood magnitude
that does not cause downstream incremental damage when comparing a failure
and non-failure event. Our analysis allowed the dam spillway to be sized
to convey the minimum allowable storm under Dam Safety Standards, N.J.A.C.
7:20 which saved the client hundreds of thousands of dollars in construction
costs.
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