Faun Lake Dam Engineering Assessment
Comprehensive Assessment Supports Hazard Reduction for Faun Lake Dam
LaBella completed a comprehensive Engineering Assessment Report for the Faun Lake Dam, currently classified by the New York State Department of Environmental Conservation (NYSDEC) as a Class B (Intermediate Hazard) structure, in Johnsonburg, New York. In accordance with state regulations, the assessment included:
- Detailed safety inspection
- Hazard classification review
- Spillway and structural stability analyses
- Reservoir drawdown evaluation
- Emergency Action Plan review
Investigation & Assessment
Our team began with a thorough desktop evaluation of available historical data, followed by an on-site inspection of the dam and downstream conditions. To reassess the dam’s hazard classification, LaBella performed a cascading dam breach analysis for both Faun Lake Dam and the upstream Beaver Dam. Hydrologic modeling was completed using HEC-HMS to estimate breach outflows, while a one-dimensional unsteady HEC-RAS model was developed to evaluate downstream flood impacts.
Reclassification
Results of the analysis indicated that a potential failure scenario would not result in loss of life or significant impacts to residential structures or critical infrastructure. Based on these findings, LaBella recommended pursuing a reclassification to Class A (Low Hazard) which, if approved by NYSDEC, would eliminate the requirement for future Engineering Assessment Reports.
Modifications
The assessment also confirmed that the auxiliary spillway has adequate capacity to safely convey the service spillway design flood, and that the dam meets required structural stability criteria. However, the low-level outlet was found to be undersized and unable to meet current drawdown requirements. To improve performance, targeted modifications to the drop inlet structure were recommended. No deficiencies were identified in the Emergency Action Plan or Inspection and Maintenance Plan.
LaBella delivered a signed and sealed report documenting all analyses, findings, and recommendations, along with a formal Hazard Classification Change Request submitted to NYSDEC for review.
