Thorne Dam Reservoir Report

Last Updated: December 6, 2025

Thorne Dam, located in Wassaic, New York, along the Wassaic Creek, was completed in 1905 and stands at a height of 38 feet with a length of 227 feet.


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Summary

This masonry dam primarily serves as a recreational site, offering a storage capacity of 44 acre-feet and a surface area of 4 acres. The dam has a high hazard potential and is classified as fair in condition assessment, with the last inspection conducted in April 2019.

Managed by a private owner, Thorne Dam is regulated by the New York State Department of Environmental Conservation (NYS DEC) and has state jurisdiction, permitting, inspection, and enforcement in place. The dam features an uncontrolled spillway with a width of 147 feet and a maximum discharge capacity of 1790 cubic feet per second. Despite its moderate risk assessment level, the dam has not undergone any recent modifications or risk management measures as of the latest data update in March 2021. For water resource and climate enthusiasts, Thorne Dam presents both a historical and practical perspective on the management of water resources in the region.

Year Completed

1905

Dam Length

227

Dam Height

38

River Or Stream

WASSAIC CREEK

Primary Dam Type

Masonry

Surface Area

4

Drainage Area

21.3

Nid Storage

44

Hazard Potential

High

Nid Height

38
       
Seasonal Comparison

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Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.