Hempstead Lake Dam

About this Project

LKB has been retained by New York State Parks Office of Parks, Recreation & Historic Preservation to provide design services for work at Hempstead Lake State Park. The Hempstead Lake Dam project requires an Engineering Assessment of the current conditions at the historic Hempstead Lake Dam, and the smaller upstream Northwest Pond Dam, to determine how to bring these structures into compliance with current NYSDEC dam safety regulations. The Engineering Assessment Report includes hydraulic and hydrological analyses of the 12.85 square mile Mill River Watershed that empties into Hempstead Lake and surrounding ponds, ultimately emptying into Mill River. We designed improvements to the 145 year old gatehouse outlet structure to bring it closer into compliance with state and federal regulations. Construction of these improvements is currently underway.

As part of the Engineering Assessment, the hydrological analysis was performed using the HEC-HMS program to determine peak flows through the watershed for various design storms. Hydraulic analysis was performed using WMS and the HEC-RAS program to determine the resultant water surface elevations and limits of flooding. The hydraulic analysis included models of existing and alternative proposed conditions. A safety inspection of the dam was performed to assess the existing conditions. LKB also developed an Inspection and Maintenance Plan for the dam, and an Emergency Action Plan as part of the Engineering Assessment Report. LKB’s environmental group also performed a Hydrologic Investigation of Hempstead Lake to assess if the lake level could be temporarily lowered prior to major storm events to provide emergency storage capacity for stormwater runoff.

In addition to the gatehouse improvements, LKB worked with other consultants to develop flood mitigation and resiliency plans throughout Hempstead Lake State Park as part of GOSR’s Living With The Bay (LWTB) project. This work includes replacement of the NW Pond Dam, open channel improvements, installation of pedestrian bridges, and wetland restoration and mitigation work. This phase of construction is due to be completed by August 2023.

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