Marshall Millpond Dam Reservoir Report

Last Updated: December 5, 2025

Marshall Millpond Dam, located in Sussex, Delaware, serves as a critical structure along the Herring Branch river.


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Summary

This dam, primarily owned by the State, was designed by DelDOT and an unknown entity. With a height of 13.5 feet and a length of 440 feet, the dam's primary purpose is for recreation, providing a maximum storage capacity of 169 acre-feet. The dam's spillway type is controlled, with a spillway width of 15 feet, ensuring proper water flow management.

The dam, with a significant hazard potential, was last inspected in May 2020 and assessed to be in fair condition. It has a very high risk rating, indicating the importance of appropriate risk management measures. The emergency action plan (EAP) for the dam was last revised in March 2016, and it meets established guidelines. Despite its age and potential hazards, Marshall Millpond Dam continues to provide recreational opportunities while requiring regular inspections and maintenance to ensure public safety and water resource sustainability.

Overall, Marshall Millpond Dam stands as a historic gravity dam with a buttress core type, significantly contributing to the region's water management and recreational activities. With its controlled spillway and fair condition, the dam remains a vital structure regulated by the Delaware Department of Natural Resources and Environmental Control (DNREC). As a focal point for water resource and climate enthusiasts, the dam presents both challenges and opportunities for effective risk management and sustainable water resource utilization in the region.

Years Modified

1924 - Hydraulic

Dam Length

440

Dam Height

13.5

River Or Stream

HERRING BRANCH

Primary Dam Type

Gravity

Surface Area

11.8

Drainage Area

7

Nid Storage

169

Outlet Gates

Other Controlled - 1

Hazard Potential

Significant

Foundations

Unlisted/Unknown

Nid Height

14
       
Seasonal Comparison

Weather Forecast

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.