Glen Elyn Upper Dam Reservoir Report

Last Updated: December 8, 2025

The Glen Elyn Upper Dam, located in Fallston, Maryland, is a private recreational dam built in 1975 with a primary purpose of providing recreational opportunities.


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Summary

Standing at a height of 19.2 feet, this earth dam holds a maximum storage capacity of 23 acre-feet, with a normal storage level of 3.5 acre-feet. The dam spans 230 feet in length and has a spillway width of 14 feet, allowing for a maximum discharge of 516 cubic feet per second.

Despite its fair condition assessment in 2021, the Glen Elyn Upper Dam poses a significant hazard potential, with a risk assessment rating of moderate. This dam is state-regulated and inspected regularly by Maryland's Dam Safety agency, ensuring that enforcement and permitting requirements are met. The last inspection in November 2020 revealed the dam's structural modifications in 2009, enhancing its resilience and safety measures.

With its picturesque location along the Little Gunpowder Falls, the Glen Elyn Upper Dam serves as a vital recreational spot for water resource and climate enthusiasts alike. While its fair condition may raise some concerns, the dam's ongoing maintenance and regulatory oversight ensure the safety of the surrounding community and the preservation of this natural resource for future generations to enjoy.

Years Modified

2009 - Structural

Year Completed

1975

Dam Length

230

Dam Height

19.2

River Or Stream

Little Gunpower Falls-TR

Primary Dam Type

Earth

Surface Area

1.3

Hydraulic Height

17

Drainage Area

0.17

Nid Storage

23

Structural Height

18

Outlet Gates

Needle - 0

Hazard Potential

Significant

Foundations

Soil

Nid Height

19
       
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.