Lake Tanglewood Dam Reservoir Report
Last Updated: January 2, 2026
Lake Tanglewood Dam, located in Henry, Illinois, stands as a critical structure for water resource management and climate resilience in the area.
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Summary
Built in 1969 by the engineering firm HNTB, this privately owned earth dam serves primarily for recreational purposes, providing a serene lake environment for residents and visitors alike. With a height of 40 feet and a length of 375 feet, the dam boasts a storage capacity of 161 acre-feet, making it a significant asset for water storage and flood control in the region.
Managed by the Illinois Department of Natural Resources, Lake Tanglewood Dam is subject to regular inspections and enforcement measures to ensure its safety and functionality. The dam's spillway, with a width of 75 feet, helps regulate water flow and prevent potential hazards, earning the structure a high hazard potential rating. Despite its moderate risk assessment, the dam's condition assessment is currently listed as "Not Available," highlighting the need for ongoing monitoring and maintenance to safeguard its long-term integrity.
As climate change poses increasing challenges to water resources and infrastructure, Lake Tanglewood Dam stands as a vital component of the region's resilience strategy. With its strategic location on Trib Sandy Creek and its significant storage capacity, this earth dam plays a crucial role in water management and flood mitigation efforts, underscoring the importance of proactive maintenance and risk management to ensure its continued effectiveness in the face of evolving environmental pressures.
Year Completed |
1969 |
Dam Length |
375 |
Dam Height |
40 |
River Or Stream |
TRIB SANDY CREEK |
Primary Dam Type |
Earth |
Nid Storage |
161 |
Outlet Gates |
Uncontrolled |
Hazard Potential |
High |
Foundations |
Unlisted/Unknown |
Nid Height |
40 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Lake Tanglewood Dam