G103 Control Structure Reservoir Report

Last Updated: December 5, 2025

The G103 Control Structure, also known as the Lake Rosalie Control Structure, is a critical flood risk reduction infrastructure located in Polk, Florida.


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Summary

Managed by the South Florida Water Management District (SFWMD), this state-regulated structure plays a vital role in managing water levels in the Zipperer Canal to prevent flooding and protect surrounding areas. With a dam height of 15 feet and a hydraulic height of 9 feet, the G103 Control Structure has a structural height of 24 feet and was completed in 1965.

Covering a drainage area of 42 square miles, the G103 Control Structure has a maximum storage capacity of 49,000 acre-feet and a normal storage level of 35,100 acre-feet, serving a surface area of 5,400 acres. Equipped with a controlled spillway with a width of 50 feet, this structure has a maximum discharge capacity of 734 cubic feet per second. Despite its low hazard potential, the risk assessment for the G103 Control Structure indicates a very high risk level, emphasizing the importance of its maintenance and monitoring for optimal performance in mitigating flood risks in the region.

The G103 Control Structure stands as a testament to Florida's commitment to water resource management and climate resilience. With its roller-compacted concrete core type and soil foundation, this structure exemplifies the state's efforts to prioritize flood risk reduction and ensure the safety of its residents. As climate change continues to impact water resources, the G103 Control Structure remains a crucial asset in safeguarding the surrounding communities and enhancing the overall resilience of the region against potential flooding events.

Year Completed

1965

Dam Length

70

Dam Height

15

River Or Stream

ZIPPERER CANAL

Primary Dam Type

Other

Surface Area

5400

Hydraulic Height

9

Drainage Area

42

Nid Storage

49000

Structural Height

24

Hazard Potential

Low

Foundations

Soil

Nid Height

24
       
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.