Mosaic Csa F4a Reservoir Report
Nearby: Mosaic Csa F4b Mosaic Csa F5
Last Updated: December 5, 2025
Mosaic Csa F4a is a privately owned Earth dam located in Fort Lonesome, Hillsborough County, Florida.
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Summary
Built in 2003, this dam serves the primary purpose of storing tailings from mining activities. With a hydraulic height of 55 feet and a structural height of 62 feet, it stands at an impressive 60 feet tall and stretches over 21,180 feet in length. The dam has a maximum storage capacity of 37,500 acre-feet and covers a surface area of 650 acres, with a drainage area of 1.02 square miles.
The dam's spillway, which is controlled, has a width of 128 feet to manage discharge during peak flow events. Mosaic Csa F4a has been deemed to have a significant hazard potential, with a very high risk assessment rating of 1. Although the condition assessment is listed as "Not Rated," the dam is subject to state regulation, permitting, inspection, and enforcement by the Florida Department of Environmental Protection. Despite not being federally owned, the dam operates under state jurisdiction and follows state guidelines for emergency action plans and risk management measures.
For water resource and climate enthusiasts, Mosaic Csa F4a represents a critical infrastructure in managing water resources in the region. With its large storage capacity and controlled spillway, the dam plays a crucial role in safeguarding against potential flooding events and ensuring the safe storage of tailings. As a privately owned structure with state oversight, Mosaic Csa F4a highlights the intersection of private and public interests in ensuring the safety and sustainability of water management systems in the face of evolving climate conditions.
Year Completed |
2003 |
Dam Length |
21180 |
Dam Height |
60 |
River Or Stream |
LONG BRANCH |
Primary Dam Type |
Earth |
Surface Area |
650 |
Hydraulic Height |
55 |
Drainage Area |
1.02 |
Nid Storage |
37500 |
Structural Height |
62 |
Hazard Potential |
Significant |
Nid Height |
62 |
Seasonal Comparison
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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.
Mosaic Csa F4a