Dam Name: | Lower Occoquan |
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NID ID: | VA15305 |
Longitude: | -77.28333 |
Latitude: | 38.6895 |
Map Section: | N/A |
County: | PRINCE WILLIAM, FAIRFAX |
River: | OCCOQUAN RIVER |
State: | VA |
Nearest City: | OCCOQUAN |
Distance: | 1.00 miles |
Owner Name: | FAIRFAX COUNTY WATER AUTHORITY |
Owner Type: | Local Government |
Dam Designer: | AMERICAN WATER WORKS SERVICE COMPANY |
Private Dam? | No |
Core: | Homogeneous Dam (Position) Concrete (Type) Known (Certainty) |
Foundation: | RK |
Purposes: | Water Supply |
Year Completed: | 1950 |
Dam Length: | 436 feet |
Dam Height: | 23 feet |
Structural Height: | 20 feet |
Hydraulic Height: | 21 feet |
Maximum Discharge: | 15800 cu ft/sec |
Maximum Storage: | 310 acre-feet |
Normal Storage: | 310 acre-feet |
Surface Area: | 19 acres |
Drainage Area: | 596 square miles |
Hazard Potential: | High |
Emergency Action Plan? | Yes |
Inspection Date: | 2012-02-07 |
Inspection Frequency: | 1 |
State Regulated Dam? | No |
State Regulating Agency: | DCR |
Spillway Type: | Uncontrolled |
Spillway Width: | 390 feet |
Volume of Dam: | 212100 cubic yards |
Federal Regulatory Agency: | |
Federal Inspection Agency: | |
Source Agency: |
Dam Safety For Boats
A large amount of water can be released from a dam without any warning at any time and by any means. For example, when the demand for electricity is high, the turbines at a dam may be turned on automatically, resulting in a significant increase in the downstream flow of water in only a matter of seconds.
If there's a need to release water through the sluiceways (outlets at the base of the dam), this operation can also create a great swell of discharged water downstream.
During flood operations, any or all spillway gates across the width of a dam can be opened to release upstream flood water that needs to pass to the next downstream reservoir. Upstream or downstream, even the most experienced boater with the strongest motor is no match for this strong flow of water plunging over a spillway of a dam. Even if you're boating far downstream of a spilling dam, recirculating current can pull a powerful boat upstream toward plunging water that could shred any boat.
Some dams equipped with navigation locks create turbulent water as well. When vessels pass through, strong flow is released near the exhaust ports of the wing wall of the lock.
Warning Systems At Dams
To warn reservoir users of potential danger, warning devices are installed at many dams:
- Horns: Horns are sounded before water is released from the powerhouses, sluiceway or spillways. When you hear these horns, leave the areas upstream and downstream of the dam immediately.
- Strobe Lights: Strobe lights are activated before the hydro plant begins generating electricity at the powerhouse or releases water through the spillway or sluiceway. When you see these strobe lights flash, leave the areas upstream and downstream of the dam immediately.
- Warning Signs: Signs direct visitors to stay clear of hazardous areas and warn of rapidly rising water and sudden spillway and turbine water surges. Take them seriously—obey all warnings!
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