Lake Thoreau Dam dam
Lake Thoreau Dam
Lake Thoreau Dam, also known as Upper South Lake, is a private-owned structure located in Fairfax, Virginia. Managed by the Department of Conservation and Recreation, this dam serves multiple purposes including flood risk reduction and recreation. Standing at a height of 56 feet with a length of 850 feet, it holds a storage capacity of 1406 acre-feet and covers a surface area of 40 acres. The dam is situated on the TR-Snakeden Branch and is regulated by the state with regular inspections to ensure its structural integrity.
With a high hazard potential and a satisfactory condition assessment as of February 2021, Lake Thoreau Dam plays a vital role in water resource management in the region. Despite being a private-owned structure, it is subject to state jurisdiction, permitting, inspection, and enforcement to maintain safety standards. The dam's emergency action plan is up to date, reflecting its commitment to preparedness in case of any unforeseen events. Located within the Baltimore District, the dam is a key feature in the local landscape, providing both recreational opportunities and essential flood protection for the surrounding area.
For water resource and climate enthusiasts, Lake Thoreau Dam offers a fascinating insight into the intersection of human infrastructure and natural ecosystems. Its design as an earth dam reflects a balance between functionality and environmental considerations, with a focus on both flood risk reduction and recreation. As a significant feature in the region, the dam's maintenance and operation are crucial for ensuring the safety and well-being of the local community. With its strategic location and state-regulated status, Lake Thoreau Dam stands as a testament to the importance of sustainable water resource management in the face of changing climate patterns.
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.
- 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.
- 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.
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, environmental 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.
Plan around the weather
Same NOAA / yr.no feed Snoflo's iOS app uses. Watch the precipitation column on the meteogram -- rain on the basin upstream typically lifts inflow 24-72 hours later.
Next 5 days, hour by hour
Temperature line with weather symbols on top, snow + rain accumulation as columns, humidity as a dotted line.
5-day forecast table
Every 3 hours, broken out across temperature, snow, rain, humidity, and wind. Each cell is colour-coded relative to the column min/max.
| Time | Condition | Temp (°F) | Snow (in) | Rain (in) | Humidity (%) | Wind (mps) | Wind dir |
|---|---|---|---|---|---|---|---|
| Loading detailed forecast… | |||||||
15-day temperature & precipitation
Daily temperatures, snow, and rain projected over the next two weeks.
Nearby streamflow gauges
USGS streamgauges around Lake Thoreau Dam -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Difficult Run Near Great Falls | 12 cfs | → |
| Broad Run Near Leesburg | 21 cfs | → |
| Long Branch Near Annandale | 0 cfs | → |
| Accotink Creek Near Annandale | 3 cfs | → |
| Potomac River Near Wash | 2,300 cfs | → |
| Seneca Creek At Dawsonville | 40 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Lake Thoreau Dam.
Boat launches
- Potomac Hills Street Fairfax County
- Rileys Lock Road Darnestown
- Ashburn Village Boulevard 20585, Lansdowne
- Edwards Ferry Road Montgomery County
- Wayne F Anderson Bikeway Alexandria
- Gravelly Point Boat Ramp
Campgrounds
- Lake Fairfax
- Marsden Tract Group Campsite
- Marsden Tract Campground
- Swains Lock Hiker-Biker Campsite
- Horsepen Branch
- Horsepen Branch Campsite
Fishing spots
- Washington Aqueduct
- Gillam Branch (Historical)
- Dalecarlia Reservoir
- Davis Branch (Historical)
- Maddox Branch
- Georgetown Reservoir
Paddle runs
- Bixler Bridge On State Route 675 To Karo Landing, Approximately 6 Miles South Of Town Of Front Royal
- State Route 675 At Edinburg, Va To State Highway 55 Southeast Of Strasburg, Va
- Headwaters Adjacent To Fdt 573 To State Route 622 Bridge
- Segment C--Nf Boundary To Confluence With North Fork Shenandoah River
- Segment B--State Route 730 Bridge To Nf Boundary
Track Lake Thoreau Dam in the Snoflo app
Save this dam as a favorite and get the local NOAA / yr.no forecast plus regional flow context wherever you are.
About Lake Thoreau Dam
Where does the data for Lake Thoreau Dam come from?
Structural and regulatory data come from the U.S. Army Corps of Engineers' National Inventory of Dams (NID). Weather forecast comes from NOAA / yr.no -- the same feed Snoflo's iOS app uses.
How often is the report updated?
NID structural data refreshes annually as the Corps publishes updated assessments. The weather forecast refreshes throughout the day.
What does the High hazard rating mean?
The Corps of Engineers' hazard potential classification grades probable consequences if the dam fails: High = probable loss of human life; Significant = no probable loss of human life but possible economic loss / environmental damage; Low = no probable loss of human life, only minor economic / environmental losses. See the Dam Data Reference card above for the full definitions.
What's "% of normal"?
The current storage value compared to the historical average storage on this calendar day. 100% = right on average; values above 100% mean above-normal storage (wet year); values below mean below-normal (dry year or drought).
Can I get alerts when storage crosses a threshold?
Yes -- alerts are managed in the Snoflo iOS app. Favorite this dam, set a threshold, and you'll get a push the moment conditions cross.
Other water bodies near here
Snoflo-tracked reservoirs and dams within driving distance of Lake Thoreau Dam.