Potomac River Dam #4 dam
Potomac River Dam #4
Potomac River Dam #4, located in Williamsport, Maryland, is a historic structure completed in 1869 by the Chesapeake & Ohio Canal Co. This gravity dam stands at a height of 20 feet and stretches 715 feet in length, creating a reservoir with a normal storage capacity of 7300 acre-feet. The dam serves a primary purpose of hydroelectric power generation and is owned and regulated by the National Park Service.
With a significant hazard potential and a state-regulated status, Potomac River Dam #4 is subject to regular inspections by the Bureau of Reclamation. The dam's maximum discharge capacity is 1,000,000 cubic feet per second, and it is responsible for managing a drainage area of 5,900 square miles. Despite its age, the dam's condition assessment is currently listed as "Not Available," highlighting the importance of ongoing monitoring and maintenance to ensure its structural integrity and safety.
For water resource and climate enthusiasts, Potomac River Dam #4 offers a glimpse into the intersection of history, engineering, and environmental stewardship. As a key component of the Potomac River's hydroelectric infrastructure, this gravity dam plays a crucial role in balancing water storage and release for both power generation and environmental conservation. Its location within the picturesque surroundings of Washington County, Maryland, makes it a focal point for those interested in sustainable water management practices and the preservation of natural resources in the face of changing climate conditions.
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 Potomac River Dam #4 -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Marsh Run At Grimes | 13 cfs | → |
| Potomac River At Shepherdstown | 1,400 cfs | → |
| Antietam Creek Near Sharpsburg | 154 cfs | → |
| Opequon Creek Near Martinsburg | 113 cfs | → |
| Tuscarora Creek Above Martinsburg | 4 cfs | → |
| Back Creek Near Jones Springs | 22 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Potomac River Dam #4.
Boat launches
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Campgrounds
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Fishing spots
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River runs
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About Potomac River Dam #4
Where does the data for Potomac River Dam #4 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 Significant 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 below 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.
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.