The View from Minnie’s Island–Measuring Water Levels on the Potomac
If you kayak, fish, hike the Billy Goat Trail, or just love being in nature, you likely check the Little Falls gauge before heading out. The US Geological Survey (USGS) gauge located at the Little Falls Dam is the most useful monitor for local Potomac River levels.
On May 15 this year, the river crested at 11.7 feet on the gauge, driven by a watershed-wide rain event that produced significant flooding in Western Maryland. As a point of reference, USGS classifies five feet as the “action level,” 10 feet as a minor flood, 12 feet as a moderate flood, and 14 feet as a major flood. The last time the river was higher was in June 2018, when the river crested at 12.4 feet.
While there are undeniably negative aspects of floods, they are a critical part of what makes the Potomac Gorge so unique and biologically rich. The Potomac is a rare large East Coast river that does not have major dams or reservoirs. This allows floods to scour riverbanks, which disrupts the growth of trees and shrubs, and creates new habitats for wildflowers.
The impact of the flood on Minnie’s Island has been positive overall. The flooding cleared away multiple fallen trees that were blocking the canoe landing and trails. Unfortunately, much of this wood is likely accumulating downstream in places like Fletchers Cove. It will be interesting to see if new native plants will be found on Minnie’s in the scoured areas.
I’m surprised to be writing about flooding, as I had planned on writing on the drought conditions that have persisted in our area over the past couple of years. As recently as early May this year, the river was at 3.2 feet, and for much of last summer the river was below 2.7 feet. The impact of droughts is especially visible in the scour plain portions of Minnie’s–areas covered by water when the river is between three and five feet. Last summer, there were significantly fewer flowering perennials in the scour plain compared to 2024.
It’s not clear how this rain will change the drought conditions that have impacted much of the Potomac watershed this year. As of May 19, the precipitation at Washington National Airport is one half-inch above the historical average, while BWI and Dulles are still well below historical averages.
The Little Falls Gauge can be monitored at: https://waterdata.usgs.gov/monitoring-location/01646500/#dataTypeId=continuous-00065-0&period=P7D. Another very useful link is the National Weather Service 10-day river level probability at https://www.weather.gov/erh/mmefs_marfc?id=BRKM2&model=NAEFS.
By Joe Saliunas, Certified Maryland Master Naturalist, Vice-Chair of Minnie’s Island Community Conservancy
Contributing Writer