Estimated flood frequency and corresponding water-surface elevations at the confluence of the Potomac and Shenandoah rivers, Harpers Ferry, West Virginia

The Harpers Ferry National Historical Park is located at the confluence of the Shenandoah and Potomac Rivers in Harpers Ferry, West Virginia and has historically been affected by flooding from both rivers. Because the drainage areas of both rivers are large and drain geographically separate regions, either river may contribute individually to flooding, or the combination of flows may be the source of flooding. Previous flood-frequency analyses have been conducted at U.S. Geological Survey streamflow-gaging stations upstream on the Potomac River at Shepherdstown, West Virginia and on the Shenandoah River at Millville, West Virginia.; and downstream on the Potomac River at Point of Rocks, Maryland. A flood-frequency analysis for Harpers Ferry can be expected to fall within the streamflows and recurrence intervals predicted at the surrounding stations. The prediction of corresponding water-surface elevations at Harpers Ferry is difficult, however, because of differences in rainfall distribution across the two regions and the timing of the peaks on both rivers.