7-26 Using a hydrologic model to analyze Tropical Storm Helene streamflow scenarios under alternative antecedent conditions

Session: Undergraduate Research, Part I (Posters)

Presenting Author:

Authors:

Abstract:

Tropical Storm Helene produced extensive geomorphic and hydrologic impacts across western North Carolina, causing widespread historic flooding. In Cullowhee, NC—west of the highest impact areas, about ten inches of rain fell over a three-day period. Most of Western North Carolina was in a drought prior to Helene; in Cullowhee, pre-storm conditions reflected a multi-year drought with groundwater levels at a 15-year low. In this work, we investigate how alternative antecedent hydrologic regimes could have altered the stormwater flood response.

This study uses field-based observations recorded during Hurricane Helene from the Cullowhee Creek Watershed, including Gribble Gap Creek, Long Branch Creek, and Cullowhee Creek to calibrate a hydrologic model, that is used to explore how alternative antecedent conditions could have altered Helene-driven streamflow magnitudes. Observational data are part of the Western Carolina Hydrological Research Station (WCHRS) and include precipitation, wind, relative humidity, soil moisture, stream discharge (velocity-area and flume measurements), and groundwater levels from ~40 wells. Discharge data from three flumes and two rating curve sites were used with the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) to simulate the streamflow responses. We systematically vary antecedent groundwater, soil moisture, and precipitation inputs to generate alternative scenarios and quantify changes in peak discharge and runoff timing for Long Branch and Cullowhee Creek. Preliminary results indicate that wetter antecedent conditions amplify peak flows and shorten lag times, suggesting that the drought state prior to Helene likely helped mitigate flood magnitudes. These simulations provide insight into how antecedent hydrologic state modulates flood hazards and can inform watershed management and flood-risk planning under variable climate and land-use conditions.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.