How Fast Does the River Run Dry? An exploration of a novel watershed metric for use in drought planning

Meghan Mussehl


This project explored the development of a new watershed metric to be used by water managers for low flow management and drought mitigation on run-of-river systems. Dubbed the dry down time, this metric is a measure of how quickly a watershed transitions from wet to dry based on a set of thresholds. Thresholds are based on percentiles (p) of a historic daily flow values from USGS stream gages. 51 unregulated basins the Northeast U.S. with historic records exceeding 20 years were assessed using different threshold combinations. Mean dry down times were 19 to 27 days while the 5th percentile was 14 to17 days, indicating that watersheds transition from wet to dry conditions on the scale of just a few weeks, providing water managers with decision making timescale. Through OLS regression it was determined that possible watershed characteristics influencing dry down time included precipitation, base flow conditions and regional geology.