Exploring the hypothesis of a “flood-reset” of the sediment and nutrient delivery in some Eastern U.S. watersheds

Abstract:

Large floods have the potential to cause a “reset” of some of the processes that deliver sediment and nutrients from the watershed to a downstream receiving water body. Conceptually, the changes can lead to either increases in transport or decreases in transport. Decreased transport could be caused by the depletion of available sediment and nutrients that are highly mobile (i.e. shifting the channel to supply-limited conditions). The result would be that in the post-flood condition, weeks to years post-flood, the observed concentrations in the river would tend to be lower than what would have been expected based on pre-flood observations, for a given discharge condition and time of year. Conversely, the disturbance of the watershed, including the channel and riparian zone could serve to increase the supply of available sediment or nutrients through the creation of fresh surfaces of mobile material. These ideas are explored here for a set of large floods in eastern U.S. rivers that have extensive sediment and nutrient data spanning several years before and after the flood. They are approached using statistical concepts derived from Weighted Regressions on Time, Discharge, and Season (WRTDS). Understanding the potential for a “flood-reset” of watershed transport is important to the process of evaluating long-term water quality change associated with the implementation of point-source and non-point-source controls in a watershed.