Bank erosion and erosion processes from dendrogeomorphology in southern U.S. prairie streams

Abstract

Streambank erosion processes influence the amount of soil material contributed to rivers and sedimentation rates in receiving reservoirs. However, the amount of data on bank erosion rates is limited both in range and extent affecting planning for mitigation and watershed management. Dendrogeomorphology is used to determine the date of wood anatomy changes in annual growth increments of roots exposed by erosion of stream banks that when coupled with measurement of the distance of roots to the channel side can be used to calculate the bank retreat rate. Erosion rates derived from dendrogeomorphology are important because these provide erosion data over longer time scales (decades). Here, we use this method to quantify erosion for three different sized watersheds (4 to 3781 km2) located in the water‐scarce southern U.S. prairies that are heavily reliant on surface water and reservoir storage. From 49 roots from the two smaller drainages, erosion ranged from 1.5 to 25.4. For 19 roots collected from the larger subbasin erosion rates were larger ranging from 7.4 to 325.0 cm/years with the larger values and variance associated with two high‐flow events that occurred a year before sampling. We also found differences in straight and meandering portions of the streams where the distance to bank was strongly and positively correlated with the years since root exposure in straight sections. In contrast, meandering bends also showed a positive but low correlation for root exposure date and distance collected. We attribute this difference to erosional processes (i.e., scour and mass wasting) occurring at these channel locations. When compared with other erosion studies across the southern U.S. prairie, our values were similar in magnitude but with low correlation to drainage area indicating site specificity of erosion mechanisms, and watershed landcover influence for different drainages, despite being in the same ecological region.