Headward Erosion Rates and Upland Connection Ages for Three Valley Floor Gullies in the North Carolina Piedmont

Keywords: Erosion, Sediment, Transport, Tree Rings, Roots, Soil, Gullies
Abstract Type: Poster Abstract

Abstract

Valley floor gullies are entrenched, narrow gullies that form in sediment fills/fans found in some low order valley floors of the Southern Piedmont. Sedimentologically disconnected from uplands, valley floor gullies may in time connect with upland gullies, allowing sediment and solutes related to changing upland land uses to travel more quickly into larger streams. The development of valley floor gullies can be dated using exposure ages of gully tree roots based on anatomical changes in root ring structure. We collected tree root cores and entire root sections, as well as gully cross-section measurements from three valley floor gullies in Guilford County, NC. The root growth rings were analyzed to determine the age of root erosional exposure and the approximate timing of gully headwall migration past roots. Gully headward erosion rates were calculated to be 3.08, 0.97, and 2.03 myr-1 for the three valley floor gullies studied. Extrapolation of root exposure age vs. distance curves predicts corresponding ages of connection with upland gullies of 25.0, 163.0 and 49.3 years. Sediment yields based on valley floor gully volumes alone are 111.3, 27.3, and 45.8 Mg km-2yr-1 respectively for the three gullies studied. These values are greater than published estimates of background yields in forests, but less than peak sediment yields of historical agriculture reported in the literature.