Sediment budgets for two mountainous basins affected by a catastrophic storm: Blue Ridge Mountains, Virginia

• Published in: Geomorphology (Amsterdam, Netherlands) Netherlands), 2001-03, Vol.37 (1), p.135-148
• Main Authors: Springer, Gregory S, Dowdy, Heather Shroyer, Eaton, L.Scott
• Format: Article
• Language: English
• Subjects: Bgi / Prodig; Blue Ridge mountains; Catchments. Hydrological cycle; debris flow; denudation; Earth sciences; Earth, ocean, space; Exact sciences and technology; Freshwater; Hydrometeorology; Marine and continental quaternary; Physical geography; sediment budget; Surficial geology; USA, Virginia, Madison Cty
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/S0169-555X(00)00066-0

On June 27th, 1995, a catastrophic storm generated thousands of slope failures in mountainous portions of Madison County, VA, USA. Within a 129-km 2 area, 16-h rainfall totals reached 775 mm. Using direct field measurements, sediment budgets were constructed for two drainage basins impacted by the event, Teal and Jenkins Hollows. Lengthwise distributions of channel erosion and deposition were examined by taking measurements within incremental 30-m-long channel segments. Comparison of sediment budgets reveals that the two hollows responded very differently to the storm event. These differences are largely due to differences in soil types, failure volumes, and natures of the resulting flows. Within Jenkins Hollow, the kinetic energy of a 4200-m 3, liquefied slope failure scoured the channel of virtually all sediment and vegetation and resulted in a sediment retention rate of 5%. In contrast, slope failures that reached the central channel of Teal Hollow failed to generate a large flow track and erosion features are coupled with deposition features. The sediment retention rate in Teal Hollow was 27%. Single storm denudation rates for the basins exceed the regional 1 ka area-normalized denudation rate of 25.5 mm ka −1; denudation was 27 mm in Teal Hollow and >38 mm in Jenkins Hollow. Following catastrophic events, considerable attention has been paid to those channels dramatically modified by debris flows. The high denudation rate for Teal Hollow, attributed to liquefaction of fine-grained soils easily transported as washload, suggests that extremely high denudation rates are possible even in low-order mountainous basins that appear relatively undisturbed by catastrophic storms.