HR: 15:20h
AN: H33J-07    [Abstracts]
TI: Restoration in Urban Streams Impacted by Legacy Sediments
AU: * Bain, D J
EM: dbain@pitt.edu
AF: University of Pittsburgh, Department of Geology and Planetary Science/200 SRCC 4107 O'Hara St., Pittsburgh, PA 15260,
AU: Smith, S M
EM: SSmith@dnr.state.md.us
AF: Maryland Department of Natural Resources, 580 Taylor Ave E2 Tawes State Office Building, Annapolis, MD 21401,
AU: Colosimo, M F
EM: ColosimoM@Washington.IJC.org
AF: International Joint Commission, United States Section, 1250 23rd Street N.W., Suite 100, Washington, DC 20440,
AB: Degraded urban streams are ideal candidates for restoration; as these restorations can provide multiple benefits ranging from increased accessible green space to enhanced nutrient processing. However, connections between the channel and floodplain are poorly understood in urban systems. In particular, urban valleys impacted by legacy sediment are challenging to rehabilitate. For example, the excavation of legacy sediment is expensive and can require the destruction of established riparian vegetation. The hardening of stream banks slows fluvial dynamics and may inhibit nutrient processing occurring in self-adjusting alluvial stream reaches. Further complications arise from the hydrologic changes that accompany urbanization, which can create unexpected hydrodynamic conditions divergent from intended channel and floodplain design. Here, we analyze data from Eastern U.S. Piedmont streams to characterize the role of floodplains in reach and watershed-scale sediment flux. A series of collocated historical cross-section resurveys and radio-isotopic reconstruction of over-bank sedimentation rates are compared. The data indicate that floodplain storage rates in some urban areas are comparable to or larger than rates of sediment remobilization from channel widening. This observation suggests urban floodplains with thick legacy deposits can remain a sediment sink even after channel entrenchment. The contemporary storage capacity has fundamental consequences for stream restoration designs, including the potential for rapid refilling of excavated bottoms and unsatisfactory reductions in watershed sediment yields.
DE: 1815 Erosion
DE: 1820 Floodplain dynamics
DE: 1825 Geomorphology: fluvial (1625)
DE: 1834 Human impacts
DE: 1861 Sedimentation (4863)
SC: Hydrology [H]
MN: 2007 Fall Meeting