Urban Stream Bank Composition and Network Sedimentation Patterns

Authors: Dan Royall*, UNC-Greensboro
Topics: Geomorphology, Soils
Keywords: fluvial, sediment, urban, regolith
Session Type: Virtual Paper
Day: 4/8/2021
Start / End Time: 8:00 AM / 9:15 AM
Room: Virtual 3
Presentation File: No File Uploaded

The evolving sedimentary characteristics of urban stream networks are poorly understood relative to those of channel erosion and enlargement caused by magnified runoff. Changes in pre- and post-urban watershed sedimentation influence stream bank composition, which in turn can influence the stability of channels, the quality of in-stream ecosystems, and the input, movement, and storage of potentially harmful substances in streams. In this case study, stream bank sediment exposures along 7 kilometers of urban North Buffalo Creek in the North Carolina Piedmont, were described and categorized to define spatial patterns in bank material composition, complexity, and diversity. The stratigraphic composition of urban stream banks was found to be highly heterogeneous, with representation from pre-Euro-American settlement deposits (original regolith, primarily alluvial), agricultural sediments, urban age sediments, mill dam (lacustrine) sediments, and human transported materials (HTM; construction subsoil and dredge). Associations between drainage area and changes in valley width, and historical sediment stratum thickness that have been observed in more rural environments are not clearly evident. Numerous factors act to obscure or modify spatial associations or patterns in this urban stream network, including 1.) the local presence of thick millpond sediment deposits whose incision leaves bank tops high and inaccessible to floodwaters, 2.) local bed aggradation zones, 3.) the variable presence of HTM which locally replaces or caps alluvium, and 4.) longitudinal fragmentation produced by the presence of road culverts that create bottlenecks across some floodplains.

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