SUSPENDED SEDIMENT YIELD RESPONSE TO URBANIZATION IN THE U.S. SOUTHERN PIEDMONT

The majority of ongoing and future population growth will be in cities, and this is likely to have significant consequences for Earth surface processes within urbanizing watersheds. Fluvial suspended sediment transport is expected to go through a transient phase of accelerated sediment flux due to increased erosion from land-clearing and channel readjustment. However, this theorized connection is poorly quantified across watersheds due to the combined complexity of natural and anthropogenic processes. In an attempt to empirically evaluate such a response, historical sediment flux records were reconstructed for 52 watersheds within the U.S. Piedmont across a gradient of population densities. As a rapidly urbanizing region, the U.S. Southern Piedmont is particularly representative of this ongoing phenomenon of accelerating urbanization. Additionally, selecting sites within a consistent ecoregion helps to control for extensive variations in vegetation, geomorphology, and historical land use. Sediment flux was calculated using annually varied nonlinear sediment rating curves based on samples reported for streamgages in the USGS National Water Information System. Human features within basins (e.g. annualized illumination and population) were extracted to polygons of the upstream delineated watershed for each of the 52 streamgages. Due to temporal constraints within the datasets, observations are limited to the most recent decades. Initial results show a trend of increasing sediment yield across watersheds as indices of urbanization increase. Nevertheless, the same increasing trend is not as apparent within sites. It is suspected that this discrepancy is either due to unforeseen spatial variation or due to the limited timeframe being examined. To test this and verify whether the effect of urbanization on sediment yield is measurable within a given watershed, other methods that examine a longer timeframe (e.g. sedimentary proxy records through geochronology) must be employed in future studies.