Baltimore Ecosystem Study Institute of Ecosystem Studies

2017 BES Annual Meeting Presentation and Poster Abstracts

Analysis of suspended sediment concentrations and yields across spatial and temporal scales in nested urban watersheds
Kemper, John T.
Co-Authors: John T. Kemper, Andrew J. Miller, Claire Welty

Abstract: Near real-time turbidity and discharge data have been collected continuously for more than four years at five stream gages representing three nested watershed scales (1-2 sq km, 5-6 sq km, 14 sq km) in the highly impervious Dead Run watershed. Sediment yields have been calculated for 60+ different storms across four years. Yields show significant spatial variation, both at equivalent sub-watershed scales and from headwaters to mouth. At equivalent watershed areas, yields are higher at DR5, a headwater catchment with older development and virtually no stormwater management, than at DR2, a headwater catchment with more recent development and more extensive stormwater management. However, at the next larger scale, this trend is reversed: yields are lower at DR4, downstream of DR5, than at DR3, downstream of DR2. Moving from the headwaters downstream, yields at DR2 are consistently lower than at DR3, while yields at DR5 are generally higher than DR4. Both trends suggest spatial variation in the dominant sediment sources within each subwatershed. Additionally, C-Q hysteresis curves display consistent counterclockwise behavior at the DR4 station, in contrast to the consistent clockwise behavior displayed at the DR3 station. Again, this further suggests variation in dominant sediment sources (perhaps distal vs local, respectively). We observe consistent seasonal trends in the relative magnitudes of sediment yield for different subwatersheds (e.g. DR3>DR4 in summer, DR5>DR2 in spring). We also observe significant year-to-year variation in sediment yield at the headwater and intermediate scales, whereas yields at the full watershed scale are largely consistent. This observation is perhaps indicative of internal storage and remobilization within the channel system.