Erosion Rates. Two axial surveys this year (March and June). Intensive survey planned for September 2005. VIMS 2004 data delivered. Much analysis remains. We are missing the 2004 Gust chamber results. Field work to date: Six seasonal axial surveys completed so far (out of 8 total).
Six seasonal axial surveys completed so far (out of 8 total).
13 stations, spaced from 12 km downstream of Rt 301 bridge to 10 km downstream of fall line. Observations include CTD, LISST, ADCP, OBS, TSS, absorbance/transmittance and VSF (volume scattering sensor).
2. August 2004 intensive study of upper Potomac completed (2nd planned for September 2005 further downstream near ETM). Observations include erosion experiments using Gust microcosm and VIMS annular flume, CTD mooring, Owen tube particle settling velocity, pumped sample laboratory grain size analysis, and along- and across-channel tidal cycle survey with CTD, LISST, ADCP, TSS & OBS. Also bed sampling at 13 axial stations for profiles of grain size, water content, Eh, % organic, and micro-chirp acoustic response.
Example along-channel water column data (Sandford group). Each plot shows salinity in 1 ppt contour intervals starting at 1 ppt. Data from CTD, OBS and LISST as a function of distance downstream from fall line. Region of 2004 and 2005 intensives shown on upper left plot.
LISST D50 (microns)
OBS Concentration (mg/liter)
Example particle size vs. concentration data (Friedrichs group). LISST shows at least two distinct particle populations: larger particles form a significant component of the suspended particle population at lower concentrations, whereas relatively smaller particles dominate at higher concentrations. Data from upper Potomac, August 26, 2004.
Sediment & Detrital Absorption
Depends on latitude, date, time of day
Depends on optical depth in the water column, and angular distribution of scattering
µ0= cosine of in-water zenith angle
a = absorption coefficient
b = scattering coefficient