Cohesive sediment erosion and the Vectrino II. Peter J. Rusello DeFrees Hydraulics Laboratory Cornell University (also with NortekUSA)

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1 Cohesive sediment erosion and the Vectrino II Peter J. Rusello DeFrees Hydraulics Laboratory Cornell University (also with NortekUSA)

3 Images taken from NYC DEP 2009 Watershed Water Quality Annual Report

4 Turbidity and cohesive sediments The primary components contributing to turbidity in the NYC Reservoir system are particles in the 1-10 μm range. Peng, et al. ( 2009) Light-scattering features of turbidity-causing particles in interconnected reservoir basins and a connecting stream. Water Research 43. This particle size range is where clays and silts reside. At this size, particle behavior is controlled by inter-particle forces (i.e. colloidal particles). Aerosols have similar behavior. In many lake beds, heavier particles settle out in tributaries or near the tributary mouth. The lake bed is composed primarily of cohesive sediments. These sediments are extremely complex. TU-Delft has ~30 parameters used to describe the mineralogical and physical state of a sediment. This neglects biology entirely.

5 Resuspension Mechanisms Runoff Events Wave induced Resuspension Schoharie Reservoir during drawdown. Internal Boundary Resuspension

6 Bed stress estimates from the Reynolds Shear Stress u w 6 x ρu 2 ρu w ρv w 4 τ(pa) Day Number (00:00:00 on Oct 1, 2007=1.00)

7 Laboratory measurements of cohesive sediment erosion Research Flume during erosion testing using PIV

8 ASETS Flume

9 Sediment test chamber 87 cm x 23.5 cm core surface

10 Low speed testing. Re-suspension, but not necessarily from the sediment core. There was no detectable change in the sediment water interface.

11 Instantaneous velocity field with local mean velocity removed.

12 At a certain point optical access is obstructed requiring a different measurement system for velocity and sediment water interface detection.

13 The Nortek Vectrino II For erosion studies it provides simultaneous velocity and distance to boundary measurements. The velocity profiles can be used in several ways to develop estimates of bed stress and characterize the turbulence. There is a lot more we can do with this data

14 Initial validation experiments Examining performance in a turbulent boundary layer

15 Vectrino II testing over a fine grained sand in the sediment test chamber.

16 Distance measurement accuracy A computer controlled stage was used to position the Vectrino II at known distances from a start position. RMS residual error is 0.33 mm

17 Comparison in TFPBL to PIV (old calibration)

18 Comparison in TFPBL to PIV (old calibration)

19 Comparison in TFPBL to PIV (old calibration)

20 Boundary Layer 1-D profiles (new calibration)

21 Wall coordinate profile (new calibration)

22 We can treat each measurement cell as an individual point measurement

23 Velocity Imaging U mm/s W mm/s

24 Turbulence Imaging u mm/s w mm/s u w mm 2 /s 2

25 Results

26 Velocity Imaging U mm/s W mm/s

27 Conclusions Mean bed stresses observed in lakes are not sufficient to re-suspend significant material. Laboratory measurements show minimal erosion under conditions typically found in the lacustrine bottom boundary layer. The Vectrino II is really just flat out cool. The data from the Vectrino II is fairly unique. Extracting all of the information from it is a work in progress and will need new analysis methods (parallels with flow field analysis such as PIV) and techniques.

Overview of fluvial and geotechnical processes for TMDL assessment

Overview of fluvial and geotechnical processes for TMDL assessment Christian F Lenhart, Assistant Prof, MSU Research Assoc., U of M Biosystems Engineering Fluvial processes in a glaciated landscape Martin