Delta sediment measurements to support numerical modeling of sediment-turbidity

Scott Wright, David Schoellhamer, Tara Morgan, Dan Whealdon-Haught, Matt Marineau

USGS Sacramento

CWEMF annual meeting 17 April 2012, Sacramento CA

U.S. Department of the Interior U.S. Geological Survey Sediment-turbidity modeling in the Delta

Delta sediment modeling is useful for a variety of reasons: - fish habitat (e.g. Delta smelt) - tidal wetlands, restoration, sea-level rise - navigation - levee integrity

Robust models require data for set- up, calibration, and testing

The Delta is large and very complex. Several data gaps exist with respect to development and testing of numerical sediment models

We began a project to fill these data gaps in December 2010, funded by the Federal Task Force on the Delta Sediment model data requirements

Hydrodynamics:

- bathymetry and levee topography - flows and velocities at upstream model boundaries - water levels at downstream boundary and interior - bed roughness (e.g. Manning’s n, drag coefficients)

Sediment:

- Sediment loads at upstream model boundaries - Sediment concentrations at interior points - Size distributions of sediment on the bed - Sediment erosion/entrainment rates - Size distributions and settling velocities of suspended sediment Sediment-turbidity monitoring

17 turbidity and sediment flux stations, co-located with flow gages

Network is designed to monitor incoming sediment loads and track movement of turbidity and sediment throughout the Delta Sediment-turbidity monitoring Sac River @ Freeport

Miner Slough

Georgiana Slough

Cache Slough

Mokelumne River

Sac River @ Rio Vista

Old River Sediment-turbidity monitoring

Turbidity is converted to sediment concentration using periodic SSC measurements and site/instrument- specific calibrations

Combined with flow data, this yields sediment flux at the stations and allows for computation of sediment budgets for various Delta regions

Tara Morgan will be talking in more detail about these data during IEP on Thursday at 3:30 pm Size distributions of sediment on the bed

Seasonal sampling, before and after the winter wet season, at 30 sites (flow gage locations)

3 samples collected at each site, channel center and both channel margins

Document regions of deposition and erosion (by changes in bed sediment texture) Size distributions of sediment on the bed

Delta channels are primarily sand bedded

Channel margins are finer in general than channel center

Central/south Delta and Cache Slough are generally finer than northern Delta

Small channels are generally very coarse, but not always. Ongoing work to explain this phenomenon Bed sediment erodibility/entrainment

Erosion Microcosm System

Gomex corer Subsample

Core is collected and subjected to known rates of shear stress, erosion is measured

Flow path Bed sediment erodibility/entrainment

Recent example from Mokelumne River 1 System has been deployed on Mokelumne River, Middle 0.5 River, Little Potato Slough, Franks Tract, Grizzly Bay, and south SF Bay Shear stress, Pa stress, Shear 0 0 2000 4000 6000 8000 10000 12000 Additional sampling will 200 occur at Delta sediment sites and San Pablo Bay

100

Turbidity, NTU Turbidity, 0 0 2000 4000 6000 8000 10000 12000 Elapsed time, sec Suspended sediment size distributions and settling velocity – floc camera

Samples are collected and video is recorded in situ (on the boat) of individual flocs settling

Edge detection used to measure size, sequential images used to measure settling velocity Suspended size and settling velocity – floc camera

System has been deployed at all of the Delta sediment stations at several locations in SF Bay

5 overlaid images Suspended size and settling velocity – floc camera Near-bed hydro- and sediment dynamics

Instrument package rotated between Delta sediment flux sites to measure in situ near-bed processes, such as velocity, turbulence, turbidity, and suspended- sediment concentration and size distribution

Data in this talk are from the at Stockton

LISST-100X: volume Delta instrument package concentration and particle size

ADV: 3D velocity and turbulence

Multi-parameter sonde: depth, turbidity, temperature, conductivity Bed roughness-flow resistance

ADV measures near-bed velocity and turbulence Bed roughness-flow resistance

Flow resistance computed from velocity and shear stress

San Joaquin River at Stockton Size distributions of suspended sediment

Measured in situ with LISST-100X

Primarily flocculated particles – samples are ~75% silt/clay by mass and ~40% silt/clay by volume (in situ)

Floc density ~ 1.5 g/cm3 Size distributions of suspended sediment

Median particle size is inversely related to shear stress

Coarsest sizes are also inversely related to shear stress, while medium sizes are directly proportional

Indicates cycles of floc formation and break up Size distributions of suspended sediment

High shear breaks up flocs, decreasing concentration of >100 um particles and increasing concentration of <100 um particles

Large flocs reform around slack tide

10-100 um range also includes coarse silt and sand primary particles Summary

- We are compiling an extensive dataset on sediment transport processes in the Delta; the project is ongoing

- Several observations will be of interest to ongoing modeling efforts, such as the manner in which sediment disperses through the Delta during floods, and suspended- sediment particle and floc dynamics

- Several research questions remain, such as the link between bed sediment size, cohesiveness, and erodibility; and the distribution of suspended sediment at channel junctions

- This dataset will allow robust testing of numerical models and improved confidence in their predictive capabilities. Data are available (provisionally) by contacting us; several articles are in preparation Questions?

Scott Wright David Schoellhamer [email protected] [email protected]

916-278-3024 916-278-3126