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Delta Sediment Measurements to Support Numerical Modeling of Sediment-Turbidity

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Delta Sediment Measurements to Support Numerical Modeling of Sediment-Turbidity 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 distributary 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 San Joaquin River 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 Sacramento River 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.
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