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Megan A. Lionberger

Publications and source records attributed to Megan A. Lionberger.

7 recordsLinked to original sources
USGS2009

Summary of Suspended-Sediment Concentration Data, San Francisco Bay, California, Water Year 2006

Suspended-sediment concentration data were collected by the U.S. Geological Survey in San Francisco Bay during water-year 2006 (October 1, 2005-September 30, 2006). Optical sensors and water samples were used to monitor suspended-sediment concentration at two sites in Suisun Bay, one site in San Pablo Bay, two sites in Central San Francisco Bay, and one site in South San Francisco Bay. Sensors were positioned at two depths at most sites to help define the vertical variability of suspended sediments. Water samples were collected periodically and analyzed for concentrations of suspended sediment. The results of the analyses were used to calibrate the output of the optical sensors so that a record of suspended-sediment concentrations could be derived. This report presents the data-collection methods used and summarizes, in graphs, the suspended-sediment concentration data collected from October 2005 through September 2006. Calibration curves and plots of the processed data for each sensor also are presented.

Data Series↗
USGS2009

A Tidally Averaged Sediment-Transport Model for San Francisco Bay, California

A tidally averaged sediment-transport model of San Francisco Bay was incorporated into a tidally averaged salinity box model previously developed and calibrated using salinity, a conservative tracer (Uncles and Peterson, 1995; Knowles, 1996). The Bay is represented in the model by 50 segments composed of two layers: one representing the channel (>5-meter depth) and the other the shallows (0- to 5-meter depth). Calculations are made using a daily time step and simulations can be made on the decadal time scale. The sediment-transport model includes an erosion-deposition algorithm, a bed-sediment algorithm, and sediment boundary conditions. Erosion and deposition of bed sediments are calculated explicitly, and suspended sediment is transported by implicitly solving the advection-dispersion equation. The bed-sediment model simulates the increase in bed strength with depth, owing to consolidation of fine sediments that make up San Francisco Bay mud. The model is calibrated to either net sedimentation calculated from bathymetric-change data or measured suspended-sediment concentration. Specified boundary conditions are the tributary fluxes of suspended sediment and suspended-sediment concentration in the Pacific Ocean. Results of model calibration and validation show that the model simulates the trends in suspended-sediment concentration associated with tidal fluctuations, residual velocity, and wind stress well, although the spring neap tidal suspended-sediment concentration variability was consistently underestimated. Model validation also showed poor simulation of seasonal sediment pulses from the Sacramento-San Joaquin River Delta at Point San Pablo because the pulses enter the Bay over only a few days and the fate of the pulses is determined by intra-tidal deposition and resuspension that are not included in this tidally averaged model. The model was calibrated to net-basin sedimentation to calculate budgets of sediment and sediment-associated contaminants. While simulated net sedimentation in the four basins that comprise San Francisco Bay was correct, the simulations incorrectly eroded shallows while channels deposited because model surface-layer boxes span both shallows and channels, and neglect lateral variability of suspended-sediment concentration. Validation with recent (1983-2005) net sedimentation in South San Francisco Bay was poor, perhaps owing to poorly quantified sediment supply, and to invasive species that altered erosion and deposition processes. This demonstrates that deterministically predicting future sedimentation is difficult in this or any estuary for which boundary conditions are not stationary. The model would best be used as a tool for developing past and present sediment budgets, and for creating scenarios of future sedimentation that are compared to one another rather than considered a deterministic prediction.

Scientific Investigations Report↗
USGS2007

Summary of Suspended-Sediment Concentration Data, San Francisco Bay, California, Water Year 2005

Suspended-sediment concentration data were collected by the U.S. Geological Survey in San Francisco Bay during water year 2005 (October 1, 2004-September 30, 2005). Optical sensors and water samples were used to monitor suspended-sediment concentration at two sites in Suisun Bay, three sites in San Pablo Bay, two sites in Central San Francisco Bay, and three sites in South San Francisco Bay. Sensors were positioned at two depths at most sites. Water samples were collected periodically and analyzed for concentrations of suspended sediment. The results of the analyses were used to calibrate the output of the optical sensors so that a record of suspended-sediment concentrations could be derived. This report presents the data-collection methods used and summarizes, in graphs, the suspended-sediment concentration data collected from October 2004 through September 2005. Calibration curves and plots of the processed data for each sensor also are presented.

Data Series↗
USGS2007

PONDCALC: A tool to estimate discharge from the Alviso Salt Ponds, California

Former commercial salt ponds in Alviso, California, now are operated by the U.S. Fish and Wildlife Service (USFWS) to provide habitat for birds. The USFWS has modified the operation of the ponds to prevent exceedingly high salinity. Ponds that were formerly hydraulically isolated from South San Francisco Bay and adjacent sloughs now are managed as flow-through ponds, and some are allowed to discharge to the Bay and sloughs. This discharge is allowed under a permit issued by the Regional Water Quality Control Board. As a requirement of the permit, the USFWS must estimate the amount of discharge from each discharge pond for the period May through November of each year. To facilitate the accurate estimation of pond discharge, a calculation methodology (hereafter referred to as 'calculator' or PONDCALC) for the discharging Alviso ponds has been developed as a Microsoft Excel file and is presented in this report. The presence of flap gates on one end of the discharge culverts, which allow only outflow from a pond, complicates the hydraulic analysis of flow through the culverts. The equation typically used for culvert flow contains an energy loss coefficient that had to be determined empirically using measured water discharge and head at the discharge structure of one of the ponds. A standard weir-flow equation is included in PONDCALC for discharge calculation in the ponds having weir box structures in addition to culverts. The resulting methodology is applicable only to the five Alviso ponds (A2W, A3W, A7, A14, and A16) that discharge to South San Francisco Bay or adjacent sloughs under the management practices for 2005.

California↗
USGS2007

Box Model of a Series of Salt Ponds, as Applied to the Alviso Salt Pond Complex, South San Francisco Bay, California

This report documents the development and application of a box model to simulate water level, salinity, and temperature of the Alviso Salt Pond Complex in South San Francisco Bay. These ponds were purchased for restoration in 2003 and currently are managed by the U.S. Fish and Wildlife Service to maintain existing wildlife habitat and prevent a build up of salt during the development of a long-term restoration plan. The model was developed for the purpose of aiding pond managers during the current interim management period to achieve these goals. A previously developed box model of a salt pond, SPOOM, which calculates daily pond volume and salinity, was reconfigured to simulate multiple connected ponds and a temperature subroutine was added. The updated model simulates rainfall, evaporation, water flowing between the ponds and the adjacent tidal slough network, and water flowing from one pond to the next by gravity and pumps. Theoretical and measured relations between discharge and corresponding differences in water level are used to simulate most flows between ponds and between ponds and sloughs. The principle of conservation of mass is used to calculate daily pond volume and salinity. The model configuration includes management actions specified in the Interim Stewardship Plan for the ponds. The temperature subroutine calculates hourly net heat transfer to or from a pond resulting in a rise or drop in pond temperature and daily average, minimum, and maximum pond temperatures are recorded. Simulated temperature was compared with hourly measured data from pond 3 of the Napa?Sonoma Salt Pond Complex and monthly measured data from pond A14 of the Alviso Salt-Pond Complex. Comparison showed good agreement of measured and simulated pond temperature on the daily and monthly time scales.

Scientific Investigations Report↗
USGS2005

Bay sediment budget: Sediment accounting 101

Comparison of a budget developed for 1955-1990 with a budget developed for 1995- 2002 showed decreasing sediment inflow and increased amounts leaving the Bay to upland disposal and sand mining, resulting in an increased rate of erosion of sediment from the Bay floor Finding a way to shift disposal from the Ocean back to the Bay could provide sediment for restoration projects and decrease dredging costs Increased erosion of the Bay is mobilizing legacy contaminants from the sediment bed Restoration projects could increase erosion and mobilization of legacy contaminants Sand mining, ignored in previous budgets, removes almost twice as much sediment from the Bay as dredging

California↗