Geology topics

L.J. McKee

Publications and source records attributed to L.J. McKee.

3 recordsLinked to original sources

USGS2013

Comparison of sediment supply to San Francisco Bay from watersheds draining the Bay Area and the Central Valley of California

Quantifying suspended sediment loads is important for managing the world's estuaries in the context of navigation, pollutant transport, wetland restoration, and coastal erosion. To address these needs, a comprehensive analysis was completed on sediment supply to San Francisco Bay from fluvial sources. Suspended sediment, optical backscatter, velocity data near the head of the estuary, and discharge data obtained from the output of a water balance model were used to generate continuous suspended sediment concentration records and compute loads to the Bay from the large Central Valley watershed. Sediment loads from small tributary watersheds around the Bay were determined using 235 station-years of suspended sediment data from 38 watershed locations, regression analysis, and simple modeling. Over 16 years, net annual suspended sediment load to the head of the estuary from its 154,000 km 2 Central Valley watershed varied from 0.13 to 2.58 (mean = 0.89) million metric t of suspended sediment, or an average yield of 11 metric t/km 2 /yr. Small tributaries, totaling 8145 km 2 , in the nine-county Bay Area discharged between 0.081 and 4.27 (mean = 1.39) million metric t with a mean yield of 212 metric t/km 2 /yr. The results indicate that the hundreds of urbanized and tectonically active tributaries adjacent to the Bay, which together account for just 5% of the total watershed area draining to the Bay and provide just 7% of the annual average fluvial flow, supply 61% of the suspended sediment. The small tributary loads are more variable (53-fold between years compared to 21-fold for the inland Central Valley rivers) and dominated fluvial sediment supply to the Bay during 10 out of 16 yr. If San Francisco Bay is typical of other estuaries in active tectonic or climatically variable coastal regimes, managers responsible for water quality, dredging and reusing sediment accumulating in shipping channels, or restoring wetlands in the world's estuaries may need to more carefully account for proximal small urbanized watersheds that may dominate sediment supply.

California↗

USGS2009

Mercury concentrations and loads in a large river system tributary to San Francisco Bay, California, USA

In order to estimate total mercury (Hg T ) loads entering San Francisco Bay, USA, via the Sacramento-San Joaquin River system, unfiltered water samples were collected between January 2002 and January 2006 during high flow events and analyzed for Hg T . Unfiltered Hg T concentrations ranged from 3.2 to 75 ng/L and showed a strong correlation (r 2 = 0.8, p < 0.001, n = 78) to suspended sediment concentrations (SSC). During infrequent large floods, Hg T concentrations relative to SSC were approximately twice as high as observed during smaller floods. This difference indicates the transport of more Hg-contaminated particles during high discharge events. Daily Hg T loads in the Sacramento-San Joaquin River at Mallard Island ranged from below the limit of detection to 35 kg. Annual Hg T loads varied from 61 ?? 22 kg (n = 5) in water year (WY) 2002 to 470 ?? 170 kg (n = 25) in WY 2006. The data collected will assist in understanding the long-term recovery of San Francisco Bay from Hg contamination and in implementing the Hg total maximum daily load, the long-term cleanup plan for Hg in the Bay. ?? 2009 SETAC.

Environmental Toxicology and Chemistry↗

USGS2006

Estimates of suspended sediment entering San Francisco Bay from the Sacramento and San Joaquin Delta, San Francisco Bay, California

This study demonstrates the use of suspended-sediment concentration (SSC) data collected at Mallard Island as a means of determining suspended-sediment load entering San Francisco Bay from the Sacramento and San Joaquin River watersheds. Optical backscatter (OBS) data were collected every 15 min during water years (WYs) 1995-2003 and converted to SSC. Daily fluvial advective sediment load was estimated by combining estimated Delta outflow with daily averaged SSC. On days when no data were available, SSC was estimated using linear interpolation. A model was developed to estimate the landward dispersive load using velocity and SSC data collected during WYs 1994 and 1996. The advective and dispersive loads were summed to estimate the total load. Annual suspended-sediment load at Mallard Island averaged 1.2??0.4 Mt (million metric tonnes). Given that the average water discharge for the 1995-2003 period was greater than the long -term average discharge, it seems likely that the average suspended-sediment load may be less than 1.2??0.4 Mt. Average landward dispersive load was 0.24 Mt/yr, 20% of the total. On average during the wet season, 88% of the annual suspended-sediment load was discharged through the Delta and 43% occurred during the wettest 30-day period. The January 1997 flood transported 1.2 Mt of suspended sediment or about 11% of the total 9-year load (10.9 Mt). Previous estimates of sediment load at Mallard Island are about a factor of 3 greater because they lacked data downstream from riverine gages and sediment load has decreased. Decreasing suspended-sediment loads may increase erosion in the Bay, help to cause remobilization of buried contaminants, and reduce the supply of sediment for restoration projects. ?? 2005 Elsevier B.V. All rights reserved.

Journal of Hydrology↗