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Bruce E. Jaffe

Publications and source records attributed to Bruce E. Jaffe.

82 records · Page 5Linked to original sources
USGS1998

Sedimentation and bathymetric change in San Pablo Bay: 1856-1983

A long-term perspective of erosion and deposition in San Francisco Bay is vital to understanding and managing wetland change, harbor and channel siltation, and other sediment-related phenomena such as particle and particle-associated substance (pollutants, trace metals, etc.) transport and deposition. A quantitative comparison of historical hydrographic surveys provides this perspective. This report presents results of such a comparison for San Pablo Bay, California. Six hydrographic surveys from 1856 to 1983 were analyzed to determine long-term changes in the sediment system of San Pablo Bay. Each survey was gridded using surface modeling software. Changes between survey periods were computed by differencing grids. Patterns and volumes of erosion and deposition in the Bay are derived from difference grids. More than 350 million cubic meters of sediment was deposited in San Pablo Bay from 1856 to 1983. This is equivalent to a Baywide accumulation rate of approximately 1 cm/yr. However, sediment deposition was not constant over time or throughout the Bay. Over two-thirds of that sediment was debris from hydraulic mining that accumulated from 1856 to 1887. During this period, deposition occurred in nearly the entire Bay. In contrast, from 1951 to 1983 much of the Bay changed from being depositional to erosional as sediment supply diminished and currents and waves continued to remove sediment from the Bay. The decrease in sediment supply is likely the result of upstream flood-control and water-distribution projects that have reduced peak flows, which are responsible for the greatest sediment transport. One consequence of the change in sedimentation was a loss of about half of the tidal flat areas from the late 1800's to the 1980's. Change in sedimentation must also have affected flow in the Bay, areas where polluted sediments were deposited, exchange of sediment between the nearshore and wetlands, and wave energy reaching the shoreline that was available to erode wetlands. Further work is needed. Studies of historical wetland change and the relationship between change and man-made and natural influences would be valuable for developing sound wetland management plans. Additionally, extending the historical hydrographic and wetland change analyses eastward into Suisun Bay will improve the understanding of the North Bay sediment system.

California↗
USGS1997

Impact of an extreme event on the sediment budget: Hurricane Andrew in the Louisiana barrier islands

This paper examines the influence of Hurricane Andrew on the sediment budget of an 80-kilometer section of the Louisiana barrier islands west of the modern Mississippi delta. Because long-term bathymetric change has been extensively studied in this area, excellent baseline data are available for evaluating the impact of Hurricane Andrew. Results show that despite the high intensity of the storm and a storm track optimally positioned to impact the study area, the storm did not have an overwhelming influence on the sediment budget when compared to the changes occurring over the previous 50 years. For the Louisiana barrier islands, a 50-year record appears to be adequate for averaging the long-term contributions of both major and minor storm events to the sediment budget.

Louisiana↗
USGS1995

How much velocity information is necessary to predict sediment suspension in the surf zone?

Instantaneous horizontal water velocity, or velocity to a power, does not contain enough information to predict suspension in the surf zone. Unlike steady uniform flow, more one than one velocity is necessary to parameterize pick-up and mixing of sediment into the water column. Using a velocity history improves predictions of suspension by more carefully specifying flow conditions (including accelerations and changes in accelerations) responsible for suspension. Suspension in the future is better predicted than suspension at the same instant as velocity measurements. Incorporating such a lag between velocity and concentration improved predictions, with optimum lag time increasing with elevation above the sea bed. These lags are largely due to the time for an observed flow event to effect the bed and mix sediment upward.

Conference Paper↗
USGS1991

Large-scale coastal evolution of Louisiana's barrier islands

The prediction of large-scale coastal change is an extremely important, but distant goal. Here we describe some of our initial efforts in this direction, using historical bathymetric information along a 150 km reach of the rapidly evolving barrier island coast of Louisiana. Preliminary results suggest that the relative sea level rise rate, though extremely high in the area, has played a secondary role in coastal erosion over the last 100 years, with longshore transport of sand-sized sediment being the primary cause. Prediction of future conditions is hampered by a general lack of erosion processes understanding; however, an examination of the changing volumes of sand stored in a large ebb-tidal delta system suggests a continued high rate of shoreline retreat driven by the longshore re-distribution of sand.

Conference Paper↗
USGS1989

Morphodynamic signature of the 1985 hurricane impacts on the northern Gulf of Mexico

Three hurricanes hit Lousiana (LA), Mississippi (MS), Alabama (AL), and the Florida (FL) panhandle in 1985, producing dramatic geomorphic changes in a wide variety of coastal environments. The impact zone for hurricanes Danny, Elena, and Juan stretched 1000 km between the Sabine River in LA to the Apalachicola River in FL. Barrier shorelines experienced repeated intense overwash events, producing beach and dune erosion exceeding 30 m, as well as producing classic examples of storm surge deposits. Pre- and post-storm airborne videotape surveys, sequential vertical mapping photography, and field surveys provide the data base for this regional hurricane impact assessment on the northern Gulf of Mexico. Hurricane impacts on the low-profile and high-profile barrier shorelines, as well as on the marine terrace cliffs were systematic and predictable. Controlling the direction of overwash flow and the impact distribution pattern is the relationship among shoreline orientation, hurricane storm track, and regional wind field. The relationship between shore-zone geomorphology and storm surge overwash controls the impact response.

Conference Paper↗
USGS1989

Erosion and deterioration of the Isles Dernieres Barrier Island Arc, Louisiana, U.S.A.: 1853 to 1988

Using cartographic and aerial photography data from the years 1853, 1890, 1934, 1956, 1978, 1984, and 1988, shoreline change maps of the Isles Dernieres barrier island arc were constructed. These data were accurately superimposed, using a computer mapping system, which removed projection, datum, scale, and other cartographic inconsistencies. Linear, areal, and perimeter measurements indicate that the Isles Dernieres are suffering rapid rates of coastal erosion, land loss, and breakup. Bayside and gulfside erosion, in combination with sediment shortage and subsidence, have caused the Isles Dernieres to narrow through time. In addition, the core of the barrier island arc does not migrate landward and instead, breaks up in place as a result of inlet breaching and development. This is in contrast to other models of landward barrier island migration during transgression. If these trends continue, the Isles Dernieres will likely evolve into a subaqueous inner-shelf shoal by the early 21st century. Loss of the Isles Dernieres barrier island arc will severely impact the Terrebonne parish estuary, resulting in decreased environmental quality and increased public risk from storms and hurricanes.

Louisiana↗
USGS1985

ROLE OF SUSPENDED SEDIMENT IN SHORE-NORMAL BEACH PROFILE CHANGES.

Field measurements of suspended sediment-transport were made across a dissipative surf zone during a storm. A correlation between high suspended mass in the water column and periods of onshore flow caused a net onshore transport of suspended sediment even though the mean near-bottom flow was directed offshore. The observed onshore migration of a nearshore bar was predicted by gradients in the cross-shore suspended-sediment transport.

Conference Paper↗