Bruce E Jaffe

ABSTRACT The 26 December 2004 Indian Ocean tsunami caused widespread devastation and loss of life throughout the Indian Ocean basin. Fatalities in Indonesia alone totaled greater than 125,000 with more than 35,000 missing and 500,000 displaced. From March 30 to April 26, a team of 17 US and Indonesian scientists conducted a tsunami field survey to collect data to improve the ability to mitigate tsunami hazard in Indonesia and worldwide. Data collected included tsunami water heights, eyewitness reports, nearshore bathymetry, topographic profiles, land level change, and tsunami deposits. Study sites spanned 800 km of coast from Breuh Island north of Banda Aceh to the Batu Islands, and included 20 sites in Aceh Province in Sumatra and on Nias Island, Simeulue Island, and the Banyak Islands. Tsunami heights near the shoreline during the 26 December 2004 event were greater than 15 m along 100s of kilometers of coast. The tsunami did not loose energy rapidly as it inundated land; heights were greater than 10 m at 1500 m inland. Extensive tsunami sand deposits were found. At Kuala Merisi in Aceh Province, tsunami deposits were found from within 100 m of the shoreline to 1800 m inland. As part of the team was mobilizing in Jakarta on 28 March 2005, a magnitude 8.7 earthquake occurred offshore of Nias and Simuelue Islands. This earthquake generated a moderately sized tsunami (maximum heights greater than 3 m) that arrived within 10-15 minutes of the earthquake. Both the 28 March 2005 and the 26 December 2004 earthquakes caused land level changes greater than 2 m. Co-seismic subsidence is resulting in coastal erosion. These data are being used to improve the understanding of tsunamis and to mitigate future disasters. For example, the data allows refinement of tsunami inundation models, which will improve the identification of tsunami hazard zones. Models that utilize the observed relations between tsunami characteristics and sediment deposits are also being developed to increase the ability to interpret paleotsunami deposits, which will aid in determining tsunami risk.

The 26 December 2004 Indian Ocean tsunami caused widespread devastation and loss of life throughout the Indian Ocean basin. Fatalities in Indonesia alone totaled greater than 125,000 with more than 35,000 missing and 500,000 displaced. From March 30 to April 26, a team of 17 US and Indonesian scientists conducted a tsunami field survey to collect data to improve the

Abstract Model predictions from a numerical model, Delft3D, based on the nonlinear shallow water equations are compared with analytical results and laboratory observations from seven tsunami-like benchmark experiments, and with field observations from the 26 ...

... Bruce Jaffe a , low asterisk , E-mail The Corresponding Author , Mark Buckley a , E-mail The Corresponding Author , Bruce Richmond a , E-mail The Corresponding Author , Luke Strotz b , E-mail The Corresponding Author , Samuel Etienne c , E-mail The Corresponding Author ...

ABSTRACT The magnetic fabric and grain size of sand deposits emplaced during the 2011 Tohoku-oki tsunami were studied in five trenches along a 1800 m long shore-normal transect on the Sendai plain as well as in a near shore sedimentary infill of a scour depression. The magnetic susceptibility in all deposits is due to ferromagnetic minerals (mainly magnetite) making the anisotropy of magnetic susceptibility (magnetic fabric) suitable for fabric analyses. The dominant magnetic fabric is planar in all trenches and stronger in finer-grained inland deposits than in the coarser sediments. This planar fabric is related to tractive shearing of the bedload basal portion of the tsunami flow that led to the deposition of traction carpet layers. Among the various fabric parameters used for this study, the vertical evolution of the shape factor (q) of the magnetic ellipsoid in each trench follows the evolution of the magnetic lineation (L) and foliation (F). These parameters provide information on the hydrodynamic energy (flow speed) fluctuations during the emplacement of the tsunami deposit. For the most proximal deposits, characterized by well-sorted reworked beach sand with minor fluctuations in grain-size distribution, the magnetic fabric is sensitive to hydrodynamic energy variations during sedimentation. Reconstruction of tsunami flow orientation in the sediments, based on the orientation of the mean Kmax calculated for each trench, appears to be unambiguous only for the sandy infills of small topographic depressions. The variations in flow direction indicators elsewhere could be related to local variation of the flow and to micro-topographic effects. These findings are encouraging for the use of the magnetic fabric proxy in the study of paleotsunami deposits.

ABSTRACT Recent advances in the development of numerical, process-based models have led to remarkable performance in reproducing measured decadal morphodynamic developments. The advantage of this type of models is that they have a detailed output allowing for a close analysis of relevant processes. Drawback is that the output is associated with a high level of presumed uncertainty, because of the large number of processes involved and the high quality level of input data required.This study aims to explore possibilities to assess uncertainty levels associated with process-based morphodynamic modeling. In a probabilistic approach we consider the outcome of an ensemble of runs including variations of model input parameters and forcing schematizations. We propose to evaluate model performance by both a skill criterion (How well does the model reproduce observed patterns?), a confidence criterion (How sensitive are model results to uncertain input?) as well as a combination of these criteria. This methodology provides an objective assessment of the performance of process-based morphodynamic models. In addition, it can determine which input parameters cause largest uncertainty in the model outcome.The San Pablo Bay case study shows that 60% of the modeled volume meets the skill and confidence criteria for the depositional period (1856–1887) and 46% for the erosional period (1951–1983). Approximately 50% of the volume allocation meets the confidence criterion for a 30 year morphodynamic forecast (1983–2013). Model results are sensitive to model input variations only to a limited extend. We attribute this to the high impact of the San Pablo Bay plan form and bathymetry. The forecast shows continuous erosion of the channel and on the northern shoals and a continuous accretion of the channel slopes, albeit more concentrated in the western part of the channel than in preceding decades.

ABSTRACT Measured bathymetries on 30 year interval over the past 150 years show that San Pablo Bay experienced periods of considerable deposition followed by periods of net erosion. However, the main channel in San Pablo Bay has continuously narrowed. The underlying mechanisms and consequences of this tidal channel evolution are not well understood. The central question of this study is whether tidal channels evolve towards a geometry that leads to more efficient hydraulic conveyance and sediment throughput. We applied a hydrodynamic process-based, numerical model (Delft3D), which was run on 5 San Pablo Bay bathymetries measured between 1856 and 1983. Model results shows increasing energy dissipation levels for lower water flows leading to an approximately 15% lower efficiency in 1983 compared to 1856. During the same period the relative seaward sediment throughput through the San Pablo Bay main channel increased by 10%. A probable explanation is that San Pablo Bay is still affected by the excessive historic sediment supply. Sea level rise and Delta surface water area variations over 150 years have limited effect on the model results. With expected lower sediment concentrations in the watershed and less impact of wind waves due to erosion of the shallow flats, it is possible that energy dissipations levels will decrease again in future decades. Our study suggests that the morphodynamic adaptation time scale to excessive variations in sediment supply to estuaries may be on the order of centuries.

ABSTRACT Bathymetric measurements show that a deep, subtidal channel in San Pablo Bay, California, has consistently narrowed during the past 150 years. This raises general questions on the seasonal and intertidal morphodynamic processes acting at the subtidal channel-shoal interface. The current work addresses these questions using a process-based morphodynamic model (Delft3D).Model results reveal considerable morphodynamic activity during a tidal cycle. Deposition on the channel margin is largest during flooding of the shoals. Erosion rates (mainly occuring during ebb) remain relatively small, so that net accretion occurs on much of the channel margin. A remarkable finding is that locally generated wind waves are responsible for shoal extension and depositional channel narrowing. High SSC in the channel is a critical factor affecting channel narrowing. Wind waves suspend sediment on the shoals leading to high suspended sediment concentration (SSC) in the channel at ebb. Sensitivity analysis shows that wind direction even determines the location of channel margin accretion. Fluvial sediment supply is another cause of high SSC in the channel. Density currents, 3D circulation flows, sea level rise or varied sediment characteristics only have a limited effect on the erosion and sedimentation patterns.A 30 year forecast shows that deeper shoals and decreasing fluvial sediment supply lower SSC levels in the channel, limit channel margin accretion, and even lead to net channel margin erosion in some areas. Channel shape thus remains subject to dynamic processes related to local variations in sediment supply, albeit to a more limited extend than in earlier decades.