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Source: https://erdc-library.erdc.dren.mil/jspui/ A study was done on the hydrodynamics and sedimentation of Humboldt Bay. California. This was done to determine the effects of channel deepening and realignment on the currents and sedimentation patterns in the area. The hydrodynamics and sedimentation were modeled with the TABS-MD modeling system. The hydrodynamics were verified to National Ocean Survey (NOS) harmonic data, and the sedimentation patterns were verified by comparison with historical dredging records. Predictions of changes in currents and sedimentation patterns were made for three different plans.

Source: https://erdc-library.erdc.dren.mil/jspui/ Field data were collected on currents, salinities, and suspended sediments intensively over a lunar day and sporadically over a fortnight in September 1988 for the purpose of identifying transport processes and conditions in central San Francisco Bay and for numerical model verification. Conditions were typical of a low freshwater inflow summer season in this area. A two-dimensional horizontal finite element model was applied and verified to field and physical hydraulic model data. The model is intended for future long-term studies of the fate of dredged material dispersed from the Alcatraz disposal site.

Source: https://erdc-library.erdc.dren.mil/jspui/ Dredged material from San Francisco Bay has been disposed of at the Alcatraz Island open-water disposal site for many years. Since the disposal site lies in an extremely high energy area, historically it has been assumed that the vast majority of the disposed material moves with the current past the Golden Gate Bridge and is then carried out into the ocean. However, recent surveys of the disposal site have shown that a large mound of material, which creates navigation problems, has formed. Since a new dredging project in the area is expected to create approximately 5 million cu yd of new material to be disposed at the site over the next 2 years, a major concern is how much of the new material will remain within the disposal site and contribute to the existing mound. To address the problem, a numerical model has been applied that computes the behavior of a dredged material disposal through three phases: convective descent, during which the disposal cloud falls under the influence of gravity; bottom collapse, occurring when the descending cloud impacts the bottom; and passive transport-diffusion, commencing when the material transport and spreading are determined more by ambient currents and turbulence than by the dynamics of the disposal operation. The model accounts for land boundaries, depth variations, ambient current variations in three dimensions and in time, several sediment classes within the dredged material , and variations of ambient density pr ofiles in time. A major limitation of the model is that erosion and subsequent redeposition of material deposited on the bottom are not modeled. Therefore, results from the numerical model were used only to provide the initial amount and distribution of material deposited within the disposal site. Analytic techniques were subsequently employed to analyze the erosional characteristics of the bottom deposits within the site. Results of the study show that for both Richmond Inner Harbor and Oakland Outer Harbor sediments disposed of in the north zone of the Alcatraz disposal site, the majority of the material will initially deposit within the disposal site limits. Some reduction of within-site deposition is achieved by ebb-tide-only disposal.

Source: https://erdc-library.erdc.dren.mil/jspui/ Dredged material from San Francisco Bay has been dumped at the Alcatraz Island open-water disposal site for many years. Since the disposal site lies in an extremely high energy area, historically it has been assumed that the vast majority of the disposed material moves with the current past the Golden Gate Bridge and is then carried out into the ocean. However, recent surveys of the disposal site have shown that a large mound of material, which creates navigation problems, has formed. Since a new dredging project in the area is expected to create approximately 5 million cu yd of new material to be disposed at the site over the next 2 years, a major concern is how much of the new material will remain within the disposal site and contribute to the existing mound. To address the problem, a numerical model has been applied that computes the behavior of a dredged material dump through three phases; namely, convective descent, during which the dump cloud falls under the influence of gravity; bottom collapse, occurring when the descending cloud impacts the bottom; and passive transport-diffusion, commencing when the material transport and spreading are determined more by ambient currents and turbulence than by the dynamics of the disposal operation. The model accounts for land boundaries, depth variations, ambient current variations in three dimensions and in time, several sediment classes within the dredged material, and variations of ambient density profiles in time. A major limitation of the model is that erosion and subsequent redeposition of material deposited on the bottom are not modeled. Therefore results from the numerical model were only used to provide the initial amount and distribution of material deposited within the disposal site. Analytic techniques were subsequently employed to analyze the erosional characteristics of the bottom deposits within the site. Results of the study show that the dumping of consolidated clumps of clays and silts will contribute to further mounding or accumulation of material within the disposal site since sufficient energy to erode these types of materials at the rate required to avoid mounding does not exist at the site.

Source: https://erdc-library.erdc.dren.mil/jspui/ A one-dimensional numerical model (HEC-6) was used to determine the effects of sediment deposition and erosion for a 2-mile reach of the San Lorenzo River in Santa Cruz, California. The numerical model was calibrated to simulate measured degradation and aggradation that occurred during a major flood event in 1982. The bed profile and water-surface elevations were calculated for the Standard Project, 100-year, and 50-year floods. Average annual deposition quantities were estimated for various initial channel conditions.

Source: https://erdc-library.erdc.dren.mil/jspui/ A combination of physical and numerical models was used to simulate the hydrodynamic, circulation, and sediment transport characteristics of San Francisco and San Pablo bays, This simulation was done in response to a request by the US Army Engineer District, San Francisco, to develop a modeling tool that can define the fate of dredged material disposed at the Alcatraz disposal site. Tide and current velocity data from the San Francisco Bay-Delta physical model were used to verify the vertically averaged hydrodynamic model, RMA-2V (Two-Dimensional Model for Free Surface Flows). This model was used to generate the velocity field for a dredged material disposal model, DIFTD (Discharge from an Instantaneous Dump). The suspended sediment concentrations from DIFID and the geometry and hydrodynamic data from RNA-ZV were used in the sediment transport model, STUDB (Sediment Transport in Unsteady Two-Dimensional Flows, Horizontal Plane), to establish sediment transport and dispersion patterns around the Alcatraz disposal site in central San Francisco Bay. Two model meshes were developed for this study: a comprehensive or global mesh of the entire system, and a more detailed inset mesh of the Alcatraz disposal area. The modeling system has its capabilities and applications. However, the results are just reasonable simulations, not fully verified ones. Each of the numerical models, RMA-ZV, DIFID, and STUDH, has individual capabilities and limitations, the greatest of which is the two-dimensional approximation of a three-dimensional phenomenon. The vertically averaged velocities and sediment fields will mask two-layer flow and other three-dimensional processes. Even with this simplification, the model results are useful in estimating the short- and long-term fates of sediments released during a disposal operation. Appendix A describes the TABS-2 modeling system in which RMA-2V and STUDH belong, and Appendix B gives details of the numerical model DIFID.

Source: https://erdc-library.erdc.dren.mil/jspui/ A tidal barrier is proposed as a control measure to prevent tidal flooding in the San Rafael Canal, San Rafael, CA. This study investigated at a feasibility level the interaction between sedimentation and the tidal barrier. For this study, a brief site trip with limited sampling of suspended sediments and bottom cores was conducted, historical dredging records for San Rafael Canal were analyzed, historical suspended sediment data from nearby San Francisco Bay were obtained, sediment characteristics for erodibility from prior flume tests conducted on San Francisco Bay bottom sediments were obtained, and freshwater inflow exceedance interval hydrographs were obtained for the 2-, 10-, 50-, 100-, and 500-year events. Finally a zero-dimensional numerical model was developed to evaluate erosion and deposition for the 1989 astronomical tides at two alternative tidal barrier locations. In the vicinity of San Rafael Canal where the tidal barrier would be located, tidal sediment movement appears to predominate rather than riverine sediment transport. Results of the numerical model substantiated by the dredging records indicated that the existing San Rafael Canal has a net depositional pattern. The increased velocities from the reduced cross section of the tidal barrier changed the numerical results to predict net erosion tendencies at both tidal barrier sites evaluated. These results indicate that the tidal barrier concrete apron will be kept relatively free of deposits that might otherwise interfere with operation of the barrier. The net erosion also indicates that erosion protection may be necessary around the tidal barrier apron. Freshwater inflow flood events can result in high velocities around the barrier with substantial capacity to erode. Except in the immediate vicinity of the tidal barrier, the San Rafael Canal will not be impacted by the proposed project.

Source: https://erdc-library.erdc.dren.mil/jspui/ This investigation was concerned with the development of an adequate navigation channel through the reach of the Arkansas River from the mouth of the Verdigris River downstream to below the new U. S. Highway 62 Bridge, as part of the Arkansas River multipurpose project. A movable-bed model reproducing about 5.7 miles of the Arkansas River in the Webbers Falls Lock and Dam pool, including the lower reaches of the Verdigris and Grand Rivers, to scales of 1:80 vertical and 1:120 horizontal was used for the study. The purpose of the study was to develop a system of training structures that would reduce or eliminate shoaling at the confluence of the Verdigris and Arkansas Rivers, develop a channel through the navigation span of the new U. S. Highway 62 Bridge, and reduce the need for maintenance dredging in the Muskogee Harbor area, without producing currents that would be troublesome for navigation. Results of the investigation indicated that : Satisfactory navigation conditions will be provided with the plan developed, except that some shoaling might occur at the mouth of the Verdigris River during low Arkansas River flows and little or no flow in the Verdigris River. Development of an adequate channel and the degree of shoaling tendencies are affected to a considerable extent by the high elevation of bedrock and gravel bars in the reach. Shoaling in the Muskogee Harbor area can be expected because of its location with respect to the river channel alignment. Shoaling will depend on the amount of sediment moving out of the Arkansas River above the mouth of the Verdigris River during high flows. There is a natural tendency for the channel downstream of the harbor area to cross toward the right bank and shoal along the sailing line approaching the navigable span of the new U. S. Highway 62 Bridge. With dikes placed in the deep channel along the right bank, a channel of adequate depth will be maintained under most conditions.