Specifications include, but are not limited to: Task 1 - Data Collection (estimated budget of $5,600 for this task) In support of the hydrodynamic, wave, and sediment modeling, a data collection effort will be conducted. Targeted data sources are listed below: ‐ Publicly available bathymetric data including USACE Hydrographic Surveys, surveyed bathymetry data (depending on availability) of Passagassawakeag River between the Belfast Armistice Bridge and Belfast Bay. ‐ The dimensions and plans for the coastal structures within the model domain including the existing breakwater, the Belfast Armistice Bridge, and the Acadia Highway bridge. ‐ Grain Size analysis of bed sediments from previous studies. ‐ Gulf of Maine Operation Forecast System (GoMOFS) tidal level and current predictions. ‐ North Atlantic Comprehensive Coast Study (NACCS) predicted return intervals for extreme water levels and wave heights. In the event data sources are not available, efforts will be made to identify other sources, and if not available, the modeling effort will be tailored, and results qualified to reflect any data limitations. Deliverables ‐ Bathymetric, topographic and coastal boundary conditions for modeling Task 2 - Coastal Modeling Task 2.1 - Wave Modeling (estimated budget of $6,100 for this task) A Delft 3D Wave model will be used to simulate the wave heights around the breakwater using the spectral SWAN model. The D-waves module computes wave propagation, wind-wave generation, energy dissipating, wave breaking, refraction, shoaling, and directional spreading. The bottom orbital velocity of waves in shallow water, an output of D-Waves, can create a bed shear stress on top of the shear stress generated by currents. Deliverables ‐ Wave characteristics and significant wave heights near the project site Task 2.2 - Hydrodynamic Modeling (estimated budget of $6,100 for this task) The synthetic tidal storm hydrographs and wave conditions for the design storm as the boundary conditions to the model will be developed from the data above. The return period of the design storm will be determined with the design team. The flow across the boundary in Belfast Bay will be calculated using the NOAA Gulf of Maine Operational Forecast System (GoMOFS). Two (2) Two-Dimensional (2-D) hydrodynamic model configurations for each the existing condition with the present breakwater and the proposed extended breakwater structure will be modeled using HEC-RAS. The conditions will be simulated for both geometries for the design storm and a daily tidal condition. The tidal hydrodynamic boundary conditions will be simulated on both existing and the proposed condition models and results of velocity, depths, water surface elevation (WSEL), and bed shear stress will be developed. The streamlines and velocity vectors will be plotted to identify the flow patterns. We will use the 2-D HEC-RAS hydrodynamic model with the currents and tidal boundary conditions to simulate tidally influenced water bodies due to the robustness and the stability in the model compared to comprehensive coastal models. Deliverables ‐ Hydrodynamic model of existing and proposed conditions Task 2.3 - Critical Shear Stress Assessment (estimated budget of $2,900 for this task) Grain size distribution from a past sieve analysis (bed gradation) will be used to determine the representative d50 grain size for a critical shear stress analysis. A Shield’s critical shear stress analysis will be performed to find out the threshold of the sediment movement, based on non-cohesive d50 grain size found above. Assuming the bed material to be non-cohesive sediments will enforce conservativeness to the sediment movement. A comparison between the existing and proposed 2-D velocity contours will indicate the possible areas of impact due to the proposed conditions. A comparison between simulated bed shear stress from both the hydrodynamic modeling as well as due to the orbital velocity of the waves with the critical shear stress will indicate the areas that are vulnerable for sediment movement. With this approach we can decide if the proposed conditions will impact new areas. Deliverables ‐ A “heat map” of shear stresses with potential to result in sediment movement within affected area due to the proposed breakwater condition
