Development, Testing and Application of the Multi-Block LTFATE Hydrodynamic and Sediment Transport Model

Transcription

1 Development, Testing and Application of the Multi-Block LTFATE Hydrodynamic and Sediment Transport Model Earl Hayter Environmental Lab October 25, 2012

2 LTFATE Multi-Block Hydrodynamic, Water Quality and Sediment Transport Modeling System CE-QUAL-ICM ADCIRC LTFATE- HYDRO CH3D MET LTFATE-SED SEDZLJ STWAVE

3 LTFATE Multi-Block (MB) Concept A conventional hydrodynamic single-block application approach typically requires long simulation time as well as large CPU memory requirements. Solution: Grid Decomposition and Message Passing Interface (MPI) code. Grid decomposition splits a single large grid into multiple smaller grids, MB, where each grid runs on it s own CPU. Message Passing Interface code allows communication amongst MB grids as the simulation proceeds. Result: Significant decreases in simulation time and CPU memory. To date, SEDZLJ applied in a 3D single block (SB) as a nested grid and 2D fully multi-block (MB) system 3

4 Nested Grid SEDZLJ SB Application The Mobile District is performing a feasibility study for channel widening of the Pascagoula Lower Sound (PLS) and Bayou Casotte (BC) navigation channels within the Mississippi Sound (MS). To support the District, ERDC modeled wave- and current-induced sediment transport in a portion of the MS centered about these channels. Objective of Modeling Study Utilize fully 3D hydrodynamic and sediment transport modeling to evaluate the impact of the proposed widening alternatives sedimentation and infilling rates.

5 Physical Setting Pascagoula River MS Sound Bayou Casotte Mobile Bay Chandeleur Islands

6 Physical Setting Pascagoula River Round Island Bayou Casotte Horn Island Petit Bois Island

7 Methodology ADCIRC and STWAVE used to generate the tidal boundary and local wave forcing for the Multi-Block (MB) LTFATE model. Performed circulation modeling of MS using MB LTFATE to generate hydrodynamic and salinity boundary conditions for the nested single block (SB) LTFATE model of the Pascagoula Lower Sound (PLS) and Bayou Casotte (BC) navigation channels within the Mississippi Sound (MS). Setup the sediment transport model using results from Sedflume and PICS analyzes and existing sediment data.

8 Methodology (continued) Calibrate the sediment transport model by comparing model simulations with measured suspended sediment concentration (SSC) profiles. Validate the sediment transport model by comparing measured and simulated sedimentation volumes in the Lower Sound and Bayou Casotte reaches of the Pascagoula Harbor Channel. Simulate three channel widening scenarios to determine impact of the channel widening on the sedimentation volumes.

9 MB-SB LTFATE MB LTFATE-Hydro is a 3D, non-orthogonal boundary-fitted hydrodynamic model that includes temperature and salinity transport. MB boundary conditions are river inflow data and tidal forcing from ADCIRC circulation model simulations and time varying wave forcing from STWAVE. MB LTFATE system provides time varying water surface elevation, flow, and salinity forcing for the SB open-water boundaries. SEDZLJ is the sediment transport model that is dynamically integrated into the LTFATE hydrodynamic module.

10 Multi-Block (5) LTFATE Grid

11 Nested SB LTFATE Bathymetry BC Channel PLS Channel

12 Nested SB LTFATE GRID

13 Sediment Transport Processes Simulated in LTFATE Erosion of mixed cohesive and non-cohesive sediment beds Advective and dispersive transport of suspended sediment Bedload transport of non-cohesive sediment Settling of flocculated cohesive sediment, and settling of individual non-cohesive sediment particles. Effect of bed slope on bedload transport and erosion rate is represented. Changes in bottom elevations due to erosion and deposition are accounted for in calculating the flow field during the next model timestep. Current- and wave-induced bed shear stresses are calculated and used in determining erosion rate.

14 Sediment Transport Model Simulations LTFATE was run for the same two month time period for the three widened channel configurations. The ratio of sedimentation volumes of the widened channels to those of the existing channel are given below. Expansion Width Bayou Casotte Channel Pascagoula Lower Sound Channel 75 East & 75 West West West

15 SB Summary 3D sediment transport modeling was performed in the MS Sound using a combination of MB and SB LTFATE, which is a state-ofthe-art hydrodynamic, salinity, temperature and sediment transport modeling system. LTFATE can represent the following forcings: time varying water surface elevation due to tides, riverine flows, wind, and spatially and temporally varying wave properties. The latter are used to calculate radiation stresses that are included in the momentum equations solved in LTFATE. The effect of bed slope on bedload transport and erosion rates is accounted for in LTFATE. Representing the impact of bed slope becomes critical at navigation channels due to relatively rapid changes in bathymetry.

16 MB SEDZLJ Development and Application The Alaska District requested assistance on evaluating sedimentation alterations due to planned POA expansion. To support the District, ERDC has further developed the MB LTFATE to dynamically link SEDZLJ within the MB system. SEDZLJ modified to dynamically link with the MB LTFATE-Hydrodynamic transport MPI routines developed to accommodate grid decomposition (MB)

17 16 Block Upper Cook Inlet, AK Grid

18 16 Block Upper Cook Inlet Grid - Port of Anchorage

19 MB SEDZLJ Development and Application The MB SEDZLJ tested to insure that sediment mass is adequately conserved in all grid blocks A 4-month 16 block LTFATE depth averaged test simulation completed in 2.5 wall clock days, which is 16 times faster than the previous single block EFDC simulation performed for the District. Further simulation time improvements can be achieved by adding additional blocks.

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