Numerical Modeling Assessment of Dredging Spoils Dispersion and Deposition, Fort Lauderdale, FL Julio A. Zyserman, DHI, Solana Beach, California Christopher G. Creed, Olsen Associates, Inc., Jacksonville, Florida

Outline of Presentation Project background Problem definition Selected modeling approach Description of model setup Presentation and discussion of results Conclusions and closing remarks © DHI October 24, 2012

Project Background Miami Port Everglades Inlet is a complete barrier to littoral drift Net southward sediment drift 56,000 yd3/yr. (42,800 m3/yr.) Sediment accumulation along North beach and Inlet channel, significant erosion along South beach Planned sediment bypass program: Sediment trap on north side of channel Remove relict spoil shoal Improvements to north jetty Periodic bypassing every 2-3 years Sponsored by Broward County and FDEP Construction planned for 2014-15 © DHI October 24, 2012

Problem Definition Need to dredge sand trap Need to remove spoil shoal Sediments to be excavated includes significant % of fines Direct (dredging) and indirect impacts (sedimentation and turbidity) Potential impacts from sediment spreading and deposition: Degradation of water quality Temporary and permanent hardbottom habitat loss: Scleractinian (stony) corals and Octocorals (soft) habitat (one of few coral reef areas in the continental US!) Temporary and permanent seagrass and seagrass habitat loss Modeling study required © DHI October 24, 2012

Selected Modeling Approach Hydrodynamic model MIKE 21 HD to compute water levels and velocities Lagrangian discrete particle model MIKE 21 PA to compute fate of spilled sediments Lagrangian approach in PA allows individual tracking of particles of different sizes, from different sources, spilled at different positions along the water column, etc. Standard output from PA: 2D time series of suspended sediment concentration (SSC) and deposited mass for every sediment fraction Additional post-processing of PA results to obtain maximum/average values Maximum thickness of deposited sediment layer, time required to reach maximum thickness and associated average rate of sediment deposition also calculated by post-processing PA results © DHI October 24, 2012

HD Model Setup Nested Cartesian grids, 30m and 10m resolution Time-varying tidal water levels at North & South boundaries Calibration against measured water levels and ADCP discharges Water level differential to mimic Florida Current Production runs cover neap-spring tidal cycle + 1 day model spin-off Seven scenarios: pure tide + 6 intensities of Florida Current (3 north- + 3 southward) © DHI October 24, 2012

PA Model Setup 69,000 yd3 (52,750 m3) of sediment to be removed from sand trap, 118,000 yd3 (90,200 m3) from spoil shoal 9,000 yd3/day (6,900 m3) dredged at both sites, distributed over 540 bucket lifts, 2 minutes/cycle duration  dredge 18 hours/day Sediments finer than 150 microns will be spilled Sediment lost at grab/lift and by wash during lift along water column Three sediment classes in PA: 40, 100 and 150 microns Spill rates range from 0.10 kg/s to 0.55 kg/s Losses at lift: 0.5 m above seabed, losses by wash at free surface © DHI October 24, 2012

Model Results (1/2) Average MIKE 21 PA output consists of 24 parameters (3 sediment sizes, two locations, two types of losses, SSC/deposited sediment) Results for three sediment sizes and two types of losses integrated Maximum and mean values calculated Additional post-processing performed to calculate: Thickness of deposited sediment layer (mm) Rate of sediment deposition (mm/day) Time to maximum thickness of deposition layer (days) Max. © DHI October 24, 2012

Model Results (2/2) Influence of velocity of Florida Current Average Max. Influence of velocity of Florida Current Average Max. Influence of position of dredger © DHI October 24, 2012

Summary and Conclusions Sand bypassing at Port Everglades Inlet is considered to be a feasible and cost-effective inlet and beach management strategy for Broward County The project will serve as a reliable long-term sand source for the beaches south of the inlet and will reduce sand shoaling in the Federal navigation entrance channel Viewed as an environmental enhancement to the County’s beach management program, the project will decrease demand on offshore sand resources located adjacent to reefs Model results will be used as justification to expand mixing zones that will be required to comply with State water quality standards during construction Model results will be used to specify the spatial extent of sedimentation and turbidity monitoring as well as coral and seagrass community characterization and monitoring Given the sensitivity of marine habitat and communities around the project site, the dredge plume fate modeling is an essential tool for the planning of project resource protection efforts © DHI October 24, 2012

Thank you very much for your attention! Any questions? Julio A. Zyserman, DHI, Solana Beach, California (jaz@dhigroup.com) Christopher G. Creed, Olsen Associates, Inc., Jacksonville, Florida (ccreed@olsen-associates.com) © DHI October 24, 2012