Sediment Management Plan Rehoboth Bay, Sussex County, Delaware Prepared for: Division of Soil and Water Conservation Delaware Department of Natural Resources and Environmental Conservation (DNREC) Submitted by: 104 West 40th Street, 14th Floor New York, NY 10018 Final Report – November 7, 2007 Rehobooth Bay Sediment Management Plan TABLE OF CONTENTS 1. INTRODUCTION AND BACKGROUND ......................................................................... 1 1.1 State Dredging Program.......................................................................................................1 1.2 Inland Bays Dredging Study................................................................................................2 1.3 State Channel Marking Program..........................................................................................3 1.4 Macroalgae Harvesting Program .........................................................................................3 1.5 Present Funding...................................................................................................................4 2. EXISTING CONDITIONS................................................................................................... 5 2.1 Study Area...........................................................................................................................5 2.2 Environmental Conditions...................................................................................................6 2.2.1 Winds ..............................................................................................................................6 2.2.2 Water Levels .................................................................................................................15 2.2.3 Currents.........................................................................................................................17 2.2.4 Bathymetry....................................................................................................................18 2.2.5 Historical Shoreline Change .........................................................................................22 2.2.6 Bottom Sediments .........................................................................................................27 3. HISTORICAL DREDGING AND DISPOSAL INVENTORY ...................................... 31 3.1 USACE Dredging..............................................................................................................31 3.1.1 Inland Waterway from Delaware Bay to Rehoboth Bay (Lewes-Rehoboth Canal) .....31 3.1.2 Waterway from Indian River Inlet to Rehoboth Bay (Massey’s Ditch) .......................32 3.1.3 Inland Waterway from Chincoteague Inlet to Delaware Bay (Assawoman Canal)......32 3.1.4 Delaware Bay to Chesapeake Bay Waterway (Delmarva Intracoastal Waterway) ......33 3.1.5 Pepper Creek, Delaware................................................................................................33 3.1.6 Indian River Inlet and Bay ............................................................................................33 3.2 DNREC Dredging..............................................................................................................34 3.2.1 Love Creek....................................................................................................................34 3.2.2 White Creek ..................................................................................................................35 3.2.3 Assawoman Canal.........................................................................................................36 3.2.4 Herring Creek................................................................................................................37 3.2.5 Guinea Creek.................................................................................................................37 3.2.6 Pepper Creek.................................................................................................................38 3.2.7 Vines Creek...................................................................................................................39 3.2.8 Massey’s Ditch..............................................................................................................39 3.2.9 Indian River Inlet and Bay Channel..............................................................................40 3.2.10 Lewes-Rehoboth Canal..........................................................................................42 3.2.11 Burton’s Island Marina/Indian River Marina ........................................................43 3.2.12 Wilson Creek.........................................................................................................43 3.2.13 Rehoboth Bay Borrow Pits ....................................................................................43 3.2.14 Bald Eagle Creek...................................................................................................43 3.2.15 Feeder Beach at Indian River Inlet ........................................................................44 3.2.16 Cozy Cove..............................................................................................................44 3.2.17 Contract Projects....................................................................................................45 i Final Report. November 7, 2007 Rehobooth Bay Sediment Management Plan 4. HYDRODYNAMIC MODELING..................................................................................... 47 4.1 Model Development...........................................................................................................47 4.1.1 Overview of Delft3D Modeling System .......................................................................47 4.1.2 Model Grid....................................................................................................................48 4.1.3 Bathymetry....................................................................................................................49 4.1.4 Boundary Conditions ....................................................................................................51 4.1.5 Calibration.....................................................................................................................54 4.1.6 Model Verification........................................................................................................67 4.2 Existing Hydrodynamic Conditions...................................................................................69 4.2.1 Water Elevations...........................................................................................................69 4.2.2 Discharge into Rehoboth Bay .......................................................................................72 4.2.3 Currents.........................................................................................................................74 5. SHOALING ESTIMATES ................................................................................................. 78 5.1 Lewes-Rehoboth Canal......................................................................................................78 5.2 Love Creek.........................................................................................................................83 5.3 Herring Creek & Guinea Creek .........................................................................................84 5.4 Massey’s Ditch...................................................................................................................86 5.4.1 Location A: Rehoboth Bay Channel North of Bluff Point............................................87 5.4.2 Location B: Pullover.....................................................................................................89 5.4.3 Location C: Massey’s Landing .....................................................................................91 5.4.4 Location D: Middle Island Shoal ..................................................................................93 5.4.5 Location E: Channel between Big Ditch and Little Ditch ............................................95 6. SEDIMENT MANAGEMENT........................................................................................... 99 6.1 Shoaling Reduction Measures............................................................................................99 6.2 Disposal Volume Reduction Measures............................................................................100 6.2.1 Mechanical Sediment Dewatering: Belt Press Dredging............................................100 6.3 Beneficial Reuse ..............................................................................................................101 6.3.1 Habitat Restoration & Development...........................................................................102 6.3.2 Beach Nourishment.....................................................................................................109 6.4 Lewes-Rehoboth Canal....................................................................................................110 6.4.1 Lewes, DE Reach........................................................................................................110 6.4.2 Cape Henlopen State Park Reach................................................................................112 6.4.3 Henlopen Acres Reach................................................................................................112