The University of the West Indies Organization of American States PROFESSIONAL DEVELOPMENT PROGRAMME: COASTAL INFRASTRUCTURE DESIGN, CONSTRUCTION AND MAINTENANCE A COURSE IN COASTAL ZONE/ISLAND SYSTEMS MANAGEMENT CHAPTER 5 ALTERNATIVES FOR COASTAL STORM DAMAGE MITIGATION By DAVE BASCO, PhD Professor, Civil and Environmental Engineering Department Old Dominion University Norfolk, Virginia, USA Organized by Department of Civil Engineering, The University of the West Indies, in conjunction with Old Dominion University, Norfolk, VA, USA and Coastal Engineering Research Centre, US Army, Corps of Engineers, Vicksburg, MS , USA. Antigua, West Indies, June 18-22, 2001 ALTERNATIVESALTERNATIVES FORFOR COASTALCOASTAL STORMSTORM DAMAGEDAMAGE MITIGATIONMITIGATION Dave Basco Old Dominion University, Norfolk, Virginia, USA National Park Service Photo STRUCTURALSTRUCTURAL ((changes to natural, physical system) • hardening (seawalls, bulkheads, revetments) • modification (headland breakwaters, nearshore breakwaters, groins) • soft (beach nourishment, dune rebuilding, sand bypassing) • combinations US Army Corps of Engineers NONNON--STRUCTURALSTRUCTURAL ((changes to man’s system) • adaptation (zoning, building codes, setback limits) • retreat (relocation, abandonment, demolition) CombinationsCombinations DoDo NothingNothing US Army Corps of Engineers COASTALCOASTAL ARMORINGARMORING STRUCTURESSTRUCTURES • seawalls and dikes • bulkheads • revetments US Army Corps of Engineers Figure V-3-6 Virginia Beach seawall/boardwalk (a) artist’s perspective (b) aerial photo, 1997 (courtesy of Virginia Beach, VA) SEAWALLSEAWALL INTERACTIONSINTERACTIONS WITHWITH ADJACENTADJACENT BEACHESBEACHES CONCERNS FALSE (OR UNKNOWN) • profile steepening • delayed beach recovery after storms • increased longshore transport • sand transport far offshore • increase average, long-term erosion rate US Army Corps of Engineers SHORELINESHORELINE STABILIZATIONSTABILIZATION STRUCTURESSTRUCTURES • headland breakwaters • nearshore breakwaters -- tombolos • nearshore breakwaters -- salients •groins • reefs, sills and wetlands US Army Corps of Engineers HEADLANDHEADLAND BREAKWATERBREAKWATER • modeled after natural rocky-headlands and parabolic-shaped beaches • embayment erodes until static, stable equilibrium bay shape reached • physical processes • effective for wave conditions with one dominant wave direction • storm response--little or no reduction in wave energy to shore-normal waves US Army Corps of Engineers NEARSHORENEARSHORE BREAKWATERSBREAKWATERS • salient or tombolo? • salient type less disturbing to longshore transport, but hard to design • tombolo created by beach nourishment to minimize downdrift inpart • both provide storm damage protection for waves striking shoreline at right angles US Army Corps of Engineers GROINGROIN FIELDSFIELDS • oldest, most common beach stabilization structure • many factors (geometry, beach, sediment, hydrodynamic) govern design • physical processes -- how do they work? • storm response -- little or no reduction in wave energy to shore-normal waves US Army Corps of Engineers GROINGROIN FIELDSFIELDS • must combine groin field construction with beach nourishment (fill up groins with sand) • must taper ends to restore natural sand bypassing of groin field • monitor downdrift impacts US Army Corps of Engineers (a) (b) Figure V-3-31 Typical groin field with sloping section REEFS,REEFS, SILLSSILLS ANDAND WETLANDSWETLANDS REEFS • platforms of biotic organisms built to a strict elevation in relation to low tide -natural -wave attenuation -artificial reefs SILLS 1. submerged, continuous, dike to hold sand (also called perched beach) 2. low-profile, continuous shoreline dike to hold marsh fringe US Army Corps of Engineers REEFS,REEFS, SILLSSILLS ANDAND WETLANDSWETLANDS WETLANDS • coastal salt marshes that are low-lying meadows of herbaceous plants subject to periodic water level inundations - very low energy shorelines - restoration now priority for many levels government US Army Corps of Engineers Figure 23A Stone sill with marsh planting Figure 23B Stone sill connecting on Chester River, Kent County, MD breakwaters with sand fill and marsh implantation on Choptank River, Talbot County, MD Figure 23C Breakwater and sill project after 5 years BEACHBEACH RESTORATION*RESTORATION* • beach nourishment • sand passing * because of importance, separate lecture solely on Beach Engineering and Management US Army Corps of Engineers NONSTRUCTURALNONSTRUCTURAL ALTERNATIVESALTERNATIVES ADAPTATION • zoning and building codes • setback limits RETREAT US Army Corps of Engineers RETREAT*RETREAT* • Corps of Engineer Studies - Cape Shoalwater, Washington (1970s) - Baytown, Texas (1970s, 1980s) • Special cases - Brighton Beach Hotel, Coney Island, NY (1888) - Cape Hatteras Lighthouse, NC (1999) • Impact of sea level rise *relocation, abandonment, demolition US Army Corps of Engineers CONCLUSIONCONCLUSION Even in land-area-rich US, the retreat alternative is very seldom selected because of economic, environmental and institutional, political and social constraints. US Army Corps of Engineers COMBINATIONSCOMBINATIONS ANDAND NEWNEW TECHNOLOGIESTECHNOLOGIES COMBINATIONS • structural - beach stabilization structures and beach nourishment - seawalls and beach nourishment NEW TECHNOLOGIES • pre-cast, concrete units • geotextile-filled bags • beach drains • permeable groins • innovative technology demonstration program US Army Corps of Engineers DODO NOTHINGNOTHING • when is “do nothing” the appropriate response? • after flood, who pays for recovery? • what government programs are available? • national coastal hazard mitigation plan* * presently, the United States government does not have a national plan for coastal disaster hazard mitigation. US Army Corps of Engineers SUMMARYSUMMARY Classes of Management and Engineering Response for Shore Protection (Pope, 1977) Type Common Phrase Armoring Draw the line Moderation Slow down the erosion Restoration Fill up the beach Abstention Do nothing Adaptation Live with it US Army Corps of Engineers .