B E A C H E S. M A R I N A S. D E S I G N. C O N S T R U C T I O N. OECS Regional Engineering Workshop September 29 October 3, 2014 Coastal Erosion and Sea Defense: Introduction to Coastal/Marine Structures David A Y Smith
OUTLINE COASTAL EROSION PREVENTION APPROACHES (HARD/SOFT) Revetments, groynes, breakwaters, jetties Beaches, dunes DESIGN CONSIDERATIONS Armour stability, overtopping, scour, residual life Level of risk to be adopted by implementing agencies
REFERENCE MATERIAL COASTAL ENGINEERING MANUAL US ARMY CORPS OF ENGINEERS CIRIA ROCK MANUAL (1991, 2007)
COASTAL ENGINEERING MANUAL (CEM) Started as the Shore Protection Manual Edited every 7 years (1977, 1984, etc.) Significantly expanded over the years Now available online in two forms Free pdf version Interactive form (available for purchase through Veri-tech Inc.)
CIRIA ROCK MANUAL FIRST EDITION 1991 SECOND LARGER EDITION 2007 CREATED IN EUROPE AVAILABLE ONLINE (FREE) HTTP://WWW.FILESTUBE.TO/CM1QPB4BDU123RE1SJNCBF
MANUALS CEM AND CIRIA LARGE, COMPREHENSIVE DOCUMENTS SIMILARITIES AND DIFFERENCES Written and edited by large working groups Regularly updated with current research CIRIA 2 nd Ed. is more prescriptive CEM includes chapters on ancillary aspects
COASTAL STRUCTURES PURPOSES: Prevent/reduce coastal erosion or flooding Protect harbours or channels Provide a buffer against natural disasters caused by hurricanes and tsunami Regain lost land through reclamation
COASTAL EROSION AND FLOODING THEY ACT AS BARRIERS Revetments, breakwaters, seawalls (Hard structures) Beach nourishment ( Soft structure) HARNESS FORCES OF NATURE TO CREATE A BARRIER Groynes, offshore breakwaters Dune creation
HARBOUR & CHANNEL PROTECTION WAVE SHELTERING Breakwaters, jetties SEDIMENT TRAINING Groynes, offshore breakwaters
PROVIDE A BUFFER THROUGH PROVISION OF A SACRIFICIAL SHORELINE Beaches (and beach nourishment), dunes THROUGH PROVISION OF A HARD EDGE Groynes, revetments, seawalls, offshore breakwaters
LAND RECLAMATION WHERE FLAT LAND FOR DEVELOPMENT IS AT A PREMIUM Dredging, coupled with land reclamation TO SATISFY DEVELOPMENT REQUIREMENTS Creation of ports, industrial areas, etc.
BARRIERS - REVETMENT
BARRIERS - SEAWALL EM 1110-2-1100 (Part VI) 1 Jun 06 Figure VI-2-7. Example of a vertical front seawall
BREAKWATERS Figure VI-2-10. Typical beach configurations with detached nearshore breakwaters Figure VI-2-11. Conventional multilayer rubble-mound breakwater The front slope of the armor layer is in most cases straight. However, an S-shaped front or a front with a horizontal berm might be used to increase the armor stability and reduce overtopping. For these types of structures, optimization of the profiles might be difficult if there are large water level variations. Figure VI-2-12 illustrates these types of front profiles. Overtopping can be reduced by a wave-wall superstructure as shown in Figure VI-2-13. Types and Functions of Coastal Structures VI-2-13
GROYNES + BEACH NOURISHMENT EM 1110-2-1100 (Part 1 Aug 08 (Change 1110-2-1100 (Part V) g 08 (Change 2) Westhampton Beach, Long Island, New York, 18 Jan 1980 (courtesy USAED, New York) Figure V-3-30. Westhampton Beach, New York, groin field and renourished beach, 1998 (courtesy USAED, New York) (d) Terminal groins. Groins on the updrift side of inlets can benefit nearby beach nourishment projec
USING NATURE ALONGSHORE TRANSPORT + GROYNES Figure VI-2-7. Example of a vertical front seawall Figure VI-2-8. Typical beach configuration with groins d. Detached breakwaters. Detached breakwaters are almost always built as rubble-mound structures. Typical cross sections are as shown for the rubble-mound groin in Figure VI-2-9. Typical beach configurations with detached nearshore breakwaters are shown in Figure VI-2-10. Whether or not the detached breakwaters become attached to shore is a function of placement distance offshore. Tombolos are more likely to form when breakwaters are constructed within the surf zone. The two examples of detached breakwaters shown in Figure VI-2-10 serve different functions. See Part V-4 for functional design guidance on detached
USING NATURE (2) ALONGSHORE TRANSPORT + BREAKWATERS EM 1110-2-1100 (Part VI) 1 Jun 06 Figure VI-2-10. Typical beach configurations with detached nearshore breakwaters
OFFSHORE BREAKWATERS EM 1110-2-1100 (Part V) 1 Aug 08 (Change 2)
SAND DUNES
DESIGN CONSIDERATIONS ARMOUR STABILITY RUN-UP AND OVERTOPPING SCOUR PROTECTION FAILURE MODES
ARMOUR STABILITY WAVE FORCES Wave height, water depth, breaking or non-breaking ARMOUR STABILITY Gravity (size and density e.g. granite vs limestone) Interlocking (packing) Structure permeability (layer thickness, number of layers) Natural rock (limited weight) Concrete units
GRANITE VS. LIMESTONE PACKING OF BOULDERS
WAVE RUN-UP AND OVERTOPPING Safety of pedestrians, cars, infrastructure Inland flooding Can lead to structural failure
Q < 0.1 l/s/m for aware pedestrians
SCOUR PROTECTION Non-breaking wave forces high velocities Smaller armour stone sizes required Create an apron of immobile material
MODES OF FAILURE - BREAKWATER
Figure VI-2-39. Toe instability on hard bottoms Figure VI-2-40. Washout of underlayer material
Figure VI-2-43. Scour due to overtopping Figure VI-2-44. Toe erosion failure of rubble slope
Figure VI-2-64. Seaward overturning of gravity wall EM 1110-2-1100 (Part VI) 1 Jun 06
SUMMARY RESOURCES CIRIA Rock Manual Coastal Engineering Manual PURPOSE OF COASTAL STRUCTURES DESIGN ASPECTS MODES OF FAILURE