Coastal Hazards - Adaptations Part 1 Local Government Association of Tasmania November 2011 This report has been prepared for: The Tasmanian Climate Adaptations Pathways Project This report has been prepared by: SGS Economics and Planning Pty Ltd ACN 007 437 729 Level 5 171 Latrobe Street MELBOURNE VIC 3000 P: + 61 3 8616 0331 F: + 61 3 8616 0332 E: [email protected] W: www.sgsep.com.au Offices in Brisbane, Canberra, Hobart, Melbourne, Sydney Table of Contents 1 Options to address hazards and protect assets ........................ 1 2 Works to Address Erosion Risks ............................................. 2 2.1 Works to reduce coastal erosion ................................................................................. 2 2.1.1 Sand Dune Stabilisation with Vegetation ......................................................... 3 2.1.2 Beach nourishment ..................................................................................... 6 2.1.3 Groynes .................................................................................................... 9 2.1.4 Artificial Headlands ................................................................................... 13 2.1.5 Offshore Breakwaters and Reefs .................................................................. 15 2.1.6 Coastal Hardening ..................................................................................... 18 2.1.7 Seawalls and Revetments ........................................................................... 19 2.1.8 Training Walls .......................................................................................... 26 2.2 Works to defend individual assets from erosion hazards ............................................... 29 2.2.1 Piles and Excavation to Rock ....................................................................... 29 3 Works to Address Inundation Hazards .................................. 35 3.1 Collective works to reduce flood hazard ..................................................................... 35 3.1.1 Dykes and levees ...................................................................................... 35 3.1.2 Flood barriers (eg. Thames Barrage) ............................................................ 38 3.1.3 Prevention of water back up into stormwater mains ........................................ 40 3.1.4 Detention/retention basins and improved management of rainfall runoff............. 42 3.1.5 Raise land levels ....................................................................................... 43 3.2 Individual Asset Measures to reduce risk from coastal flood hazards ............................... 47 3.2.1 Flood skirts .............................................................................................. 48 3.2.2 Flood barriers ........................................................................................... 51 3.2.3 Lifting existing dwellings ............................................................................ 53 3.2.4 Elevated substructure – type 1 (raised slab or floor) ....................................... 55 3.2.5 Elevated substructure – type 2 (stilt houses) ................................................. 59 3.2.6 Elevated substructure – type 3 (Non-inhabited ground floor) ............................ 62 3.2.7 Modular homes and moveable dwellings ....................................................... 64 3.2.8 Water resistant and waterproof construction .................................................. 66 3.2.9 Waterproof lower levels ............................................................................. 68 3.2.10 Floating houses and other structures ............................................................ 71 4 Works to address infrastructure and public assets ................. 73 4.1 Sealed sewer systems ............................................................................................ 73 4.2 Raised roads/services ............................................................................................. 73 4.3 Liftable bridges ..................................................................................................... 75 4.4 Alternate routes via higher land ............................................................................... 75 4.5 Floating roads ....................................................................................................... 76 4.6 Independence from connection to services ................................................................. 78 4.7 Management measures for parks and public open spaces ............................................. 79 Page i of 103 Table of Contents 5 Climate change and natural assets ....................................... 81 5.1 Wetlands & salt marshes......................................................................................... 82 5.2 Beaches ............................................................................................................... 85 5.3 Changes to other natural assets ............................................................................... 88 6 Other risk management measures ........................................ 89 6.1 Early warning systems, emergency response .............................................................. 89 6.2 Avoidance ............................................................................................................ 91 6.3 Planned Retreat .................................................................................................... 93 7 Key References ................................................................... 96 Appendix B Coastal Adaptations combined revision 20120116.doc Table of Contents Figures Figure 1 Dune stabilisation using appropriate local species ................................................... 3 Figure 2 Before and after photos of beach restoration efforts. Florida Coastline. USA ................ 6 Figure 3 The effects of a groyne on sediment flow, deposition and erosion. Adapted from Sediment Budgeting (O’Keeffe 1978).................................................................................. 9 Figure 4 Artificial Headlands, Byron Bay, NSW .................................................................. 13 Figure 5 An offshore breakwater encourages deposition on the beach. Sometimes sediment is deposited all the way out to the breakwater, forming a coastal feature known as a tombolo. Adapted from Sediment Budgeting (O’Keefe, 1978) .............................................. 15 Figure 6 An offshore breakwater at Semaphore Park, Adelaide SA ....................................... 15 Figure 7 Variation in Design Type of Seawalls ..................................................................... 18 Figure 8 The Seawall at Kingston Beach Tasmania ............................................................ 19 Figure 9 Failed sea wall at Port Fairy Victoria, offshore, below water level ............................. 21 Figure 10 Rock revetment that is aesthetically pleasing and provides intertidal habitat on a low energy estuarine shore at Bobbin Head, Cowan Creek, Hawkesbury River, NSW. Copywright Daniel Wiecek, DECCW ..................................................................................... 23 Figure 11 A piled coastal structure not structurally affected by shoreline erosion (NSW) ............ 29 Figure 12 Piled foundations are used for this waterside home on the Thames, as they allow the house to move slightly and water to travel underneath should any flooding occur................ 30 Figure 13 Woolloomooloo Pier, Sydney, built on piles (old commercial wharf converted to apartments) .................................................................................................................... 30 Figure 14a&b Houses on an eroding beach at Kitty Hawk, North Carolina, once situated on top of a dune32 Figure 15 House in Texas – used to be on land .................................................................. 32 Figure 16 Example of a Sea Dyke ..................................................................................... 35 Figure 17 House surrounded by own dyke, Mississippi floodplain ........................................... 37 Figure 18 St Helens road inundated at surface levels (~2.8m AHD) above the concurrent sea surface level (~1.1mAHD) due to restricted outflow. ........................................................ 40 Figure 19 Example of the level of a flood skirt .................................................................... 48 Figure 20 Example of other flood protective products such as an air brick cover. ...................... 48 Figure 21 Example of a Flood Barrier System ..................................................................... 51 Figure 22 Example of a suspended concrete slab prepared for pouring ................................... 55 Figure 23 Raised slab via waffle....................................................................................... 55 Figure 24 Elevated dwellings in Galveston, on the Gulf of Mexico, USA. .................................. 59 Figure 25 An example from a wide range of ‘coastal home’ designs offered, South Carolina, USA.62 Figure 26 Examples of modular homes on raised foundations ............................................... 64 Figure 27 Examples of moveable houses ........................................................................... 64 Figure 28 Raised Electrical Wiring ...................................................................................