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Coastal Geomorphology Goal 18: Pre-1977 Development Focus Group Meeting #2 MARCH 6, 2019 Beachfront Protective Structure > Looking to clarify static/structural vs. dynamic erosion- control options > Conceptual definition (for all or unknown treatments) plus a list of examples > Goal 18 does not prohibit all forms of shorefront protection for post-77 development, only the use of “structures” Coastal Erosion: Approaches for Mitigation Jonathan Allan and Meg Reed OPTIONS (ordered from most passive to most active) • Do nothing! • Retreat or relocate • Coastal Engineering: need to distinguish between “soft” vs “hard” options – Soft coastal engineering includes: • Sand beach renourishment (few examples implemented (lots East Coast)) • Gravel beach (dynamic revetment) • Willow plantings – Hard coastal engineering (erosion control structures) includes: • Seawalls • Riprap = most common on the Oregon coast • Bulkheads (wooden) • Sand burritos/sand bags • Offshore breakwaters (none on the OR coast) • Groins Sand Renourishment (‘soft’ engineering): • Involves placement of sediment either on the beach or in the nearshore; • Maintains natural beach; • Typically involves using sediment coarser than what is on the natural beach; • Few examples in Oregon (e.g. Tillamook Bay north jetty (5,000 yd3)) • Expensive… several million/mile of beach; Mark Gadsby https://commons.wikimedia.org/wiki/File:Beach_Replenishment._- Bryan Oakley, Rhode Island Sea Grant _geograph.org.uk_-_319208.jpg https://seagrant.gso.uri.edu/cashing-in-on-offshore-sand-deposits/ Seawalls/Bulkheads/Riprap (‘hard’ engineering) • ‘Fixes’ the shoreline in place, while rest of coast may continue to recede (beach may narrow due to rising sea levels); • Uses mass to mitigate the erosion; • Expensive (particularly walls) Nelscott, Lincoln City. J. Allan DOGAMI Neskowin, Tillamook County. J. Allan DOGAMI Sand Burrito/Bags (‘hard’ engineering) • Burrito’s are not too dissimilar from walls/revetments in that they ‘fix’ the shoreline in place, while rest of coast may continue to recede (beach may narrow due to rising sea levels); • Temporary fix; • Uses mass to mitigate the erosion; • Can be expensive. Easily damaged. Sutton Lake, OR. J. Allan DOGAMI Manitoba, TITANtubes North Carolina, O. Pilkey https://commons.wikimedia.org/wiki/File:TLB_Geo Tubes.jpg Offshore Breakwaters (‘hard’ engineering) • Shore parallel structures that provide protection by reflecting, dissipating and refracting waves, which reduces the wave energy and littoral sand transport in their lee at the shore; • Structures may be either detached or attached to the shore; • Very expensive to construct (challenging environment), may enhance rip development, large visual impact; • Due to the lower energy in their lee, sand accumulates forming a bulge (a salient), which eventually may attach to the breakwater (becomes a tombolo,… e.g. Haystack Rock, Cannon Beach); and, • Was considered by the USACE as an engineering solution to ongoing erosion of coastal bluffs near the Spencer Creek bridge (Beverly Beach)… to protect Highway 101. Jeremy Bolwell, Borth, United Kingdom, 2017 https://www.geograph.org.uk/photo/5323751 (Simm et al., 1996) Groins (‘hard’ engineering) • Shore perpendicular structures that disrupt alongshore sand transport; • May be low or high sided (depending on wave energy); • Suitable for micro-tidal environments (tidal range is narrow); • Requires periodic recharge to minimize downdrift effects; • None implemented on the Oregon coast other than a few groin like barbs constructed on Highway 101 at Gold Beach, immediately north of Hunter Creek. Redcar, United Kingdom Hunter Creek, Gold Beach, OR Buck, 2011: https://commons.wikimedia.org/wiki/File:Redcar_MMB_09.jpg Bayocean Natatorium, with damage Tillamook County Pioneer Museum Even Hard Engineering Fails June 1978, Cape Lookout Nov 1984, Cape Lookout Sep 2004, Gleneden Beach Jan 2006, Neskowin What are the implications of coastal engineering structures to the beach? CONCERNS INCLUDE: • Active erosion – Enhanced scour at the toe of the structure (toe erosion) – Focusing of wave energy to other parts of the beach (end effect) • Impoundment (structures ‘lock’ up sand supply) • Passive erosion Active erosion – Toe scour a) Beach with no coastal structure b) Beach impoundment due to construction of seawall or home (note toe scour) c) Beach impoundment due to construction of revetment (After Griggs et al., 1994) End effect or background erosion? Neskowin, Tillamook County. J. Allan DOGAMI Neskowin, Tillamook County. J. Allan DOGAMI Twin Rocks, Tillamook County. Don Best Passive Erosion Effects a) Initial beach profile showing beach width b) Beach response to sea level rise. Dune erodes landward, while beach width remains the same c) Beach response to sea level rise where seawall (or revetment) has fixed the (After Griggs et al., 1994) shoreline position An Oregon challenge… structures may be ‘perched’ on the beach or bedrock Gleneden Beach, Lincoln County. J. Allan DOGAMI Dynamic revetments aka ‘cobble berm’: A form of beach renourishment using ‘gravels’ • Uses gravel size material (~0.5 to 30 cm), ideally rounded, competent rock; • Placement does not require special care (minimal engineering required… may be dumped in place); • Generally less expensive to construct compared with conventional Ventura, CA, P.D. Komar engineering structures. Cost is in transport (can be substantial); • Does not fail when the material moves; • Indistinguishable from natural cobble beaches (providing you use similar type of rock and shape); South Columbia River jetty, Clatsop County. J. Allan DOGAMI Dynamic revetment examples Columbia River Tillamook Cape Lookout South Columbia River jetty, Clatsop County Newport Cape Lookout State Park, Tillamook County HMSC, Lincoln County Surfrider Resort, 2010 BPS Definition Discussion WHAT DO OTHER STATES DO? Washington Shoreline Protection > Governed by “Shoreline Master Programs” > Stipulate where and what type of shoreline stabilization measures are permitted. > Identify a continuum of soft to hard stabilization techniques, with preference for soft solutions. > "Hard" structural stabilization measures refer to those with solid, hard surfaces, such as concrete bulkheads, while "soft" structural measures rely on less rigid materials, such as biotechnical vegetation measures or beach enhancement. There is a range of measures varying from soft to hard … Generally, the harder the construction measure, the greater the impact on shoreline processes, including sediment transport, geomorphology, and biological functions. WAC 173-26-231/241 California Coastal Act Section 30235: Revetments, breakwaters, groins, harbor channels, seawalls, cliff retaining walls, and other such construction that alters natural shoreline processes shall be permitted when required to serve coastal- dependent uses or to protect existing structures or public beaches in danger from erosion and when designed to eliminate or mitigate adverse impacts on local shoreline sand supply. Section 30253: New development shall not require the construction of protective devices that would substantially alter natural landforms along bluffs and cliffs. Referred to as shoreline protective devices (not a legal term) 3 primary physical impacts: encroachment, fixing the back beach, and sand retention California Coastal Act, Chapter 3 Massachusetts > Coastal or Shoreline Engineering Structure means, but is not limited to, any breakwater, bulkhead, groin, jetty, revetment, seawall, weir, riprap or any other structure which by its design alters wave, tidal, current, ice, or sediment transport processes in order to protect inland or upland structures from the effects of such processes. > Structure means any man-made object which is intended to remain in place in, on, over, or under tidelands, Great Ponds, or other waterways. Structure shall include, but is not limited to, any pier, wharf, dam, seawall, weir, boom, breakwater, bulkhead, riprap, revetment, jetty, piles (including mooring piles), line, groin, road, causeway, culvert, bridge, building, parking lot, cable, pipe, pipeline, conduit, tunnel, wire, or pile-held or other permanently fixed float, barge, vessel or aquaculture gear. Code of Massachusetts Regulations, 310 CMR 9.02 Natural & Structural Measures for Shoreline Stabilization https://coast.noaa.gov/digitalcoast/training/living-shorelines.html DLCD BPS Definition Concept #1 BEACHFRONT PROTECTIVE STRUCTURES. Ocean shore erosion control structures designed to remain in a fixed position in order to mitigate the effects of ocean erosion. This includes, but is not limited to, seawalls, rip-rap revetments, wood or steel bulkheads, geotextile sand bags, breakwaters, groins, concrete or mortar reinforcement such as shotcrete, and similar structures. Beachfront protective structures do not include dynamic treatments such as sand nourishment, dynamic gravel or cobble revetments or similar non-structural erosion mitigation measures. DLCD BPS Definition Concept #2 BEACHFRONT PROTECTIVE STRUCTURES. A fixed structure that is intended to remain in a static position with the purpose of reducing wave energy and erosion to development. BPS are purposefully constructed in an ordered and systematic form, intended to maintain that form over time. This includes, but is not limited to, riprap revetments, seawalls, groins, breakwaters, jetties, bulkheads, concrete or mortar reinforcement such as shotcrete, geotextile sand bags, and gabions. Beachfront protective structures do not include dynamic treatments such as sand nourishment,
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