Coastal Geology I: Coasts and Beaches

September 30^th

Karl F. Nordstrom

Read and know Sverdrup (2004) Chapter 12, pp. 300-320; review your notes on waves.

Coastal characteristics

    Large temporal and spatial scale (due to tectonics, geologic structure and climate change)

         Primary (non-coastal origin) and secondary coasts

         Evolution over long term (hundreds to thousands of years)

         Coastal types: tectonic, fjord, moraine, drowned valley (ria), delta, barrier island, barred                              (with spits), reef, mangrove and salt marsh

    Beaches and dunes are critical elements at smaller temporal and spatial scale

    Sources and sinks for beach materials

         Affect sediment budgets, locations of erosion/deposition and characteristics of beach materials

         Sources: eroding headlands and other coastal formations, streams, artificial nourishment

         Sinks: submarine canyons, inlets (not a permanent loss), shore protection structures

    Human alterations (dominant in many locations)

Beach change

    Onshore-offshore sediment transport (storm cycles)

         Onshore winds

             Blow water onshore and raise water levels (create offshore current at depth)

             Increase wave heights and turbulence

             Saturate upper beach and cause erosion

             Create a flatter, upper beach and a break point bar

             Cause dune erosion and overwash

         Offshore winds

             Blow water offshore and lower water levels (create onshore current at depth)

             Decrease wave heights and turbulence (water percolates into beach and deposition occurs)

             Post-storm wave action replaces beach but not dune

    Dynamic equilibrium (great short-term mobility but a return to pre-disturbance conditions)

    Pre-disturbance conditions not achieved where sediment or space restricted

    Longshore transport is a major cause of sediment loss

         Waves break at angles, causing longshore flow

         Sediment in suspension in turbulent surf and swash moves alongshore (downdrift)

    Landforms migrate onshore and alongshore in response to sediment budgets and sea level rise

         Sediment transported to spits and into inlets

         Overwash converts bay bottoms to marsh; marsh to upland

         Many natural features can be re-established farther inland if space is available

Coastal construction (buildings and infrastructure)

    Structures prevent landforms from migrating landward

    Buildings often built too close to water

    Beach erosion is followed by subsequent damage to landward structures by waves

    Destruction/reconstruction cycles (structures rebuilt Òbigger and betterÓ)

Shore protection strategies

    Shore-perpendicular structures

         Groins (on beach)

             Trap sand but do not prevent the mechanism for longshore transport

             Accretion occurs updrift and erosion occurs downdrift

             Diversion of some sediment offshore to form bars

             New groins rebuilt to allow some sand to pass (e.g. notched groins in NJ)

         Jetties (at inlets)

             Prevent deposition in navigation channel (accretion updrift and erosion downdrift)

             Confine tidal flows, scouring channel

    Shore-parallel walls

         Bulkheads (backup protection to beach; hold upland in place)

         Seawalls (large, freestanding structures that provide protection against direct wave attack)

         Revetments (diminish wave energy through runup)

         Bigger/better structures must be built as erosion of beach continues

    Breakwaters (costly; sand starvation downdrift still a problem)

    Beach nourishment

         Now is the principal choice for shore protection

         Increases long-term management options

         Sand usually brought to beach from offshore by pipeline or from land source by truck and reshaped

         Requires long-term periodic commitment

         Borrow sources may be finite

    Sand backpassing

         Lonshore recycling of sediment

         Way of overcoming diminishing sources for nourishment projects

    Sand bypassing

         Usually at inlets but rare

    Dunes (natural feature treated here as human artifact because of widespread modification)

         Direct protection against overwash and flooding

         Sand in storage that can replace losses on beach

         Unique habitat (often ignored in management actions)

         Sand fences speed growth; vegetation plantings stabilize surface

         Battleground for land use wars because of location between beach and development

    Grading (bulldozing)

         Easily accomplished

         Usually a post-storm response

         Creates a landform with different internal characteristics and growing conditions

Land use controls and construction criteria

    Restriction zones (maintain natural protection; prevent economic loss, protect threatened species)

    NJ Coastal Area Facilities Review Act

         Restricts construction and sand removal

    Endangered species program

         Controls access by vehicles, pedestrians

    Municipal actions critical: zoning regulations, dune building operations

    Compatible designs (reduce loss to buildings)

         Required in Federal Insurance Administration program

             Elevate above flood levels and waves

             Make windproof (rare)

Implications for future management

         Retreat or protect buildings in place?

         Maintain beaches as artifacts or natural systems?

Coastal Geology II: The New Jersey Shore and Beach Management

October 1^st

Delaware Bay shore

    Barrier beach transgressing (moving landward) over marsh in north and eroding upland in south

    Dominant waves generated locally by winds blowing across the bay

    Wave energies low (relative to ocean)

         Short fetch distance (max 45 km) for wave generation

         Wave height about 0.5 m and period about 4.5 s with strong onshore winds

    Narrow beach (20 m) due to low-energy waves

    Low dune heights (<2.5 m) due to limited source of sand

    Erosion still occurs despite low wave energies

Cape May

    Terminal groins at western end of city

         Classic case of sand starvation downdrift

         Erosion of undeveloped land downdrift not considered a problem in past

         Changing perception of value of eroding natural habitat

             Natural area now protected using beach nourishment (new precedent)

    Seawall along city required because beach eliminated due to jetties at Cape May Inlet

    Corps nourishment project implemented to overcome sand deficit

    Flat beach maintained as recreation platform and raked to eliminate litter (common in NJ)

         Natural topography and vegetation prevented by raking

The barrier island coast

    Barrier islands form on flat coast as equilibrium (wave created and shaped) feature

    Coast is flat because it is a coastal plain, reworked by waves at higher water levels in past

         Inundation during Cretaceous period (e.g. where pine barrens are)

         Pleistocene reworking created former barrier island at marsh margin along G.S. Parkway

    Barrier islands separated by inlets that are now major controls on shoreline changes

Cape May Inlet

    Good example of sand starvation downdrift (at Cape May) with accretion updrift (Wildwood Crest)

    Sand bypass included in design but not implemented due to cost; problem at many inlets with jetties

Wildwood and Hereford Inlet

    Beach too wide for many tourists - a rare problem

    Accretion caused by sand transported past Hereford Inlet; new shore not built upon

    Dune not desired or allowed to grow because it would interfere with view of sea, access

Inlet dynamics (Figure 1 in handout)

    Natural changes are cyclic and involve breaches in the ebb tidal delta or updrift barrier island

    Longshore transport brings sediment to inlet, filling channel

    Downdrift deflection of channel erodes tip of next barrier island downdrift

    Ebb tidal flows deposit sediment at mouth of channel near downdrift shoreline

    Ebb delta protects shoreline downdrift

    Result is accretionary bulge in barrier island downdrift

    Changes in erosion and deposition zones when breaches occur

         Ebb delta breaching

             Flooding through ebb delta during storms creates new channel updrift

             New channel becomes more efficient and captures tidal flow

             Previous channel shoals and sediment is driven onshore to downdrift barrier

             New channel is later deflected downdrift due to net drift, completing cycle

         Barrier breaching

             Dramatic changes to shoreline; more common before intensive human development

             Updrift barrier low and narrow due to rapid accretion (easily breached)

             Flow through breach scours channel that becomes more efficient

             Former (downdrift) channel shoals; sand driven onshore by waves to downdrift island

             Channel deflected downdrift by new longshore transport, returning to initial condition

             Breaching of updrift barrier now prevented in many locations by shore protection structures

    Jetties and shore protection structures at other inlets have greatly reduced natural mobility (Figure 2)

Avalon

    Example of how natural values can be retained or restored given appreciation of dunes

    Remnant high dunes provide example of vegetation that once characterized other NJ barriers

    Section of properties purchased after storm of March 1962

         Memory of storm had not faded; post-storm accretion had not occurred; owners willing to sell

         Beach in this area not needed for protection; sand used as source to fill other areas

         Residents accept dunes as a viable means of protecting properties

    Beaches and dunes in eroding part of town built up using municipal earth-moving equipment

         Dune higher than natural dune because it is designed as barrier for hurricane protection

         Surface un-natural (sediment dumped; composed of coarse material not transported by wind)

         Planted with single species  - American beach grass (Ammophila breviligulata)

         Vegetation evolves (species diversity, aesthetic appeal and natural function

    Examples of use of geotextiles

         Used in the same way as rock structure but temporary (breakwater at Townsend Inlet)

         Used as resistant membrane within dune (near 8^th Street)

Sea Isle City

    Narrow beach, dune insufficient for protection (slated for beach nourishment like most NJ towns)

    Example of ÒdisposalÓ dune

    Groin field creates seaward bulge in shoreline; slower rate of erosion where shore is protected

    Condominiums near beach create eddies; alter wind direction and sand transport; scour beach

         Increase wind-blown sand hazard

         NJ CAFRA regulations prevent new high rises near beach, except Atlantic City, Long Branch

Strathmere

    Whale Beach severely damaged in March 1962 storm

         Seaward row of buildings destroyed

         One of few locations where building line following storm was not the same as pre-storm line

         Maintained in vulnerable state by short-term projects

             Protected because shorefront road is required for coastal access and as evacuation route

             Dune replaced in trucking operation following each moderate-intensity storm

    Corson Inlet example of sand bypassing inlet through transport on ebb tide delta

Ocean City

    Beach nourishment has created wide beach and opportunity for restoration of natural values

         Beach replenishes volume of sand but does not necessarily restore natural environments

         Many residents prefer flat, raked beach and landscape typical of suburbs

             Nourished beach initially managed for one value (recreation)

             Only the beach below the upper limit of normal wave uprush may function naturally

             Result is loss of natural image and environmental heritage

         Municipality built dunes using fences and plantings of American beach grass

         Prevention of trampling and raking to protect piping plovers resulted in incipient dunes seaward

         Dune has new ecological value and increased value for aesthetics and nature-based tourism

         Residents still want view of sea, making large dune difficult to achieve (lawsuit)

Absecon Island

    Margate/Longport examples of flat raked beach (little value other than as unattractive platform)

         Were approved for nourished beach, but state required dune, and residents refused

    Atlantic City (good example of effects of high rise structures on beach)

         Dune considered compatible despite intensive development (enlightened beach manager)

         Dune partially bulldozed and has geotube buried within it to provide backup erosion protection

Brigantine

    Jetty updrift of Absecon inlet created wide beach/dune

         Natural features survive because new construction not allowed in accreting area

         North end of island undeveloped but dune not completely natural because fences used

    Little Beach (next island to north) is only undeveloped barrier island in state (Brigantine Refuge)

Long Beach Island

    Sand starvation of southern tip of island due to protection structures updrift

         Rapid erosion and inability of dunes to build up to establish cross-shore environmental gradients

         Reveals problem of trying to establish undeveloped natural enclaves near developed areas

    Narrow beach, dune and barrier in developed areas result in great vulnerability to hazard

         Storm damage and rebuilding on this island were presented in previous lecture (3-part photo)

Island Beach State Park

    Undeveloped, but not completely natural because fences used to repair breaches in dune

    Dune is linear and lacks topographic and vegetational diversity associated with dynamism

Bay beach at Seaside

    Short fetch for wave generation across Barnegat Bay (lagoon)

    Smaller beach than beach in Delaware Bay because wave heights, periods and tidal range smaller

    Flooding and erosion problems still occur because human structures too low and close to bay shore

Lavallette

    Example of low, narrow, linear dune representing compromise between protection and view

    Residents reluctantly accepted dune as a condition of obtaining money for post storm repairs

    Here, as at Avalon and Ocean City, evidence for eventual public support of restoration

Headlands section of NJ coast (Manasquan to Long Branch)

    Streams create inlets and interfere with transportation (many artificially closed)

    Manasquan Inlet

         Net transport of sand to north in northern NJ because of sheltering effect of Long Island

         Another example of jetties creating accretion updrift and erosion downdrift

             Private ownership of beach prevents sand bypass

             Groins (now beach nourishment) used to mitigate downdrift erosion

         Jetties create more stable inlet and allow development closer to throat (natural features lost)

    Manasquan example of landform disequilibrium and sand inundation caused by attempt to maintain views

Northern spit zone

    Sea Bright/Monmouth Beach

         Seawall prevents inlet from forming and remaining

         Example of use of beach fill to protect a protection structure (value of fill questioned)

         Reveals that seawall not end stage in development of an eroding developed coast

    Sandy Hook

         Erosion in south (accentuated by seawall); deposition in north

         Sand starvation in south resulted in need for beach fill; sediment then moves north

         Beach nourishment allowed by NPS because the spit is a recreation area, not a natl. park

Raritan Bay

    Eroding upland; narrow beaches similar to Delaware Bay (similar tide, waves)

    Natural beaches truncated by structures; new nourished beaches and dunes overly large

    Beaches used because close to population centers; low energies favorable for children, waders