GEOL 106 Lecture 25: GEOL 106. NOTEdocx
25 May 2018
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11.7 Natural Service Functions of Coastal Processes
- tourism by coastal erosion and wave action: cliffs, rocky headlands, sea arches
- without erosion of dunes, cliffs, bluffs inland from beach, or erosion of updrift beaches, there would
be little sand to form beach (e.g. eastern shore of Cape Cod in Massachusetts
- sandy beach natural service functions:
1. transporting and storage of sand
2. supplying sediment to ecosystems like coastal lagoons, estuaries, sand dunes
3. dissipating waves as buffer to coastal erosion (sand helps protect sea cliff from erosion)
4. breaking down pollutants and organic materials
5. cycling nutrients
6. providing nesting and roosting sites for shorebirds and seabirds
7. filtering and discharge of groundwater through beach sand and gravel
8. maintaining biodiversity in coastal zone (e.g. California grunion)
9. providing food sources for migrating and resident shorebirds and fish such as corvine and surf
perch
10. providing valuable cultural aesthetic resource for people as well as recreational opportunities
11.8 Human Interaction with Coastal Processes
- most problems in highly populated and developed areas
o Atlantic, Gulf, Pacific coasts of US, Great Lakes, some parts of Canada
- efforts to stop coastal erosion: engineering structures that impede littoral transport
o these artificial barriers interrupt movement of sand, causing beaches to grow in some areas
and erode in others thus damaging valuable beachfront property
11.3 Cast Study Maryland Barrier Islands pg. 384
- development along coastline here; removal of coastal dunes → shoreline has no protection from
storm waves/ from formation of washover channels by storm surge
- 1933 storm surge from hurricane on Ocean City
- construction of jetties to stabilize Ocean City inlet → Assateague Island have lost about ii m per year
of sand → shoreline retreat: interfered with southward movement of sand
o beaches immediately north of inlet became considerably wider → lengthening of recreational
pier
THE ATLANTIC COAST
- northern Florida to New York
o barrier islands, long narrow islands of sand separated from mainland by lagoon or bay
THE GULF COAST
- coastal erosion is serious problem here
- has numerous barrier islands
- human modification of coastal zone has accelerated erosion by 30 to 40% compared with prehistoric
rates
- caused by coastal engineering structures, subsidence as result of groundwater and petroleum
withdrawal, damming of rivers that supply sand to beaches
THE PACIFIC COAST
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- human modification of Pacific Coast
- trend is for more and accelerated coastal defenses using rock and concrete, seawalls
THE GREAT LAKES
- erosion problems, troublesome on Lake Michigan shoreline
- high lake levels caused by above normal precipitation
- during periods of high water → wave erosion has destroyed many buildings, roads, retaining walls,
other structures
- below average lake level → wide beaches develop that dissipate energy from storm waves and protect
shore
o but as lake level rises, beach becomes narrower, storm waves exert considerable energy
against coastal areas
- erosion of lakeshore bluffs
o alogn Lake Michigan → have eroded back at rate of 0.4 m per year
- severity of erosion depends on:
1. coastal dunes: dune protected bluffs erode at slower rate
2. coastline orientation: sites exposed to high energy storm winds erode faster
3. groundwater seepage: seepage at base of bluff causes slope instability and increased erosion
4. protective structures: engineering structures are locally beneficial but often accelerate
coastal erosion in adjacent areas
- recently, artificial sand has been added to Great Lake beaches → some have been made coarser and
heavier than natural sands → reduce erosion potential
CANADIAN SEACOASTS
- longest ocean coastline in the world
- serious erosion problems
- sandy and muddy beaches are eroding more rapidly than rocky beaches
- entire islands off Nova Scotia have disappeared into se
- Canadian Arctic along Beaufort Sea: high erosion rates
- 1 billion dollars on projects related to coastline including erosion control
11.9 Minimizing the Effects of Coastal Hazards
- interactions among coastal processes are complex → efforts to combat them are often failures or
have unintended consequences
- 2 approaches to stabilizing beach at present location:
1. hard stabilization: engineering structures to protect shoreline from direct wave erosion
2. soft stabilization: adding sand to replace sand that has been eroded from beach = beach
nourishment
HARD STABILIZATION
- seawalls, groins, breakwaters, jetties → improve navigation or retard erosion
- structures interfere with littoral transport of sediment along beach → too often cause undesirable
deposition and erosion in their vicinity
SEAWALLS
- structures on land parallel to coastline to help retard erosion and protect buildings from damage
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- concrete/ large stone blocks (riprap)/ pilings of wood or steel/ cemented sandbags/ other materials
- may not be effective at base of seacliff or lakeside bluff because cliff is eroded from both land and
water
- vertical designs reflects incoming storm waves and redirects energy to shore → can promote beach
erosion over decades and produce narrower beach with less sand
- generally cause environmental and aesthetic degradation → must be tailored to specific sites
- should be used rarely, if ever, where beach preservation is a goal
-
GROINS
- linear structures placed perpendicular to shore usually in groups called groin fields
- designed to trap portion of sand from longshore drift
- small amount of sand collects updrift of each groin → builds irregular but wider beach
- problem: although trapped sand is deposited updrift of groin, erosion occurs downdrift of these
structures because longshore drift has been depleted of sand → groin or groin field results in a wider,
more protected beach in a desired area but causes erosion of adjacent shoreline
- once groin has trapped all sediment it can hold → sand in groin is transported around its offshore end
to continue its journey along beach
- erosion may be minimized by artificially filling each groin
- beach nourishment: requires extracting sane from ocean floor and placing it onto beach
o when nourished, groins will draw less sand from longshore drift and downdrift erosion will be
reduced
o despite beach nourishment etc., groins often cause undesirable erosion in downdrift area →
must carefully evaluate
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
11. 7 natural service functions of coastal processes tourism by coastal erosion and wave action: cliffs, rocky headlands, sea arches. Development along coastline here; removal of coastal dunes shoreline has no protection from storm waves/ from formation of washover channels by storm surge. Northern florida to new york: barrier islands, long narrow islands of sand separated from mainland by lagoon or bay. The gulf coast coastal erosion is serious problem here. Human modification of coastal zone has accelerated erosion by 30 to 40% compared with prehistoric rates caused by coastal engineering structures, subsidence as result of groundwater and petroleum withdrawal, damming of rivers that supply sand to beaches. Human modification of pacific coast trend is for more and accelerated coastal defenses using rock and concrete, seawalls. The great lakes erosion problems, troublesome on lake michigan shoreline. High lake levels caused by above normal precipitation. During periods of high water wave erosion has destroyed many buildings, roads, retaining walls, other structures.
