GEOL 106 Lecture Notes - Lecture 26: Integrated Coastal Zone Management, Coastal Erosion, Coastal Engineering
25 May 2018
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11.10 Perception of and Adjustment to Coastal Hazards
PERCEPTION OF COASTAL HAZARDS
- coastlines are dynamic and shorelines erode, accumulate, move in time frames of months and years
- people’s past eperiee, proiit to oastlie, proailit of sufferig property damage influence
their perception of coastal erosion as a natural hazard
- coastal residents in Bolinas California were likely to experience damage in hear future and were
generally well informed and saw erosion as direct and serious threat
- other people living few hundred meters from possible hazard although aware of hazard, knew little
about its frequency, severity and predictability
- further inland, people were aware coastal erosion exists but had little perception of it as a hazard
- many people do not perceive waves and currents as hazards
o waves that have large heights and wavelengths and plunging waves can be dangerous for
wading and swimming → more powerful than spilling waves that are safe for waders and
swimmers
o rip currents: commonly produced by plunging waves with large wavelengths, are responsible
for 80% of lifeguard rescues on seashore
o people try to enter water where there are few breaking waves → only to be caught in rip
current
ADJUSTMENTS AND MANAGEMENT OF COASTAL HAZARDS
ADJUSTMENTS
- strong currents cannot be prevented, as well as around engineering structures, best adjustments are
improving education about and awareness of conditions that create this hazard
o restrict swimming to supervised locations when lifeguards are on duty
o warnings about rip currents and tidal currents posted
- general beach and surf forecasts issued by National Weather Service
- NOAA’s o COAST esite: ifo aout oastal ae
- for coastal erosion hazard, adjustment categories:
1. beach nourishment that tends to imitate natural processes: soft solution
2. land use change that attempts to avoid problem by not increasing hazard or by relocating
threatened buildings: managed retreat solution (also soft solution)
3. shoreline stabilization through structures like groins and seawalls (hard solution)
a. e.g. seawall can be constructed along entire beach or coastal point of particular
interest may be defended by coastal engineering
MANAGEMENT
- adaptive management and integrated coastal zone management
- adaptive management:
1. includes use of science, statistical analysis, modeling with goal of reducing management
uncertainty
2. promotes sustainable coasts and beaches; sustainability is long term intergenerational
process to help ensure that future generations inherit quality environment
3. communicates alternatives for discussion and negotiation → management is open process
4. recognizes that future change is inevitable and that management can change as conditions
change
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- integrated coastal zone management:
1. to maintain ecological function and integrity of coastal zone
2. to encourage sustainable solutions to coastal zone management
3. to reduce or minimize potential and present conflicts resulting rom development in coastal
zone, use of coastal resources, recreational use of coastal zone
- managing coastal erosion:
1. determine rates of erosion
a. based on historic shoreline change
b. or on statistical analysis of oceanographic environment like waves, wind, sediment
supply that affect coastal erosion
2. committee on coastal erosion management of National Research Council recommends maps
be made showing erosion lines and zones (E liens and E zones)
a. E line: location of expected erosion in give number of years
b. E zones: similar to hazard zones in floodplains
3. NRC recommendations are made concerning setbacks (minimum standards for state or local
coastal erosion management programs)
a. setback: distance from shoreline beyond which development such as homes is
allowed
- ever-increasing coastal defenses in attempt to control erosion
- learning to live with coastal erosion through flexible environmental planning and wise land use in
coastal zone
o most structures in coastal zone are temporary and expendable; only few critical facilities may
be considered permanent
o development must be in best interests of general public rather than for few who profit from
it
- beaches belong to all people to enjoy, not only those fortunate enough to purchase beachfront
property
o e.g. Hawaii, Texas: local property owners cannot deny access to others; virtually all of ocean
beaches are public property and coastal zoning now requires avenues for public access
- 5 principles:
1. coastal erosion is natural process rather than natural hazard
2. any shoreline construction causes change → interferes with natural processes
3. stabilization of coastal zone through engineering structures protects property no the beach
itself
a. most protected property belongs to few people at a large expense to general public
4. engineering structures designed to protect a beach may destroy it in the end
5. once constructed, shoreline engineering structures produce costly trend in coastal
development that is difficult, if not impossible, to reverse
- guidelines to purchasing land:
1. allow for good setback from beach, sea cliff, lakeshore bluff
2. be high enough above water level to avoid flooding and take account rising sea level in making
this determination
3. construct buildings to withstand adverse weather, especially high winds
4. if hurricanes are possibility, be sure there are adequate evacuation routes
11.4 Case Study The Cape Hatteras Lighthouse
- decision was to move structure
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- pg. 393
11.5 Case Study Pointe du Hoc, France
- pg. 394
CHAPTER 7 MASS WASTING
- La Conchita California 2005: tons of water saturated soil and rock tore through upper part of
community
o raining for days prior to slide
o larger landslide occurred in same location in 1995
o neither residents or officials recognized it as a imminent hazard
7.1 An Introduction to Landslides
- mass wasting: any type of downslope movement of earth materials; rapid downslope movement of
rock or soil as a more or less coherent mass
- earthflows, debris flows, rockfalls, avalanches, landslides
SLOPE PROCESSES
- slopes: most common landforms on Earth
o dynamic, evolving systems
o processes that are active in these systems usually do not provide uniform slops
o most slopes are composed of several segments that are either straight or curved
- e.g. El Capitan in Yosemite Valley in Yosemite National Park California
o high cliff face (free face) of hard granite that forms straight, nearly vertical slope segment
o free face and adjacent valley wall regularly shed pieces of rock that accumulate at base of
cliff to form a talus slope
o both free face and talus slops are segments of overall slope → frequent rockfalls keep soil
from developing on free face and much of talus slope
- gentler hillslopes develop on other types of rocks
o e.g. weaker metamorphic rocks and lack a free face
o these slops have 3 segments:
1. upper convex slope
2. straight slope on hillside
3. lower concave slope
- slopes are usually composed of different slope segments:
1. free face: more common on strong hard rocks or in arid environments where there is little
vegetation
2. talus
3. upper convex: more common on softer rocks or in humid environments where thick soil and
vegetation are present
4. straight
5. lower concave slopes: same as upper convex slopes
- which slope segments are presen depends on rock type and climate of area
o there are many exceptions to the general rules depending on local conditions
o e.g. gentle, convex, red coloured slopes in foreground can be formed on weak, easily eroded
metamorphic rock (schist) in semiarid climate on Santa Cruz Island CA
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