GEOL TEST 2

Coast

Area of contact between land and sea - Extend inland until meets a different geographic setting

Shoreline

Precise boundary where water meets adjacent dry land

East Coast

Passive Margin Coastlines (submergent)

Barrier Islands and like sand idk

West Coast

Active Margin Coastlines

Sea cliffs and Rocky coastlines

Two major processes (forces) shape coastline

Waves, Tides

Waves

Waves do erosion (move sediment)

Tides

• Twice daily rise and fall of sea level

• Changes where waves act

how Wave formation

• Wind blowing over water

Size of waves depend on

Wind speed, duration, and distance

• Wind speed

• faster=bigger waves

Wind duration

longer=bigger waves

Distance wind blows (fetch)

further=bigger waves

Wave Characteristics

Length (L), Height (H), Period (T)

Length

Distance between crests or between troughs

Height

Vertical distance between crest and trough

Period

Time for successive waves to pass a fixed point

Waves of Oscillation

(unmoving; further from shore)

Waves of Translation

(moving; closer to shore)

Wave refraction

waves bend as they approach the shore

Longshore currents

• Currents parallel to the beach within the surf zone

• They are the most important to modifying coastlines

Longshore (littoral) drift

Sediment carried by swash and backwash along the beach

Tides

• Another force that occurs along every shoreline

• They are the twice daily rise and fall of the sea, caused by the gravitational attraction of the Moon, and to a lesser degree, the sun

High Water

a water level maximum (high tide)

Low Water

a water level minimum (low tide)

Tidal Range

the difference between high and low tide

Spring Tide

full moon and new moon (14.77 days)

Neap Tide

1st quarter and 3rd quarter (14.77 days)

While waves erosion, its the tides:

change level of beach that waves act on and erosion takes place when waves interact with the bottom

Factors that impact coastlines

• Tectonic setting

• Materials present at the shore

• Energy of water striking the coast

Rifted (passive) continental margins

tend to be dominated by depositional features

Active continental margin

tend to be dominated by erosional features

Erosional and depositional landforms

result of the action of ocean waves

Erosional coasts have

• Sea cliffs

• Sea stacks

• Sea arches

• sea caves

Depositional coasts have

• Beaches

• Spit

• Barrier Island

Wave energy is focused on____

headlands

Headlands

prominent cliffs that jut out into deep water

attack the sides of headlands and form sea caves, sea arches, and sea stacks.

Depositional Coasts

Occurs when amount of sediment exceeds wave/current ability to transport it

Beaches

Relatively narrow strips of sand, pebbles, or cobbles deposited along a shoreline

90% of beach sediment comes from _____ that drain to coast distributed by _____

Streams, Long shore currents

wave action ____, _____, and ____ sediment

erodes, deposits, and moves

The beach is ____ every day

different

Barrier Islands

Long, low, narrow islands parallel to the coastline made of sand that flank main shoreline and separate bays from open ocean. Created by long shore currents

Why are barrier islands unstable

• Easily washed over due to low relief

• Sand migrates constantly with the wind

• Constantly retreating landward with time

Spit

Narrow strip of sand that grows across the mouth of bay due to long shore current (hooks are hook shaped)

• Similar to barrier island but it’s connected to mainland

Settlement in the Dynamic Environment

• Wave - Continues eroding and modifying

• Stability requires protections from waves

Structural approaches to “Controlling” Coastal erosion

• Seawalls

• Groins

• Jetties

non-Structural approaches to “Controlling” Coastal erosion

• Beach nourishment

• Land use planning

Human Interference Dam

Impacts

• Coastal zone short of fresh water

• Cutoff sand supply

  • erosion > deposition

• Reduces protection

Groins

walls built along beach extending into water

• block sand movement along beach

• cause sand to accumulate on up-drift side of groin

Breakwater

A hard, rocky structure built parallel to shore and attached to the sea floor

• A few feet above sea level

• Designed to break waves and make quiet water behind for safe harbor

• intercept waves and protect boat moorings

• provide safe harbors

• radically change shoreline creating sediment deposits

Jetties

Designed to stabilize channel

• Protect channel from large waves and sand deposition

• Constructed in pairs at mouth of a river or inlet

Beach Re-nourishment

Adding sand to beach

• mimics nature but has to be redone

• Aesthetically preferable

• Controversial

  • expensive and temporary fix

Hazards in Coastal areas

• Sea level rise

• hurricanes

• Tsunamis

Sea Level Rise

• Sea level was 120 meters lower during the last ice age

• About 18,000 years ago, sea level began to rise as the glacial ice melted

• In NYC

  • Sea level has risen 40 cm since 1850

  • Global warming is predicted to increase the rate of sea level rise

Hurricanes

• Tropical cyclones (hurricanes, typhoons, etc.)

  • Intense storms that form in tropical waters when ocean is warmest

They uplift water collum

What does a hurricane need?

• High winds

  • Winds up to 200 mph damage buildings

• Heavy rainfall

  • causes floods in area where storm passes over; also downstream

  • Most damaging if it coincides with high tide

Worlds water resources

• Oceans 97%

• Glaciers, Snow, and permafrost 2.05%

• Ground water .593%

• Lakes, swamps, and rivers 0.0147%

• Only 2.7% of globsl water is frshwater. most is locked in ice caps and less than .7% is available for human use

Where is groundwater

• fractures

• space between pores

• cavities

• in the zone of saturation (saturated) below the zone of aeration (unsaturated or partially saturated), split by the water table

What controls groundwater availability

• Precipitation/snow melt - resupply

• Porosity

• Permeability

Porosity in Sediments

• 30% porosity in well sorted sediment

• 15% in poorly sorted sediment

• low porosity in well-sorted, cemented sediment

Permeability

The ease of flow

Aquifer

Storage Bodies, Highly permeable

Aquiclude

Impermeable aquifers

Groundwater flow

• gravity moves groundwater

• AND hydraulic head - pressure

Typical rates of groundwater flow are as follows:

• Ocean currents - 3 km /hour, Steep river channel - 30 km /hour

• Groundwater - 0.00002 km /hour ~ 200 meters/year

Consequences of Groundwater withdrawal

Water table lowering – pumping

• Subsidence - over pumping

• Saltwater intrusion

• Reduced stream flows and may cause shrinking of lakes

• Contamination – domestic/commercial

• Depletion – aquifer can be non renewable

Artesian wells

formed when a well is drilled into a confined aquifer and the neatural pressure causes water to rise toward the ground surface

Water table lowering/pumping

reduced stream flows and may cause shrinking of lakes

subsidence

- overpumping

• depletion

• saltwater contamination

• contamination - domestic/commercial

pumping wells

• forms cones of depression

• reverse flow

• accelerate flow

• cause water table drawdown

• may dry up springs and wells

• reverse flow pf rivers/ contaminate quifer

• dry up rivers and wetlands

Ogallala Aquifer

• Recharged during retreat of continental ice shet — mostly “fossil water” last ice age more than 11000 years ago

• Water reserve was 2B acre feet

Moving water

• california

  • more rain in northeast than south

• Canal system (california aqueduct) built to move

Surface Water

Rain & snowmelt that runs off land surface and collects in lakes and rivers

most easily accessible fresh water

Stream

any body of water that flows in a channel

rivers

large streams

two types of streams

Ephemeral (Intermittent) and permanent

Drainage Basins

Region from which a particular stream gets all it’s water

• Individual drainage basins separated by high topography (drainage divides)

Rivers carry sediment in a number of forms

• suspended load

• dissolved load

• bed load

Competence

size of largest particles carried

• Faster (high velocity) water carries larger particles

Carrying Capacity

quantity of sediment carried by a river

• Depends on velocity of river and amount of water flowing (Discharge)

Discharge

Volume of water moving past a point over a unit time Q=WxDxV

W=average width of river

D=Average depth of river

V=velocity of the water

unit is feet idk kms

Braided streams

Steeper profiles (generally) and can carry coarse sediment (gravel, boulders)

• Found in mountain and glacial regions where there is a lot of snowmelt in spring

Bars

ridge of sediments (middle or along side)

Meandering stream

usually found in lowland areas; slow, with with looping channels

• carry sand, silt, and mud

• Meandering streams are not stable but move back and forth across floodplain

• constantly eroding and depositing sediment

cut bank

outside of loop where erosion takes place

point bar

inside of loop where deposition takes place

Deltas

when a river enters a large body of water, the current slows down

• Sediments carried by the current drop out of the water

• Main channel of river often breaks up into small channels (distributaries)

Floodplains

Areas of flat ground bounding a river channel on either side

• usually narrow in mountains/hills but wide in low-land areas

What is a flood?

• Water coming down a river is more than can fit in the channel

• Water is forced over the bank and flows over the floodplain (overbank flow)

All rivers ____

flood! Some flood at very predictable times (like spring)

Types of floods

• Flash floods

• regional floods

• ice-jam floods

• Dam failure

flood stage

maximum amt of water that can be held in river

Recurrence Interval

Average time between events of a given size

Recurrence interval depends on

• Depends on

  • Climate of region

  • Width of floodplain

  • Size of channel

  • Recurrence interval (T) = (N+1)/m

Upstream flood

• intense rain

• small area

• floods done after rain

• short lived

Downstream flood

• Large area

• lat time - delay (floods awhile after rain

• large volume

• sum of many smaller rivers and streams

• long- lived

because water flows faster during floods _______

more sediment erosion occurs

Much sediment is redeposited when ______

the flood is over

One benefit of flooding sediment redepositing is ____

refertilization of soil on floodplain

Human impacts upon rivers

• civilization

• farming/drainage modifications

• artificial food control