Coastal Erosion

Question 1

• Loss of coastal sediments
• Manifested as shoreline retreat (or landward movement of the shoreline)
• Involves the breaking down and removal of material along a coastline by the movement of wind & water. It leads to the formation of many landforms and, combined with deposition, plays an important role in shaping the coastline. It can be seen in the narrowing of the beach and/or lessening volume of sand on the beach (ie lowering of sand height).
• There is _______ when the sediment supply is higher than the loss, a stable beach when addition and removal are at the same rates and erosion when removal is faster than supply.

Answer 1

Coastal Erosion, Accretion / Accumulation

Question 2

Erosion is greatest along _____? like La Union

Answer 2

Siliclastic Coasts

Question 3

_____ is greatest along siliciclastic coasts, localized in areas with ports, groins and seawalls, place where there are hard structures on the foreshore, and varies across different sites.

Answer 3

Erosion

Question 4

Causes of coastal erosion in the Philippines:

Answer 4

• Shifts in river mouth position
• Beach mining
• Degradation of coastal habitats
• Hard coastal structures
• Sea level rise
• Storms

Question 5

Rerouting of the Agno River channel by the US Army Corps of Engineers in the mid 1930’s to alleviate flooding inland led to _____ in Labrador and land gain in Lingayen.

Answer 5

Erosion

Question 6

Coast fed by the former river mouth →
Coast fed by the presently active river mouth →

Answer 6

Erosion, Accretion

Question 7

• Loosens beach deposits making them more susceptible to erosion

Answer 7

• Pebble Extraction
• Magnetite Sand Mining

Question 8

Removal of sand and gravel →
Removal of an armor that protects the beach from waves →

Answer 8

Volume Loss, Enhanced Erosion

Question 9

In carbonate beaches, the sediment is supplied by organisms that live in nearby habitats such as seagrass meadows and coral reefs. The destruction of these habitats cause the ____ in the number of organisms that could contribute new sand grains. Less supply would mean a _____.

Answer 9

Decline, Slowly Eroding Coastline

Question 10

At least _____ of the energy from wind generated waves is absorbed depending on how healthy these ecosystems are and their physical and ecological characteristics

Answer 10

70-90%

Question 11

Wave breaking occurs near the coast→
Wave breaking occurs on the reef crest→

Answer 11

No Reef, With Fringing Reef

Question 12

• Decrease in sediment supply especially on carbonate islands and purely carbonates coast
• Removal of natural wave buffers

Answer 12

Degradation of Coastal Habitats

Question 13

• Coasts are divided into natural compartments called ____.
• Each cell contains a complete cycle of sedimentation including sources, transport paths, and sinks.
• The presence of sand on any particular beach depends on the transport of sand within the cell.

Answer 13

Littoral Cells

Question 14

______ transfers sediment along the coast naturally. When a solid based pier or port is built along this path, the sediment is _____. In this image we see that most of the sediment are trapped on one side while on the other a deficit/erosion occurs.

Answer 14

Longshore Transport, Obstructed

Question 15

______ are man-made structures designed to trap sand as it is moved down the beach by the longshore drift. When a ______ works as intended, sand moving along the beach in the so-called downdrift direction is trapped on the updrift side of the ______, causing a sand deficit and increasing erosion rates on the downdrift side.

Answer 15

Groin

Question 16

Accretion occurs updrift of it while erosion ensues downdrift due to groins

Answer 16

Shoreline Offset

Question 17

Another man-made structure designed to protect the coast against erosion. Unlike groins, they are built parallel to the shore.

Answer 17

Seawall

Question 18

When a hard structure such a seawall is built along a shoreline undergoing ______, the shoreline will eventually migrate landward to (and potentially beyond) the structure. The effect of this migration will be the gradual loss of beach in front of the seawall as the water deepens and the shoreface moves landward.

Answer 18

Long-term net erosion

Question 19

As Sea Level goes up, the beach is translated landward and upward (R) proportional to the rate of SLR (
Sea Level Rise). Predicted magnitude of erosion is _____ the magnitude of SLR

Answer 19

Bruun Rule, 50-200x

Question 20

Why would sea-level rise cause erosion?

Answer 20

• More landward penetration of waves
• Increases accommodation space for sediments
• Enhances offshore sediment transport

Question 21

Rates of sea level rise in the Philippines is ____ than the global average. Coastal erosion is inevitable.

Answer 21

Higher

Question 22

During ____ coastal erosion can occur rapidly. Hurricanes and other extreme storms generate ______ and ______, eroding the beach and dune system and reshaping the coastal landscape These pictures show the aftermath of a typhoon to islands in Palawan. The loss of sand causes the beach to become narrower and lower in elevation.

Answer 22

Storms, Storm Surges, Large Waves

Question 23

Beaches can recover from storm events provided there is _____ sediment supply.

Answer 23

Sufficient

Question 24

How do we respond to Erosion?

Answer 24

• Establish the trends of coastal erosion
• Identify the possible cause or causes of erosion for mitigation
• Identify possible measures to address coastal erosion

Question 25

• Building at a safe distance from the waterline

Answer 25

Hazard Avoidance

Question 26

____ through processes of accretion and erosion can be analyzed in a geographic information system (GIS) by measuring differences in past and present shoreline locations (NOAA). We can use google earth, shoreline tracing, free satellite images, and topo maps for this analysis. ______ is done using a GPS unit to trace the water line. overlaying historical images will give us a picture whether the coast is accreting, stable or eroding over a certain number of year

Answer 26

Shoreline Change Analysis, Shoreline Tracing

Question 27

Hazard Avoidance Method: _______ where structures of any kind cannot be built on the banks of rivers and streams and the shores of the seas and lakes throughout their entire length within a zone… These zones are subject to the easement of public use only for recreation, navigation, floatation, fishing and salvage.

Answer 27

Implementation of Easement Policy

Question 28

Erosion response where the need to relocate communities from chronically eroding or erosion-prone areas (e.g., river deltas)

Answer 28

Relocation

Question 29

Erosion Response where we protect the coast but hard structures should be our last option

Answer 29

Coastal Protection

Question 30

Soft measure where it involves adding sand of same quality (e.g, same grain size and color) to the beach, dune or nearshore area

Answer 30

Beach Nourishment

Question 31

Soft measure where they serve as source of sediment and traps for sediment, they serve as natural wave attenuators

Answer 31

Rehabilitation of coral reefs, seagrasses and mangroves

Question 32

A _____ to addressing shoreline erosion is necessary as the natural processes and human activities that cause shoreline erosion do not follow political jurisdictional boundaries.

Answer 32

Regional Approach