Lecture 5: Streams and the Hydrologic Cycle found in polar regions, high mountain ranges, and some subpolar

regions around the world.

EARTH AS A SYSTEM: THE HYDROLOGIC CYCLE They play a significant role in shaping landscapes, contributing to
the Earth's hydrological cycle, and influencing global climate
Water is constantly moving among Earth’s different spheres—the patterns.
hydrosphere, the atmosphere, the geosphere, and the
biosphere. ICE SHEETS
This unending circulation of water is called the hydrologic
cycle. massive expanses of ice that cover large areas of land, primarily
Earth is the only planet in the solar system that has a global in polar regions.
ocean and a hydrologic cycle. distinct from glaciers in that they are not confined to valleys or
mountains but instead spread out over extensive flat or gently
EARTH’S WATER sloping terrain.
Water is almost everywhere—in the oceans, glaciers, rivers, GROUNDWATER
lakes, air, soil, and living tissue.
All these “reservoirs” constitute Earth’s hydrosphere. Groundwater refers to water that is located beneath the Earth's
In all, the water content of the hydrosphere is an estimated 1.36 surface in soil pore spaces, fractures, rock layers, or other
billion cubic kilometers (326 million cubic miles). geological formations.
The vast bulk of it, about 96.5 percent, is stored in the global crucial component of the Earth's hydrological cycle, interacting
ocean. with surface water bodies such as rivers, lakes, and wetlands, as
Ice sheets and glaciers account for an additional 1.76 percent, well as with the atmosphere through processes like evaporation
leaving just slightly more than 2 percent to be divided among and precipitation.
lakes, streams, groundwater, and the atmosphere.
ATMOSPHERE
OCEANS
Water in the atmosphere plays a crucial role in Earth's climate
An ocean is a vast body of salt water that covers a significant system and weather processes.
portion of Earth's surface
RIVERS
OCEANS VS. SEAS
atural flowing watercourse that moves water from higher
Oceans are deeper than seas elevations to lower elevations, typically draining into a larger body
Oceans are vast bodies of water that surround continents, while of water such as an ocean, sea, lake, or another river.
seas are generally smaller and partially enclosed by land
Oceans tend to have a more consistent and higher salinity 1. Nile River
(salt content) compared to seas. the longest river in the world
located in NE Africa
SEAS IN THE PHILIPPINES has a total length of approximately 6,650 kilometers (4,130 miles),
making it the longest river globally based on traditional definitions
South China Sea Visayan Sea
that measure from the source to the mouth.
Philippine Sea Samar Sea
Bohol Sea Celebes Sea
Sibuyan Sea Sulu Sea 2. Amazon River
Camotes Sea Found in South America
largest river in the world by volume of water discharged and by
drainage area.
SALINE LAKES carries more water than any other river, contributing about 20% of
the total river flow into the world’s oceans.
bodies of water that have a high concentration of dissolved salts,
typically much higher than freshwater lakes but lower than
3. Cagayan River
seawater.
Rio Grande de Cagayan
The term "saline" refers to the presence of salt, usually in the
Longest river in the Philippines (505 km long)
form of sodium chloride (table salt), although other salts such as
It originates in the Caraballo Mountains and flows through several
magnesium, calcium, and potassium salts can also contribute to
provinces, including Nueva Vizcaya, Quirino, Isabela and
salinity.
Cagayan.
DEAD SEA
SWAMP
Also known as the “salt sea”
A type of wetland characterized by saturated muddy, and often
It’s technically not a sea at all, but a landlocked Salt Lake
partially submerged land.
between Jordan and Israel.
Are typically found in low-lying areas, along riverbanks, and in
Its waters are mainly drawn from the Jordan River, and the high
coastal regions.
salinity means no life can survive here (hence insightguides.com
the “Dead” in its name) SOIL MOISTURE
The extremely high concentration of dissolved mineral salts in the
water causes the water to be denser than that of plain fresh water. amount of water present in the soil, including both liquid and
Since our body weight is lighter (less dense) than the density of vapor phases.
the water, our body is more buoyant in the Dead Sea, making it
easy to float LAKE (Freshwater)

GLACIERS contains water with low salinity or salt content, typically less than
0.5 parts per thousand (ppt)
large, persistent body of ice that forms over many years as snow They do not have direct connections to the ocean or sea.
accumulates and compresses into dense ice.
1. Lake Baikal Because the total amount of water vapor in the atmosphere
Siberia, Russia remains about the same, the average annual precipitation
is the deepest (1.6 km) and oldest freshwater lake in the world. worldwide must be equal to the quantity of water evaporated.
it holds about 20% of the world’s unfrozen freshwater, making it Conversely, over the oceans, evaporation exceeds precipitation.
the largest freshwater lake by volume. Because the level of the world ocean is not dropping, the system
must be in balance.
2. Pinatubo crater lake In the diagram, the 36,000 cubic kilometers of water that annually
a body of water formed within the caldera of Mt. Pinatubo. makes its way from the land to the ocean causes enormous
June 15, 1991 – caldera was created during the cataclysmic erosion.
eruption of Mt. Pinatubo In fact, this immense volume of moving water is the single most
After the eruption, a crater lake began to form within the caldera important agent sculpting Earth’s land surface.
as rainwater and groundwater accumulated in the depression left
by the eruption. WEATHERING EROSION
involves the physical breakdown (disintegration) the removal and transport
3. Laguna de Bay and chemical alteration (decomposition) of rock of weathered rock material
Found in Luzon at or near Earth’s surface by water, wind, or ice
Largest freshwater lake in the Philippines in terms of surface area
(900 km2) is fed by 21 rivers
RUNNING WATER
SNOW AND ICE
Much of the precipitation that falls on land either soaks into the
collectively hold a significant portion of the Earth’s freshwater ground (infiltration) or remains at the surface, moving downslope
reserves. as runoff.
The amount of water that runs off compared to the amount that
WATER’S PATHS infiltrates depend on several factors:
❖ the intensity and duration of rainfall
The hydrologic cycle is a gigantic, worldwide system powered by ❖ the amount of water already in the soil
energy from the Sun, in which the atmosphere provides a vital link ❖ the nature of the surface material
between the oceans and continents. ❖ the slope of the land
Evaporation: liquid water changes into water vapor (gas), is how ❖ the extent and type of vegetation
water enters the atmosphere from the ocean and, to a much When the surface material is impermeable or when it becomes
lesser extent, from the continents. saturated, runoff is the dominant process.
Winds transport this moisture-laden air, often great distances. Runoff is also high where slopes are steep and in cities where
Complex processes of cloud formation eventually result in large areas are covered with impermeable buildings, roads, and
precipitation. parking lots.
The precipitation that falls into the ocean has completed its cycle
and is ready to begin another. The water that falls on the SHEET FLOW
continents, however, must make its way back to the ocean.
What happens to precipitation once it has fallen on land? is a type of water flow that occurs when water moves evenly over
A portion of the water soaks into the ground (called infiltration), a surface in a thin, continuous layer
slowly moving downward, then moving laterally, and finally it is characterized by a relatively uniform distribution of water
seeping into lakes, streams, or directly into the ocean. across a surface, often resembling a "sheet" of water flowing in a
When the rate of rainfall exceeds the ground’s ability to absorb it, broad, shallow manner
the surplus water flows over the surface into lakes and streams, a unconfined
process called runoff.
RILLS
Much of the water that infiltrates or runs off eventually returns to
the atmosphere because of evaporation from the soil, lakes, and sheet flow eventually develops threads of current that form tiny
streams. channels called rills
Also, some of the water that soaks into the ground is absorbed by are small channels or grooves that form on the surface of soil or
plants, which then release it into the atmosphere. loose sediment due to the erosion caused by flowing water
This process is called transpiration. they are typically narrow and shallow, ranging from a few
Because both evaporation and transpiration involve the transfer of millimeters to a few centimeters in depth and width
water from the surface directly to the atmosphere, they are often
considered together as the combined process of GULLIES
evapotranspiration.
Rills meet to form gullies
STORAGE IN GLACIERS are larger and deeper channels than rills, characterized by more
significant erosion and excavation of the soil or rock substrate
When precipitation falls in very cold places—at high elevations or they are typically several centimeters to meters wide and deep,
high latitudes— the water may not immediately soak in, run off, or with steep sides and a distinct channel shape
evaporate. When gullies reach an undefined size, they are called rivers.
Instead, it may become part of a snowfield or a glacier. In this
way, glaciers store large quantities of water on land. STREAMS RIVERS
If present-day glaciers were to melt and release all their water, Water that flows in a a general term for streams that carry substantial
sea level would rise by several dozen meters. channel, regardless of size amounts of water and have numerous tributaries
Such a rise would submerge many heavily populated coastal
areas.
TRIBUTARY
WATER BALANCE
smaller river or stream that flows into a larger river, lake, or
The figure shows the Earth’s overall water balance, or the volume another body of water
of water that passes through each part of the cycle annually. Every stream drains an area of land called a drainage basin, or
The amount of water vapor in the air at any one time is just a tiny watershed
fraction of Earth’s total water supply. T
 Each drainage basin is bounded by an imaginary line called a
divide, something that is clearly visible as a sharp ridge in some 4. Trellis pattern
mountainous areas but can be more difficult to determine when rectangular drainage pattern in which tributary streams are nearly
the topography is subdued parallel to one another and have the appearance of a garden
The outlet, where the stream exits the drainage basin, is at a trellis
lower elevation than the rest of the basin. forms in areas underlain by alternating bands of resistant and less
-resistant rock and is particularly well displayed in the folded
DRAINAGE BASINS Appalachian Mountains, where both weak and strong strata
outcrop in nearly parallel belts
Drainage divides range in scale from a small ridge separating two
gullies on a hillside to a continental divide that splits an entire WATER GAPS
continent into enormous watersheds.
occur where a stream cuts across ridges of resistant rock
RIVER SYSTEM
STREAMFLOW CHARACTERISTICS
Includes not only its network of stream channels but its entire
drainage basin The water in stream and river channels moves under the
divided into 3zones based on the process that dominates in each. influence of gravity.

THREE ZONES IN A RIVER SYSTEM TWO TYPES OF STREAMFLOW

1. Zone of Sediment Production 1. Laminar flow

where most of the sediment is derived Water moves in nearly straight-line paths parallel to the stream
located in the headwaters region of the river system channel
Much of the sediment carried by streams begins as bedrock that
is subsequently broken down by weathering and then moved 2. Turbulent flow
downslope by mass wasting and by way of sheet flow and rills. movement of water is characterized by irregular and fluctuating
motions
2. Zone of Sediment Transport Strong turbulent behavior occurs in whirlpool and eddies, as well
Downstream from the zone of sediment production, sediment as in roiling whitewater rapids.
acquired by a stream is transported through the channel network Even streams that appear smooth on the surface often exhibit
along sections referred to as trunk streams. turbulent flow near the bottom and sides of the channel, where
When trunk streams are in balance, the amount of sediment flow resistance is greatest.
eroded from their banks equals the amount deposited elsewhere
in the channel WHITEWATER RAPIDS

section of a river or stream where the water flows rapidly over

3. Zone of Sediment Deposition
irregularities such as rocks, boulders, or other obstacles, creating
When a river approaches the ocean or another large body of
turbulent and frothy white water.
water, it slows, and the energy to transport sediment is greatly
reduced. FACTORS AFFECTING FLOW VELOCITY:
Most of the sediments either accumulate at the mouth of the river
to form a delta, are reconfigured by wave action to form a variety 1. Channel slope or gradient
of coastal features, or are moved far offshore Gradient: the slope of a stream channel, expressed as the
vertical drop of a stream over a specified distance
DRAINAGE PATTERN
When the gradient is steeper, more gravitational energy is
Drainage systems, which are interconnected networks of streams, available to drive channel flow.
can exhibit a variety of patterns.
The pattern that develops depends primarily on the kind of rock 2. Channel cross-sectional shape
present and/or the structural pattern of joints, faults, and folds. As water in a stream channel move, it encounters a significant
amount of frictional resistance.
TYPES OF DRAINAGE PATTERNS The cross-sectional shape (a slice taken across the channel)
determines, to a large extent, the amount of flow in contact with
1. Dendritic pattern the banks and bed of the channel.
it is the most common drainage pattern This measure is referred to as the wetted perimeter.
resembles the branching pattern of a deciduous tree (dendritic The most efficient channel is one with the least wetted perimeter
means “treelike”) for its cross-sectional area.
forms where the underlying material is relatively uniform in its In the figure in the right, although the crosssectional areas of the
resistance to erosion and hence does not control the pattern of two are identical, the narrow and deep one has less water in
streamflow contact with the channel (a smaller wetted perimeter) and
determined chiefly by the direction of slope of the land therefore less frictional drag.

2. Radial pattern 3. Channel size and roughness

when streams diverge from a central area like spokes from the All other factors being equal, flow velocities are higher in large
hub of a wheel channels than in small channels.
develops on isolated volcanic cones and domal uplifts The depth of the water in a given channel also affects the
frictional resistance that the channel exerts on flow.
3. Rectangular pattern A final factor is how rough a channel is.
exhibits many right -angle bends Elements such as boulders, irregularities in the channel bed, and
develops when the bedrock is crisscrossed by a series of joints woody debris create turbulence that significantly reduces flow
and/or faults velocity.
Because fractured rock tends to weather and erode more easily
than unbroken rock, the geometric pattern of joints guides the
paths of streams as they carve their valleys
 DISCHARGE The sediments carried by the river are deposited along its banks,
creating floodplains
The size of a stream channel is largely determined by the amount
of water supplied from the drainage basin FLOODPLAINS
used to compare the size of streams
volume of water flowing past a certain point in a given unit of time a flat or nearly flat land adjacent to a stream or river that
measured in cubic meters per second or cubic feet per second experiences periodic flooding
determined by multiplying a stream’s cross-sectional area by its are natural features of river systems and are formed by the
velocity deposition of sediment carried by the river during

STREAM EROSION RIVER BED

Streams cut channels into bedrock through three main processes: is the bottom surface of a river channel, where the water flows

1. Quarrying RIVER BANK

involves the removal of blocks from the bed of a stream channel.
refers to the sides of the river channel, the area that contains the
result of the impact forces exerted by flowing water.
water within its boundaries
2. Abrasion TYPES OF STREAMS VALLEYS
The process by which the bed and banks of a bedrock channel
are ceaselessly bombarded by particles carried into the flow 1. V-shaped Valleys
formed through erosional processes, typically in mountainous or
3. Corrosion upland areas where rivers cut down through resistant rock layers
a process in which rock is gradually dissolved by the flowing have steep sides and a narrow channel at the bottom, often found
water in regions with active tectonics or glaciation

POTHOLES 2. U-shaped Valleys

commonly found in mountainous regions, particularly those
Circular depressions which are created by the abrasive action of
affected by glaciation
particles moving in fast-moving eddies
wider and more gently sloping than V -shaped valleys, with a
TRANSPORT OF SEDIMENTS BY STREAMS: characteristic U -shaped cross -section resulting from the erosive
action of glaciers
Streams transport their load of sediment in three ways
❖ in solution (dissolved load) 3. Submarine Valleys
❖ in suspension (suspended load) found underwater and are formed by processes such as erosion
❖ by sliding, skipping, or rolling along the bottom (bed load) by submarine currents or the collapse of underwater slopes
can be quite large and may influence ocean circulation patterns
DEPOSITION OF SEDIMENT BY STREAMS
WATERFALLS
Deposition occurs whenever a stream slows, causing a reduction
in competence. natural phenomenon where a river or stream flows over a vertical
drop or a series of steep steps in its course
CAPACITY COMPETENCE formed through erosional processes as water erodes the
The maximum load of solid It is a measure of a stream’s ability to underlying rock layers, typically resulting in the creation of
particles a stream can transport transport particles based on size rather cascades, plunges, or horsetails.
per unit time than quantity. Cascade: characterized by water flowing over a series of rock
steps or ledges, creating a stepped or tiered appearance
Plunges: a vertical drop where water falls freely without making
Put another way, particles are deposited when the flow velocity is
contact with the underlying rock surface
less than the settling velocity.
Horsetail: water maintaining contact with the underlying rock
As a stream’s flow velocity decreases, sediment begins to settle,
surface as it cascades down, creating a broad, fan-like shape
largest particles first.
are often formed in areas where a river encounters a sudden
FLOW VELOCITY SETTING VELOCITY change in elevation, such as a cliff or a resistant rock layer
It refers to the speed at Pertains to the speed at which sediment The force of the flowing water gradually erodes the rock, creating
which water moves within a particles, once suspended in water, settle to the a vertical drop.
river riverbed due to gravity. The rate of erosion depends on factors such as the volume of
water, the speed of flow, and the type of rock

STREAM VALLEY ANGEL FALLS

consists of a channel and the surrounding terrain that directs world's tallest waterfall, with a total height of 979 meters (3,212 ft)
water to the stream can be found in Venezuela
includes the valley floor, which is the lower, flatter area that is It plunges uninterrupted for 807 meters (2 ,648 feet) from the
partially or totally occupied by the stream channel, and the sloping summit of Auyán -Tepuí in the Canaima National Park
valley walls that rise above the valley floor on both sides
ALIWAGWAG FALLS
How do stream valleys form?
highest waterfalls in the Philippines with more than 130
formed through a combination of erosional and depositional cascading waterfalls and a stair-like boulder formation
processes Cateel, Davao Oriental, Mindanao
Over time, flowing water erodes the surrounding rock and soil,
carving out a channel
FLOODS SHORELINE

part of the natural behavior of a stream and occur when the flow line that marks the contact between land and sea
of a stream becomes so great that it exceeds the capacity of its Each day, as tides rise and fall, the position of the shoreline
channel and overflows its banks migrates.
Over longer time spans, as sea level rises or falls, the average
TYPES OF FLOODS position of the shoreline gradually shifts.
specific interface or line where land and water meet;
1. REGIONAL FLOODS dynamic place that can change rapidly in response to natural
occur over a larger geographical area, such as a region or forces.
multiple regions, rather than being confined to a single river basin
or locality SHORE
typically triggered by significant weather events, such as heavy
rainfall, snowmelt, tropical storms, or hurricanes, which affect a land along the edge of a body of water
broad area
COAST
2. FLASH FLOODS
a rapid and intense flooding event that occurs within a short larger geographical region that includes the shore as well as the
period, typically within six hours of heavy rainfall, a dam or levee adjacent land area
failure, or sudden snowmelt
BEACH
can strike suddenly, without warning, and with great force
swift rise in water levels, powerful currents, and the potential to accumulation of sediment found along the landward margin of a
cause significant damage to infrastructure and endanger lives water body

3. DAM-FAILURE FLOODS BEACHES IN THE PHILIPPINES

occur when a dam, which is a barrier constructed to hold back
water and create a reservoir, fails to contain the water it's 1. Boracay (Aklan)
designed to control White sand- due to skeletons of shells of foraminiferas (single-
can result from various causes, including structural weaknesses, celled marine organisms), collars, and other organisms
overtopping due to excessive inflows, foundation instability, piping
or erosion of the dam structure, or even deliberate sabotage 2. Black sand beaches in Albay
Black sand- the result of eroded volcanic materials such as
FLOOD CONTROL basalts (dark-colored volcanic rocks)

1. ARTIFICIAL LEVEES 3. Sila Island (Northern Samar)

earthen mounds built on river banks to increase the volume of Pink sand- originally white-colored sand beach turned pinkish
water the channel can hold ever since washed-up red-colored corals spread all over time

❖ Levees 4. Valugan Beach (Batanes)

➢ are embankments or barriers built along riverbanks or Boulder Beach- huge andesite boulders were produced by Mt.
coastlines to prevent flooding by confining water within a Iraya volcano and these boulders were broken down, polished,
certain area and rounded by strong waves in Batanes.
➢ They are typically constructed using compacted soil,
concrete, or other materials and are often reinforced with COASTLINE
vegetation or structural supports.
2. CHANNELIZATION much broader boundary between land and water
involves altering a stream channel in order to make the flow more has features, including rocky cliffs, sandy beaches, or marshy
efficient shores
This may simply involve clearing a channel of obstructions or subject to erosion and other natural procedures.
dredging a channel to make it wider and deeper
WAVE-CUT CLIFF
3. FLOOD CONTROL DAMS
also known as simply cliff or a coastal cliff
built to store floodwater and then release it slowly, in a controlled
formed by the erosion of waves against a coastline
manner.
BERM
LECTURE 6: COASTAL ZONES AND PROCESSES
nearly horizontal or gently sloping strip of land or sand found
THE SHORELINE AND OCEAN WAVES
along the backshore of a beach.
The restless water of the ocean is constantly in motion.
FORESHORE
Winds generate surface currents, the gravity of the moon and sun
procedures tides, and density differences create deep ocean part of the shore exposed at low tide and submerged at high tide
circulation. area where the ocean meets the land
Further, waves carry the energy from storms to distant shores,
where their impact erodes the land NEARSHORE
Teetering on the edge Bluff failure caused by storm waves in
March 2016 resulted in the apartment in Pacifica, California, extends from the shoreline to where waves break (surf zone) at
being condemned. the outer edge of the surf zone
When these buildings were erected in the 1970’s they were safely area of the ocean where the water is shallow enough to be
away from the cliffs. affected by wave action
Over the years, several measures were attempted to reduce
erosion of the sandstone cliffs. OFFSHORE
All proved to be inadequate.
 area beyond the nearshore zone: water is deeper and further from Wave-cut platforms- gently sloping, flat, or slightly inclined
the shore surface of rock that extends from the base of a wave-cut cliff out
Associated with activities such as oil, drilling, fishing, and shipping into the sea
Marine terraces- relatively flat or sloping landforms that parallel
SAND MOVEMENT ON THE BEACH the coastline and are typically found above present-day sea level
Sea arches- natural rock arch formed by the erosive action of
1. Swash waves on coastal rock formations
movement of water rushing up the beach after a wave breaks, Sea stacks- vertical column or pillar of rock that stands isolated
carrying sediment and debris landward from the coastline, often adjacent to cliffs headlands
The uprush of water from each breaking wave (the swash) is at
an oblique angle to the shoreline. 2. Depositional features
➢ Split
2. Backwash elongated ridge of sand that projects from the land into the
flow of water back down the beach after the swash mouth of an adjacent bay
straight down the slope of the beach. Often the end of a spit that is in the water hooks landward in
response to the dominant direction of the longshore current.
3. Beach drift ➢ Bay
The effect of this pattern of water movement is to transport body of water partially enclosed by land, usually with a wide
sediment in a zigzag pattern along the beach face. mouth opening to the sea or another larger body of water,
can transport sand and pebbles hundred or even thousands of such as a lake or another bay
meters each day ➢ Bars
occur as incoming waves carry sand at an angle up the beach The term baymouth bar is applied to a sandbar that
while the water from spent waves carries it directly down the completely crosses a bay, sealing it off from the open ocean.
slope of the beach. Similar movements occur offshore in the surf Such a feature tends to form across a bay where currents
zone to create a longshore current. are weak, allowing a spit to extend to the other side
These waves approaching the beach at a slight angle near ➢ Tombolos
Oceanside, California, produce a longshore current moving from ridge of sand that connects an island to the mainland or to
left to right. another island, forms in much the same manner as a spit
LONGSHORE CURRENT Tropical storms: The ultimate coastal hazard
Waves approaching the shore at an angle also produce currents Powerful tropical storms characterized by low-pressure systems and
within the surf zone that flow parallel to the shore and move strong winds
substantially more sediment than beach drift.
Because the water here is turbulent, these longshore currents ❖ Hurricane (North Atlantic Ocean and Northeastern Pacific
easily move the fine suspended sand and roll larger sand and Ocean)
gravel along the bottom. ❖ Cyclone (South Pacific and Indian Ocean)
When the sediment transported by longshore currents is added to ❖ Typhoon (Northwestern Pacific Ocean)
the quantity moved by beach drift, the total amount can be very
large. STORM SURGE

RIP CURRENT Without question, the most devastating damage in the coastal
zone is caused by storm surges.
concentrated movements of water that flow opposite the direction It not only accounts for a large share of coastal property losses
of breaking waves. (Sometimes rip currents are incorrectly called but is also responsible for a high percentage of all hurricane-
rip tides, although they are unrelated to tidal phenomena) caused deaths.
Most of the backwash from spent waves finds its way back to the dome of water 65 to 80 kilometers (40 to 50 miles) wide that
open ocean as an unconfined flow across the ocean bottom sweeps across the coast near the point where the eye makes
called sheet flow. landfall.
However, sometimes a portion of the returning water moves The worst surges occur in places like the Gulf of Mexico, where
seaward in the form of surface rip currents. the continental shelf is very shallow and gently sloping.
extends outward from shore and interferes with incoming waves. local features such as bays and rivers can cause the surge to
do not travel far beyond the surf zone before breaking up and can double in height and increase in speed.
be recognized by the way they interfere with incoming waves or
by the sediment that is often suspended within the rip current. Super Typhoon Yolanda: made landfall on November 8, 2013 (Guian,
can be hazardous to swimmers, who, if caught in them, can be Eastern Samar)
carried out away from shore.
The best strategy for exiting a rip current is to swim parallel to the STABILIZING THE SHORE
shore for a few tens of meters.
powerful currents of water moving away from shore. They can Exceptional storms are capable of eroding beaches and cliffs at
sweep even the strongest swimmer out to sea. rates that greatly exceed the long term average.
Such bursts of accelerated erosion not only significantly affect the
IF CAUGHT IN A RIP CURRENT natural evolution of a coast but also can have a profound impact
on people who reside in the coastal zone.
✓ Don't fight the current
✓ Swim out of the current, then to shore HARD STABILIZATION
✓ If you can't escape, float or tread water
✓ If you need help, call or wave for assistance Structures built to protect a coast from erosion or to prevent the
movement of sand along a beach
SHORELINE FEATURES can take many forms and often results in predictable yet
unwanted outcomes.
1. Erosional Features
Wave-cut cliffs Hard stabilization includes:
1. Jetties As the term implies, this practice involves adding large quantities
typically built from a shoreline out into a body of water, often the of sand to the beach system.
sea or a river, to direct currents and prevent sediment deposition. Extending buildings and beaches seaward makes along the
They're also used for docking boats or ships. shoreline less vulnerable to destruction by storm waves and
can be made of various materials such as concrete, rocks, or enhances recreational uses.
wood, depending on their intended purpose and environmental Without sandy beaches, tourism suffers
factors. not a permanent solution to the problem of shrinking beaches.
may act as a dam against which the longshore current and beach The same processes that removed the sand in the first place
drift deposit sand. eventually remove the replacement sand as well.
At the same time, wave activity removes sand on the other side. Nevertheless, the number of nourishment projects has increased
Because the other side is not receiving any new sand, there is in recent years, and many beaches, especially along the Atlantic
soon no beach at all. coast, have had their sand replenished many times.
Virginia Beach, Virginia, has been nourished more than 50 times.
Jetties help to:
2. Relocations
Stabilize the shorelines Instead of building structures such as groins and seawalls to hold
Manage sediment transport the beach in place or adding sand to replenish eroding beaches,
Provide safe harbors for maritime activities another option is available.
Many coastal scientists and planners are calling for a policy shift
2. Groins from defending and rebuilding beaches and coastal property in
To maintain or widen beaches that are losing sand, groins are high-hazard areas to relocating storm-damaged buildings in those
sometimes constructed. places and letting nature reclaim the beach
A groin (groin = ground) is a barrier built at a right angle to the
beach to trap sand that is moving parallel to the shore.
usually constructed of large rocks but may also be composed of
wood.
often do their job so effectively that the longshore current beyond
the groin becomes sand-starved.
As a result, the current erodes sand from the beach on the
downstream side of the groin.

3. Breakwaters
Hard stabilization can be built parallel to the shoreline.
protects boats from the force of large breaking waves by creating
a quiet water zone near the shoreline.
However, when a breakwater is constructed, the reduced wave
activity along the shore behind the structure may allow sand to
accumulate.
If this happens, the marina will eventually fill with sand, while the
downstream beach erodes and retreats.
Marina- a specifically designed harbor with facilities for mooring
boats and yachts, often offering services such as fueling, repairs,
and amenities for boaters and visitors.
At Santa Monica, California, where the building of a breakwater
has created such a problem, the city uses a dredge to remove
sand from the protected quiet water zone and deposit it
downstream, where longshore currents and beach drift continue
to move the sand down the coast.
Dredge- the action of using such a tool or machine to remove
material from the bottom of a body of water

4. Seawalls
Another type of hard stabilization built parallel to the shoreline is a
seawall, which is designed to armor the coast and defend
property from the force of breaking waves.
Waves expend much of their energy as they move across an
open beach.
Seawalls cut this process short by reflecting the force of unspent
waves seaward.
As a consequence, the beach to the seaward side of the seawall
experiences significant erosion and may in some instances be
eliminated entirely.

ALTERNATIVE TO HARD STABILIZATION

Armoring the coast with hard stabilization has several potential

drawbacks, including the cost of the structure and the loss of sand
on the beach.

1. Beach nourishment
One approach to stabilizing shoreline sands without hard
stabilization is beach nourishment.