STORM SURGE

PRESENTED BYASWATHY.K.V

S1 CASAD, M TechROLL NO:7

What is a Storm Surge?

It is an abnormal rise of water generated by a

storm, over and above the predicted

astronomical tide.

Generated by extreme weather conditions

Waves on top of surge devastate area2

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Storm tide It is the water level rise during a storm due to thecombination of storm surge and the astronomical tide.

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What causes Storm Surge?

Storm surge is caused primarily by the strong winds in a hurricane or tropical storm.

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The wind circulation around the eye of a hurricane

blows on the ocean surface and produces a vertical

circulation in the ocean

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Once the hurricane reaches shallower waters near the coast, the vertical circulation in the ocean becomes disrupted by the ocean bottom

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Storm Surge

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At least five processes can be involved in altering tide levels during storms

The Pressure effect

The pressure effects of a tropical cyclone will cause the water level in the open ocean to , rise in regions of low atmospheric

pressure

fall in regions of high atmospheric pressure

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Direct wind effect Strong surface winds cause surface currents at a

45 degree angle to the wind direction, by an effect

known as the Ekman Spiral.

Wind stresses cause a phenomenon referred to as

"wind set-up“.

It is the tendency for water levels to increase at

the downwind shore, and to decrease at the

upwind shore.10

Effect of the Earth's rotationThe Earth's rotation causes the Coriolis effect

It bends currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

When this bend brings the currents into more perpendicular contact with the shore it can amplify the surge

And when it bends the current away from the shore it has the effect of lessening the surge

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Effect of wavesPowerful wind whips up large, strong waves in

the direction of its movement.

Rainfall effectHurricanes may dump as much as 300 mm of

rainfall in 24 hours over large areas, and higher rainfall densities in localized areas.

As a result, watersheds can quickly surge water into the rivers that drain them.

This can increase the water level near the head of tidal estuaries as storm-driven waters surging in from the ocean.

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Factors that Influence Storm SurgeCentral Pressure

Lower pressure will produce a higher surge.

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Storm Intensity

Stronger winds will produce a higher surge

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Storm Forward Speed On the open coast, a faster storm will produce a higher surge.

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Angle of Approach to Coast

A storm that moves onshore

perpendicular to the coast will produce a higher storm surge

parallel to the coast or moves inland at an oblique angle will produce lower surge

Shape of the Coastline

Storm surge will be higher when a hurricane makes landfall on a concave coastline

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Width and Slope of the Ocean Bottom Higher storm surge occurs with wide, gently sloping continental shelves

Lower storm surge occurs with narrow, steeply sloping shelves

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Local Features

Storm surge is highly dependent on local

features and barriers that will affect the flow of water

Example : The coast of North Carolina, which has the complexities of such features as barrier islands, inlets, sounds, bays, and rivers.

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Measuring Storm SurgeTide stations measure the variation in water level

along the coast.

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High Water Marks :HWMs are lines found on trees and structures marking the highest elevation of the water surface for a flood event, created by foam, seeds, or other debris.

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Pressure Sensors :Provide information about storm surge duration, times of arrival and retreat, and maximum depths.

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Dangers of Surge

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Devastating to low-lying coastal regions

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Inland Surge

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Hurricane Katrina

A maximum storm surge of more than 25ft (8 m)

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Before Hurricane Katrina

After Hurricane Katrina

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Hurricane Sandy

New York City

October 2012,

with a high tide

of 14 ft (4.2 m)

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New Orleans,LouisianaAugust 8,

2012

Before

After

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Before and After

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Cyclone PhailinGopalpur in Odisha

October 2013

winds raging at 200km an hour whipping up a storm surge of a over 3 metres inundated areas up to half a kilometre inland

Mitigation  Construction of dams and floodgates (storm

surge barriers)Examples :• Floodgates in Netherlands• Thames Barrier in London• Saint Petersburg Dam in Russia

Creation of housing communities at the edges of wetlands with floating structures.

Such wetlands can then be used to accommodate runoff and surges without causing damage to the structures.

It also protect conventional structures at somewhat higher low-lying elevations. 31

ConclusionThe storm surge is an additional rise in sea level above

the expected astronomical tide

The severity of a storm surge depends on

whether it coincides with a low or high tide.

It leads to the devastation of low-lying coastal regions

and Inland Surge.

The effect can be reduced by consructing certain barriers.

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