Storm Surge Storm Surge Prediction, Prediction,

Tsunamis and Tsunamis and EstuariesEstuariesNovember 5November 5

Storm Surge = Storm Tide (Observed Water Level) – Astronomical (Predicted) Tide - Does not include waves

http://www.floridadisaster.org/bpr/Response/Plans/Nathaz/hurricanes/storm_surge.htm

Storm Surge Animations at http://openioos.org/hurricane/retro/2005/latest_anim.html?d=archive/katrina

Consistent Vertical Datum essential to monitoring, modeling, and mitigating storm surge

Emergency Managers need water level relative to NAVD88 to estimate inundation

Storm surge models use Mean Sea Level as datum – some use NGVD29 which was MSL in 1929 – have to adjust to present MSL then to NAVD88

Surge models use bathymetry referenced to MLLW – must adjust this to model datum (MSL)

Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model

There are 14 SLOSH Basins that cover the State of Florida

Cedar Key SLOSH Basin

SLOSH model Envelope of High Water (EOHW) for Hurricane Dennis (8/05)

TsunamisTsunamis Tsunamis are low-frequency ocean waves Tsunamis are low-frequency ocean waves

generated by submarine earthquakes. The sudden generated by submarine earthquakes. The sudden motion of seafloor over distances of a hundred or motion of seafloor over distances of a hundred or more kilometers generates waves with periods of more kilometers generates waves with periods of around 12 minutes.around 12 minutes.

The waves are not noticeable at sea, but after The waves are not noticeable at sea, but after slowing on approach to the coast, and after slowing on approach to the coast, and after refraction by subsea features, they can come refraction by subsea features, they can come ashore and surge to heights ten or more meters ashore and surge to heights ten or more meters above sea level.above sea level.

the Alaskan tsunami on 1 April 1946 destroyed the the Alaskan tsunami on 1 April 1946 destroyed the Scotch Cap lighthouse 31m above sea level. Scotch Cap lighthouse 31m above sea level.

Wave travels at Shallow Water Gravity Wave Wave travels at Shallow Water Gravity Wave speed:speed:

Arrival times predictable – Farther from source, Arrival times predictable – Farther from source, longer warning timelonger warning time

ghC p

Figure 17.8 in Stewart. Tsunami wave height four hours after the great M9 Cascadia earthquake off the coast of Washington on 26 January 1700 calculated by a finite-element, numerical model. Maximum open-ocean wave height, about one meter, is north of Hawaii. From Satake et al. (1996).

Figure 17.7 in Stewart. (a) Hourly positions of leading edge of tsunami generated by a large earthquake in the Aleutian Trench on April 1, 1946 at 12h 58.9m GMT. (b) Maximum vertical extent of tsunami on Oahu Island in Hawaii and the calculated travel time in hours and minutes from the earthquake epicenter. (c) & (d) Tide gauge records of the tsunami at Honolulu and Valparaiso. From Dietrich, et al. (1980).

Sumatra Tsunami:

On the morning of December 26, 2004 a magnitude 9.3 earthquake struck off the Northwest coast of the Indonesian island of Sumatra. The earthquake resulted from complex slip on the fault where the oceanic portion of the Indian Plate slides under Sumatra, part of the Eurasian Plate. The earthquake deformed the ocean floor, pushing the overlying water up into a tsunami wave. The tsunami wave devastated nearby areas where the wave may have been as high as 25 meters (80 feet) tall and killed nearly 300,000 people from nations in the region and tourists from around the world. The tsunami wave itself also traveled the globe, and was measured in the Pacific and many other places by tide gauges. Measurements in California exceeded 40 cm in height, while New Jersey saw water level fluctuations as great as 34 cm. Links:http://www.dhisoftware.com/general/News/Tsunami/IndianOceanRed2.aviNational Center for Tsunami Research:http://nctr.pmel.noaa.gov/indo_1204.html

California Tsunami Animation:http://www.usc.edu/dept/tsunamis/video/calvid/

Sumatra Tsunami heights and arrival timeshttp://nctr.pmel.noaa.gov/indo20041226/Figure_1_sign.jpg

DART™ (Deep-ocean Assessment and Reporting of Tsunamis)

A DART™ system consists of a seafloor bottom pressure recording (BPR) system capable of detecting tsunamis as small as 1 cm, and a moored surface buoy for real-time communications. An acoustic link is used to transmit data from the BPR on the seafloor to the surface buoy. The data are then relayed via a GOES satellite link to ground stations, which demodulate the signals for immediate dissemination to NOAA's Tsunami Warning Centers and PMEL.

DART™ real-time tsunami monitoring systems, positioned at strategic locations throughout the ocean, play a critical role in

tsunami forecasting

http://nctr.pmel.noaa.gov/Dart/index.html

EstuariesEstuaries Estuaries are semi-enclosed basins where fresh water Estuaries are semi-enclosed basins where fresh water

mixes with ocean watermixes with ocean water In Estuary, fresh water measurably dilutes salinityIn Estuary, fresh water measurably dilutes salinity Tidal mixing is very important for coastal ocean and Tidal mixing is very important for coastal ocean and

estuariesestuaries Bathymetry and tidal range determine strength of tidal Bathymetry and tidal range determine strength of tidal

mixingmixing Tides drive water in (flood) and out (ebb) of estuary as Tides drive water in (flood) and out (ebb) of estuary as

water rises and fallswater rises and falls Tidal Excursion: how far water parcel moves up/down Tidal Excursion: how far water parcel moves up/down

estuary over a tidal cycleestuary over a tidal cycle Tidal Residual circulation is flow averaged over many Tidal Residual circulation is flow averaged over many

tidal cycles – net motion of watertidal cycles – net motion of water Tidal mixing, fresh water inflow, and winds are Tidal mixing, fresh water inflow, and winds are

primary forcing functions for Residual Circulationprimary forcing functions for Residual Circulation

Tidal residual flow is “superposed” on Tidal residual flow is “superposed” on tidal flow – driven by fresh water inflow tidal flow – driven by fresh water inflow and windsand winds

Fresh water inflow varies on time scales Fresh water inflow varies on time scales of weeks to seasons to yearsof weeks to seasons to years

Wind-driven effects vary on time scales Wind-driven effects vary on time scales of 1-5 days – 2 parts: direct and coastal of 1-5 days – 2 parts: direct and coastal set-up (down)set-up (down) direct: water moves in direct: water moves in direction of wind – direction of wind – balance between balance between slope of sea surface and slope of sea surface and wind stress wind stress

coastal: large-scale wind effects on coastal: large-scale wind effects on coastal coastal ocean changes water level at ocean changes water level at mouth – mouth – changes water level in changes water level in estuaryestuary

So…So…1.0

-1.0

tidal

2.0

-2.0

wind

0.1 mean

Instantaneous velocity is the sum of tidal, wind, and mean

Tidal asymmetry – max velocity on Tidal asymmetry – max velocity on ebb is different than on flood – ebb is different than on flood – duration of ebb is longer than flood duration of ebb is longer than flood due in part to residual (mean) due in part to residual (mean) circulation superposed on tide – circulation superposed on tide – phase shift with depth – tide turns phase shift with depth – tide turns sooner at surface than at depthsooner at surface than at depth

Also due in part to nonlinearity – Also due in part to nonlinearity – crest (high tide) travels in deeper crest (high tide) travels in deeper water than trough (low tide) – high water than trough (low tide) – high overtakes low, max velocity doesn’t overtakes low, max velocity doesn’t occur at mid-tideoccur at mid-tide

A

B

0

0 Top

0Bottom

A

0

flood

flood

flood

ebb

ebb

ebbB

HeadRiver flow: R

Mouthopen sea

Fresh

Salty Si

So

← Vi

→ Vo

•Tidal Mixing determines nature of estuary•Fresh water inflow, bathymetry, tidal range determine strength of mixing•Tidal Residual Circulation is required to balance salt in estuary•Salty water flows in at depth, mixes with fresh water in estuary, then flows out as fresher surface flow•Shallower bathymetry, higher tidal range, larger fresh water inflow mean greater mixing

Tidal prism – volume of water that flows in/out during tidal Tidal prism – volume of water that flows in/out during tidal cyclecycle

VVpp=Area x tidal range=Area x tidal range Amount of mixing determines Estuarine flow Amount of mixing determines Estuarine flow Ratio of river input (R) to tidal flow (T) is one measure of Ratio of river input (R) to tidal flow (T) is one measure of

mixing: mixing: T=Total Tidal Transport (average)T=Total Tidal Transport (average)

= V= Vpp/(Tidal Period/2)/(Tidal Period/2)

3

3

10R

T :mixed Well

1010R

T :mixedPartially

1R

T :Salt wedge