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Tropical Weather » Tidal Flooding Along the Upper Texas Coast
Tidal Flooding Along the Upper Texas Coast
Introduction
Because of our very low elevation above sea level on the upper Texas coast, tidal flooding remains a significant hazard to
waterfront communities. For tropical systems, ranging from tropical depressions to hurricanes, storm surge is the dominate
factor. Storm surge is a large dome of water often 50 to 100 miles wide that sweeps across the coastline near and to the
right of where the system makes landfall. The stronger the system, the slower its forward motion, and the shallower the
offshore water, the higher and more prolonged the surge will be.
However, even if the tropical system is not forecast to make landfall along the Texas coastline, it is important to continually
monitor its size, position and strength. This is because abnormally high water levels along the Texas coast are highly
dependent on meteorological conditions, more-so than the astronomical conditions used to produce tide charts. In addition
to storm surge itself, various factors lead to above normal tides including wind direction, wind speed, fetch and duration.
These factors are described below.
Wind Direction
The initial transport of water is 45 degrees to the right of the wind direction. So, an east wind will actually transport more
water in a northerly direction (toward Galveston) than a south wind which would "push" water more to the east of the region.
Wind directions that are favorable for elevated water levels, assuming other variables that are also met, include NE, ENE, E, ESE,
SE. An easy way to figure out which way the "push" of water is headed is to turn your back to the wind, then point 45
degrees to the right.
Wind Speed
Stronger wind speeds (out of the NE, ENE, E, ESE, or SE) correspond to a "stronger" push. In addition, there will be higher
waves on top of the elevated water level. Higher winds speeds essentially "trap" water up along the upper Texas coast and
bays as conditions are not conducive for the water to recede back into the Gulf.
Fetch and Duration
The fetch is the geographic distance that the wind travels. Duration corresponds to the amount of time a significant sustained
wind prevails along the fetch. Both are important factors determining just how much water will "pile up" along the coast. For
instance, a fetch of 25 mph easterly winds extending all the way to the west coast of Florida and maintaining itself for 3 days
will transport more water toward Texas than, say, a fetch extending from just off the Louisiana coast that has only been
prevailing for 24 hours.
Putting It All Together
When the conditions described above all come together, water levels along the Texas coast will rise above astronomical levels
that one would see in area tide tables. The lowest lying elevations and roads, especially Galveston Bay locations, appear to begin
flooding when observed tides reach around 4 feet. Structural damage to roads and personal property often results, but by far
the most significant impact is usually the resulting beach erosion. Several million dollars worth of erosion has been estimated by
such events in just the past 5 to 8 years. In addition, many "front row" beach homes have been lost and/or involved in litigation
due to the vegetation line being pushed back to behind their property. According to the Texas Open Beaches Act, the public
beach is defined seaward of the vegetation line. Previous effects that tides have had on various communities are listed on the
next page. Elevated water levels will continue until one of two things happen: the wind direction turns to more of a southerly,
westerly or northerly direction, or wind speeds decrease.
Where to Obtain Tide Levels
The NWS Houston/Galveston produces a daily tide forecast that is
sent to the media and internet. The forecast is also put on NOAA Weather Radio each day. We particularly like the
PORTS data, which shows real-time water levels
at various locations versus the predicted astronomical level (tide table).
| Critical Water Levels |
| |
4.0 feet |
4.5 feet |
5.0 feet |
5.5 feet |
6.0 feet |
6.5 feet |
| Galveston, Bolivar Peninsula |
Lowest street begin flooding especially on the west end of Galveston. Portions of HWY 6 between I-45 and Hitchcock begin to flood. |
Parts of HWY 87 become impassable. |
Ferry services to and from Bolivar ceases. Many feeder roads near the bay begin to flood. |
|
|
Kemah
Seabrook
Clear Lake
Texas City |
Toddville Road begins flooding. Lower portions of Red Bluff Road between Bay Area Blvd and HWY 146 begin flooding. |
Parts of Toddville Road closed. |
Water 3 feet deep and in homes along Toddville Road. |
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| Chambers County |
West Bayshore Road between Anahuac and Oak Island begin to flood. HWY 124 between High Island and FM 1985 begin flooding. |
FM 562 northeast of Smith Point begins to flooding. |
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FM 1985 between FM 562 and HWY 124 begins to flood. |
| Surfside |
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Water approaching dunes. Portions of FM 523 between HWY 332 and FM 2004 begin to flood. FM 2918 near the mouth of the San Bernard River begins to flood. |
Streets near the beach begin to flood. Lowest lying portions of HWY 288 near Freeport begin to flood. |
San Luis Pass Bridge may close depending on HWY 257 road conditions in Brazoria County. |
|
| Jamaica Beach (bayside) |
Lower streets begin flooding. |
Flooding moves further inland. |
Half the village becomes inundated. |
3-4 feet of water on streets and in homes. |
| Matagorda Area |
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Water on FM 2031. |
Bridge is closed. |
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| Sargent Area |
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Bridge is closed. |
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