Gulf bay double whammy: Rising seas, dammed rivers

October 23, 2006

PHILADELPHIA, Oct. 23, 2006 -- New research finds that every U.S Gulf Coast bay in Texas and Louisiana is vulnerable to significant flooding and expansion within the coming century due to a combination of rising seas and reduced silt flowing from dammed up rivers.

"Looking back over the past 10,000 years, we find the evolution of each of these bays is punctuated by rapid flooding events that result in landward shifts in bay environments of tens of kilometers and increases in bay area up to 30 percent within a century or two," said John Anderson, the W. Maurice Ewing Chair in Oceanography and professor of earth science at Rice University in Houston. "These flooding events can be triggered by either a rapid increase in sea level or a rapid decrease in the amount of silt flowing into the bay, and there's ample evidence to suggest that both of those will occur in each of these bays during the coming century."

Anderson will present his findings today at the Geological Society of America's 118th annual meeting at the Pennsylvania Convention Center in Philadelphia.

Anderson's results are based on his research group's analysis of dozens of sediment core samples drilled during the past decade from Galveston, Corpus Christi and Matagorda bays, all in Texas; Calcasieu Lake in Louisiana; and Sabine Lake, which straddles the Texas-Louisiana border.

"Over the past 10,000 years, there are an average of a half-dozen of these flooding events in each bay," Anderson said. "They don't correlate with any global increase in sea level, and they happen at different times in different bays, so we're confident that the driving factor in these events is a decrease in the amount of river-borne sediment flowing into the bay."

In the past century, multiple dams were constructed on each of the rivers flowing into each of these bays. Anderson said there is ample evidence that the dams have reduced the amount of sediments flowing from the rivers into the bays.

In addition, there is a growing body of evidence that sea level will increase more rapidly in the 21st Century than it has in several thousand years.

Based on marine sedimentary records, oceanographers know that sea level has been rising for the past 10,000 years, but the rate at which it's rising has been slowly falling for about 5,000 years. But that trend is apparently changing, with the latest satellite data indicating that seas worldwide are rising at an average rate of five millimeters per year - a striking contrast to the rate of two millimeters per year that was recorded by tide gauges throughout most of the 20th Century.

In some locations, warming water temperatures, land subsidence and other factors can exert a local influence, causing sea level to rise even faster. This also appears to be the case along the Texas-Louisiana coast, which is sinking by an average of two millimeters per year, and up to twice that much in certain areas.

"Bay-head deltas are just like the wetlands that have been disappearing in southeastern Louisiana in recent decades," Anderson said. "They have to be renewed with river-borne sediments in order to maintain themselves in the face of steadily rising seas."

Anderson said the geological record shows that sediment flowing into the five bays has tended to just keep pace with rising sea level over the past 10,000 years. The flooding events mark points in time when this delicate balance was upset. The most dramatic event occurred in Galveston Bay between 7,300-7,100 years ago. In that geological instant, the boundary between river and bay receded about 35 kilometers upstream.

"At that time, the head of the bay was somewhere north of I-10, but sediments flowing back into the bay from the Trinity River pushed that back south to the present location, creating Lake Anahuac in the process," Anderson said. "The creation of Lake Livingston and other lakes on the Upper Trinity has significantly reduced the amount of sediments flow into the bay, and data collected by the Texas Bureau of Economic Geology and the United States Geological Survey indicate that the headland marshes are teetering on the brink."
-end-
Anderson's group is currently studying Alabama's Mobile Bay, and they hope to eventually integrate those findings into their overall analysis. Members of the team include professors Antonio Rodriguez of the University of North Carolina and Alex Simms of Oklahoma State University, Rice graduate student Kristy Milliken and former Rice graduate student Jessie Maddox.

The research is supported by the National Science Foundation.

Rice University

Related Sea Level Articles from Brightsurf:

Sea-level rise will have complex consequences
Rising sea levels will affect coasts and human societies in complex and unpredictable ways, according to a new study that examined 12,000 years in which a large island became a cluster of smaller ones.

From sea to shining sea: new survey reveals state-level opinions on climate change
A new report analyzing state-level opinions on climate change finds the majority of Americans believe in and want action on climate change--but factors like state politics and local climate play important roles.

UM researcher proposes sea-level rise global observing system
University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science researcher Shane Elipot proposes a new approach to monitoring global sea-level rise.

How much will polar ice sheets add to sea level rise?
Over 99% of terrestrial ice is bound up in the ice sheets covering Antarctic and Greenland.

Larger variability in sea level expected as Earth warms
A team of researchers from the University of Hawai'i (UH) at Mānoa School of Ocean and Earth Science and Technology (SOEST) identified a global tendency for future sea levels to become more variable as oceans warm this century due to increasing greenhouse gas emissions.

Sea-level rise could make rivers more likely to jump course
A new study shows that sea level rise will cause rivers to change course more frequently.

UCF study: Sea level rise impacts to Canaveral sea turtle nests will be substantial
The study examined loggerhead and green sea turtle nests to predict beach habitat loss at four national seashores by the year 2100.

Wetlands will keep up with sea level rise to offset climate change
Sediment accrual rates in coastal wetlands will outpace sea level rise, enabling wetlands to increase their capacity to sequester carbon, a study from the Marine Biological Laboratory, Woods Hole, shows.

How sea level rise affects birds in coastal forests
Saltwater intrusion changes coastal vegetation that provides bird habitat. Researchers found that the transition from forests to marshes along the North Carolina coast due to climate change could benefit some bird species of concern for conservation.

As sea level rises, wetlands crank up their carbon storage
Some wetlands perform better under pressure. A new Nature study revealed that when faced with sea-level rise, coastal wetlands respond by burying even more carbon in their soils.

Read More: Sea Level News and Sea Level Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.