|
The Once and Future Danube River DeltaPast changes in World Heritage site offer lessons for proposed river projects |
|
|
 | |  |
|
| Enlarge ImageGeologist Liviu Giosan, WHOI, and colleagues have been reconstructing the evolution of the Danube River Delta, along the Black Sea coast of Romania and Ukraine. Based on evidence collected from sediments, Giosan believes the delta formed in the sequence shown in this animation. The Tulcea lobe, or section, of the delta started to form first and has been building and evolving continuously. The building of the other lobes has not necessarily followed a linear path, and the researchers are still not quite sure when the Chilia I and II lobes were formed in the 6,000-year evolution of the modern Danube Delta.
(Jack Cook and Katherine Joyce, WHOI Graphic Services. Background image courtesy of NASA. ) |
|
|  |
|
| Enlarge ImageUsing a small "dormitory" boat, WHOI geologist Liviu Giosan and colleagues cruise through a man-made canal in the St. George lobe of the Danube Delta is search of sites from which they could draw sediment cores. The history of the 6,000-year-old river delta is written in the sand and soil buried beneath the wetlands. (Courtesy of Liviu Giosan, Woods Hole Oceanographic Institution) |
|
|  |
|
| Enlarge ImageLiviu Giosan (left) of WHOI, and Emil Vespremeanu (in blue) and Ionutz Ovejanu (yellow) of the University of Bucharest use an auger to bore holes into the swale on a beach ridge on the St. George II lobe of the Danube Delta. (Courtesy of Liviu Giosan, WHOI) |
|
|  |
|
| Winds peel back the sands and reveal a useful, stratified outcrop in a dune on the Caraorman beach ridge plain (on the St. George I lobe). (Photo by Liviu Giosan, WHOI) |
|
|
Related Links |
|
|
“The Danube Delta is like the Everglades,” said Liviu Giosan, who grew
up near the Romanian wetlands. More than 300 bird species and 45
freshwater fish species make homes in the fertile labyrinth of marshes,
dunes, and channels.
The triangle-shaped, sediment-rich region at the mouth of the
Danube River is also rich with human history. The area has been settled
since the Stone Age, and the ancient Greeks, Romans, and Byzantines
built trading ports and military outposts along the coast. A
traditional maritime culture persists on the delta, and the United
Nations has declared the region a World Heritage site.
The Danube Delta is also a great place for a geologist to study
how the coast stretches, contracts, and undulates with time and human
interference.
The Danube is Europe’s second-longest river and a major artery
for trade and transportation. Starting in the Black Forest in Germany,
it winds 2,850 kilometers (1,770 miles) through nine countries before
pouring into the Black Sea from Romania and Ukraine. A proposed project
to dredge several arms and channels of the river for shipping will
fundamentally alter the delta, said Giosan, a coastal geologist at
Woods Hole Oceanographic Institution.
“We have experience from other parts of the world with the damage
that occurs from altering rivers and wetlands,” he said. “Why not learn
from that?
Watching the river flow
The delta—named for its resemblance to the Greek letter Δ—serves as a
sieve filtering fresh water and sediment from the European interior
before it reaches the salty sea. Buried in the sediments lies a
geologic record of a moving, changeable shoreline that has shaped human
history; in recent years, history has been shaping the river. For
several years, Giosan has been working with geographer Emil Vespremeanu
of Bucharest University and WHOI geologist Jeff Donnelly to dig into
the Danube’s secrets.
They traveled in small “dormitory” boats from Tulcea, where the roads
end, to a base station near the Black Sea coast. They cruised small
canals and arms of the river to take sediment cores from old beach
ridges, and they used sonar to chart the shape of the seafloor near the
mouth. Blending field geology with computer modeling, they are
reconstructing the forces that changed the flow and structure of the
delta in the past and figuring out what this can tell us about how the
delta could change in the future.
“We need to understand the river mouth, where a delta is built,” said
Giosan. The traditional understanding of deltas holds that the river
carries all the mud and sand deposited at the river mouth. But Giosan
questioned this old assumption, and he and his colleagues are showing
that not all the sediment is brought by the river. Waves, currents, and
tides also help build the delta from the seaward side by moving and
depositing sediments at the coast.
In fact, the river can serve as a natural barrier to the flow of water
and sand that builds and erodes the coast. Evidence suggests that the
ancient port of Istria may have been shoaled behind a barrier beach
when changes in river flow through the delta brought more sand
southward along the Black Sea coast. Preliminary findings by Giosan and
colleagues also suggest that the Danube Delta may be much younger than
previously thought.
“The construction of a delta is a delicate balance between river
discharge and coastal currents and waves,” he said. And that balance is
in peril.
Dredging a new channel
In the 1860s, European leaders internationalized the Danube region and
dredged one navigable channel through the delta—called the Sulina
arm—to open the European interior to bigger ships. For 150 years,
Europeans have established commissions and written treaties to protect
and exploit this vital waterway.
As with so many rivers around the world, the Danube has been dredged,
dammed, and altered for centuries. It now delivers just 30 percent of
its original load of water and sediment to the delta. “When a river no
longer brings new sediment to maintain the shoreline,” Giosan said, “it
becomes imperative to understand how fast the coast will erode under
the waves.”
The imperative became clear in 2004 when the former Ukrainian
government unveiled plans to revive inland ports by dredging a
170-kilometer (105-mile) shipping channel along the Chilia arm of the
Danube, on the border with Romania. To date, a 3-kilometer (1.8-mile)
canal has been carved through ecologically sensitive territory,
prompting protests from environmentalists and the governments of
Romania, the United States, and the European Union.
The controversy prompted Giosan to send testimony to the International
Commission for the Protection of the Danube. “Any major modification in
one region of the delta will affect the other parts,” wrote Giosan.
“Dredging the Chilia arm for a deep-water navigation channel will most
likely change the water and sediment regime all along the
Danube-influenced Black Sea coast.”
Giosan believes that an improperly designed project could fundamentally
change the flow through the delta. Increasing the water flow through
Chilia would significantly increase the sediment load in that arm and
increase erosion along the coast.
At the same time, it could deplete other arms of needed fresh water and
delta-building sediment, allowing salt water to penetrate the wetlands
and turning fertile habitat into a brackish wasteland.
The technical details of the Ukrainian project are sketchy, and Giosan
and colleagues hope the new government might reconsider the project
long enough to get an impact study requested by the international
scientific community. Perhaps scientists’ voices can be heard before
the dredges are sent in.
— Mike Carlowicz
This research was funded by the WHOI Coastal Ocean Institute and a WHOI Independent Study Award.
Posted: July 11, 2005 [top] |
|
