Woods Hole Oceanographic Institution

How do deltas form and evolve
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A "dormitory" boat on the Danube River delta, the largest wetland in Europe. (Photo by Liviu Giosan, WHOI)
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Collecting and studying sediment cores can shed light on how deltas form and evolve. (Photo by Liviu Giosan, WHOI)

They traveled in small “dormitory” boats from Tulcea, Romania, where the roads end, to their base station near the Black Sea coast. They cruised along canals and tributaries to find ancient beach sediments and used sonar to map the seafloor near the mouth of the Danube River. On two expeditions funded by the WHOI Coastal Ocean Institute, WHOI geologists Liviu Giosan and Jeff Donnelly teamed with colleagues from Bucharest University to reconstruct the evolution and dynamics of one of the world’s most environmentally and economically important river deltas.

“The Danube delta is like the Everglades,” said Giosan. More than 300 bird species and 45 freshwater fish species live in its labyrinth of marshes, dunes, and channels. At the mouth of the 2,840-kilometer (1,776-mile) river, the delta forms the largest wetland in Europe and has been dredged and altered to create canals and shipping channels.

Giosan and Donnelly are trying to understand how river flow, sediment load, sea level change, and coastal currents combine to form a delta. A first challenge from the new research comes to the traditional view, which holds that rivers carry all the sediment deposited at their mouths. But the research team’s sediment cores, seafloor maps, and theoretical models suggest that the river actually serves as a natural barrier, partly blocking the natural flow of waves and sand along the coast.

Besides the fundamental implications on river delta geology, the results are expected to be important for the management of shipping lanes and coastal water supplies, and for protection of coastal habitat.

This research was supported by the WHOI Coastal Ocean Institute and a WHOI Interdisciplinary and Independent Study Award.

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