River of many returns

Lessons from Yellow River could aid efforts to restore Mississippi River Delta

Rice University’s Jeff Nittrouer has studied river delta formations the world over. He hopes his next project, an in-depth look at China’s Yellow River, will offer new ideas about how to restore delta landscapes worldwide, including the largest in North America, the vanishing Mississippi River Delta.

“There’s an ongoing debate about how we, as a society, are going to efficiently manage delta landscapes worldwide, which are presently undergoing catastrophic drowning due to sea-level rise, and reductions in river sediment fluxes,” said Nittrouer, an assistant professor in the Department of Earth Science. “Closer to home, the conversation concerns sustaining the Mississippi River Delta and associated Louisiana wetlands, which have been subject to enormous erosion over the past century. One of the most promising proposals for mitigating land loss in Louisiana is engineering sediment diversions along the main river channel to jump-start land building. However for the United States, this is new territory, and so far, there’s been a lot of talk, but not much action.”

Nittrouer is the principal investigator on a new four-year, $2 million research grant from the National Science Foundation to study the Yellow River, known in China as the Huanghe. The multi-institutional effort will bring together many researchers from the U.S. and China to examine the geological, socioeconomic and engineering lessons learned from a decadeslong Chinese effort to build new coastal land at the mouth of the Yellow River. The scientific research will comprise field work, experimental designs and physical and economic modeling.

These Landsat satellite images show the growth of new coastal lands in the Yellow River Delta in northeast China between 1979 (bottom) and 2000 (top). A new federally funded study of the Yellow River delta could provide new information for U.S. experts who are seeking to rebuild the Mississippi River Delta. Credit: NASA Earth Observatory

The Yellow River, so named for the color of its sediment-rich waters, is the world’s sixth longest river. It’s also one of the world’s most densely populated and heavily developed river basins.

“The Huanghe’s delta system is undergoing dramatic changes in the sense that parts of it are growing rapidly while parts of it are also degrading rapidly, mainly as a result of human influences,” Nittrouer said. “What makes the Huanghe unique is that it carries so much sediment that it has a tendency to avulse rather frequently; the river channel catastrophically shifts course and follows an alternative course, thereby distributing water and sediment to another location along the coastline. Over geological timescales, many avulsions will help produce a river delta and lend to the development of the coastal landscape. An analogy would be to consider stepping near the end of a fire hose and letting the end line and nozzle spray back and forth from side to side. In the case of a river near its delta, the system sweeps across the landscape, delivering sediment and building new coastal land.”

Nittrouer said that rivers, particularly near their outlet at the coastline, tend to avulse periodically. This is caused by a lowering of the water slope as the river approaches the ocean, which results in a slowing of the river’s water flow and the settling of sediment within the channel. Continual deposition of sediment essentially fills up the channel so that the water must find an alternative course to the ocean, hence a river avulsion. Over time, repeated avulsions produce a river delta’s characteristic fan shape.

“Throughout human history, this process has been problematic for societies living near the mouths of rivers,” Nittrouer said. “During big flood events, a catastrophic avulsion may redistribute water and sediment many tens of miles away from the communities that rely upon these river resources, or worse yet, an avulsion may destroy whole towns that are suddenly situated in the river’s new path.

“The Chinese have extensive experience in regard to taming the Huanghe,” he said. “Additionally, for the past six or seven decades Chinese engineers have been engineering the Huanghe to produce artificial avulsions so as to control the dispersal of water and sediment and grow new land over different areas of the coast.”

Jeff Nittrouer

Since this is type of engineering is essentially what has been proposed to mitigate rapidly disappearing wetlands in the Mississippi River Delta, the Huanghe study could provide important lessons for policymakers and engineers working on the Mississippi Delta, Nittrouer said.

Moreover, the research will also be broadly applicable to hundreds of millions of people who live in communities affected by river avulsions around the globe, he said.

“River deltas are arguably the most dynamic coastal landscapes on Earth,” Nittrouer said. “Approximately 70 percent of the world’s population lives in coastal settings, and many coastal communities are affected, either directly or indirectly, by deltaic systems. The sustainability side of this comes from understanding and predicting how these landscapes will evolve in the future, due to human influences on river sediment load, the dispersal of sediment to the coastline and usage of the deltaic landscape itself.”

Nittrouer said the Yellow River research program will bring together geoscientists from Rice, the California Institute of Technology, China’s Ocean University in Qingdao and Boston College, engineers from the University of Illinois at Urbana Champaign and Tsinghua University in Beijing, economists from Johns Hopkins University and hydrologists from the Yellow River Institute of Hydraulic Research.

Fieldwork on the Huanghe Delta region is slated to begin this fall.