Sharp turns cause rivers to meander, migrate

Feb. 7 (UPI) -- Engineers and builders need to understand how rivers shift and meander over time, but new research suggests the conventional thinking on the behavior of bending rivers is flawed.

According to new research by geologists, current river migration models are unnecessarily complicated. The latest analysis, published this week in the journal Geology, showed that a river's rate of migration is closely correlated with the sharpness of its bends.

"When we look at the rivers we have studied, the sharper the bend, the tighter the bend, the faster it moves," Zoltán Sylvester, a research scientist at the University of Texas at Austin, said in a news release. "It's a simple relationship."

Previously, scientists thought there was a limit to the influence of a river's curves on its migration. The sharpest bends, researchers predicted, created turbulence and slowed a river's flow, limiting erosion and curbing the migration rate.

The latest analysis showed the opposite is true. There is no cap on the influence of a river's bends. The sharper the bend, the faster the water flows. Faster water fuels greater erosion, and accelerated erosion rates speed up a river's migration.

The research also showed the influence of a sharp bend on erosion and migration occurs just downstream from the curve, not directly alongside it.

Scientists improved the river migration model by studying the movements of seven rivers in the Amazon Basin. Landsat images collected over the last 30 years allowed researchers to measure the shifts of hundreds of river bends.

Of course, external geological factors -- the type of underlying bedrock and topography of the surrounding land -- can also influence a river's migration, but the simple relationship between the sharpness of a river's curves and its migration rate provide a starting point for scientist looking to predict where and how a section of river will move in 20 or 30 years.

"The authors' method for relating curvature to migration rate provides a very nice framework for determining where a simple migration model is appropriate," said Jonathan Schwenk, a postdoctoral fellow at Los Alamos National Lab who studies river behavior. "I would love to see this analysis extended to rivers flowing through different environments to really get a sense of the factors that make simple models and the theory diverge from observed migration patterns."