Newswise — FAYETTEVILLE, Ark. – With sea levels rising due to warmer temperatures globally, scientists have focused on river deltas as hot spots for environmental change. A study by geologists at the University of Arkansas provides a new framework for assessing why and where river deltas branch and will help government agencies plan for sustainable development in these sensitive areas.

The findings show that the average angle of branching river channels – so called “distributary” networks such as those found on river deltas – matches the angle of channels joining together.

“Many of the world’s river deltas are at risk of submerging due to rising sea levels, subsidence and human alteration,” said John Shaw, assistant professor of geosciences in the J. William Fulbright College of Arts and Sciences. “In many of these areas, large land-building sediment diversions are being designed to engineer new landforms, similar to those built in the Netherlands and being developed in southern Louisiana, near the mouth of the Mississippi River. Our work may help with such planning.”

Previous studies have focused on many other aspects of delta channels, including width, depth and location of islands. This new study suggests that angles can also be predicted.

Because the work applies to distributary systems in general, Shaw said, it could be used to predict the behavior of deltas in remote parts of the world where direct measurements are scarce to non-existent. Their work also provides valuable data for government agencies trying to decide what to do with valuable property on or near river deltas.

“Many of the world’s river deltas are at risk of submerging due to rising sea levels, subsidence and human alteration,” said John Shaw, assistant professor of geosciences in the J. William Fulbright College of Arts and Sciences. “In many of these areas, large land-building sediment diversions are being designed to engineer new landforms, similar to those built in the Netherlands and being developed in southern Louisiana, near the mouth of the Mississippi River. Our work may help with such planning.”

Capitalizing on a recent study of tributary confluences – where two river channels merge into one – Shaw and graduate student Thomas Coffey analyzed digital elevation models of channel networks and noticed similarities between river confluences and the splitting channels of deltas. The tributary study found confluence angles averaged 72 degrees, except for rivers in arid lands, where the angles were more acute.

Shaw and Coffey predicted that that the splitting angles of distributary networks were roughly the same as the confluence angles of tributary systems. To test this theory, they chose 10 deltas from around the world that exhibited well-developed distributary networks. From these deltas, they gathered 197 “bifurcation” measurements. Their data revealed an average branching angle of 70.4 degrees, remarkably close to the theoretical prediction.

“Branching river channel networks are a classic example of pattern formation in nature,” Shaw said. “This remarkable symmetry, we think, is a useful tool for understanding river delta channel networks and designing and implementing responsible plans for land use.”

Shaw noted that there was a distinct difference between the two systems. With greater distance from the split, branching delta channels tended to bend toward one another, thus decreasing the angle, while tributary confluences maintained the same angle, regardless of the distance from the confluence.

The researchers’ study was published in a November issue of Geophysical Research Letters. For a more detailed explanation of the study, read a blog post written by Shaw.

-30-