New Method Allows For Predicting River Delta Shapes

Mississippi birdfoot delta. (Credit: NASA Landsat)

Researchers at MIT have determined a new way to find what shape river deltas will take, which will help them determine how lands could change for people who live in river delta regions and whether the lands will become more or less habitable, according to a release from the school.

River deltas tend to take one of two shapes: a smooth round “cuspate” form like the Nile River delta, or a bird-foot shaped, “crenulated” form like the Mississippi River delta. Scientists from MIT and Woods Hole Oceanographic Institution were able to determine that whether the delta takes one shape or the other is a function of the strength of the river pushing silt into the delta versus the strength of ocean waves pushing back against the river.

Using a global wave model developed by the National Oceanic and Atmospheric Administration, scientists simulated river sediment flux and wave height, frequency and direction for many river deltas on Indonesia’s island of Java. They determined that a ratio of river to ocean wave strength of one or greater yielded crenulated shapes, while ratios less than one were linked to cuspate shapes.

Top image: Mississippi birdfoot delta. (Credit: NASA Landsat)