Drainage Patterns on a Sandy Beach

November 08, 2015

Braided drainage

Photographer: Carol Simpson
Summary Authors: Declan G. De Paor; Carol Simpson
Shown above is an accordant drainage pattern on a sandy beach following an ebb tide. Braided drainage in rivulets developed here, on the uniformly sloping sand surface of Nantucket Beach, Massachusetts. However, as you can see, small tributaries enter the main rivulets at right angles to the drainage channels, modifying the drainage morphology into a trellis pattern. The intriguing features are the holes. One would expect pebbles or shells to be sitting in at least some of them if they were scour signatures. Since no pebbles are visible, though, we wonder if mini sinkholes developed where the underlying wet sand was more fluid than the top layers. Note that some rivulets seem to converge on holes from different directions. Field of view is approximately 2 x 3 ft (0.6 x 0.9 m).