Grewingk River, Kachemak Bay

The silt-ladened Grewingk Glacier is connected to the sea by the Grewingk River, both named in 1880 by W.H. Dall of the U.S. Coast and Geodetic Survey for the geologist Constantin Grewingk. Melting glaciers generally produce high river discharges and large volumes of sediment. Rivers emanating from glaciers often develop braided patterns with multiple channels separated by bars or islands. Although the threshold between meandering (sinuous, single channel river pattern) and braiding is not clearly understood, three factors are probably necessary for braiding to occur: 1) an abundant bedload supply (portion of a river’s sediment load supported by the channel bed), 2) erodible banks, and 3) high stream power (the potential energy for a given river channel length). The resulting beach sediments can be highly dynamic with erosion events caused by storm-driven waves and deposition events caused by glacier surges and retreats. During periods of relative sediment stability, animals such as the blue mussel and plants such as the rockweed colonize the beach face creating multi-colored patterns. Click on the picture and download CoastView to explore the Grewingk River and Kachemak Bay. See more posts on the CoastView website here.