Mariner Lagoon is situated at the base of the Homer Spit, about 1 mile (1.6 km) southeast of the community of Homer, Alaska. The lagoon was formed when Coal Bay was bisected by a road causeway in the 1940s to provide more reliable access to a deepwater harbor at the end of the spit. Coal Bay was originally the name for the shallow embayment on the north side of the spit. The name is a translation by the U.S. Coast and Geodetic Survey of the Russian ‘Zaliv Ugolnoy’. Construction of the causeway created Mud Bay on the north side of the spit and Mariner Lagoon on the south side.

Beginning in 1899, coal mines were developed in the vicinity of the mouth of Bidarki Creek, in the sea cliffs about 1.5 miles (2.4 km) west of Homer. A large dock was built at the end of the Homer Spit and a narrow-gauge railroad ran for 7 miles (11 km) along the beach to transport coal from the mines to the dock. The mines were operated until 1923 and then intermittently until 1951. Before the road causeway was built, vehicles would drive along the beach at low tide, but the dynamic nature of barrier beaches such as the one forming Mariner Lagoon created hazards and unreliable access to the deepwater harbor.

Barrier beaches typically form parallel to the shoreline often protecting a salt marsh or mudflat such as Mariner Lagoon. In a natural barrier beach system, the primary process of sediment distribution is longshore transport, where waves breaking on shore transport sand parallel to the coast helping to create the elongated form of the barrier beach. The source of sediment for the beaches at Mariner Lagoon and the Homer Spit is the eroding sea cliffs west of Homer. In 2003-2004, a digital video system recorded the timing and magnitude of alongshore sediment transport along this shoreline. Strong seasonality in sediment migration rates was shown by the contrast of rapid winter and slow summer sediment transport. These data indicate that sediment migration is driven by eastward propagating wind waves as opposed to net westward directed tidal currents. The greatest weekly averaged rates of movement, exceeding 20 feet per day (6 m/d) coincided with wave heights exceeding 6.5 feet (2 m) suggesting a correlation between wave height and sediment migration. Because Kachemak Bay is partially enclosed, waves responsible for sediment transport are locally generated by winds that blow across lower Cook Inlet from the west and southwest, the directions of greatest fetch. Read more here and here. Explore more of Mariner Lagoon here: