Mariner Lagoon is located at the base of the Homer Spit in Kachemak Bay, approximately 1 mile (1.6 km) southeast of Homer, Alaska. The lagoon was created in the 1940s when a road causeway bisected Coal Bay to provide reliable access to a deepwater harbor at the end of the spit. Originally, Coal Bay referred to the shallow embayment on the north side of the spit. The U.S. Coast and Geodetic Survey translated its name from the Russian “Zaliv Ugolnoy.” The construction of the causeway resulted in the formation of Mud Bay on the north side of the spit and Mariner Lagoon on the south side.

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

Barrier beaches typically form parallel to the shoreline, often protecting salt marshes or mudflats, such as Mariner Lagoon. In a natural barrier beach system, the primary process of sediment distribution is longshore transport. Waves breaking on the shore move sand parallel to the coast, shaping the barrier beach. The sediment source for the beaches at Mariner Lagoon and Homer Spit is the eroding sea cliffs west of Homer. In 2003-04, a digital video system recorded the timing and magnitude of alongshore sediment transport along this shoreline. The data showed strong seasonality in sediment migration rates, with rapid winter and slow summer transport. This indicates that sediment migration is driven by eastward-propagating wind waves rather than westward-directed tidal currents. The highest weekly average movement rates, exceeding 20 feet per day (6 m per day), coincided with wave heights over 6.5 feet (2 m), suggesting a correlation between wave height and sediment migration. Since Kachemak Bay is partially enclosed, locally generated waves are driven by winds from the west and southwest, the directions with the greatest fetch. Read more here and here. Explore more of Mariner Lagoon and Kachemak Bay here: