Moriches Inlet is an inlet connecting Moriches Bay and the Atlantic Ocean.

It forms the eastern border of Fire Island, New York and the western border of the barrier island on which West Hampton Dunes, New York is the closest community.

The inlet which split West Hampton from Fire Island was formed by a Nor'easter in 1931.

The 1931 storm created a geographic quirk for the eastern tip of the West Hampton island which is in the town of Brookhaven but in order to access it via land from Brookhaven a person must go through several miles of Southampton (town), New York.

Between 1933 and 1938 Moriches Inlet widened to 4,000 feet (1,200 m) wide and deepened with sand being deposited on both the bay and ocean. The widening subsided in 1938 when the Great Hurricane of 1938 opened up the Shinnecock Inlet further east between Shinnecock Bay and the ocean.

In an attempt to stabilize the deterioration of the barrier island, local authorities built groynes on the inlet in 1952–1953. Local authorities have consistently urged that the inlet be kept open to allow boats from the mainland of Long Island to have access to the ocean. The United States Army Corps of Engineers took over the maintenance of the inlets and jetties in the 1980s.

Moriches Inlet, NY. Moriches Inlet is located on the south shore of Long Island, NY, 72.4 km (45 miles) west of Montauk Point and 128.7 km (80 miles) east of New York City. The inlet connects Moriches Bay to the Atlantic Ocean and is protected by two rock jetties. A northeast storm in January 1980 breached the barrier island approximately 305 m (1,000 ft) east of Moriches Inlet. The initial breach width observed on 16 January was estimated at 91.4 m (300 ft), and the depth was approximately 0.6 m (2 ft) mean low water (mlw). The breach was surveyed on 20 January and had widened to 213.4 m (700 ft) with an average depth of just over 0.4 m (3 ft) mlw. The breach continued to grow, and by the fall of 1980 it was approximately 884 m (2,900 ft) wide with a maximum depth around 3.0 m (10 ft) mlw. Current velocity in the breach prior to its closure was estimated at as much as 1.5 m/sec (5 ft/sec).

The breach caused local concern about increased exposure to storm flooding in the backbay, as well as possible harm to the shellfish industry due to increased bay salinity. As a result, the New York District was requested to close the breach and began the filling operation in October of 1980. A monitoring program of the inlet and breach was conducted during construction of the fill to ensure that the system was responding as expected. Several design modifications were made during construction as a result of the monitoring program. A complete description of the monitoring program is given by Schmeltz et al. (1982), and the construction procedures are described by McCarthy et al. (1982). This breach was recently simulated with a numerical morphologic model (Kraus and Hayashi 2005), for which further documentation on the evolution of the breach width and depth is given.

The method selected for the breach fill included construction of two temporary sheet-pile walls 9.1 m (30 ft) apart and parallel along the bay side of the breach. The initial option of placing the sand with no temporary retaining structures was discarded because of the potential for a high loss of fill material as the operation was to take place during the winter storm season. In addition to minimizing fill losses during construction, the expected advantages of the sheet-pile walls included control of tidal currents through the fill area and trapping part of the east to west littoral drift. Construction of the retaining walls on the bay side of the breach provided protection from wave attack and the bay side wall was further stabilized by driving short sheet-pile spurs at right angles to the main wall on the bay side.

Approximately half of the 0.9 million cu m (1.2 million cu yd) required to close the breach was obtained from an upland source and the other half was acquired by bay dredging. The fill material from upland sources was placed between the sheet-pile walls and along the ocean side of the breach. The dredged fill was placed between these two “protective arms” to minimize the loss of the dredged sand while it was in a slurry state. Several weeks after closure operations began, a storm with a 2-year return period struck, damaging the exposed sheet pile walls and eroding some of the fill.
Engineers on site observed that without the sheet-pile walls in place, the majority of the fill would have been lost. By early December, the breach was nearing closure (Figure 6). To facilitate the final closure, a sheet-pile spur was constructed to deflect the ebb current away from the breach and through the inlet. As a result, sand began to naturally accumulate in the breach, and it was closed on 15 December. Sand placement continued through January of 1981, and the sheet-pile walls were removed with construction activities complete by the beginning of February 1981. Material losses were approximately 15 percent of the total placed, including losses from the storm. Subsequent to the closure, New York state constructed a rubble revetment on the bay side of the barrier island contiguous with the jetty and running along the bay shoreline of the barrier island.