causeway

A causeway is a raised road or way that connects two pieces of land across water, a marsh, or a shallow lake. It is typically built on an embankment of earth, rock, or concrete, forming a continuous ridge that sits above the water or ground level. Unlike a bridge, a causeway usually presents a continuous solid fill along its length, with openings such as culverts or small arches to allow drainage and, in some designs, tidal flow beneath or beside the roadway.

Construction commonly involves layering compacted fill, sometimes faced with stone or concrete, and may incorporate drainage features, wind or flood protection, and safety shoulders. Some causeways include a separate arch or bridge section over channels or deeper water, while others rely entirely on fill for their cross-section. Maintenance focuses on controlling settlement, drainage, scour at the base, and protection against erosion from waves and currents.

Causeways are used to shorten travel distances, provide year-round access to islands, and protect routes from inundation in flood-prone areas. They are common in coastal, estuarine, and wetland environments, and can be found in various forms worldwide, from simple earth-fill embankments to engineered structures with sluice gates or drainage culverts. The presence of a causeway can alter sediment transport and hydrology, affecting tidal flats, wetlands, and navigation channels, and may require ongoing environmental and structural management to balance accessibility with ecological considerations.