Flooding and erosion of Maine's coastal wetlands

Property on and adjacent to coastal wetlands usually floods during the annual high tide, during heavy rains or spring snowmelt, or during periods of storm surge. These areas, from a regulatory standpoint, are part of a coastal wetland since they are at or below the reach of the tides. Coastal property flooding problems may be chronic, with regular inundation by high tides or minimal storm surges. Flooding may be less frequent and occur only in larger storm events and high storm surges.

Erosion of marsh surfaces can be caused by:

Sea-level rise. Coastal wetlands persist when sediment is delivered to the marsh surface at the same pace as sea-level rise, which has been fairly steady over the last century. However, if sea-level rise accelerates and sedimentation rates cannot keep up, marsh loss could occur.

Tidal currents. At high speeds, ebbing and flooding tidal currents can erode marsh surfaces, especially along the edges and outer banks where a tidal channel bends.

Wind-driven waves. Waves, especially those associated with storms, can erode marsh surfaces at high tide. At lower tides, waves can erode marsh banks along tidal channels. This relates to the aspect (or direction) that a marsh faces and the fetch (distance) that the wind can blow over the water. A longer fetch will allow larger waves to form. Typically in Maine, marsh surfaces or channels that face northeast are most susceptible to erosion.

Boat wakes. Motorboat wakes can cause abnormally large waves to erode the edges of the marsh. 

Foot traffic. In some areas, traditional public access has cut across marsh surfaces to access fishing or recreational locations. Heavy foot-traffic on marsh surfaces, even for a short amount of time, can damage marsh vegetation and erode the surface of the marsh.

Ice floes. Winter high tides can lift frozen blocks of ice, mud, and plants off the marsh and expose the underlying surface to additional erosion. In other instances, ice floes actually transport sediment from one area of the marsh to another.