Subsidence and Sea-Level Rise in Southeastern Louisiana: Implications for Coastal Management and Restoration

Impacts of Subsidence and Sea-Level Rise

The effect of subsidence on coastal environments of Louisiana varies from direct lowering of roads and levees to rapid degradation of marsh vegetation and soils. As the land subsides and sea level rises, the threat of flooding wetlands and commercial and residential infra-structure increases.

• Coastal Marshes and Land Loss:
  Published reports indicate that coastal marshes can typically accrete at a rate that keeps pace with a slow rate of sea-level rise. As the rate of sea-level rise increases, coastal mashes cannot maintain their elevation, and they submerge and are transformed to open water. Some Louisiana marshes cope with today's conditions, future increased sea-level rise may approach or cross this critical threshold.

• Human Effects on the Coastal Wetland Environment:
  Since the arrival of the first settlers, mankind has been changing the Mississippi River delta plain. Variations in subsidence of the delta plain are frequently compounded by drainage of wetlands for agricultural, residential, or industrial development. Drainage causes additional subsidence of soils and reduces elevations to below current sea level in many areas. Levees are necessary to protect the developed areas from flooding. The roads and railways that cross Louisiana coastal wetlands and provide access to coastal communities and inshore and industrial facilities are being progressively lowered by subsidence and threatened by increases in sea level.