How do levees contribute to erosion in the Mississippi River delta?

Levees contribute to erosion in the Mississippi River delta primarily by disrupting the natural process of sedimentation that sustains the landform.1

Under natural conditions, periodic flooding allows the river to deposit suspended silt and organic matter across the delta plain, which helps the area aggrade and resist the erosive forces of marine processes. However, the extensive system of levees "walls in" the river, trapping this vital sediment within the main channel.2341

By preventing the river from overflowing its banks, levees starve the surrounding delta of the new material needed to offset natural subsidence and the constant, unopposed attack of waves and currents. Consequently, the delta becomes increasingly vulnerable to erosion and shrinks in area, as it is no longer receiving the annual silt additions required to maintain its structure against the sea.21