Unintentional impacts

• Since the 1930s, 29 locks and dams were built to allow safe navigation of the river; these created 29 ‘discrete pool locations’ which slows down the flow of the river, which increases deposition
• These enhanced deposition rates have caused the flow of materials to reduce by 60% from 400 million tonnes in 1800, to 170 million tonnes in 1980; this means less material enters the coastal system which leads to a net vertical subsidence of wetlands
• Following the great flood of 1927, the national government funded 5600km of levees along the river Mississippi; this interrupted the flow of material from the river onto the wetland of coastal floodplain, and prevented bank erosion which decreased sediment from the middle course of the river
• These two factors caused by the construction of levees meant the wetlands were not topped with fresh sediment, leading to a net vertical subsidence of wetlands
• The construction of the army base diverted the flow of the river in 1963, this led to Birds Foot Delta losing 10% of its coastal wetlands from 1996-2010
• The delta is experiencing a net vertical subsidence of 1.5cm/year as there’s no fresh supply of sediment due to the diversion of the river; this, coincided with rising eustatic (global) sea levels due to global warming, is causing land to be lost rapidly
• From 1932-2010, Louisiana lost 70km of wetlands annually, totalling to 5000km squared - which is a loss of 25% of its wetlands, primarily due to the diversion of the river in 1963
• An additional loss of 75km squared of the land is predicted to be lost annually for the next 50 years