Louisiana is losing coastal wetlands at an alarming rate. To combat significant coastal land loss, the state of Louisiana created a Coastal Master Plan for restoration and flood protection in 2007, with updates every five years (every six in the future). The 2017 Coastal Master Plan consists of 120 different restoration projects across the Louisiana coast including sediment diversions, hydrologic restoration, barrier island restoration, marsh creation, ridge restoration, shoreline protection, and structural and nonstructural protection. These projects along the entire coast of Louisiana will work together to help stem natural and human induced land loss. All projects are valuable to decreasing this land loss, but certain projects can have broader impacts. CRCL highlights the following restoration projects from the Coastal Master Plan that are critical to slowing this land loss.
Mid-Barataria and Mid-Breton Sediment Diversions
Barataria Land Bridge and Large Scale Marsh Creation
Calcasieu Ship Channel Salinity Control Measures
The Mississippi river is the eighth largest river system in the world by discharge, and drains over 40% of the contiguous US. The formation of the Mississippi River Delta began approximately 7,500 years ago at the end of the last glacial period, when sea level rise slowed enough to allow for sediments to accumulate at a faster rate than sea level rise. All major current deltas around the world were formed during this era of Holocene sea level rise deceleration, but not all delta formation and maintenance is driven by the same forces.
Deltas can be river-, wave-, or tide-dominated. Due to the high river discharge and small tidal range, the Mississippi Delta is a river-dominated delta, producing the elongated shape resembling fingers of levees extending seaward. The large drainage area and high discharge supplies the northern Gulf of Mexico with the seventh highest sediment load in the world. As the Mississippi River fills with sediment, it tries to find an easier route to the Gulf. This has led to the river switching course roughly every 600 to 1,000 years since its formation.
Over the course of its history, the Mississippi has had six Holocene Delta complexes, excluding the current Atchafalaya and Wax Lake Deltas that takes roughly 30% of the Mississippi River flow. Each delta complex is in various stages of compaction, subsidence, and building; natural deltas are dynamic systems, constantly in a state of change. The delta switching, combined with the high sediment load, has resulted in the current wetland rich Louisiana coast, with 30,000 sq. km (11,500 sq. mi) of delta plain and 41% of the coastal wetland area of the United States.
The Louisiana coast is an incredibly productive ecosystem largely because of these extensive wetlands. Numerous species of fish, birds, and invertebrates use the coastal waters for a portion of their life history and some reside there for their entire life. The wetlands act as fishery nursery grounds, increasing productivity by providing foraging opportunities and protection from predation. The productivity of shrimp and blue crab, which support important commercial fisheries, is closely linked to the marsh.
The Louisiana commercial fishing industry is one of the most productive in the country (2nd only to Alaska in pounds/year. The Gulf of Mexico (GoM) accounted for 18% of total US landings (by weight) and 16% of the total US landings revenue in 2009. Of that, Louisiana supplied 70% of the GoM landings and 45% of GoM revenue. Louisiana’s coastal wetlands provide many other benefits than solely fishery production, including recreational uses and storm protection. Recreational fishing in Louisiana accounted for 4 million trips in 2009. Hurricane protection supplied by coastal wetlands alone has been estimated at over $23 billion dollars for the US.
Rapid land loss has led to Louisiana accounting for 80% of total coastal wetland loss in the U.S. Humans have altered the coastal ecosystem for centuries through levees, impoundments, canals, and river diversions. Beginning in the 18th century, natural levees were reinforced in attempts to control the annual flooding of the Mississippi River. By 1926, the levees extended from Illinois to New Orleans. In the mid-20th century, the US Army Corps of Engineers concluded that if allowed to flow freely, the Mississippi River would switch course to the Atchafalaya by 1990.
Completed in 1963, the Old River Control Structure stopped the river from switching by maintaining a 70/30% split of the water to the Mississippi and the Atchafalaya Rivers. The complete leveeing of the lower portion of the Mississippi River has stopped the natural delta switching process that created the delta plain.
Recent land loss (both direct and indirect) from oil and gas canals and a decrease in sediment supply following soil conservation measures has hastened the natural land loss from subsidence of a contracting delta. Manmade canals significantly alter the hydrology of the wetlands. The canals themselves can funnel saltwater upland and their spoil banks decrease flow across the wetlands, leading to water impoundments that eventually cause large scale marsh die offs. Since 1932, Louisiana has lost almost 4,900 sq km (1,900 sq mi) of coastal land. From 1985-2010, Louisiana’s wetlands have disappeared at an average rate of ~44 sq km (16.5 sq mi) per year, or the equivalent of one football field an hour if taken as a constant rate.