The Holocene Evolution of the Big Branch Shoreline, Louisiana:Implications on Restoration Efforts

摘要

The Big Branch marshes contribute a diverse set of coastal wetland habitats to thernnorthern fringe of Lake Pontchartrain, Louisiana. This marsh has endured in nearly its presentrnform since sea level approached its present level. Throughout the Holocene, it has been arntransgressive shoreline. The shoreline morphology is a product of the framework of thernunderlying Pleistocene surface. The alternating points and embayments are the surfacernmanifestation of differential erosion that occurred during the Wisconsin. This irregular shorelinernhas facilitated the development of marshes sheltered behind the points and their flankingrnbeaches. An initial supply of shoreline sediment was transported along with the shoreline duringrnthe last transgression. Recent erosion of Pleistocene sediments at the headlands has suppliedrnadditional sediment to the beach and bar environments at the points and, through longshorerntransport, to the entire shoreline. Behind the slowly retreating protective shoreline environments,rnextensive marsh environments have developed and endured. Although the shorelines havernbecome considerably less sandy and have consistently retreated since 1860, care must be taken inrnthe approach used to combat the change. Methods should be used to enhance the naturalrnprocesses, such as introducing sand at the points. The grain size should match that in the existingrnbeach and bar environments to allow continued transport processes to nourish the entirernshoreline. Conversely, though solid structures may deflect wave energy, they would inhibit therntransport of sediment that has maintained the shoreline and allowed the formation of the marshes.