Abstract
Marsh terracing is a wetland restoration technique that is being implemented in the northern Gulf of Mexico. Marsh terraces are segmented berms of soil built within shallow coastal ponds, designed to increase marsh area and reduce wave energy. Approximately 980 linear km of marsh terraces have been constructed over almost 30 years in Louisiana and Texas to combat subsidence and sea-level rise; however little research has been conducted to determine their effectiveness. The objective of this study was to assess marsh terrace performance. The change in marsh terrace areas was measured over time through remote sensing. This analysis was conducted using one-meter resolution imagery from the National Agriculture Imagery program (NAIP) from 2003 until 2017 from five Louisiana coastal parishes. Twenty terrace fields of study between 10 and 14 years old were randomly selected within each parish. Results show more predominant deposition (55%) than erosion (45%) in marsh terraces. Terrace fields with high channel density and thereby an external sediment supply show more deposition compared to low channel density fields. This is the first study assessing multiple marsh terrace fields performance. Results are promising, especially considering the current rate of sea level rise and subsidence in Louisiana.
Highlights
Marsh terraces are usually built in shallow ponds, where natural marshes have been converted to open water [6]
Marsh terrace change over time was analyzed by two databases: (1) a marsh terrace geodatabase in ArcGIS platform as shapefiles created by Ducks Unlimited (DU) [35] and (2) approximately 120 aerial images from the National Agriculture Imagery Program (NAIP) [40] from five parishes in coastal
In the marsh terrace fields of study, performance over time showed more predominant deposition (55%) than erosion (45%)
Summary
Marsh terracing is a wetland restoration technique consisting of segmented and discontinuous ridges of sediment built in coastal marsh areas [1,2,3] aligned in a variety of patterns (chevron, squares, circles, checkerboard, etc.). Berm length and spacing vary depending on design pattern and location [4,5]. Marsh terraces are usually built in shallow ponds, where natural marshes have been converted to open water [6]. They are constructed at the same elevation of the surrounding marsh to allow periodic inundation of the terraces [3]. Marsh vegetation is planted around the perimeter of the terrace and in the intertidal area to prevent terrace erosion, enhance stability, and ecosystem diversity [7]
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