DOI: 10.5061/dryad.sn02v6x9s
title: Relationship of dredged canals and wetland loss in Louisiana

description: The direct effects of converting wetlands to open water by dredging can be
 magnified by indirect effects. For example, the dredged canal allows for
 recovery of mineral fluids 1000s of m belowground which may induce
 geological subsidence or faulting; dredged material deposited at the
 surface to form continuous levees may create hydrologic stressors on the
 wetland plants resulting in a conversion to open water habitat as a result
 of both soil waterlogging and drying, less organic matter and sediment
 accumulation, or greater erosion. We quantified indirect effects by
 demonstrating a robust dose-response relationship between coastal land
 loss and dredging canals in the Mississippi and Niger river deltas over 60
 years. Importantly, the ratio of land loss to canal area increases with
 time – a legacy effect. We also found that flood protection levees on the
 main channel did not magnify the effect of dredging on wetland loss by
 inhibiting sediment flow into adjacent wetlands along its banks.
description: Published and unpublished data are reported for digitized areas
 of land and canal for 15' and 7.5' maps in the Louisiana coastal
 zone. No transformations of the data were done.
description: # **Percent dredged canal density and wetland loss in Louisiana**
 [https://doi.org/10.5061/dryad.sn02v6x9s](https://doi.org/10.5061/dryad.sn02v6x9s) The dose-response relationships between the percent dredged canals and percent land loss in Louisiana and Nigeria coastal zone were quantified using land and water data. Published data in 7.5' and 15' quadrangle maps for the Louisiana deltaic coastal zone from 1932 to 1990 are included in this data file as well as some unpublished data records. The %land loss relative to the baseline land area at the start of the interval was calculated. A direct relationship between dredged area and land to water conversion is demonstrated that accelerates over decades. ## Description of the data and file structure The data are in an excel spreadsheet accompanied by location maps for the Louisiana coast. The units for the area of land and water are 'acres' (the original reporting units). The percent land or percent canal in maps of different dates are in %. * Worksheet Baseline Numbering: The base map identification numbering is given that is common to all data sets from 7.5' and 15' quadrangle maps of the Louisiana coast. * Worksheet Britsch and Dunbar 1993: The data from these authors are for map in the early 1930s, 1958, 1974, 1983 and 1990. The worksheet includes the area of canal and land in 15' quadrangle maps, and the calculated % canal and land in each quadrangle map. The Quadrangle number is the base map number identified in the Worksheet 'Baseline Numbering' * Worksheet Scaife et al. 1983: These are data that Scaife et al. (1983) used to measure the relationship between % land loss from 1955 to 1978 and the canal density relative to that existing in 1958 in 7.5 minute quadrangle maps for St. Breton Sound, Barataria and Terrebonne Parishes. The Quadrangle number is the base map number identified in the Worksheet 'Baseline Numbering' * Worksheet Turner and Rao 1990: These are data that Turner and Rao (1980) developed when studying the relationship between pond size and distance from canals in Terrebonne and Barataria Parishes, but did not report in the journal article. Maps identified as 'near' or 'far' maps include a portion of the Mississippi River or not, respectively.The Quadrangle number is the base map number identified in the Worksheet 'Baseline Numbering' * Worksheet Bass and Turner 1997: These are data that Bass and Turner (1997) used to quantify the relationship between the % canal in 1990 of land in 1956 and the land loss from 1956 to 1990. Ninety nine percent of the land was wetland. The sites were in Terrebonne, Barataria and St. Bernard Parishes. The Site number refers to the number in the original paper by Bass and Turner (1997). ## Sharing/Access information This is a section for linking to other ways to access the data, and for linking to sources the data is derived from, if any. none Data was derived from the following sources: Bass, A. & Turner, R. E. Relationships between salt marsh loss and dredged canals in three south Louisiana estuaries. J. Coastal Res. 13, 895-903 (1997). Britsch, L. D. & Dunbar, J. B. Land loss rates: Louisiana coastal plain. J. Coastal Res. 9, 324–338 (1993). Scaife, W. W., Turner, R. E. & Costanza, R. Coastal Louisiana recent land loss and canal impacts. Environ. Managmt. 7, 433–442 (1983). Unpublished data acquired from the Corps of Engineers, New Orleans District, LA is merged with this data. Turner, R. E. & Rao, Y. W. Relationships between wetland fragmentation and recent hydrologic changes in a deltaic coast. Estuaries 13, 272-281 (1990). ## Code/Software no codes Excel software