100+ Years of Land Change for Coastal Louisiana By: National Wetlands Research Center, Lafayette and Baton Rouge, LA and Louisiana Coastal Area (LCA) Land Change Study Group

Abstract Coastal Louisiana has lost an average of 35 square miles of land per year for the last 50 years. During the 20 th century, coastal Louisiana has already lost 1.2 million acres (1,900 sq. mi.) of land and, if nothing is done, it is expected to lose another 430,000 acres (670 sq. mi.) in the next 50 years. The acreage lost and projected to be lost over this 100+ year period is greater than the size of Delaware and Washington, DC-Baltimore, MD metropolitan area combined. Using U.S. Geological Survey data, generated in conjunction with the Louisiana State Department of Wildlife and Fisheries, there are 878,000 acres of fresh marsh, 1.63 million acres of non-fresh marsh, and 1.15 million acres of forested and scrub/shrub wetlands. This makes a total of 3.67 million acres of coastal wetlands in Louisiana. Thus, within the lower 48 states, Louisiana accounts for 30% of total coastal marsh and 45% of intertidal coastal marsh. Included all coastal wetlands (marsh, mangrove, and forested), Louisiana has 14% of the total for the conterminous United States. During the 1990’s, this loss accounted for an estimated 90% of the coastal marsh loss in the lower 48 states.

History Previous land loss rates = 39.4 mi 2 /year* = 34.9 mi 2 /year * Wetland loss during this period was 44 mi 2 /year

Change Map Classified Landsat Thematic Mapper Satellite Imagery Gain Loss Total Net Loss = 239 mi 2 Net Loss Rate =23.9 mi 2 /yr Barataria and Terrebonne Basins = 65% of Net Loss Atchafalaya Delta Upper Terrabonne Bay Barataria Bay

Change Map Western Terrebonne Bay - Internal Marsh Ponding and Atchafalaya Delta Gain Loss

Western Terrebonne Bay – Internal Marsh Ponding and Atchafalaya Delta

Change Map Upper Terrebonne Bay Area - Fringing Shoreline Erosion Gain Loss

Upper Terrebonne Bay Area - Fringing Shoreline Erosion 1860 – 2050 Animation

Change Map Barataria Bay and Little Lake Area - Fringing Shoreline Erosion Gain Loss

Barataria / Grand Isle - Fringing Shoreline Erosion Animation

1978 Land / Water Land Water

2000 Land / Water Land Water

Predicted 2050 Land / Water Land Water

Land / Water Difference Land Loss Land Gain Land Water Atchafalaya Bay Barataria Bay

1978 Land / Water Land Water Atchafalaya Bay

2000 Land / Water Land Water Atchafalaya Bay

Predicted 2050 Land / Water Land Water Atchafalaya Bay

Land / Water Difference Land Loss Land Gain Land Water Atchafalaya Bay

1978 Land / Water Land Water Barataria Bay

2000 Land / Water Land Water Barataria Bay

Predicted 2050 Land / Water Land Water Barataria Bay

Land / Water Difference Land Water Land Loss Land Gain Barataria Bay

Land Water Barataria- Terrebonne Area Atchafalaya Delta Mississippi Delta Predicted Coastal Louisiana Trends: Land Loss Predicted Land Loss Land Gain Predicted Land Gain

Atchafalaya Delta: Predicted Land Water Land Loss Predicted Land Loss Land Gain Predicted Land Gain

Barataria- Terrebonne: Predicted Land Gain Predicted Land Gain Land Water Land Loss Predicted Land Loss

Mississippi Delta: Predicted Land Gain Predicted Land Gain Land Water Land Loss Predicted Land Loss

Major Factors for Predicted Land Gains CWPPRA Projects Caernarvon Diversion Davis Pond Diversion Mississippi River Delta Building Atchafalaya Delta Building 54 mi 2 15 mi 2 14 mi 2 53 mi 2 25 mi 2 Total Predicted Gain: 161 mi 2

Predicted Coastal Louisiana Land Loss Net Land Loss = 2,038 mi 2 (with predicted gain) and 2,199 mi 2 (without) Curve derived from Quadratic Spline: y = a + bx +cx 2, where y is the land in square miles and x is the duration in years.

In Summary - A: Louisiana has 3.67 million acres of coastal wetlands of which: 1,630,000 acres are non-fresh marshes, 878,000 acres are fresh marshes, and 1,150,000 acres are wetland forests and shrubs. Within the 48 U.S. contiguous states, coastal Louisiana accounts for: 30% of the total coastal marsh, 45% of the intertidal marsh, and 14% of all coastal wetlands.

In Summary - B: Coastal Louisiana has lost 1.2 million acres of wetlands this century and possibly another 430,000 acres from 2000 to Louisiana’s total coastal land area loss from1956 to 2050 exceeds the size of the State of Delaware and Washington, DC-Baltimore, MD metropolitan area combined. Louisiana accounts for 90% of the total coastal marsh loss within the 48 U.S. contiguous states.

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