U.S. Department of the Interior

U.S. Geological Survey

Slidell

Covington

Mandeville

Hammond

Donaldsonville

Thibodaux

Larose

Houma

Grand Isle

Morgan

City

Intracoastal

City Cameron

Johnsons Bayou

Venice

Alligator Point

New Orleans

Port 

Fourchon

Gulf of Mexico

Vermilion Bay

West Cote

Blanche Bay

East Cote

Blanche Bay

Atchafalaya Bay

Fourleague Bay

Terrebonne Bay

Barataria Bay

Timbalier Bay

Lake 

Maurepas

Bayou Lafourche

Chandeleur Islands

Garden

Island Bay

East Bay

West Bay

South Pass

Marsh

Island

Lake Pontchartrain

Lake Borgne

Lake Salvador

Breton Sound

White Lake

Grand Lake

Sabine Lake

Calcasieu 

Lake

Subprovince 4 Gulf of Mexico

Subprovince 3

Subprovince 2

Subprovince 1

Slidell

Covington

Mandeville

Hammond

Donaldsonville

Thibodaux

Larose

Houma

Grand Isle

Morgan

City

Intracoastal

City Cameron

Johnsons Bayou

Venice

Alligator Point

New Orleans

Port 

Fourchon

Gulf of Mexico

Vermilion Bay

West Cote

Blanche Bay

East Cote

Blanche Bay

Atchafalaya Bay

Fourleague Bay

Terrebonne Bay

Barataria Bay

Timbalier Bay

Lake 

Maurepas

Bayou Lafourche

Chandeleur Islands

Garden

Island Bay

East Bay

West Bay

South Pass

Marsh

Island

Lake Pontchartrain

Lake Borgne

Lake Salvador

Breton Sound

White Lake

Grand Lake

Sabine Lake

Calcasieu 

Lake

Subprovince 4 Gulf of Mexico

Subprovince 3 Subprovince 2

Subprovince 1

2004 54

2006 56

Slidell

Covington

Mandeville

Hammond

Donaldsonville

Thibodaux

Larose

Houma

Grand Isle

Morgan

City

Intracoastal

City Cameron

Johnsons Bayou

Venice

Alligator Point

New Orleans

Port 

Fourchon

Gulf of Mexico

Vermilion Bay

West Cote

Blanche Bay

East Cote

Blanche Bay

Atchafalaya Bay

Fourleague Bay

Terrebonne Bay

Barataria Bay

Timbalier Bay

Lake 

Maurepas

Bayou Lafourche

Chandeleur Islands

Garden

Island Bay

East Bay

West Bay

South Pass

Marsh

Island

Lake Pontchartrain

Lake Borgne

Lake Salvador

Breton Sound

White Lake

Grand Lake Sabine Lake

Calcasieu 

Lake

Subprovince 4 Gulf of Mexico

Subprovince 3 Subprovince 2

Subprovince 1

1990

By Steve B. Hartley

Modified Methodology for Projecting Coastal Louisiana Land Changes over the Next 50 Years

Slidell

Covington

Mandeville

Hammond

Donaldsonville

Thibodaux

Larose

Houma

Grand Isle

Morgan

City

Intracoastal

City Cameron

Johnsons Bayou

Venice

Alligator Point

New Orleans

Port 

Fourchon

Gulf of Mexico

Vermilion Bay

West Cote

Blanche Bay

East Cote

Blanche Bay

Atchafalaya Bay

Fourleague Bay

Terrebonne Bay

Barataria Bay

Timbalier Bay

Lake 

Maurepas

Bayou Lafourche

Chandeleur Islands

Garden

Island Bay

East Bay

West Bay

South Pass

Marsh

Island

Lake Pontchartrain

Lake Borgne

Lake Salvador

Breton Sound

White Lake

Grand Lake Sabine Lake

Calcasieu 

Lake

Subprovince 4 Gulf of Mexico

Subprovince 3 Subprovince 2

Subprovince 1

2001 51

EXPLANATION

Land

Land loss

Land gain

Subprovince boundary

20 10 0 20 40 60 80

Kilometers

Scale 1:750,000

20 10 0 20 40 60 80

Miles

Hartley, S.B., 2009, Modified methodology for projecting coastal Louisiana 

land changes over the next 50 years: U.S. Geological Survey 

Scientific Investigations Map 3098, 

1 sheet, scale 1:750,000.

Suggested citation:

Scientific Investigations Map 3098

Introduction

 The coastal Louisiana landscape is continually undergoing geomorphologic changes (in 

particular, land loss); however, after the 2005 hurricane season, the changes were intensified 

because of Hurricanes Katrina and Rita (Barras, 2006). These two hurricanes changed the 

landscape of coastal Louisiana, thus altering the projection of future land and water patterns. 

The U.S. Geological Survey (USGS) National Wetlands Research Center (NWRC) has 

assessed changes in land and water patterns in coastal Louisiana for many years by using 

Landsat Thematic Mapper (TM) satellite imagery (Barras, 2006). The purpose of this study is 

to provide information on potential changes to coastal Louisiana by using a revised 

methodology and by taking into account the catastrophic damage caused by Hurricanes 

Katrina and Rita. This study captures these patterns and projects land loss or gain rates over 

50 years.

Background

 The Louisiana Coastal Area (LCA), Louisiana Ecosystem Restoration Study (Barras and 

others, 2003) used land loss or gain rates to project landscape changes over 50 years but 

noted the limitations of the methodology used to compute rate change (Barras and others, 

2003). The projected landscape in the LCA study assumes that the historical events and 

processes contributing to land loss or gain would continue into the future at the same 

intensity and thus provided for extreme event years. The amount of land loss caused by the 

2005 hurricane season, however, was 42 percent (562 km2) (Barras, 2006, 2007) of the total 

land loss (1,329 km2

) that was projected for the next 50 years (Barras and others, 2003). To 

capture the landscape patterns caused by the 2005 hurricane season, Landsat 5 TM satellite 

imagery (from 2001, 2004, and 2006) provided by the USGS Center for Earth Resources 

Observation and Science was used. The imagery shows the differences in landscape 

patterns for before and after storm events.

Objective

 The objective of this study is to capture the landscape changes that occurred after the 

2005 hurricane season and extend those changes into the future by modifying the 

methodology of the LCA study.

Methodology

 The methodology used to project land loss is similar to that used in the LCA study 

(Barras and others, 2003). The LCA methodology used existing historical data, derived from 

interpretation of aerial photography, and new data, based on classified Landsat TM satellite 

imagery, to assess current land loss and gain trends from 1978 to 2000 for coastal Louisiana 

and project those trends over 50 years. This study is designed to extend the LCA analysis by 

incorporating the massive amount of land loss evident after the 2005 hurricane season 

(Barras, 2006, 2007).

In the LCA study, 183 polygons were delineated by the Land Change Study Group 

(Barras and others, 2003) to compute geographic-specific change rates within areas thought 

to have similar erosion rates based on geomorphology of the area and whether or not the 

area was under active management. There are several consequences to this methodology. 

One consequence is that the LCA methodology caused areas in the mapping to turn entirely 

to water before a threshold was reached. Another consequence is that managed areas, 

which were considered as undergoing ambient erosion rates in the LCA methodology, 

actually did not undergo ambient erosion rates, or in some cases like Coastal Wetlands 

Planning, Protection and Restoration Act (CWPPRA) projects, not until after the life cycle of 

the project (20 years).

To capture these anomalies, we used a similar methodology using classified Landsat TM 

satellite imagery from 1990, 2001, 2004, and 2006 to calculate the “background” or ambient 

land-water change rates but divided the Louisiana coastal area differently on the basis of (1) 

geographic regions (“subprovinces”) and (2) specific homogeneous habitat types. Defining 

polygons by subprovinces (1, Pontchartrain Basin; 2, Barataria Basin; 3, Vermilion/Terrebonne 

Basins; and 4, the Chenier Plain area [Barras and others, 2003]) allows for a specific erosion 

rate to be applied to that area. Further subdividing the provinces by habitat type allows for 

specific erosion rates for a particular vegetation type to be applied. This revised methodology 

assumes that erosion rates for habitat types by subprovince are under the influence of similar 

environmental conditions (sediment depletion, subsidence, and saltwater intrusion).

Initially, the approach was to use the seven habitat types (four “marsh” types, one 

“swamp,” one “other,” and one “water”) from a 2001 vegetation survey (Linscombe and 

others, 2001) within each of the four geographic provinces (Barras and others, 2003) of 

coastal Louisiana to produce a matrix of 28 unique polygons. These unique polygons would 

allow for comparable erosion rates to be applied to a specific region and habitat type. The 

final analysis consisted of 24 polygons because the habitat type “water” (Lakes Maurepas 

and Pontchartrain) was included only in subprovince 1 from the 2001 vegetation survey and 

because “swamp” was not found in subprovince 4. The final 24 polygons were then used to 

calculate a background change rate for three time periods (1990–2001, 1990–2004, and 

1990–2006). Background change rates for each polygon were calculated by taking the 

difference in water or land, depending on loss or gain, among each time period and dividing it 

by the time interval. This calculation gives an annual change rate for each polygon per time 

period. Background change rates for each time period were then used to compute the 

projected change in each subprovince and habitat type (table 1) over 50 years by using the 

same compound rate functions used in the LCA study (Barras and others, 2003). The maps 

show only an approximation of where erosion may occur on the basis of intensity values of 

the Landsat TM imagery.

 Actively managed areas and the CWPPRA areas were not masked out and dealt with 

separately as in the LCA study. The reason for not masking out managed areas is because 

those areas have the same opportunity for influence by a large disturbance event, such as 

those that occurred during the 2005 hurricane season. Other reasons not to mask out 

managed areas include natural subsidence, sediment depletion, saltwater intrusion, and 

wave erosion, which are still ongoing events in these areas even though they are considered 

managed.

Results

 The maps show projected land changes based on the revised methodology and inclusion 

of damage by Hurricanes Katrina and Rita. The map at the top left shows land and water areas 

for 1990; the map at the bottom left shows a 50-year projection for land loss for 2001 (before 

the 2005 hurricane season) to 2051; upper right shows 2004 (before the 2005 hurricane season) 

to 2054; and bottom right shows 2006 (after the 2005 hurricane season) to 2056. Comparison of 

projected land change values between the LCA study and this study shows that this revised 

methodology—that is, using a reduced polygon subset (reduced from 183 to 24) based on 

habitat type and subprovince—can be used as a quick projection of land loss. The LCA study 

showed a total projected loss of 1,329 km2

 over the next 50 years using a time period from 

1978/90 to 2000, while this study projects a loss of 1,386.3 km2

 using a time interval of 

1990–2001, a difference of about 1.15 km2

/year. The small difference between these projected 

numbers can be attributed to a couple of factors. The first is the different time intervals used 

to calculate change rates. The second is the exclusion of managed areas.

 Projected land loss decreases from 1,386.3 km2

 using the 1990–2001 time interval to 

1,171.4 km2

 using the 1990–2004 time interval (table 1). This decrease in projected land loss 

demonstrates that land loss was decreasing before the 2005 hurricane season, which could 

be attributed to the effects of CWPPRA projects or imagery used for 2004 having lower water 

levels. This decreasing trend was reversed after the 2005 hurricane season. Projected land 

loss increased to 2,190.1 km2

 (table 1) using the 1990–2006 time interval erosion rates, thus 

showing the massive amount of projected land loss caused by inclusion of the 2005 hurricane 

season. Barras (2006) cautioned about using the immediate posthurricane imagery because of 

persistently high water levels in some places that precluded their definitive identification as 

either flooded marsh or as marsh removed by the storm surge. He stated that estimates of 

permanent losses cannot be made until several growing seasons have passed and the 

transitory impacts of the hurricanes are accounted for (Barras, 2006). Therefore, the projected 

land loss for the period 2006–56 is only a preliminary analysis.

 Land change projections show an increase in land loss in subprovinces 1 and 4 (fig. 1). 

Projected province 1 increases can be attributed to Hurricane Katrina, and projected 

subprovince 4 increases can be attributed to Hurricane Rita (Barras, 2007). Projected land 

loss by habitat shows that fresh and intermediate marshes may erode faster than would 

brackish and saline marshes (fig. 2). The reason for this is that Hurricane Katrina’s path 

intersected the fresh and intermediate marshes of the Mississippi River Delta, while 

Hurricane Rita’s path left thousands of acres of fresh and intermediate marsh inundated for 

months because of impoundments (Louisiana Department of Wildlife and Fisheries, Fur and 

Refuge Division, 2007).

References

Barras, J., Beville, S., Britsch, D., Hartley, S., Hawes, S., Johnston, J., Kemp, P., Kinler, Q., 

Martucci, A., Porthouse, J., Reed, D., Roy, K., Sapkota, S., and Suhayda, J., 2003, Historical 

and projected coastal Louisiana land changes—1978–2050, appendix B of Louisiana 

Coastal Area (LCA), Louisiana Ecosystem Restoration Study: U.S. Geological Survey 

Open-File Report 2003–334, 39 p., accessed Sept. 16, 2006, at 

http://pubs.er.usgs.gov/usgspubs/ofr/ofr03334.

Barras, J.A., 2006, Land area change in coastal Louisiana after the 2005 hurricanes—a series 

of three maps: U.S. Geological Survey Open-File Report 06–1274.

Barras, J.A., 2007, Satellite images and aerial photographs of the effects of Hurricanes Katrina 

and Rita on coastal Louisiana: U.S. Geological Survey Data Series Report 07–281.

Linscombe, G., Chabreck, R.H., and Hartley, S.B., 2001, 2001 Louisiana coastal 

marsh-vegetative type map (database): Louisiana Department of Wildlife and Fisheries, Fur 

and Refuge Division, and the U.S. Geological Survey National Wetlands Research Center, 

accessed Sept. 16, 2006, at http://brownmarsh.net/data/III_8.htm.

Louisiana Department of Wildlife and Fisheries, Fur and Refuge Division, 2007, Louisiana’s 

Alligator Management Program: Gator Notes, v. 2, no. 1, accessed Feb. 25, 2009, at 

http://www.wlf.louisiana.gov/pdfs/experience/April%202007%20Newsletter.pdf.

Image Source:

Landsat 5 Thematic Mapper satellite imagery is provided 

by the U.S. Geological Survey Center for Earth 

Resources Observation and Science (EROS).

The background image represents data from

1990, 2001, 2004, and 2006 that are classified 

to land or water.

Table 1. Projected land loss by subprovince and habitat type.

km2 km2

/yr km2 km2/yr km2 km2/yr

Subprovince

1 388.1 7.8 387.6 7.8 642.9 12.8

2 365.7 7.3 392.4 7.8 391.4 7.8

3 394.9 7.9 303.9 6.1 417.2 8.3

4 237.5 4.8 87.5 1.8 738.6 14.8

Totals 1,386.2 27.8 1,171.4 23.5 2,190.1 43.7

Habitat type

Fresh 124.1 2.5 8.9 0.2 787.3 15.7

Intermediate 326.0 6.5 303.3 6.1 570.8 11.4

Brackish 298.9 6.0 306.3 6.1 377.2 7.5

Saline 573.8 11.5 509.1 10.2 430.6 8.6

Swamp 63.4 1.3 43.8 0.9 24.2 0.5

Totals 1,386.2 27.8 1,171.4 23.5 2,190.1 43.7

 2001–51 2004–54 2006–56

0

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1 2 3 4

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Subprovince

2001–51

2004–54

2006–56

0

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800

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2001–51

2004–54

2006–56

Figure 1. Projected land changes over the next 50 years by subprovince.

Figure 2. Projected land changes over the next 50 years by habitat type.