! I TECHNICAL REPORT GL-90-2
LAND LOSS RATES
REPORT 3
LOUISIANA COASTAL PLAIN
by
J.B. Dunbar
Geotechnical Laboratory
DEPARTMENT OF THE ARMY Waterways Experiment Station, Corps of Engineers 3909 Halls Ferry Road, Vicksburg, Mississippi 39180-6199
and
L. D. Britsch and E. B. Kemp Ill
US Army Engineer District, New Orleans PO Box 60267, New Orleans, Louisiana 70160-0267
March 1992 Report 3 of a Series
Approved For Public Release; Distribution Is Unlimited
Prepared tor US Army Engineer District, New Orleans New Orleans, Louisiana 70160-0267 Form Approved REPORT DOCUMENTATION PAGE OMB No. 0704-0188
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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) B. PERFORMING ORGANIZATION REPORT NUMBER See reverse. Technical Report GL-90-2
9. SPONSORING I MONITORING AGENCY NAME(S) AND ADDRESS(ES) 1O. SPONSORING I MONITORING AGENCY REPORT NUMBER US Army Engineer District, New Orleans, New Orleans, Louisiana 70160-0267
11. SUPPLEMENTARY NOTES This report is available from the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161.
12a. DISTRIBUTION I AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Approved for public release; distribution is unlimited.
13. ABSTRACT (Maximum 200 words) Land Loss mapping and rate curve development for 62 quadrangles in the Louisiana Coastal Plain shows that land loss rates and trends vary signif i- cantly throughout coastal Louisiana. Land loss rates for each quadrangle were defined for 4 time periods: 1930's to 1956-58, 1956-58 to 1974, 1974 to 1983, and 1983 to 1990. Differences in land loss rates among the individual quadrangles are a function of the geologic and hydrologic setting and the factors which contribute to land loss such as subsidence, storm induced erosion, channelization of streams and rivers, and canal dredging. Of the 62 quadrangles mapped, 9 quadrangles are losing more than 1 percent of their land area each year, and 12 quadrangles are losing between 0.5 and 1.0 percent per year during the 1983 to 1990 period. On a regional scale, the land loss rate for the entire Louisiana Coastal Plain has decreased from an average yearly rate of 41.83 square miles in the 1956-58 to 1974 period to 25.34 square miles during the 1983 to 1990 period. The percentage of land being lost is also decreasing from 0.51 percent per year in the 1956-58 to 1974 period to 0.35 percent per year during the 1983 to 1990 period. The regional land loss rate will probably continue to decrease slowly until a background rate is reached. 14. SUBJECT TERMS 15. NUMBER OF PAGES Coastal Louisiana Mississippi River Deltaic Plair. 65 Land loss Wetland loss Louisiana Chenier Plain Wetlands 16. PRICE CODE
17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT UNCLASSIFIED UNCLASSIFIED
NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Prescribed by ANSI Std. Z39-18 298·102 7. (Continued) • USAE Waterways Experiment Station, Geotechnical Laboratory 3909 Halls Ferry Road, Vicksburg, Mississippi 39180-6199 USAE District, New Orleans PO Box 60267 New Orleans, Louisiana 70160-0267 PREFACE
This investigation was authorized by the US Army Engineer District, New Orleans (CELMN), under the heading "Louisiana Coastal Plain, Land Loss Mapping: 1983-1989" by DA Form 2544, No. CELMN-ED-91-20, dated 8 November 1990 and amended 19 February 1991, 6 June 1991, 12 July 1991, and 16 August 1991. This investigation was performed and the report prepared during the period 8 November 1990 to 31 January 1992. The Program Manager for this study was Mr. E. B. Kemp III, Chief, Geology Section, Engineering Division (ED-FG), CELMN. Land loss mapping and rate curve development were performed by Mr. J. B. Dunbar, Geologic Environments Analysis Section (GEAS), Engineering Geology Branch (EGB), Earthquake Engineering and Geosciences Division (EEGD), Geotechnical Laboratory (GL), Waterways Experiment Station (WES). This report was prepared by Messrs. J. B. Dunbar, WES; L. D. Britsch, CELMN; and E. B. Kemp III, CELMN. This investigation was conducted under the direct supervision of Messrs. R. J. Larson, Chief, GEAS, and Joe Gatz, Chief, EGB, and under the general supervision of Drs. A. G. Franklin, Chief, EEGD, and W. F. Marcuson III, Chief, GL. Dr. Robert W. Whalin was Director of WES. COL Leonard G. Hassell, EN, was Commander and Deputy Director of WES during the preparation of this report.
1 CONTENTS Page PREFACE ••• ...... 1 PART I: INTRODUCTION •• ...... 3 Background ••••••••• ...... 3 Purposes and Scope •.••••••••••••••••••••• 3 PART II: DATA SOURCES AND MAPPING PROCEDURES. 5 Data Sources ...... 5 Land Loss Interpretation and Classification ••••••.•••••••••••••••••• 5 Land Loss Mapping and Area Measurement •••••••••••.•••••••••••••••.•• 7 PART III: LAND LOSS RATES ••••••.••••••••••••••••••• 8 Land Loss Rates of Individual Quadrangles •••• 8 1930's Base Land and Water Data. 17
Composite Land Loss Rates ••• 23 PART IV: CONCLUSIONS •••.•••••••••••• 27 REFERENCES •• 28 APPENDIX A: LAND LOSS RATE CURVES •••••• Al APPENDIX B: PERCENT LAND LOSS RATE CURVES ••••••••••••••••••••••••••••••••• Bl
2 LAND LOSS RATES: LOUISIANA COASTAL PLAIN
PART I: INTRODUCTION
Background
1. This study is the third in a series by the US Army Engineer District, New.Orleans (CELMN), and the US Army Engineer Waterways Experiment Station (WES) on land loss rates in coastal Louisiana. Earlier studies by Britsch and Kemp (1990) and Dunbar, Britsch, and Kemp (1990) defined land loss rates and presented land loss rate curves for individual US Geological Survey (USGS) 15-minute (min) quadrangles in the Mississippi River Deltaic and Chenier Plains, respectively (see Figure 1) . Together, these two geomorphic regions form an area consisting of 62 USGS 15-min quadrangles, an area of approximately 18,000 square miles.* In both studies, land loss rates for three time periods (1930's to 1956-58, 1956-58 to 1974, and 1974 to 1983) were identified for each quadrangle. This study is a continuation of these earlier studies and presents the most recent land loss rate and trend data for the 1983 to 1990 time period.
Purposes and Scope
2. The purposes for this study are to document on maps the location of the land loss and determine the magnitude of the loss that has occurred in coastal Louisiana between the 1930's and 1990. Specific objectives of this study are to: (a) map the land loss that has occurred for the 1983 to 1990 time period for each 15-min (1:62,500 scale) USGS quadrangle in the study area, (b) determine land loss rates for each quadrangle mapped and for the entire Louisiana coastal plain, and (c) identify significant historic land loss trends. Data from this study are being used by CELMN to assist planning studies and wetland restoration projects. This report will not evaluate site-specific causes for land loss in coastal Louisiana but will address generic causes for the land loss.
* Multiply square miles by 2.589998 to obtain square kilometres.
3 °g ,,o \ o:;il 1;;1 ";J MISSISSIPPI ~ -- -- LOUISIANA I Nr2-- I ~ &l r -N- ~1>iii~ ) DELTAIC PLAIN :;; 3: ~ ~ ::!! > CHENIER PLAIN
~ Crowley e Lafayette ...... V" \,.!1.. <:,. \\ r300 ""' ) " #
290 GULF 0 F MExico ~ 20 0 20 40MI
Figure 1. Index map to the study area showing 15-min quadrangles in the Louisiana Coastal Plain PART II: DATA SOURCES AND MAPPING PROCEDURES
Data Sources
3. Land loss mapping was accomplished by comparing four vintages of aerial photography with a base map and delineating the land loss that occurred over the period of record on the base map. Sources of map and photographic data used in this study are identified in Table 1. For the 1990 land loss update, WES and CELMN engaged NASA to fly a special high altitude photographic mission (ER-2 flight, December 8-9, 1990) over coastal Louisiana. Land loss mapping was conducted from the photography (scale: 1:62,500) obtained during the NASA overflight. 4. In addition to the photography, 12-channel Thematic Mapper Simulated (TMS) digital data (approximately 24-m resolution) of the study area was used as an aid in the land loss mapping for interpretation of problem areas. Land loss mapping was based on the photography rather than the digital data since previous mapping was photography based. 5. The base maps used were either US Coast and Geodetic Survey Air Photo Compilation Sheets (T-sheets) or early USGS 15-min topographic quadrangle maps. Both types of base maps are based on interpretation of early aerial photography. T-sheets were the preferred base map for this study as they are the earliest and most comprehensive base map available for Louisiana's coastal plain. T-sheets were photographically reduced to a USGS 15-min (1:62,500) quadrangle map format for mapping. For those areas where T-sheet coverage was not available, the earliest available USGS 15-min topographic quadrangle map was used for the base map. Both T-sheets and early 15-min USGS quadrangle maps were photographically transferred onto stable transparent film to produce the mapping base.
Land Loss Interpretation and Classification
6. This study documents changes from land to water over a period of approximately 60 years. Land loss is considered to be any land area present on either the base maps or 1930's photography that was interpreted as water on later photographic coverages. Land loss identified during the mapping
5 Table 1 Sources of Map and Photographic Data
Date Source Original Scale 1932-33 US Coast and Geodetic Survey 1:20,000 Air Photo Compilation Sheets (T-sheets)
1933-55 USGS 15-Minute Topographic 1:62,500 Quadrangle Maps
1933-35 Tobin Surveys, Black-And-White 1:62,500 Aerial Photo Mosaics
1956-58 Tobin Surveys, Black-And-White, 1:24,000 Aerial Photo Mosaics
1974 NASA Color IR 1:120,000
1983 National High Altitude Program, 1:58,000 Color IR
1990 NASA Color IR 1:62,500
6 includes both loss from man-made causes as well as loss due to natural processes. Most of the land loss classified as man-made is the direct result of dredging for various types of canals and waterways. All land loss not the direct result of man's activities was considered natural loss. 7. Because the distinction between land and water is so critical to the accuracy of this study, it is important to identify the criteria used to distinguish between land and water. Water was classified as any area of water having no permanent vegetation visible at the surface. Permanent vegetation, for purposes of this investigation, is that which is attached to the substrate, not floating vegetation such as hydrilla and hyacinths. Land was simply defined as everything on the photography (or base map) not classified as water. Generally, the only land areas on the photography without some visible vegetation were beaches and dredged sediments.
Land Loss Mapping and Area Measurement
8. A detailed discussion of the land loss mapping process is omitted from this report as it was described in detail by Britsch and Kemp (1990). In summary, land loss mapping during this study consisted of comparing the land areas on the base maps (transparent film positive of 15-min USGS quadrangle map) to land areas on the photography and delineating areas of land loss on the overlay base map. Land loss areas were defined for each photographic period examined. The resulting land loss map identified the overall land loss that had occurred during the four time periods mapped (1930's to 1956-58; 1956-58 to 1974; 1974 to 1983; and 1983 to 1990) and whether it was man-made (i.e., dredged canals) or natural loss. 9. Land loss areas were determined by optical scanning (digitizing) of individual overlays prepared for each map. Black ink overlays were prepared for each map for both the natural and man-made land loss identified for each period. The amount of land loss during each period was calculated for each map by optically scanning the ink overlays and computer processing the scanned (digitized) data. Land loss rates were determined for each period and a rate curve was constructed for each quadrangle. Examples of the different steps involved in land loss mapping and additional information about the mapping procedure are described in more detail by Britsch and Kemp (1990) .
7 PART III: LAND LOSS RATES
Land Loss Rates for Individual Quadrangles
Land Loss Rates in Square Miles Per Year 10. Land loss rates in square miles per year for the 62 USGS quadrangle maps in the Louisiana Coastal Plain are identified in Table 2. Rate curves for these quadrangles are presented in Appendix A. Time periods for which the land loss rates are based are shown in Table 2 and graphically by horizontal bars on the land loss rate curves in Appendix A. A summary of land loss rates for the different time periods mapped is presented in Figures 2a through 2d. 11. Quadrangles with land loss rates greater than 1, 2, and 3 square miles per year are shown by Figures 2a through 2d for the different time periods. For time period 1 (Figure 2a), there were no quadrangles with land loss rates greater than 2 square miles per year. The number of quadrangles with land loss rates greater than 1 square mile per year is as follows: 3 quadrangles in time period 1, 17 quadrangles in time period 2, 8 quadrangles in time period 3, and 7 quadrangles in time period 4. This series of illustrations shows that the greatest land loss has occurred in the Modern Delta, the South-Central Deltaic Plain, and the Western Chenier Plain. Land Loss Rates in Percent Per Year 12. As another method of presenting the land loss trend data, the 1930's base maps were digitized in order to determine the percentage of land loss for each quadrangle. Land loss rates as a percent of the land area present in each time period are identified in Table 3 and the individual rate curves for the percent data are presented in Appendix B. Land loss rates in Table 3 are expressed as average percent land loss per year and were derived by dividing the land loss rate (in square miles per year) for each quadrangle by the land area present at the beginning of each time period mapped. Land loss data presented as a function of percent allow comparison between quadrangles with small initial land areas and quadrangles with large land areas. With land loss rates expressed as percent loss, the comparison is independent of the total amount of land present for each quadrangle. The loss rate for each quadrangle is the amount of land loss as a percentage of the available land present. It is then possible to compare quadrangles which
8 Table 2 Louisiana Coastal Plain Land Loss Rates
Avg. Loss Avg. Loss Avg. Loss Avg. Loss Quadrangle Time in Square Time in Square Time in Square Time in Square Name Period 1 miles/year Period 2 miles/year Period 3 miles/year Period 4 miles/vear
Abbeville 1935-1954 0.07 1954-1974 0.23 1974-1983 0.24 1983-1990 0.43 Barataria 1939-1956 1.08 1956-1974 1.20 1974-1983 0.70 1983-1990 1.06 Bay Dogris 1932-1958 0.42 1958-1974 1.44 1974-1983 1. 26 1983-1990 1.15 Bayou Du Large 1932-1958 0.18 1958-1974 1.61 1974-1983 0.65 1983-1990 0.47 Bayou Sale 1937-1956 0.31 1956-1974 0.36 1974-1983 0.19 1983-1990 0.07 Belle Isle 1940-1956 0.38 1956-1974 0.32 1974-1983 0.15 1983-1990 0.07 Black Bay 1932-1958 0.21 1958-1974 0.37 1974-1983 0.52 1983-1990 0.22 Bonnet Carre 1936-1958 0.10 1958-1974 0.44 1974-1983 0.19 1983-1990 0.07 Breton Island 1932-1958 0.26 1958-1974 0.18 1974-1983 O.ll 1983-1990 0.05 Caillou Bay 1932-1958 0.22 1958-1974 0.40 1974-1983 0.43 1983-1990 0.21 Cameron 1933-1955 0.08 1955-1974 2.47 1974-1983 0.60 1983-1990 0.25 Cat Island 1932-1958 0.07 1958-1974 0.09 1974-1983 O.ll 1983-1990 0.07 Chef Menteur 1932-1958 \.0 0.49 1958-1974 0.41 1974-1983 0.28 1983-1990 0.28 Chen. Au Tigre 1935-1951 0.08 1951-1974 0.36 1974-1983 0.13 1983-1990 0.32 Constance Bayou 1932-1955 0.64 1955-1974 0.82 1974-1983 0.50 1983-1990 0.59 Covington 1932-1958 0.02 1958-1974 0.18 1974-1983 0.02 1983-1990 0.18 Cut Off 1939-1958 0 . .22 1958-1974 0.53 1974-1983 0.39 1983-1990 0.51 Derouen 1932-1956 0.24 1956-1974 0.22 1974-1983 0.24 1983-1990 0.25 Dulac 1932-1958 0.37 1958-1974 0.98 1974-1983 1. 99 1983-1990 1.49 East Delta 1932-1958 1.17 1958-1974 1. 90 1974-1983 0.27 1983-1990 0.34 Empire 1932-1958 0.35 1958-1974 1.12 1974-1983 2.66 1983-1990 2.08 Forked Island 1935-1955 0.01 1955-1974 0.15 1974-1983 0.14 1983-1990 0.27 .Fort Livingston 1932-1958 0.34 1958-1974 0.53 1974-1983 0.89 1983-1990 0.54 Gibson 1939-1958 O.ll 1958-1974 1. so 1974-1983 0.45 1983-1990 0.54 Grand Lake East 1932-1955 0.29 1955-1974 0.41 1974-1983 1. 54 1983-1990 0.62 Grand Lake West 1933-1955 0.05 1955-1974 1.12 1974-1983 1. 30 1983-1990 0.44 Hahnville 1935-1958 O.ll 1958-1974 0.57 1974-1983 0.43 1983-1990 0.17 Hog Bayou 1932-1955 0.54 1955-1974 0. 72 1974-1983 0.15 1983-1990 0.56 Houma 1939-1958 0.13 1958-1974 0.24 1974-1983 0.17 1983-1990 0.29 Jeanerette 1937-1956 0.08 1956-1974 0.08 1974-1983 0.06 1983-1990 0.10
(Continued) Table 2 (Concluded)
Avg. Loss Avg. Loss Avg. Loss Avg. Loss Quadrangle Time in Square Time in Square Time in Square Time in Square Name Period 1 miles/year Period 2 miles/year Period 3 miles/year Period 4 miles/year
Johnsons Bayou 1933-1955 0.09 1955-1974 3.12 1974-1983 1.02 1983-1990 0.30 Lac des Allemands 1945-1958 0.13 1958-1974 O.ll 1974-1983 0.66 1983-1990 0.19 Lake Decade 1931-1956 0.25 1956-1974 1. 31 1974-1983 0.38 1983-1990 0.26 Lake Felicity 1932-1958 0.29 1958-1974 1. 32 1974-1983 1. 61 1983-1990 1. 35 Leeville 1932-1958 0.28 1958-1974 0.40 1974-1983 0.90 1983-1990 0.73 Marsh Island 1932-1956 0.23 1956-1974 0.39 1974-1983 0.24 1983-1990 0.25 Mitchell Key 1932-1956 0.05 1956-1974 0.03 1974-1983 0.07 1983-1990 0.02 Morgan City 1931-1956 0.20 1956-1974 1.37 1974-1983 0.93 1983-1990 0.31 Morgan Harbor 1932-1958 0.19 1958-1974 0.32 1974-1983 0.38 1983-1990 0.32 Mount Airy 1939-1958 0.05 1958-1974 0.08 1974-1983 0.08 1983-1990 0.12 New Orleans 1935-1958 0.17 1958-1974 0.26 1974-1983 0.14 1983-1990 0.15 Oyster Bayou 1931-1956 0.07 1956-1974 0.18 1974-1983 0.15 1983-1990 0.07 Pecan Island 1935-1951 0.06 1951-1974 0.79 1974-1983 0.75 1983-1990 0.62 I-' Point Chicot 1932-1958 0.08 1958-1974 0.08 1974-1983 0.07 1983-1990 0.15 0 Point au Fer 1931-1956 O.ll 1956-1974 0.16 1974-1983 0.17 1983-1990 O.ll Pointe ala Hache 1932-1958 0.28 1958-1974 0.75 1974-1983 0. 71 1983-1990 0.75 Pontchatoula 1939-1958 0.07 1958-1974 0.09 1974-1983 0.08 1983-1990 0.05 Rigo lets 1932-1958 O.ll 1958-1974 0.24 1974-1983 0.26 1983-1990 0.12 Slidell 1939-1958 0.06 1958-1974 0.15 1974-1983 0.05 1983-1990 0.04 Southwest Pass 1932-1958 0.10 1958-1974 0.12 1974-1983 0.02 1983-1990 0.02 Spanish Fort 1936-1958 0.03 1958-1974 0.01 1974-1983 0.003 1983-1990 0.01 Springfield 1939-1958 0.01 1958-1974 0.01 1974-1983 0.03 1983-1990 0.003 St. Bernard 1932-1958 0.29 1958-1974 1.23 1974-1983 0.70 1983-1990 0.26 Sulphur 1933-1955 0.05 1955-1974 1. 82 1974-1983 0.40 1983-1990 0.28 Sweet Lake 1933-1955 0.13 1955-1974 1.80 1974-1983 0.84 1983-1990 0.68 Terrebonne Bay 1932-1958 0.18 1958-1974 0.29 1974-1983 0.49 1983-1990 0.35 Thibodaux 1949-1958 0.003 1958-1974 0.02 1974-1983 0.07 1983-1990 0.26 Three Mile Bay 1932-1958 0.08 1958-1974 O.ll 1974-1983 0.10 1983-1990 0.19 Timbalier Bay 1932-1958 0.21 1958-1974 0.22 1974-1983 0.41 1983-1990 0.31 Venice 1932-1958 0.61 1958-1974 1. so 1974-1983 0.54 1983-1990 1.60 West Delta 1932-1958 1.41 1958-1974 2.00 1974-1983 1.04 1983-1990 1.64 Yscloskey 1932-1958 0.12 1958-1974 0.60 1974-1983 0.53 1983-1990 0.14 LAND .LOSS RATES TIME 1 (1930's-1956-58)
o~ •t-; g "o MISSISSIPPI : LOUISIANA I I ~ II>(/) rJ> - N. ~1J>~ ~ ;; 3: ~ DELTAIC PLAIN :!! J> CHENIER PLAIN
Lake Charles Crowley e ~"""'
I-' I-' ) d I
RATES (Ml2/YEAR) ,,. c=J 0.0- 1.0 GULF ~ 1.0 - 2.0 0 F MExico ~
~ 0 ~ ~~
Figure 2a. Summary of land loss rates in square miles per year for time period 1 (1930's to 1956-58) LAND LOSS RATES TIME 2 (1956-58-1974)
,,. ·~ ·~ ;; MISSISSIPPI ·~ ·: LOUISIANA I I
l:l l> -N-i !\/!- °' DELTAIC PLAIN ~ ~ 1 :!! l> CHENIER PLAIN
~~ Crowley e
JO' I-' l'V ) d I RATES (M12/YEAR) C:J 0.0-1.0 ,,. b.SS5I 1.0 - 2.0 E::z::3 2.0 - 3.0 GULF ~ 3.0-4.0 0 F
SCALE MExico '" 20 4QMI
Figure 2b. Summary of land loss rates in square miles per year for time period 2 (1956-58 to 1974) LAND LOSS RATES TIME 3 (1974-1983)
,,. ":;ii ·~ .. MISSISSIPPI ·~ : LOUISIANA I I "'r- -N-~ ~1)>~ ~ 1 DELTAIC PLAIN ~ ~)> CHENIER PLAIN
Crowley e Lafayette• -=<= '=» ,,.
I-' w ) "
RATES {M12NEAR} c=J 0.0-1.0 ,,. ~ 1.0-2.0 GULF t·:·:·:·~ 2.0 - 3.o 0 F
SCALE MExico
20 0 20 40MI
Figure 2c. Summary of land loss rates in square miles per year for time period 3 (1974 to 1983) LAND LOSS RATES TIME 4 (1983-1990)
"" ·:;: ·~ ; MISSISSIPPI °&l : LOUISIANA I I ~ .. r- -N ~'ij ~;i:: !\")> ~ DEL TAIC PLAIN ~ CHENIER PLAIN
Lake Charles Crowley e ~""""'
I-'.,,. ) d
RATES (M12NEAR) C:=J 0.0 . 1.0
29'• ~ 1.0-2.0 GULF t·:·:·:·j 2.0 - 3.o OF MExtco ~
~u 40MI
Figure 2d. Summary of land loss rates in square miles per year for time period 4 (1983 to 1990) Table 3 Louisiana Coastal Plain Average Percent Land Loss Rates
Average Average Average Average Quadrangle Time Percent Time Percent Time Percent Time Percent Name Period 1 Loss/Year Period 2 Loss/Year Period 3 Loss/Year Period 4 Loss/Year
Abbeville 1935-1954 0.08 1954-1974 0.25 1974-1983 0.27 1983-1990 0.50 Barataria 1939-1956 0.56 1956-1974 0.69 1974-1983 0.46 1983-1990 0.73 Bay Dogris 1932-1958 0.24 1958-1974 0.89 1974-1983 0.91 1983-1990 0.90 Bayou Du Large 1932-1958 0.08 1958-1974 0. 77 1974-1983 0.36 1983-1990 0.27 Bayou Sale 1937-1956 0.35 1956-1974 0.44 1974-1983 0.26 1983-1990 0.10 Belle Isle 1940-1956 0.17 1956-1974 0.15 1974-1983 0.07 1983-1990 0.03 Black Bay 1932-1958 0.21 1958-1974 0.39 1974-1983 0.58 1983-1990 0.26 Bonnet Carre 1936-1958 0.09 1958-1974 0.41 1974-1983 0.19 1983-1990 0.07 Breton Island 1932-1958 1.42 1958-1974 1. 55 1974-1983 1.26 1983-1990 0.65 Caillou Bay 1932-1958 0.26 1958-1974 0.50 1974-1983 0.59 1983-1990 0.30 Cameron 1933-1955 0.05 1955-1974 1. 55 1974-1983 0.53 1983-1990 0.23 Cat Island 1932-1958 0.61 1958-1974 0.92 1974-1983 1.33 1983-1990 0.96 I-' tn Chef Menteur 1932-1958 0.48 1958-1974 0.46 1974-1983 0.34 1983-1990 0.35 Chen. Au Tigre 1935-1951 0.08 1951-1974 0.38 1974-1983 0.15 1983-1990 0.37 Constance Bayou 1932-1955 0.43 1955-1974 0.62 1974-1983 0.43 1983-1990 0.52 Covington 1932-1958 0.03 1958-1974 0.27 1974-1983 0.03 1983-1990 0.28 Cut Off 1939-1958 0.10 1958-1974 0.24 1974-1983 0.19 1983-1990 0.25 Derouen 1932-1956 0.12 1956-1974 O.ll 1974-1983 0.12 1983-1990 0.13 Dulac 1932-1958 0.18 1958-1974 0.51 1974-1983 1.13 1983-1990 0.94 East Delta 1932-1958 1.16 1958-1974 2.70 1974-1983 0.68 1983-1990 0.91 Empire 1932-1958 0.22 1958-1974 0.75 1974-1983 2.01 1983-1990 1. 92 Forked Island 1935-1955 0.01 1955-1974 0.12 1974-1983 O.ll 1983-1990 0.22 Fort Livingston 1932-1958 0.40 1958-1974 0.69 1974-1983 1. 31 1983-1990 0.90 Gibson 1939-1958 0.04 1958-1974 0.59 1974-1983 0.20 1983-1990 0.24 Grand Lake East 1932-1955 0.16 1955-1974 0.24 1974-1983 0.95 1983-1990 0.41 Grand Lake West 1933-1955 0.02 1955-1974 0.53 1974-1983 0.68 1983-1990 0.25 Hahnville 1935-1958 0.05 1958-1974 0.24 1974-1983 0.19 1983-1990 0.08 Hog Bayou 1932-1955 0.66 1955-1974 1.04 1974-1983 0.27 1983-1990 1.04 Houma 1939-1958 0.05 1958-1974 0.10 1974-1983 0.07 1983-1990 0.12 Jeanerette 1937-1956 0.05 1956-1974 0.05 1974-1983 0.04 1983-1990 0.07
(Continued) Table 3 (Concluded)
Average Average Average Average Quadrangle Time Percent Time Percent Time Percent Time Percent Name Period 1 Loss/Year Period 2 Loss/Year Period 3 Loss/Year Period 4 Loss/Year
Johnsons Bayou 1933-1955 0.04 1955-1974 1. 23 1974-1983 0.53 1983-1990 0.16 Lac des Allemands 1945-1958 0.06 1958-1974 0.05 1974-1983 0.29 1983-1990 0.09 Lake Decade 1931-1956 0.13 1956-1974 0.69 1974-1983 0.23 1983-1990 0.16 Lake Felicity 1932-1958 0.14 1958-1974 0.67 1974-1983 0.91 1983-1990 0.83 Leeville 1932-1958 0.33 1958-1974 0.52 1974-1983 1.28 1983-1990 1.17 Marsh Island 1932-1956 0.21 1956-1974 0.38 1974-1983 0.25 1983-1990 0.27 Mitchell Key 1932-1956 1. 24 1956-1974 0.74 1974-1983 3.06 1983-1990 1.20 Morgan City 1931-1956 0.09 1956-1974 0.64 1974-1983 0.49 1983-1990 0.17 Morgan Harbor 1932-1958 0.18 1958-1974 0.31 1974-1983 0.39 1983-1990 0.34 Mount Airy 1939-1958 0.02 1958-1974 0.04 1974-1983 0.04 1983-1990 0.05 New Orleans 1935-1958 0.08 1958-1974 0.12 1974-1983 0.07 1983-1990 0.07 Oyster Bayou 1931-1956 0.20 1956-1974 0.54 1974-1983 0.50 1983-1990 0.24 Pecan Island 1935-1951 0.03 1951-1974 0.44 1974-1983 0.47 1983-1990 0.40
I-' Point Chicot 1932-1958 0.66 1958-1974 0.80 1974-1983 0.81 1983-1990 1.86 °' Point au Fer 1931-1956 0.33 1956-1974 0.53 1974-1983 0.62 1983-1990 0.42 Pointe ala Hache 1932-1958 0.13 1958-1974 . 0. 37 1974-1983 0.37 1983-1990 0.40 Pontchatoula 1939-1958 0.05 1958-1974 0.07 1974-1983 0.06 1983-1990 0.04 Rigo lets 1932-1958 0.10 1958-1974 0.23 1974-1983 0.26 1983-1990 0.12 Slidell 1939-1958 0.09 1958-1974 0.24 1974-1983 0.08 1983-1990 0.07 Southwest Pass 1932-1958 1.45 1958-1974 2.82 1974-1983 0.86 1983-1990 0.93 Spanish Fort 1936-1958 0.10 1958-1974 0.03 1974-1983 0.01 1983-1990 0.03 Springfield 1939-1958 0.01 1958-1974 0.01 1974-1983 0.03 1983-1990 0.003 St. Bernard 1932-1958 0.14 1958-1974 0.61 1974-1983 0.38 1983-1990 0.15 Sulphur 1933-1955 0.02 1955-1974 0.78 1974-1983 0.20 1983-1990 0.14 Sweet Lake 1933-1955 0.05 1955-1974 0. 77 1974-1983 0.42 1983-1990 0.35 Terrebonne Bay 1932-1958 0.40 1958-1974 0.73 1974-1983 1. 39 1983-1990 1.13 Thibodaux 1949-1958 0.001 1958-1974 0.01 1974-1983 0.03 1983-1990 0.10 Three Mile Bay 1932-1958 0.26 1958-1974 0.38 1974-1983 0.36 1983-1990 0. 72 Timbalier Bay 1932-1958 0.91 1958-1974 1. 26 1974-1983 2.93 1983-1990 3.01 Venice 1932-1958 0.63 1958-1974 1.87 1974-1983 0.96 1983-1990 3.11 West Delta 1932-1958 1. 23 1958-1974 2.55 1974-1983 2.24 1983-1990 4.42 Yscloskey 1932-1958 0.08 1958-1974 0.40 1974-1983 0.38 1983-1990 0.10 contain little land area (i.e., Cat Island, Mitchell Key, Point Chicot, etc.) with quadrangles that are nearly all land (Cut Off, Gibson, Houma, etc.). Table 3 shows that quadrangles with little land area have some of the highest land loss rates in the study area. 13. A summary of land loss rates expressed as average percent per year for the different time periods mapped is presented in Figures 3a through 3d. For time period 1, the maximum rate is less than 2 percent per year. In time periods 2, 3, and 4, the maximum rates are greater than 2 percent per year. Comparing quadrangles with loss rates greater than 0.5 percent over the four time periods mapped shows rather specific trends for the past 60 years. The 0.5 percent rate is empirically established for comparison purposes. The highest land loss rates based on percentage change are occurring along the coast. Percentage loss rates are highest in the Modern Delta, in the coastal quadrangles of the Eastern and Southern Deltaic Plain, and in the Western Chenier Plain. Percentage land loss rate trends are generally consistent among the four time periods mapped for these same areas except for the Western Chenier Plain, where the rates are more variable
1930's Base Land and water Data
14. From the 1930's land data, it is possible to determine the gross land changes that have occurred in coastal Louisiana. Beginning in the early 1930's, there was approximately 8,511 square miles of land in the study area. By the end of the 1990 time period, the total land loss that occurred was 1,526 square miles or approximately 17.8 percent of the original land area. Of the 17.8 percent total loss, 74.4 percent occurred in the Deltaic Plain and 25.6 percent in the Chenier Plain. Figure 4 summarizes the general land changes that have occurred in coastal Louisiana during approximately the past 60 years and shows the percent contribution that occurred in each period. In time period 2 (1956-58 to 1974), the greatest amount of land was lost with nearly half of the total loss occurring during this period. For time periods 3 and 4, the loss contribution has decreased for each period from the proceeding time period.
17 AVG PERCENT LAND LOSS PER YEAR TIME 1 (1930's-1956-58)
·:;i o~ "" MISSISSIPPI 8 ~ LOUISIANA I I i "'r- -N- ~\>~ ~. DELTAIC PLAIN :;; l!: ~ ~ > CHENIER PLAIN
Crowley e Lafayette e. -=<=. ~
JO"
...... CX> )
PERCENT c=::=:J 0.0. 0.1 ~ 0.1 • 0.5 29° l:·:·:-:1 0.5 • 1.0 GULF &'SS1 1.0 . 2.0 OF MExtco ~ 20 0 20 40MI I ......
Figure 3a. Summary of land loss rates in percent per year for time period 1 (1930's to 1956-58) AVG PERCENT LAND LOSS PER YEAR TIME 2 (1956-58-1974)
,,. ":;i ·~ ; MISSISSIPPI ·~ : LOUISIANA I I
-N-~ 3:\J>~ ~ ~;; ~3: ~ DELTAIC PLAIN ~ J> CHENIER PLAIN
Crowley e ==-=-
30°
...... \0 )
PERCENT C::J 0.0 • 0.1 ~ 0.1 • 0.5 l:·:·:·:I o.5 • 1.0 ,.. i;ssi 1.0 • 2.0 GULF ~ 2.0 • 3.0 0 F MExico ~ w 0 w ~-
Figure 3b. Summary of land loss rates in percent per year for time period 2 (1956-58 to 1974) AVG PERCENT LAND LOSS PER YEAR TIME 3 (1974-1983)
08 3'o ogi\ o~ a; MISSISSIPPI ~ " LOUISIANA I I
i "'J> -N- - "' ~1~~ ~ ~ DELTAIC PLAIN ;! J> CHENIER PLAIN
...... ,.h ... 1..... Crowley e ""'"=- "=> r300 !\) 0 ~~-~·~#!'AI-lit~;."~ J PERCENT i===::::J 0.0. 0.1 ~ 0.1 • 0.5 1:·:·:·:1 o.5 • 1.0 &S'S! 1.0 . 2.0 290 ~ 2.0 - 3.0 GULF 1::::::::::1 >3.0 0 F MExico SCALE
20 0 20 40MI I ...... m
Figure 3c. Summary of land loss rates in percent per year for time period 3 (1974 to 1983) AVG PERCENT LAND LOSS PER YEAR TIME 4 (1983-1990)
,,. ~ "2 ~. ~ MISSISSIPPI °: LOUISIANA I I
t !:! > - N ~1~-!:! '"> ;; ;i:: DEL T AIC PLAIN :! > 1 I I CHENIER PLAIN
~~ Crowley e Lafayetle • '?- "%_ \ 30•
I\) I-'
PERCENT c====i 0.0. 0.1 ~ 0.1 • 0.5 i..:...:UJ~ 0.5. 1.0 ,.. &.SS1 1.0 • 2.0 G UL F >3.0 l,::::::::I 0 F
SCALE MExico
w 0 w ~~
Figure 3d. Summary of land loss rates in percent per year for time period 4 (1983 to 1990) LOUISIANA COAST AL PLAIN LAND LOSS 1930's TO 1990
17.8 % LAND LOSS '2. 1A;_,(l~ ~~ 2 82.2 % 7162 M\ ~=====----__::!,~ 6985 Ml2 LAND REMAINING
Figure 4. Pie chart showing gross land loss changes between the 1930's and 1990. Time periods mapped are as follows: Time 1 (1930's to 1956-58), Time 2 (1956-58 to 1974), Time 3 (1974 to 1983), Time 4 (1983 to 1990)
22 Composite Land Loss Rates
Louisiana Coastal Plain 15. composite land loss rate curves for the entire study area (see Figure 1) are presented in Figure 5. The curves are expressed in square miles per year and average percent per year, respectively. The land loss rate in time period 4 (1983 to 1990) for the Louisiana Coastal Plain is 25.34 square miles per year or 0.35 percent per year. The rate curves show the trend has been consistently decreasing from its peak in time period 2. Mississippi River Deltaic and Chenier Plains 16. Land loss rate curves for the Deltaic Plain are presented in Figure 6. For time period 4, the land loss rate for the Deltaic Plain (SO quadrangles, see Figure 1) is 19.98 square miles per year or 0.36 percent per year. Land loss rate curves for the Chenier Plain (12 quadrangles) are presented in Figure 7. For time period 4, the land loss rate for the Chenier Plain is 5.36 square miles per year or 0.33 percent per year. For both the Deltaic and Chenier Plains, the cumulative land loss rate has been decreasing since time period 2.
23 46.0
~40.0
~35.0
~30.0 w ~26.0 g '-'20.0 ~16.0 14. 61 ~10.0 LOUISIANA COASTAL PLAIN 6.0 LAND LOSS RATE CURVE
.0.0 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS)
a. Curve expressed in square miles per year
1.0 LOUISIANA COASTAL PLAIN PERCENT LAND LOSS RATE CURVE
0. 51
0.35
0. 17
0.0 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS)
b. Curve expressed in percent per year
Figure 5. Land loss rate curves.for the Louisiana Coastal Plain
24 30.0
Ci'. i1i 25. 0
}:20.0~ w 19.98 ~ 16.0
§10.0 12.52
6.0 MISSISSIPPI RIVER DELTAIC PLAIN LAND LOSS RATE CURVE
0,0 -+-.-.,...... ,...,...... ,,.,...... ,...... T'T'T.,...,...,r-T"T'"..,...... T'T'T"'T"T">r-T"T'"l"T"T"T'TT'T"T"T.....,...,r-n-rTTTTT"T"'T""1'"TT"I 1930 1940 1960 1960 1970 1980 1990 ELAPSED Tit'E CYEARS>
a. Curve expressed in square miles per year
0 1 • MISSISSIPPI RIVER DELTAIC PLAIN PERCENT LAND LOSS RATE CURVE
0.45 I.... 0.6 0.40 0.36
0.0 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARS)
b. Curve expressed in percent per year
Figure 6. Land loss rate curves for the Mississippi River Deltaic Plain
25 15.0
~ 13. 81
l:~ 10. 0 w ~ ~_J(/') 6.0 5.36
CHENIER PLAIN 2.09 LAND LOSS RATE CURVE 0.0 1930 1940 1960 1960 1970 1980 1990 a.APSED Til"E CYEARS>
a. Curve expressed in square miles per year
1.0 CHENIER PLAIN PERCENT LAND LOSS RATE CURVE
0.71
0.45
0.33
0.0 1930 1940 1960 1960 1970 1980 1990 a.APSED TIME CYEARS)
b. Curve expressed in percent per year
Figure 7. Land loss rate curves for the Chenier Plain
26 PART IV: CONCLUSIONS
17. Land loss mapping from the 1930's to 1990 for 62 USGS quadrangles in the Louisiana Coastal Plain indicates:
~· The location and magnitude of land loss is highly variable throughout the coastal plain.
Q· The land loss rate for the entire study area has decreased from its high of approximately 42 square miles per year in 1974 to approximately 25 square miles per year in 1990.
£· The percentage of land being lost in the study area is also decreasing from its high of approximately 0.51 percent per year in 1974 to approximately 0.35 percent per year in 1990.
g. Total land area has decreased from 8,511 square miles in the 1930's to 6,985 square miles in 1990.
~· Approximately 17.8 percent of the available land in the study area has been lost since the 1930's.
i· The highest land loss rates and percentage loss are occurring along the coastline. Rates are highest in the Modern Delta and in the eastern and south-central portions of the Deltaic Plain.
g. Natural land loss rates will probably continue to decrease slowly until a background rate is reached. The land loss rate for time period 1 (14.61 square miles per year or 0.17 percent per year) may be representative of the natural background rate because it reflects the land loss rate in the coastal area prior to the major impacts from man's activities.
h· Land loss data are being used in conjunction with engineering geology and subsidence data to identify those areas where mitigation and/or restoration is most feasible.
27 REFERENCES
Dunbar, J. B., Britsch, L. D., and Kemp, E. B. 1990. "Land Loss Rates: Report 2, Louisiana Chenier Plain," Technical Report GL-90-2, US Army Engineer Waterways Experiment Station, Vicksburg, MS.
Britsch, L. D. and Kemp, E. B. 1990. "Land Loss Rates: Mississippi River Deltaic Plain," Technical Report GL-90-2, US Army Engineer Waterways Experiment Station, Vicksburg, MS.
28 APPENDIX A: LAND LOSS RATE CURVES
Al 0. 6., ABBEVILLE 1.6 LAND LOSS RATE CURVE 0.43 J 1.20 ~0.4 ~1.2
~H ~.... I: I: ~0.3 10.9 0.23 0.24 ~...... ~0.2 ~0.6 ..J BARATARIA ~0.1 0.07, ~0.3 LAND LOSS RATE CURVE
0.0 I I I I I I I I I I j I I I I I I I I I I I I 11IIIIIj11I111 I I I I I I I I I I I I I I I I 11 I I I I I I 0.0 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED Til'E CYEARS) :;.:. N 1.6 ., 1.44 .. BAYOU DU LARGE
I LAND LOSS RATE CURVE ~ ~ 1.26 ~1.8 ~1.2 ~ 1.15 • I ~ ~1.6 H .... I: I:
10.9 11.2
...... 0.9 ~0.6 ..J ~ ~0.6 ~ ~0.3 I ~ 0.47 BAY DOGRIS 0.3 LAND LOSS RATE CURVE
0.0 ~ 111111111111111111111111111111111111111111111111111111111111 0.0 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TitE CYEARS) ELAPSED TitE CYEARS) 1.0 , BAYOU SALE 1.0 l BELLE ISLE LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~0.8 ~0.8 ....~ ....~ :c :c 10.6 10.6
~ ~ 0.36 1. 0.38 ~0.4 ~0.4 _J _J I ~: ~0.2 ~0.19 ~0.2 '" I j ' ~ 0.0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I II I 11 I I I I I j I I I I I I I I 1jIIII11 I I I j •.• ''''''''',,''''''' ',,'''''''',,''''' ''''''''' '~. ~: 07 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS> ELAPSED Til"E CYEARS> :i:o w 1.0 , BLACK BAY 1.0 l BONNET CARRE LAND LOSS RAT~ CURVE LAND LOSS RATE CURVE ~ ~0.8 ~0.8 ....~ ....~ :c :c ~0.6 0.52 10.6 i ~ 0.44 ~ ~ ~0.4 ~0.4 _J _J 0.21 ~0.2 ~0.2 ;0.10 j I I ~.07 0.0 II I I I I I ii I I I I I I I I I I I I I I I I I I I I I I I Ii I I I I I I I I I I I I I I I I I I I I I I I I I I I 0.0 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TitE CYEARS> ELAPSED Til"E CYEARS> 1.0 BRETON ISLAND 1.0 CAILLOU BAY LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~ ~0.8 ~0.8 ..... ~..... :c :c 10.6 10.6 ...... 0.40~ ~0.4 ~0.4 ...J 0.26 ...J
~ ~ ~0.2 ~0.2 '0.22~ ~ 0.05
0.0 1111111111111111 I 11111111111111111I11II1111 I I I I I I I I I 1111 I I I I I 0,0 I I I I I I Io Io I I I I I I I I I I I I I I I I I I I I I I I I Ii I I I I I I Ii Ii I Ii I I I I I I I I I 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TitE CYEARS) !I>' "" 3.0 CAMERON 0.6 CAT ISLAND LAND LOSS RATE CURVE LAND LOSS RATE CURVE 2.47 ~2.6 ~0.4 ~ ~ ~..... ~2.0 10.3:c 11.6 ...... ~0.2 ...J~ 1.0 ...J
1 0. 07 1 0. 09___,. ___ 0._ 1 1
~ ~0.1 I t --=--·~ '~,07 0.6 0.25 I
0.0 Io o; o o o 1111ill1111 a iiiiill iilli I ill I I I I ii iii ii iiii iiiii i I I iii 0,0 la a a o iiilloiii o o a 01OO11100oOOiii001111 o o O O O O O O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED Til'E CYEARS) ELAPSED TitE CYEARS) 1.0 CHEF MENTEUR 1.0 CHENIERE AU TIGRE LAND LOSS RATE CURVE LAND LOSS RATE CURVE ,0.8~ ~.... i···.... :c :c ~0.6 0.49 10.6
§ I o ~41 ~ 0.36 ~0.4 ~0.4 2 ~.281 0.2~ ...J 30.2 30.2 - 1 0 0Z ~ ~2 •
0.0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I Ii Iii ii I I If I I I I I I I I I I I I I I I I I I 0.0 I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I ii I I I I I I I I I I I I I I I I I I I I I I I I 11 I I I I 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TitE CYEARS> ELAPSED Tit'E CYEARS) !J:I (J1 1.6 CONSTANCE BAYOU 0.6 COVINGTON LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~ '1.2 ~0.4 ....~ ....~ :c :c 10.9 0.82 10.3 0.18 0.18 s0.6 ~0.2 ...J ...J
30.3 30.1
0.0 0,0 I 1 I I iiiiiii I iiiiiii I I I I iiiiilil lliiiiii I I I I I I I I ii I I I I I I I I I I I I 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED Til'E CYEARS> ELAPSED Til'E CYEARS> 1.0 , CUTOFF 0.6 l DEROUEN LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~0.8 ~0.4 (/)
~ H~ H:c :c 10.6 10.3 0.24 0.24 0.25 I ...... 0.~2 ~ --=! ...... : ~0.4 ~0.2 ...J ...J
30.2 30.1 0.22
0.0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ii I I I I I I I Ii I I I I I I I I I I I I 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED Tit'E CYEARS) ELAPSED Til'E CYEARSl ;J:I
"' 2.5 , DULAC 2.6 ] EAST DELTA LAND LOSS RATE CURVE LAND LOSS RATE CURVE 1.99 ~2.0 ~2.0 i 1.90 (/) ~ H H~ :c :c
11.6 11.6
...... ~1.0 ~ 1.0 ...J .::J
30.5 0.34 0.37 ~ •.• j ~7
0.0 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED Til'E CYEARS> ELAPSED Til"E CYEARS> 3.0 EMPIRE 0.6 FORKED ISLAND LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~2.6 ~ i···... ;:2.0 I: 10.3 0.27 11.6 ...... ~0.2 0.15 0.14 .J~ 1. 0 .J
~ 0.6 ~0.1
0.0 Io o o o o o o I I IO.~ ... ?~ IO O 0 I I I I I I I I I I I Iii iii i I I Ii Iii i I I Iii iii iii i 0.0 I I I I 1111111111II1111IIIIiliilij111111111 I I I I I I I I I 111 I I I I I I I I I 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED Til'E CYEARS) ELAPSED Til'E CYEARS) :i::i -.I 1.0 FORT LIVINGSTON 2.0 GIBSON LAND LOSS RATE CURVE 0.89 LAND LOSS RATE CURVE ~0.8 ~ 1.50 ...~ ~1.6 I: ...I: ~0.6 11.0 ...... ~0.4 0.34 0.54 .J ~ 30.6 30.2
0.0 I I ii I iiiii I I ii I iiiii I iiiiiii I iiiiii i iiiiii iii ii iii iiiiiil iii i 0.0 l 111111111 1• 111111 ••1illilli llJlllll I 111 ji I ii ii I I I j I I Ji iii ii j 1930 1940 1960 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED Til"E CYEARSl ELAPSED Til'E CYEARS) 2.0 , GRAND LAKE EAST 2.01 GRAND LAKE WEST LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~ 1.54 ~ ~1.6' ~1.6 ...... ~ 1.30 I: I: ~ ~ 1.0 11.0 OJ OJ ~ ~ ~0.6 ~0.6 0.29
0.0 I 111111111111111111111111111111111111111111111111111111111 t·l I 0.0 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED Til'E CYEARS> ELAPSED Til'E CYEARS> ):" CX> 1.0 , HAHNVILLE 1.0 HOG BAYOU LAND LOSS RATE CURVE l LAND LOSS RATE CURVE ~ I 0.72 ,0.8 ~0.8 f3 ...... J .....~ I: I: 0.57 10.6 10.6
OJ OJ ~0.4 ~0.4 ...J ...J ~0.2 0.17 ~0.2
0.0 Iii iii I I I I I I I I iii ii I I I I I Iii I I 11111 I I iii I I I I I I Io o Io o o o o o o o 00 00 0.0 liiiiiiiiiiililliiiiliiliiiiiiiiiiiliiiiiiiliil iiiiiiii I Iii ii 1930 1940 1960 1 960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED Til'E CYEARS) ELAPSED Tit'E CYEARS) 0.6 , HOUMA 0.61 JEANERETTE LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~ ~0.4 ~0.4 Cf) LLJ ..J ...~ ...J: 0.29 J: ~0.3 10.3 ; ...... ~0.2 ~0.2 ..J ..J 0.10 0.08 30.1 ~0.1 ~ 0,08 ~ I I o I -=::::::::::: 0 , 06
0.0 I 111111111111111111111111111111111111111111111111111111111111 0.0 I111111111111111111111111111111111111111111111111111111111111 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TitE CYEARS) ELAPSED Til"E CYEARS> ~ \0 4.0 , JOHNSONS BAYOU 1.0 1 LAC DES ALLEMANDS LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~3.6 3.12 ~0.8 ~3.0' Cf) ...... ~ ~ 0.66 J: 10.6 2.0 r··...... 81.6 ~0.4 ..J ..J
31.0 30.2 1 0.13 0.6
0.0 0.0 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED Til"E CYEARS> ELAPSED Til"E CYEARS> 1.6 , LAKE DECADE 2.01 LAKE FELICITY LAND LOSS RATE CURVE LAND LOSS RATE CURVE 1. 31 ~ i 1. 61 ~1.2 ~ (/) ~1.6' 1 "'?? 1.35 .....~ H ~ / I: I: ~0.9 § 11.0 ...... ~0.6 J ~ ~0.3 0.25 0.,26 ~··· L... ~~29 0.0 I 1 I I I I I I I I I I I I I I I I I I 11 I I I I II I I I I I I I I I I I I I I I I I I I I I I II I I I I I I I I I 0.0 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED Til"E CYEARS> :i:< ELAPSED Til"E CYEARS> I-' 0 1.0 , LEEVILLE 0.6 l MARSH ISLAND LAND LOSS RATE CURVE 0.90 LAND LOSS RATE CURVE ~0.8 ~0.4 (/) ~ H H~ I: I:
10.6 10.3
..... 0.24 0.25 ~0.4 i0.2 1 0.23 J 0.28 J ~0.2 ~0.1
0.0 I I I I I I I I I I I I I I Iii I I ii I I I I I ii I 111111I1111 I I I I I ii ii I j i I I I I I I I I I 0.0 I• I I 1111111III1111III11111111111 I I I I I I I I Ji 11 I I I I I I I I I I I I I I I I I 1930 1940 1960 1960 1970 1980 1990 1930 1940 1 960 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS) 0.6 MITCHELL KEY MORGAN CITY LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~t.8
~t.6 1.37 !···...... :c :c 10.3 11.2 0.93 ~0.9 ~0.2 ~- ..J ..J 30.6 0.07 30.1 0.31 0. 05 0. 03 ·-..:::::::. 0. 02 0.3 ~--·-=::::::::::=..:::::::::-:----; ~ ~
0,0 Io oo oo O O iO i O Oi O O O O O O O ii Oi 0 0 0 O iiii O 0 0 0 iilil O O O 0 0 ii 0 0 0 0 0 I I I fill 0,0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TitE CYEARS) ELAPSED TitE CYEARS> ::t" I-' I-' 0.6 MORGAN HARBOR 0.6 MOUNT AIRY LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~ 0.38 ~0.4 ~0.4 ...... ~ :c :c ~0.3 10.3 §
~ ~ ~0.2 ~0.2 ..J ...I 0.12 30.1 30.1 I 0.~ 0.08 0,~
0.0 0.0 I• ii 11111111111IiiiijiI11111111111 I I I I ii I I ii I I I 11111 I I I I I I I 11 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS> ELAPSED TIME CYEARS) 0.6 NEW ORLEANS 0.6 OYSTER BAYOU LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~ ~0.4 f3 .J H H~··· I: :c 10.3 0.26 10.3 0. 18 ~0.2 0.~~~14:: ~0.2 0.15 .J .J ~0.1 ~0.1 ' 0~~~- ~·0~
0,0 I 1111111 i I Ii Iii I I I Iii Ii Iii iii I 1111 I Ii I I I Iii I I I I I Iii Iii I I I I I I I 0.0 I 11111I11 I I I I I I I I I I I I I I I I I I I Ii Iii I I I Ii Iii I I I I I I I I I I I I I I I I I I I I 1930 1940 1 960 1960 1 970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS) :i::< ~ "' 1.0 PECAN ISLAND 0.6 POINT CHICOT LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~ 0.79 ~0.8 ~ H 0.62 I···H 10.6I: 10.3I:
~ ~ ~0.4 ~0.2 0.15 .J .J
30.2 30.1 0.08 0.08 ;
0.0 0.0 I 1 iii iii iii iii iii iii i Ii I iii I I I I I I I I I I I I I I I I I I I I 0 I 0 0 I 0 0 I 0 0 0 < 0 < 1930 1940 1960 1 960 1970 1980 1990 1930 1940 1950 1960 1 970 1980 1990 ELAPSED TIME CYEARS> ELAPSED TIME CYEARS) 0.6 , POINT AU FER 1.0 l POINT ALA HACHE LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~ ~0.4 ~0.8 (/) ~ ~ ..... 0.75 0.75 :c / 0.71 ~0.3 § i··· I ~ ~ 0.17 ~0.2 0.16 80.4 ...I ~·------: .:.I ~}1 ~-1: ~0.1 ~0.2 -l 0.28
0.0 I I I I I I I I I I I I I I I I I I I I j I I I.-. I I I I I I I I I I I I I I I I 111II111 j I I I I I I 11 I I 0.0 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED Til'E CYEARS) ELAPSED Til'E CYEARS) ):I I-' w 0.5 , PONTCHATOULA 0.6 l RIGOLETS LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~0.4 ~0.4 (/)w ...... I .....~ :c :c a0.3 10.3 I 0.26
~ ~ ~0.2 ~0.2 ...I ...I I 0. 11 / 0. 12 0.09 0.08 ~0.1 0.07 : ~0.1 ...... ------: ~
0.0 I 111111111111111111111111111111111111111111111111111111111111 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME C YEARSl 0.5 SLIDELL 0.5 SOUTWEST PASS LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~0.4 f3 ....I H i···H I: I: ~0.3 10.3 §
~ ~0.2 0. 15 ~0.2 ....I ....I 0.12 0.~ ~ 30.1 0 . 06 0 . 05 0 . 04 30.1 ' :~ ~02 0:0~
0.0 I. I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 0.0 I o o o o o o o o oo o o o o o o O O O O O O O I I I I I 01 I I I I I 0 0 0 I I 0I000111111111111 I 1930 1940 1950 1960 1970 1980 1990 1930 1940 1 950 1 960 1 970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS) :J>I I-' ~ 0.1 SPANISH FORT 0.1 SPRINGFIELD LAND LOSS RATE CURVE LAND LOSS RATE CURVE
H H~ iI: I:
~ I~ 0. 03 § ~ ~ ~ 0.01 0.01 3 ~ 0.003 0.01 t------=~-- .z~ I 0. 01 ...... _ ' ::::::> 2~=03~ '
0.0 I 1I11 I I I I I I I I I I I I I 11 I I I I I I I I I I I 11 I I I I I I I I I I I I I I I I If iii i Ii j 111 0,0 I iiiilii iii iii I I I iii I I I I I I I I 1111 ii I I Ii I I I I I I I I I I I I I I I I I I I I I 11 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS) 1. 5 -, ST. BERNARD 2.5 1 SULPHUR LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~ 1.23 ~ >- ~2.0 (/)' El ~ 1. 82 ~ ...... J ~ 1.0 I:
11.6
I~ ~ (/) ~ 1.0 ~ ..10.6 ...J
0.29 ~ 0.26 ~ 0. 6 -I I "-.. 0.40 ~28 ~ /0.05 0.0 I 1IIIII111 j I I I I I I 1111 I I I I I I I I 11III11II11jIII11 I I I I (I I I I 11 I I I I 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS) >I-' 01 2.6 -, SWEET LAKE 1.0 l TERREBONNE BAY LAND LOSS RATE CURVE LAND LOSS RATE CURVE ~ ~ ~2.0 ~0.8 (/)w 1. 80 w(/) ...... J ...... J I: I: ~ 1.5 ~0.6 1 0.49 g ~ ~ ~ ~ 1.0 ~0.4 g ...J 0.68 1 0.18 ~0.5 ~0.2
0.0 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARSl ELAPSED TIME ( YEARS> 0.0 I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1 970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS)
APPENDIX B: PERCENT LAND LOSS RATE CURVES
Bl 1.0 .., ABBEVILLE 1.0 PERCENT LAND LOSS RATE CURVE
ii'. <( 0.73 w >- ~ 0.69 >- I f-z' w ' u u~ Cl'.w 0.50. 0.. ffi I 0.~~·~.;; ~0.5 0. ~0.5 (/) (/) 0 _J § _J 0z 0.25 0.27 <( _J 3 0.08 I BARATARIA PERCENT LAND LOSS RATE CURVE I 0.0 I I I I I I I I I I j I I I I I I I I I j 11I1111111111II11I11I11I11 I I I I I I I I I I 111 j 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARSl tD ELAPSED TIME CYEARS) N
1.0 ' 0.89 0.91 0.90 BAYOU DU LARGE ~ "" 1 PERCENT LAND LOSS RATE CURVE ii'. <( 0.77 w iii >- >- f-z' ' wu Cl'.w ~ 0.. ffi ~0.5 a.. ~0.5 (/) (/) (/) 0 _J ~_J 0 z 0.24 :5 ~ I I ~ 0.27
BAY DOGRIS I /121.08 PERCENT LAND LOSS RATE CURVE 0.0 I 1l11I11IIjII111 I I I I j I I I I I I I I I j I I I I I 11iIjIII111IIIjI111II1 Ii j 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARSl 0 0 1. , BA YOU SALE 1. BELLE ISLE PERCENT LAND LOSS RATE CURVE 1 PERCENT LAND LOSS RATE CURVE
~r r~ I § ~0.6 °· 44 ~0.6 ~ 0~·~ ~ ~ ~ ~261 ~
0.10 I I 0.,17 I -2.:.,15 ~07 ~03, 0.0 I I I I I I I I I I j I I I I I I 11 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1 j 0.0 I I I I I I I I I I I I 111 I I I I I I I I I I I I I I 1 j I I I I I I I I I I I I 1111IIIJ11 I I I I I I I j 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS> ELAPSED TIME ( YEARS> tp w 1 0 1 0 • , BLACK BAY • BONNET CARRE PERCENT LAND LOSS RATE CURVE . 1 PERCENT LAND LOSS RATE CURVE
~ ~ ~ ~ ~ 0.58 ~ a_ a_ ~0.6 ~0.6 ~ ~ I 0.41 ...J ...J
~ 0.21 ~ ' ;a.09 ' . ~ 0,.07
0.0 I I I I I I I I I I I I I I 11III1 JI I I I I I I I I I I I I 11IIIIII11 I I I I I I I I 11 I I I I I I I 0.0 1 930 1 940 1 950 1 960 1 970 1 980 1 990 1 930 1940 1960 , 960 , 970 1 980 1990 ELAPSED TIME CYEARS> ELAPSED TIME CYEARS> 2.0 ., 1.0 ., CAILLOU BAY PERCENT LAND LOSS RATE CURVE 1.55 1. 42 ~ 1.5 ~ ' ~ ; I 0.59 ~a... '"'1. 0 '-'0.5 § 0.65 § / 0.30 ~0.5 3 I 0.26 BRETON ISLAND PERCENT LAND LOSS RATE CURVE
0.0 I 1 I I I I I I I Ii I I I I 11 I I I j I I I I I I I I I J 1 I I I I I I I I j I I I I I I I I I j I I I I I I 1·f11 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME ( YEARS) ELAPSED TIME ( YEARS) tJj ""' 2. 0 ., CAMERON 1.5 PERCENT LAND LOSS RATE CURVE 1.33 I I- 52 1. 55 ~ 1.5 ~ I-' / 0.96 ~ ~ 1.0 ~ 0.92 u ~ a...w ~ '"'1.0 '"' (f) (f) I 0.61 0 ...J § 0z 0.53 30.5 < ...J0.5 CAT ISLAND 0.23 PERCENT LAND LOSS RATE CURVE
0.0 II I: I I I I I I II I I!.~.-.~~ I I I: I I I I II I I I I I I I I II I I I I I I I I I'·'= 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME (YEARS) ELAPSED TIME ( YEARS) 1.0 CHEF MENTEUR 1.0 CHENIER AU TIGRE PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
~ ~ ~ ffi~ a... ffia... ~0.5 0.48 0.46 ~0.5 0.38 0.37 § ' I ------~34 ,0.;is, ~
~ 3 0.15 0.08
0.0 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARSl ELAPSED TIME ( YEARSl tp U1 1.0 CONSTANCE BAYOU 1.0 COVINGTON PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
~ ~ ~ 0.62 ~ u~ ffi a... ~ ~ 0.52 a...~ ~0.5 ~0.5 (/) 0.~ -!:".:?' § § 0.27 0.28 ~ < _J ~ ' 0.~~~~J 0.0 0.0 1930 1940 1 950 1960 1 970 1980 1990 1930 1940 1950 1960 1 970 1980 1990 ELAPSED TIME CYEARSl ELAPSED TIME CYEARS) 1.0 ..., CUT OFF DEROUEN PERCENT LAND LOSS RATE CURVE 1.01 PERCENT LAND LOSS RATE CURVE
~ L5 >- >-~ I-' ' ~ g u u ffi ffi CL CL ~0.5 ~0.5 (/) (/) 0 _J ~_J Cl 121.24 121.25 Cl 5 ·~·1? I 5 0.13 '0.y 121.12 121. 11 121. 12 . -
0.0 111111111 i j Iii I I I I Ii j I I Iii I I I I j I I Iii I I I I j ii I I I I I I I j i I I Iii I I I j 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARSl ELAPSED TIME CYEARSl tD 0\ 1.5 ..., DULAC 3.51 EAST DELTA PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE 3.0 1. 13 ~ >-~ w ~2.5 ~1.0' 0.94 I- ~ u ffi ffi2.0 CL CL ~ ~ (/) ~ ~ 1.5 _J _J ~0.5 ~ 1.0 1. 16 121.18 ~ 0.5 J 0.91 0.68 I 0.0 II I I I I I I I I I I I I I I I I I I I I I I I I I I I I) I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 0.0 1930 1940 1960 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME ( YEARSl ELAPSED TIME CYEARSl 3.0 EMPIRE 1.0 FORKED ISLAND PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
~2.5 2.01 ~> ~ 1.92 ..... ~2.0 ~u ffi Cl'.w a... a... ~ 1.5 ~0.5 (/)gs § ..J ~ 1.0 ~ 5 0.22 0. 12 0.5 0.22 0. 11
0.0 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1 960 1 970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARSl tD -.J 2.0 FORT LIVINGSTON 1.0 GIBSON PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
fr: ~ 1.5 ~ 1-z w 0.59 ~ ~ w 1 . ]1 a...ffi ~ 1.0 ~0.6
§ 0.90 § 0 z 0.24 :3 0.5 ~ 0.20
0.40
It I I I I I I I I I l 111II111 t I I I J Ji ii t I I I I I 111I1111 I I l I I I I I I 111 I I I I I I 0.0 0.0 I I I 11111 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 11I11II1111 j 1930 1940 1 950 1960 1 970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARSl ELAPSED TIME ( YEARS) 1.5 , GRAND LAKE EAST 1.0 l GRAND LAKE WEST PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
~>- ~ I 0.68 ' 0.95 ~ i 1.0 a..ffi a...... 0.6 § ~...J 30.6 0. 41 ~ -0.16 ----- 0.0 0.0 I 111111111111111111111111111111111111111111111111111111111111 1930 1940 1950 1930 1940 1960 1960 1970 1980 1990 1960 1970 1980 1990 ELAPSED TIME CYEARS> ELAPSED TIME CYEARS) tp co 1.0 , HAHNVILLE HOG BAYOU PERCENT LAND LOSS RATE CURVE 1.61 PERCENT LAND LOSS RATE CURVE
>-~ I 1.04 1.04 ' ~ ~u ffia...... 0.6 r·~ I 0.66
~...J § 0.24 ~0.5 ~ 0. 19 0.~ ;---.,.~08'
0.0 I I I I I I I I I I I I I I I I I I I I I I I I I I I ii I (I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS> ELAPSED TIME CYEARS> 1.0 HOUMA 1.0 JEANERETTE PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE ~ ~ a...ffi ..... 0.5 I..... 0.5 § § ~ ~ 121.1121 121.12 121.~ '~ 121.~~ 0.05 0.05 121.1214 0.07
0.0 I 111IIII11 j I I I I I I I I I JI I I I I I I I I j I I I 11II11 (I I I 11111IjIII11 I I I I j 0.0 I I I I 1111 I I I I I I I I I I I I I 11111IIII11 I I I I I I I I I I I I I I I I I 11 I I I I I I I I I I 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARS) tJ:I ELAPSED TIME (YEARS) IO 2.0 JOHNSONS BAYOU 2.0 LAC DES ALLEMANDS PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE 11.5 1.23 I'·· ~ 1.0 ..... 1.0 § § ~0.5 121.53 ~0.5 121. 29
121. 16 I 0.06 0,~ O~
1 0.0 f 1 I I I I I I I I JI I I I I I I I I j 11iliilIIjII11 I I I I I I I I I I I I I Iii iii i 1raa11 0.0 l1111111111111111111111~1111111---;=:,,,,,,iilliiillllliiiiiii 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME ( YEARS) 1.0 LAKE DECADE 1.5 LAKE FELICITY PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
~ 121.69 ~ ~ ~ 0.91 g ~ 1.0 0.83 ffi !:0.5 ~...... ~ ~ 3 30.6 0.13 0.16 0. 14
0.0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I j I I I I I I I I 11III11IIIIj1II11 I I I I I 0.0 I I I I I I I I I It•• I I I I I I 1 j I I I I I I I I I I I I I I I 11 I I I I I I I I I I I I j I I 11 I I I I I I 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARSl ELAPSED TIME CYEARS> tCI ...... 0 2.0 LEEVILLE 1.0 MARSH ISLAND PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
1. 28 I... 1.17 ,______, ...... 1.0 I...... 0.6 § § 0.38
30.5 0.33 3 ~ .. __ 0.~ ~25 ~
0.0 I I I I I I I I I I I I' I I 11IIIj1 I I I I I I I I I I I I I I I I I I j I I I I I I I 11 j I I I I I I I I I I 0.0 I I I I I I I I I I I I I I 111 I I I I I I I I I I I I I j 1IIIII111 j I I I I I I I I I 1930 1940 1950 1960 1970 1980 1990 1930 '"""'"' 1940 1950 1960 1970 1980 1990 ELAPSED TIME ( YEARS> ELAPSED TIME CYEARS> 4.0, MITCHELL KEY 1.0 MORGAN CITY PERCENT LAND LOSS RATE CURVE I PERCENT LAND LOSS RATE CURVE 3.6 I 3.06 ~3.0 ~2.6 w i a. ~ ~2.0 ~0.6 ~ _11. 6 I 1.24 ~ 3 t.I ~74 0.6
0.0 0. 0 I I I I I I I I I iii iii I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 IJj ELAPSED TIME ( YEARS) ELAPSED TIME CYEARS) ...... 1.0, MORGAN HARBOR 1.0 MOUNT AIRY PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
I~0.6 I~0.6 0.39 ~ 0. 31 b= • "'""'0. 34 ~
3 0 .•~~ 3
05
0.0I•I111111ljIII11iii1111111111ij11111IIIij111 Iii Iii I 11111 I II ij 0 . 0 I1 Ii 1111 iiIiiIi1~1°1~~ ii ii 1ii 1 I 11 ~:~~I I ii ii 1 ~ ° 1 ~~ 1 °' 1930 1 1 iliillil 1930 1940 1950 1 960 1970 1980 1990 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS) 1.0 NEW ORLEANS 1.0 OYSTER BAYOU PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
I.... 0.6 I.... 0.6 § ~ 0.50 3 3 0.12 0.24 0.~ : ·~.07 0.07 0.20 • I I I
0.0 I• I I I I ii I I I ii I iii 11ij111IIiiiI11111 I I I I I I ii I I I I I I I I I I I I I I 111 j 0.011IIII11ii111111 ii ii (iiiiii 111 Ill I I I Ii 11)1 I I I ii I I I JI I I I I I I 11 j 1930 1940 1960 1960 1970 1980 1990 1930 1940 1 960 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS) tD I-' N 2.0 1.0 PECAN ISLAND POINT CHICOT 1.86 PERCENT LAND LOSS RATE CURVE . PERCENT LAND LOSS RATE CURVE
~ 1.6
0.47 0.44 0.40 I..., 1.0 .... 0.6 I ...... _ I - § 0.80 § 0.66
~ 30.6
0.0III11111Ill11111111111111111 I I I I Ii I I I Iii ji I I 111 I I I j I I I I I I 111 j 0.0 I I I I I I I ill I I ii ii I ii I (ii I Ii I I 11111 I I I I I iij I I I I I I I I I I I I I I I I ii I j 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME ( YEARS) 1.0 POINT AU FER 1.0 POINTE ALA HACHE PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
I ~0.~2-~ I~0.6 I~0.6 0.53 0. 37 0. 37 0. 40 § ~ ,..__-=-...... ,,,,=---~=· -~ ,____-L:.-::___~ ~ 0.33 0.42 ~ 0.~
0.0 I I I I I I I I 11jII11 I I I I I) I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 0.0 I I I I I I I I I 1jIIiIII11I11111111 I ij iii I I I I I I 111IIII111IIIiiiI11 I I 1930 1940 1 960 1 960 1 970 1980 1990 1930 1940 1960 1960 1970 1980 1991'! ELAPSED TIME CYEARS) ELAPSED TitE CYEARS) tD I-' w 1.0 PONTCHATOULA 1.0 RIGOLETS PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
~
~~0.6 I~0.6 ~ § ~ ~ -~;;--=·0~~ 0.05 0.07 0.06 0.04 0.10 0.12 0.0 I 1·1 I I I I I I I j I I I I I I I I I j I 11III11 I I I I I I I I I I I j I I I I I I I I I j J Ji iii iii j 0.0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS> 1. 0., SLIDELL 3.0 PERCENT LAND LOSS RATE CURVE
~2.6
>-~ >- ' ~2.0 ~u a..ffi ...... 0.6 ...... 1.6 I 1.45 ~_J ~ 0.24 31.0 3 0.86 0.93 SOUTHWEST PASS 0.~ ~08 0.07 0.5~ PERCENT LAND LOSS RATE CURVE I I
0.0 I 111111111111111111111111111111111111111111111111111111111111 0.0 1980 1990 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS) to t-' "" 1. 0., SPANISH FORT SPRINGFIELD PERCENT LAND LOSS RATE CURVE 1.01 PERCENT LAND LOSS RATE CURVE
>-~ ~ ' ~ u~ u~ a..ffi ffia...... 0.6 ...... 0.6
~_J ~_J ~ 3
0.10 0.01 0.03 0.0l111111111111111111111111111;,,,,~;llljlill1111'111~ 0.0111111111/111111?,·,~,1,111 I I lllJ I I ~;~~11111!1~1°1~~~1~~1 1930 1940 1960 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARSl ELAPSED TIME CYEARSl 1.0, ST. BERNARD SULPHUR PERCENT LAND LOSS RATE CURVE ""l PERCENT LAND LOSS RATE CURVE ~ 0.78 >- -~ I-rn' 0.61
a..ffi .... 0.5 I.... 0.5 gCl) §
3 3 0.14 0.15 ~0;14 le.02 •.• I...... ,...... ,...... ,...... ,, ...... ,, ...... ,, ... L 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME ( YEARS) ELAPSED TIME CYEARS) tD I-' (J1 1.0, SWEET LAKE 2.01 TERREBONNE BAY PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE 0.77 ~
0.05 I 0.40
0.0 I 111111111111111111111111111111111111111111111111111111111111 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARSl ELAPSED TIME CYEARSl 1.0, THIBODAUX 1.01 THREE MILE BAY PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE
~ ~ I 0.72 >- § ffi ; D...... ,0,5 "'0.5 0.38 ~ ~ I 0.36
3 3 0.10 ~
0. 0 I , , 1 , , , , 1 , 1 , , 1 • , • , , 1 1 , , , 1 , , , J 1 1 1 , , 1 1 r , , , 1 , , , ; ,:;=;:, 1 1 1 , ; , , , , , , 1 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS) tD I-' ·O"I 3.5, TIMBALIER BAY 3.51 VENICE 3. 11 PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE 3.0 3.0 ~ 2.93 3. 01 ~ >;;:2.5 >;;:2.5 1.87 12.0 12.0 I ..., ..., ~1.5 ~1.5 ...J ...J
31.0 31.04 0.63 0.91 0.5 0.5
0.0 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1950 1960 1970 1980 1990 ELAPSED TIME CYEARS) ELAPSED TIME CYEARS) 5. 0., WEST DELTA 4.42 1.01 YSCLOSKEY PERCENT LAND LOSS RATE CURVE PERCENT LAND LOSS RATE CURVE 4.5
~4.0 w ~ >- >- ~3.5 z ' w ~ ~3.0 2.55 w a.. 2.24 ~ ~0.6 ~2.5 0.40 (/) 0.38 (/) 2 I 32.0 ...I 0 1. 23 ~ 1.5 ...J ~ I 0.08 / 0.10 :: :1. '' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' " ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' "' '' ' ' ' ' ' 0.0 1930 1940 1950 1960 1970 1980 1990 1930 1940 1960 1960 1970 1980 1990 ELAPSED TIME CYEARSl ELAPSED TIME CYEARS) tP ...... -.J