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Environmental Atlas of the Lake Pontchartrain Basin

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Lake Pontchartrain Atlas:
Preface
Table of Contents
Introduction
Environmental Overview
Environmental Status & Trends
Restoration
Physical Environments
Basin Geology
Biological Resources
Environmental Issues You are at the Environmental Issues section of the Environmental Atlas of Lake Pontchartrain
Bibliography
Resources
Contributors
Acronyms
Contact:
Jack Kindinger
Environmental Issues: Coastal Land Loss | Shoreline Change and Rates | Urbanization | Aggregate Dredge Holes | Dredge Pit Characterization | Bonnet Carré Diversion | Water Quality | Sediment Quality & Dispersal

Environmental Issues - Shoreline Change and Shoreline Change Rates

Contributors: Zganjar, Westphal, Penland

Shorelines compiled in this map were derived from either topographic or near-vertical aerial surveys conducted between 1869 and 1995 (Figure 15 a, b and c). The high-water line is used as the official shoreline on cartographic data and is interpreted and determined on near-vertical aerial photographs according to the location of the wet and dry beach contact or the high-water line. To evaluate change in gulfside shoreline position, shore-normal transects were constructed at approximately two minute intervals of longitude or latitude and used to measure the change in location of two corresponding shorelines in different years (Figure 16). Average rates of movement were calculated by dividing absolute measurements by elapsed time. Tables 15 and 16 present the transect measurements of gulfside shoreline change for the South Chandeleur Islands. For gulfside change measurements, a negative (-) sign signifies landward movement or erosion and no sign (positive) signifies a seaward movement or progradation. The total area (m2) of each island were measured for the three intervals between 1869 and 1996 and are shown in Table 17.

Map Legend

Figure 16: 1869 vs. 1996
Map showing gulfside shoreline change of the Southern Chandeleur Island 1869 to 1996 and location of transects.

Figure 16: Location of gulfside shore-normal transects for Southern Chandeleur Islands.

Table 15: Gulfside Shoreline Erosion Rates in (m/yr)
for Southern Chandeleur Islands
Transect
1869-1996
1869-1989
1989-1996
1 n.a. 5.9 n.a.
2 0.2 1.0 -15.0
3 -6.1 n.a. -29.0
4 n.a. -4.9 n.a.
5 n.a. -7.6 n.a.
6 -10.2 -7.9 -50.1
7 -9.5 -8.7 -23.6
8 -9.3 -9.2 -10.7
9 -8.7 -9.0 -2.1
10 -8.5 -8.7 -5.3
11 -9.2 -9.0 -12.9
12 -5.2 -4.8 -11.9
13 n.a. n.a. n.a.
14 n.a. n.a. n.a.
15 n.a. n.a. n.a.
16 n.a. n.a. n.a.
17 n.a. n.a. n.a.
18 n.a. n.a. n.a.
19 n.a. n.a. n.a.
20 n.a. n.a. n.a.
21 n.a. n.a. n.a.
22 n.a. n.a. n.a.
23 n.a. n.a. n.a.
24 n.a. n.a. n.a.
25 n.a. n.a. n.a.
26 n.a. n.a. 47.7
27 n.a. n.a. -31.6
28 n.a. n.a. n.a.
29 n.a. n.a. n.a.
30 n.a. n.a. n.a.
31 n.a. n.a. n.a.
32 n.a. n.a. n.a.
33 n.a. n.a. n.a.
34 n.a. n.a. n.a.
35 n.a. n.a. n.a.
36 n.a. n.a. n.a.
37 -17.5 n.a. 38.0
38 -16.0 -17.4 8.4
39 -15.1 -16.3 5.7
40 -14.9 -16.0 3.6
41 -14.9 -15.7 1.3
42 n.a. n.a. -9.0
43 n.a. n.a. -16.0
44 -14.5 -14.6 -12.7
45 -14.5 -6.1 -11.9
46 -15.0 -15.1 -12.9
47 -15.6 -15.9 -11.1
48 -16.2 -16.5 -9.6
49 -16.2 -16.6 -7.7
50 -16.9 -17.5 -6.7
51 -17.4 -18.5 1.9
52 -18.5 -19.8 4.6
53 -19.8 -21.1 2.6
54 n.a. n.a. n.a.

Table 16: Average Gulfside Shoreline Movement in (m/yr)
for Southern Chandeleur Islands
  Breton Island Grand Gosier,
Curlew Islands
1869-1989 -5.7 -16.2
1989-1996 -15.8 -0.7
1869-1996 -7.4 -16.2

Table 17: Area Measurements by Island (m2)
for the Southern Chandeleur Islands
  Breton Island Grand Gosier,
Curlew Islands
1869 332 453
1989 164 277
1896 86 176

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