Environmental Atlas of the Lake Pontchartrain Basin

	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

• Introduction
• Shoreline Changes of Lake Maurepas
• Shoreline Change Rates of Lake Maurepas
• Shoreline Changes of Northern Lake Pontchartrain
• Shoreline Change Rates of Northern Lake Pontchartrain
• Shoreline Changes of Southern Lake Pontchartrain
• Shoreline Change Rates of Southern Lake Pontchartrain
• Shoreline Changes of Lake Borgne
• Shoreline Change Rates of Lake Borgne
• Shoreline Changes of the Northern Chandeleur Islands
• Gulfside Shoreline Change Rates of the Northern Chandeleur Islands
• Bayside Shoreline Rates Changes of the Northern Chandeleur Islands
• Shoreline Changes of the Southern Chandeleur Islands
• Gulfside Shoreline Change Rates of the Southern Chandeleur Islands
• Bayside Shoreline Change Rates of the Southern Chandeleur Islands

Shorelines compiled in this map were derived from either topographic or near-vertical aerial surveys conducted between 1855 and 1995 (Figure 12 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 bayside shoreline position, shore-normal transects were constructed at approximately 15 second intervals of longitude or latitude and used to measure the change in location of two corresponding shorelines in different years (Figure 14). Average rates of movement were calculated by dividing absolute measurement by elapsed time. Tables 12 and 13 present the transect measurements of bayside shoreline change for the North Chandeleur Island. For bayside change measurements, a negative (-) sign signifies a seaward movement or erosion and no sign (positive) signifies a landward movement or accretion. The total area (m2) of each island were measured for the three intervals between 1869 and 1996 and are shown in Table 14.

Figure: 14 1855 vs. 1996

Figure: 14 Location of bayside shore-normal transects for Northern Chandeleur Island.

Table 12: Bayside Shoreline Erosion Rates in (m/yr) for North Chandeleur Island.

Transect 1855-1996 1855-1989 1989-1996 6 n.a. n.a. n.a. 7 n.a. n.a. -15.6 8 n.a. n.a. 1.3 9 n.a. n.a. -3.9 10 n.a. n.a. -14.3 11 11.8 13.9 7.3 12 9.3 9.6 4.9 13 13.1 15.0 -2.3 14 3.9 5.8 0.4 15 5.1 6.3 8.4 16 4.3 6.0 0.0 17 6.6 8.8 -1.7 18 4.6 6.7 -1.0 19 6.3 4.1 n.a. 20 0.4 0.5 -1.0 21 1.4 1.5 0.1 22 1.3 1.3 2.0 23 -0.2 -0.3 1.0 24 0.6 0.6 0.9 25 2.2 2.2 1.4 26 0.7 0.7 1.3 27 -0.1 0.1 0.0 28 1.6 1.7 -0.3 29 5.8 6.1 0.9 30 0.2 0.3 -0.3 31 4.1 4.2 1.6 32 0.8 0.7 2.1 33 4.3 4.5 0.4 34 0.0 -0.1 1.3 35 2.6 2.7 0.0 36 0.0 0.0 -1.1 37 -0.7 -0.8 0.9 38 3.7 3.8 0.6 39 0.1 0.0 2.0 40 0.2 0.2 0.0 41 0.2 0.3 -2.3 42 0.9 0.8 2.6 43 3.1 3.3 -1.3 44 2.7 3.0 -3.7 45 3.3 3.7 -4.1 46 7.3 6.7 0.0 47 n.a. n.a. 4.7 48 n.a. n.a. 0.3 49 4.5 4.8 -0.6 50 3.1 3.0 4.4 51 2.4 3.1 -2.0 52 0.4 0.5 -2.4 53 0.2 0.3 -0.4 54 n.a. 3.9 -0.4 55 1.4 1.4 0.9 56 0.8 0.9 -0.3 57 n.a. -0.6 2.6 58 5.1 n.a. -1.0 59 0.3 0.2 0.6 60 3.7 3.5 1.4 61 1.6 1.7 -0.6 62 5.1 5.4 -0.1 63 4.6 3.8 -0.6 64 -0.9 -0.9 -1.6 65 1.0 -1.1 5.7 66 1.0 1.1 -0.3 67 3.0 3.1 1.1 68 2.5 2.6 1.1 69 8.4 4.2 -1.7 70 3.4 3.3 6.7 71 6.1 6.5 2.1 72 n.a. n.a. -1.9 73 9.2 9.8 -0.7 74 6.4 6.7 0.1 75 6.0 4.8 28.7 76 5.1 3.4 37.7 77 5.2 4.6 16.4 78 4.8 4.1 17.9 79 0.3 0.3 0.0 80 1.1 1.1 1.3 81 2.8 2.9 0.3 82 -0.5 -0.5 -0.7 83 -1.5 -2.0 8.0 84 -0.3 -0.8 8.3 85 -0.1 -1.2 21.3 86 1.4 n.a. n.a.

Table 13: Average Bayside Shoreline Movement in (m/yr) for North Chandeleur Island

1855-1989 2.9 1989-1996 2.2 1855-1996 2.9

Table 14: Area Measurements (m2)

1855 2763 1989 1749 1996 1753