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 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 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 17). Average rates of movement were calculated by dividing absolute measurement by elapsed time. Tables 18 and 19 present the transect measurements of bayside shoreline change for the South Chandeleur Islands. For bayside change measurements, a negative (-) sign signifies a landward movement or erosion and no sign (positive) signifies a seaward movement or progradation. The total areas (m²) of each island were measured for the three time intervals between 1869 and 1996 and are shown in Table 20.

Figure 17: 1869 vs. 1996

Figure 17: Location of bayside shore-normal transects for Southern Chandeleur Islands.

Table 18: Bayside Shoreline Erosion Rates in (m/yr) for Southern Chandeleur Islands.

Transect 1869-1996 1869-1989 1989-1996 3 n.a. -7.7 n.a. 4 -2.1 -1.9 -6.6 5 1.6 2.3 -11.6 6 n.a. 6.6 n.a. 7 8.8 6.7 45.1 8 9.0 9.8 -3.4 9 9.4 10.0 -0.3 10 8.7 9.2 -1.0 11 -0.3 -0.3 -1.6 12 n.a. n.a. -2.4 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. 1.0 21 n.a. n.a. 4.3 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. n.a. 27 n.a. n.a. -16.6 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 n.a. n.a. n.a. 38 n.a. n.a. n.a. 39 n.a. n.a. n.a. 40 16.0 18.5 -27.7 41 15.3 15.4 -23.4 42 16.4 17.9 -9.7 43 12.1 12.8 -1.3 44 13.5 12.8 26.1 45 12.3 12.7 5.3 46 13.1 14.0 -2.3 47 14.5 15.5 -1.3 48 10.1 11.1 -5.6 49 11.6 12.5 -3.3 50 13.5 13.8 7.7 51 15.1 16.0 -1.1 52 14.5 15.1 3.7 53 19.1 22.6 -10.9 54 n.a. n.a. n.a.

Table 19: Average Bayside Shoreline Movement in (m/yr) for Southern Chandeleur Islands.

Breton Island Grand Gosier, Curlew Islands 1869-1989 -3.9 15.0 1989-1996 2.0 -2.9 1869-1996 5.0 14.1

Table 20: Area Measurements by Island (m2) for the Southern Chandeleur Islands.

Breton Island Grand Gosier, Curlew Islands 1869 332 453 1989 164 277 1996 86 176