| ![](../images/dot_clear.gif) | ![](../images/669corner-ul.gif) | Lake Pontchartrain Atlas: | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | Environmental Issues | ![You are at the Environmental Issues section of the Environmental Atlas of Lake Pontchartrain](../images/pointer.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | ![](../images/dot_clear.gif) | | ![](../images/669corner-ll.gif) | | ![](../images/dot_clear.gif) | | ![](../images/dot_clear.gif) | ![](../images/dot_clear.gif) | ![](../images/dot_clear.gif) | | | ![](../images/spacer.gif) | 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 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 | ![Map showing Bayside Shoreline Change Rates of Southern Chandeleur Island 1869 to 1996.](images/pg146fig1.gif) | 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 | | « Previous | Next » |