| | | Lake Pontchartrain Atlas: | | | | | | | | | | | | | | | | | | | | | Environmental Issues | | | | | | | | | | | | | | | | | | | | | | 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. Figure 16: 1869 vs. 1996 | | 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 | | « Previous | Next » |