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 1850 and 1995 (Figure 10 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 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 11). Average rates of movement were calculated by dividing absolute measurement by elapsed time. Tables 7 and 8 present the transect measurements and shoreline change rates for Lake Borgne. A negative (-) sign signifies landward shoreline movement or erosion and no sign (positive) signifies a lakeward shoreline movement or progradation.

Figure 11: 1850 vs. 1995

Table 7: Shoreline Movement in Meters

Transect 1850-1995 Rate (m/yr) 1930-1995 Rate (m/yr) 1960-1995 Rate (m/yr) 1 -207 -1.4 -26 -0.4 -35 -1.0 2 -272 -1.9 -56 -0.9 -43 -1.2 3 -262 -1.8 -69 -1.1 -34 -1.0 4 -202 -1.4 -119 -1.8 -57 -1.6 5 -202 -1.4 -132 -2.0 -13 -0.4 6 -272 -1.9 -137 -2.1 -66 -1.9 7 -209 -1.4 -172 -2.6 -63 -1.8 8 -352 -1.4 -21 -0.3 -20 -0.6 9 -652 -2.4 -175 -2.7 0 0.0 10 -767 -4.5 -206 -3.2 -12 -0.3 11 -1217 -5.3 -380 -5.8 -320 -9.1 12 -467 -8.4 -306 -4.7 -241 -6.9 13 -527 -3.2 -398 -6.1 -317 -9.1 14 -239 -3.6 -120 -1.8 -67 -1.9 15 -257 -1.6 -233 -3.6 -76 -2.2 16 -387 -1.8 -164 -2.5 -98 -2.8 17 -427 -2.7 -145 -2.2 -57 -1.6 18 -410 -2.9 -135 -2.1 -29 -0.8 19 -356 -2.8 -192 -3.0 -53 -1.5 20 -452 -2.5 -260 -4.0 -58 -1.7 21 -332 -3.1 -157 -2.4 -42 -1.2 22 -218 -2.3 -103 -1.6 -51 -1.5 23 -220 -1.5 -100 -1.5 -25 -0.7 24 -303 -2.1 -164 -2.5 -47 -1.3 25 -489 -3.4 -222 -3.4 -77 -2.2 26 -427 -2.9 -199 -3.1 -52 -1.5 27 -185 -1.3 -146 -2.2 -73 -2.1 28 -379 -2.6 -209 -3.2 -92 -2.6 29 -250 -1.7 -138 -2.1 -55 -1.6 30 -244 -1.7 -139 -2.1 -74 -2.1 31 -158 -1.1 -142 -2.2 -78 -2.2 32 -274 -1.9 -68 -1.0 -47 -1.3 33 -277 -1.9 -158 -2.4 -111 -3.2 34 -238 -1.6 -206 -3.2 -122 -3.5 35 -461 -3.2 -223 -3.4 -97 -2.8 36 -203 -1.4 -239 -3.7 -112 -3.2 37 -120 -0.8 -223 -3.4 0 0.0 38 -318 -2.2 -357 -5.5 -69 -2.0

Table 7: Measured change of shoreline position (m) along Lake Borgne for three time intervals and the corresponding shoreline movement rate (m/yr) for each transect.

Table 8: Average Shoreline Movement in (m/yr) for Lake Borgne.

1850-1995 -2.40 1930-1995 -2.69 1960-1995 -2.17