Environmental Atlas of the Lake Pontchartrain Basin

	Basin Geology: Geology | Quarternary Framework | Geomorphology | Bathymetry | Geologic Resources

Basin Geology - Geomorphology

• Shoreline Types of the Lake Pontchartrain Basin - Summary
• Shoreline Types

A 'shoreline type' is a homogeneous length of coastline with uniform geological and ecological attributes. Shoreline type is used to describe that part of the coastline affected by the daily action of the wave and tides. A shoreline type classification was developed for the Marginal Deltaic Basin consisting of Lakes Maurepas, Pontchartrain and Borgne where most of the population lives in the LPB.

The concept of a shoreline type map is to provide a tool for planners and managers to use for coastal management and restoration. Shoreline types are defined by their geological and ecological attributes, including shoreline geomorphology and the characteristic of the sediments or materials comprising a particular shoreline type. Ecological attributes are primarily the vegetation types. The combination of these attributes led to the identification of 14 shoreline types. The shoreline type classification was used to map the shorelines of Lakes Maurepas, Pontchartrain, St. Catherine and Borgne as well as Pass Manchac and Rigolets Pass (Table 1). Using a 1996 aerial videotape survey and U.S. Geological Survey 1:24,000 quadrangle maps, shoreline distribution was mapped. This mapping effort established a baseline upon which future events, such as hurricanes, can be assessed or the change in shoreline type as a result of coastal development or coastal restoration projects can be measured.

A total of 564.2 km (350.6 mi) of shoreline were mapped (Table 2). Of this total, 470.1 km (292.1 mi) were natural and 94.1 km (58.5 mi) were human-made (Table 3). The most common natural shoreline type was brackish marsh at 228.8 km (142.2 mi) followed by swamp at 81.9 km (50.9 mi) and salt marsh at 69.8 km (43.4 mi). The most common human-made shoreline type is riprap at 58.9 km (36.4 mi) followed by bulkhead at 26.7 km (16.6 mi) and seawall at 8.2 km (5.1 mi).

Swamp and fresh marsh shoreline types dominate Lake Maurepas. Lake Pontchartrain is characterized by a great diversity in shorelines and the majority of all the human-made shoreline types are found here. Lake Borgne is dominated by brackish marsh and salt marsh with a majority of shell and sand shoreline types found here. This distribution of shoreline types reflects the position of each lake relative to the east-west salinity gradient and proximity to major population centers. The Lake Maurepas shoreline types reflect a fresh to low salinity environment and the proximity of the region's largest cypress forest. The Lake Pontchartrain shoreline types reflect a salinity gradient position between the more fresh Lake Maurepas and the more saline Gulf of Mexico with the population centers on the perimeter. The Lake Borgne shoreline types represent close proximity to the Gulf of Mexico and remoteness from any population center.

Conversion Factors 1 in = 2.54 cm 1 ft = 0.3028 m 1 mi = 1.609 km

Table 1: Summary of Shoreline Types by Location

Location Shoreline Type Miles Lake Maurepas Bulkhead 0.1 Riprap 0.6 Fresh Marsh 4.0 Natural Bank 1.2 Swamp 28.0 Swamp & Fresh Marsh 8.4 Total 42.3 Location Shoreline Type Miles Pass Manchac Bulkhead 0.8 Fresh Marsh 7.3 Natural Bank 2.5 Swamp 0.1 Swamp & Fresh Marsh 1.6 Total 12.4 Location Shoreline Type Miles Lake Pontchartrain Bulkhead 11.8 Riprap 34.6 Seawall 4.3 Sand beach 8.6 Shell Beach 0.3 Fresh Marsh 1.8 Intermediate Marsh 5.9 Brackish Marsh 30.1 Natural Bank 0.1 Swamp 22.8 Swamp & Fresh Marsh 4.6 Swamp & Intermediate Marsh 0.3 Swamp & Brackish Marsh 0.1 Total 125.3 Location Shoreline Type Miles Rigolets Bulkhead 0.7 Riprap 0.1 Sand Beach 0.2 Brackish Marsh 17.7 Total 19.0 Location Shoreline Type Miles Lake St. Catherine Bulkhead 2.9 Brackish Marsh 16.0 Total 18.9 Location Shoreline Type Miles Lake Borgne Bulkhead 0.3 Riprap 1.1 Seawall 0.8 Sand Beach 2.0 Shell Beach 6.9 Brackish Marsh 78.4 Salt Marsh 43.4 Total 133.0

Table 2: Summary of All Shoreline Types
Location Shoreline Type Miles All Shorelines Bulkhead 16.6 Riprap 36.4 Seawall 5.1 Sand Beach 10.9 Shell Beach 7.3 Fresh Marsh 13.1 Intermediate Marsh 5.9 Brackish Marsh 142.2 Salt Marsh 43.4 Natural Bank 3.9 Swamp 50.9 Swamp & Fresh Marsh 14.6 Swamp & Intermediate Marsh 0.1 Swamp & Brackish Marsh 0.3 Total   350.6

Table 3: Summary of Natural and Human-Made Shoreline Types
Shoreline Type Miles Natural Sand Beach 10.4 Shell Beach 7.3 Fresh Marsh 13.1 Intermediate Marsh 5.9 Brackish Marsh 142.2 Salt Marsh 43.4 Natural Bank 3.9 Swamp 50.9 Swamp & Fresh Marsh 14.6 Swamp & Intermediate Marsh 0.1 Swamp & Brackish Marsh 0.3 Total 292.1   Shoreline Type Miles Human-made Bulkhead 16.6 Riprap 36.4 Seawall 5.1 Beach Replenishment 0.4 Total 58.5