Trafficability and Navigability of Delta-Type Coasts. Trafficability and Navigability of Louisiana Coastal Marshes. Photo-Interpretation Keys of Selected Coastal Marshland Features.

摘要

This report consists of fourteen aerial photographs, scale 1:23,600, selected as illustrating typical features of the coastal marsh region of Louisiana. A short description accompanies each photograph. In using photographic keys for the interpretation of coastal and marshland features of Louisiana the fact should be borne in mind that the Gulf of Mexico is a comparatively tideless sea, the normal tidal range along the Louisiana coast being about 14 inches. Extreme wind from the north at times depresses water levels two feet and more. A few days of strong south or southeast wind raises water levels a foot or more above tidal estimates. A hurricane may flood large parts of the marsh region to a depth of six feet, or even more in extreme cases. During such storms, drastic changes in the coastal marshland take place. The processes of erosion and deposition are tremendously accelerated, and effects upon plant and animal life are extreme. Hurricanes are most likely to occur in September or October, but occasionally take place in other months. The coasts and marshes of delta regions subject to tides of several feet differ in many respects from those of relatively tideless areas. The effect of 'wind tide' is relatively less important, mud flats and other features exhibit characteristic differences, the salt- marsh zone is broader and rate of tidal scour in marsh streams is accelerated.