decrease in sediment being transported downstream by the Mobile River as a 

 result of upstream impoundments, or by short periods of high discharge 

 (floods). The greatly increased velocity of water flowing over the delta 

 during such floods could cause much erosion in a short period. 



2. Mobile Harbor Region (Mobile quadrangle): The main cause of 

 accretion in this region has been human disposal activities as opposed to 

 natural processes. This region will be discussed in the chapter dealing with 

 socioeconomic features, under the category of artificially-made lands. 



3. Western Shore Region (Mobile quadrangle): This region of Mobile Bay 

 shows signs of erosion for almost its entire north-south distance. Between 

 1917 and 1974, erosion has ranged from 12 m (39 ft) at Pt. Judith to 149 m 

 (488 ft) at Cedar Point. The areas between Dog River Point and Fowl River 

 Point and between Del champs Bayou and Cedar Point show the most severe 

 erosion (Figure 1). 



4. Mississippi Sound, North Shore (Biloxi quadrangle): The northern 

 shoreline of Mississippi Sound in Alabama is mostly made up of low-lying salt 

 marsh with numerous tidal creeks and, with the exception of some residential 

 and commercial-fisheries development, remains in its natural state. The 

 southern shoreline is composed of sandy barrier islands that protect the 

 northern marshy coast from the full impact of erosional agents, such as wave 

 action and tropical storms. 



Between 1917 and 1958 the northern shore experienced net shoreline 

 erosion at selected points which varied from 47.8 m (157 ft) on Marsh Island 

 (Grand Bay) to 132.2 m (434 ft) on Marsh Island (Portersville Bay). These 

 represent erosional rates ranging from 1.2 m (3.8 ft) to 3.2 m (10.6 ft) per 

 year for those specific points. The generalized areas of erosion for eastern 

 Mississippi Sound are shown on Figure 8. Most erosion has occurred on 

 exposed marshy headlands and on exposed shorelines of the offshore islands. 

 It was estimated (1976) that many of the exposed shorelines in this region 

 are eroding at an average rate of 1 to 2 m (3 to 7 ft) per year. 



5. Dauphin Island Area (Biloxi quadrangle): Dauphin Island is part of a 

 chain of barrier islands protecting Mississippi Sound from the erosional 

 forces of the Gulf of Mexico. These barrier islands absorb almost the full 

 impact of winds, wave action, tides, and currents. As with all other islands 

 of this type, the Dauphin Island shoreline is constantly changing. Several 

 times since 1917, and as recently as 1979 (Hurricane Frederic), the island 

 has been overwashed as a result of severe weather. 



There has been a general trend of erosion along the gulf shore of the 

 island and a general elongation of the western end of the island. Shoreline 

 erosion on the entire gulf shore for the period 1942-74 averaged 63.7 m (209 

 ft) or 1.9 m (6.3 ft) linearly per year excluding accretion on the western 

 tip of the island. This accretion added a total of 2.9 km (1.8 mi) to the 

 length of Dauphin Island from 1917 to 1974. 



6. Eastern Shore Region (Pensacola quadrangle): Most of this region has 

 undergone accretion or has maintained a state of dynamic equilibrium between 



96 



