Somewhat the same situation exists in Perdido Bay (Pensacola quadrangle), 

 although erosion effects are not as pronounced because of the bay's smaller 

 size (Hardin et al . 1976). 



The aspects of severe weather disturbances that cause the greatest 

 changes to shorelines and near-shore bottoms are storm surges, waves, and 

 currents (Hayes 1967). Since much of the shoreline of Alabama is below 3 m 

 (10 ft) in elevation there is great erosional danger from a hurricane storm 

 surge. When a storm surge advances up a converging estuary such as Mobile or 

 Perdido Bays, its height increases as the water becomes more confined. The 

 storm surge progresses more rapidly on a rising tide and may form a wall-like 

 wave of water moving up the estuary (Chermock 1974). 



By far the most significant event in terms of shoreline erosion took 

 place in September 1979, Hurricane Frederic, which caused massive shoreline 

 changes. 



In Baldwin County immediately west of Perdido Bay (Pensacola quadrangle) 

 the shoreline receded about 24 m (80 ft), and for about the next 19.3 km (12 

 mi) west to the vicinity of Little Lagoon (Pensacola quadrangle), about 30 m 

 (100 ft). All along the Fort Morgan Peninsula (Pensacola quadrangle), exten- 

 sive dune erosion took place. 



In Mobile County, Dauphin Island (Biloxi quadrangle) was overwashed along 

 the entire 17.7 km (11 mi) long western end. All the low areas on the 

 eastern portion of the island were flooded and the southern shoreline 

 receded from 3 to 30 m (10-100 ft). Along the western end of the island, 

 the southern shore receded about 6 to 15 m (20-50 ft) and the entire spit 

 was lowered from an elevation of 1.5 to 3 m (5 to 10 ft); National Geodetic 

 Vertical Datum (NGVD) to an elevation of 0.6 to 1.5 m (2 to 5 ft) (U.S. Army 

 Corps of Engineers 1981). 



The following information on sediment budget variations is from Hardin et 

 al . (1976). 



The sediment budget for the coastal system is the net amount of sediment 

 in the coastal area after considering the quantity of material being 

 introduced, the quantity temporarily stored (dunes), and the quantity 

 being removed from the coastal system. Beaches are nourished and 

 maintained by sand-size sediment contributed by major streams, updrift 

 shoreline erosion, onshore movement of shelf sand by wave action (Brown, 

 and others, 1974), and by current circulation. Sand losses are caused by 

 transportation offshore into deep water, accretion along and against 

 natural barriers and man-made structures, deposition in tidal deltas and 

 hurricane washover fans, excavation for proposed construction, and eolian 

 processes (Brown et al . 1974). 



Sediment is carried to coastal Alabama by the Mobile and Perdido River 

 systems. No data on the quantity of suspended sediment transported by the 

 Perdido River is currently available (Boone 1973). Suspended sediment load 

 transported yearly by the Mobile River into the delta and bay system ranges 

 from 1.9 million to 7.5 million metric tons (2.1 million to 8.3 million short 



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