ecological characterization atlas of coastal alabama - Data Center

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 t is 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, erosi on has ranged from 12 m ( 39 ft) at Pt . Judi th to 149 m
(488 ft) at Cedar Point . The areas between Dog River Point and Fowl River
Point and between Delchamps 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 is ands 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
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