PRICE 



25 



At the southern end of Florida there is a mangrove barrier ridge with an irregular lagoon 

 behind it. The mangrove growth is a completely unsmoothed archipelago, partially protected by 

 Cape Romano, a barrier peninsula which is partly smoothed by hurricane erosion where the 

 coast is entirely open. This is a low- to zero-energy coast. 



On the northwestern part of the Yucatan peninsula the mangrove swamp fills the karst 

 re-entrants on a slightly steeper karst plain, making a somewhat smoother coast. All the marine 

 mangrove swamp shoreline is cross-channeled by tidal scour. 



Another example of a completely unsmoothed coastal feature is the crow-foot delta of the 

 Mississippi, which the wave energy has not been able to reduce. Although the sides of the "leg" 

 may have somewhat smooth shorelines, the "feet" (passes) are strongly protuberant features. 



On the drowned karst coast of Florida there are areas where a low-lying coastal strip 

 was filled in by sand during a previous high sea level. This produced a low sandy plain that 

 probably originally had a smoother shoreline than it has today. The coast has been abundantly 

 cross-channeled by tidal scour in the sand, presumably between buried karst elevations. This 

 is considered a zero energy coast and the longshore currents, longshore sediment drift, and 

 wave attack have been too weak to smooth the coast. It has been made irregular by tidal scour, 



A moderately smoothed coast is found in Louisiana west of the delta. The coast is lobate. 

 Bay barriers of sand or oyster reefs smooth the shoreline but are not well aligned. In places 

 they are retreating rapidly due to decreasing sand supply in the longshore drift accompanying a 

 shift of run-off volume from the Mississippi to the Atchafalaya River. Atchafalaya Bay has no 

 longshore sand drift, and, in consequence, an irregular barrier oyster reef replaces the usual 

 smooth bay barrier of sand. 



[40] 



n 



FLA, STRAITS 



"^DEEP WATER WAVE ENERGY, 



(t shows unmeasured hurricane excess) 



GRADIENT IN FT PER STATUTE MILE 



RAMP 



\\^\ 



SUBMERGED 

 KARST 



SHELF SLOPE 



original gradients on slightly 

 'graded deltaic and limestone 

 plains 



SUBMERGED DELTAS a HILLS (H) 

 standing ungroded above ramp and 

 plain grodients. 



Figure 15. Relation of energy, obstacles, original gradients, and lithology of bottom to 

 gradients of ramp and submerged land surfaces on continental shelf. 



