predominant wave approach from the southeast and east. Calculations from 

 wave-refraction analysis of longshore sediment transport along the Chandeleur Islands 

 indicate potential representative rates of 4 x 10"' m-^/yr to thexiorth, under 3 m high, 

 lO-second period, azimuth 135° wave conditions, and 3 x 10 m'^/yr, also to the north, 

 under 0.5 m and 5-second period, azimuth 135° wave conditions. 



Active longshore transport processes on Louisiana barriers provide two further 

 mechanisms for permanent loss of barrier sediments: (I) spit progradation, and (2) tidal 

 inlet migration. As marginal spits prograde away from the shallow delta platforms by 

 downdrift spit accretion into deeper interdeltaic marginal basins such as Timbalier Bay, 

 increasing volume of sediment is required to maintain the subaerial integrity of the 

 system. In some instances, spits prograde into even deeper tidal inlets, and require 

 considerably larger sediment volumes. Examples of spit progradation into marginal 

 deltaic basins are found on the north end of the Chandeleur Islands, Breton Island, and at 

 Raccoon Point in the Isles Dernieres. Examples of progradation into tidal inlets occur at 

 Borataria Pass, Caminada Pass, Little Pass Timbalier, Cat Island Pass, and Wine Island 

 Pass. A prominent example of sediment loss into spit and tidal inlet complexes is 

 provided by the westward migration of the Timbalier Islands. Between 1887 and 1978, 



Wine I. Timbalier isiand East Timbalier I. Boycw 



_ . . . Linle Pan. LaFowcho 



-10 



•Y'i-'i" Early ^• 



-:,- Early ^•-';'v};V>'",-,;p<;' ■'.-,',";'■•" Late IVIT^-Tvii 

 ';" LaFourche 't; V ,\-, '_',';.;. ;,i;.'--^,'; ;LaFourche vV^ ;'c 



--'•'- Delta ,; ;,',;^ 'X'-'-''-;~''--r-r''^''-;-'' ■ ''^"^ J-f-~-''^''V; 



50 



LEGEND 



Timbalier Island 



D 

 D 



Shoreface 



Distributary Flanli 

 Beach Ridge Plain 



Distributary Moutti Bar 



Delta Front 



,--' Prodella 



M 



Backbarrier Marsh 

 I and Bay 



Interdistributary Bay Fill 



Kilometers 



Figure 8. A stratigraphic strike section (top) and stratigraphic dip section 

 (bottom) of the Timbalier Islands showing facies relationships and the infilled 

 channel of Cat Island Pass offshore. 



22 



