Lohse (1955) showed that longshore currents move sand southward from Mustang Island 

 and along the upper Texas coast to Big Shell beach area in central Padre Island. Off Big 

 Shell, at the westernmost bend of the northwest gulf shoreline, sedimentary material moving 

 counterclockwise along the upper coast combines with sand and shell moving clockwise 

 along the lower coast from the apex of the Rio Grande Delta. The convergence of material 

 off central Padre Island creates an abundance of terrigenous sediment and shells; thus, large 

 volumes of sand are available to eolian transport inland, while shell detritus is concentrated 

 on the beach by eolian deflation of the sand (Watson, 1971). The shoreface is characterized 

 by shell debris and excessive loose sand in steep beach profile. Little Shell, located farther 

 northward on Padre Island, is a secondary nodal point of sediment accumulation. 



In the littoral transport convergence area, there is a positive correlation between shell 

 content and foredune development. In this area high continuous foredunes and very high 

 backshore shell content occur together and are self-reinforcing. The dunes retard overwash 

 and the shell cannot be removed and accumulates; while at the same time the high, steep 

 backshore prevents all but the severe storms from damaging the foredunes (Watson, 1971). 



The littoral processes which converge in central Padre Island consist of longshore 

 currents and waves impinging upon the shoreface. These, in turn, are basically controlled by 

 energy from surface winds which have a resultant net energy almost uniformly from east to 

 west, or obliquely along the upper and lower Texas coasts into the westernmost bend 

 (Lohse, 1955). Littoral transport, as seasonally modified by winter and summer (i.e., 

 offshore and onshore) sand movement, provides the sedimentary material to maintain the 

 barrier islands and the equilibria of their subenvironments. 



Lohse and Cook (1958) described the relationship of south Padre Island to the 

 development and destruction of Rio Grande subdeltas during the past 3,500 to 4,500 years. 

 This study shows that Padre Island south of Mansfield Channel is geologically younger than 

 the part north of the channel. The narrow width and generally lower elevations of the 

 southern part are directly related to a shorter period of growth. Fisk (1959) describes the 

 geologic lustory of central Padre Island, and presents data based on numerous borings and 

 cores. 



Mason and Folk (1958), Hayes (1964), and Milling and Behrens (1966) described the 

 characteristics of beach and dune sands of Mustang and Padre Islands. They showed that the 

 sands of Padre Island can be divided into three groups according to geographical location 

 and petrologic province: (a) southern Padre Island (Rio Grande source), (b) central Padre 

 Island, and (c) northern Padre Island (northern rivers source). The southern province has 

 slightly coarser sand (mostly fine sand) than the northern province (mostly very fine sand), 

 and the sand of the central area is a bimodal mixture of the two sources. Because the beach 

 sand of Padre Island is well sorted, dune sands from this source represent the same grade-size 

 characteristics with little increase in sorting. The major difference between the beach and 

 dune sediment is the progressive decrease in shell and opaque mineral content from the 

 beach in an inland direction. 



