Abstract: Reef Morphology and Sediment Transport, Lucaya, Grand Bahama Island

Dennis K. Hubbard, Larry G. Ward, Duncan M. Fitzgerald

Between August 1974 and April 1975 three saturation dives were made in the Perry Hydrolab off Lucaya, Grand Bahama Island. During the 16 days spent on the bottom, studies of reef zonation and sediment transport to a depth of 80 m were conducted. The physiographic zones of the area, although highly variable, are similar to those found by Goreau and Land in the Jamaican reefs. Eight zones were identified in the Lucaya reef area: (1) shoreface sands, (2) shallow-rock terrace, (3) inner-rock ridge, (4) shallow reef (reef crest), (5) inner sand flat, (6) fore reef (terrace and escarpment), (7) fore-reef slope, (8) deep fore reef and wall.

Textural analysis and tracer studies indicate that the sand which is produced primarily in the fore reef is moving seaward across the fore-reef slope and over the top of the wall. Transport over the wall is through chutes that cut through the deep fore reef onto the outer fore-reef slope. Sediment traps placed in these chutes at a depth of 60 m indicate that approximately 200 g of sediment per day is transported over a 1-meter section of the wall. Lower rates were measured during calm periods when gravity creep was the sole method of observed transport. Higher rates were associated with more severe wave conditions that created a strong return flow from water trapped along the beach.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA