Lack of Evidence for Onshore Sediment Transport from Deep Water at Decadal Time Scales: Fire Island, New York.

摘要

Fire Island, New York, is a 50-kilometer-long barrier island that has remained positionally stable without any formation of breach inlets for nearly 200 years. Some researchers have attributed its stability to a major supply of sand moving onshore from relatively deep water (i.e., >10 m depths). Others have demonstrated via sediment budgets that the principal sand sources at decadal to century time scales are littoral sediments derived from eroding beaches bluffs, and cannibalization of inlet shoals in shallower depths (i.e. < or = 10 m). Published sediment budgets indicate that the quantity in question is the order 105 m(cubed)/year. The possibility that this deep-water source sand is significant, active, and persistent at decadal to century time scales has led to reluctance to mine deep-water shoals for beach nourishment of Fire Island Herein, the authors review five factors related to the potential for a significant deep-water sand source in this setting: (1) spatial and temporal frames of reference necessary for this flux of sand, (2) studies of scour and sediment transport over offshore features, (3) sediment size distribution across the foreshore, (4) depth of closure (DOC), and (5) contribution of abandoned inlet shoals. The authors conclude that evidence for an onshore flux of sediment (i.e., order of 105 m(cubed)/yr) is lacking and suggest that reluctance to mine the nourishment is unfounded.