Beach Erosion in the Town of Jupiter Island: Causes and Remedial Measures

Dean, Robert G.; ,

Beach Erosion in the Town of Jupiter Island: Causes and Remedial Measures

by Robert G. Dean, Univ of Florida, Gainesville, United States,

Document Type: Proceeding Paper

Part of: Coastal Zone '91

Abstract:

St. Lucie Inlet, located on the lower east coast of Florida, was cut across a barrier island in 1892 and jetties were constructed on the north and south sides of the inlet in 1926 and 1981, respectively. The inlet flood and ebb tidal shoals have acted as sinks, accumulating approximately 28.8 million cubic meters of sediment since the inlet was cut. This sand removal from the active nearshore system has caused severe long-term beach recession rates exceeding 9 m/yr on Jupiter Island immediately downdrift (south) of St. Lucie Inlet. This erosion is greatest on the north end of Jupiter Island and has rendered the northern portion of the island literally uninhabitable and the northern 11 km now consists of public lands managed by various federal and state agencies. The Town of Jupiter Island extends over a 12 km shoreline segment, commencing from the southerly limit of the public lands. Long-term shoreline change conditions range from 2 m/yr recession at the north Town limit to nearly a stable shoreline at the south limit. Since 1973, the Town has engaged in a concerted and expensive program of beach nourishment with cumulative placement exceeding 6 million cubic meters. The sediment, obtained from an offshore source, is finer than the native which results in two undesirable effects: (1) the equilibrium profile slope is milder than the native, thereby resulting in less additional dry beach width per unit volume placed, and (2) it appears that the longshore 'spreading out' rates are greater than would occur with coarser sediment. The latter conclusion is based on computations with the usually adopted sediment transport factor of 0.77. A hypothetical periodic beach nourishment scenario is considered using coarser sediment and predictions of volume remaining in the area placed presented versus time. Monitoring has proven that the nourishment program has been a boon to sea turtle nesting, presumably through the provision of a wider beach.

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