Florida's West Coast inlets: shoreline effects and recommended action

Abstract

This report responds to the 1986 Beaches Bill which, in recognition of thepotential deleterious impact on Florida's beaches of inlets modified for navigation,mandated a study of those inlets with identification of recommended action to reducethe impacts. This report addresses west Coast inlets; East Coast inlets are thesubject of a companion report.There are 37 inlets along that portion of Florida's West Coast commencing fromPensacola Bay Entrance to Caxambas Pass at the south end of Marco Island. Compared tothose on the East Coast, most West Coast inlets have not had the deleterious effectson the adjacent beaches, yet all modified inlets without proper management have thepotential of impacting unfavorably on the adjacent shorelines. Moreover, at presentthere is interest in opening three West Coast entrances which either have been openin the past (Midnight Pass) or which have opened occasionally (Navarre Pass andEntrance to Phillips Lake).A review of inlets in their natural condition demonstrates the presence of ashallow broad outer bar across which the longshore transport Occurs. These shallowand shifting bar features were unsuitable for navigation which in many cases has ledto the deepening of the channels and fixing with one or two jetty structures. Inlets in this modified state along with inappropriate maintenance practices have thepotential of placing great ero$ional stress along the adjacent beaches. Moreover.channel dredging can reduce wave sheltering of the shoreline by ebb tidal shoals andalter the equilibrium of the affected shoreline segments. The ultimate in poor sandmanagement practice is the placement of good quality beach sand in water depths toogreat for the sand to reenter the longshore system under natural forces; depths of 12ft. or less are considered appropriate for Florida in order to maintain the sand inthe system.With the interference of the nearshore sediment transport processes by inletsmodified for navigation, if the adjacent beaches are to be stabilized there must bean active monitoring program with commitment to placement of dredged material ofbeach quality on shoreline segments of documented need. Several East Coast inletshave such transfer facilities; however. the quantities of sand transferred should beincreased. Although an evolution and improvement in the technical capability tomanage sand resources in the vicinity of inlets is expected, an adequate capabilityexists today and a concerted program should be made to commence a scheduledimplementation of this capability at those entrances causing greatest erosionalstress on the adjacent shorelines.A brief summary review for each of the 37 West Coast inlets is presentedincluding: a scaled aerial photograph, brief historical information, several itemsrelated to sediment losses at each inlet and special characteristics relevant toState responsibilities. For each inlet, where appropriate, the above infor~tion isutilized to develop a recommenced action. (PDF has 101 pages.)