BACKBARRIER CONTROL ON TIDAL INLET MORPHOLOGY

The formation of New Inlet along the outer coast of Cape Cod in January 1987 introduced a number of large scale morphological changes to the backbarrier. Immediate hydraulic changes included an increase in tidal range, tidal prism, and wave energy. This overall increase in hydraulic regime has continued to drive backbarrier evolution as the system strives to achieve equilibrium between an increase in sediment transport and stable inlet morphology. A large database of aerial photos taken annually since the formation of New Inlet exists and has aided in evaluating the role of the backbarrier in modulating the evolution of an inlet system. Growth and migration of the flood tidal delta and large intertidal sand shoals are responsible for constricting and modifying channel flow; such that the configuration of the main inlet channel is largely a function of changes taking place in the backbarrier. In 1997 a new ebb channel was breached and by 1999 had captured the entire tidal prism from the former main ebb channel. The formation of the new channel was a response to flow constriction caused by progradation of the spit platform and by shoal growth in the backbarrier. Because the new main channel was breached updrift of the former channel a large volume of sediment in the ebb tidal delta was bypassed and is working its way on shore in the form of bars, but the story does not end there. Because inlet sediment bypassing has been established, this would suggest that the inlet is approaching an equilibrium condition; however, recent data collection suggests that sediment is still moving into the backbarrier and, ultimately continuing to modify the morphology of the entire inlet system. In order to better understand this evolving system a two-dimensional finite element circulation model is being implemented in an effort to predict sediment transport and finally the future configuration of a dynamic inlet system.