Kenneth J. Connell

Modeling sediment storage and transfer for simulating regional coastal evolution

he regional coastal evolution model Cascade was enhanced to better describe the transfer and storage of sediment. Focus was on the cross-shore exchange of material from the subaerial to the sub-aqueous portion of the beach and on shoal evolution at coastal inlets. Cross-shore material exchange now includes erosion due to wave impact and overwash, and barrier and dune build-up by wind. Cascade was validated with a data set from Ocean City, Maryland, for the long-term response of a barrier island to these types of cross-shore exchange. The sub-model of the inlet shoals now includes the flood shoal, which previously has not been described by Cascade, and all coupling coefficients specifying the transfer of material between the inlet morphological elements were obtained through analytical expressions. The capability of Cascade to simulate inlet shoal evolution was evaluated with data from the south shore of Long Island, New York. Predictions have yielded robust and reliable results, although further testing is required to determine empirical coefficient values needed in the model. (Less)

Coastal Evolution Modeling at Multiple Scales in Regional Sediment Management Applications

Abstract : A numerical model called GenCade is introduced that simulates shoreline change relative to regional morphologic constraints upon which these processes take place. The evolution of multiple interacting coastal projects and morphologic features and pathways, such as those associated with inlets and adjacent beaches can also be simulated. GenCade calculates longshore sediment transport rates induced by waves and tidal currents, shoreline change, tidal inlet shoal and bar volume evolution, natural bypassing, and the fate of coastal restoration and stabilization projects. It is intended for project- and regional-scale applications, engineering decision support, and long-term morphology response to physical and anthropogenic forcing. Capabilities of the model are illustrated by an application to the south shore of Long Island, NY. The Long Island application has multiple coastal structures and features that are maintained to varying degrees of frequency. Cumulative response of the beaches from a variety of coastal projects leads to complexity in regional coastal management. GenCade is presented as a tool to unify management of local projects at regional scales.

COASTAL BARRIER BREACHING: COMPARISON OF PHYSICAL AND NUMERICAL MODELS

Two movable-bed physical model experiments of breach growth in a sandy barrier were conducted in a 3.3-m wide, 64-m long flume with a wave generator capable of generating 0.5 m waves. Breaching was initiated both without waves (Case BR1) and with waves (Case BR2) in separate tests by maintaining a head across the barrier. Breach channel deepening was controlled by the head difference across the barrier. Breach widening was found to occur primarily through episodic avalanching. The avalanched material was transported by the rapid flow both along the breach channel and transverse to the flow. In the presence of waves, breach widening was accelerated and dominated by swash processes. The numerical model of Kraus and Hayashi (2005) was assessed through comparison to measurements. The analysis furthered understanding of breach processes and identified several enhancements to improve predictive capability of the numerical model. (Less)

Morphologic modeling of multiple barrier island breaches for regional application

Abstract : This paper introduces a time-dependent model of regional barrier island breaching for multiple openings, whether as permanent inlets or as new breaches to the same bay. The model allows an arbitrary number of breaches and is forced by tide, storm surge, and wave set up. Limitations on the hydrodynamics, hence calculated breach evolution, are those associated with the Keulegan inlet model. The model includes possible closure or limited breaching by shoaling of the breach channel by longshore transport. Capabilities of the multiple breaching model are examined through eight sensitivity tests.