Journal of Coastal Research 19 4 812–827 West Palm Beach, Florida Fall 2003 The Coastal-Tract (Part 1): A Conceptual Approach to Aggregated Modeling of Low-Order Coastal Change Peter J. Cowell 1 , Marcel J.F. Stive 2,3 , Alan W. Niedoroda 4 , Huib J. de Vriend 3,5 , Donald J.P. Swift 6 , George M. Kaminsky 7 , and Michele Capobianco 8 1 University of Sydney Institute of Marine Science NSW 2006, Australia 2 Department of Civil Engineering and Geosciences Delft University of Technology PO Box 5048 2600 GA Delft, The Netherlands 3 Delft Hydraulics PO Box 177 2600 MH Delft The Netherlands 4 URS Greiner Woodward- Clyde USA 5 University of Twente PO Box 217 7500 AE Enschede, The Netherlands 6 Department of Ocean, Earth and Atmospheric Sciences Old Dominion University Norfolk, Virginia, USA 7 Washington Department of Ecology Coastal Monitoring & Analysis Program Olympia, Washington, USA 8 SATE Srl—Systems and Advanced Technologies Engineering Venice, Italy ABSTRACT COWELL, P.J.; STIVE, M.J.F.; NIEDORODA, A.W.; DE VRIEND, H.J.; SWIFT, D.J.P.; KAMINSKY, G.M., and CA- POBIANCO, M., 2003. The coastal-tract (part 1): a conceptual approach to aggregated modeling of low-order coastal change. Journal of Coastal Research, 19(4), 812–827. West Palm Beach (Florida), ISSN 0749-0208. Evolution of coastal morphology over centuries to millennia (low-order coastal change) is relevant to chronic problems in coastal management (e.g., systematic shoreline erosion). This type of coastal change involves parts of the coast normally ignored in predictions required for management of coastal morphology: i.e., shoreline evolution linked to behavior of the continental shelf and coastal plain. We therefore introduce a meta-morphology, the coastal tract, defined as the morphological composite comprising the lower shoreface, upper shoreface and backbarrier (where pre- sent). It is the first order-system within a cascade hierarchy that provides a framework for aggregation of processes in modeling low-order coastal change. We use this framework in defining boundary conditions and internal dynamics to separate low-order from higher-order coastal behavior for site-specific cases. This procedure involves preparation of a data-model by templating site data into a structure that complies with scale-specific properties of any given predictive model. Each level of the coastal-tract cascade is distinguished as a system that shares sediments internally. This sediment sharing constrains morphological responses of the system on a given scale. The internal dynamics of these responses involve morphological coupling of the upper shoreface to the backbarrier and to the lower shoreface. The coupling mechanisms govern systematic lateral displacements of the shoreface, and therefore determine trends in shoreline advance and retreat. These changes manifest as the most fundamental modes of coastal evolution upon which higher- order (shorter-term) changes are superimposed. We illustrate the principles in a companion paper (The Coastal Tract: Part 2). ADDITIONAL INDEX WORDS: Shoreface, backbarrier, scale, coastal tract, coastal cell, coastal-tract cascade, tem- plating, data-model, behavior-oriented models, sediment-sharing systems, morphological coupling, sea level, sediment supply, coastal management, sea-level rise, transgression, barrier, continental-shelf, sediments, accommodation space, numerical-model. INTRODUCTION Coastal management and engineering requires predictions of low-order (large-scale) coastal change to determine wheth- er shoreline and seabed movements involve systematic trends. Such trends may cause chronic problems that require long-term planning and major engineering interventions. Morphological change entailing temporary fluctuations may cause acute problems, but these can usually be remedied with 03300F received and accepted in revision 10 January 2003. local measures. Coastal management strategies are very dif- ferent for the two types of problem, and usually involve very different levels of expense. If estimates of the long-term change cannot be quantified, then it seems unlikely that pre- dictions will discriminate adequately between chronic and acute coastal change. Aggregated-scale approaches have been developed to side- step upscaling problems (e.g., DE VRIEND, 1998) from which emerge inadequacies in conventional perceptions and defini- tions of the coast and coastal processes. In particular, the boundary conditions and internal dynamics are poorly de-