PX and PXT: New Methods for Calculating Shoreline Change Rates
Abstract
It is imperative that coastal erosion studies produce valid erosion rates and erosion hazard predictions to aid in the development of public policy and protect coastal resources. Currently, the SingleTransect method is the most common shoreline change model, which calculates a rate at each shorenormal transect without regard to influences of data from adjacent transects along a beach. Improving on SingleTransect, the University of Hawaii Coastal Geology Group has developed the PX (Polynomial in distance X) and PXT (Polynomial in distance X and Time) shoreline change rate calculation methods, which model all the shoreline positions within a beach simultaneously using polynomial techniques. PX is a special case of PXT that models shoreline change rates spatially along a beach. PXT not only models the shoreline change spatially, but it lets the rate change with time (acceleration). This is an important advance, as beaches may not erode or accrete at a constant (linear) rate. A linear sum of basis functions characterizes the shoreline change rate for both PX and PXT. These methods are an improvement on previous methods as they produce more meaningful, i.e., statistically significant rates and erosion hazard predictions. To date, PX and PXT improve the significance in the rate by 25% on Maui. We use an information criterion (gMDL) to (1) identify the number of coefficients of the basis functions that are needed to describe shoreline change in PX and PXT, and (2) compare different methods to determine which method best describes shoreline change. We present an overview of the PX and PXT methods and results from a shoreline change study of the beaches of southeast Oahu, Hawaii, utilizing these rate calculation methods.
 Publication:

AGU Fall Meeting Abstracts
 Pub Date:
 December 2007
 Bibcode:
 2007AGUFM.H41B0507G
 Keywords:

 4200 OCEANOGRAPHY: GENERAL;
 4217 Coastal processes;
 4299 General or miscellaneous