Title:
A new method for predicting shoreline positions
from historical data
Abstract:
Shoreline rate-of-change values are routinely extrapolated
into the future in order to predict the expected location
of a shoreline. These rate values represent linear summaries
of the process, which have impacted the coast through
time, as implicitly reflected in historical shoreline
position/time data. The reliability of using linear methods
for predicting future shoreline positions decreases for
shorelines which behave in a nonlinear, cyclic, or chaotic
manner. The goal of extrapolation is to provide the best
estimate of future shoreline behavior as based on the
past. Since the magnitude and direction of a long-term
trend can be called into question by short-term changes,
identifying the timing, persistence, and cause of short-term
change is critical for predicting a shoreline's future.
We have developed a robust linear prediction method in
order to detect short-term changes in the long-term trend.
This procedure identifies the linear or high-order polynomial
model which best fits the data according to the Minimum
Description Length (MDL) criterion. According to this
method, however, only linear models are extrapolated for
predictions. For non-linear models, the date at the most
recent critical point is considered the approximate timing
of a trend reversal. Tow lines are used for extrapolation
of non-linear models: One in which all pre-change data
are weighed to zero (i.e. old data are not believed to
contribute useful information about the future) and one
in which all pre-change data are assigned increasing weights
(from 0 to1) until a line is selected according to the
MDL criterion. In the latter case, the old data are believed
partially to contribute useful information about the future.
By using a line or pair of lines for extrapolation, along
with knowledge of the process-response system (if known),
problems implicit in using non-linear models for predictions
are avoided.
In our study, we have applied this shoreline prediction
procedure to a segment of the Texas Gulf coast and the
North Carolina barrier island system. Of the selected
sample sites, 14% showed linear behavior according to
the MDL criterion, 21% had a single change in the long-term
trend (quadratic), and 65% displayed two major changes
in the long-term trend (cubic).
|
Authors:
Fenster, M.S., Dolan, R., and Elder, J., |
Source:
Journal of Coastal Research, v. 9, no. 1, p. 147-171. |
Year:
1993 |
Reprint
(PDF) |
|
