The Shoreline is Measured using Metric Aerial Photographs and Ground Surveys.
In the schematic figure above, the position of the shoreline taken from a number of photographs of differing vintage is plotted. The position today is set as our reference point i.e. zero. The eye tells you that the position of the shoreline was not the same in each photograph. Sometimes it was landward of the present position sometimes seaward. However, no systematic change is evident. This coast is neither eroding or accreting.
A Coast that is Eroding.
In this second example, the shoreline today is landward of its position over most of his history. Compared to the start of the record the coast as on average eroded. Along the US Atlantic Coast the average rate of change of the shoreline is 1.5 m/yr. Even so, some place are not eroding but rather accreting. In this second example the change has been progressive. The rate of erosion has been constant and we might be tempted to use this nearly constant rate of change to predict where the shoreline will be in the future.
A Coast that is Accreting.
Some coasts are building seaward. Sand transported from elsewhere layers on the shore and the beach becomes wider. Over the years significant new land is built. If you are so lucky to have this circumstance in front of your beach house, all the new land is your! it is like a hot, blue-chip stock. As the years go by it is worth more and more. In the case shown the trend is steady and linear. The rate of change does not seem to change.
