Depositional events at the shoreline can be considered non-uniformly spaced samples of (relative) sea level; the shoreline trajectory constructed from shoreline positions in a cross-section through a delta can therefore be considered a proxy to the sea level curve. The problem is that depositional events are stacked on top of each other in the space domain and in order to infer the sea level curve, one must convert the shoreline trajectory from space- to time-domain. Therefore a method is presented that does exactly that. Shoreline trajectories from a number of cross-sections are used to infer the sea level curve, for two cases: (1) the sea level curve is periodic; (2) depositional events are sufficiently frequent. Here the concept is presented, together with a qualitative analysis of all possible deviations from the simple cases that would cause an error of the inferred sea level curve with respect to the true sea level curve. In this short note the concept of the method is presented; a comprehensive analysis will be presented elsewhere, which will follow after processing of the data from experiments that were conducted in the Eurotank flume facility.