## 3 Materials and Methods
### Accuracy Assessment  
Field campaigns were carried out on dates close to the last available orthophoto to validate the last cartographies. The collection of topographic profiles on the major geomorphological subsystems (beach, dunes and marshes) helped to delineate the most problematic features. The system with the largest data availability, the SVB estuary, was used as a test site to carry out an accuracy assessment. This procedure allows for an estimation of errors associated with the results. Although these errors increase with the age of the orthophoto, the method is useful to identify the areas with a large probability of errors. The accuracy assessment compares the values on test pixels recorded in the field (reference points), with the corresponding pixels in the map. Besides recording reference points in the field, a flight with an Unmanned Aerial System (UAS) was also performed. \begin{table}
\begin{tabular}{l l} \hline
**Feature** & **Description, Eco-Geomorphological Role** \\ \hline _Drainage Network (1)_: Estuarine channel system, including minor forms related to their bottom and margins. \\ \hline Channel 1 (2) & Main river channel. It is the estuary in the strict sense, which extends upstream to the edge of the salt wedge [31]. \\ Channel 2 (2) & Distributary channels directly derived from the main channel. \\ Channel 3 (2) & Distributary channels derived from the secondary distributary channels. \\ Artificial channel (2) & Non-natural channels within the fluvial network. \\  & Sandy environment located preferentially in the lower intertidal zone. It is an unstable area characterized by the constant resuspension of sediment by tidal flood and ebb currents [57]. \\ Flood tidal delta (2) & Accumulation of sand on the shoreward side of an inlet, initially formed during storm surges and maintained by flood currents [58]. \\ Ebb tidal delta (2) & Accumulation of sand on the seaward side of an inlet formed by the ebb tidal current [58]. \\ \hline _Rocky units (1)_: Bedrock, boulders and cobbles which occur in the intertidal zone (EUNIS classification). \\ \hline Cliff (2) & Very steep, vertical, or overhanging rock slopes \\ Rocky platform (2) & Flat (planar) platforms carved into rocks formed by weathering and wave erosive action. \\ \hline \end{tabular}
\end{table} 
Table 1: Cont. According to the Spanish regulations for UAS operations, the flying height was 120 m above ground level, obtaining an orthomosaic with a 0.03 m pixel size. The accuracy of the maps was assessed with a confusion matrix. Confusion matrices are a common tool used for the assessment of cartography accuracy. They are widely accepted, although the bias of the test pixels also biases the accuracy of the confusion matrix [27] and references therein. Therefore, to minimize the bias of the text pixels, at least ten test pixels were considered for each feature. According to [43], the proportion of area (\(p_{ij}\)) of a mapped feature \(i\) and reference feature \(j\) is estimated according to (3):  
\[p_{ij}=\left(\frac{n_{ij}}{n_{i+}}\right)\star\left(\frac{N_{i+}}{N}\right) \tag{3}\]  
where \(n_{ij}\) is the number of reference points classified as mapped feature \(i\) and reference feature \(j\), \(n_{i+}\) and \(N_{i+}\) are the number of pixels per sample and in the entire map in stratum \(i\), and \(N\) is the number of pixels in the entire map.