Assumptions & limitations for coastal erosion

The datasets on coastal erosion in the Netherlands come with several assumptions and limitations:

• Coastline monitoring is based on the Annual Coastal Measurements Programme (JARKUS), which are vertical lines approximately 250 metres apart. This means that coastal changes between these lines are not directly measured. For national-scale assessments this is generally not a significant limitation, but it should be taken into account for local assessments.
• The methods for measuring the bathymetry have changed since 1965. Measurements up to the 1980s are considerably less accurate than more recent surveys (since the 1990s). The changes in measurement systems have introduced small differences between measurements made in consecutive years of data, which need to be accounted for when analysing long-term trends.
• The dune height dataset covers two specific measurement periods (2008–2013 and 2013–2017) and does not provide a continuous time series. Therefore, it gives a snapshot of dune height change, rather than an ongoing monitoring record.
• The dune height is measured using laser altimetry (Light Detection and Ranging (LiDAR)) from an airplane. Vegetation in the dunes may affect the accuracy of these measurements, as it can be difficult to distinguish between the ground surface and the vegetation cover.
• The sand nourishment dataset contains all recorded sand nourishments since 1952. However, older records may be less complete or precise than more recent data. The dataset only provides information at the dune foot level and does not show how sand is distributed across the beach profile.
• Only the currently active sand sourcing areas are shown in the offshore sand sourcing areas dataset. However, many more areas have been designated for future use but are not yet included.