Bed elevation has been measured annually by Rijkswaterstaat since 1926, with single beam echo sounders until 1999, and multibeam echo sounders since 1999. Single beam measurements were taken at cross sections spaced 25 m, and were averaged over 1 km. Multibeam measurements covered the entire length of the river, and were averaged over 100 m. All bed elevation data are cross-section averaged. The error in bed elevation data (defined as two times the standard deviation) has been estimated to be up to 0.2-0.5 m until 1990; 0.2-0.3 m, between 1990-1999, and 0.05-0.1 m since 1999 (Wiegmann, 2002)
Grain size data has been measured by Rijkswaterstaat, using a digging bucket until 1984, and grab samplers since 1984. The data set includes measurements from 1966, 1976, 1984, 2008, 2016, 2017, and 2020. Samples have been taken at cross-sections spaced 500 m to 1 km. Three samples (spaced 65 m) have been taken at each cross section. The uncertainty of grain size data is high due to the high natural spatio-temporal variability and limited spatial and temporal sampling density.