Bed elevation and bed surface grain size (D50) Bovenrijn and Waal, 1926-2020

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.<br>

荷兰水利总司（Rijkswaterstaat）自1926年起每年开展河床高程监测，1999年之前采用单波束测深仪（single beam echo sounder），1999年起改用多波束测深仪（multibeam echo sounder）。单波束测量在间距为25米的断面上进行，数据按1公里跨度进行平均；多波束测量覆盖整条河道，数据按100米跨度进行平均。所有河床高程数据均经过断面平均处理。河床高程数据的误差（定义为两倍标准差）估算结果如下：1990年之前可达0.2~0.5米，1990—1999年间为0.2~0.3米，1999年以来为0.05~0.1米（Wiegmann, 2002）。
沉积物粒度数据同样由荷兰水利总司（Rijkswaterstaat）采集，1984年之前使用挖斗式采样器，1984年起改用抓斗式采样器。本数据集涵盖1966、1976、1984、2008、2016、2017及2020年的实测数据。采样断面间距为500米至1公里，每个断面上采集3个间距为65米的样品。由于自然时空变异性较强且采样的时空密度有限，粒度数据的不确定性较高。