Series length: The series lenths differ from a couple of years upto over 100 years.
For example the data of river Rhein at station Rees cover a period from 1814 upto 1997. There's a gap from 1841 till 1854 and 1834 is missing.
The coordinates of all locations are available from:
http://www.hydraulicengineering.tudelft.nl/public/gelder/paper56-database-rivers.xls Owner of the data is the Global Runoff Data Centre (GRDC) in Koblenz (Germany). The data are available via the website of dr.ir. P.H.A.J.M. van Gelder on the above URLs.