I came across this interesting data source, and though I might as well share it.
Description: A global database of the the width of the large rivers (GWD-LR). The river width is derived from “satellite-based water masks and flow direction maps … by applying the algorithm to the SRTM Water Body Database (WBD) and the HydroSHEDS flow direction map. Both bank-to-bank river width and effective river width excluding islands are calculated for river channels between 60S and 60N”. The results are evaluated against the existing data on the river width of the Congo and Mississippi Rivers.
The data is described in detail on the website and in Yamazaki, D., O’Loughlin, F., Trigg, M.A., Miller, Z.F., Pavelsky, T.M., & Bates, P.D. 2014. Development of the Global Width Database for Large Rivers. Water Resources Research 50: 3467–3480 [link]
Data: The data is available as ESRI ‘BIL/BSQ/FLT’ raster format with the HDR file at various resolutions (the original resolution is 3 arc seconds). The data is free (it is not immediate apparent if there are any user-restrictions), but to download the data you’ll have to send an email to the developer of the data set.
Presentation: The web page may not be the most glossy around, but it provides all the information needed. This does include a document detailing the methods and software code used to create the data set.
Bottom line: A very specialistic data set, with what seems to be a clear aim at the scientific community. I don’t think there are many other similar data sets. So if you need information about the width of the (major) rivers in your area of interest, this definitely is something you will need to check out.
As a side thought… How useful would OpenStreetmap be to determine river width? It does seem to provide very accurate depictions of the rivers in my home country (admittedly one of the better covered countries), but perhaps is is not consistent enough yet to be useful at a global level?