When downloading in bulk from AWS S3, the data comes in the form of netCDF files. There are 3 primary netCDF variables you will need to query. The "rivid" variable is a 1 dimensional array of all the ID numbers of the rivers contained in that file. The "time" variable is a 1 dimensional array of the time stamps of the discharge data in that file, usually in units of  number of days since 1 January of the start of the decade. The "Qout" variable is a 2 dimensional array with 1 column per river and 1 row per time step. Typically, users want to select all timesteps (all rows, axis 1) for a specific river (1 column, axis 2). We recommend Python and the Xarray package for writting scripts to query this data. 

NetCDFs containing retrospective discharge simulation data are structured according to the Climate and Forecast Conventions. The NetCDFs include average river water discharge downstream of each river reach labeled as "Qout" and are ordered by the unique identifier for each river reach, the "rivid" variable. Each "rivid" has a corresponding latitude and longitude for a point related to individual river reaches.