Fail nicer with no data in dv
discharge_perc_10 <- readNWISdata(stateCd = "AL", parameterCd="00060", statCd = "01100")
Error in as.POSIXct.default(retval$dateTime, tzLib[tz = retval$tz_cd[1]]) :
do not know how to convert 'retval$dateTime' to class "POSIXct"
Similarly, figure out a way to pass asDateTime as an argument in readNWISdata