raster hydrograph format data function

The format_data function is adding the index date columns to the flow_data in the example below, which I think is a little confusing for the user?

StaID = '04288000'
flow_data, md = dataretrieval.nwis.get_dv(site=StaID, parameterCd='00060', start="1900-01-01")
# format the data for raster hydrograph
df_formatted = hyswap.rasterhydrograph.format_data(flow_data, '00060_Mean', year_type="calendar", begin_year=1950, end_year=2000)