Why is the QMED different in WINFAP to that reported by the NRFA (where AMAX are present on 1st October)?

Time stamps are not reported in the files that WINFAP uses to assign Hydrometric Years to a given AMAX value. The Hydrometric Year starts on the 1st October, and values are assigned to a day based on a start time of 9am. WINFAP will assign a value based on the date only thus a value that occurs prior to 9am on the 1st October, will be assigned to the wrong Hydrometric Year. As you cannot have more than one value per Hydrometric Year the next value is rejected.

For a small number of stations this can make a difference to the QMED value.

The NRFA, which has access to the time stamp information, presents the QMED on the station web page in the ‘Peak flow data’ tab. The NRFA has access to the time stamps and utilises this as part of the calculation process thus presents the correct value of QMED.

This will be amended within a future release of WINFAP.