The report is focussed more on Cumbria than Lancashire -see the follow up questions at the end. However the tables in the report do demonstrate just how unusual the events of boxing day 2015 in Whalley both in the build up (rainfall in November / December) and on the day.
[Taken from the report]
17,500 flooded properties
Affected much of northern England
Some locations were flooded more than once
Record 24, 36, 48 hour UK rainfalls
New highest recorded flows in England (~1,700m3/s) on Eden, Lune, Tyne
Highest-ever recorded flows at many river gauging stations
Some locations had their highest floods in the historical record
[With thanks to Hydrology Research]
In December 2015, northern England experienced two major flooding events with extreme, even in some locations unprecedented, rainfalls and flooding. New 24-, 36-, and 48-hour UK rainfall records were created of 341.4, 401.4, and 405.2 mm, respectively. Three river-flow gauging stations, with flows of around 1,700 m3/s exceeded the previous peak flow record for England and Wales. There was widespread flooding, including major towns and cities, some of which had recent flood alleviation schemes. In Cumbria, the flood events in 2005, 2009 and 2015 compared with previous and historical events raise questions about the stationarity of the flood data and flood-producing mechanisms. These possible effects are less apparent elsewhere in northern England. This paper discusses whether present methods of estimating flood risk are able to cope with such extreme events and suggests topics for future research. In the meantime, for studies where flood estimates are important, practical hydrologists are faced with the difficult task of producing design flood estimates which fit with our understanding of these events.
For full report click here Dec 2015 Floding in the North of England hydrology report Peter_Spencer_v1
Table taken from the above report. Of the rivers mentioned the Calder had the second highest flow rate.