The Winster goes nowhere near Arnside, which is on the other side of the Kent estuary.
Difficult to see how it can be solved without dropping the deliberately raised water table in the Foulshaw and Meathop Mosses, which are both nature reserves. There has been a deliberate attempt to return them to marshland over the last 15 or so years. If you add that to continued complaints over years about the inability of the authorities to make the Winster valley drainage work and you've got a lot of water with nowhere to go.
Just found this 2018 document (8 page pdf) which overviews the drainage in the area, the flood risk, and the history.
It explains how the Winster and associated waterways are protected and linked, and how they relate to the railway embankment
(Unfortunately it won't let me copy the text so I can't post a preview)