From the FGW▸ (First Great Western) website:
Friday 18th January
Heavy rain remains forecast today, and as a result flooding may occur later in the day. There is a risk that this could affect train services, especially later in the evening.
Didcot - Oxford. Water levels on the River Thames are rising rapidly, creating a high risk of flooding and disruption the line between Didcot and Oxford.
From: http://www.firstgreatwestern.co.uk/Content.aspx?id=2122
Hope they have some replacement buses on standby!!!!!!!