Copied from the national rail website:

Flooding between Swindon and Bristol Parkway

Time Reported: 05:48
Route Affected: London Paddington – Reading – Didcot Parkway - Swindon – Bristol Parkway - Cardiff Central / Swansea
TOC/s Affected: First Great Western
Description: Train services between Swindon and Bristol Parkway are being disrupted due to flooding.

Train services between London Paddington and Swansea will be diverted and will no longer call at Bristol Parkway. Services will call additionally at Patchway. Road replacement transport will operate between Patchway and Bristol Parkway. This will add up to 20 minutes to journey times.

All London Paddington to Cardiff Central services in both directions are suspended. Customers should use First Great Western services between London Paddington and Swansea.

There is currently no estimate for a normal train service to resume

Also the A429 road is blocked due to flooding where it passes under the railway at Kingsway bridge