I have located an article that appeared in the Bristol Mercury & Daily Post on February 14th 1899. It does not specifically refer to any damge to the bridge but mentions the flooding and rail services.

'Severn Valley Floods. Though the Great Western Railway main line between Lydney and Woolaston has been submerged as recently as two years ago and on other more remote occasions, the effect of the flood has been more or less harmless, at any rate nothing approaching the damage and inconvenience occasioned by the storm on Sunday. The tide in the morning swept across the railway for a distance of about a mile and quarter from a point a quarter of a mile below water. By mid-day the tide had sufficiently gone down for traffic on the down line to be resumed. The remarkable part of the affair is the fact that the down line, which the tide first met, was not much disturbed, but the up line for the distance of a mile is simply lifted, sleepers and rails together, and thrown 12 or 14 feet. The ballast seems to have gone along with it in a concrete mass, and the lines of rails present a peculiar appearance. The tide on Sunday night was scarcely so heavy, and that on Monday morning still less, owing in some degree, to the slackening down of the gale. Passenger traffic between London and South Wales was diverted through the Severn Tunnel again on Monday as on the previous day. Fortunately one passenger train each way was run through on Monday morning before the tide was in, but at 10.30 the rails were three feet under water.'

I hope this is of some interest