The chief Contractor for the building of the Severn Tunnel, Thomas Walker noted in the 1870s*...

The sea-wall which protected the meadows south­west of the camp has been entirely destroyed for a distance of many miles, and the wasting of the land still continues.
In consequence of the destruction of the sea-wall, the equinoctial spring-tides flow over a vast extent of meadow-land; and on one occasion, as we shall afterwards have to relate, the water passed over the whole of the meadows to a depth of more than 5 feet.

The Roman road from the camp continues its course till it intersects the main road at the hamlet of Crick, about 1 mile to the west of which is the present village of Caerwent, once the famous Roman station, ' Venta Silurum.' The Roman walls remain in fair preservation, and it is believed that when this station was held by the Roman Legions, the tide from the Severn flowed up to the base of the southern wall, and that the rings to which the boats were moored still remain.
Where these tides flowed is now a rough piece of marsh land, through which the little river Neddern passes to join the Severn.
The whole of the ground in the marsh is rotten, and before the tunnel was commenced there were enormous springs of bright clear water rising up in several places.

He also reports on a storm surge which combined with a high tide to flood the meadows around Portskewett...

At 7 p.m. on the 17th October, the night-shift,consisting of about 90 men, had descended the Marsh Pit, to proceed with their work...

A perfect storm of wind was blowing at the time from the south-west, and it was known that one of the highest tides of the year would occur that night, but no tide had ever been known to come so high as the works at [Marsh Shaft: around the area of the rail junction at "The Pill" industrial estate]...

Suddenly, in the darkness, a great tidal-wave burst over the whole of the low-lying ground between the shaft and the river. It must have come on as a solid wall of water, 5 or 6 feet high. It entered all the houses, most of which were only of one storey, and rose above the beds on which the children were asleep, The children were saved by being placed upon high tables, or even on shelves...

The tidal-wave, passing beyond the houses, reached first the boilers that worked the winding and pumping engines at the shaft, extinguishing the fires, and then flowed down the pit with a fall of 100 feet. There was a ladder-way from the top to the bottom of the shaft, and by it, when the first force of the water had passed, one or two men who were in the bottom managed to make their escape ; one unfortunate man, after climbing the ladder for about half the height, was thrown back by the force of the water and killed...

The tidal wave had not only drowned the Marsh Pit, but had come up with sufficient force to flow in considerable quantity over the sea-wall on the Gloucestershire side of the river, and the meadows around the shaft were, on the morning of the 18th, covered with water, which stood 8 inches over the rails of the tramway.
To the westward of the Marsh Pit the same tidal wave had flooded the whole of the meadows, and the sea bank round the cutting at the western end of the tunnel not being completed, the cutting was full of water...

The height of the tidal wave was found to be 10 feet above the calculated height for the tide on that night. Large quantities of timber, which had been stacked at the Marsh Pit, were floated away to some distance, and one large larch-tree, 15 inches in diameter, was landed upon the top of the post-and-rail fence east of the Marsh Pit; the fence being 4 feet 6 inches above the level of the meadows.