Pressure on a bridge which was badly damaged by flood water last week was the equivalent of 500 cars a second using it, experts said yesterday.

Large chunks of stone were ripped off the Mercury Bridge at Richmond as heavy rains caused the river Swale to swell dramatically last week.

The bridge has been closed to both vehicles and pedestrians for more than a week and contractors are expected to move in within days to make it safe.

Yesterday, a North Yorkshire County Council report revealed that at the height of the flood more than 400 tonnes of water was passing through the bridge every second - the equivalent weight of more than 500 cars.

County environmental services director Mike Moore said the bridge, built in 1846, was now very unstable and workers would have to be brought in as quickly as possible to make it safe.

Discussions have been held with the Army over installing a temporary pedestrian bridge but this plan had to be dropped due to access difficulties and the length of bridge needed.

Work to repair the bridge is expected to cost about £500,000 and take up to six months to complete. A footbridge across the river could be up within four weeks and a free bus service is being provided for people to get to the swimming pool on the other side of the bridge.