USACE’s Pittsburgh District said it was concerned that inspection by divers revealed the scour risk to the dam at the navigation facility near Clinton, Pennsylvania. While some scour was expected to be found by the divers it was the extent of the erosion that surprised USACE.

Procurement preparations are underway to have a permanent solution to the problem in place before winter. Until the works are completed USACE has instigated a programme of round-the-clock monitoring by staff, hourly gauge checks, and co-ordination with local emergency and water management services.

Following the discovery, USACE has launched scour surveys of the other seven Allgheny River navigation dams using remotely operated vehicles (ROVs).

While stressing the risk for stability at No6 should there be a barge impact or problems from lateral ice load during the winter, the dam remains operational. There is also a small hydro power plant at the dam.

USACE said there was ‘no immediate threat to public safety’ but noted the long-term commercial and recreational consequences for the region as well as potential severe damage to the power plant should the dam fail. In addition, water quality problems would be caused for water supply and sewage treatment services.

The water pool would be lost until the dam was replaced or repaired, USACE said. It added that a large wetland would also dry up.

‘We are very concerned that ice collecting on the dam or large chunks of ice slamming into the dam may cause it to fail,’ said Colonel Michael Crall, an engineer in Pittsburgh District.

Separate to the extensive scour discovery at No6, a recent assessment by USACE has highlighted that all eight navigation dams on the Allgheny River, and also those on the Ohio and Monongahela rivers, require critical repairs.