Following the ‘near-miss’ in March, when Dwr Cymru Welsh Water and Bannau Brycheiniog National Park staff failed to inform cave users of a planned water release, both organisations have – with SWOAPG support – reviewed their procedures to ensure that this can’t happen again. They will now:
- provide at least a month’s notice of a scheduled release (which we will pass on to our Members – along with a reminder the day before);
- erect warning signs at Porth yr Ogof a week beforehand;
- aim to conduct their tests early in the morning so that the impact on cave and river users is minimised;
- have staff onsite at the cave to monitor the effects; and
- continue to liaise with SWOAPG to monitor and minimise the impact on users.
BBNPA has also considered ‘closing’ the cave on days when releases are scheduled, although we have advised them against this, since the river is likely to have returned to normal levels in times for groups to still use the cave that day. Nevertheless, any providers intending to use the cave on scheduled release days should of course conduct their own risk assessment on arrival.
The background to these releases is that DCWW is required to periodically test the mechanism for draining the reservoir in emergencies, which means fully opening and then closing the ‘scour valve’. This takes around 3 hours (with a 2-hour delay between opening the valve and water reaching the cave) and at peak flow releases 5cumecs into the river – which has a significant effect at the cave, but likely a much lesser impact in the gorge.
The next scheduled release is on Thu 22 Oct and is expected to be complete by 12pm; the full announcement from DCWW follows below:
“This notification is intended for all individuals involved with, or planning to access, the Porth Yr Ogof Cave system located south of Ystradfellte Reservoir.
“As part of our routine six-monthly reservoir safety testing programme, we will be undertaking a controlled release of water from Ystradfellte Reservoir. This operation may affect water levels entering the cave system and could result in a rapid increase in water levels within the caves.
“The operation is scheduled to commence at 06:00 on Thursday, 22 October 2026. The process of fully opening and subsequently closing the valve is expected to take approximately three hours. This early start time has been selected to minimise disruption to any planned group visits or activities within the cave system.
“The released flow is expected to take approximately two hours to reach the caves. Based on current assessments, river levels at the main cave entrance should return to normal by 1200 at the latest.
“During the operation, personnel will be positioned at key locations, including the reservoir valve, the cave entrance, and, subject to availability, the upstream road bridge, to monitor conditions and support the safe execution of the test.
“One week prior to the release, warning notices will be installed at several locations, including the car park entrance and access paths leading to the cave entrances, to provide advance notification of the planned activity.”