The causes of flooding in Mountain Ash, Ferndale and Blaenllechau during Storm Dennis two years ago have been revealed. The latest and final section 19 reports into the events of February 2020 in RCT show the primary source of flooding in Mountain Ash was significant run-off from the steep hillsides overwhelming watercourses, which overflowed.
In total, 67 properties, including 44 residential and 23 non-residential buildings were internally flooded. Two culvert inlets were found to have provided “inadequate standards of protection” both when water was free flowing and when there was a blockage.
The remaining four culvert networks identified as sources of flooding were judged as having adequate standards of protection. Despite these culvert networks having sufficient capacity to manage the expected flows, the culvert infrastructure was seen to be in “poor condition” and its capacities reduced due to blockages caused by moving debris.
