THE CAUSES of flooding in Rhondda Cynon Taf (RCT) during Storm Bert last year have been confirmed.
The council has now published all five section 19 flood investigation reports relating to Storm Bert in November 2024 focusing on Aberaman, Pontypridd, Nantgarw, Porth, and Treherbert.
Storm Bert brought record-breaking rainfall and river levels across RCT on November 23-24 and an initial report highlighted that the flooding resulted in internal flooding to 438 properties and flooded rail and road networks, town centres, and business parks.
This report also set out the future programme of work including producing section 19 reports for five affected locations which were Cardiff Road in Aberaman, Pontypridd town centre, Oxford Street in Nantgarw, Britannia Street in Porth, and Abertonllwyd Street, Dunraven Street, and Hill Street in Treherbert.
Cardiff Road, Aberaman
Storm Bert resulted in 29 homes and a non-residential property being flooded internally here plus significant highway flooding.
The main cause was significant overland run-off generated from the steep hillsides above Aberaman, draining to lower ground via ordinary watercourses.
The report says many of these were overwhelmed with water and overtopped.
Surcharging of various combined sewers as well as the accumulation of local surface water were also found to have contributed.
The council has carried out 14 actions and proposes a further six in relation to the flooding that occurred while Welsh Water has proposed two future actions.
Pontypridd
The storm in Pontypridd resulted in internal flooding to 23 homes and 39 non-residential properties, significant highway flooding, and flooding to the National Lido of Wales.
The main sources of flooding were the River Taff exceeding its channel capacity as well as the surcharging of various combined sewers.
The River Rhondda was also a contributing source of flooding at Mill Street.
River level data from Natural Resources Wales’ monitoring stations at Pontypridd and Trehafod show that both rivers were almost four times their typical levels in Storm Bert.
This limited the combined sewer network’s ability to manage flows resulting in an overload that led to various drainage assets surcharging and causing flooding.
Water seeping into the foundations of homes and businesses, plus localised surface water accumulation, were also identified as flooding sources.
NRW has proposed six actions while Welsh Water has identified seven actions relating to sewer flooding and the council has identified seven further actions to manage local sources of flooding.
Oxford Street, Nantgarw
The storm saw flooding here to 18 homes and three non-residential properties plus significant highway flooding.
The main source was found to be the River Taff overtopping its banks at the location of a previously-removed service crossing.
NRW river level data from its Upper Boat monitoring station revealed the river was more than four times its typical level in Storm Bert (5.07m) – only 0.42m lower than its highest-ever recorded level.
Highway surface water accumulation also exacerbated the flooding caused by factors like river flows entering surface water drainage systems and the sheer intensity of rainfall.
NRW proposes four actions while the council has also put forward four actions to manage surface-water flooding.
Britannia Street in Porth
Storm Bert saw flooding to 24 homes here along with significant flooding to the highway.
The report says the primary source of flooding was the River Rhondda overtopping its southern riverbank at several locations.
Data from NRW’s Trehafod monitoring station showed the river level at more than three metres higher than its typical level (3.6m) – just 0.36m lower than the highest ever recorded.
Flows from a manhole associated with the ordinary watercourse at Coedcae Road contributed to main river flooding at Brook Street caused by obstructing debris.
Surface water accumulation on the highway exacerbated the situation caused by factors like main river flows entering surface water drainage systems and the sheer intensity of rainfall.
NRW has proposed three future actions while the council has proposed three actions for ordinary watercourses and surface water.
Abertonllwyd Street in Treherbert
The storm saw internal flooding to 37 homes and two non-residential properties here plus significant highway flooding.
The main source was overland run-off that was generated from the steep hillsides above Treherbert draining to lower ground via ordinary watercourses.
Many of these became overwhelmed and overtopped. Local accumulation of surface water was also a contributing flood source resulting from intense rainfall and overwhelmed infrastructure.
The council has carried out 14 actions and proposes a further six here.
The council is responsible for managing the risk from surface water, ordinary watercourses, and groundwater sources but main river flooding is the responsibility of Natural Resources Wales (NRW) and sewer flooding is managed by Dŵr Cymru Welsh Water.
