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Cwmaman Flood Alleviation Scheme


Rhondda Cynon Taf County Borough Council (RCT) as the Lead Local Flood Authority (LLFA) will be commencing a land drainage improvement scheme on the 24th July in the Cwmaman Area. The proposed scheme will be part of a Upper catchment management plan which aims to alleviate flood risk to 37 residential properties and 3 critical infrastructure sites.

The LLFA is acting in accordance with its Local Flood Risk Management Strategy (LFRMS) high level objective to ‘Reduce the Consequences of Flood Risk.’ The strategy was published in January 2013 in accordance with Clause 10 of the Flood and Water Management Act 2010. The LFRMS objective aligns with the four overreaching national objectives set out within the National Strategy for Flood and Coastal Erosion Risk Management Wales.

The area in which the works are proposed is Cwmaman, which is within the Aberaman South Electoral Ward which is identified as being the 4th highest risk ward within RCT's Flood Risk Management Plan (FRMP); The FRMP results shows a strong correlation between the observed flooding from the 1980's and the flood maps produced by Natural Resources Wales (NRW).

Description of Works

The catchment of the Nant Aman Fawr has been subject to a hydrological investigation to gain a greater strategic understanding of the flood risk at a wider catchment scale. The investigation formed part of the delivery of measure 30 assigned to Location RCT0007 within the FRMP. This has initially identified an opportunity to reduce peak flows; through modifying the existing upper silt trap pond and outlet structure already in the ownership of the Council. The works proposed will involve the redesign of the existing weir to provide storm water attenuation within the upper catchment area. The outlet structure will comprise of a large diameter culvert/pipe and an overflow weir. The embankments around the existing silt trap pond are to be modified to enable greater attenuation of storm water during heavy periods of rainfall. The works will also aim to reduce the height of the existing blockstone banks within the existing silt trap pond; creating a shelf that will encourage ecosystem/wetland improvements for both terrestrial and aquatic fauna.

The primary aim of the initial proposed works is to reduce the peak storm flows of water from the catchment thus reducing the risk of flooding within the Glanaman Road area of Cwmaman by reducing the risk of overloading the urban drainage systems.

These initial proposed works will aim to reduce the peak flow within the upper catchment by almost 6.4% during a 1 in 30 year storm event (3.3% chance of occurring) and a 1.2% reduction during 1 in 100 year storm event (1% chance of occurring). Please note that the storm events described refers to the likelihood of the magnitude of a storm event happening each year rather than a time period; further information on this topic can be found within the FRMP.

In undertaking these works the scheme will aim to deliver on the following objectives within Council’s LFRMS.


Reduce distress by decreasing the population exposed to flood risk.


Reduce community disruption by reducing the amount of residential and commercial property exposed to flood risk.


Reduce risk to life by reducing the number of people exposed to risk of flooding of significant depth and velocity.


Reduce disruption to critical infrastructure or support the preparation of plans to allow their operation to be maintained.


Improve or not detrimentally affect water quality


Where possible, improve naturalness - reducing modifications to channels, water bodies and, where appropriate, create or enhance natural floodplain storage linked to nature conservation and landscape initiatives.


Ensure projects are designed and constructed in a sustainable way.


Maintain, or where possible, improve the status of Special Areas of Conservation (SACs), Sites of Special Scientific Interest (SSSIs), Sites of Importance for Nature and Conservation (SINC) sites and contribute to the RCT biodiversity action plan.


Develop a better understanding of the risks of flooding from surface runoff, groundwater and ordinary watercourses and plan how best to communicate and share information with communities and businesses on all forms of flooding.

Also undertaking these works the scheme aims to deliver multiple benefits as per the ‘Wales Future Generations Act Wales’.

  • A More Prosperous Wales – This work will help keep a community route open and provide resilience to the residents of Glanaman road in alleviating the risk of flooding (Climate change).
  •  A Resilient Wales – The proposed works will have no adverse affect on the bio diverse natural environment and will enhance the areas ability to adapt to change. It will give us greater capacity to manage water flows resulting from climate change.
  • A More Equal Wales – This work will be to the benefit of all parts of society, all will be allowed to fulfil their potential by improving access to and from the area.
  • A Wales of More Cohesive Communities – As an organisation the safety of our communities is paramount and this work will also significantly reduce risk.

Completion of Consultation on Notice of Intention to Start Land Drainage Improvement Works

This proposed flood risk alleviation scheme is deemed permitted development under Part 14 (Development by Drainage Bodies) of the Town & Country Planning (General Permitted Development) Order 1995.  As such the council has completed a consultation process under The Environmental Impact Assessment (Land Drainage Improvement Works) Regulations 1999 and 2006.

Following the consultation there were no evidenced representations in relation to the likely significant effects on the environment of the proposed improvement works; therefore the works will now proceed.

Project Commencement

The advanced Ecology works have now been completed; with the main phase of construction to begin on the 24th July. Construction will take place within the works area located on the Nant Aman Fawr, 0.5km away from the nearest residential area.