Flood Risk Assessment Swansea

Flood Risk Assessment Services in Swansea

Swansea’s position on the Bristol Channel coast, at the mouth of the River Tawe and surrounded by steep valley topography, creates a distinctive and challenging flood risk environment. The city faces the full spectrum of flood risks, from coastal storm surges to fluvial flooding and intense surface water events in its valleys and hillside communities. Wales’s distinct regulatory framework, governed by TAN15 and Natural Resources Wales, requires specialist knowledge that sets Welsh flood risk work apart from practice in England and Scotland.

Aegaea provides specialist flood risk assessment, hydraulic modelling, and drainage consultancy services across Swansea and the wider Swansea Bay area. Our team has detailed knowledge of TAN15 requirements, NRW’s consultation expectations, and the mandatory SAB process for SuDS approval that applies across Wales.

Swansea’s Flood Risk Landscape

Coastal and Tidal Flood Risk

Swansea Bay forms a sweeping arc from the Mumbles Peninsula in the west to Port Talbot in the east, and the city’s waterfront areas are its most valuable development land. The Bristol Channel has the second highest tidal range in the world, and this extreme tidal influence amplifies the impact of storm surges on coastal flood levels.

The December 2013 tidal surge event caused significant flooding along the South Wales coast, including damage to Swansea’s promenade and seafront properties. The event coincided with a high spring tide and generated water levels that tested coastal defences along Swansea Bay. More recently, Storm Dennis in February 2020 brought combined tidal and fluvial conditions that caused flooding in the Tawe valley and coastal areas.

The SA1 Swansea Waterfront development, one of Wales’s largest waterfront regeneration projects, occupies the former docks area east of the city centre. The site’s low-lying position and proximity to both the sea and the River Tawe means that comprehensive coastal and fluvial flood risk assessment was required for the development framework. Individual development plots within SA1 continue to require site-specific FCAs addressing tidal flood risk, finished floor levels, and flood resilience.

The Maritime Quarter, adjacent to the SA1 area, and the Strand/Wind Street area near the river mouth also face coastal and tidal flood risk. These areas have seen significant commercial and residential development, and flood risk has been a defining constraint for building design and site layout.

Swansea Bay Tidal Lagoon proposals (though not currently progressing) highlighted the scale of tidal influence in this location and prompted detailed coastal flood risk analysis for the bay area. Regardless of whether the lagoon proceeds, the understanding of tidal processes and flood risk generated by the project has informed subsequent development proposals along the waterfront.

The River Tawe

The River Tawe flows southward through the Swansea Valley from its source in the Brecon Beacons, passing through Pontardawe, Clydach, and Morriston before entering the city and discharging to Swansea Bay. The Tawe catchment covers approximately 240 square kilometres, with steep upper reaches that generate rapid runoff during heavy rainfall.

The lower Tawe passes through significant development areas, including the Hafod, Morfa, and the SA1 Waterfront. The river’s tidal reach extends inland to the barrage at the Tawe locks, and combined fluvial-tidal analysis is required for development near the river in this zone. Upstream of the tidal reach, the Tawe has experienced significant flood events, including the February 2020 Storm Dennis floods that caused damage in the Swansea Valley.

The Lower Swansea Valley, once one of the most heavily industrialised areas in Wales, has undergone extensive regeneration over several decades. The area’s industrial legacy means that flood risk and contaminated land issues frequently overlap, requiring integrated assessment. Development proposals in the lower Tawe corridor must address both current flood risk and the potential for climate change to increase both river flows and tidal levels.

The Clyne Valley and Smaller Watercourses

The Clyne River flows through the western suburbs of Swansea, passing through Killay, Upper Killay, and Blackpill before reaching Swansea Bay. The Clyne Valley Country Park provides some natural floodplain storage, but development adjacent to the river requires flood risk assessment, particularly where the floodplain narrows.

Numerous smaller watercourses flow through Swansea’s valleys, including the Llan, the Nant-y-Fendrod, and the Burlais Brook. These watercourses respond rapidly to rainfall due to the steep topography, and historic flooding events have affected communities in Cwmbwrla, Penlan, and Bonymaen. SEPA equivalent NRW flood maps identify significant risk areas along these watercourses.

Ordinary watercourses, which fall under Swansea Council’s jurisdiction rather than NRW’s, are also significant. Many of these smaller watercourses have been culverted through residential areas, and the limited capacity of these culverts creates a risk of surcharging and surface water flooding during extreme events.

Surface Water Flooding

Swansea’s steep topography and high rainfall make surface water flooding a particular concern. The city receives significantly more rainfall than eastern parts of the UK, and intense convective storms can generate rapid surface water runoff that overwhelms drainage systems.

NRW’s surface water flood maps show extensive areas at risk across Swansea, particularly in the valley bottoms and low-lying coastal areas. The city centre, Uplands, Brynmill, and Mount Pleasant areas have all experienced surface water flooding, and the limited capacity of the drainage network in these older urban areas exacerbates the problem.

Climate change projections suggest that rainfall intensity will increase, further increasing surface water flood risk. Development proposals must demonstrate that surface water runoff from the site will be managed to avoid increasing risk elsewhere, and the mandatory SAB process ensures that SuDS are designed to a consistent national standard.

Welsh Regulatory Framework

TAN15 and Flood Consequences Assessment

TAN15 provides the policy framework for managing flood risk through the planning system in Wales. The updated TAN15, which came into effect in June 2023, introduced a more rigorous approach to development in flood risk areas, including specific tolerability criteria that must be met for development to proceed.

Under TAN15, development proposals within flood risk zones identified on NRW’s Flood Map for Planning must be accompanied by a Flood Consequences Assessment. The FCA must demonstrate that the consequences of flooding are tolerable for the development’s intended use, with specific criteria for flood depth, velocity, rate of onset, and duration. The tolerability criteria vary depending on the vulnerability classification of the proposed development.

For Swansea developments, TAN15 is particularly relevant for coastal development along Swansea Bay and the SA1 area, riverside development along the Tawe corridor, and development in areas identified at surface water flood risk. The updated TAN15 takes a more precautionary approach than its predecessor, and developers should engage early with both NRW and Swansea Council to understand the requirements for their specific site.

Natural Resources Wales

NRW is the statutory body responsible for flood risk management from main rivers and the sea in Wales. NRW maintains the flood risk maps that underpin TAN15, provides flood warnings, manages main river flood defences, and acts as a statutory consultee on planning applications with flood risk implications.

NRW’s consultation responses on Swansea planning applications are a critical input to the decision-making process. Where NRW objects on flood risk grounds, Swansea Council will typically refuse the application unless the objection can be resolved. Aegaea works proactively with NRW to address flood risk concerns before they become formal objections, saving time and cost for clients.

SuDS Approval Body (SAB)

Wales’s mandatory SAB process, unique in the UK, requires all qualifying developments to obtain separate drainage consent before construction can begin. Swansea Council administers the SAB process and assesses drainage designs against the national standards for SuDS in Wales.

The national standards set requirements across six areas: runoff destination (hierarchy of infiltration, watercourse, surface water sewer, combined sewer), hydraulic control (runoff rates and volumes), water quality (treatment standards based on hazard level), amenity (contribution to the built environment), biodiversity (ecological benefit from SuDS features), and construction (buildability and phasing).

The SAB process adds complexity and cost to Swansea developments, but it also drives better drainage outcomes. Aegaea supports clients through both the TAN15 planning process and the SAB approval process, ensuring that drainage strategies are designed to satisfy both requirements efficiently.

Key Development Areas in Swansea

SA1 Swansea Waterfront

The SA1 development area continues to evolve, with new residential, commercial, and educational buildings being delivered on the former docks land. Each development plot requires site-specific FCA addressing coastal flood risk, Tawe fluvial risk, and surface water management. The mandatory SAB process applies to all qualifying developments within SA1.

Swansea Central and the Copr Bay Phase 2

The Swansea Central regeneration area, including the Copr Bay development with its arena and public realm, represents the most significant city centre investment in a generation. Flood risk from the Tawe, coastal influence, and surface water has been a key consideration throughout the masterplanning process. Future phases of development around the Strand and Oystermouth Road corridor will require continued flood risk assessment.

University of Wales Trinity Saint David Campus

The Waterfront Campus on the SA1 site required comprehensive flood risk assessment given its coastal and riverside location. Continued expansion of the campus generates ongoing demand for flood risk and drainage consultancy, and the educational vulnerability classification of the development influences the TAN15 tolerability requirements.

Llansamlet and Enterprise Zone

The Swansea Vale and Llansamlet areas, including the Enterprise Zone, have experienced significant commercial and industrial development. The area’s position in the lower Tawe Valley means that fluvial and surface water flood risk must be assessed for development proposals. The interaction between the Tawe, its tributaries, and the surrounding hillside drainage adds complexity to flood risk assessments in this area.

Aegaea’s Swansea Services

Aegaea provides comprehensive flood risk and drainage services across Swansea, including Flood Consequences Assessments under TAN15, hydraulic modelling of the Tawe and coastal processes, SuDS design and SAB approval applications, NRW pre-application consultation support, drainage strategies meeting both planning and SAB requirements, and combined flood risk and contaminated land assessment for brownfield sites.

Our understanding of the Welsh regulatory framework, TAN15 requirements, and the SAB process ensures that Swansea clients receive integrated flood risk and drainage advice that supports both planning and construction approvals. We work with developers, architects, and planning consultants across Swansea and South West Wales.

Contact Aegaea

If you are planning a development in Swansea and need a Flood Consequences Assessment, drainage strategy, or SuDS design, contact Aegaea. We can advise on TAN15 requirements, SAB approval, and the likely scope of work for your site, helping you navigate Swansea’s flood risk requirements from the earliest stages.