Cardiff Bay barrage: management of groundwater issues

Abstract

The Cardiff Bay barrage, a 1·1 km long structure across the mouth of Cardiff Bay impounding a 200 ha freshwater lake, was central to the UK government's urban development programme to regenerate the docklands area of Cardiff. The Cardiff Bay Barrage Act 1993 included a groundwater protection scheme for buildings, providing owner/occupiers with recourse to remedial works or compensation should circumstances prove that construction of the barrage caused or probably caused groundwater damage. To allow a comparison of pre- and post-impoundment groundwater levels underlying south Cardiff, a groundwater monitoring system comprising 236 automated data loggers covering an urban area of 15 km2 was established between 1995 and 1999. To mitigate the possibility of a rise in groundwater levels in certain identified areas, various types of groundwater control systems were installed prior to impoundment in November 1999. Management (including collection and interpretation of data) and maintenance of such an extensive system have required great effort, resourcefulness and logistics. This paper presents a brief history of the scheme and an overview of the management of such a diverse and challenging groundwater project.

Establishing an urban geo-observatory to support sustainable development of shallow subsurface heat recovery and storage

“…Red mudstones of the Triassic aged Mercia Mudstone Group bedrock form a low permeability base to the aquifer (Edwards 1997;Heathcote et al 2003). Post impoundment of the barrage, changes in groundwater levels between 2.5 -3.5 m were measured in the sand and gravel aquifer but were limited to the fringes of Cardiff Bay (Williams 2008). Pumping tests show that the hydraulic conductivity of the sand and gravel aquifer is relatively consistent, with average values of 50 m/d (Heathcote et al 2003) with groundwater levels 3-4 m below the surface.…”

“…Due to the possibility of rising groundwater levels impacting underground structures such as basements, the 'Cardiff Bay Barrage Act, 1993' required groundwater monitoring to be undertaken for a period of 20 years following the closure of the barrage. In response, 236 monitoring boreholes, many of which can be seen in Figure 1, and six dewatering schemes were installed to monitor and manage groundwater levels (Edwards 1997;Heathcote et al 1997;Sutton et al 2004& Williams 2008. The majority of the boreholes monitor groundwater in the glaciofluvial sand and gravel aquifer.…”

“…Edwards (1997) defined the Tidal Flat Deposits to be of low to intermediate permeability overlying the sand and gravel aquifer, generally confining the sand and gravel aquifer in the south of the city centre. However in some localised areas the Tidal Flat Deposits are absent resulting in hydrogeological connections between the sand and gravel and the made ground aquifers (Williams 2008). Groundwater in the sand and gravel aquifer generally flows towards the rivers and the coast (Edwards 1997).…”

Effect of anthropogenic heat sources in the shallow subsurface at city-scale

“…A hydraulic head distribution was provided through a detailed hydraulic model produced by BGS, shown in Figure 3. In several regions of the city the groundwater levels are artificially controlled to mitigate the rise in groundwater levels in particular areas with a large number of basements [8]. The difference in hydraulic head within the region is small, giving a shallow hydraulic head gradient of approximately 1.6 × 10 -3 .…”

Groundwater heat pump feasibility in shallow urban aquifers: Experience from Cardiff, UK

“…Locally, the Glaciofluvial deposits are up to 30 m thick in buried valleys under the modern drainage channels (Anderson and Blundell, 1965) and these sediments typically comprise highly-permeable sands and gravels, making them a target for open loop GSHP systems and Aquifer Thermal Energy Storage (ATES). Groundwater levels in the sand and gravel aquifer have been monitored and managed since 1999 by Cardiff Harbour Authority (CHA) in response to the impoundment of Cardiff Bay by a coastal barrage (Edwards, 1997;Heathcote et al, 1997;Heathcote et al, 2003;Williams, 2008). As a result, groundwater levels have stabilised to around 3-4 m below surface across the southern part of the city (Farr et al, 2017).…”