The Cardiff Bay Barrage has raised the mean water level in Cardiff Bay by 4.2 m. When the scheme was proposed, there were concerns that this rise in base level would cause a corresponding rise in shallow groundwater levels, impacting housing in south Cardiff. An extensive hydrogeological investigation and associated groundwater modelling were undertaken, resulting in published conclusions that the risk of impact was small, and within the range of engineering control measures. As part of the consent to proceed, an extensive water level monitoring system has been operated, and the effect on housing has also been monitored.

Now that the scheme is complete, it is possible to review the modelling work undertaken to predict the effects and to compare the predictions with measurements, thus validating the modelling work. Direct comparison of water levels is difficult, but cumulative frequency curves show that no unexpected adverse effects have occurred. The prediction that, with suitable engineering works, there would be no impact on housing, is substantiated.

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