Site Investigation at Mosshouse Reservoir, Neath


Our investigation overcame logistical challenges and provided resolution on the nature of dam construction materials which was previously unknown. The Conceptual Ground Model we developed included the interface with the underlying natural geology in the lower portions of the dam slope, which was supported by rock outcrop inspection in nearby areas.


Detailed groundwater information (during and post fieldwork) allowed the client to make an informed assessment of the integrity of the dam and whether it was leaking. The piezometers also enabled groundwater monitoring for the longer term. Our brief included the following:

  • Review of reservoir structural and service plans to position investigation locations.
  • Revision of proposed client scope to accommodate site constraints and encountered ground & groundwater conditions.
  • Detailed Construction Phase Plan and Method Statements due to investigation on a grassed dam slope which was open to the public. This included installation of anchors at the dam slope crest.
  • Supervision of a focused ground investigation with a specialist slope climbing rig on the dam slope consisting of dynamic sampling to depths of 11m or where bedrock was proved.
  • Installation of piezometers to monitor groundwater levels and the likelihood of the suspected leak in accordance with relevant guidance (BS and EA).
  • Provision of detailed groundwater observations during investigation point construction and field groundwater level monitoring post completion.
  • Inspection of nearby rock outcrops.
  • Production of ground investigation report.

Pre-commencement planning and agreement enabled the investigation to be undertaken safely and careful positioning of investigation points avoided potential damage to the dam and its associated infrastructure.


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