CITY OF CARDIFF, CARDIFF BAY BARRAGE PROJECT

The Cardiff Bay Barrage Scheme involved the construction of a tidal barrage across the mouth of the Rivers Taff-Ely estuary. A freshwater lake was created on the landward side of the barrage from the impounded waters from the rivers. The scheme has lead to the redevelopment of the waterfront of Cardiff creating new businesses, housing and leisure facilities.

The pre-construction groundwater modelling studies identified that impoundment of the Bay could have a potential impact on the groundwater levels underlying South Cardiff City. A monitoring system was established in 1995 to measure groundwater levels both pre- and post-impoundment of the Bay. The system has expanded over the years and currently comprises Hydrokit groundwater level monitoring instrumentation installed in some 230 boreholes distributed over 15km2, each recording groundwater levels at intervals of 30 minutes. Other environmental parameters comprising rainfall, atmospheric pressure, tide and river levels are also recorded. These statistics make the Cardiff Bay Groundwater Monitoring system one of the largest single systems of its kind.

The County Councils Drainage Services, retained under a Service Level Agreement by the Harbour Authority, have responsibility for the downloading, verification and storage of the data from the electronic loggers, and the general maintenance of the groundwater monitoring system.

All loggers are normally visited routinely once a month to download data and to inspect the condition of the storage chambers. Monthly reports to the Harbour Authority identify the operational status of the monitoring system and actions undertaken to deal with any instrument “failures.” The aim is to evaluate instrument performance and enable any problems or malfunctions to be investigated and rectified as quickly as possible.
Full recovery of reliable data from individual instruments is not generally achieved for a variety of reasons. The main reasons for incomplete recovery relates mainly to specific instruments that are either removed for safekeeping during nearby construction works or damage to the sensitive electronic equipment caused by ingress of rainwater into the chamber. A target of 95% minimum data recovery for each downloading visit has been established.

All field recordings are transferred to a Database that stores the data in digital format. The 'database' has been developed within the Oracle Database software package. All graphical presentations of the data are produced from the data stored in the database. The amount of digital data transferred to the database is about 0.5 gigabytes every year, possibly making the Cardiff Bay Groundwater Monitoring database one of the largest databases of its kind. The collected monitoring data is summarised in reports produced on a 6 monthly basis. An independent expert reviews these reports. Once reviewed, the comments are reported to the Harbour Authority. The reports & comments are then made available to the public.