Volume Ten - Pre-Victorian to the Present Day - Even more aspects - Investigation into the Condition of the Ely River Subway 1991 . . .

The Subway was successfully dewatered by 13th April 1991. Prior to undertaking the survey, air quality within the structure was checked and temporary lighting was installed throughout its length.  The air quality within the Subway was continually monitored throughout the operations with the following values being obtained: oxygen 18.7%; toxic gases 2 parts per million.  No flammable gas content was detected. These values remained constant for the duration of the works.

Methodology :

Prior to the survey, record drawings held in the archives by Associated British Ports were examined.

The survey consisted of a detailed inspection and dimensional survey of the entire remaining length of the tunnel and remaining toll house, supplemented by photographic records, with all information that could be recorded with the naked eye noted.

At the start of the survey each cast iron ring was assigned a number. A sequential numbering system was adopted, starting at the northern portal with Ring One.  Each ring was inspected in turn and the condition noted. In addition, service pipes and ducts were located and their status and position noted with particular attention paid to the location and degree of water ingress over the duration of the survey.

Electro-magnetic equipment was attached to the demolished end of the Subway and signals transmitted to enable the position of the last remaining ring on the Penarth Dock side to be located. The position of maximum response was located and marked with a road nail.

At the conclusion of the survey a video record of the inside of the Subway was made, though insufficient lighting resulted in much detail being lost.

The detailed account of the findings are presented in the following section.