Further ground movements in 1975 led the city council to dig shafts at the former King Edwards school building on Havelock Road, and to drill boreholes into the remaining sections of the canal tunnel, to investigate the situation. The tunnel was entered via these shafts towards the Western end and pumped out. This allowed recording, measuring and photography before the tunnel was finally filled with flyash to prevent further ground movement. At this time the former Western tunnel portal was located beneath the then R J Mitchell museum to the North of Kinsbridge Lane. This area is today bounded by the multi storey car park, BBC site and Kingsbridge Lane pedestrian area. Early maps of this location show a water feature in the grounds of Kingsfield and later Kingsbridge House and the school on the site. This appears on both the 1846 street map of Southampton and the 25 inch Ordnance Survey map dated 1897. A line drawn between this and an earthwork feature shown on the 1846 map in what later became Palmerston Park approximates to the documented length of the canal tunnel of between 560 or 580 yards. This feature lay just to the North of "Canal View" on this map, but no other details of the canal are shown around the tunnel area.