Spring". Walker was entrusted by Hawkshaw to proceed with efforts to rescue and then complete the tunnel following the 1879 flooding. To achieve this required holding the Great Spring in check, which in turn was accomplished via the installation of greatly-increased pumping facilities, while a diver also had to be sent down a shaft and along the tunnel heading to close a watertight door in the workings, sealing off the waters. During November 1880, this troublesome task was finally achieved by the lead diver, Alexander Lambert, who was equipped with Henry Fleuss' newly developed self-contained breathing apparatus (SCBA); however, work in the area of the Great Spring was unable to continue until January 1881, at which point the Great Spring was temporarily sealed off. On 26 September 1881, the two headings met, marking a key milestone in the tunnel's construction, efforts transferred to addressing the tunnel's final structure along with the long deep cuttings at either end. During October 1883, work was again disrupted by further flooding originating from the Great Spring, which was further compounded by the appearance of a spring tide only a week later; again, Lambert and other divers managed to save the day and seal the works. It was recognised that water ingress problems were to continue, thus a heading was driven at a gradient of 1 in 500 from the original Sudbrook shaft, continuing until it reached the fissure through which the Great Spring flowed. By diverting the water into the new heading, the walled-in section of the tunnel could be more easily drained and finished. There were additional mishaps which afflicted the construction site; at one point, there was an unintentional breakthrough of the bed of a pool, known as the "Salmon Pool", on the English side of the tunnel. It had been originally assumed that the continuous brickwork lining of the tunnel would withstand the groundwater pressure, thus the drainage sluice valve on the side heading was closed and all but one of the pumps were taken from the site. However, on 20 December 1885, the pressure rose so high (up to 395 kN per sq m) that a number of bricks were discovered to have been pushed out of the lining. To address this, the sluice valve was opened gradually, allowing the pressure to subside but necessitating the long-term operation of additional pumping engines. In the intervening period, the Severn Railway Bridge,