Page:Walker (1888) The Severn Tunnel.djvu/268

Rh river. The one at the south side is 15 feet diameter; and the one at Sudbrook, which is at the north side, is 18 feet diameter.

The ventilating fan, which is at the north side of the river, is 40 feet diameter and 12 feet wide. It can be worked at a velocity of 60 revolutions per minute: less than half this speed is estimated to be sufficient to ventilate the tunnel.

I enclose herewith a statement of the several pumping shafts, and of the pumps that work through them to drain the tunnel, which, in addition to the water from the cutting at each side, and some very slight leaks through the brickwork of the tunnel, has intersected an underground stream of a considerable size. The water from this stream has to be pumped into the Severn from a shaft 29 feet diameter, which has been constructed to catch this water.

There are arrangements for shutting off and diverting the stream water by means of sluices from the 29-feet diameter shaft, and also for intercepting the drainage water from the cuttings and pumping it up from shafts at each side of the Severn.

In addition to the two ventilating shafts there are five pumping shafts with a power capable of pumping 38 million gallons of water per diem. The maximum amount of water to be pumped has been 30 million gallons, and the minimum has been 23 million gallons per diem up to the present time, so that there is an excess of pumping power of 8 million gallons per diem; but when the whole of the permanent pumping and engine power, which