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Author Topic: Strood Caverns  (Read 2613 times)

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Strood Caverns
« Reply #1 on: April 24, 2012, 19:46:10 »
Strood Caverns.
From 'The Water Supply of Kent,' W. Whitaker. 1908, see links for further infomation.
Pages 202-204.
Strood.
...'3. Waterworks, on the southern side of the high road , about a third of a mile W. of St. Nicholas Church. 1849 and later.
Communicated by Mr. W. Banks. City Surveyor, Rochester (?1892).
About 106 feet above Ordnance Datum.
Pump about 280,000 gallons a day, lowering the level 5 feet.
Yearly supply 97 million gallons.
At an extension made in 1886, a "natural heading" was found. There had been a fall before, and along the fissure there was a width of sand of 2 to 3 feet, to a height of 7 or 8.
Whilst the above was being printed a detailed account of the natural gallery was published in a paper by Mr. S. Silis (Rochester Naturalist, 1907, vol. iii, do. 97, pp. 466-471 and four plates) and from this the following remarks are taken. The occurrence is so peculiar that no apology is needed for their length, especially as the paper is locally published and therefore not generally accessible.
"A cavern or natural chamber, with a water-course opening out of it, was discovered in 1879....
This chamber was found to be roughly Z shaped on plan, the stem of the letter lying in the line of fault, which cut the workings from north to south. The upper arm which ran...west by north was 28 feet long and 10 feet wide, with a height from floor to roof of 12 feet at its western end to 17 feet where it joined the stem.
The stem, measuring 16 feet in length between the arms, lay south by south west, the sides slightly converging toward the lower end, the width at junction with upper arm being 12 feet and at the lower arm 9 feet.
The lower arm was somewhat lozenge shaped cutting south east 18 feet long and 10 feet wide, as measured in the centre of its length. At the lower end it narrowed down to 3 feet in width and finished in a large fissure which extended from floor to roof.
At the western end of the upper arm a stream of water enters the cavern by the way of what appeared to be a tunnel-shaped fissure, partially filled with sand and clay.
The cavern, when opened, was piled with blocks of chalk and debris, and the walls and roof were cracked and splintered to such an extent that ultimately brickwork under-pinning was found to be necessary to prevent further extensive falls of chalk.
Later work proved the fissure at the western end of the cavern to be much more extensive than it was at first supposed, but it was not until the year 1903 that the extent of this water-course was realised.
The work in hand at this period included the deepenings of an adjoining adit which drained this channel. As the work proceeded the water flowing from the fissure obtained a more easy egress and washed out quantities of fine sand and clay disclosing a passage of far greater dimensions than was suspected.
The sand being so fine was swept down and held in suspension by the water in such quantities that a difficulty was experienced in keeping the pumps clear, and it became expedient to remove as much as possible by digging.
Many tons of clay and sand were removed in this way and day by day the passage deepened and extended until it took the form of a roughly fashioned adit from four to five feet wide and from five to six feet high.
The passage or adit was explored for a distance of 130 feet from the cavern and at the point where the work was stopped appeared to continue in much the same form.
When the adit had been so far cleared of detritus the floor was found to be paved with a layer of tabular flint which crossed the passage. The sides of the adit were scored and in many places deeply undercut by the action of the stream. The stream would appear to have found its way primarily along the flint floor and, being intercepted by the fault which crosses the cavern, was diverted toward the big fissure at the end, where it found an exit to the river."
(Medway).
"The level of the flint layer....is about one foot above the low water mark of ordinary tides in the river, and the rise of the tidal waters to 17 or 18 feet above this level would pen up the stream until the ebb released the waters, which would scour down the channel with added force.
The fine sand and clay washed down from the strata overlying the chalk through pipes or fissures would gradually silt up the stream bed. This silting would be assisted by the periods of comparative quiescence when the stream was held up by the tides, and precipitation of sand held in suspension would be rapid.
The force of the stream being insufficient to remove this silt, a fresh passage was carved out above it in the chalk already softened by the water's action...
The roof of the passage is roughly arched throughout.....
During the operation of removing the silt, which was mixed with quantities of drift flints, and chalk blocks fallen from the sides of the passage, numerous small streams were discovered issuing from fissures along the sides, but as the work proceeded beyond these fissures the streams ceased to flow and the supply gradually increased from ahead.
The general direction of the passage was west by north west.....At various points...occur pockets or enlargements.....at distances varying from 20 feet to forty.
If the course of the stream is traced in a series of straight lines, from...its source, it will be seen that at each change of direction there is one of these chambers.
Not only is the enlargement horizontal but vertical, and the roof is drilled deeply as if by a large tool in many places. The greater the angle of deviation the more considerable is the enlargement.....
There are five of these enlargements...and in the fifth which is right at the end...at which the work of 1903 finished, a mass of chalk has fallen from the roof which forms a bar right across the passage. Over this barrier the water steadily wells from the unexplored regions beyond...
The roof slopes from the cavern toward the end of the passage and this gives one the impression that the passage must be rapidly approaching its termination," but he thinks this not the case.
The passage "is normally full to the roof with water, and consequently the whole area of sides and roof is always under its solvent influence. The chalk through which the natural passage is driven is particularly soft and susceptible to this action...
The roof was studded in places with delicate fossil remains protruding from the eroded surfaces."
In making a short adit, to connect two pump-wells, a mess of hard chalk, with large flints and nodules of iron-pyrites all concreted together, was met with, "along the fault and appeared to be wedge-shaped and of immense proportions."
One of the plates gives sections of the adits and another a plan of the wells and adit, both being by Mr. W. Banks and dated 1903. The other two are views of the natural adit, from photographs.'

 

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