The following is a return showing the number of Buildings and Houses destroyed or injured by the Bursting of the Bradfield Reservoir on the 12th. of March, 1864.
EXTENT OF DAMAGE:
T = Totally Destroyed
P = Partially Destroyed
F = Flooded Only
[N.B: The original table gives the figures for each individual street: however, due to the length and complexity of the said table, I have truncated it here, giving the 'totals' only. - M. Armitage. 10/May/97]
|Manufac- tories, Tilts, &c.||Rolling, Grinding, Corn and other Mills||Work- shops, Ware- houses, Store Rooms &c.||Drapers', Grocers', and other Sale Shops||Dwelling Houses||Malt Houses, Breweries, Public and Beer- Houses.||Buildings not otherwise described.||Yards of Fence Walling|
|T - 12
P - 25
F - 80
|T - 4
P - 17
F - 22
|T - 17
P - 11
F - 135
|T - 3
P - 15
F - 451
|T - 39
P - 376
F - 4096
|T - 2
P - 22
F - 162
|T - 53
P - 11
F - 71
|T - 4478|
There were also eleven churches, chapels, or schools flooded. Three tanneries, skin yards, &c. were partially destroyed. There were fifteen bridges totally destroyed, and five partially destroyed.
MR. RAWLINSON'S REPORT ON THE FLOOD.
Mr. Rawlinson, the Government Inspector, has presented to Sir George Grey the following report on the bursting of the Bradfield dam, and the condition of the other works of the Sheffield Water Company. During the week commencing Monday, 14th March, he had interviews with the Chairman and Directors of the Waterworks Company, and the Coroner and jury; visited the district which had been inundated, as also the ruptured embankment.
Mr. Beardmore came down to Sheffield on the 21st of March, and, jointly with Mr. Rawlinson, made an examination of the works, attended the inquest, and minutely examined and inquired into the several matters as herein reported.
The report of Mr. Rawlinson and Mr. Beardmore is as follows:
The district is, geologically, millstone grit, consisting at this site of beds of shale and open-jointed sand rock. At the intersecting line of the embankment and the valley, the bed of the stream is about 700 feet above the sea, and this point is some six and a half miles above or up stream, from Owlerton, a suburb of Sheffield. From the embankment upwards, the gradient of the valley and stream is a rise of about 90 feet per mile.
From the embankment down stream to Owlerton, the gradient of the valley is about 70 feet per mile, or, in the entire length betwixt these points, 450 feet. The valley through this distance is narrow, with steep banks on both sides. The dip of the strata at the site of the embankment is south and east. In the valley there are some springs; the water is bright, and for the most part pure.
The area of the gathering ground above Dale Dyke embankment is about 4300 statute acres; the water area of the reservoir, when full, 78 acres; the greatest depth of the embankment 95 feet; and the capacity of the completed reservoir was estimated at 114 millions of cube feet. The length of the embankment, at the top, was 1254 feet; its greatest width at the base, or valley line, was upwards of 500 feet. The top width of the embankment was 12 feet; the outer and inner slopes were 2½ to 1. The puddle wall, at the top, was 4 feet wide, and increased in width, or thickness, by an addition of 1½ inches for each foot vertical in depth, making a width, or thickness, of 16 feet at the ground line. At some points of the works the puddle trench was said to have been sunk to a depth of 60 feet below the surface. Two lines of plain socket jointed cast iron pipes (1¼ inch in thickness and nine feet lengths) were laid, obliquely, through and beneath the embankment, from the north west to south east. These pipes commenced on the inside, at an inlet bay of masonry, and ended outside, at the foot of the slope in a valve house. The sluice valves were on the outer ends of the pipes.
In excavating the puddle trench, steam engine power was used to an extent, as estimated by Mr. Gunson, of about 20 horse power driving pumps; three of 12 inches diameter and one of 13 inches diameter. These engines and pumps worked more or less during two years; part of the time night and day. Dale Dyke embankment contained some 406,200 cubic yards of material, 388,000 cube yards of ordinary material, and 18,200 cube yards of puddle.
The flood removed and washed away, in little more than half an hour's time, some 92,000 cube yards of material, or nearly one fourth of the whole embankment.
At the commencement of this work (1858) a catch water reservoir was made, and a conduit, or artificial river-course for the water of the stream, was excavated along the south side of the valley, and at or above top water level of the proposed Dale Dyke reservoir, to intercept and remove the ordinary flow of water and floods from the valley during the formation of the embankment. This intercepting reservoir is now in existence; but the conduit was broken down by a flood in June 1863, and was never afterwards restored. This flood filled the reservoir to a depth of 50 feet in two days. The conduit was not only not restored, but was further destroyed by excavations made in the sides of the valley, removing shale and rock to place in the embankment. From the date of the rupture of the conduit (June 1863) to the completion of the embankment (April 1864), no provision existed to discharge the waters of the valley, other than the two pipes of 18 inches diameter each. The by wash consists of a semi circular bay of masonry, 64 feet round, the water falling some three feet, and passing through a chamber of masonry 24 feet wide. From this point a by wash channel, partly stepped at the top, and then sloping rapidly, would discharge any overflow water into the river below the outlet valve house. The masonry of this by wash is well executed; but in my opinion the dimensions are far too small to remove floodwaters from an area of 4300 acres, even with the reservoir area to assist. A flood on the top of a full reservoir should have been provided for. The dry weather flow of water from 4300 acres in Dale Dyke district may have been about 2 1/6th cubic feet per second. An ordinary flood would give some 540 cube feet per second. An extreme flood, 800 cube feet per second; two pipes of 18 inches diameter, 500 feet in length, and acting under 90 feet head of pressure, would discharge about 84 cubic feet per second, and not 168 cube feet, as stated by Mr. Leather in his evidence.
The reservoir was filled 50 feet in depth by a flood which continued through two days, as stated by Mr. Gunson in June, 1863, and the valves appear to have been closed for a complete filling of the reservoir early in this spring; on March 10, the water in the reservoir must have attained almost its full height; on the 11th March it appears Admiral Fitzroy sent out his usual forecast that a gale might be expected, and as Mr. Gunson had noticed that the wind blew from the west or south west, which was down the valley, he went to examine the state of the embankment. He did not observe the least sinking of the embankment. While, however, he was at home that evening, a messenger arrived summoning Mr. Gunson, the resident engineer, and Mr. Craven, the contractor, to the embankment, as "Mr. Hammerton had observed a crack in passing over the embankment, after the workmen had gone home." This crack increased, and by 11.30 p.m. the embankment gave way, suddenly sweeping all within reach of its waters to destruction.
The time has been ascertained at which the embankment burst, and also at which the flood struck the several mills and places down the stream to Sheffield. The calculations worked out from these times, indicate that the flood travelled to Owlerton at a rate of 261 feet per second, or about 18 miles per hour. Cross sections having been taken show that about 40,000 cube feet of water, seven per second, rushed along the slope of the valley at this rate. Everything solid which stood in the direct course of the flood was swept away; huge rocks were torn up and were floated along just as pine timber would have been floated in an ordinary water way. One of these stones so floated, weighs upwards of thirty tons, and is, in dimensions, not unlike one of the largest stones at Stonehenge. Hundreds of tons of smaller stones were torn up and swept along. Of the first mills encountered by the flood, namely, Bradfield and Damflask corn mills, not a vestige remains to show where they stood, the buildings, site, and subsoil (rock and shale), having been scooped out and swept away, as also the ground for a considerable distance round. Of the Bradfield corn mill, at the date (of 13th April) not a fragment of either mill or of machinery had been found. Mills, mill dams, with the materials and machinery, bridges, houses, and other buildings, with their sleeping population, trees, and large stones from the bed of the river and sides of the valley, were swept down suddenly to destruction. At Owlerton the valley opens out, so as to allow the flood to spread, and this saved a far greater destruction taking place in the portion of the town of Sheffield affected. The water, however, rose in some parts of the town nine feet in height; floors of buildings, yards, and streets were filled with floating refuse, and covered thick with timber, stones, sand, and mud. Below Sheffield the flood does not appear to have done much serious damage.
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