The following report was written by renowned geologist Joseph Prestwich (1812-1896), a Fellow of Geological Society since 1833, and was read in his absence at the Society's meeting on 7 April 1852.
A PDF scan of the article is available on the Lyell Collection web site.
April 7, 1852.
On some of the Effects of the Holmfirth Flood,
By Joseph Prestwich, Jun., Esq., F.G.S.
The broad tract of hilly country, which stretches north and south on the borders of Lancashire and Yorkshire, rises, in some places between Manchester and Huddersfield, to the height of nearly 2000 feet. The central ridge is here composed of the Millstone Grit Series, the elevated surfaces of which form extensive barren moors, and from which, owing to their lithological character and the large fall of rain, the surface-drainage is very considerable. On its eastern slope, the water is carried off by numerous small streams, falling into the various tributaries of the Humber. Their usual course is through narrow and picturesque valleys, which penetrate deep into the hills ; amongst them is that of the Holme, which commences in the central range of hills, winds for nine miles east and north, and then joins the valley of the Colne at Huddersfield : it is well-wooded, and the scenery is generally bold and fine. At a short distance from the top of the valley, the Holme is joined by the Digley streamlet ; the latter, however, being apparently the main stream, and draining, according to Capt. Moody, about 1920 acres of surface. It at first flows through a narrow and uncultivated ravine, which, three miles above the small town of Holmfirth, opens out into a narrow valley. This valley has always been subject to occasional floods, arising, however, from natural causes : one of the most disastrous occurred in 1777. The bottom of the valley shows beneath the turf an accumulation, several feet thick, of local gravel and rolled fragments of rocks. In some places debris of this description overlies 2 to 3 feet of imperfect peaty matter, which again appears to repose on similar detrital accumulations. This drift, however, is much water-worn, and does not seem to contain any masses of rock at all approaching to the dimensions of those transported by the late flood.
The following outline map shows the course of the stream and the situation of the principal places referred to.
Between 1840 and 1844, an embankment 96 feet high (but which afterwards subsided to 87 feet), about 480 feet wide at base, 16 feet at top, and 340 feet in length, was thrown across the valley of the Digley, three miles above Holmfirth. By this means an artificial lake, known as the Bilberry Reservoir, about a quarter of a mile long, 300 to 400 feet broad, with a surface of rather more than 11 acres, and in the centre from 70 to 80 feet deep, was formed. It was calculated that, when full, this reservoir held 86,248,000 gallons of water. The dam was constructed of a wall of clay-puddle, 8 feet wide at top, and 16 feet at bottom, with a mass of the debris of the valley, consisting of earth and stones, on either side. The inner slope was paved with squared stone, and had a base 3 to 1 ; the outer slope, a base of 2 to 1.
On the night of the 4th of February last, the giving way of this embankment caused the sad catastrophe, of which the papers have so recently given an account. The object of the present communication is merely to notice briefly a few facts bearing upon the geological question, and having reference to the transporting power of water.
The portion of the embankment destroyed extends to its full depth, and forms a gap about 140 feet in width at top, and 25 feet at bottom. The weight of the materials thus swept away, and scattered in gradually decreasing quantity for a distance of half a mile, cannot be much less than 40,000 to 50,000 tons. A large proportion, however, is deposited within the first 300 feet. At this point a stone-built mill, two storeys high, was situated : all that portion of it in the way of the flood-stream was at once swept down, and the site covered with 6 to 10 feet of debris. As far as this the valley is very narrow, and the action of the water on the slopes on its side tore up the surface to a depth of 10 to 20 feet (forming a small cliff-like bank where it had been a slope previously, see fig. 2), and carrying away large masses of rock to considerable distances. It is to be observed, however, that the first rush of the waters out of the reservoir excavated a circular pool in the old water-channel at the foot of the embankment. The rock in this pass has a dip of about 5° nearly in a direction down the valley, and consists of a pebbly quartzose conglomerate, of a character easily recognised.
Just below the mill the valley opens out from a breadth of 30 to 50 yards to that of 100 to 200 yards, and the force of the flood became necessarily much diminished; still the meadows extending from this point to Digley are almost entirely covered to a depth of from 1 to 2 feet, with masses of rock mixed with sand and gravel, derived from the embankment and the sides of the pass above-mentioned. The bulk of the debris scattered over the valley consists of angular fragments of rock not exceeding 1 or 2 feet in diameter ; but amongst them a few large rough blocks stand out in prominent relief. As the portion of the outcrop of the rock exposed to the action of the torrent was not large, the sides of the valley being much covered with debris, these larger masses are not numerous. There are four which particularly attract attention. One of these, a block measuring 7 feet in extreme length by 5 feet in breadth, and 2½ feet in depth, and weighing probably from 5 to 6 tons, has been transported a distance of about half a mile, and now lies in the valley near Digley Mill. There is near it another mass of about the same size. A third block, rather nearer the reservoir, measures 12 feet by 6½, and 2 feet deep, and may weigh 7 or 8 tons. The most remarkable block, however, lies in the middle of the valley, near Upper Digley Mill, and at a distance of a third of a mile from the parent rock ; it is 22 feet long, 6 feet broad, and 3½ feet thick, and probably weighs about 20 tons.
Although the greater part of this portion of the valley is covered with debris, there are places where its surface has been torn up to the depth of from 4 to 5 feet. This also occasionally occurs in other places lower down the valley, but generally the centre of the valley has been covered with debris, which the denudation of the banks in the narrower passes has furnished. In the middle of the open part of the valley, above Upper Digley Mill, an old oak-tree still stands, notwithstanding the many hard blows it received, and of which the marks remain on the bark. In fact, all down the valley, trees, chiefly ash, have stood, where buildings have given way. It is also to be observed that, although many have been uprooted, few have been broken down. These results probably are due to the branches having been in most cases above the reach of the flood, and to the absence of foliage.
At Digley Mill, the valley contracts to a width generally not much more than sufficient for the passage of the stream, and continues so for nearly a third of a mile. The mill, which was a substantial stone-building, four storeys high, stood at the entrance of this pass, and at the other end of it, but rather on one side, was Bank End Mill. The flood swept the first mill entirely away, with the exception of the tall massive square chimney, which remains almost uninjured ; whilst the last-named mill is cut in two, the remaining half presenting a clean open section. The ruins of these mills and the debris derived from the denudation of the sloping banks of the pass are thickly scattered for a distance of half a mile along the valley where it again expands above Holme Bridge. The church of this village stands in the valley, which is here 700 to 800 feet wide. One of the stone posts placed at the entrance of the church-yard was broken in two, and one part, 6½ feet long by 1½ foot square, I found at a distance of 150 yards lower down the valley. All the slabs on the tombs were removed to distances of from 50 to 200 yards ; and this occurred where the waters having spread out had lost much of their force. All down this part of the valley, as far as Holmfirth, a distance of 2½ miles from Digley Mill, are found pieces of a peculiar dark-grey micaceous flagstone, 6 to 12 inches in length and 2 to 3 inches thick, both in a rough state and in squared blocks used for building. This bed crops out close by the above-named mill, and was used in its construction. The rocks in this second pass consist of grits and sandstones.
At Hinchliffe Mill, between Holme Bridge and Holmfirth, the valley is again contracted, and at this point a row of six small stone houses was entirely swept away. The height to which the water rose above its ordinary level was here 26 feet. Below this the valley again becomes wider, and presents for a distance of 1½ mile a surface covered with wreck, but to a less extent than higher up. The walls and fences are levelled, and some houses swept away ; but the five or six mills have sustained comparatively little damage. The fields are covered with gravel and fragments of rock, but none of the fragments are of a very large size ; a few only may be 1 to 2 tons in weight. In Holmfirth, at which we next arrive, the bridges were dismantled, and several buildings levelled to the ground or partly destroyed; but most of the debris remains in situ. In the churchyard, which stands rather above the river, some large flagstones were however removed to a distance of from 50 to 100 yards down the stream.
Below this spot the effects of the flood are less marked. Stone walls have been thrown down, some small buildings and bridges destroyed, and no inconsiderable injury otherwise done ; whilst the fields, that were overflowed, are covered in places by sand and gravel, which, however, gradually decreases in quantity and becomes finer. The last strong action of the flood is exhibited at Berry Brow, within two miles of Huddersfield. The stone walls of the churchyard, which is situated in the valley, have, on the two sides transverse to the valley, been thrown down, and the stones carried a distance of 100 to 150 feet. Near Huddersfield the waters rose 6 to 8 feet, but, beyond covering some of the meadows with sand, they did no material damage.
The large iron boilers of various mills destroyed in the course of the stream were carried to considerable distances by the flood. That at Digley Mill, which weighed 10 to 12 tons, was found more than a mile lower down the valley. At Smithey’s Place, two miles below Holmfirth, an equally large boiler was swept away, and now lies in the bed of the river at Berry Brow.
Notwithstanding the force and violence of the torrent, fishes, with which the reservoir was well stocked, were transported a long way comparatively uninjured ; many were picked up around Holmfirth in a state perfectly fit for use. I could find no shells or fragments of shells in the transported gravel or sand ; neither did I observe any in the bed of the reservoir.
The fragments of rock show but little or no water-wear. They are chipped, much broken, and angular.
Of the slope of the valley I cannot speak. Between the Reservoir and Holmfirth, judging from the number of mills, the descent must be considerable. The passage of the flood-waters down to Holmfirth is said to have been effected in a quarter of an hour, and in an hour the waters had retired. The main fall of the flood was, however, almost as rapid as the rise. In some of the descriptions of this catastrophe, it is said that the debris of the embankment was carried down the valley to a distance of three miles, but this, owing to the structure of the valley, appears to me to be questionable; for, as before mentioned, the valley consists of open flats and narrow passes, and it is in these latter that the force of the flood has been especially felt. This is particularly apparent in that part of the valley which is only 20 to 30 yards wide, just below Digley Mill. The diagram, fig. 2, p. 226, shows generally the form of the excavation effected at the base of these passes : c marks the position and usual highest level of the stream; a represents the sloping surface, to a height of 10 to 20 feet above the stream, as it existed before the flood ; b indicates by a dotted line the surface as it now exists after the flood. In these parts of their course the waters rose from 20 to 30 feet. Field-walls, houses, mills, and bridges, in these narrower places, were swept away with irresistible force, and many hundred tons of debris scattered over the valley.
But it seems to me that the debris has in almost every case been deposited, as might be expected, in the more open space succeeding each pass; and there the trail of debris gradually diminishes. At the passes, the waters, being again pent up, have torn up fresh materials and transported them to the next open space. This is repeated in gradually decreasing force nearly all the way to Huddersfield.
It would be very desirable, while the effects of the Holmfirth flood are still recent, that exact measurements should be made of the width of the valley in its different parts, of the fall of the ground from the reservoir to the junction of the Holme with the Colne, of the height to which the water rose in various parts of the flood-stream, of the time taken for the water to rise and run off, &c., so that the velocity and power of the flood might be determined, and its results more accurately recorded. For if such are the remarkable effects of a temporary flood caused by a body of water comparatively so small, and along a valley where its power could not be maintained, we may form some conception of the enormous power which a more continuous flood, with more sustained action, would possess.