History of the Huddersfield Water Supplies
By T. W. Woodhead

CHAPTER XII

DIGLEY RESERVOIR

In view of such facts, a survey of the area was made and it was found that the most suitable remaining site was the Digley Valley, Holmbridge, where an impounding reservoir could be made by constructing an embankment across the Digley Brook (See Figure 55 below). Higher up the valley is the Bilberry Reservoir owned by the Holme Valley Waterworks Company, who also owned two others further south, Boshaw Whams and Holme Styes.

Figure 55. Plan of Proposed Digley Reservoir (click on image for larger version)

On the Digley site are two mills, the Bilberry Mill, now derelict at the foot of the embankment of Bilberry Reservoir and Digley Mills, occupied by Messrs. Greenwood Limited, Worsted Manufacturers. Within the catchment area, near the Greenfield (Isle of Skye) Road are waterworks belonging to the Holmfirth District Council.

Figure 54. Digley Valley. Proposed Site of New Reservoir Looking East.
On the right Bilberry Mill. Centre, Digley Mills

In 1936 steps were taken to purchase Digley Mill and farms within the reservoir catchment area, to purchase the reservoirs belonging to the Holme Valley Company, and sell to the Holmfirth District Council, which is in need of a larger supply, the Holme Styes Reservoir and arrange with this Council re their waterworks near the Greenfield Road.

In October a Parliamentary Bill was introduced called "The Huddersfield Corporation Water Bill" applying for powers to carry out the scheme. In the House of Lords this Bill was given the Royal Assent on July 6th, 1937.

On December 20th, 1938, an amicable agreement was reached with the Directors of the Holme Reservoir who accepted the Corporation’s offer for the purchase of their three Reservoirs for the sum of £24,000 and £3,000 towards coasts in full settlement of their claim of £123,318. this agreement made it unnecessary to proceed further with the arbitration, resulting in a considerable saving in costs.

Meanwhile a geological survey of the valley was made by Mr. Edward Morton, M.Sc., and his report was issued on November 27th, 1936.

In this report Mr. Morton points out that the valley is typical of the valleys in this part of the Pennines and will serve well to illustrate the difficulties to be overcome (Figure 56 below. is from his survey).

Figure 56. Geology of Digley (click on image for larger version)

The Digley Brook cuts through the alternating beds of sandstones or shales from the Pule Hill Grits to the Kinderscout Grits, which dip to the east downstream. As seen from the map part of the floor of the reservoir will rest on a thick bed of shale between Pule Hill Grit and the Kinderscout Grit. It is of interest that the Readycon Dean Series, consisting of sandstones, grits and flags, and with interbedded shales, is absent in this area, and the strata is shaly from the Kinderscout Grit to the Pule Hill Grit.

Running through the valley from south-west to north-east is the Digley Fault which crosses the valley on the downstream side of Digley Mill and runs through the embankment of the proposed reservoir. Another one, the Brownhill Fault, on approaching the embankment, curves in a southerly direction ; on the official Survey map it is shown with a northerly curve.

Nine boreholes were sunk along the site of the embanment and in the neighbourhood of the faults, and the knowledge gained from these, together with investigations of the geological structure of the basin of the proposed Digley Reservoir, led to the conclusion that the site does not appear to be one where any insuperable engineering difficulties are likely to be encountered in the creation of a watertight reservoir. On of these bore-holes yielded a sulphur water which will have to be cut off.

The occurrence and situation of the Digley Mill Fault may be regarded as advantageous in connection with the construction of the proposed embankment. The fault evidently acts as a barrier preventing the subterranean waters which have percolated into the Kinderscout grits in the upper part of the valley, from passing beyond the fault in the downstream direction. This fault also represents a probably means of security against any loss of water through the Pule Hill rock on the north-eastern side of the reservoir basin. A further point of interest is the occurrence of several beds of shale underneath the south-eastern portion of the basin. Should it prove necessary, in order to avoid leakage, to seal up the fissures in the several grit beds, these shale beds should enable each gritstone bed to be suitably treated with cement grout. One of these shale beds, 55 feet in average thickness, is important in that it lies at a relatively shallow depth below stream in the south-eastern area but also extends continuously from the proposed embankment to the Digley Fault, by which it is severed, thus forming an impermeable bottom to the deepest part of the basin, where it will be a valuable adjunct to the watertight barrier formed by the intended dam to the passage of water through the strata down the valley eastwards.

The proposed water level of the reservoir is 797 feet O.D. ; it will have a capacity of 600 million gallons and the estimated cost is £580,000. in addition to this is the Bilberry reservoir with a capacity of 67 million gallons, to the embankment of which the Digley Reservoir will extend. The drainage area of these two reservoirs is 2,242 acres, Bilberry Reservoir 1,835 acres, and Digley Reservoir 407 acres.

Meanwhile, to comply with the Safety of Reservoirs Act, 1930, the reservoir at Bilberry had to be inspected and the Waterworks Committee appointed Mr H.P. Hill, Engineer, Manchester, to undertake the work. For this purpose it was necessary to empty the reservoir to facilitate inspection. In December, 1938, a scraper elevator was purchased for use in cleaning the sludge from the inner slope of the embankment to assist the engineer in carrying out this work. Figure 57, below, shows the great depth of silt in the reservoir when emptied for inspection. It will be useful as a settling tank for the new reservoir.

Figure 57. Bilberry Reservoir, emptied for inspection, showing great deposit of silt

It is proposed to construct a Filter House just below the reservoir at Digley ; to construct a Service reservoir at Newsome, and a booster plant at Thongsbridge to augment the Deerhill supply to Shepley.

On Friday, December 9th, 1938, and confirmed at the Council Meeting on January 4th, 1939, the tender for the construction of Digley Reservoir (Contact No. 1) was accepted and placed with Mr. J. McColville of Cardiff, for the amount of £478,196. However, at a meeting of the Waterworks Committee on February 21st, 1939, the contractor attended and explained difficulties which had arisen respecting the contract and asked permission to withdraw the tender ; this the Committee allowed him to do and decided to re-advertise for new tender.

In addition to the making of the reservoir, much further work is necessary as indicated above, which will involved a total expenditure of about £700,000, and it is calculated that a period of five years will be required for the completion of the scheme. On completion the total capacity of the storage and service reservoirs will be about 2,396,000,000 gallons.

It is expected that there will be available (after providing compensation water) about three million gallons per day for domestic and trade for use within the limits of the Huddersfield Water Area. It is estimated that this augmentation of the resources will be sufficient to provide for the requirements of the Huddersfield Water Undertaking for the next thirty-six years. It is proposed to use this supply mainly to improve the supplies in the south-eastern part of the Borough and the adjoining districts at Kirkheaton and Lepton. This will reduce the call now made on the Blackmoorfoot Reservoir, and will also enable the water in the highest reservoirs to be reserved for parts of the district which lie at high altitudes.

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