Humberside Geologist no 10
published 1992
(read to the Hull Geological Society on Thursday 10th November 1949)
When I was asked, many months ago, to give a talk to the Society, it was agreed that water supply would be an acceptable topic. I read a paper to the Society in March, 1938 dealing with water supply generally and it is, therefore, intended to confine the following remarks to consideration of the chalk of the East Riding of Yorkshire as a source of water supply, particularly to that part of the county south and east of the Wolds.
As a preliminary, the following information should be noted. The area of the Riding is 1174 square miles. The total population is a little more than 500,000, of which the City of Kingston upon Hull accounts for about 300,000 and Bridlington, Beverley, Driffield, Norton and Filey together contain a further 50,000, or so.
The total population south and east of the Wolds excluding Bridlington is about 420,000 of which some 380,000 are at present dependent on the Hull Corporation for their supply of water.
With the exception of Hull and Beverley and the coastal resorts of Bridlington and Filey, the population is principally engaged in agriculture or attendant trades and occupations, there being an almost complete absence of large industries. Water is, therefore, over a wide area, chiefly for domestic and farm use. In Hull and Beverley, however, there are many industries which require large quantities of water. The majority of these are supplied by Hull Corporation but a number augment their supplies from private wells or boreholes and in the aggregate the quantity of water so obtained is considerable.
Having briefly indicated the nature of the water requirements of the Riding, I will proceed to express my opinion as to the water resources of the chalk of the Wolds in relation to these requirements.
A number of Engineers and Geologists have written about this subject, the earliest paper to which I shall refer being that read by Mr. J.R. Mortimer (1) to the Institute of Civil Engineers in 1878 and the latest Dr. Versey's (2) Presidential Address to the Yorkshire Geological Society in Hull in November, 1948. Two former Water Engineers of the Hull Corporation, Mr. F.J.Bancroft (3) and Mr. C.B.Newton have also contributed articles on this matter. Unfortunately the views of these authors have received little attention.
Generally speaking the Yorkshire Wolds take the shape of an inverted letter "L"; they stretch northwards from the Humber to the vicinity of Driffield and then eastwards to the sea at Flamborough. They consist of the upper, middle and lower chalk, and on the west and north rise abruptly from the Vale of York and Vale of Pickering respectively to a height of about 700 feet. Eastwards and southwards the Wolds gradually sink beneath the glacial clays and sands of the Plain of Holderness.
The capacity of the Wolds as a gathering ground or water-shed can be estimated from,
(1) The area of absorbent surface.
(2) The average yearly rainfall in inches.
(3) The amount of percolation.
and these will be considered in the order given.
(1) The area of absorbent surface. Mortimer states that "the out-crop of the chalky or area of absorption, is about 420 square miles" but this figures is undoubtedly too high, as a considerable portion of the chalk is covered by impermeable strata. Careful measurement of the maps of the Geological Survey Department shows that the area of chalk free from any impervious covering, is about 300 square miles and this figure will be taken as the area of absorption.
(2) The average yearly rainfall in inches. According to "The Water Supply of the East Riding of Yorkshire" (4), the long period average annual rainfall (1868-1902) varies from about 24.5" in the low-lying parts of the Riding to 33.5" in the high Wolds. Over the whole of the absorbent chalk area the average is 30.6".
(3) The amount of percolation. The problem of determining how much of the rainfall actually percolates into the underlying strata has received consideration from many authorities. It is almost impossible to make a direct measurement of this quantity, though attempts have been made to do so, on some gathering grounds, by measuring the total yields of those springs and pumping stations which are assumed to come within the influence of the catchment area. Percolation gauges have also been in use for many years, but according to Boswell (5) the results obtained from different gauges vary enormously, showing the amount of percolation to be anything from 20% to 80% of the rainfall.
In consequence of this lack of positive information many assumptions have been made and varying figures put forward. Some authorities suggest that percolation is a constant figure, regardless of rainfall whereas others express it as a percentage of the rainfall. I have thought for a long time that neither of these views are correct, but that percolation must be affected by the amount of rainfall, the prevailing state of the weather and especially in the summer months, the intensity of the rainfall.
In an endeavour to obtain first-hand information on the subject I have investigated the records obtained from a weir on the Hull Corporation's gathering ground at Bransdale on the Southern part of the Yorkshire Moors about 20 miles north-east of the Wolds. In conjunction with the weir is an automatic recorder provided with weekly charts on which the flow over the weir is shown by a continuous line. There are also five rain gauges, one of these being the daily automatic recording type. It is thus possible to compare the rainfall with the run-off over any desired period and, indeed, to trace the effect of separate falls of rain.
The yearly rainfall over the gathering ground during the period in which readings have been taken has varied between 31.8 and 47.4 inches, the average over the period being 40.1 inches.
On Fig. 1 are shown the average figures of rainfall run-off and evaporation, all expressed in inches, for each month of the year, obtained from Bransdale during the period August 1936 - July 1949, except that the whole of the year 1946 is omitted, as the recorder was out of commission for some months owing to the weir plates being damaged by a severe storm.
The amount of rainfall lost by evaporation is, like percolation, impossible of direct measurement. The line marked 'evaporation', therefore, represents the difference between rainfall and run-off, on assumption that all the rainfall not measured over the weir as 'run-off' has been lost by evaporation - whether direct or by way of vegetation or other causes is immaterial.
These lines show that, taken generally, the monthly evaporation bears a more constant relationship to the rainfall than does the run-off. It will be seen that for the month of March the run-off exceeds the rainfall and evaporation appears to be a negative quantity. This is the result of frost in January and February which retards the run-off until the thaw follows in March. The chart shows that whereas August evaporation is about 70%, in December evaporation is only about 30%, of the rainfall.
When annual evaporation is plotted against annual rainfall, the points lie fairly closely to a straight line, from which can be deduced the formula :-
Evaporation at Bransdale = 0.34 x Rainfall + 5"
The question arises as to whether evaporation is likely to be generally the same on the Wolds as at Bransdale.
Bransdale has the greater rainfall; its elevation rises to 1,400 feet against 700 feet and its surface is greater in relation to area as measured on the map; it is not cultivated to such an extent as the Wolds and, as far as my observations go, rain does not appear to sink into the soil as quickly. Both areas are almost treeless.
When all these factors are taken into consideration, there seems justification for the assumption that evaporative conditions will be about the same for both areas and, therefore, the above formula should be applicable to the Wolds. If this is so, evaporation, calculated on the average rainfall of 30.6", will be approximately 15.5" and this, when subtracted from the rainfall leaves some 15" as the amount of percolation.
Other estimates of percolation put forward by authorities possessing particular knowledge of the East Riding are Mortimer (1) 75% of rainfall; Kendall, 10"; Versey (2), 8" and Bancroft (3) 4" in a dry season. Although Mortimer's estimate is probably too high, I feel convinced that the others are too low. Besides the evidence in support of this conviction, which will be mentioned later, it should be stated that there is no surface flow from the Wolds, which are, in fact, referred to by Kendall (6) as "the streamless Wolds". Consequently it follows that all rain not lost by evaporation must percolate into the chalk and flow underground until it can escape from some spring or is otherwise abstracted.
It is to be observed that during a dry summer most crops growing on the Wolds do not seem to suffer greatly from lack of rain, although the covering of soil over a large layer of the Wolds does not exceed 3 or 4 inches. It appears that rain which has already percolated into the Chalk must be withdrawn, even from a considerable depth, and the effect of this would be equivalent to a reduced percolation.
Although I have shown that it is probable that the mount of percolation, in a normal year, is equal to about 15" of rainfall, it is proposed in the following calculations to base all estimates on a percolation of 12" only. Even this conservative estimate is sufficient to indicate the very great quantity of water entering the chalk of the Wolds each year.
One inch of rainfall per annum per square mile is equivalent to about 40,000 gallons of water a day and therefore, the 300 square miles of the absorbent area of the Wolds, at 12" of percolation, will provide 144,000,000 gallons of water per day, potentially available as a source of water supply.
Where does all this water go ???
Approximately one third, or 100 square miles of the Wolds drains to the west the north or almost directly eastwards to the sea, and the total flow of water from this portion of this Wolds will be about 48,000,000 gallons daily. Along the western and northern escarpments the chalk rests upon impermeable strata and numerous well-defined springs break out in various localities, some of these springs being of such magnitude that water mills were built along their courses. A number of springs are utilised for the purpose of public supplies, but the total quantity of water so used probably does not exceed 2,000,000 gallons per day.
About 96,000,000 gallons of water flow, on the average, every day from the 200 square miles of the Wolds which drain to the south and east, and as the chalk gradually dips below the glacial clays, numerous springs break out along the fringe. This occurs particularly in the angle between the northward and eastward stretches of the Wolds, where large springs come to the surface over a considerable area and form the source of the River Hull. At Hempholme Lock, where the river is still non-tidal the flow, all from springs, was about 50,000,000 gallons per day in May, 1949 and still remained at about 20,000,000 gallons at the end of October, notwithstanding the very long period of exceptionally low rainfall.
It was at Kelleythorpe, near Driffield, in this north-east angle of the Wolds, that the Hull Corporation obtained powers in 1930 to construct a pumping station with wells and adits, but the works were never commenced.
A little further to the north-east there are springs of a different kind, usually known as kelds, which bubble up from the bottom of pools and rarely cease flowing.
The vicinity of Arram, eight miles south of Driffield, has often been suggested as the site for the construction of a waterworks, but I have always had some doubt regarding its suitability. A number of springs rise over a fairly wide area, but none of them are large and they seem to flow at an almost constant rate, regardless of whether the seasons are wet or dry. In my opinion this indicates conditions where numerous small supplies of water may be obtained from bores sunk at different points, but no large quantity at any one site. This appears to be confirmed by a 36" borehole sunk to a depth of 180 feet at Aike, near Arram during 1949. The yield of the bore on test, was less than 20,000 gallons an hour and the water showed the presence of iron, a most unusual feature. The chalk appears to be dense and the water to flow in an easterly direction. If the information obtained from Aike is applicable to the surrounding district it does not seem as though the whole of the water from the Wolds in this region can be accounted for by its apparently slow movement to the east.
The main flow of water from the southern portion of the Wolds is probably in a southerly or south-easterly direction to the Humber. Great quantities of water used to issue from springs in the vicinity of Cottingham and Springhead, near Hull, and in the chronicles of Meaux Abbey in the 12th Century, Abbot Burton refers to the stream along which the water flowed as a "torrens". Sometime later, wide dykes or drains were cut to carry the water to the River Hull and the Humber, and so drain the extensive marshes which, until then, existed. Even now, wells thereabouts often overflow during a wet winter, notwithstanding the very great quantity of water which is abstracted by the three large Pumping Stations of the Hull Corporation Water Department which are situated in that neighbourhood. The average daily quantity pumped by these Stations is about 16,000,000 gallons. A further three or four million gallons of water are probably abstracted daily from private wells and boreholes for industrial purposes in Hull and district. The fact that such a large volume of water is being pumped from so small an area indicates that the amount of percolation cannot be less than the estimate I have given.
Bridlington and other authorities within the area south-east of the Wolds probably take an additional 2,000,000 gallons. It is probable, therefore, that the total quantity of water used from the whole of the chalk of that area of the Wolds which drains to the south and east, does not exceed some 22,000,000 gallons per day. This is only a small part - less than 25% of the total quantity of water that is available, the great resources in the north-east angle of the Wolds remaining practically untouched.
So far consideration has been given only to the quantity of water which must flow out of the chalk to make room for further rainfall, but the storage capacity of the chalk and its effect on the flow of springs must not be overlooked. According to Kendall (7) the Yorkshire chalk is the hardest and most dense of any in this country with a porosity of only about 17%. Assuming that the pores are full of water, which is the usual condition, there is approximately one gallon of water in each cubic foot of chalk. This is the water of capillarity which will not normally run out of the pores and is therefore useless as a source of water supply. The chalk is, however, freely jointed or fissured, especially towards the top, and it is through these joints or fissures that the main flow of water takes place. In the aggregate, the volume of these interstices is sufficient to form a vast reservoir, the water contained in them being referred to by Bancroft (3) as "the water of cisternage". This capacity for storage is the reason why springs keep running throughout long dry periods and is one of the features which renders the chalk very valuable as a source of water supply.
To obtain water from the chalk it is usual to construct bore-holes, wells, or where large quantities of water are required, underground tunnels known as adits. The latter are necessary, since the water flows mainly through the joints or fissures, and it is essential to cut across as many of them as possible; it is also important that the adits should be driven at right-angles to the flow of the water. The true direction of the flow is not easy to determine on a new site, and in many instances adits are not driven in the proper direction to make best use of the water available.
Wells or boreholes must be sunk to, and adits driven at, the correct level, as the chalk varies greatly, at different depths, in its water yielding capacity. This was shown very clearly during the construction of the underground works at the Hull Corporation's Pumping Stations at Dunswell and Cottingham in 1923/1929 by A.C.Potter & Co., in whose service I was engaged at the time.
At Dunswell a new pumping station was being constructed comprising 17 shafts, sunk to depth of 96 feet below O.D. or about 100 feet below ground, the shafts being spaced fairly uniformly on a line about 5,200 feet long running approximately from north to south. An adit 6' 6" high by 4' 6" wide was driven throughout the whole of this length connecting the bottom of the shafts. The shafts were lined with cast-iron cylinders and where these passed through the chalk they were grouted to prevent the access of surface water. During construction the adit was driven in sections from various shafts and whereas in the southern section a large quantity of water was met with, the northern end was absolutely dry. It is of courser well-known that the chalk and the base of the over-lying boulder clays slopes to the south-east at about 10 feet per mile, and as a consequence the adits which were driven horizontally were hearer the top of the chalk at the southern end.
The Cottingham Pumping Station, which lies to the west of Dunswell was built about 60 years ago, there being three 14' diameter pumping wells, a number of shafts and an adit connecting the bottoms of all these at a depth of 50 feet below 0.D., or about 75 feet below ground level.
The new works at Cottingham were to consist of the deepening of the existing wells and shafts and the construction of additional shafts and an adit about 4,000 feet long at a depth of 100 feet below O.D. i.e. 50 feet below, and in line with, the old adit. During construction of the new adits, branches were driven under each of the three wells. These new adits were almost completely waterless and it was possible to stand and remain quite dry, underneath the wells from which about 7,000,000 gallons of water was being pumped daily.
At both Dunswell and Cottingham 20" diameter boreholes were sunk from the bottom of a number of the shafts to a depth of 400 feet without any evidence of additional water being obtainable.
When it became clear that the new lower adit at Cottingham, and the northern end of the adit at Dunswell, were dry an investigation was made to ascertain the reason for these unexpected conditions. The conclusions reached which were not of a very definite nature, were based on the assumption that the flow of underground water in the area was from the south-west and that pumping at each of the two stations had an effect on the other.
When informed of these conclusions I was doubtful of their validity as it appeared that important facts had been overlooked. For instance although there was heavy pumping at Dunswell exceeding 12,000,000 gallons of water per day for long periods during the construction of the adits, no effect was noticeable on either the pumping level or the quantity available at Cottingham.
Whilst walking along the adit at Dunswell during its construction, I first became convinced that there was water at a higher level as at one of the shafts where the grouting was apparently not effective, great jets of water were pouring down into the adit from outside the cast-iron lining.
Some three years ago, at my suggestion, holes were drilled through the Dunswell shaft linings at various depths, and at levels corresponding with the rubble chalk, water entered the shafts through the holes in almost every case, although the water level in the adit was some 40 feet below. More recently, boreholes, lined with perforated tubes through the rubble chalk, have been sunk at Dunswell, and in every instance additional water has continued to flow from the higher level, down the bores to the adits. This recent work has shown that there is no lack of water at the northern end of the Dunswell site and that the dryness of the adit there was owing to its having been constructed below the main water-bearing stratum.
The conditions existing at Dunswell and Cottingham are sometimes referred to as a 'perched water table' but, in my opinion this is not a correct definition. The water is, in fact only 'perched' in the sense that the adits were constructed at too great a depth. I have known similar cases in various parts of the country.
Bores have also been put down to determine the direction of the flow of water at Dunswell and information obtained indicates that the flow is from the north/north-west. If this proves to be correct, there is little likelihood of pumping at either the Cottingham or Dunswell station affecting the yield of the other.
It is customary to talk of a cone of depression round a well or borehole from which water is being pumped. Although this applies to homogenous water-bearing strata, where the water has a free passage from higher to lower levels, it does not apply to many chalk areas. There seems little doubt that, in the area around Dunswell and Cottingham, almost the whole of the available water is in the top of the broken chalk, which lies just below the glacial deposits. The passage of water downwards seems to be effectively sealed by numerous marl bands, some of which, although very thin, are apparently continuous over a considerable area. Many of these marl bands were visible in the adits, and the cores taken from the boreholes, during the construction of the works at the stations.
It is interesting to note Mortimer's (1) observations on the flow of water in this district. He states " The best quality and the largest quantity of water is found on the top of the chalk rock in Hull ..... it thus seems clear that the flow of the pure fresh water towards the sea is on the surface of the subterranean reservoir along the rubbly and open rock which is everywhere the character of the upper beds of the chalk."
Before concluding I should like to make reference to the purity of the chalk water, and the relative cost of water obtained from the chalk and upland sources. With regard to the former, the Wartime Pamphlet No. 12 of the Geological Survey of Great Britain states "The quality of the water in the Wolds is excellent." As regards cost, pre-war figures showed that, in general, the capital expenditure of water undertakings obtaining supplies from underground sources was less than 60% of the expenditure of those depending on impounding reservoirs for the same quantity of water supplied.
I have endeavoured to make clear, in the foregoing remarks that there is available from the chalk of the Wolds, a vast quantity of water of excellent quality sufficient to meet all the domestic and trade requirements of the existing population or of any population likely to inhabit the area within the foreseeable future. This has been known and attention called to it for many years.
Mr. F. J. Bancroft (3) basing his estimates on the yield after three dry years, said "The point I wish to emphasise is that the water which is annually absorbed must pass away, or the water-level would permanently rise and the land be flooded. Thus, if my figures are correct, 47 million gallons a day could be pumped from the Yorkshire Chalk area without drawing a gallon of the "water of cisternage", and whatever portion of this supply is not so pumped, is flowing away into the rivers and the sea."
Dr. H.C. Versey (2) states "There is ample water in the chalk to supply, even with large increases in consumption, the whole of the population of the East Riding and of some adjacent areas."
Dr. Stevenson Buchan in a talk on "Underground Reservoirs" in Radio Newsreel on the 2nd July, 1949 said "The chalk of Yorkshire, for instance, could yield supplies as great again as the quantities now abstracted. Quite a useful margin of safety if it doesn't rain there next Winter".
In my opinion these facts should be sufficient to show that, far from there being any necessity to bring water into the East Riding from outlying districts, the resources of the Wolds would not only provide an ample supply for the whole of this area, but there would be water available for other less fortunate districts. Yet, during the last two years, shortage of water has almost continuously existed in the district south-east of the Wolds, including the City of Kingston upon Hull, and restrictions irksome to domestic users and detrimental to industry, have had to be put into force by the water supply authorities.
In conclusion, may I quote the title of the Water Act, 1945 which reads "An Act to make provision for the conservation and use of Water Resources and for Water Supplies and for Purposes connected therewith." The Act seems to have been framed for such an area as the East Riding of Yorkshire.
1. Mortimer, J.R. 1878 . The Chalk Water Supply of Yorkshire. Proc. Inst. Civ. Eng. vol LV.
2. Versey, H.C. 1948. The Hydrology of the East Riding of Yorkshire. Proc. Yorkshire Geol. Soc. XXVII
3. Bancroft, F.J. 1904 .(Water & Gas Engineer of the Hull Corporation) Presidential Address to the British Association of Waterworks Engineers.
4. Anon. 1906 . The Water Supply of the East Riding of Yorkshire. Mem. Geol. Surv.
5. Boswell, P.G.H. 1943 . Assessment of Percolation. Trans Inst. of Water Eng. XLVIII
6. Kendall P.F. 1898. The Geological Conditions of Underground water supply . Trans. Hull Geol. Soc. V pt. I
7. Kendall, P.F. & Wroot, H.E. The Geology of Yorkshire.
Meditor's note - Mr. C. Green joined the Hull Geological Society in 1929 and was joint Secretary of the Society with J.W.Stather from 1932 to 1938. He was then Secretary of the Society until June 1953 when he died.
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