in France. One of the earliest artesian wells in London was that sunk in 1844 to supply the fountains in Trafalgar Square. It goes down 898 feet to reach the upper chalk formation. Since the date of its construction, however, the water level of London’s underground water has steadily dropped, and the Trafalgar Square supply is no longer artesian. Actually a pumping chamber has been constructed well below the level of the Square and the fountains play by mechanical power.
<Callout type="tip" title="Tip: Mechanical Power for Fountains">Artisan wells that can no longer rely on natural pressure require mechanical assistance to pump water.</Callout>
The water from artesian and deep wells is generally very even in temperature summer and winter. In a true artesian well the water rises to at least ground level and it sometimes happens that the natural lift is enough to carry it to the storage tanks without pumping.
Abyssinian Tube Wells. For a temporary supply, and for cottages in the country, “Abyssinian” tube wells are useful. They are made up of strong mild steel tubes, driven into the soil, one length being screwed on to another or, in fairly soft ground, the joint is made by means of collars. The bottom length has a hardened steel spike and is perforated for a length of about 2 feet to let the water in.
Fig. 145 shows one method of driving. The lowermost length is shown in the ground and the next length is connected to it, A being the collar joint. At B two plates are firmly clamped to the upper length by means of bolts. At E is a similar clamp carrying two pulleys. Over these pulleys run ropes, marked D, attached to a heavy weight, or monkey, C. The monkey is pulled up by means of the cords and then allowed to fall, driving the tube in by its impact on the clamp B.
An alternative way is to put a protecting cap over the upper end of the tube, with a separate rod above it carrying the monkey. In this case the impact comes on the cap, no clamp being used. This method is said to avoid damaging the tube, which sometimes occurs with the clamp method.
When the water is reached a pump is screwed on to the uppermost length; for a short time the water is muddy, due to the clearing of the earth out of the perforations and the forming of a cavity around the bottom of the tube, but once this has been done the water runs clear.
In any tube well, if the water level is not within 28 feet of the pump valve, the valve must be taken down the tube to within such distance of the estimated lowest level of the water. Increasing the Yield of Wells. When pumping is carried on from a well, water is drawn in from every direction, so that, if another well is sunk within the area from which the first well draws its supply, the yield of the latter will be affected.
The area drained by wells is an uncertain factor. To increase the yield of a well, adits or tunnels are often driven horizontally at the bottom, a series of wells being sometimes connected in this way to concentrate the pumping arrangements in one well.
Upland Surface Water. We come next to the consideration of upland surface water and large inland lakes as a source of supply. The former is the water obtained by storing in reservoirs the water which flows directly off the surface, and that which issues in springs, within uncultivated tracts of moorland.
Such water is wholesome and soft, and many large towns have availed themselves of this source of supply, including Liverpool (from Vyrnwy in Wales), Bradford, Birmingham (from Wales), Leicester, Derby, Nottingham and Sheffield (from the Derwent Valley).
<Callout type="important" title="Important: Soft Water from Upland Sources">Water from upland sources is soft and free from dissolved organic matters, making it ideal for drinking.</Callout>
The supply from lakes at a high altitude, safeguarded from pollution, is of a high order of purity. In the case of upland surface supplies, the “gathering ground”, or catchment area, is generally at a high altitude.
Thus, in the Derwent Valley scheme, before referred to, the catchment area forms part of the hilly country known as The Peak district, and for the most part is moorland. It has an area of nearly 32,000 acres, all over 580 feet above sea-level; 26,800 acres are at a height of over 1000 feet and 11,600 acres are above 1500 feet.
The catchment area in such schemes is the area of land draining towards a stream or streams, and is bounded by the watershed line —a line on opposite sides of which the water flows in opposite directions. The quantity of water available from such a source is estimated in either of two ways: (1) by ascertaining the rainfall in the district, and calculating the quantity available after deducting a certain amount, approximately 12 to 15 inches per annum of depth, for loss by absorption and evaporation, the loss due to absorption depending, of course, on the nature of the geological formation; (2) by gauging the flow of the streams flowing from the valley for as long a period as possible, and, if a storage reservoir is to be formed, deducting a small amount of evaporation.
The methods of gauging the flow are numerous, including weirs, floats, current meters, Pitot tubes, and other contrivances. From the weir the discharge can be calculated direct, but from the other methods the mean velocity is obtained, from which the discharge is found by the simple formula: Quantity = sectional area x velocity, orQ = AV.
The supply in all years is not the same and also is greater in winter than in summer; therefore large storage reservoirs are constructed to store up part of the winter supply, and the excess rainfall of wet years, in order to provide a supply in time of drought. Such reservoirs take the form of artificial lakes, made by damming the outlet of the valley.
The best site for a storage reservoir is a part of the valley where a comparatively short embankment will form a reservoir of large capacity. Compensation Water. Where a reservoir is formed on a stream used by mill owners, farmers and manufacturers, a certain part of the supply must be set aside to compensate them.
Usually about one-third to one-fourth of the whole available supply is set aside as compensation water, often stored in separate “compensation” reservoirs. The available capacity or storage room in a reservoir is the volume contained between the highest and lowest working levels, and is less than the total capacity by the volume left for the collection of sediment.
No hard-and-fast rule can be laid down for this, but it occupies in many good examples about one-sixth of the greatest depth of water at the deepest part of the reservoir. The storage reservoir is often adapted for use as a compensation reservoir also.
The storage capacity of an impounding or storage reservoir is very considerable. The two reservoirs which were constructed as a first instalment under the Derwent Valley scheme have a total capacity of 3940 million gallons.
River Water. A large number of towns obtain their water supply from rivers, but many have had to abandon this source owing to increasing pollution by sewage and refuse from manufacturers. London is the most notable example of a town taking its main supply from a river.
As the dry weather flow of the river may be insufficient, storage reservoirs may be formed to impound the flood waters. This is done in the case of London, two impounding reservoirs having been already provided at Staines, having a total area of 421 acres, with a capacity of 3300 million gallons, while reservoirs have been constructed at Chingford in Essex, with a total area exceeding that of Hyde Park.
Improved methods of purification and sterilisation have of late years made it possible to utilise rivers formerly regarded as unfit, so that there is no doubt that rivers will continue to afford a valuable source of supply for towns. With respect to supplies from rivers it is worth mentioning here the much-debated question of self-purification of rivers.
It has been pointed out that water taken some miles below a source of pollution is purer than a sample taken nearer the source of pollution, and the opinion has been expressed that a river flowing with a mean velocity of about 4 miles per hour will purify itself within a distance of about 16 miles from the point of pollution.
Some authorities say that when pathogenic or disease-bearing bacteria pass into relatively pure water, they are in an unnatural medium and die off. On the other hand, some conclude that sedimentation is the chief cause of self-purification. If this be so, there is no guarantee that harmful microbes will not be present and be carried down by the next flood which stirs up the river bed.
River water is usually softer than that derived from wells and springs. It seldom happens that the supply can be delivered by gravitation, but it is usually cheaper to pump the water than to bring it from a great distance by gravitation.
Stored Rainwater. The last source with which it is necessary to deal is that furnished by the storage of rainwater. It is a source which rarely needs to be considered and then only in the case of an isolated country house.
Generally, it is only used as a supplementary source, but at times it is the only one. Rainwater is very soft, therefore good for cooking and washing, but it is too soft to be very palatable, though somewhat improved by filtration.
It is only out in the open country that this source is used and the question of the rain taking up impurities in its fall does not arise. The collecting area is generally the roofs of the buildings. Slate should be chosen as the roof covering, it being less absorbent than tiles.
If the water is to be used for drinking purposes, there should be no lead gutters or flats, owing to the possibility of solvent action of the soft water. The gutters and rainwater pipes should be of iron, protected against corrosion preferably by a process such as that introduced by Dr. Angus Smith and consisting of dipping the articles, when hot, into a hot solution of bituminous composition,
Surface Water Collecting Grounds. If the roofs do not furnish a sufficient collecting area, a special collecting area must be formed. It should be carefully fenced in to guard it from pollution and may be of either of the following forms: (1) a sloping surface of concrete finished with cement or asphalt, falling to a collecting channel communicating with the storage tank; or (2) a similar surface covered with special tiles to form a false floor supporting about a foot of earth covered with grass.
The rainfall is partly filtered and purified by the earth and grass and passes through to the collecting floor below and thence into the channel. Any such surface should be isolated by a channel sunk around it and to a lower level.
Rainwater Separators. Where roofs are used as the collecting surface, gutters should be regularly cleansed and a rainwater separator can be used. This is a device for diverting the first part of the flow, charged with the washings of the roofs and gutters, to waste; it then automatically directs the after-flow to the storage tank.
An example is illustrated in Fig. 146, the working of which is clear from the sketch. In estimating the quantity that will be collected, allowance must be made for the quantity diverted to waste and for the loss by evaporation from the surface of the water in the underground storage tank.
The proportion of rainfall available for actual supply is approximately as follows: 1. With roofs and similar collecting surfaces, a separator being used, about 65 per cent. 2. Ditto, but without a separator, about 85 per cent. 3. With a grass-collecting surface (part of the rain being retained by the soil), about 60 per cent.
Rainwater Storage Tanks. The storage tank should preferably be capable of containing from 90 to 120 days’ requirements, according to the annual rainfall of the district, though much smaller tanks are often used.
The shape of the tank on plan is not important but it must be watertight, not only to keep the water in, but to keep impurities out. From the foregoing a formula can easily be deduced to give the area requisite for the collecting surface, or the quantity obtainable from any given surface.
Suppose we are dealing with case (1) above, in which 65 per cent. is obtainable. Let G = gallons required, or obtainable, per annum. A =area of collecting surface in square feet. R = rainfall in inches per annum. There are approximately 6-25 gallons in a cubic foot.
Quantity in cubie feet = area in square feet x rainfall in feet. G R . S05 = A x To * 65 per cent. + (Oh ees A x RX 65 X 6-25 —_ 12 x 100 from which, by simplifying, G = 0:34AR.
Transposing, G A= 034R For case (2) above, on the same reasoning we get—
G G=0« See 444 R and A oie and for case (3), G G =0°31AR and A = DSLR Example. A household of seven people, requiring 15 gallons per head per day, is to be supplied only from rainwater collected from roofs and similar surfaces, a separator being used. The average rainfall is 28 inches per annum.
Determine (1) the area of collecting surface necessary for the supply, and (2) the depth of a circular storage tank having an internal diameter of 16 feet, sufficient to hold 100 days’ supply.
G=7 X15 & 365 = 38,325 gallons per annum. R = 28 inches. G __ 88,825 0:34R 0-34 « 28 100 days’ supply, A= = 4026 sq. feet.
exelp L100 Contents of tank in cu. ft. = 3-06 = 1680 cu. ft. cubic contents Depth of tank = ————— area 1680 1680 ~ 0-7854D2 0-7854 x 16 x 16 = 8 feet 4 inches.
The collecting area must therefore be 4026 square feet and the tank must have a depth of 8 feet 4 inches below the overflow pipe.
Construction of Storage Tanks. The tank could be constructed of brickwork or concrete, lined with cement mortar or asphalt, or of ferro-concrete. It could be roofed over with ferro-concrete in any case and must have a good-sized manhole cover to provide means of access.
It should also have two or three ventilating pipes, carried up a foot or two above the ground and covered with conical shields to keep out impurities.
Small Filter Systems. As the water is to be used for drinking purposes, a filter should also be provided. The filters should be constructed of a bed of fine sand 1 foot 6 inches thick, supported by a bed of washed gravel 1 foot thick. Such an arrangement will efficiently filter about 400 to 450 gallons per square yard per day; therefore one about 2 feet square, the smallest size that could be constructed conveniently, would be of ample size.
To permit of cleansing, however, the filters should be in duplicate. Adjoining them should be a small filtered-water tank holding about three days’ supply. The general arrangement of the parts of such a scheme might be as shown in Fig. 150 in plan and section. The sketch is diagrammatic, and to simplify the pipe lines, the R.W. drain from the house is shown travelling parallel with the filtered water on its way back to the house.
Actually this will need adapting to the site and home plan. It will be seen that the rainwater pipes lead to a separator, marked R.W.S., from which one pipe enters the storage tank and another goes on to waste. From the storage tank a supply pipe is taken to a pair of filters, either of which can be thrown out of use by a valve, for the purpose of cleansing.
Each filter therefore has its own outlet pipe to the clean water tank. The overflow from this tank should go back into the rainwater storage tank and not be wasted.
Key Takeaways
- Artisan wells require mechanical assistance when their natural pressure is insufficient.
- Upland surface water sources are soft and free from organic matter, making them ideal for drinking.
- River water can be used as a supply source but requires purification methods to ensure safety.
Practical Tips
- Use mechanical pumps or other means of assistance when necessary to maintain the flow of water from wells.
- Regularly clean gutters and install rainwater separators to prevent contamination and ensure efficient collection.
- Construct storage tanks that can hold at least 90-120 days' worth of supply for reliability.
Warnings & Risks
- Be cautious when using river water as a source, as it may be contaminated by sewage or refuse from nearby industries.
- Ensure proper filtration and purification methods are in place to prevent the spread of disease.
Modern Application
While historical techniques like artesian wells and surface water collection remain relevant for certain remote areas, modern infrastructure has improved efficiency and safety. Understanding these principles can still be valuable for off-grid or emergency situations where traditional methods might be necessary.
Frequently Asked Questions
Q: How does the use of an Abyssinian tube well differ from a conventional well?
An Abyssinian tube well is driven into the soil using mechanical force, typically by dropping a heavy weight on a pulley system. This method avoids damaging the tube and allows for temporary or small-scale water supply in rural areas.
Q: What are the key factors to consider when selecting a source of surface water for a town's supply?
Key factors include the altitude of the catchment area, which affects the purity and softness of the water; the need to protect the water from pollution; and the availability of storage reservoirs to manage seasonal variations in water supply.
Q: How can one estimate the required collecting surface for rainwater collection?
The formula provided is G = 0.34AR, where G is the gallons per annum needed, A is the area of the collecting surface in square feet, and R is the annual rainfall in inches. This helps determine the necessary roof or specially designed collection area.