WO1995004194A1

WO1995004194A1 - Method and structure for extracting ground water in an area with impounded aquifers or with aquifers situated at different altitudes

Info

Publication number: WO1995004194A1
Application number: PCT/BE1994/000047
Authority: WO
Inventors: Frans De Vos
Original assignee: Frans De Vos
Priority date: 1993-07-28
Filing date: 1994-07-28
Publication date: 1995-02-09
Also published as: BE1007358A3; AU7181694A

Abstract

In the method according to the invention a network of water pipes (8) is arranged between at least two preselected locations where ground water can be pumped up in a manner such that each location of an ith(2 « i « N) layer is connected to a location of an i-1th layer which is situated at a higher altitude and has a ground water table at a higher altitude. The hydrostatic pressure of the water pumped up in the first location is used as energy source for pumping up water in the second location. In this way, by making an appropriate selection of locations, in particular first of all by remote sensing, water can be extracted with less energy or even without using any external energy source.

Description

"Method and structure for extracting ground water in an area with impounded aguifers or with aguifers situated at different altitudes"

The present invention relates to a method for extracting ground water in an area with impounded aquifers and/or with aquifers at different altitudes and having ground water tables situated at different levels by pumping up said ground water.

Pumping up ground water for producing irrigation and/or drinking water is performed all over the world but has the disadvantage of requiring quite a lot of energy. In the "Third World Countries" where there is a lack of irrigation and/or drinking water in the dry season, the shortage of water usually only exists on the surface in these barren areas, and there are usually sufficiently large water resources in the bottom, at a certain depth under the surface.

The above-mentioned water problem is locally solved in these countries by digging wells up to the water table or top of the water layer which is present, after which this water can be pumped up by means of human or animal power or by means of an elec¬ trical engine or combustion engine.

However, this temporary solution requires much force and energy so that this is an expensive way of extracting ground water, even in developed countries. In the so-called "Third World Countries, such a solution can usually even not be realized on a sufficiently large scale due to the expensive fuels or the lack of electri- city required for the pumping installations.

Moreover, in a hilly or mountainous region, the population always digs these wells in the valley since the distance between the water table and the ground surface is minimal there. This is disadvan¬ tageous in that a high population density is obtained around the wells, which results in overpopulation, over- grazing of the scarce vegetation by the cattle, desert formation, diseases, famine, the lacking of water supplies at higher levels, and so on.

In view of these major problems, an object of the present invention is to provide a method for extracting ground water which requires much less or even no supply of energy.

To this end, the method according to the invention is characterized in that a network of water pipes comprising at least one water pipe is arranged in said area, between at least two preselected locations where ground water can be pumped up, in a manner such that said locations are grouped in N > 2 layers each comprising at least one of said locations and such that each location of an i^th (2<i<N) layer is connected by one of said water pipes into a location of an i-l^th layer which is situated at a higher altitude and has a ground water table at a higher level than the ground water table at said location of said i^th layer, and water is supplied through said water pipe from said location of said i-l^th layer to an installation for pumping up ground water in said location of said i^th layer, the hydrostatic pressure of said water coming from said location of the i-l^th layer being used as energy source for this latter installation. In the method according to the invention, ground water is not only pumped up in lower locations but also in locations situated at higher altitudes. By using the hydrostatic pressure of the water pumped up at the higher locations for pumping up ground water in the lower locations the energy requirements can be reduced considerably. In this respect, it has been found that a small amount of water pumped up at the higher loca¬ tion(s) can provide the necessary energy for pumping up a much larger amount of water in the lower locations, depending on the altitude differences. Moreover, the risk of depletion of the aquifers at the lower locations is reduced due to the supply of water from the higher aquifers.

A further advantage of the method accord¬ ing to the invention is that pumping installations driven by the hydrostatic pressure of water can be kept very simple but reliable and are therefore ideal for use in "Third World Countries"

A very advantageous embodiment of the method according to the invention is characterized in that water is pumped up in at least one location of the first of said layers by siphoning the water through one of said water pipes towards at least one location of the second of said layers.

In this embodiment even no energy has to be supplied for pumping up ground water in the highest location so that the entire system can be designed such that it requires no additional supply of energy.

In a further embodiment of the method according to the invention, said locations are grouped in N>3 layers and said water which is supplied from a location of a j^th (l≤j≤N-1) layer to a location of an j+l^th layer comprises ground water pumped up in said location of said j^th layer.

As it will be shown hereinafter, starting from a small ground water production at the highest location, this ground water production can be multiplied at each layer of the network resulting in a much higher ground water production in the lower locations where the ground water reserves are usually larger. An important aspect of the method accord¬ ing to the present invention consists in the selection of the locations where ground water will be pumped up, i.e. in determining the best locations for pumping up ground water.

In an advantageous embodiment of the method according to the invention, the following steps are performed in order to preselect said locations : a) determining on the basis of hypsographics of aquifers established for example by remote sensing of said area, those locations having a ground water table, and b) determining on the basis of hydrogeological and/or geological maps, the locations where ground water can be pumped up.

At present, hypsographics of aquifers can be established by means of satellites. These hypso¬ graphics and possible further investigations for example by radar scatterometry give a good indication of the potentials of a certain area to produce ground water by applying the method according to the invention, i.e. of the available altitude differences of the aquifers. Further studies are then made on the basis of hydrogeological and/or geological maps to examine the possibilities of pumping up ground water from these aquifers. These studies also allow to determine whether the examined aquifers are confined or unconfined.

Preferably, a further selection is made amongst said locations where ground water can be pumped up, i.e. the right detailed locations where groundwater will be pumped up are determined on the basis of local investigations and studies, more particularly on the basis of electro-seismic investigations performed in particular to determine points or lines of intersection of fault surfaces or zones with the underground water table. Finally, pumping test are preferably performed in these locations i.a. in order to determine the ground water production potentials of these loca¬ tions. When designing said network of water pipes and selecting said locations, these ground water production potentials should be taken into account. In addition to the above described method, the present invention also relates to a structure for extracting ground water in an area as claimed in claim 9 and any subsequent claims.

Further particularities and advantages of the present invention will become apparent from the following description of some preferred embodiments of the method and the structure according to the invention. This description is only given by way of example without limiting the scope of the invention. The reference numerals relate to the annexed drawings wherein :

Figure 1 shows a vertical section of a structure for extracting ground water according to the invention.

Figure 2 shows a more detailed view of the embodiment in Figure 1.

Figure 3 shows a view of the part which is represented in Figure 2 by F3.

Figures 4-6 are variants of the embodiment in Figure 3. Figures 7 and 8 are schematic perspective views of possible structures for extracting ground water in a certain area according to the invention.

Figure 9 shows yet another variant of the embodiment in Figure 1. The present invention provides a method for extracting ground water in an area with impounded aquifers and/or with aquifers situated at different altitudes and having therefore ground water tables situated at different levels, which method allows to pump up said ground water while requiring only little or even no supply of energy. According to the present invention, a network of water pipes 8 is arranged in said area, between at least two preselected locations where ground water can be pumped up by either primary 1 or secondary pumping installations 12. Referring to Figures 7 and 8, the water pipes 8 are disposed between the locations in such a manner that these locations are grouped in N>2 layers, each comprising at least one of said locations and such that each location of an i^th (2<i<N) layer is connected by a water pipe 1 to a location of an i-l^th layer which is situated at a higher altitude and has a ground water table at a higher level than the ground water table at the location of the i^th layer.

The water pipes 8 arranged between the different locations are not only used to supply water to the lower locations but this water is more particularly also supplied to an installation for pumping up ground water in these lower locations, the hydrostatic pressure of this water being used as energy source for the pumping installations at the lower locations.

In a preferred embodiment of the inven¬ tion, the locations of the first and the second layer of the network are preselected in such a manner that the ground water table of a location of the first layer is situated at a level which is at least 30 m higher than the level of the ground water table of a location of the second level. From the second layer on, the differences between the ground water table levels in two successive locations of the network may be much smaller for example at least 4 to 5 m, since the hydrostatic pressure of the water supplied to the highest of these two successive locations can partially also be used as energy source for pumping up water in the lower locations. In other words, if said locations are grouped in N>3 layers, they are preferably selected in such a manner that the ground water table of a location of a k^th (2<k<N-l) layer of the network is situated at a level which is at least 4 m higher than the level of the ground water table of a location of a k+l^th layer to which said k^th location is connected. As can be seen in Figures 7 and 8, a network of pipes 1 divides the locations where ground water can be pumped up into N layers, in this case into three layers I, II and III. Figure 8 shows that the number of locations may increase towards the lower layers. In other words, the lower the locations of a layer, the more wells may be provided per layer. The important advantage of having more than two layers of locations consists in that only a small amount of water has to be pumped up at the location or locations of the first layer I, i.e. the highest location, in order to be able to pump up a large amount of water in the lowest locations. Indeed, each time the water is supplied from one layer to a subsequent layer of lower locations, the ground water which can be pumped up is multiplied with respect to the amount of water supplied from a higher location of a previous layer of the network.

Suppose for example a ^' total altitude difference of 500 and a water production at the highest location of 1 m³/h, the water tables being situated in each location at a depth of 50 m from the soil surface.

When using the hydrostatic pressure of this water to pump up water at one lower location, i.e. 500 m lower, a water production of 10 m³/h (+lm³/h = 11 m³/h) could in theory be achieved in this single lower location when taking no account of the energy losses due to friction, etc.

In case two additional locations are selected between the highest and the lowest location, and the total amount of water is each time supplied to a lower location, the theoretic maximum water production in each of these locations is as follows : Location 1 : lm³/h

Location 2 .¹⁶⁶ ' ^xl =3 .3m³/h _Location _! ■ 166.6xU⁺3.3⁾ ₌₁₈ . _{lm h}

Loca tion 4 _; 1 6.6x(3_o3+18.7)

It will be clear that such an exponential increase of water production possibilities may require more than one well in the lower locations to achieve such high pumping capacities.

In location 4, a total amount of about 100 m³/h (= 81,3 m³/h + 18,7 m³/h) would in theory be avail¬ able which is much more than the 11 m³/h which are theoretically available when using no intermediate locations. Instead of supplying all the water of a location to the subsequent lower location, a portion of this water can already be used at this location itself. The method according to the present invention allows therefore to exploit the higher aquifers and to pump up a large amount of ground water from the lower aquifers without requiring additional energy for these latter pumping installations.

In general, the water production is kept in each location below a maximum production capacity which is determined in such a manner that there is an equilibrium between the water supply to the aquifer and the water which is withdrawn therefrom. In this way, depletion of the aquifer is prevented.

In a preferred embodiment, no additional energy is even required for pumping up the ground water at the highest location. In this embodiment, the ground water is siphoned through the water pipe or pipes leading towards one or more locations of the second layer of locations.

Depending on the surface relief and the variation in ground water tables, either of the same or of different aquifers, the network of pipes may connect the different locations in parallel and/or in series.

An important aspect of the present inven¬ tion is the preselection of the locations where ground water can be pumped up, more particularly in such a manner that the necessary differences in altitude and water table levels as explained hereinabove can be achieved. Further, it is also important to determine whether the aquifers in those locations are either confined or unconfined aquifers. According to the inventor, impounded confined aquifers replenish them¬ selves partially by the rotation of the earth and the resulting centrifugal forces. Indeed, subsurface confined water streams are usually mutually connected. A first selection is made on the basis of hypsographics of aquifers established for example by remote sensing of the area (with infrared, micro-waves, etc.) with current means such as satellites. For this general location of the ground water tables, use can further be made of radar scatterometry. Indeed, in areas of variable soil moisture, which is a good guide to deeper ground water, radar scatterometry gives a good guide to moisture content.

In a next step, the locations where ground water can be pumped up are selected on the basis of hydrogeological and/or geological maps. Such hydrogeological assessment of ground water resources involves primarily the mapping of surface lithologist and structures to help assess the subsurface disposition of sedimentary aquifers. Preferably, a further selection is made amongst the locations where ground water can be pumped up, or in other words the right detail locations are determined, on the basis of local investigations and studies, more particularly on the basis of electro- seismic investigations. These electro-seismic investi- gations are performed to determine the most interesting location into detail, in particular by determining the point or line of intersection of the fault surface or zone with the underground water table. By these elctro-seismic investigations, it is further also possible to discover subsurface dams. In this way, the local ground water production potentials are determined. With respect to this further selection, it should be noted that images of various sorts, such as the electro- seismic images, but also radar images, provide abundant information that can be blended with observations on run-off versus infiltration potential in recharge areas. Here the intention is to concentrate on specific advan¬ tages offered by remote sensing. In this context the condition for subsurface water accumulation is involving various kinds of trap which are familiar to most geol¬ ogists. Among many sites for ground water accumulation are those provided by subsurface dams. These include faults that juxtapose aquifers with aquitards and igneous dykes, whose crystalline nature blocks flow where the dyke trends across the direction of subsurface flow. Both exhibit discontinuous linear features at the surface that are often more easily seen and extrapolated on images than on the ground.

While faults in sedimentary sequences provide opportunities for subsurface dams, in areas dominated by impermeable crystalline rocks the scatter¬ ing associated with faulting provides the only opportun¬ ity for infiltration and eventual recovery of ground water. Remote sensing is pre-eminent in delineat¬ ing such zones. Of special interest is the evaporation of large fracture systems from elevated areas of high precipitation to lower, drier ground. The fractures potentially can transfer water laterally over tens to hundreds of kilometres. Because the secondary porosity involved in fracturing can become sealed by fines, evaluating fracture zones requires consideration of rock types involved and the nature of weathering. In all climates micaceous rocks are easily sealed. In humid areas, or those once subject to high chemical weather- ing, feldspars in granitic and gneissic rocks, and ferromagnesian minerals in more mafic rocks, break down to clay that clog the potential pathways. In dry climates many granites break down by mechanical means to form gravelly regoliths and fracture zones still retain their permeability.

In all climates, inert quartzites and soluble carbonates are the ideal hosts for fracture controlled aquifers. Generally, the resolution of satellite imagery is too coarse resolution to permit detection of such features, through multispectral data may assist in delimiting lithologics with the contrasted engineering properties.

The structure according to the invention for extracting ground water according to the hereabove described method comprises installations for pumping up ground water in the different locations and a network of pipes as described hereinabove. These ground water pumping installations 12 of a location of an i^th (2<i<N) layer comprises a hydro-energy transformation device 9 for transforming the hydrostatic pressure of the water supplied from a location of an i-l^th layer into energy for pumping up ground water in the location of the i^th layer.

As shown in Figure 1, the structure for extracting ground water according to the invention may comprise a primary ground water pumping installation 1 in a location of a first layer, situated at a certain height indicated by altitude A, and which is composed of a pump 2 with a suction line 3 situated in a vertical primary well 4 and an outlet 5. Said primary well 4 hereby reached under the level of the underlying water table 6.

The outlet 5 preferably leads to a reser¬ voir 7 onto which a water pipe 8 is connected whose second end is situated at an altitude B, which is situated beneath altitude A of the primary pumping installation 1.

Said water pipe 8 ends in a hydro-energy transformation device 9 which for example consists of a turbine, a hydromotor or such, whereby this energy transformation device 9 has an outlet 10 through which the water, coming from the primary pumping installation 1, is carried off, for example to be used as irrigation water or drinking water.

A bypass may possibly be provided in the above-mentioned pipes which will be used when the pump

2 pumps up the water at a smaller height than it should, whereby in this case the pumped up water may end up directly in the water pipe 8 under a certain pressure.

The working of the structure of the invention is in principle essentially based on Bernouil- li's law, i.e. departing from the mass balance and the energy balance, the total energy in a liquid remains constant along a streamline.

If we take the altitude B at which the hydro-energy transformation device 9 is situated as the reference altitude or the altitude with zero height, the water table under the primary pumping installation will be situated at a height H, or, in other words, this water already has a certain amount of potential energy proportional to the height H at which the water is situated. If this water is pumped over a height HI to the surface by means of the primary pumping installa¬ tion 1, this requires an amount of energy in the form of fuel, electricity, solar panels or such which is propor- tional to the increase in potential energy of the water and thus proportional to the height HI. Possibly, an amount of water situated in higher reservoir can also be used as source of energy for this first pumping instal¬ lation 1. In particular, if a pressure line for supplying drinking water is already present at a higher altitude, or if such a line can be arranged, the hydro¬ static pressure of the water supplied through this line can also be used as a source of energy for the first pumping installation or installations situated in the location(s) of the first layer I. In this case, the first pumping installation(s) also comprises a hydro- energy transformation device for transforming the hydrostatic pressure of the water supplied to said first pumping installation(s) into energy for driving these latter installation(s) . Important to note is that when use is made of such pressurized water for driving the first pumping installation(s) , the differences in ground water table levels between the locations of the first layer I and those of the second layer II may be smaller than the 30m of the above described preferred embodiment and should preferably comprise at least the difference in ground water table level as indicated in the above preferred embodiment for the subsequent successive locations, i.e. for example at least 4 to 5m.

If the pumped-up water is subsequently led through a water pipe 8 to a lower altitude B, according to the above-mentioned law of Bernouilli, the total amount of energy at the inlet and the outlet of this water pipe 8 will remain constant, but the potential energy, i.e. the hydrostatic pressure, will be trans¬ formed in kinetic energy or thrust.

Both the supplied energy and the potential energy which is already present in the water determines the hydrostatic pressure of the water in the lower location. Compared to the amount of energy built up in this way, energy losses due to friction can be ignored. The obtained hydrostatic pressure can be transformed by a hydro-energy transformation device 9 in more conven- tional forms of energy. It can be transformed among others into mechanical energy by a hydromotor or into electric energy by means of a turbine. This electric energy can not only be used for pumping up water but may also be used for other applications such as for domestic use.

As shown more into detail in Figure 2, the hydro-energy transformation device 9 belongs to a secondary installation 12 for pumping up ground water in a location of a second or any subsequent layer of the network, i.e. situated at a lower altitude B. This pumping installation 12 gets the required work energy from the water coming from the primary pumping installa¬ tion 1, more particularly through the intermediary of the hydro-energy transformation device 9. As the pumped-up water from altitude A runs to altitude B, it builds up a thrust or hydrostatic pressure which supplies the required energy to pump up the water in the secondary well 4 which is situated at a lower altitude. Figures 3 to 6 show a number of embodi¬ ments for a secondary pumping installation 12.

Figure 3 shows a secondary pumping instal¬ lation 12 whereby the hydrostatic pressure of the water coming from the primary pump unit 1 is transformed by the hydro-energy transformation device 9 comprising a turbine generator 13 which drives an electric diving pump 15 in a well 4 via a control unit 14. The whole can hereby be supported by a battery 16 and/or solar cells 17.

In the variant of the secondary pumping installation 12 according to Figure 4, the hydrostatic pressure of the water coming from the primary pumping installation 1 is transformed in a rotation movement of a vertical shaft 20 by means of a mechanical turbine or blade wheel 18, either or not via a reducer 19. Said shaft 20 is connected at its end to a centrifugal pumps 21 which makes it possible to push up the water from the well 1 via a line 22.

According to another variant as represen¬ ted in Figure 5, a piston pump 23 is used to pump the water out of the well 1, whereby this piston 23 is driven for example by means of a crank-connecting rod system 24, which is driven in turn, in this case via a transmission 25 and/or possibly via a reducer by a mechanical turbine or blade wheel 26 which gets its energy from the hydrostatic pressure of the incoming water.

According to another variant, shown in Figure 6, use is also made of a piston pump 23, but in this case it is driven by a piston engine 27, for example with a double acting cylinder. Two control lines 28, 28A are hereby alternately supplied with water by a control unit 29. Naturally, the piston engine 27 is not restricted to an engine with a double acting cylinder, but it may consist of two single acting cylinders, a hollow cylinder or the like.

Figure 7 represents a possible structure for extracting ground water according to the invention which is composed of a primary pumping installation 1 and a series connection of several secondary pumping installations 12. Every secondary pumping installation 12 hereby gets its energy from the hydrostatic pressure of the water which is pumped up in location at one or several higher altitudes. With this device, one has the choice at every secondary pumping installation 12 to use, on the one hand, either the water pumped up to this altitude or the water coming from the higher altitude as irrigation and/or drinking water or, on the other hand, to send all the water available at this altitude to a subsequent pumping installation at a lower altitude.

As shown in Figure 8, also a parallel connection of secondary pumping installations 12 is possible. Hereby, the energy for two or several pumping installations 12 is supplied by the hydrostatic pressure of the water coming from a pumping installation 1 at a high altitude.

Naturally, also a combination of series and parallel connections is possible, as a result of which the device can be entirely integrated in the environment and can be entirely adapted to specific environmental factors such as geography, population density, etc. According to a particular embodiment, as represented in Figure 9, the primary pumping installa¬ tion 1 and water pipe 8 are combined with a siphon 30. Said syphon 30 is made by connecting a bypass line 31 with a non-return valve 32 in parallel with the pump 2. When the device is started by means of the pump 2 in the primary pumping installation 1, the longest leg 33 of the syphon 30 which is situated downstream of the non-return valve 32 is filled with a continuous water column. Because of the difference in levels of said water column in the longest leg 33 of the syphon 30 a suction force is obtained at the non-return valve 32, as a result of which the latter opens, and subsequently a suction force in the shortest leg 34 of the syphon 30, situated upstream of the non-return valve 32. Subsequently, the pump 2 may be disconnec¬ ted and the water, due to the weight of the hanging water column in the longest leg 33 of the syphon 30, is continuously siphoned over from the primary well 4 to the lower altitude B as long as the water column is not interrupted.

In case the primary 1 and the secondary pumping installation 12 are arranged above the same aquifer, as this is the case in Figure 9, a further suction line can be inserted in the well of the primary pumping installation 1 and connected with an additional pipe to the well of the secondary pumping installation, more particularly to a line extending to the bottom of this latter well. In this case, a further siphoning effect can be achieved. From the above description, it will be clear that the invention is by no means limited to the embodiments described above and represented in the drawings ; on the contrary, many modification can be applied to the described methods and structures for extracting ground water according to the invention without leaving the scope of the present invention.

Claims

CLAIMS i 1. A method for extracting ground water in an area with impounded aquifers and/or with aquifers situated at different altitudes and having therefore ground water tables situated at different levels by pumping up said ground water, characterized in that a network of water pipes comprising at least one water pipe (8) is arranged in said area, between at least two preselected locations where ground water can be pumped up, in a manner such that said locations are grouped in N > 2 layers each comprising at least one of said locations and such that each location of an i^th (2<i≤N) layer is connected by one of said water pipes (8) into a location of an i-l^th layer which is situated at a higher altitude and has a ground water table at a higher level than the ground water table at said location of said i^th layer, and water is supplied through said water pipe (8) from said location of said i-l^th layer to an installation (12) for pumping up ground water in said location of said i^th layer, the hydrostatic pressure of said water coming from said location of the i-l^th layer being used as energy source for this latter installation (12).

2. A method according to claim 1, charac- terized in that said locations are preselected in such a manner that the ground water table of a location of the first layer of the network is situated at a level which is at least 30 m higher than the level of the ground water table of a location of the second layer.

3. A method according to claim 1 or 2, caracterized in that the ground water table of a loca¬ tion of a k^th (2<k<N-l) layer of the network is situated at a level which is at least 4 m higher than the level of the ground water table of a location of a k+l^th layer to which said k^th location is connected.

4. A method according to any one of the claims 1 to 3, characterized in that water is pumped up in at least one location of the first of said layers (I) by siphoning this water through one of said water pipes (8) towards at least one location of the second of said layers (II) .

5. A method according to any one of the claims 1 to 4, characterized in that said locations are grouped in N>3 layers and said water which is supplied from a location of a j^th (l≤j≤N-1) layer to a location of a j+l^h layer comprises ground water pumped up in said location of said j^th layer.

6. A method according to any one of the claims 1 to 5, characterized in that at least one location of a j^th (l≤j≤N-1) layer is connected by at least two of said water pipes (8) to at least two locations of a j+l^th layer, water being supplied through these latter water pipes (8) from said location of said location of the j^th layer to respective installations (12) for pumping up ground water in said two locations of said j+l^h layer, the hydrostatic pressure of said water being used as energy source for these latter installations (12) .

7. A method according to any one of the claims 1 to 6, characterized in that in order to preselect said locations, the following steps are performed : a) determining on the basis of hypsographics of said aquifers established for example by remote sensing of said area, those locations having a ground water table, and b) determining on the basis of hydrogeological and/or geological maps, the locations where ground water can be pumped up.

8. A method according to claim 7, charac¬ terized in that a further selection is made amongst said locations where ground water can be pumped up on the basis of local investigations and studies, more particu¬ larly on the basis of electro-seismic investigations performed in particular to determine points or lines of intersection of fault surface or zones with the under¬ ground water table, ground water being preferably pumped up at the location of these points or lines of intersec¬ tion.

9. A structure for extracting ground water in an area with impounded aquifers and/or with aquifers situated at different altitudes and having therefore ground water tables situated at different levels by pumping up said ground water, characterized in that said structure comprises at least two installations (1, 12) for pumping up ground water in different loca¬ tions in said area, and a network of water pipes com¬ prising at least one water pipe (8) for connecting said locations in such a manner that said locations are grouped by said network in N>2 layers each comprising at least one of said locations and such that each location of an i^th (2<i≤N) layer is connected by one of said water pipes (8) to a location of an i-l^th layer which is situated at a higher altitude and has a ground water table at a higher level than the ground water table at said location of said i^th layer, the ground water pumping installation (12) of a location of an i^h (2<i<N) layer comprising a hydro-energy transformation device (9) for transforming the hydrostatic pressure of the water supplied from a location of an i-l^th layer into energy for pumping up ground water in said location of the i^th layer.

10. A structure according to claim 9, characterized in that said ground water pumping instal¬ lations (1, 12) are connected by said network of pipes (8) in series and/or in parallel.

11. A structure according to claim 9 or 10, characterized in that at least one of said ground water pumping installations (12) comprises a diving pump (15) while the hydro-energy transformation device (9) thereof comprises a turbine (13) for supplying electric current to said pump, said turbine (13) being either or not supported by solar cells (17) and/or by a battery (16).

12. A structure according to any one of the claims 9 to 11, characterized in that at least one of said ground water pumping installations (12) com¬ prises a centrifugal pump (21) while the hydro-energy transformation device (9) thereof comprises a mechanical turbine or blade wheel (18) with vertical shaft (20) , either or not provided with a reducer (19) , for driving said centrifugal pump.

13. A structure according to any one of the claims 9 to 12, characterized in that at least one of said ground water pumping installations (12) co pri- ses a piston pump (23) while the hydro-energy transfor¬ mation device (9) thereof comprises a crank-connecting rod system (24) for driving said piston pump (23) and a mechanical turbine or blade wheel (26) for driving said crank-connecting rod system (24) .

14. A structure according to any one of the claims 9 to 13, characterized in that at least one of said ground water pumping installations (12) compri¬ ses a piston pump (23) while the hydro-energy transfor¬ mation device (9) thereof comprises a piston engine (27) for driving said piston pump (23) , said piston engine (27) being driven by the thrust in the water which is alternately led by a control unit (29) via two control lines (28, 28A) .

15. A structure according to claim 14, characterized in that said piston engine (27) consists of a double acting cylinder.

16. A structure according to claim 15, characterized in that said piston engine (27) comprises two single acting cylinders.

17. A structure according to claim 15, characterized in that said piston engine (27) consists of a bellows cylinder.

18. A structure according to any one of the claims 9 to 17, characterized in that the ground water pumping installation (1) of a location of the fist layer (I) of the network comprises a pump (2) connected by one of said water pipes (8) to a ground water pumping installation (12) of a location of the second layer (II) of the network, this latter water pipe (8) and said pump (2) being combined with a syphon (30) .

19. A structure according to claim 18, characterized in that said syphon (30) consists of a bypass line (31) with a non-return valve (32) connected in parallel with said pump (2) of the ground water pumping installation (1) of said location of the first layer (I) of the network.