Title of Invention

METHOD AND DEVICE FOR COLLECTING FRESH WATER

Abstract

A method of collect1ng fresh water coming from an undersea fresh water spring (1) at the bottom of the sea, in which the fresh water is collected in a first duct (2) whose bottom end (22) is placed facing said spring and surrounds in leakt1ght manner at least part of the orifice of the spring, is characterized in that the fresh water is collected at a flow rate that is less than or equal to a given rate and in a second duct (3) of diameter smaller than the diameter of said first duct, the second duct having its top end (32) opening out at the surface and its bottom end (31) extending inside said first duct, and when the flow rate from the spring exceeds said given rate, the excess flow from the spring overflows from the top end (22) of said first duct into an open-bottomed tank (4) containing air (6), said tank holding air capt1ve above an air/water interface (6) situated inside said tank, and the top end (2 ) of said first duct being situated beneath the level of said air/water interface (6) inside said tank.

Full Text

A METHOD AND A DEVICE FOR COLLECTING FRESH WATER The present invention relates to a method of collecting fresh water coming from an undersea fresh water spring. The present invention also relates to a fresh water catchment device. Such fresh water springs are undersea resurgences of fresh water at the bottom of the sea. Various methods and devices are already known for collecting fresh water from undersea springs, such as those described in particular in French patent application FR 2 701 974 or in international application WO 00/79309 in the name of the Applicant. In those methods and devices, a tank structure having its concave side facing downwards is put into position over the fresh water spring, and the fresh water is trapped in the top portion of the tank structure because its density is lower than that of sea water. That structure has an open bottom so as to enable sea water to be evacuated and/or so as to enable it to be filled with fresh water. There are several difficulties in implementing a method and a device for collecting fresh water in satisfactory manner at sea. Firstly, it is necessary for the catchment device to be simple and easy to install on the sea bottom and to be inexpensive to make. Secondly, the method and the device for collecting fresh water must avoid mixing between the fresh water and sea water so as to ensure that pure fresh water is collected. Finally, it is necessary to ensure that the method and device do not disturb the hydraulic load on the fresh water spring. The fresh water from an undersea spring makes its way through natural underground ducts, and it is possible to disturb the spring and possibly to interrupt it irreparably by exerting excessive hydraulic back pressure on the flow orifice of the spring, leading to damage or modifications in said natural underground ducts that are fragile. For any given spring, hydrogeologists can determine a value for a limited back pressure that can be tolerated and that should not be exceeded in order to avoid disturbing the flow from said spring, with said hydraulic back pressure generally lying in the range 0 to 0.1 (104 pascals (Pa)). In the absence of any catchment device, the hydraulic pressure at the outflow orifice from the fresh water spring depends on the depth of water situated above said orifice, where this pressure increases at a rate of 1 bar per 10 meters of depth. This hydraulic pressure is independent of the natural flow rate of the spring. However, in the presence of a catchment device, head losses arise due to friction acting on the water flowing through the device. The friction head loss is proportional to the rate the water flows through the catchment device. Fresh water springs can be subject to natural variations in flow rate, in particular in the event of flooding, and such variations can amount to the flow rate being multiplied by a factor of 5 or even 10. These variations in flow rate lead to hydraulic back pressure in the spring due to the increase in head loss associated with the water passing through the ducts of the catchment device, when installed.. More generally, and in practice, it is difficult to combine the two conditions of not mixing sea water with the fresh water and of avoiding excessive hydraulic back pressure in the spring while nevertheless implementing a catchment device that is simple and inexpensive to make and to install, and that is technically reliable, without requiring any energy to be supplied, e.g. for pumping. The methods and devices described in FR 2 701 974 are specially adapted to collecting fresh water along the coast and cannot be used with springs situated far out to sea, at the sea bottom and at a great distance from the coast. In any event, those collection methods and devices do not make it possible to avoid mixing between salt sea water and fresh water while it is being collected. In WO 00/79309, various methods and devices for collecting fresh water are described, in which fresh water is collected in an open-bottomed tank in the form of a bell or cap overlying the fresh water spring at the bottom of the sea, together with a pipe rising from the top of said tank to the surface of the sea. In a first embodiment of WO 00/79309, the open bottom of the tank is moored to the sea bottom at a certain distance above the sea bottom, thus making it easier to install the device in the event of the sea bottom being cluttered, e.g. by rocks or uneven relief. Under such conditions, it is nevertheless not possible in practice to avoid sea water mixing with fresh water inside the tank. In a second embodiment of WO 00/79309, the open bottom of the tank fits against the sea bottom in leaktight manner so as to avoid salt sea water mixing with the fresh water after an initial stage of emptying the tank which is initially filled with sea water. In that second embodiment, check valves are provided to allow water to be exhausted in the event of the flow rate from the spring increasing, thereby avoiding excessive hydraulic back pressure being applied to the spring. Nevertheless, the flow rate increases that occur in practice are such that it is necessary to provide a very large number of check valves. Unfortunately, these valves are relatively fragile mechanical devices that are calibrated for a given flow rate, and they also increase the cost of the device. Those collection methods and devices are therefore unsatisfactory, both from an economic point of view and from a technical point of view. In addition, the catchment device is not easy to install when the sea bottom close to the spring is not level since, under those circumstances, it is difficult to provide leaktightness between the sea bottom and the open bottom of the tank, which has a diameter that is relatively large. To summarize, prior methods and devices for collecting undersea fresh water present the following omissions and drawbacks: • either the system is completely leaktight against salt water, but any increase in the flow rate of fresh water in the event of flooding (where the flow rate can vary in a ratio of 1 to 10 over a few hours) leads to an increase in head loss associated with friction and to a rise in the hydraulic pressure in the spring that can lead to irreparable damage in the natural duct; • or the system requires open surfaces to be present in the surrounding salt water whenever it is episodically evacuating excess fresh water, thereby leading to contamination at the fresh water/salt water interface; and • finally, pumping in those prior systems can lead to negative pressure variations in the event of an increase in the flow rate of the spring, and can thus lead to a phenomenon whereby salt water is sucked in and then pollutes the pipe upstream. The object of the present invention is thus to provide methods and devices for collecting fresh water that are simple and inexpensive to make and install, that operate in a manner that is technically reliable over time and that combine the advantages of no mixing of sea water and fresh water, with no risk of excessive hydraulic back pressure in the spring, so as to avoid irreparably damaging the natural ducts, and that does not require any energy to be supplied, in particular by pumping. To do this, in a first aspect, the present invention provides a method of collecting fresh water coming from an undersea fresh water spring at the bottom of the sea, in which the fresh water is collected in a first duct t1 whose bottom end is placed facing said spring and surrounds in leaktight manner at least part and preferably all of the orifice of said spring. According to the method of the invention, the fresh water is collected at a rate that is less than or equal to a given rate and in a second duct t2 of diameter smaller than the diameter of said first duct, the second duct having its top end opening out at the surface and its bottom end extending inside said first duct over a length l and when the flow rate from the spring exceeds said given rate, the excess flow from the spring overflows from the top end of said first duct into an open-bottomed tank containing air, said tank holding air captive above an air/water interface situated inside said tank, and the top end of said first duct being situated beneath the level of said air/water interface inside said tank. It will be understood that the top end of said first duct opens out into the inside of said tank. This avoids any contact, and thus any pollution, between the fresh water and the salt water, while also limiting the hydraulic back pressure on the spring that is generated by the device. In a preferred implementation, the fresh water is collected at the end of said second duct at a rate corresponding to the mean flow rate of said fresh water spring. As explained below, said first duct tx is dimensioned and the value of H is determined in such a manner that: P1 X g X H + G + P1 where: • P1 = density of fresh water; • g = 9.81 meters per second per second (m/s2) ; • P1 = head loss in said first duct when the fresh water flows at said given, flow rate, in particular the mean flow rate of the spring; • APS = the limiting hydraulic back pressure that can be tolerated by said fresh water spring; this is a value that known or that can be determined for any spring, where APS is prefercably less than or equal to 104 Pa; and • G = the Archimedes' thrust gain associated with the phenomenon of replacing the weight of a column of sea water with the weight of the column of fresh water in said first duct. This gain G can be written as follows: G = (p1 X g X H1) - (p2 X g X H1) where: • H1 = the height of the air/water interface in the tank relative to the sea bottom at the spring; and • p2 = the density of sea water. The height H and the dimensions of the first duct are thus determined as a function of APS. According to another preferred characteristic of the method, in order to ensure that the second pipe t2 remains continuously in contact with the water flowing in said first duct t1 said length t is greater than or equal to H. In general, the limiting hydraulic back pressure (APS) that can be tolerated at the spring is less than equal to 0.1 bar (104 Pa). In another aspect of the invention, the present invention provides a devices for collecting fresh water coming from an undersea fresh water spring and that is suitable for use in a method of the invention, the device comprising: • a first duct t1 of diameter at its bottom end enabling it to cover said spring in full or in part; • a second duct t2 of diameter at its bottom portion less than the diameter of the top portion of said first duct t1; and • an open-bottomed tank suitable for co-operating with said second duct t2 in such a manner that when the bottom end of said second duct t2 is immersed inside said first duct, itself being positioned facing said spring, with its bottom end surrounding said spring in leaktight manner in full or in part, then the top end of said first duct t1 is covered by said tank and opens out to the inside thereof via said open bottom, the solid wall of said tank being leaktight so as to be capable of holding air captive between said tank wall and the level of water inside said tank. In particular and advantageous embodiments of the device of the invention: • the device includes first mooring means for mooring said first duct t1 to the sea bottom and/or to a baseblock resting on the sea bottom, and second mooring means for mooring said second duct and/or said tank as moored in this way to the sea bottom and/or to said first duct; • said tank is secured to said second duct and surrounds it in leaktight manner; • said tank is constituted by a canopy, which may in particular be flexible or rigid, and that has said second duct t2 passing through it in leaktight manner; • said canopy has a top portion in the form of a substantially hemispherical cap or bell; • said flexible canopy is suitable for adopting the shape of a substantially hemispherical cap or bell at the bottom of the sea when it is moored and compressed air is injected under said canopy; • the device includes means for injecting compressed air into the inside of said tank; • the diameter of the open bottom of said tank is such that the area of its opening is not less than the section area of the spring; • the length of said first duct t1 is greater than or equal to the height of natural or other objects and/or relief lying on the sea bottom in the vicinity of said undersea spring in a radius corresponding to that of the open bottom of the tank; • the top portion of Said first duct t1 surrounding the bottom portion of said second pipe is flared, being funnel-shaped, with its smaller base at the bottom; this embodiment encourages good overflow of the excess fresh water into the tank, whenever that is necessary; • the diameter D1 of said first duct t1 at the bottom end of said second duct t2 is such that the annular area between said first and second ducts at this level is greater than or equal to the section area of said first duct (i.e. greater than D12/4 for a circular section); • said second duct rises directly to the surface, preferably substantially vertically from the top end of said first duct, and the fresh water is recovered at the surface and transported to land, preferably by ship; and • said second duct can be lowered to rest on the sea bottom so as to reach the coast, thereby conveying the water to the coast, preferably opening out on land at an altitude that is lower than sea level.. The present invention also provides a method of putting a fresh water collection device into place, the method being characterized in that the following steps are performed: 1) positioning said first pipe t1 above said undersea fresh water spring and mooring said first pipe t1 to the sea bottom in such a manner that the bottom end of said first pipe t1 surrounds said fresh water spring in leaktight manner in full or in part; 2) lowering said second pipe t2 and said tank to the sea bottom and mooring them to the sea bottom and/or to said first pipe t1 in such a manner that the bottom end of said second pipe t2 is contained inside the top portion of said first pipe t1; and 3) injecting air into the inside of said tank in such a manner as to obtain an air/water interface at the top portion of said first pipe at a said height for the air/water interface inside said tank, preferably at a said height H. The method and device of the invention for collecting fresh water are advantageous on several grounds. Firstly, they enable fresh water to be collected while preventing any contact and thus any mixing between fresh water and salt water, thereby serving to collect fresh water that is pure. The air inside the tank creates an interface through which the salt water cannot pass, so it cannot contaminate the fresh water that is collected via said second duct t2. Secondly, the method and the device of the invention enable fresh water to be collected, with fresh water being collected at a substantially constant rate and without any risk of excessive back pressure, thereby avoiding any hydrogeologcil disturbance to the spring that might result therefrom, and this is achieved without using any mechanical means for regulating the rate of flow inside said first and second ducts, i.e. means such as exhaust check valves, and in particular means at the junction between said first and second ducts or in the tank. Overall, the method and the device of the invention enable the rate of flow taken from the spring and the hydraulic load on the outlet of the spring to be adjusted independently of the natural flow rate of the spring, while avoiding any risk of salt water penetrating into the pipe leading to land via said second duct in the event of excessive pumping, with this being achieved by control means based on a principle that is hydraulic and not mechanical, and thus without requiring additional mechanical control means to be implemented. As shown in Figure 1, if the fresh water flows from the spring at a rate exceeding the given limit rate, then it can follow two paths at the top end of said first pipe, namely: • a first path C2 whereby it rises to the surface via said second duct t2 at the given rate, preferably the mean delivery rate of the spring; and • a second path C1 whereby it passes into the annular space inside said first duct t1 and outside said second duct t2 at a rate that corresponds to the difference between the delivery rate of the spring and said given rate. It is possible to determine the dimensions of the ducts t1 and t2 and the height H between the air/water interface in the tank and the top end of the first pipe in such a manner that when the flow rate from the spring corresponds to the desired extraction rate, in particular to the mean flow rate of the spring, then all of the fresh water follows the path C2 via said second duct and the back pressure at the spring remains less than or equal to the limiting back pressure that the spring can tolerate. Adjusting the height H of the interface has a direct influence on the flow rate passing into the second duct t2 and also on the value of the back pressure applied to the spring. In practice, it is possible to proceed as follows: 1) the mean flow rate of the spring is measured; and 2) the height H is determined in such a manner that the expression P1 x g x H + G + P1 is true. The head losses P1 in said first pipe t1 are associated with the shape and, of course, the surface state of the material constituting the inside walls of said ducts, and also on the speed of the water flowing in said first pipe. Thus, when there are floods and the flow rate of fresh water from the spring increases, it is observed that the rate flowing through said second duct t2 is constant regardless of the flow rate from the spring, and the height H remains constant, with the excess flow passing along said second path C1. The fresh water flows out from the top end of said first duct t1 into the air along the outside wall of said first duct t1 and then into the salt water at the air/water interface in the bottom portion of said tank, thus having the effect of expelling an equivalent quantity of water through the bottom portion of said tank, with the volume of air thus remaining constant inside said tank and with the hydraulic back pressure that can be accepted by the spring never being exceeded. The value H remains constant. Nevertheless, in the event of water being extracted accidentally at a rate greater than the natural delivery rate from the spring, the fresh water level in the top portion of said first duct will go down and pass beneath the bottom end of said second duct t2, thereby having the effect of causing air to enter into said second duct t2 (3) and not salt water since the system becomes temporarily unprimed. In practice, said tank is lowered to the sea bottom while it contains no air and thus while it is full of sea water, and when it is in position over the top end of said first duct t1, air is injected into the inside of the tank and it is the quantity of air injected into said tank that serves to adjust the height H. It will be understood that the shape and the magnitude of the volume of said tank have no effect on the hydraulic catchment principle applied to the fresh water, so they are as small as possible and best adapted to the ease with which said tank can be installed on the sea bottom. The bottom end of said first duct is sealed by ensuring that the periphery of the duct matches the outline of the relief of the sea bottom around the spring. Said first duct can be held to the sea bottom by ballast weights or by a peripheral fender resting on the bottom. To minimize head losses in the first duct t1 and thus the back pressure they induce on the: spring, it is advantageous to use a pipe t1 that is as short as possible and of the greatest possible diameter. In practice, the first pipe t1 extends over a height of water that is preferably greater than the altitude of the relief on the sea bottom in the immediate vicinity of the spring and/or of obstacles and clutter, whether natural or otherwise, as constituted mainly by rocks. The open bottom of the tank can thus be secured to the sea bottom and/or to said first, pipe, where it is free at a certain distance above the spring, and in particular above said relief and/or objects, whether natural or otherwise, in the vicinity of the spring. Other characteristics and advantages of the present invention appear in the light of the following detailed description of an embodiment made with reference to accompanying drawings, in which Figures 1 and 2 show respectively a catchment device: installed on the sea bottom over an undersea fresh water spring (Figure 1), and the tank 4 (Figure 2). A fresh water catchment device has been made that is adapted to collect fresh water from the so-called "la Mortola" spring situated in Italy between Menton and Vintimille. That spring presents an average fresh water flow rate of 100 liters per second (L/s). Hydrogeologists have determined that the maximum hydraulic back pressure that that spring can tolerate is 0.1 bar. That spring is situated at a depth of 36 meters (m) and its orifice opens out at the base of blocks of rock that are 5 m high. It is situated at 800 m from the shore. Given the configuration of the orifice of the spring and the obstacles surrounding said orifice on the sea bottom, a first duct t1 (2) having a total height of 7 m was used, presenting a main tubular portion with a circular section having a diameter of 0.4 m. Said first duct t1 (2) was terminated at its bottom end 2, by a downwardly-flared funnel, having a bottom end in the form of a circle of diameter 1.3 m, so as to ensure that said spring was indeed surrounded, given the shape of the outlet orifice from the spring. The bottom first funnel 21 is made of rigid sheet material, which could be plastic or metal, surrounding the circular end of the main - portion of said first duct t1 (2) at its bottom end. _Said bottom funnel 21 has a height of 4 m. In its top portion, said first duct t1 (2) presents a second funnel 22 having minor and major bases that are circular in section, likewise made by disposing metal sheet or thermoformed plastic around the top end portion of said first duct. The upwardly-flared shape of the top portion of said first duct is to facilitate overflow of the excess fresh water from the spring inside the tank 4. The open bottom base of the first funnel 21 is secured to a baseblock 8 resting on the sea bottom and surrounding the spring. It could also be surrounded by a fender of sand or concrete or by some other peripheral ballast weight for establishing leaktightness relative to the sea bottom. The main portion of said first duct t1 (2) could be constituted by a flexible hose or a rigid pipe. It extends vertically upwards from said spring. Said tank 4 is constituted by a rigid top canopy 41 pierced in its center by a second duct t2 (3) that is preferably rigid, and has a diameter of 0.4 m. The rigid canopy constituting the top portion of said tank 4 forms a hemispherical cap 41 of diameter 1.8m and its bottom is extended by a frustoconical surface referred to below as a cone 42 that presents a height of 2 m around said first duct. It is through the open bottom of said cone 42 that surplus fresh water escapes in the event of flooding from the spring. In Figure 1, the base of the cone 42 is held by mooring means 72 to said first duct t1 (2) in such a manner that the base of said cone is situated at a height of 5 m above the sea bottom. The presence of the cone 42 is optional. It is possible for the bottom of the cap 41 to be moored directly to said first duct. The portion of said second duct t2 (3) situated inside said tank 4 has a length of 1 m. When 2 m3 of compressed air is injected under said canopy constituting the tank 4, after its open bottom 43 has been moored to the sea bottom or to the first duct, a length l of 0.3 m of the bottom portion 31 of said second duct t2 (3) can be inserted into the top portion of said first duct t1 (2). The height H between the air/water interface 6 inside the tank 4 and the air/water interface at the top end of said top funnel 22 of said first duct t1 (2) is 0.2 m. The bottom end 31 of said second duct t2 (3) has webs or gussets 9 at its periphery serving to reinforce and to center said bottom end of the second duct inside said funnel 21 at the top end of said first duct. About halfway up said first duct, Figure 1 shows a flow meter 10. It is the characteristics of the flow meter 10 that led to a portion of said first duct t1 (2) being narrower at this level, simply for the purpose of matching a flow meter 10 that was available. Reinforcing elements 71 are also fitted to the base of said first duct t1 (2) and serve likewise for mooring purposes by being bolted to a baseblock 8 surrounding the outlet from the spring 1 in leaktight manner. The value for H and the dimensioning of said first and second pipes 2 and 3 and also of the volume of compressed air injected into said tank 4 were determined as follows: When the spring is in flood and its delivery rate exceeds 100 L/s, in particular when it reaches its maximum rate of 500 L/s, the flow passing along said pipe t2 via the path C2 remains at about the mean rate of 100 L/s, while the flow of fresh water following the path C1 in the annular space between the bottom end of said second pipe t2 and the top end of said first pipe t1 generally has a maximum value of 400 L/s. The spring water rising along said first duct t1 (2) encounters two possible paths C1 and C2 at the base of said second duct t2 (3). Via the path C1, the fresh water overflows from the top end of said first duct t1 (2) and flows in air along the outside wall of said top second funnel 22 and then flows into the salt water, thereby expelling a quantity of fresh water through the bottom portion of the tank such that the volume of compressed air 5 contained in the tank 4 remains constant, as does the height H. Via the path C2, the fresh water passes into said second duct t2 (3) flowing at the spring's mean rate of 100 L/s, given the dimensioning of said first pipe and the determined value H, and also because the maximum hydraulic back pressure that can be tolerated by the spring is 0.1 bar. The fresh water always follows the path that presents it with the least "resistance". For the path C1 this "resistance", starting from the air/water interface, is essentially determined by the energy p1gH where p1 = the density of fresh water, and g = 9.81 m/s2. It can thus be seen that when H increases, passage via C2 is encouraged. For the path C2, the "resistance" encountered by the fresh water, when flowing along the pipe t2, is equal to the head losses generated by its flow in said pipe t2, but is calculated in conventional manner as a function of the diameter and the length of said pipe t2 and of the flow rate. The rigid canopy 41 and the cone 42 constituting said tank 4 can be made of a plastics material, a composite material, or of steel. As mentioned above, this fresh water catchment system can operate without a pump since given that the density of fresh water is less than that of sea water, the fresh water rises naturally to the surface. Nevertheless, if the second duct t2 (3) is taken back down to the sea bottom in order to reach the coast, then the altitude at which said second duct t2 (3) opens out must be far enough below sea level in order to compensate at least for the head losses in the pipe t2. WE CLAIM : 1. A method of collecting fresh water coming from an undersea fresh water spring (1) at the bottom of the sea, in which the fresh water is collected in a first duct t1 (2) whose bottom end (21) is placed facing said spring and surrounds in leaktight manner at least part and preferably all of the orifice of said spring, the method being characterized in that the fresh water is collected at a flow rate that is less than or equal to a given race and in a second duct t2 (3) of diameter smaller than the diameter of said first duct, the second duct having its top end (3) opening out at the surface and its bottom end (31) extending inside said first duct, and when the flow rate from the spring exceeds said given rate, the excess flow from the spring overflows from the top end (22) of said first duct into an open-bottomed tank (4) containing air (6), said tank holding air captive above an air/water interface (6) situated inside said tank, and the top end (22) of said first duct being situated beneath the level of said air/water interface (6) inside said tank. 2. A method as claimed in claim 1, wherein the fresh water is collected at the end of said second duct at a rate corresponding to the mean flow rate of said fresh water spring (1) 3. A method as claimed in claim 1 or 2, wherein said second duct extends inside said first duct over a length / that is greater than or equal to the height H of the top end (22) of said first duct above the leveL of said air/water interface (6) inside said tank. 4. A method as claimed in any one of claims 1 to 3, wherein the height H and said first duct t1 (2) are such that: PlXgXH + G + P1 where: . p1 = the density of the fresh water; . g = 9.81 m/s2; . P1 = the head loss in said first duct to the bottom end of said second duct when the fresh water flows at said given rate, in particular the mean flow rate of the spring ; . APS = the limiting hydraulic back pressure that can be tolerated by said fresh water .spring; this value is known or can be determined for any spring, with APS preferably being less than or equal to 104 Pa; and . G = the gain of the Archimedes' thrust associated with the phenomenon of replacing the weight of a column of sea water by the weight of the column of fresh water in said first duct. 5. A catchment device for collecting fresh water coming from an undersea fresh water spring (1), the device being usable for implementing a method as claimed in any one of claims 1 to 4 and comprising : . a first duct t1 (2) of diameter at its bottom end (21) enabling it to cover said spring in full or in part ; . a second duct t2 (3) of diameter at its bottom portion (31) less than the diameter of the top portion (22) of said first duct t1 (2); and . an open-bottomed tank (4) suitable for cooperating with said second duct t2 (3) in such a manner that when the bottom end (31) of said second duct t (3) is immersed inside said first duct (2), itself being positioned facing said spring (1), with its bottom end (21) surrounding said spring in leaktight manner in full or in part, then the top end (22) of said first duct t1 (2) is covered by said tank (4) and opens out to the inside thereof via said open bottom, the solid wall of said tank being leaktight so as to be capable of holding air captive between said tank wall and the level of water inside said tank. 6. A device as claimed in claim 5, comprising first mooring means (71) for mooring said first duct t1 to the sea bottom and/or to a baseblock (8) resting on the sea bottom, and second mooring means (72) for mooring said second duct and/or said tank as moored in this way to the sea bottom and/or to said first duct. 7. A device as claimed in claim 5 or 6, wherein said tank (4) is secured to said second duct and surrounds it in leaktight manner. 8. A device as claimed in claim 7, wherein said tank (4) comprises a canopy (41) having said second duct t2 (3) passing through it in leaktight manner. 9. A device as claimed in claim 8, wherein said canopy (41) has a top portion in the form of a substantially hemispherical cap or bell. 10. A device as claimed in any one of claims 5 to 9, comprising means for injecting compressed air into the inside of said tank. 11. A device as claimed in any one of claims 5 to 10, wherein the top portion of said first, duct t1 (2) surrounding the bottom portion of said second pipe t2 (3) is flared to form a funnel (22) having its smaller base at its bottom end. 12. A device as claimed in any one of claims 5 to 11, wherein the diameter of said first duct, at the bottom end of said second duct is such that the annular area between said first and second ducts at said level is greater than or equal to the sect1onal area of said first duct. 13. A device as claimed in any one of claims 5 to 12, wherein said second duct rises directly to the surface, preferably substant1ally vert1cally, and the; fresh water is recovered at the surface and transported to land, preferably by ship. 14. A device as claimed in any one of claims 5 to 12, wherein said second duct t2 (3) can be lowered and rests on the sea bottom in order to reach the coast, thereby conveying the water to the coast, preferably opening out on land at an alt1tude that is lower than sea level. 15. A method of installing a fresh water catchment device as claimed in any one of claims 5 to 14 on the sea bottom, the method comprising the following steps : 1) posit1oning said first pipe t1 (2) above said undersea fresh water spring (1) and mooring (51) said first pipe t1 to the sea bottom in such a manner that the bottom end of said first pipe t1 surrounds said fresh water spring in leakt1ght manner in full or in part ; 2) lowering said second pipe t2 and said tank (4) to the sea bottom and mooring (52) them to the sea bottom and/or to said first pipe t1 (2) in such a manner that the bottom end of said second pipe t2 (3) is contained inside the top port1on (22) of said first pipe t1 (2); and 3) inject1ng air into the inside of said tank (4) in such a manner as to obtain an air/water interface at the top port1on of said first pipe at a said height for the air/water interface inside said tank, preferably at a said, height H. A method of collect1ng fresh water coming from an undersea fresh water spring (1) at the bottom of the sea, in which the fresh water is collected in a first duct (2) whose bottom end (22) is placed facing said spring and surrounds in leakt1ght manner at least part of the orifice of the spring, is characterized in that the fresh water is collected at a flow rate that is less than or equal to a given rate and in a second duct (3) of diameter smaller than the diameter of said first duct, the second duct having its top end (32) opening out at the surface and its bottom end (31) extending inside said first duct, and when the flow rate from the spring exceeds said given rate, the excess flow from the spring overflows from the top end (22) of said first duct into an open-bottomed tank (4) containing air (6), said tank holding air capt1ve above an air/water interface (6) situated inside said tank, and the top end (2 ) of said first duct being situated beneath the level of said air/water interface (6) inside said tank.

Documents:

177-KOLNP-2006-ABSTRACT-1.1.pdf

177-KOLNP-2006-CORRESPONDENCE-1.1.pdf

177-kolnp-2006-granted-abstract.pdf

177-kolnp-2006-granted-assignment.pdf

177-kolnp-2006-granted-claims.pdf

177-kolnp-2006-granted-correspondence.pdf

177-kolnp-2006-granted-description (complete).pdf

177-kolnp-2006-granted-drawings.pdf

177-kolnp-2006-granted-examination report.pdf

177-kolnp-2006-granted-form 1.pdf

177-kolnp-2006-granted-form 18.pdf

177-kolnp-2006-granted-form 3.pdf

177-kolnp-2006-granted-form 5.pdf

177-kolnp-2006-granted-gpa.pdf

177-kolnp-2006-granted-reply to examination report.pdf

177-kolnp-2006-granted-specification.pdf

177-KOLNP-2006-LETTER PATENT.pdf