EP1911893A1 - System for collecting subsea water springs - Google Patents

Abstract

The system has a collecting enclosure (2), whose height exceeds with free air above a sea level (3) of height higher than an overflow height (5), and an overflow unit for permitting continuous overflow of a fraction of flow of collected submarine fresh water spring (1) with free air. An adjusting unit has mobile walls (9) adjusting the overflow height with respect to operating conditions of the collected spring. A suction-rose (10) draw fresh water from the collected spring. Pipes (11) are installed on a sea-bed and connect the suction-rose upto a pumping installation comprising pumps.

Description

Technical field of the invention

The present invention relates to the field of freshwater capture from submarine sources in the coastal zone.

Prior art

Many submarine freshwater sources, resurgences of Karstic geological structures, called Karstic aquifers in the following, have flows sufficiently important to justify their commercial exploitation. An average flow rate of the order of 20,000 cubic meters / day is generally sufficient for the installation of a collection system, according to the present invention, to be economically viable.

The Karst consists of limestone rocks with interconnected cavities and underground canals resulting from the dissolution of the rock by carbonic acid in a chemical process that transforms dissolved carbon dioxide into rainwater. The Karstic aquifers are therefore complex and their configuration difficult to establish. A characteristic of these resurgences is that they spring up most often at the bottom of a cone due to erosion caused by the current of the source.

Attempts to capture freshwater sources were conducted, but generally without much success, as they altered the hydraulic balance of the source and introduced seawater into the canal system through hunting or by effect Venturi. A difficulty in capturing only fresh water from these sources comes from the complexity of Karstic aquifers and the existence of multiple channels communicating with the marine environment.

A partial inventory of underwater sources from Karstic aquifers, as well as existing installations in the Mediterranean basin, has been made, among others, by the BRGM (France). From Turkey to Spain only one large facility exists to date; located in Argolis (Greece), the Anavalos / Kiveri dam can theoretically pump more than 20,000 cubic meters / hour. It consists of a conventional construction dam made of semi-elliptic concrete isolating the sea from sources very close to the coast. Evacuation of non-pumped source flow is below sea level, which results in the development of abundant vegetation on the surface of the reservoir.

Several capture attempts have failed or have been abandoned, for example in Taranto Bay (Italy) or La Mortola (Italy). Small installations pumping a few cubic meters / hour exist, capturing only partially the source and consisting of a tube or bell placed at the point of resurgence of the source (examples: Etang de Thau or Ville d'Yport, France). Most of the exploitation attempts date back to the 1960s and 1980s, and there have been no major settlements recently installed along European coasts.

The most recent capture attempt was made in 2003-2004 at La Mortola where a 'Tulip' was installed about 30 meters deep to study the source for exploitation. The installation did not produce the desired results and the 'Tulip' was removed.

Most of the installations put in place attempted to regulate the pumped flow at the measured flow rate of the source; however, this flow rate is variable and difficult to measure accurately given the irregularity of the karstic ducts (diameter, roughness) and the turbulent flow of the source.

Summary of the invention

The invention provides a system for capturing subsea freshwater sources at a seabed comprising a seabed-based collection chamber as described in claim 1. Dependent claims define advantageous modes of production. The capture chamber comprises a rigid structure at least partially surrounding the captured source and one or more waterproof panels surrounding the rigid structure to isolate the captured source of the surrounding marine environment. The catchment chamber has a height exceeding in the open air above the level of the sea from a height greater than an overflow height, the collection chamber includes means for continuous overflow and the free air a fraction of the flow of the source received. The capture system further comprises means, for example mechanical adjustment of the overflow height depending on operating conditions of the source, one or more suction strainers for taking fresh water from the source captured in the source. capture chamber, and one or more pipes placed on the seabed connecting one or the plurality of suction strainers to a pumping installation comprising one or more pumps. The aim of the overflow height adjustment is not to modify a natural hydraulic balance of the source before capture. The adjustment can be done and locked definitively during the installation of the speaker. It can also remain permanently adjustable to adjust the overflow height to variations of the source for example depending on the seasons.

In a first preferred embodiment of the invention, the adjustment means comprise one or more movable walls slidable to allow adjustment of the overflow height. The fresh water not sampled in the collection chamber overflows over the movable walls or walls towards the outside of the enclosure to a level lower than that of the waterproof panels 6 but such that the overflow height is at least greater than the difference in density between seawater and freshwater multiplied by the depth of the measured source measured at high tide.

In a second preferred embodiment of the invention, the underwater source capture system further comprises one or more freshwater level probes in the collection chamber. The measured level is used for regulating a pumping rate of the freshwater contained in the collection chamber so as to always ensure an overflow flow. An output of the level probe carrying the signal of the continuous probe is coupled to means for controlling the flow rate of the pumps of the pumping station. In a third preferred embodiment of the invention, the sensing system of Underwater sources further comprises a flexible skirt of flexible synthetic material for sealing between the collection chamber and the seabed. The flexible skirt is attached to the watertight panels of the catchment chamber and deployed around the perimeter of the catchment enclosure by resting on the seabed where it is held in place by a mass of material, for example heavy, spilled on the soft skirt.

figures

The invention will be described in more detail from examples of embodiments of the invention with reference to Figure 1 which illustrates a capture chamber according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The operating principle of the present invention is to maintain the natural equilibrium of the hydraulic loads of the source in order to avoid the entry of seawater into the Karstic aquifer or the cone of the resurgence, as it has observed, especially during low water periods.

avec :

• Hk: hauteur de l'aquifère Karstique au-dessus du niveau de la source sous- marine (mesurée au fond du cône de la résurgence), tenant compte des pertes de charge dans le réseau de canaux de la source ;
• 1,025 : densité moyenne de l'eau de mer ; et
• Hs : hauteur de la colonne d'eau de mer au-dessus de la source, autrement dit la profondeur mesurée au fond du cône de la résurgence à marée haute.

In addition the flow taken must always be significantly lower than the flow rate of the source. The captured source will only charge if: $$\mathrm{hk}>1,025*\mathrm{Hs}$$

with:

• Hk: Height of the karstic aquifer above the level of the submarine source (measured at the bottom of the cone of the resurgence), taking into account the head losses in the channel network of the source;
• 1,025: average density of seawater; and
• Hs: height of the seawater column above the source, ie the depth measured at the bottom of the cone of the resurgence at high tide.

Referring to FIG. 1, to ensure a quasi constant hydraulic load of the source, a capture system comprises a capture chamber 2 placed around a captured submarine source 1. The capture chamber 2 is equipped with means allowing an overflow at the free air and continuously a fraction of the flow of the captured source 1. The overflow means of the capture chamber 2 can adjust a height of overflow (Hd) indicated by a double arrow 5 in FIG. 1. The adjustment of the overflow height has the effect of adjusting the pressure created by a freshwater column, whose level is indicated by the reference 4 in Fig.1, contained in the capture chamber 2 and s Exercising on the captured source 1. The overflow height 5 above sea level 3 takes into account a difference in density between fresh and sea water and the height of the seawater column Hs.

In order to ensure that part of the flow of the captured source 1 is overflowed in the open air, a height (H) in the level 4 freshwater enclosure must be between the height of the Karstic aquifer. and the level of the sea at high tide: $$\mathrm{hk}\mathrm{>}\mathrm{H}\mathrm{>}\mathrm{1}\mathrm{,}\mathrm{025}\mathrm{*}\mathrm{Hs}$$

The overflow height (Hd) 5 is defined as a difference in level between the level of fresh water inside the collecting chamber 4 and the level 3 of the sea at high tide, namely: Hd = H - Hs

The overflow height 5 is in particular determined by the height H of the freshwater column. The overflow height 5 thus depends on the depth at which the underwater source captured 1 springs. For example, for a spring gushing at the bottom of the cone 20 meters below the level 3 of the sea, the height of overflow 5 required for to compensate for the only difference in density between fresh and salt water is 0.50 meters, according to: Hd = (1.025-1.00) * Hs.

The invention is further based on the principle that the sensing system has no fixed or movable portion capable of modifying the initial flow conditions of the source in the collection chamber 2 or to open the collection chamber 2 in the marine environment. Regulation of a pumping rate of the fresh water contained in the collection chamber 2 to a fresh water outlet, ensures that the pumping rate of the fresh water is always lower than the flow rate of the source 1 The regulation is done by a simple slaving of the pumping rate of the fresh water at level 4 of the fresh water in the collecting chamber 2 by means of one or more level probes sending automatically and continuously a signal of level means for controlling the pumping rate of the pumps of the pumping station. Flow control can be achieved by switching on or off one or more pumps and / or by adjusting the individual flow rate of one or more pumps. When the level 4 of fresh water falls in the collection chamber 2, the pumping rate of the fresh water is reduced or even interrupted when the overflow flow becomes zero.

In a preferred embodiment of the invention, the overflow height 5 is also adjustable. By increasing the overflow height (Hd) 5, a hydraulic overload can be created, increasing the elevation of the Karstic aquifer level, either to prevent entry of seawater into it, or to reduce the flow of the captured source and thus increase the volume of fresh water in reserve in the Karstic aquifer. In the exemplary embodiment of FIG. 1, the adjustment of the overflow height (Hd) 5 is by means of movable walls 9 being able to slide vertically, the fresh water not taken in the collecting chamber overflowing over the mobile walls.

The capture chamber 2 consists of a rigid structure surrounding the captured source 1 and anchored or resting on the seabed. The isolation of fresh water from the source 1 of the surrounding marine environment is provided by waterproof panels 6 surrounding the rigid structure. The rigid structure and the watertight panels exceed above sea level 3 by a height greater than the overflow height (Hd) 5 required at the catchment site and sufficient to prevent the highest waves recorded at high tide at high tide. The capture chamber is of sufficient rigidity and mass to withstand the currents and the strongest swells recorded at the catchment site.

In the exemplary embodiment of FIG. 1, the seal with the seabed is provided by flexible skirts 7 of flexible synthetic material sealingly attached to the waterproof panels 6 of the structure and resting on the seabed while conforming to the profile thereof. The flexible skirts 7 deployed around the perimeter of the capture chamber 2 are held in place and pressed against the seabed by a mass of heavy material 8, poured on them from the surface by a barge equipped for this work (no shown in Fig. 1).

The capture enclosure 2 may consist of a closed enclosure if the site is located away from the coast (not shown in Fig. 1), or, if the geographical situation allows, a curtain joining two points of the coast closing a creek for example. The configuration of the capture chamber 2 is adapted in each case to the topography of the site operated.

The volume of water retained in the collection chamber 2 must be sufficient not to create pressure drops that would modify the hydraulic balance of the system and to delay the variations in level in the collection chamber due to flow variations. of the captured source. A suction strainer 10 is placed in the collection chamber 2. The strainer 10 is profiled to promote laminar flow at the suction and thus avoid any risk of cavitation of the suction pumps. It is possible to place more than one suction strainer 10 in the capture chamber 2 depending on the number of pumps installed.

The suction strainer (s) are connected to a pumping installation (not shown in Fig. 1) comprising in particular the pumps and the flow control means, by one or more pipes 11 placed on the seabed.

Claims (4)

Underwater freshwater spring collection system (1) at a seabed comprising a catchment chamber (2) resting on the seabed, the catchment enclosure comprising a rigid structure at least partially surrounding the captured source (1) and one or more watertight panels (6) enveloping the rigid structure in order to isolate the captured source from the surrounding marine environment,
the catchment chamber having a height exceeding in the open air above the level (3) of the sea from a height greater than an overflow height (5), the collecting chamber (2) comprising means allowing the continuous and free overflow of a fraction of the flow of the captured source, means for adjusting the overflow height (5) as a function of the operating conditions of the source, one or more suction strainers (10) for taking fresh water from the source captured in the collection chamber - one or more pipes (11) placed on the seabed connecting one or more of the suction strainers to a pumping installation comprising one or more pumps. The submerged freshwater source collection system according to claim 1 wherein the adjusting means comprises one or more movable walls (9) slidable to allow the overflow height adjustment, the fresh water not removed in the collecting chamber (2) projecting over the movable wall or walls at a level lower than that of the watertight panels (6) but such that the overflow height (5) is at least greater than the difference in density between the sea water and freshwater multiplied by the depth of the captured source measured at high tide. The subsea freshwater source sensing system of any of claims 1 or 2, further comprising one or more level probes delivering a level signal is continuously transmitted to means for controlling the pumping rate of the pumps of the pumping station for the fresh water contained in the collecting chamber (2).
The regulation is done by simply controlling the rate of pumping of fresh water at level 4 of the fresh water in the collection chamber 2 by means of one or more level probes automatically sending a continuous signal. level means for controlling the pumping rate of the pumps of the pumping station. When the level 4 of fresh water falls in the collection chamber 2, the pumping rate of the fresh water is reduced or even interrupted when the overflow flow becomes zero. Freshwater submarine spring collection system according to any one of claims 1 to 3 further comprising a flexible skirt (7) of flexible synthetic material for sealing between the collecting chamber (2) and the seabed, the flexible skirt being fixed to the waterproof panels (6) of the catchment chamber and deployed around the perimeter of the catchment chamber while resting on the seabed where it is held in place by a mass of material (8) spilled on the soft skirt.

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