PROTECTION SYSTEM FOR WATER TANKS

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a passive water reservoir protection system for protection of water reservoir structures from static forces generated by and / or transferred by floating ice.BACKGROUND OF THE INVENTION

[0002] There are several requirements for a dam or other structures of a water reservoir. One such requirement is resilience to static ice loads generated by thermal expansion of ice or water fluctuations. Thermally expanding ice has the ability to exert a force on the dam, as may ice blocks during water level changes through geometric wedging. If the dam cannot withstand these forces, the dam may be damaged or even collapse. The different mechanisms leading to static ice loads on dams have been reviewed for example by Comfort et al. (2003) in the Canadian Journal of Civil Engineering.

[0003] In the Norwegian thesis "Islast mot dammer med varierende vannstand" by Foss, Aslak Bøhle, NTNU, 2017, ice loads on dams with variating water levels are investigated.

[0004] Design guidelines for ice loads differ between countries. In Norway, ice loads are currently assumed to be 100kN / m, with some exceptions.

[0005] In prior art, it is known to use flexible mats secured to vertical reservoir structures, where the flexible mats absorb at least some of the forces applied by the ice towards the structure.

[0006] JPS62276117 have the purpose of reducing ice pressure loads on a sluice by a method in which a flexible buffer material is provided between the skin plate of a sluice and the iced face in such a way that the buffer material is deformed when water surface is frozen to absorb the expansion by freezing. A guide rail is provided on the surface of a skin plate and coupled with a guide rail provided to an expanded urethane buffer material. The buffer material is held on the surface of the plate in such a way as to enable the material to freely move according to the changes of water level in a water channel. A weight for regulating buoyancy is attached to the buffer material and the buoyancy is regulated so as to expose a part of the buffer material on the water surface all the time. When the water surface is frozen, the breakage of the gate and also the separation of paint film by the iced face and floating objects can be prevented. The life of the gate can thus be lengthened.

[0007] It is also known that several systems are developed to reduce ice loads induced by drifting ice. Examples of these are US 4755157 A, CA 2252197 A1, US 2018170487 A1, US 5224800 A, US 4547093 A. Although these systems are able to reduce kinetic forces induced by drifting ice, they will not work for static ice-loads since they rely on the horizontal ice movement (drifting induced by current or wind) to work.

[0008] US 2 449 963 describes how thimber logs may be used to protect structures against damage by ice. US 4 295 758 describes a working platform for oil drilling operations in ice covered sea areas, which essentially comprises oil drilling equipment, an oil drilling pipe connecting the oil drilling equipment to the sea bottom, and a floating frame having a buoyancy and a strength enough to stand the pressure of an ice covering and being movable in accordance with movement of ice covering; the floating frame is disposed surrounding such a surface area of the ice covered sea as lying around the oil drilling pipe, whereby the pipe is protected by the floating frame against action of the pressure of ice covering during oil drilling operations.

[0009] One objective of the present invention is to provide an alternative protection system for water reservoir structures.SUMMARY OF THE INVENTION

[0010] The present invention relates to a passive water reservoir protection system for protection of a water reservoir structure from static forces generated by and / or transferred by ice floating on a water body of a water reservoir; wherein the passive water reservoir protection system comprises: a floating element; a mooring system; characterized in that the passive water reservoir protection system comprises a skirt element being suitable to separate the ice into a first ice section provided on a structure facing side of the skirt element and a second ice section provided on a side opposite of the structure facing side of the skirt element; the skirt element has outer surfaces configured to be in contact with respective ice sections; the outer surfaces of the skirt element are made of a material minimizing adhesion strength of ice; the mooring system for securing the skirt element at a distance from the water reservoir structure; the floating element is secured to an upper end of the skirt element, wherein the horizontal extent of the floating element is larger than the horizontal extent of the skirt element; the floating element is secured to or integrated in the skirt element; the skirt element is suspended centrally below the floating element.

[0011] In particular, the term "static forces" refers to static ice loads generated by thermal expansion of ice or static ice loads generated by compression of ice for example due to water fluctuations in the water reservoir.

[0012] In one aspect, wherein the skirt element is oriented vertically in the water body when unaffected by external forces.

[0013] The term "external force" is here referring to forces others than those of a stationary water body and those of the mooring system. Such external forces are forces created by currents in the water body, waves in the water body, wind above the water body, ice above the water body etc.

[0014] In one aspect, the mooring system comprises a mooring element secured to the floating element or the skirt element and a wire connected between the mooring element and a fixed structure.

[0015] In one aspect, the skirt element and the floating element both have positive buoyancy in water. Here, the mooring system may provide mooring of the lower end of the skirt element to a fixed structure provided on the water reservoir bed. Alternatively, the skirt element may have negative buoyancy in water and the floating element may have positive buoyancy in water. Here, the mooring system may provide mooring of the upper and / or lower end of the skirt element to a fixed structure on the water reservoir bed or to a fixed structure provided on a land side of the water reservoir.

[0016] In one aspect, wherein the protection system further comprises a weight provided in the lower part of the skirt element.

[0017] The skirt element, the floating element and the weight in total has positive buoyancy in water.

[0018] Hence, under some conditions, the floating element may be provided in contact with the water reservoir structure, while the skirt element is still secured at a distance from the water reservoir structure.

[0019] In one aspect, the horizontal extent of the skirt element is between 10 mm and 100 mm.

[0020] In one aspect, the skirt element is made of an elastically compressible material.

[0021] An elastically compressible material is a material which may be compressed when affected by external forces, and which will return to its original form when not affected by the external forces anymore.

[0022] In one aspect, the skirt element is made of a material having static modulus of elasticity ranging from 0,75 - 2500 N / mm2.

[0023] In one aspect, the skirt element is made of a high-density polyethylene material having static modulus of elasticity ranging from 500-1500 N / mm2. In one aspect, the skirt element is made of a closed pore elastomer material having static modulus of elasticity ranging from 0,75-181 N / mm2. In one aspect, the skirt element comprises a combination of the high-density polyethylene material and the closed pore elastomer material. In one aspect, the skirt element comprises a core made of the closed pore elastomer material covered with a layer of the high-density polyethylene material.

[0024] In one aspect, the vertical height of the skirt element is larger than an expected ice thickness for the water reservoir or the sum of the vertical height of the skirt element and the vertical height of the floating element is larger than an expected ice thickness for the water reservoir.

[0025] In one aspect, the outer surfaces of the skirt element are made of a material having an ice adhesive strength less than 600 kPa. For some materials, the ice adhesive strength may vary with temperature. It should be noted that the ice adhesive strength referred to here is the typical icing temperature range, i.e. the interval - 30°C to 0°C, preferably the temperature where the properties of ice are changing most, i.e. the interval -7°C to -1°C.

[0026] In one aspect, the outer surfaces of the skirt element are made of high-density polyethylene having an ice adhesive strength of ca 150 kPa. In one aspect, the outer surface of the skirt element is made of a closed pore elastomer having an ice adhesive strength of ca 150 kPa.

[0027] In one aspect, the mooring system is configured to allow the floating element and the skirt element to move with variations in water level of the water body.

[0028] In one aspect, the distance is the horizontal distance between the skirt element and the structure.

[0029] In one aspect, the distance is between 0,1 - 10 m, preferably 1 - 5 m, and even more preferred 2 - 4 m at an expected water level.

[0030] In one aspect, the system further comprises one or more pressure sensors for measuring the pressure applied by the ice on the skirt element.

[0031] In one aspect, the pressure sensor is integrated in the skirt element.

[0032] In one aspect, the system further comprise a communication unit connected to the pressure sensor for sending pressure data from the pressure sensor to a receiver.

[0033] According to the above, it is achieved that the ice is separated into two sections of ice, a first ice section provided on a structure facing side of the skirt element, i.e. between the skirt element and the structure, and a second ice section provided on a side opposite of the structure facing side of the skirt element.

[0034] In one aspect, the floating element and the skirt element are provided as one single body. Alternatively, the floating element and the skirt element are provided as separate bodies connected to each other. The protection system may comprise several floating elements connected to each other. Each floating element may comprise one skirt element. Alternatively, there may be one common skirt element suspended below two or more floating elements. In yet an alternative, there may be more than one skirt elements suspended below each floating element.

[0035] In one aspect, the skirt element and / or the buoyancy element may be coated with a wax, a painting or another type of coating, to improve its properties with respect to protection of the water reservoir structure from static forces from ice.

[0036] The term "water reservoir structure" is here used herein for any type of barrier used to stop or restrict the flow of water into or out from a water reservoir. The barrier to which the protection system is intended for may typically be an artificial (i.e. human-designed) barrier and not a natural barrier such as rock, mountains etc. One common water reservoir structure is a dam. Examples of other reservoir structures are spillways, bridge foundations, sluices, salmon ladders etc.

[0037] The term "passive" is used herein to describe that once installed, there is no active control of the properties of the barrier itself. It should be noted that the pressure sensors and communication unit are powered by a battery. However, the pressure sensors and communication unit does not control the properties of the water reservoir protection system.

[0038] Ice may form on the water body during colder periods. The ice may be comprised of a single layer, vertically stacked layers of different growth history, the layers of which may be interspersed by water or slush, or an accumulation of ice blocks termed "rubble ice". The properties of the ice formed on the water body will vary during the year and from year to year. However, based on weather data, it is possible to calculate an expected ice thickness for a water reservoir.

[0039] It should also be noted that some water reservoirs have variations in water level. The variations in water level may be caused by weather conditions, or they may be caused by the production of a hydro power plant etc. Hence, for many water reservoirs it is possible to calculate an expected maximum water level and / or an expected minimum water level and hence a design water level.

[0040] The surface area of a water reservoir may vary depending on the water level. Hence, if the water level changes from a level with a relatively large surface area to a level with a relatively smaller surface area, the ice floating on top of the water body may fracture and be compressed due to the smaller available area of water to float on. Similar compression may be induced if the dam is slanted, or if part of the ice cover remains attached to the dam. According to the above, also static ice loads generated by movements of ice due to these water fluctuations in the water reservoir will be reduced by the above protection system.DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention will now be described in detail with reference to the enclosed drawings, wherein: Fig. 1 illustrates a side view of a water reservoir with a protection system; Fig. 2a illustrates a side view of the floating element and the skirt element; Fig. 2b illustrates a front view of a section of the floating element and the skirt element; Fig. 3 illustrates the protection system at low filling level; Fig. 4 illustrates compression of the skirt element; Fig. 5 illustrates how ice may slide along the skirt element; Fig. 6 illustrates how the skirt element behaves during ice wedging; Fig. 7 illustrates a side view of the mooring system of the protection system; Fig. 8 illustrates a top view of the mooring system of the protection system; Fig. 9 illustrates a side view where parts of the protection system is in contact with the dam; Fig. 10 illustrates a top view illustrating how the protection system may move in relation to the structure; Fig. 11 illustrates a side view of the water reservoir with an alternative embodiment of the protection system; Fig. 12 illustrates an enlarged view of the water reservoir system of fig. 11; Fig. 13 illustrates a side view of yet an alternative embodiment of the protection system.

[0042] It is now referred to fig. 1 and fig. 8, where a water reservoir 1 is shown to comprise a water reservoir structure 2, a water body 3, ice 4 floating above the water body 3, land sides 5a, 5b, 5c and a water reservoir bed 6. Typically, the water body 3 will be enclosed by the bed 6, land sides 5a, 5b, 5c and the water reservoir structure 2.

[0043] As used herein, the land sides 5a, 5b, 5c are natural barriers such as rock, mountains etc., while the water reservoir structure 2 is an artificial or human-designed barrier. In the present embodiment, the water reservoir structure 2 is a dam, such as a rock-filled dam, a concrete dam etc. However, the water reservoir structure 2 may also be a spillway, a bridge foundation, sluices, salmon ladders etc.

[0044] The water reservoir 2 may allow water to flow into the reservoir, for example via a river. Similarly, the water reservoir 2 may allow water to flow out from the reservoir, for example over a weir integrated in the dam, through an intake to a power plant etc.

[0045] For most water reservoirs it is possible to calculate an expected water level EWL. The expected water level EWL may be a maximum water level and / or an expected minimum water level and / or an expected average water level. It should be noted that this expected water level EWL is typically calculated when no ice is present. Hence, the expected water level EWL drawn in fig. 1 is an example only.

[0046] For most water reservoirs it is possible to calculate an expected ice thickness EIT based on weather data.

[0047] As discussed in the prior art section above, water reservoir structures 2 are subjected to static forces generated by and / or transferred by the ice 4 floating on the water body 3. In fig. 1, it is also shown a passive water reservoir protection system 10 for protection of the water reservoir structure 2 from these static forces.

[0048] The passive water reservoir protection system 10 comprises a skirt element 21 and a floating element 11 secured to the skirt element 21. In 2a, it is shown that the floating element 11 is secured to an upper end of the skirt element 21. Here, the horizontal extent E11 of the floating element 11 is larger than the horizontal extent E21 of the skirt element 21, where the skirt element 21 is suspended centrally below the floating element 11. A height H11 for the floating element 11 and a height H21 for the skirt element 21 is also shown. The sum of the vertical height H21 of the skirt element 21 and the vertical height H11 of the floating element 21 is in the present embodiment larger than the expected ice thickness EIT for the water reservoir 1. Typically, the sum of the vertical height H21 of the skirt element 21 and the vertical height H11 of the floating element 21 is 10 - 30 % larger than the expected ice thickness for the water reservoir 1.

[0049] The skirt element 21 is oriented vertically in the water body 3 at a distance D from the water reservoir structure 2. To keep the skirt element 21 at the distance D from the structure 2, the passive water reservoir protection system 10 comprises a mooring system 50 best shown in fig. 7 and 8. Here it is shown that the mooring system 50 comprises a mooring element 51 secured to the floating element 11 or the skirt element 21 and a wire 52 connected between the mooring element 51 and a fixed structure 55. In fig. 7 and 8 the system 10 comprises two fixed structures 55 on the water reservoir bed 6 and two fixed structures 55 provided on the land sides 5a, 5b. Depending on the shape of the reservoir 1, there can be one or several fixed structures 55 on the land side(s) only, there can be one or several fixed structures 55on the water reservoir bed 6 only and / or there can be one or several fixed structures 55 on the structure 2 itself (for example if the structure 2 is substantially U-shaped when viewed from above).

[0050] In the embodiment shown in fig. 7 and 8, the structure 2 is linear. Here, also the skirt element 21 and the floating element 11 are linear and oriented substantially in parallel with the structure 2. However, such a parallel orientation is not essential for the protection system 10 to provide enough protection against static forces.

[0051] However, an important feature is the distance D, causing the ice to be separated into two sections of ice (see for example fig. 1), a first ice section 4a provided on a structure facing side of the skirt element 21, i.e. between the skirt element 21 and the structure 2, and a second ice section 4b provided on a side opposite of the structure facing side of the skirt element 21. This will be apparent from the description below.

[0052] In fig. 2a it is further shown that the skirt element 21 has outer surfaces 21a, 21b configured to be in contact with respective ice sections 4a, 4b.

[0053] In fig. 2a, it is further shown that the protection system 10 comprises a weight 31 provided in the lower part of the skirt element 21. This may contribute to the vertical orientation of the skirt element 21 and makes it easier to achieve vertical orientation of the skirt element 21 without mooring the skirt element to the reservoir bed 6. However, the skirt element 21, the floating element 11 and the weight 31 in total has positive buoyancy in water.

[0054] In the embodiment shown in fig. 2a, the skirt element 21 and the floating element 11 both have positive buoyancy in water, while the weight 31 has negative buoyancy in water.

[0055] It is now referred to fig. 2b. Here it is shown that the protection system 10 further comprises a number of pressure sensors 41 for measuring a parameter representative of the pressure applied by the ice 4 on the skirt element 21. The pressure sensors 41 are integrated in the skirt element 21. The protection system 10 also comprises a communication unit 42 connected to the pressure sensors 41 for sending pressure data from the pressure sensor 41 to a receiver 43. Hence, it is possible to remotely monitor the status of the static forces. Other sensors, such as temperature sensors, wind sensors etc. may also be connected to the communication unit 42.

[0056] It is now referred to fig. 3. Here it is shown a reservoir 1 with relatively large variation between a maximum expected water level EWLmax and a minimum expected water level EWLmin. As shown here, the skirt element 21 is not oriented in a vertical direction at low water levels as the lower end of the skirt element 21 is provided in contact with the reservoir bed 6. It should also be noted that the mooring system 50, in particular the length of the wires 52, must be designed with respect to these variations in water levels.

[0057] It is now referred to fig. 4. Here it is illustrated that the skirt element 21 is made of an elastically compressible material. The elastically compressible material of the skirt element 21 is compressed or deformed when affected by ice sections 4a, 4b, but will return to its original shape when not affected by the ice sections anymore.

[0058] In one embodiment, the skirt element 21 is made of a closed pore elastomer material having static modulus of elasticity ranging from 0,75-181 N / mm2. One such material is sold under the name Sylodyn ®< . Alternatively, skirt element 21 is made of a high-density polyethylene HDPE material having static modulus of elasticity ranging from 500-1500 N / mm2. Various other materials with static modulus of elasticity ranging from 0,75 - 2500 N / mm2 is also possible. It should be noted that the material should not allow water ingress, as water ingress may change the material properties, in particular at freezing temperatures.

[0059] As is apparent from fig. 4, the skirt element 21 will reduce static forces generated by and / or transferred by the ice 4 to the structure 2 as some of these static forces will be absorbed by the compression of the skirt element 21.

[0060] As the skirt element 21 will return to its original shape, the possibility for water to flow into the space between ice sections 4a, 4b will be reduced, thereby reducing the growth of the ice in the horizontal direction. The material of the skirt element itself will also delay changes in temperatures, which under some circumstances will reduce ice formation and the mechanical impact of ice.

[0061] It is now referred to fig. 5. Here it is illustrated that the skirt element 21 is made of a material minimizing adhesion strength of ice, thereby allowing ice to slide along the skirt element 21 as indicated by arrows in fig. 5. In the present embodiment, the outer surfaces 21a, 21b of the skirt element 21 are made of a high-density polyethylene HDPE having an ice adhesive strength of ca 150 kPa.

[0062] As is apparent from fig. 5, the skirt element 21 will reduce static forces generated by and / or transferred by the ice 4 to the structure 2 because the ice is allowed to slide along the skirt element and cause rotation of the floating element 11 instead of pushing against the structure 2. Hence, the skirt element 21 together with the floating element 11 will divert compressive forces through inducing buckling failure and shear motion. The floating element 11 also contributes to create a joint that weakens the ice and induces buckling failure at a lower stress.

[0063] Consequently, both the floating element 11 and the skirt element 21 create a weak hinge or joint in the ice that induces failure at much lower stresses than in an undisturbed ice cover.

[0064] It is now referred to fig. 6. Here, it is shown that the wedging effect of ice is reduced due to the compressible material of the skirt element 21. As is apparent, the skirt element 21 will reduce static forces on the structure 2 and reduce horizontal growth of the ice.

[0065] It is now referred to fig. 9 and 10. First, it should be noted that the protection system 10 comprises several interconnected sections 10a, 10b, 10c, 10d, 10e, each section comprising a floating element 11, a skirt element 21 and a weight element 31 and each section connected to other sections and / or to fixed structures 55 by means of the wires 52 of the mooring system 50.

[0066] Due to relatively large variations in the water level, the wires 52 of the mooring system must be relatively slack at some water levels while relatively tensioned at other water levels. Fig. 7 and 8 show a relative tensioned wire 52 where the sections are held relatively stationary at a first position P1. Fig. 9 and 10 show a relative slack wire 52 where the sections are allowed to move between a position P2 and a position P3 for example due to wind, waves etc.

[0067] It should be noted that in fig. 9, even though the floating element 11 is provided in contact with the water reservoir structure 2, the skirt element 21 is still secured at a distance D from the water reservoir structure 2. However, in most situations, the distance D may be between 0,1 - 10 m, preferably 1 - 5 m, and even more preferred 2 - 4 m at an expected water level.

[0068] In the above embodiments, the cross section of floating element 11 may be an air-filled or foam-filled ring, tube or pipe made for example of a plastic material. The horizontal extent E11 of the floating element 11 may be 300 - 1000 mm, while the horizontal extent E21 of the skirt element 21 may be between 10 mm and 100 mm. The communication unit 42 may be located inside the floating element 11 as shown in fig. 2b. The mooring element 51 may comprise a ring, hook etc. for connection to the wire 52. In the above embodiments, the mooring element 51 is secured to the skirt element 21 adjacent to the interface between the skirt element 21 and the floating element 11.

[0069] It is now referred to fig. 11 and fig. 12. Here, the floating element 11 is integrated in the skirt element 21, i.e. the floating element 11 and the skirt element 21 are provided as one single body. The protection system 10 may still comprise several sections of floating elements 11 and skirt elements 21.

[0070] Here, the combined floating element 11 and skirt element 21 are made of a core of the closed pore elastomer material mentioned above sandwiched between two layers of the high-density polyethylene HDPE material mentioned above. The closed pore elastomer material has a high positive buoyancy and is referred to in fig. 12 as the floating element 11. Also here, the protection system 10 comprises a weight element 31 provided in the lower end.

[0071] The wire 52 of the mooring system 50 may be connected to a mooring element 51 in the upper end of the combined floating element 11 and skirt element 21 and / or the wire 52 of the mooring system 50 may be connected to a mooring element 51 in the lower end of the combined floating element 11 and skirt element 21.

[0072] It should be noted that the weight 31 is not an essential feature of this embodiment. However, to obtain the vertical orientation, the wire 52 should be connected between a mooring element 51 in the lower end of the combined floating element 11 and skirt element 21 and a fixed structure 55 located on the reservoir bed 5 as shown in fig. 11.

[0073] It is now referred to fig. 13. Here, the mooring system 50 is using the water reservoir structure 2 as a fixed structure, for example a bolt secured to the structure 2, as indicated as 55 in fig. 13, to which a wire 52 is fastened. The mooring system 50 further comprises a mooring weight 56 suspended in the wire 52. In fig. 13, there is a first mooring wire 52 between the lower end of the skirt element 21 and the mooring weight 56 and there is a second mooring wire 52b between the mooring weight 56 and the fixed structure 55. Preferably, a further wire is secured between the mooring element 51 and further fixed structures 55, for example as shown in fig. 8 and 10.

Claims

1. Passive water reservoir protection system (10) for protection of a water reservoir structure (2) from static forces generated by and / or transferred by ice (4) floating on a water body (3) of a water reservoir (1); wherein the passive water reservoir protection system (10) comprises: - a floating element (11); a skirt element (21) being suitable to separate the ice (4) into a first ice section (4a) provided on a structure facing side of the skirt element (21) and a second ice section (4b) provided on a side opposite of the structure facing side of the skirt element (21); - the skirt element (21) has outer surfaces (21a, 21b) configured to be in contact with respective ice sections (4a, 4b); - the outer surfaces (21a, 21b) of the skirt element (21) are made of a material minimizing adhesion strength of ice; - a mooring system (50) for securing the skirt element (21) at a distance (D) from the water reservoir structure (2); - the floating element (11) is secured to an upper end of the skirt element (21), wherein the horizontal extent (E11) of the floating element (11) is larger than the horizontal extent (E21) of the skirt element (21); - the floating element (11) is secured to or integrated in the skirt element (21); characterized in that the skirt element (21) is suspended centrally below the floating element (11).

2. Passive water reservoir protection system (10) according to claim 1, wherein the skirt element (21) is oriented vertically in the water body (3) when unaffected by external forces.

3. Passive water reservoir protection system (10) according to claim 1 or 2, wherein the protection system (10) further comprises a weight (31) provided in the lower part of the skirt element (21).

4. Passive water reservoir protection system (10) according to any one of the above claims, wherein the skirt element (21) is made of an elastically compressible material.

5. Passive water reservoir protection system (10) according to any one of the above claims, wherein the skirt element (21) is made of a material having static modulus of elasticity ranging from 0,75 - 2500 N / mm2.

6. Passive water reservoir protection system (10) according to any one of the above claims, wherein the vertical height (H21) of the skirt element (21) is larger than an expected ice thickness for the water reservoir (1) or the sum of the vertical height (H21) of the skirt element (21) and the vertical height (H11) of the floating element (11) is larger than an expected ice thickness for the water reservoir (1).

7. Passive water reservoir protection system (10) according to any one of the above claims, wherein outer surfaces (21a, 21b) of the skirt element (21) are made of a material having an ice adhesive strength less than 600 kPa.

8. Passive water reservoir protection system (10) according to any one of the above claims, wherein the mooring system (50) is configured to allow the floating element (11) and the skirt element (21) to move with variations in water level of the water body (3).

9. Passive water reservoir protection system (10) according to any one of the above claims, wherein the distance (D) is the horizontal distance between the skirt element (21) and the structure (2).

10. Passive water reservoir protection system (10) according to any one of the above claims, wherein the distance (D) is between 0,1 - 10 m, preferably 1 - 5 m, and even more preferred 2 - 4 m at an expected water level.

11. Passive water reservoir protection system (10) according to any one of the above claims, wherein the system (10) further comprises: - one or more pressure sensors (41) for measuring the pressure applied by the ice (4) on the skirt element (21).