EP0435732B1 - Spillway for high water for barrages and similar structures - Google Patents

Abstract

For the purpose of effecting a quasi-permanent raising of the normal water level of an impounded reservoir and thereby augmenting its storage capacity except during the passage of major floods, the invention consists of rigidly fixing to the sill of the spillway a water level raising means comprising at least one vertical plate capable of resisting the water loads when spilling moderate heads (for discharging the floods of shorter recurrence intervals) but bending at its lower portion where it is fixed to the sill at a predetermined head not higher than the maximum water level in order to discharge larger floods.

Description

The present invention relates to a spillway spillway for dams and similar structures, of the type defined in the preamble of claim 1.

Known weirs of this type are described in "Engineering for Dams", W.F. Creager et al. , Flight. 3, pp 870-876 John Wiley & Sons, Inc. New York / Chapman & Hall, Ltd. London, as well as in document US-A-2 118 535.

In the publication "Engineering for Dams" the rising elements are formed by a series of boards or panels arranged vertically and by stakes which support the boards on the downstream side and which are embedded at their base in the weir threshold. When the water reaches a certain level, the stakes bend in the region of their embedding and the boards or panels are driven out by the water and lost. Patent US-2 118 535 describes a system similar to the previous one, but in which the rise, produced in the form of a single rigid plate of wood, metal or other material, is connected to the threshold of the spillway by an articulation of horizontal axis allowing the plate to pivot down and downstream when the stakes which support it bend.

The current state of practice in the design and construction of dams with overhanging thresholds means that these structures must be dimensioned for flood conditions (millennial for example) leading to significant heights of overhanging blade (of the order of 1 to 5m depending on the works).

With an equal dimensioning of the bodies of evacuation of the floods, the barrier with free overflow threshold offers compared to a work provided with valves the best safety vis-a-vis the hydrological hazard which remains one of the major risks for the dams.

In return, the adoption of a completely free overhanging threshold leads to a loss of the useful retaining edge corresponding to the maximum height of the overhanging blade, that is to say the aforementioned difference of said first and second predetermined levels. This loss can represent, in particular for small or medium-sized works, a significant part of the useful volume of the reservoir (this part can reach or exceed 50%).

• 1°/ augmenter de façon quasi-permanente la capacité de stockage d'un barrage à seuil déversant libre;
• 2°/ maintenir et/ou accroître la sécurité de fonctionnement propre aux ouvrages à seuil déversant, en permettant de façon fiable le passage des crues exceptionnelles, tout en tolérant un déversement des crues de faible ou moyenne importance, sans intervention extérieure et sans modification majeure de l'ouvrage.

The problem that the present invention seeks to solve can be summed up in two main objectives following, which can be searched simultaneously or alternatively:

• 1 ° / almost permanently increase the storage capacity of a dam with a free overflow threshold;
• 2 ° / maintain and / or increase the operational safety specific to overflowing threshold works, by reliably allowing the passage of exceptional floods, while tolerating a spill of low or medium-sized floods, without external intervention and without major modification of the book.

Various devices have already been proposed and currently exist to increase the storage capacity of a reservoir. In majority, these devices are essentially constituted by valve systems, which close the overflow threshold when the valves are closed. The valves, of whatever nature, conventional or inflatable, of automatic or manual operation, are generally of a fairly high investment cost and they require periodic maintenance and maneuvers. They also require continuous human monitoring or a controlled mechanism reacting to the water level of the reservoir, a mechanism which is often expensive and sophisticated and which is never completely immune to failure. Finally, for an equal discharge capacity, the operational safety and reliability of a gated structure is lower than that of a structure with a free overflow threshold (not gated).

Some devices exist, which temporarily increase the storage capacity of a reservoir, such as sandbags or cofferdams (also called flash boards). These devices, described in the aforementioned book "Engineering for Dams", however remain of limited scope and, because they require human intervention prior to each flood, they present a significant operating hazard.

There is also, on certain large embankment dams, a section of fusible dam, leveled at a lower coast than that of the rest of the structure and operating according to the principle of the erosion of its constituent materials, erosion which is generated by a extreme rise in the level of the reservoir during a flood of very exceptional importance. The purpose of this fuse dam is in fact to avoid the uncontrolled and catastrophic discharge of an extreme flood on the whole of a structure, by concentrating the effects of the flood on a section specially equipped to break by erosion and thus offer additional evacuation capacity. After the rupture of the fusible dike, major repair work would be necessary to allow normal operation of the structure again.

To the knowledge of the applicant, it therefore seems that no existing device satisfactorily meets the objectives indicated above, with simple operation and for a moderate investment cost.

According to the present invention, the above problem is solved by the features contained in the characterizing part of claim 1.

Under these conditions, it is clear that the storage capacity of the dam is increased by an amount corresponding to the height of the raising element or elements. The raising element (s) can be manufactured at a very moderate cost compared to the valves and, in the case where they are installed on the overflow threshold of an already existing dam, this installation can be done without the need for d '' make major modifications to the overflow threshold of the dam as we will see below. It is also clear that for medium floods, as long as the level water does not reach said third predetermined level, which can be determined so as to be in practice equal or slightly lower than said second predetermined level (maximum level or highest water level), the water may pass through above the said rising element or elements to evacuate the flood, without this resulting destruction of the rise and, consequently, without this resulting in a decrease in the increased storage capacity of the dam. On the other hand, if, in the event of an exceptional flood, the water level reaches said third predetermined level, the raising element or elements automatically fold around the embedding line under the sole action of the pushing forces. water, therefore without any external intervention, thus restoring the discharge threshold to its full evacuation capacity corresponding to the maximum height of the discharge blade for which the dam was designed.

At its lower part, the plate forming each raising element can be engaged in a groove provided in the threshold itself or in a mounting piece rigidly fixed to the threshold. Or, the plate forming each raising element can have, in transverse vertical section, a substantially L-shape and its horizontal branch can be rigidly fixed to the threshold for example by a bolted connection of the embedding type. Sealing at the base of the plate can be ensured by filling the embedding groove with a suitable filling material, or by a suitable seal or by both. When the rise is formed of several plates juxtaposed along the crest of the overflow threshold, seals can also be arranged between the vertical edges of the plates

The invention can be applied both to the spillway of an existing dam and to that of a dam under construction. In the first case, the crest of the overhanging threshold is preferably leveled at a level lower than said first predetermined level and the one or more rising elements are embedded on the leveled threshold. In this case, the storage capacity of the dam can be kept equal to that it had before the overflow threshold was lowered, or it can be increased depending on whether the elevating element or elements are given a height such as their sound or their vertex finds at said first predetermined level, or at a level higher than this, but lower than said third predetermined level. Whatever the height of the elevation element (s), within the limits indicated above, greater security is obtained than with the undisturbed overflow threshold, since the opening which is obtained after folding of the element (s) rise at a higher height than in the case of an undisturbed overflow threshold, thus allowing to evacuate a higher flood flow than the maximum flow of the exceptional flood for which the dam was originally designed.

Similarly, in the design of a new dam, it will be possible to adopt a greater difference between the first and second predetermined levels (which contributes to increasing safety) without fear that this would lead to a reduction in the storage capacity of the dam, since this storage capacity can be maintained, or even increased, without reducing security, by providing one or more augmentation elements in accordance with the present invention.

In the case where several risers are provided, each riser or a group of risers can be dimensioned so as to bend for a predetermined water level lower than that at which another element or group of risers rise will fold, the latter itself being dimensioned so as to fold for a lower water level than that to which a third element or group of rise elements will fold, and so on. In this way, a progressive increase in the evacuation capacity is obtained, if necessary, depending on the extent of the flood.

It will also be noted that, if one or more rising elements have bent under the thrust of an exceptional flood, they can be easily and economically replaced by other rising elements, without having to carry out major repairs, after the flood has been evacuated.

Other characteristics and advantages will appear during the description which follows of various embodiments of the present invention given by way of example, with reference to the appended drawings in which:

Figure 1 is a perspective view showing a structure, such as a dam, and its outlet spillway floods with a free discharge threshold, to which the invention can be applied.

Figures 2a and 2b show, in vertical section and on a larger scale, the crest of the free overflow threshold of the dam of Figure 1 for two different water levels.

Figure 3 is an elevational view of the weir of Figure 1, seen from the downstream side and equipped with a fusible link implemented in the present invention.

FIG. 4 is a plan view of the weir of FIG. 3.

Figure 4a is a view similar to that of Figure 4, showing another possible arrangement of the elements of the fuse riser implemented in the invention.

FIG. 5 shows, on a larger scale, a horizontal section of a seal that can be used between two adjacent elements of the riser of FIGS. 3 and 4.

Figures 6 and 7 show, on a larger scale and in vertical section, two embodiments of the embedding of the rising elements.

FIGS. 8a to 8e are views in vertical section making it possible to explain the operation of the fuse riser implemented in the present invention, before, during and after the passage of a flood.

Figures 9a and 9b are graphs showing the forces which, in service, can be applied to a riser used in the present invention.

FIG. 10 is a graph representing the variations of the moments of the driving and resistant forces as a function of the height of water above the overflow threshold, as well as the variations of the flow of water discharged as a function of the height of the overflow blade.

FIG. 11 is a view in vertical section showing a lifting element used in the present invention, with which is associated a folding trigger device.

FIGS. 12a to 12c show, on a larger scale, various protective devices which can be provided at the upper end of the trigger device of FIG. 13.

Figures 13a to 13c are cross-sectional views for comparing the maximum heights of overflow blades in the case of the present invention for risers having different heights (Figures 11a and 11b) and in the case of a threshold known free discharge (Figure 11c).

FIGS. 14a to 14d are views in vertical section making it possible to explain the operation of a double fusible riser according to another embodiment of the invention.

Figures 15 to 17 show, in vertical section, other embodiments of a lifting element used in the present invention.

FIG. 18 is a perspective view showing a detail of the raising element in FIG. 17.

The structure 1 shown in FIG. 1 can be an embankment dam or a concrete or masonry dam. However, it should be noted that the invention is not limited to the type of dam shown in FIG. 1, but that, on the contrary, it can be applied to any type of known dam with a free overflow threshold. .

In figure 1, the reference number 2 designates the crest of the dam, the number 3 its downstream facing, the number 4 its upstream facing, the number 5 a spillway spillway, the number 6 the weir threshold 5 and the number 7 an evacuation channel. The spillway 5 can be located in the central part of the dam 1 or at the end of it or even excavated on a bank without this altering the possibility of using the invention.

For a structure with a free overflow threshold, the level RN of the normal reservoir in operation (see also Figure 2a) is that of the crest 8 of the overflow threshold 6. This level RN determines the maximum volume of reservoir that can be kept by the reservoir formed by the dam. The vertical distance R, called revenge, between the crest 8 of the weir and the crest 2 of the dam is the sum of two terms, namely, on the one hand, an increase h₁ in the water level due to a flood, up to a maximum level RM or highest water level (PHE), allowing the discharge of the maximum flood (Figure 2b) for which the structure is dimensioned, and, on the other hand, an additional height h₂ intended to protect the ridge 2 of the dam against the oscillations of the water level at its maximum level RM (effect of wind, waves, etc.)

In a conventional dam with a free overflow threshold like the one shown in FIG. 1, the reservoir portion located between the normal retention level RN and the maximum level RM is not stored and is therefore lost for operation. One of the aims of the invention is to enable the level of normal exploitation of the reservoir to be raised almost permanently, and therefore to increase its storage capacity, except during the passage of exceptional floods.

To this end, the invention provides for fixing by embedding on the overhanging threshold 6 a rise 10, constituted by at least one element 11, in the form of a plate, for example five elements 11a-11e as shown in FIGS. 3 and 4 , said rise 10 or the rise elements 11 being able to resist, without breaking, the water load corresponding to a moderate spill (allowing the passage of the most frequent floods) and being rendered fusible by folding around a installation line for a predetermined water load corresponding to a level N at most equal at the maximum level RM and then allowing the passage of the strongest floods.

Of course, the number of elevating elements 11 is not limited to five elements as shown in Figures 3 and 4, but may be smaller or larger depending on the length of the weir 5 (measured in the longitudinal direction of the dam) . Preferably, the number of elevating elements 11 is chosen so as to obtain low unit masses allowing easy installation and replacement of said elevating elements.

As shown in FIG. 4, a conventional seal 13, for example made of rubber, is provided at each of the two ends of the riser 10 between it and the lateral flanks 14 of the weir 5. When the riser 10 is formed by several elements 11, seals 13 (FIG. 5) are also provided between the vertical lateral edges, two by two facing each other, adjacent elevation elements 11 as is also visible in FIG. 4. All the seals 13 must be such that they do not prevent the folding of the elevating elements 11 relative to one another and relative to the lateral flanks 14 of the weir 5 when it is made necessary for the evacuation of a flood. important.

Each elevating element 11 is constituted by a plate made of a metal (suitably protected against corrosion) or other material capable of being folded. At its lower end, the plate 11 can be engaged in an embedding groove 12 formed in the threshold 6 of the weir 5, the groove 12 having a width slightly greater than the thickness of the plate 11 as shown in the figures 6 and 7. The seal at the base of the plates 11 can be ensured by a seal 15 disposed between the threshold 6 and the lower part of the plates 11, for example on the upstream side thereof, and / or by a filling material 16, such as by example of sand, put in the groove 12 on either side of the plates 11.

As shown in Figures 6 and 7, the embedding line 17 around which the elevation elements 11 will bend, can be materialized by a support member, continuous or disconstinu, disposed on the downstream side of the elevation elements 11; said support member may be constituted by a longitudinal bar 18, fixed to each elevating element 11, or by a spoiler 19 fixed to the masonry of the threshold 6 in the region of the downstream edge of the groove 12. It should also be noted that the elevating elements 11 may comprise, in one or both of their faces, at the level of the embedding line 17, a weakening (not shown) in the form of a groove, continuous or discontinuous, which facilitates the folding of the raising element 11 around the line 17 under a predetermined force.

In Figure 4, all the elements (11a-11e) of the riser 10 are arranged in the same vertical plane. They can also be staggered as shown in Figure 4a. In this case, other fixed elevation elements 20, that is to say non-folding, also in the form of plates, are rigidly fixed to the threshold 6 between the elements 11 so as to restore the continuity of the elevation 10, the fixed elements 20 extending parallel to each other and to the general direction of flow of the water in the weir. The crest line of the rise 10 is no longer straight, but broken, in a crenelation, so that the length of discharge over the rise 10 is notably increased, which allows, as will be seen below, for a given water level and a given evacuation rate, to reduce the height (thickness) of the overflow blade, therefore to increase the height of the rise and consequently further increase the water storage capacity of the dam .

As shown in FIG. 8a, the increase 10 of the present invention makes it possible to raise the level of the normal retention of the level RN (level of the normal retention of the free overflow threshold 6, that is to say without the increase 10) up to the level RN 'corresponding to the height of the rise 10 above the threshold 6. As will be explained below, each rise element 11 is dimensioned so as to resist bending for a water load of less than one predetermined level N, itself at most equal to the maximum level RM already mentioned above. Thus, assuming for example that said predetermined level is equal to the RM level, as long as the water level remains below the RM level for low or medium-sized floods and is between the RN 'and RM levels, the water spills over the rise 10 as shown in figure 8b, without the rise being destroyed. In this case, after evacuation of the flood, the water level drops to level RN 'or to a lower level if water is drawn into the reservoir.

On the other hand, if the water level reaches, in the aforementioned hypothesis, a predetermined level N equal or slightly lower than the maximum level RM in the case of a strong flood or exceptional flood, at least one element 11 of the rise 10 is folded by the push of the water around the line 17 as shown in Figure 8c, thus allowing the evacuation of the strongest floods. After evacuation of a strong flood having caused the folding of the rise 10, the overflow threshold 6 is found in the state shown in Figure 8d, the water level having returned to approximately the level of the normal reservoir RN or even lower. We can possibly provide some spare elements 11, permanently available on the dam site, to allow repair of the surge 10 if necessary and thus restore the level of the normal restraint at RN 'level as shown in Figure 8e. It should be noted, however, that the non-replacement of one or more elements 11 after an exceptional flood which has led to the folding of at least one element 11 does not reduce the operational safety of the structure.

The risks of malfunction due to floating bodies can be easily eliminated by upstream protection using conventional techniques adaptable to each particular case. The protection can for example be constituted by floating lines on the reservoir, at a certain distance upstream from the weir, or by stop devices fixed on the upstream facing of the dam.

We will now give a numerical example of the design of a fusible link implemented in the present invention. Usually, the dams and overflow weirs are dimensioned so that the level of the lake (level of the reservoir) reaches the maximum level RM for the exceptional flood envisaged (project flood). This flood may for example be the flood occurring only one year in a thousand (millennial flood).

d'après laquelle on peut voir que H est sensiblement égal à 2 m dans l'hypothèse faite plus haut. Toujours dans cette hypothèse, en l'absence de dispositif de vannes ou de hausses, le niveau du seuil 6 du déversoir 5 est arasé à 2 m en-dessous du niveau maximal RM pour permettre l'évacuation de la crue millénale, et on perd donc un volume utile d'eau correspondant à une tranche de 2 mètres.To fix the ideas, we will assume that the flow of this project flood is for example 200m³ / s and that the free spillway threshold 6 is 40 m long. Under these conditions, the height H of the water layer necessary to evacuate the flow of the project flood corresponds to 5m³ / s per linear meter of threshold. This height H can be calculated by the following formula: $${\text{Q = 1.8 H}}^{\text{3/2}}$$

according to which we can see that H is substantially equal to 2 m in the hypothesis made above. Still in this hypothesis, in the absence of a valve or rising device, the level of the threshold 6 of the weir 5 is leveled 2 m below the maximum level RM to allow the evacuation of the millennial flood, and we lose therefore a useful volume of water corresponding to a 2 meter section.

For the determination of the height of the elevating elements 11, the invention is based on the observation that the maximum flow achieved on average over 20 years is much lower than that of the project flood. It can be around 50m³ / s in the example chosen here. According to formula (1) this flow then corresponds to a sheet of water having a height of about 0.8m. If it is admitted that elevating elements 11 can be destroyed on average every 20 years, then one can give the elevating elements a height of 2 m - 0.8 m = 1.2 m, thus allowing the passage to -above elevation elements 11 of a 0.8 m high water layer corresponding to the flow of 50m³ / s. In this case, the level of the normal reservoir RN 'is raised to 1.20 m above the level of the normal reservoir RN of the overflow threshold 6 free, that is to say without the elevating elements 11. If we choose elevation elements 11 having a height greater than 1.2m, the height of the admissible sheet of water will be less than 0.8m and it will be necessary to allow the destruction of the elevation elements, for example every 10 years, but the level of normal restraint will be further increased. On the other hand, if we choose elevation elements 11 having a height less than 1.2m, we can admit a sheet of water having a height greater than 0.8m, the elevation elements being then destroyed only all 50 or 100 years, but the level of normal withholding will then be lower than in the previous cases. The choice of the height of the elevating elements 11 is therefore essentially an economic choice. In general, it is probably desirable to fix the time interval between two successive total destructions of the fusible riser at approximately 20 years, which would lead to a theoretical height of 1.2 m for the augmentation elements in the example considered here.

It is also advantageous that the destruction of all the raising elements 11 does not occur exactly for the same level of water. We can provide for example that a single element such as element 11c of Figures 3 and 4 is destroyed when the water reaches a first level N1 located about 10cm below the maximum level RM, that at least one other element 11, such as the elements 11b and 11d, are destroyed when the water reaches a second level N2 situated approximately 5cm below the maximum level RM, and the other elements 11, such as the elements 11a and 11e, are destroyed when the water reaches said maximum level RM.

In this way, the destruction of the first element 11c by a medium-sized flood may be sufficient for the flow of the flood without additional rise in the water level, which avoids the destruction of the other elements 11a, 11b, 11d and 11e . However, the margin of 10 cm which is thus taken is added to the maximum admissible overhanging blade height, so that the height of the rising elements and, consequently, the slice of water gained (RN'-RN) becomes equal at 1.1m (2m-0.8m-0.1m) in the example considered here.

The folding of the elevation element or elements 11 and, consequently, their destruction depends on the balance between, on the one hand, the motor moment Mm, that is to say the moment of the forces which tend to bend the rising element considered, and, on the other hand, the resistant moment Mr, that is to say the moment of the forces which oppose the folding of said rising element to the embedding. If a trigger device, directly linked to the water level, is not provided to trigger the folding of the raising element with precision for a predetermined water level, the water height corresponding to the above-mentioned equilibrium cannot be fixed only with a margin of uncertainty of up to 0.2m. In these conditions, it is necessary, for safety, to reduce the height of the elevation element (s) 11 by a quantity corresponding to this margin of uncertainty, for example 0.2 m. However, it is possible to avoid having to reduce the height of the raising elements by providing a trigger device which will be described later with reference to FIG. 11.

It is possible, for the flow rate of 50m³ / s considered in this example, to reduce the height of the maximum permissible overhanging blade before folding the lifting elements to less than 0.8m, by ensuring that the crest line of the elements 11 of the rise 10, considered together, is no longer disposed parallel to the crest of the overflow threshold 6, but along a non-rectilinear line, for example a broken line as shown in FIG. 4a, to lengthen the length of discharge of the flow mentioned above. If this length is doubled, the flow rate of 50m³ / s is then distributed over 80m instead of 40m and the height of the corresponding maximum admissible blade is reduced from 0.8m to 0.5m. This allows, all other things being equal, to raise the height of the elevating elements 11 by 0.3 m and to consequently increase the volume of water stored in the reservoir.

Figures 9a and 9b show the forces which, in service, can be applied to a riser 11 of the present invention. For the description which follows, it will be assumed that the element 11, in the form of a plate, has a thickness e and a height H les above the threshold 6. In FIGS. 9a and 9b, RM designates as before the maximum level, H₂ denotes the height of the maximum permissible overhanging blade above the raising element 11 and z denotes the water level. The driving forces, which tend to bend the raising element 11, are the thrust P of water on the upstream face of the raising element 11. The resistant forces, which oppose the folding of the elevating element 11, are the inherent resistance of the elevating element 11.

• a) si : 0 < z < H₁ : $$\text{P =}\frac{\text{1}}{\text{2}}{\text{· γ}}_{\text{w}}\text{· z²}$$
  
  $$\text{Mm =}\frac{\text{1}}{\text{6}}{\text{· γ}}_{\text{w}}\text{· z³}$$
  
• b) si : H₁ < z : $$\text{P =}\frac{\text{1}}{\text{2}}{\text{· γ}}_{\text{w}}{\text{· H}}_{\text{1}}^{\text{2}}{\text{+ γ}}_{\text{w}}\text{· H₁ · (z - H₁)}$$
  
  $$\text{Mn =}\frac{\text{1}}{\text{6}}{\text{· γ}}_{\text{w}}{\text{· H}}_{\text{1}}^{\text{3}}\text{+}\frac{\text{1}}{\text{2}}{\text{· γ}}_{\text{w}}{\text{· H}}_{\text{1}}^{\text{2}}\text{· (z-H₁)}$$
  

In the present example, to simplify the calculations, it will be assumed that the embedding line 17 around which the folding of the rising element 11 will occur, is located at the threshold 6. Under these conditions, to calculate the value of P and the value of the corresponding motor moment Mm with respect to line 17, two cases should be considered as a function of the water height z above the threshold 6. The values of P and Mm and the value of resistant moment Mr are summarized below, said values being given per unit of length of the elevating element 11.

• a) if: 0 <z <H₁: $$\text{P =}\frac{\text{1}}{\text{2}}{\text{Γ}}_{\text{w}}\text{Z²}$$
  
  $$\text{Mm =}\frac{\text{1}}{\text{6}}{\text{Γ}}_{\text{w}}\text{Z³}$$
  
• b) if: H₁ <z: $$\text{P =}\frac{\text{1}}{\text{2}}{\text{Γ}}_{\text{w}}{\text{· H}}_{\text{1}}^{\text{2}}{\text{+ γ}}_{\text{w}}\text{· H₁ · (z - H₁)}$$
  
  $$\text{Mn =}\frac{\text{1}}{\text{6}}{\text{Γ}}_{\text{w}}{\text{· H}}_{\text{1}}^{\text{3}}\text{+}\frac{\text{1}}{\text{2}}{\text{Γ}}_{\text{w}}{\text{· H}}_{\text{1}}^{\text{2}}\text{· (Z-H₁)}$$
  

In both cases : $$\text{Mr =}\frac{\text{1}}{\text{6}}{\text{σ}}_{\text{at}}\text{· E²}$$

In the above-mentioned formulas, P, Mm, Mr, e, H₁ and z have the meanings already indicated above. γ _w is the density of water and σ _a is the elastic limit of the material used for the construction of the rising element, for example steel.

In the graph in FIG. 10, the plots A and B respectively represent the variations of Mr and Mm as a function of the water height z above the threshold 6, and the plot C represents the variation of the flow of water discharged Q as a function of the height H of the blade overflow [Q = 1.8. H ^3/2 , H being equal to (z-H₁) before folding of the rising element 11 and to z after folding of said element]. Traces A, B and C were obtained from the formulas indicated above and for H₁ = 1.2m, e = 2cm, γ _w = 1 and σ _a = 30 kg / mm².

By considering the plots A and B, we see that the motor moment Mm reaches the same value as the resistant moment Mr for a value of z, (H₁ + H₂), of about 2m, that is to say for the maximum level RM in the numerical example considered here. In other words, the folding of the raising element 11 will take place when the water level reaches the maximum level RM. From the graph in Figure 10 and from formulas (5) and (6), we see that, without changing the value of the height H₁ of the rising element 11, if we had wanted that the folding of the latter occurs for a value of z smaller or greater than 2m, it would have been necessary respectively to decrease or increase the value of e and / or the value of σ _a compared to the values indicated above.

From the above, we see that, by an appropriate dimensioning in height (H₁) and in thickness (e) of the rising element 11 and by an appropriate choice of its constituent material (elastic limit σ _a ), we can cause the riser 11 to be bent to a predetermined water level.

In the graph of FIG. 10, we have also drawn, at A ', the variations of the resistant moment Mr' as a function of z in the case where the rising element 11 is composed of two adjoining plates 11 and 21 of different heights , the seal between these two plates being ensured by a seal 22 as shown in FIG. 11. The two plates 11 and 21 can be embedded in the same groove 12, in which case a spacer 23, continuous or discontinuous, can be scheduled between two plates at the bottom, or they can be embedded in different grooves

By considering the plots A 'and B we see that the motor moment Mm reaches the same value as the resistive moment Mr' for a value of z, (H₁ + H'₂), of about 2.25m. We also see that if we applied to the lower part of the downstream plate 11 all of the water pressure at the time when z reaches a value between (H₁ + H₂) and (H₁ + H'₂), we would obtain a sudden break in equilibrium for this value of z. Naturally, in this case, if it is desired that the folding still takes place for a value of z equal to 2m or less, it would then be necessary to size the plate 11 (its thickness e and / or its elastic limit σ _a ) so that its moment resistant Mr (line A in Figure 10) is weaker than what is shown in this figure.

This can be taken advantage of to cause folding of the raising element 11 in an even safer manner and with greater precision with regard to the level of water at which the folding takes place. Indeed, arrangements can be made for water to enter the space between the two plates 11 and 21 of FIG. 11 when the water reaches a predetermined level N, the dimensioning of the plates being such that at this instant the resistive moment suddenly passes from a value Mr 'greater than the value of the motor moment Mm to a value Mr substantially smaller than the value of said motor moment Mm. For this purpose, a triggering device such as that shown in FIG. 11. This triggering device essentially consists of a vent pipe 24 which, in normal service, places the space between the plates 11 and 21 in relation to the atmosphere, the upper end 24a of the pipe vent 24 being located at a level N equal to the level for which it is desired that the folding of the plate 11 occurs. The pipe 24 can be bent and pass through the plate 21 as shown in FIG. 11. An orifice 25 having a smaller cross-section than that of the pipe 24 is provided at the lower part of the downstream plate 11, near the threshold 6 , to evacuate the space between the plates 11 and 21 the water due to possible leaks at the joint 22 or the water which could enter through the upper orifice of the pipe 24, because of the waves, before the level of water has actually reached level N.

In the case where several rising elements 11, 21 are provided and must bend for different water levels, such as the levels N₁, N₂ and RM (FIG. 3) at least one vent pipe 24 is associated with each rising element and each pipe 24 extends upwards to a level N equal to the level N₁ or N₂ or RM for which the corresponding element must bend.

The upper end of each vent pipe 24 can be equipped with a device for protection against floating bodies, so as not to be blocked by them, or with a device for protection against waves, so that one or more successive waves do not inadvertently trigger the folding of the plate 11. Such protection devices are shown in Figures 12a to 12c. The protection device of FIG. 12a essentially consists of a funnel 26, the upper edge 26a of which is at a level higher than the level N and which has at least one small hole 27 at a level lower than the level N. In FIG. 12b, the protection device consists of the pipe 24 itself, the upper end of which is bent in the form of a siphon 28. Finally, the protection device of FIG. 12c consists of a bell 29 , which covers the upper end 24a of the vent pipe 24 and of which the vertex 29a is at a slightly higher level than the level N.

It may be advantageous, in order to improve the safety of an existing structure, the overflow threshold 6 of which was initially leveled, depending on the project flood initially chosen, at a level determining the level of the normal reservoir RN (FIG. 13c), to level the threshold 6 a few decimeters below its current coast (corresponding to RN) and to embed on the leveled threshold 6 a fuse increase 10, in accordance with the present invention, composed of at least one increase element 11 dimensioned in height and thickness as described above to fold around line 17 when the water level reaches a predetermined level at most equal to the maximum level RM corresponding to the project flood. Under these conditions, the probability of opening of the increase 10 is not modified but, in the event of an exceptional flood, the flow section available after total destruction of the increase 10 is notably increased for the same water level in the reservoir, which makes it possible to safely pass a flood having a flow rate much higher than that of the flood for which the structure was originally dimensioned. In the case where the height chosen for the elevating elements 11 is equal to the leveling height of the threshold 6 (FIG. 13a), one simply obtains an increase in the safety of the structure, without changing the level of the normal restraint RN , compared to the existing structure before the threshold 6 is lowered (Figure 13c). However, it is possible both to increase the safety of the structure and to raise the level of the normal restraint to a level RN 'by giving the elevating elements 11 a height such that their apex is at a level higher than the level RN, but lower than the maximum level RM (figure 13b).

In the embodiment shown in Figure 11 it was assumed that the two plates 11 and 21 were embedded in the same groove 12 and joined to one another. However, it is possible to envisage embedding the two plates 11 and 21, or a greater number of plates, for example three plates 11, 21 and 31 (FIG. 14a), in one or more recessed grooves spaced on the threshold. 6, the plates having different heights, which grow from upstream to downstream, and being dimensioned (e, σ _a ) so as to fold successively from downstream to upstream for hydrological conditions of increasing severity as illustrated by FIGS. 14a to 14d in the case of two plates 11 and 21. In this way, if the folding of the downstream plate 11 was sufficient to evacuate a medium-sized flood, having caused a rise in the water level up to at a first predetermined level N₁ (RN '<N₁ <RM), the plate 21 remains upright (Figure 14c) and the normal retention level is only partially reduced (RN''instead of RN' before folding the plate downstream 11). If the folding of the plate 11 was not sufficient to evacuate the flood and if the water level reaches a second predetermined level N₂ (N₁ <N₂ ≦ RM), the upstream plate 21 in turn folds as shown on the figure 14d. After folding of the plate 11 and, if necessary, of the plate 21 and after evacuation of the flood, the plate or plates 11 and 21 can be replaced by unfolded plates.

In the embodiments which have been described so far, each plate 11 (or 21 or 31) forming a raising element was engaged in a groove provided in the threshold 6. However, the plate 11 (or 21 or 31) can be engaged in a groove formed in a mounting part 32, continuous or discontinuous, which is itself rigidly fixed to the threshold 6, for example by means of bolts and threaded rods 33 sealed in the masonry of the threshold 6 as shown in Figure 15. From preferably, the threshold 6 is leveled at least by an amount corresponding to the height of the mounting piece 32.

According to another embodiment, instead of embedding the plate 11 (or 21 or 31) by engaging its lower part in a groove, the embedding can be carried out as shown in Figure 16. In this figure, the plate 11 ', seen in vertical section, is curved in the shape of L and its horizontal branch 11'a is rigidly fixed to the threshold 6 by a connection of the embedding type, that is to say a connection where no movement relative is only authorized, for example by means of several bolts and threaded rods 33 (only one is visible in FIG. 16) sealed in the masonry of the threshold. When several plates are provided, like plates 11 'and 21' (Figure 16), they can be fixed together at threshold 6 by the same bolts and threaded rods 33. According to a variant, instead of using curved L-shaped plates , straight vertical plates can be used, like the plates 11 of FIGS. 8, 13, 14, 15, which are then rigidly fixed to the threshold 6 by brackets, the vertical branches of the brackets being fixed to the plates for example by welding, while that their horizontal branches can be fixed to the threshold 6 in a manner similar to that shown in Figure 16. In the latter case, it is the thickness of the material constituting the brackets and its elastic limit σ _a that must be taken in consideration for the calculation of the resistant moment Mr which determines the level of water for which the "folding" of the rising elements occurs.

FIG. 17 shows, in vertical section, an elevation element 11 composed of two plates 11i and 11j which are removably stacked one on the other. If desired, several plates 11j can be provided and stacked one on the other. Plates 11i and 11j can be held together by at least two pairs of plates 34, one pair of which is visible in FIGS. 17 and 18, which are rigidly fixed to one of the two plates 11i and 11j and which straddle the other plate. Instead of the plates 34, it is also possible to use bars extending over the entire length of the plates 11i and 11j. A seal 35 is provided between the plates 11i and 11j and, if necessary, between the plates 11j when there are several. The plates can all have the same vertical dimension or different vertical dimensions; for example, the upper plate 11j has a smaller vertical dimension than that of the plate 11i. With such a construction of the rise element, not only are the operations for setting up the rise easier, but it is also possible to give the rise different heights depending on the season, without requiring special human supervision from the point of view of flood evacuation.

In conclusion, the height of the rise 10, therefore of its element or elements 11, depends on an economic choice, on the desired progressiveness in the folding of the various rise elements, on the precision of the water level at which the folding (precision which can be improved by providing a trigger device as described above with reference to Figure 11) and the shape of the peak line of the rise, line which can be straight or square. In the numerical example described above, the height of the resulting rising elements can vary between 0.9m and 1.5m, allowing, depending on the options taken, to gain between 45 and 75% of the slice of water which would be lost without the use of the fusible link.

From the above, it is clear that the fuse increase implemented in the present invention allows to substantially and almost permanently increase the storage capacity of a dam or other structure with a free discharge threshold, while maintaining or increasing the operational safety specific to structures with a free discharge threshold, by reliably allowing the evacuation of exceptional floods by automatic opening (folding of 'at least one element of the increase) without any monitoring or any human intervention or control device. It is also clear that the surge can be manufactured and installed on the weir sill of a dam or other structure for a lower cost than that of previously known valves, and without major modification of the weir sill.

It is understood that the embodiments of the present invention which have been described above have been given for purely indicative and in no way limitative, and that numerous modifications can be easily made by those skilled in the art without however, depart from the scope of the present invention as defined by the appended claims.

Claims (12)

1. Overflow spillway for dams and similar structures comprising an overspill sill (6) whose crest (8) is set at a first predetermined level (RN), lower than a second predetermined level (RM) corresponding to the maximum reservoir level for which the dam is designed, the difference between the said first and second predetermined levels (RN and RM) corresponding to a predetermined maximum discharge of a design flood and a water level raising means (10) on the sill (6) of the spillway (5), the said water level raising means (10) comprising at least one water level raising element (11) in the form of a substantially vertical plate whose lower portion is rigidly fixed to the sill (6) of the spillway (5), the said element having a predetermined height (H1) which is less than the difference between the aforementioned first and second predetermined levels (RN and RM) and which corresponds, for a headwater level substantially equal to the said maximum level (RM) to a mean flood with a predetermined lower discharge than the predetermined maximum discharge, the said element (11) being so designed that it bends about a zone (17) near by its fixed lower portion when the headwater reaches a higher level than the top of the water level raising element, characterised in that the water level raising element (11) is maintained at its lower portion by fixing the plate itself to the sill (6) of the spillway (5), and characterised in that the plate forming the water level raising element (11) is of such thickness at its fixed lower portion and made of a material with such a yield point that the moment of the forces applied to the plate by the water comes to equal the resisting moment at the fixed lower portion of the said element when the headwater reaches a third predetermined level (N) higher than the top of the water level raising element (11) but not higher than the second predetermined level (RM).
2. Overflow spillway as claimed in Claim 1, characterised in that the plate (11) forming the water level raising element is let into a slot (12) in the sill (6) or into a mount (32) affixed to the sill (6).
3. Overflow spillway as claimed in Claim 1, characterised in that the plate (11) forming the water level raising element is bent to an L shape with its horizontal leg (11a) rigidly fixed to the sill by fixing means of a type preventing any relative movement between contact surfaces of the said plate and sill.
4. Overflow spillway as claimed in Claims 1 to 3, characterised in that in the case of an existing spillway (5), the crest (8) of the overspill sill (6) is lowered to a lower level than the said first predetermined level (RN) and the water level raising element (11) is rigidly fixed on the lowered sill and is given a height such that its top is at a level (RN) at least equal to the said first predetermined level (RN) but lower than the said third predetermined level (N).
5. Overflow spillway as claimed in Claims 1 to 4 characterised in that a seal (15) is provided between the overspill sill (6) and the lower portion of the water level raising element (11).
6. Overflow spillway as claimed in Claims 1 to 5, characterised in that the said water level raising element consists of a pair of plates (11 and 21) of different heights with a seal (22) between the two.
7. Overflow spillway as claimed in Claim 6, characterised in that it comprises at least one vent pipe (24) which under normal service conditions maintains a space between the two plates (11 and 21) at atmospheric pressure, the top end of the vent pipe being at a level equal to the said third predetermined level (N).
8. Overflow spillway as claimed in Claims 1 to 7, characterised in that a plurality of water level raising elements (11) are located side-by-side along the crest (8) of the spillway sill (6) with seals (13) between adjacent edges of the said elements.
9. Overflow spillway as claimed in Claim 8, characterised in that the thickness and yield point of the water level raising elements (11) are such that at least a first one of said elements (11c) bends when the headwater reaches the said third predetermined level (N1), the said third level being lower than the said second predetermined level (RM), that at least a second one of said elements (11b, 11d) bends when the headwater reaches a fourth predetermined level (N2) between the second and third predetermined levels (RM and N1) and that at least a third one of said elements (11a, 11e) bends when the headwater reaches a fifth predetermined level higher than the fourth level (N2) but not higher than the second predetermined level (RM).
10. Overflow spillway as claimed in Claims 1 to 8, characterised in that the water level raising means (10) comprises at least two elements (11 and 21) located one after the other in the upstream-downstream direction and being of different heights in increasing order in the upstream-downstream direction, the thicknesses and yield points being so selected that the downstream element (11) bends when the headwater reaches the said third predetermined level (N1) lower than the second predetermined level (RM) and that the upstream element (21) bends when the headwater reaches a fourth predetermined level (N2) higher than the third predetermined level (N1) but not higher than the second predetermined level (RM).
11. Overflow spillway as claimed in Claims 1 to 10 characterised in that said element (11) comprises at least two stacked vertical plates (11i, 11j).
12. Overflow spillway as claimed in Claims 1 to 10 characterised in that the water level raising means (10) comprises a plurality of vertical plates (11) in a staggered pattern between permanent vertical plates (20) such that the crest line of the water level raising means has a crenellated shape.

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