WO2023224494A1

WO2023224494A1 - Method and device for removing rocks from a dam

Info

Publication number: WO2023224494A1
Application number: PCT/NO2023/050117
Authority: WO
Inventors: Tom Jacobsen
Original assignee: Jarala As
Priority date: 2022-05-19
Filing date: 2023-05-19
Publication date: 2023-11-23
Also published as: NO20220592A1

Abstract

Method for removing sediments comprising fine-grained material as well as rocks and boulders with a diameter of at least 10 cm deposited at inlets or hatches in an intake dam through a pipe construction (1), wherein: - the pipe construction (1) is established with aa circular cross-section and an inlet opening (3) in front of the intake or hatch (5) and an outlet opening (8) outside a dam wall (2) at a height lower than the water level in the intake dam and with a water trap (9) at its lower end, while being so dimensioned that the velocity equals or exceeds the velocity given by Durand's formula for flow rate: (I), where k = a constant 0.8; g = acceleration of gravity 9.81 m/s²; D = internal diameter; and Ss = relative specific gravity of sediments, while the pipe construction (1) in a high intermediate area is arranged over an overflow threshold (2b) in the dam wall (2) and with a vent opening (7) upstream of the overflow threshold (2b).

Description

Method and apparatus for removing rocks from a dam

According to the preamble to claim 1, the present invention relates to a method for removing sediments comprising boulders, rocks as well as fine-grained material deposited at inlets or hatches in an intake dam. According to another aspect, the invention relates to an apparatus for the same objective as set forth in the preamble to claim 13.

Background

Water intakes in streams and rivers are often established by building a dam that stops the water and raises the water level to form an intake dam. The water is typically channelled from the intake dam, through an intake grate and into a waterway (tunnel, pipe or canal).

Streams and rivers will often bring with them sand, gravel, rocks and boulders of variable size (sediments). This happens especially when there is a high water flow and the water has enough speed and force to move the sediments. When an intake dam is established, the speed of the water will be reduced and the sediments will fall to the bottom, and/or the water will be directed at high speed towards the intake. In both cases, the result will be that sediments are directed towards the intake, and if there is an intake grate, the sediments will remain against it and block the water intake. The water will then choose the easiest route and flow past the overflow of the dam and further down the watercourse.

The sediments carried by the stream or river (watercourse) can be anything from fine sand and gravel to rocks and boulders. Particularly in steep streams, rocks and boulders up to a metre or more in size can be deposited.

If the intake is a power station, not taking in water used for power generation will result in significant losses. The value of lost production can add up to very large sums in a short period of time.

In cases where there is no separate intake grate, sediment can be carried with the water and deposited elsewhere in the waterway, causing problems, or possibly even all the way to the turbine, causing damage thereto.

Intakes in streams and steep rivers are often established without a road connection and in many cases also without a power supply or network. It is therefore difficult or impossible to monitor such intakes, and blockages due to sediments will often not be detected until a long time has passed. If a blockage due to sediments has been detected, it will nevertheless often take a long time and require a lot of planning to remove sediments from intake dams; transportation of equipment and personnel requires a lot of resources and in many cases favourable weather and/or weather conditions to transport personnel and/or equipment to the intake dam.

US patent no. 2 688461 and CN 104420499 A are two examples among many that describe devices for material transport based on the siphon principle, but which are not related to the transportation of rocks of significant size.

Prior art technology

Intake dams are typically cleaned up by excavating sediments with an excavator. Where the intake is roadless, the excavator must typically be flown in by helicopter or driven in by off-road vehicles.

Another method used is to open the bottom hatch, drain the water and flush out the sediments by allowing the water to flow over the sediments to erode and carry them away.

In both cases, and if the intake is roadless, planning and sufficiently good weather conditions are required to reach the intake by foot through the terrain or by helicopter.

It is furthermore well known that siphon structures can be used to divert water out of the reservoir in order to divert floods.

Objectives of the invention

The objective of the invention is to remove sediment from small intake dams. This can be from anywhere in the intake dam where one wishes to remove sediment, but it will typically be in front of intakes to power plants, waterworks, fish farms and irrigation. It is also an objective that the sediment is only removed when there is excess water, which would otherwise flow over the spillway to the dam and further down the watercourse, and that the inventive device therefore starts and stops automatically accordingly. It is furthermore an objective that the device starts removing sediments when there is sediment transport in the river. It is also an objective that the device be free from moving parts and is highly reliable, and that it is resistant to icy conditions and heavy loads during floods. It is furthermore an object that it removes all the sediments that come with the watercourse and that are carried towards and possibly deposited in front of the inlet, including even the largest particles (boulders), so that the inlet opening of the device according to the invention is not clogged. Such rocks can, in extreme cases, be over one meter in size (diameter). The invention is therefore also referred to as a "boulder excluder". It is also an object that the invention can be manufactured in parts with a certain maximum weight, so that it can be transported in parts, for example by helicopter, and that the parts can then be assembled at the construction site with hand-held and portable equipment.

The present invention

The objects set forth above are achieved by a method according to the invention as defined by claim 1. According to another aspect, the invention relates to a device as set forth in claim 13. Preferred embodiments are set forth in dependent claims.

The invention essentially consists of a pipe construction the shape of which being such adapted that the upstream end is positioned in front of the intake opening or intake grate or another location in an intake dam from which one wishes to remove sediments, including rocks and boulders. The pipe is arranged to pass over an overflow threshold of the dam or at a similar height.

Although an intake dam will normally be small in size, it can also be larger. The invention can therefore also be used in a dam or reservoir of any size. There will normally be an overflow threshold that diverts excess water, but this is not a requirement.

The outlet opening of the pipe construction that constitutes the main element of the device according to the invention is placed downstream of the dam and at a lower level than the water level in the dam so that the height difference between the water level in the intake dam and the outlet opening ensures that the water flows through the invention. The flow rate is affected by the vertical position of the outlet opening. The intended minimum flow rate is ensured by placing the outlet opening at a level that is sufficiently low to achieve this flow rate through the pipe construction. This is what is meant by the phrase "dimensioned so that the velocity is equal to or exceeds the velocity given by Durand's formula for flow rate". This is sufficient to suck in rocks and boulders up to the size as the pipe and to keep these rocks / boulders moving up through the pipe and down the downstream side, so that all rocks and boulders that are sucked in are removed, regardless of size.

The inventive device will normally be given a rounded shape on the inlet opening so that singular loss in the inlet opening is reduced as much as possible. Furthermore, the outlet opening can be designed with a gradually expanded cross-section to recover the kinetic energy and reduce the required head of water. The outlet opening of the boulder excluder will be downstream of a water trap. This is shaped by turning the outlet opening sufficiently upwards so that the siphon is completely filled with water at all times when water flows through the boulder excluder.

The inner diameter of the pipe construction will typically be larger than 20 cm, preferably in the range of 50 to 160 cm, more preferably 60 to 140 cm.

At the upstream side of the boulder excluder, and at the level of the overflow threshold, there will be a vent hole. This hole is sealed by water when the water level rises above the overflow threshold, so that air flowing out of the boulder excluder is replaced by water and the flow of water increases.

According to a preferred element, the water flow only starts when the water level in the intake dam reaches such a high level that the water flow over the dam (overflow loss) is as great as the water flow through the boulder excluder. This ensures that water that would otherwise have passed through the intake and been used for power generation, for example, is not used to remove sediments. This is achieved by placing the lowest internal point in the boulder excluder above the overflow at the same level as the aforementioned water level. Similarly, the vent hole will ensure that the water flow through the boulder excluder is interrupted when the water level in the intake dam drops below the aforementioned level.

This means that sediments are removed using only the surplus water that would have passed the overflow over the dam anyway, and thus the removal of sediments has no cost in the form of lost water (or other energy loss for that matter).

A small protrusion or "jump" may be arranged inside the rock suction device to mix air into the water, this air be flowing out through the siphon together with the water and contributes to the rock suction device eventually being completely filled with water and the water flowing through at full capacity.

The inventive device may be made of several different materials, such as steel or concrete (as part of the dam), but it will preferably be made of polymer materials that are entirely or largely recyclable, such as polyethylene, or combinations of different polymer materials, with or without fibre reinforcement. Such materials can be made lightweight, durable, robust against external stress, rust-free while being easy to transport and easy to assemble.

It will often be appropriate to manufacture the device in parts that are easy to transport by offroad vehicles or helicopter. Typically, the device will be manufactured from polyethylene (PE) or especially HDPE (High Density Polyethylene), which has particularly good properties in terms of wear, resistance, strength, weldability and price. The combination of these properties makes polyethylene the best choice of material. Polyethylene pipes can be welded together with welding joints that can be powered by handheld equipment.

PE and HDPE pipes can be used with wall thicknesses that, together with the construction in segments, mean that common low pressure classes (PN10 and even PN6) have sufficient ring stiffness against vacuum. Wall thicknesses in the range 1/26 - 1/17 of the outer pipe diameter are sufficient (SDR17 corresponds to PN10 and SDR26 corresponds to PN6).

Although the inventive device preferably be started automatically at a certain water level in the dam, for example by overflow, it can also be started by an operator. This can be done by installing an additional pipe from inside the intake dam that opens into the boulder excluder, so that it draws air through the siphon and starts the boulder excluder. Such a pipe will typically be opened with a valve if the boulder excluder is to be started by an operator.

If desired, an additional pipe can also be fitted with an open inlet that is positioned at such a height that it takes in water automatically when the water reaches a certain water level and starts the boulder excluder before the water level has reached the overflow threshold. A variation of this consists of utilising such an additional pipe that includes a flexible or movable part so that its inlet can be easily height-adjusted as needed.

The boulder excluder can also be started by closing a tight lid over the outlet opening and then sucking air out of the boulder excluder with a vacuum pump.

It will often be appropriate to design a pit in front of the inlet so that sediment can be sucked into the boulder excluder from the bottom of the pit. Since rocks fall into the pit along sloping side edges, the pit will ensure that sediments are removed from a larger area in front of the inlet.

The boulder excluder can be made at any desired angle to fit next to existing structures or into new designs.

Further details of the invention

Figure 1 is a side view of a typical design of the boulder excluder placed above an overflow threshold in an intake dam.

Figures 2A to 2C are front views showing different variants of a detail of the present invention.

Reference is now made to figure 1, which shows the device (also referred to as the boulder excluder) in the form of a pipe construction 1 mounted above an overflow threshold 2b in a dam wall 2. The inlet opening 3 of the boulder excluder is located in front of the inlet 4, which is shown equipped with an inlet grate 5. Sediments 6 are deposited in front of the inlet opening 3 of the boulder excluder. Sediments are collected in a pit 20 that is designed so that sediments do not settle against the inlet. The pit has a sloping bottom with an angle v that can vary, but which typically is larger than 5 degrees and often significantly larger, such as at least 20 degrees and often at least 35 degrees.

An air-vent opening 7 on the upstream side of the highest point of the pipe construction, over the overflow threshold 2b of the dam wall, is positioned so that it is covered by water when the water level is so high that the boulder excluder should start, but which lets in air and interrupts the flow of water through the boulder excluder when the water level is so low that it is desired to stop the boulder excluder.

Furthermore, the figure shows that the outlet opening 8 of the boulder excluder can be arranged downstream of a water trap 9. This is designed in such a way that the pipe end forming the outlet opening is curved sufficiently upwards so that the water trap, which is filled with water 10 when water flows through the boulder excluder, retains a sealing "pocket" of water even when the flow of water ceases. A lid 17 helps to ensure that the water does not evaporate, but remains in the siphon 9 over time. Furthermore, the lid 17 makes it possible to evacuate air from the upper part of the boulder excluder, i.e. the part that is positioned above the overflow threshold 2b, by means of a vacuum pump 18 to thereby start the boulder excluder regardless of the water level in the dam. By "upper part" of the boulder excluder is understood the part upstream of the overflow threshold 2b.

A small protrusion 11 inside the boulder excluder helps to mix air into the water, through an abrupt change of direction of rocks that hit the protrusion.

The inlet opening 3 has smoothly rounded walls that allow water to flow along a smoothly curved surface 12 to minimise singular loss. For this purpose, a rounding r/D of at least 0.15 is preferred, where r is the radius of curvature and D is the inner diameter of the inlet opening. The inner diameter at the inlet opening is typically 5-10% smaller than the inner diameter in the rest of the boulder excluder to ensure that rocks that are able to pass the inlet opening do not get stuck further down in the boulder excluder.

At the outlet opening 8, the rock suction device can be designed with a gradually increasing cross-section that converts the kinetic energy in the water into positional energy so that the energy loss in the outlet opening is reduced and the height difference between the upstream water level and the outlet is optimally utilised to give the water flow speed. A secondary pipe 14 may be connected between the intake dam and the downstream side of the boulder excluder, that is, the side downstream the overflow threshold of the dam wall 2. The secondary pipe 14 may be opened by a valve 15 allowing the boulder excluder to be started by an operator when the inlet opening 16 of the secondary pipe 14 is below the water level in the dam.

If the valve is open at all times, the pipe 14 may serve to automatically start the boulder excluder when the water level in the dam increases to a level above the inlet opening 16 even if the water is at a lower level than the overflow threshold. For this purpose, the inlet opening 16 of the secondary pipe 14 is, in such case, placed at the height at which the water level is intended to activate the pipe construction 1.

The inlet opening 16 is positioned at a height lower than the overflow threshold, typically at a vertical distance in the range of 5-100 cm, preferably 10-60 cm, more preferably 10-40 cm lower than the overflow threshold.

The figure also schematically shows a welding sleeve 19 that can be used to join two pipe sections. The primary pipe of the boulder excluder (the pipe construction) can of course also be composed of more than two pipe sections.

Figure 2A shows in a front sectional view that the pipe construction 1 passes over the overflow threshold 2b and that there is a small positive height difference h from the overflow threshold s to the lowest point in the pipe, which essentially corresponds to the thickness of the pipe. Unless pipe flow is initiated in some other way, it will start automatically when water flows over the overflow threshold with a height equal to h.

Figure 2B shows a variant of the same as figure 2A, in which the pipe construction is supported by blocks or similar, resulting in a positive height difference h'that is somewhat greater than the pipe thickness and which means that the height difference h' can be adjusted as desired.

Figure 2C shows another variant of the same, where the pipe construction 1 is arranged in a depression on the overflow threshold 2b, which results in the height difference h" from the general level of the overflow threshold to the lowest point in the pipe (above the overflow threshold) being reduced compared to what is shown in Figure 2A.

The different variants shown in Figures 2A to 2C demonstrate that the level for automatic startup of the boulder excluder can be achieved by simple means in addition to the possibility of using the secondary pipe 14 as a start-up pipe. It is essential for the function of the boulder excluder that the velocity in the pipe is sufficient to keep the sediments in suspension so that the pipe does not clog. A recognised way of calculating this velocity is to use Durand's formula for velocity in pipes. The pipe construction must therefore be dimensioned so that the velocity is equal to or exceeds the velocity given by Durand's formula for flow velocity:

where k = a constant 0.8; g = acceleration of gravity 9.81 m/s²; D = internal diameter; and Ss = relative specific gravity of sediments,

As a calculation example, the following values are used: k = 0,8 g = 9.81 m/s2

D = 1.0 m

Ss = 2.7

The dimensioned speed thus becomes 4.62 m/s.

As can be seen from Durand's formula, the velocity is affected by the diameter as well as the density of the sediments (rocks). At typical relative density as indicated in the example and with a diameter in the range of approximately 0.5 meters, a flow velocity of 3.5 m/s will be sufficient, while at diameters in excess of 1 meter, the desired minimum flow velocity may be 5 m/s.

Claims

1. Method for removing sediments comprising fine-grained material as well as rocks and boulders with a diameter of at least 10 cm deposited at inlets or hatches in an intake dam through a pipe construction (1), characterised in that:

- said pipe construction (1) is established with an inlet opening (3) in front of said intake or hatch (5) and an outlet opening (8) outside a dam wall (2) at a height lower than the water level in the intake dam,

- said pipe construction (1) is internally executed with a substantially circular cross-section of diameter larger than the largest rocks to be removed,

- said pipe construction (1), in the area downstream of the high intermediate area, is provided the form of a water trap (9)

- the pipe construction being so dimensioned that the velocity equals or exceeds the velocity given by Durand's formula for flow rate:

- the pipe construction (1) in a high intermediate area is led over an overflow threshold (2b) in the dam wall (2).

- the pipe construction (1) is designed with at least one vent opening (7) upstream of the overflow threshold (2b).

2. Method according to claim 1, wherein the water level that initiates the flow of water through the pipe construction at the same time is the water level that provides an overflow over the dam corresponding to the water flow through the pipe construction.

3. Method according to claim 1 or 2, wherein the pipe construction is made of a material selected from polyethylene (PE) and high density polyethylene (HDPE).

4. A method in accordance with any of the preceding claims, wherein the pipe construction is transported to the user site as elements that are welded together at the site of use.

5. Method according to any one of the preceding claims, wherein the pipe construction (1) is made with a circular cross-section with a diameter greater than 20 cm, preferably with a diameter in the range from 50 to 200 cm, more preferably from 60 to 160 cm.

6. Method according to any one of the preceding claims, wherein the pipe construction is carried out for a minimum flow velocity higher than 3.5 m/s, more preferably higher than 5.0 m/s.

7. Method in accordance with any one of the preceding claims, wherein the pipe construction (1) at its highest point is provided with a vacuum pump (18) arranged to pump out air from the pipe construction.

8. Method according to any one of the preceding claims, wherein the pipe construction (1) is provided with a secondary pipe (14) arranged as a start-up pipe, with an outlet opening inside the pipe construction (1) downstream of the high intermediate area and an inlet opening (16) located inside the dam at the height at which the water level it is intended to activate the pipe construction (1).

9. Method according to any one of the preceding claims, wherein the inlet opening (3) of the pipe construction (1) has a diameter that is at most 95% of the inner diameter of the pipe construction (1) and preferably less than 90% of the same.

10. Method according to any one of the preceding claims, wherein the inlet opening (3) of the pipe construction (1) is rounded such that r/D is at least 0.05 and preferably greater than 0.15 where r is the radius of curvature and D is the inner diameter of the inlet opening (3).

11. Method according to any one of the preceding claims, wherein the vent opening (7) is positioned at such a height that the water flow stops when the level in the intake dam is lower than the level that provides maximum water flow through the pipe construction (1).

12. Method according to claim 8, wherein the secondary pipe (14) is provided with a valve (15).

13. Device comprising a pipe construction (1) for removing sediments comprising fine-grained material as well as rocks with a diameter of at least 10 cm deposited at inlets or hatches in an intake dam through said pipe construction (1), characterised in that

- the pipe construction (1) has with an inlet opening (3) arranged to be placed in front of said intake or hatch (5) and an outlet opening (8) outside a dam wall (2) at a height lower than the water level in the intake dam,

- the pipe construction (1) internally has a substantially circular cross-section of diameter larger than the largest rocks to be removed,

- the pipe construction (1), in the area downstream of the high intermediate area, has the form of a water trap (9) - the pipe construction (1) is so dimensioned that the flow rate is equal to or exceeds the rate given by Durand's formula for flow rate:

where k = a constant 0.8 - 1.0; g = acceleration of gravity 9.81 m/s²; D = internal diameter; and Ss = relative specific gravity of sediments,

- the pipe construction (1) in a high intermediate area is arranged to be positioned over an overflow threshold (2b) of a dam wall (2)

14. A device according to claim 13, wherein the device comprises a secondary pipe (14) with an inlet opening (16) at a defined level in the intake dam and a connection to the pipe construction (1) downstream of the overflow threshold (2b) and that the secondary pipe (14) has a valve (15) that can be opened and closed.

15. A device according to any one of claims 13-14, wherein the device is provided with a vacuum pump (18) arranged to evacuate air from the upper part of the device.

16. A device according to any one of claims 13-15, wherein the pipe construction (1) is substantially made of polymer, fibre-reinforced polymer or composite material, preferably polyethylene.