A sand retaining and discharging structure for the lower reservoir of a pumped storage power station and its operation method

Abstract

The present invention discloses a sediment retention and drainage structure for the lower reservoir of a pumped-storage power station and its operation method, belonging to the technical field of water conservancy and hydropower engineering. The structure includes a lower reservoir and a bypass flood discharge and sediment drainage channel. A dam is provided at the tail of the lower reservoir, and a sediment retention dam is provided in each gully around the lower reservoir to form a closed reservoir basin. The bypass flood discharge and sediment drainage channel connects the tops of the sediment retention dams in each gully around the lower reservoir in series, and both ends of the bypass flood discharge and sediment drainage channel are connected to a discharge chute, which starts at the abutment of the dam and extends to the river channel downstream of the dam. The structure can not only intercept bedload sediment but also discharge suspended sediment, with good sediment retention and drainage effects, meeting the long-term operation requirements of the pumped-storage power station unit and helping to extend the service life of the unit. There is no need to use the river bend terrain to straighten the bend to arrange a flood discharge and sediment drainage tunnel or a flood discharge and sediment drainage open channel, and the requirements for the terrain conditions of the lower reservoir are low.

Description

Technical Field

[0001] The invention relates to a sand retaining and discharging structure for a lower reservoir of a pumped storage power station and an operation method thereof, belonging to the technical field of water conservancy and hydropower engineering. Background Art

[0002] Driven by the goals of reaching peak carbon emissions by 2030 and achieving carbon neutrality by 2060, the clean energy supply side is being accelerated. However, new energy systems such as wind power and photovoltaics are subject to significant contingency factors and low guaranteed rates. Pumped-storage power stations offer unique advantages in energy storage, peak load regulation, and frequency regulation. They are key components in promoting the development and utilization of new energy and building a new power system dominated by new energy. They also play an important role in the stability and safety of power grid operations. Due to the frequent startup and shutdown of pumped-storage hydropower station units, large head differences, and susceptibility to wear, pumped-storage hydropower stations place very high demands on the sediment content of the lower reservoir water. Relying solely on the reservoir's own sedimentation to reduce sediment levels in the event of a settling event takes a long time, resulting in frequent unit shutdowns and a significant impact on power generation efficiency.

[0003] Chinese patent document CN103938591A discloses a method for reducing siltation in reservoirs of sediment-laden rivers. The method divides the reservoir into two reservoir areas, clear water and muddy water, and uses a sediment transport culvert to efficiently discharge the sediment-laden water far upstream of the dam out of the reservoir, achieving the goals of both storing water and discharging sediment in the reservoir and expanding the reservoir's precipitation flushing distance. Fine-grained sediment that overflows from the sediment-blocking submerged dam into the reservoir area in front of the dam is discharged to the outside of the reservoir through the dam's spillway by using a submersible sand pump for reservoir dredging. For the wide, shallow, and curved sedimentation patterns in the reservoir river channel, a submersible sand pump is used for dredging to create a straight river channel in the reservoir area that is conducive to the transport of density currents, thereby improving the reservoir's natural sediment discharge effect.

[0004] However, for the lower reservoir of a pumped-storage power station, the sediment-blocking dam or submerged dam at the end of the reservoir can only intercept bedload sediment, not suspended sediment, and its sediment-blocking effect is extremely limited. The method of building a sediment-blocking dam at the end of the reservoir to intercept bedload sediment and then discharging suspended sediment through a flood discharge tunnel requires high topography at the lower reservoir, requiring a clear river bend to straighten the flood discharge tunnel. For high-sediment rivers and gully-prone terrain, this method cannot meet the long-term operation requirements of pumped-storage power station units, significantly shortening the unit lifespan. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a sand retaining and discharge structure for the lower reservoir of a pumped storage power station and an operation method thereof.

[0006] The present invention is achieved through the following technical solutions:

[0007] A sediment retention and drainage structure for the lower reservoir of a pumped-storage power station comprises a lower reservoir and a bypass flood discharge and sediment drainage channel. A weir is provided at the tail of the lower reservoir, and a weir is provided in each gully around the lower reservoir to form a closed reservoir basin. The bypass flood discharge and sediment drainage channel is connected to the sediment drainage channel inlet connecting section and the sediment drainage channel outlet connecting section of each weir, thereby connecting the tops of the sediment drainage dams in each gully around the lower reservoir in series, and both ends of the bypass flood discharge and sediment drainage channel are connected with a discharge chute, which starts from the dam shoulder of the weir and extends to the river channel downstream of the weir.

[0008] The sediment retaining dam is a concrete gravity dam, comprising a dam body and a spillway. A traffic road is provided on the top of the dam body. The top of the dam body is provided with a sediment discharge channel outlet connecting section, a water retaining dam section, a gateless spillway section, a gated spillway section, a gateless spillway section, a water retaining dam section and a sediment discharge channel inlet connecting section in sequence from one end to the other end of the dam body. The spillway is provided on the downstream dam surface of the dam body, and the upstream end of the spillway is connected to the downstream ends of the gated spillway section and the gateless spillway section.

[0009] The elevation of the inner bottom surface of the sand drainage channel outlet connecting section, the elevation of the inner bottom surface of the sand drainage channel inlet connecting section, the elevation of the water inlet of the overflow dam section with gates and the road surface elevation of the traffic road are consistent.

[0010] A gate A is provided at the water inlet of the overflow dam section with a gate, and a gate B is provided in the connecting section of the sediment discharge channel inlet.

[0011] A drainage hole is provided in the middle of the dam body.

[0012] A stilling pool is provided on the downstream side of the dam body, and the stilling pool is connected to the downstream end of the spillway. Spillway side walls are provided on both sides of the spillway on the downstream dam surface of the dam body, and one end of the spillway side wall is connected to the retaining dam section, and the other end is connected to the side wall of the stilling pool.

[0013] The bottom elevation of the bypass flood discharge and sediment discharge channel gradually decreases from upstream to downstream, and the slope is calculated according to the open channel uniform flow formula. Calculate, where Q For traffic, A is the cross-sectional area of ​​the flow, C is Xie Cai coefficient, R is the hydraulic radius ，i is the bottom slope.

[0014] The bypass flood and sediment discharge channel includes a bottom plate, which includes a gravel cushion layer and a concrete surface layer laid on the gravel cushion layer. A drainage ditch is provided on the side of the bottom plate close to the bank slope, and a concrete lining is provided on the drainage ditch along the bank slope. A concrete side weir is provided on the water side of the bottom plate, and the top of the concrete side weir on the water side is provided with a circular chamfer, and the bottom of the water side is provided with a bottom plate corner guard, and the height of the concrete side weir should not be greater than 1.2m.

[0015] The method for operating the sediment retaining and discharging structure of the lower reservoir of a pumped storage power station comprises the following steps:

[0016] A. Dry season: Close gate B and open gate A. The bypass flood discharge and sediment drainage channel will not overflow. The incoming water will flow through the overflow dam section and spillway with gates and then enter the lower reservoir for water replenishment.

[0017] B. Floods below the design standard: Based on local meteorological and water situation forecasts, close Gate A before the onset of rainstorms and flash floods to prevent sediment-laden water from entering the lower reservoir, ensuring the normal operation of the pumped-storage power station units. Simultaneously, open Gate B to allow sediment-laden water to enter the bypass flood discharge channel and ultimately be discharged through the discharge chute into the river downstream of the sediment dam at the reservoir tail end;

[0018] C. Flood exceeding the design standard: When a flood exceeding the design standard occurs, the overflow dam section with gates and the overflow dam section without gates will overflow as a whole, and the flood will enter the lower reservoir through the spillway. Alternatively, when the bypass flood discharge and sediment discharge channel collects water exceeding the design standard, the flood will enter the lower reservoir through the concrete side weir of the bypass flood discharge and sediment discharge channel. At this time, due to muddy water entering the lower reservoir, the pumped storage power station units will be shut down. Wait until the sediment settlement is stable and the sand content in the water body reaches the standard before the pumped storage power station units are restarted.

[0019] The beneficial effects of the present invention are as follows: after a closed reservoir basin is formed, during the dry season, sediment is intercepted by the sediment dam, and only clean water is allowed to enter the lower reservoir; during the flood season, the sediment-carrying water is discharged into the river channel downstream of the dam through the bypass flood and sediment discharge channel and the chute, thereby preventing the sediment-carrying water from entering the lower reservoir. This structure can not only intercept bedload sediment, but also discharge suspended sediment, with good sediment interception and discharge effects, meeting the long-term operation requirements of the pumped storage power station unit and helping to extend the service life of the unit. There is no need to use the river bend terrain to straighten the bend to arrange flood and sediment discharge holes or flood and sediment discharge open channels, and the requirements for the terrain conditions of the lower reservoir are low. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a plan layout diagram of the present invention;

[0021] Figure 2 It is a downstream axonometric view of the sediment barrier dam of the present invention;

[0022] Figure 3 It is an upstream axonometric view of the sediment barrier dam of the present invention;

[0023] Figure 4 Schematic diagram of the structure of the sediment retaining dam according to the present invention from a top view;

[0024] Figure 5 It is a partially enlarged schematic diagram of the sediment retaining dam of the present invention;

[0025] Figure 6 It is a cross-sectional schematic diagram of the reservoir bypass flood and sediment discharge channel of the present invention.

[0026] In the figure: 1-sediment retaining dam, 2-bypass flood discharge and sediment drainage channel, 21-concrete surface layer, 22-gravel cushion layer, 23-drainage ditch, 24-concrete lining, 25-concrete side weir, 3-spilling chute, 4-overflow dam section with gate, 5-overflow dam section without gate, 6-spillway side wall, 7-water retaining dam section, 81-sediment drainage channel outlet connection section, 82-sediment drainage channel inlet connection section, 91-gate A, 92-gate B, 10-traffic road, 11-stilling basin, 12-drainage hole, 13-lower reservoir, 14-barrier dam. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0028] like Figures 1 to 6 As shown, the sediment retention and drainage structure of the lower reservoir of a pumped storage power station described in the present invention includes a lower reservoir 13 and a bypass flood discharge and sediment drainage channel 2. A dam 14 is provided at the tail of the lower reservoir 13, and a sediment retention dam 1 is provided in each gully around the lower reservoir 13 to form a closed reservoir basin. The bypass flood discharge and sediment drainage channel 2 is connected to the sediment drainage channel inlet connecting section 82 and the sediment drainage channel outlet connecting section 81 of each sediment retention dam 1, thereby connecting the tops of the sediment retention dams 1 in each gully around the lower reservoir 13 in series, and both ends of the bypass flood discharge and sediment drainage channel 2 are connected with a discharge chute 3, which starts from the dam shoulder of the dam 14 and extends to the river channel downstream of the dam 14. After the closed reservoir basin is formed, during the dry season, the sediment (mainly bedload sediment) is intercepted by the sediment barrier 1, and only clean water is allowed to enter the lower reservoir 13; during the flood season, the sediment-carrying water (i.e., water containing suspended sediment) is discharged into the river channel downstream of the dam 14 through the bypass flood and sediment discharge channel 2 and the chute 3, thereby preventing the sediment-carrying water from entering the lower reservoir 13. This structure can not only intercept the bedload sediment, but also discharge the suspended sediment, with good sediment interception and discharge effects, meeting the long-term operation requirements of the pumped storage power station units and helping to extend the service life of the units. There is no need to use the river bend terrain to straighten the bend to arrange flood discharge and sediment discharge holes or flood discharge and sediment discharge open channels, and the terrain conditions of the lower reservoir 13 are low.

[0029] The sediment retaining dam 1 is a concrete gravity dam comprising a dam body and a spillway. A traffic road 10 is provided on top of the dam body. On the downstream side of the traffic road 10, a sediment discharge channel outlet connection section 81, a water retaining dam section 7, a gateless overflow dam section 5, a gated overflow dam section 4, a gateless overflow dam section 5, a water retaining dam section 7, and a sediment discharge channel inlet connection section 82 are constructed in sequence from one end of the dam body to the other. The spillway is constructed on the downstream dam face of the dam body, and the upstream end of the spillway is connected to the gated overflow dam section 4 and the downstream end of the gateless overflow dam section 5. When in use, the sediment discharge channel outlet connection section 81 on the sediment retaining dam 1 at the upstreammost reservoir peri-gully serves as the sediment discharge channel inlet connection section 82. That is, both the sediment discharge channel outlet connection section 81 and the sediment discharge channel inlet connection section 82 on the sediment retaining dam 1 are used to discharge water to the downstream bypass reservoir flood discharge sediment discharge channel 2. When the traffic road 10 is not flowing water, it also serves as an internal road for easy maintenance. The downstream dam surfaces of the overflow dam section 4 with gates and the overflow dam section 5 without gates are designed as WES curves. The spillway includes a slope section and an anti-arc section. The upper end of the anti-arc section is connected to the lower end of the slope section.

[0030] The elevations of the inner bottom surfaces of the sediment discharge channel outlet connection section 81, the inner bottom surfaces of the sediment discharge channel inlet connection section 82, and the water inlet of the gated spillway section 4 are consistent with the surface elevation of the traffic road 10. During the dry season, gate A91 is opened and gate B92 is closed, allowing clean water to flow over the dam crest, through the gated spillway section 4, and into the lower reservoir 13 for replenishment. When the upstream water becomes turbid due to heavy rain, gate A91 is closed and gate B92 is opened, allowing the sediment-laden water to be discharged into the bypass flood discharge sediment discharge channel 2 and ultimately discharged through the chute 3 into the river channel downstream of the sediment dam 1 at the reservoir tail.

[0031] A gate A91 is installed at the water inlet of the overflow dam section 4 with a gate, and a gate B92 is installed in the sediment discharge channel inlet connecting section 82.

[0032] A drainage hole 12 is installed in the middle of the dam body. The drainage hole 12 runs through the sediment dam and is used to drain water to prevent water from overflowing the dam top and affecting traffic during the dry season.

[0033] A stilling pool 11 is built on the downstream side of the dam body, and the stilling pool 11 is connected to the downstream end of the spillway. Spillway side walls 6 are built on both sides of the spillway on the downstream dam surface of the dam body, and one end of the spillway side wall 6 is connected to the water retaining dam section 7, and the other end is connected to the side wall of the stilling pool 11. When in use, the lower ends of the spillway side walls 6 on both sides of the spillway gradually approach each other to guide the water flow into the stilling pool 11 for stilling. The superelevation of the spillway side walls 6 should meet the requirements of the flood water level verification to prevent the flood from overflowing the side walls and scouring the bank slopes on both sides of the sediment retaining dam 1.

[0034] The bottom elevation of the bypass flood discharge and sediment discharge channel 2 gradually decreases from upstream to downstream, and the slope is calculated according to the open channel uniform flow formula. Calculate, where Q For traffic, Ais the cross-sectional area of ​​the flow, C is Xie Cai coefficient, R is the hydraulic radius ，i When in use, bypass flood and sediment discharge channel 2 does not consider channel superelevation, and its cross-sectional flow velocity should be controlled to meet the requirements of no siltation and no erosion.

[0035] The bypass flood and sediment discharge channel 2 comprises a base plate, comprising a gravel cushion layer 22 and a concrete surface layer 21 laid on top of the gravel cushion layer 22. A drainage ditch 23 is constructed on the side of the base plate near the bank slope, and a concrete lining 24 is constructed along the bank slope. A concrete side weir 25 is constructed on the waterside of the base plate. The top of the concrete side weir 25 is chamfered on the waterside, and the bottom of the concrete side weir 25 is protected by a bottom plate corner guard. The height of the concrete side weir 25 is no more than 1.2 meters. During operation, backfill is performed based on the dam excavation and topographical conditions to ensure the stability of the bypass flood and sediment discharge channel 2. The bypass flood and sediment discharge channel 2 can intercept and drain gully floodwater and surface water and sediment from the reservoir bank to a certain standard. The drainage ditch 23 is used to collect water from the bank slope during the dry season to avoid affecting internal traffic flow. The height of the concrete side weir 25 is no more than 1.2 meters to prevent it from obstructing pedestrian vision when the bottom of the bypass flood and sediment discharge channel 2 also serves as internal traffic. The top of the concrete side weir 25, facing the water, is chamfered to ensure smooth flow during excessive flooding. A 30-50 cm wide floor protector is built into the bottom of the concrete side weir to prevent excessive flooding from eroding the foundation of the bypass flood and sediment discharge channel 2.

[0036] The method for operating the sediment retaining and discharging structure of the lower reservoir of a pumped storage power station comprises the following steps:

[0037] A. Dry Season: Close gate B92 and open gate A91. Bypass flood discharge channel 2 remains open, allowing water to flow through overflow dam section 4 and the spillway before entering lower reservoir 13 for replenishment. Sediment is intercepted by sediment dam 1, while clean water flows through overflow dam section 4 and the spillway into lower reservoir 13 for replenishment.

[0038] B. Floods below the design standard: Based on local meteorological and water situation forecasts, close gate A91 before the arrival of rainstorms and flash floods to prevent the sand-carrying water from entering the lower reservoir 13, ensuring the normal operation of the pumped-storage power station units. At the same time, open gate B92 to allow the sand-carrying water to enter the bypass flood discharge and sediment discharge channel 2, and finally be discharged into the river channel downstream of the reservoir tail sand dam 1 through the discharge chute 3.

[0039] C. Exceeding the Design Standard Flood: In the event of an exceeding design standard flood, both the gated spillway section 4 and the ungated spillway section 5 overflow, allowing floodwater to enter the lower reservoir 13 via the spillway. Alternatively, if the bypass flood discharge and sediment drainage channel 2 collects water exceeding the design standard, floodwater enters the lower reservoir 13 via the concrete side weirs 25 of the bypass flood discharge and sediment drainage channel 2. At this time, due to the muddy water entering the lower reservoir 13, the pumped-storage power station units are shut down. The pumped-storage power station units can be reopened after sediment sediment has settled and the water sediment concentration reaches the standard. Operations management personnel must regularly desilt the area in front of the sediment barrier 1 based on siltation conditions to prevent sediment from entering the lower reservoir 13 if the area in front of the sediment barrier 1 is filled. The bypass flood discharge and sediment drainage channel 2 can also serve as an internal operation and management road to save investment. This road is strictly prohibited from public access and is only used by internal management personnel for operation and maintenance. To ensure the safety of life and property, this road is strictly prohibited when the bypass flood discharge and sediment drainage channel 2 is flowing. In order to prevent the risk of reservoir bank landslides from affecting the stability of the lower foundation of bypass flood and sediment discharge channel 2 when the water level fluctuates drastically, this road is strictly prohibited from being used when the water level of the lower reservoir 13 fluctuates.

Claims

1. A sediment retention and discharge structure for the lower reservoir of a pumped storage power station, characterized by: The invention comprises a lower reservoir (13) and a bypass flood discharge and sediment drainage channel (2), wherein a dam (14) is provided at the tail of the lower reservoir (13), and a sediment drainage dam (1) is provided in each gully around the lower reservoir (13) to form a closed reservoir basin, and the bottom elevation of the bypass flood discharge and sediment drainage channel (2) gradually decreases from upstream to downstream, and both ends of the bypass flood discharge and sediment drainage channel (2) are connected to a chute (3), and the chute (3) starts at the dam shoulder of the dam (14) and extends to the river channel downstream of the dam (14); The sediment dam (1) is a concrete gravity dam, comprising a dam body and a spillway, a traffic road (10) being provided on the top of the dam body, a sediment discharge channel outlet connecting section (81), a water retaining dam section (7), a non-gate overflow dam section (5), a gate overflow dam section (4), a non-gate overflow dam section (5), a water retaining dam section (7) and a sediment discharge channel inlet connecting section (82) being provided on the top of the dam body from one end to the other end, the spillway being provided on the downstream dam surface of the dam body, and the upstream end of the spillway being connected to the gate overflow dam section (4) and the downstream end of the non-gate overflow dam section (5); The bypass flood discharge and sediment drainage channel (2) is connected to the sediment drainage channel inlet connection section (82) and the sediment drainage channel outlet connection section (81) of each sediment retention dam (1), thereby connecting the tops of the sediment retention dams (1) in the gullies around the lower reservoir (13) in series; The elevation of the inner bottom surface of the sand drainage channel outlet connecting section (81), the elevation of the inner bottom surface of the sand drainage channel inlet connecting section (82), the elevation of the water inlet of the overflow dam section (4) with a gate, and the elevation of the road surface of the traffic road (10) are consistent; A gate A (91) is provided at the water inlet of the overflow dam section (4) with a gate, and a gate B (92) is provided in the sand discharge channel inlet connecting section (82).

2. The sediment retaining and draining structure for the lower reservoir of a pumped storage power station according to claim 1, characterized in that: A drainage hole (12) is provided in the middle of the dam body.

3. The sediment retaining and draining structure for the lower reservoir of a pumped storage power station according to claim 1, characterized in that: An energy dissipation pool (11) is provided on the downstream side of the dam body, and the energy dissipation pool (11) is connected to the downstream end of the spillway; spillway side walls (6) are provided on both sides of the spillway on the downstream dam surface of the dam body, and one end of the spillway side wall (6) is connected to the retaining dam section (7), and the other end is connected to the side wall of the energy dissipation pool (11).

4. The sediment retaining and draining structure for the lower reservoir of a pumped storage power station according to claim 1, characterized in that: The bottom slope of the bypass flood discharge and sediment discharge channel (2) is calculated according to the open channel uniform flow formula: Calculate, where Q For traffic, A is the cross-sectional area of ​​the flow, C is Xie Cai coefficient, R is the hydraulic radius ，i is the bottom slope.

5. The sediment retaining and draining structure for the lower reservoir of a pumped storage power station according to claim 1, characterized in that: The bypass flood discharge and sediment discharge channel (2) includes a bottom plate, which includes a crushed stone cushion layer (22) and a concrete surface layer (21) laid on the crushed stone cushion layer (22). A drainage ditch (23) is provided on the side of the bottom plate close to the bank slope, and a concrete lining (24) is provided on the drainage ditch (23) along the bank slope. A concrete side weir (25) is provided on the water side of the bottom plate, and the top of the concrete side weir (25) on the water side is provided with a circular arc chamfer, and the bottom of the water side is provided with a bottom plate corner guard, and the height of the concrete side weir (25) should not be greater than 1.2m.

6. A method for operating the sediment retaining and draining structure of the lower reservoir of a pumped storage power station according to any one of claims 5, characterized in that: The following steps are involved: A. Dry season: Close gate B (92) and open gate A (91). The bypass flood discharge channel (2) does not overflow. The incoming water flows through the overflow dam section (4) and the spillway and then enters the lower reservoir (13) for water replenishment. B. Flood below the design standard: Based on the local meteorological and water situation forecast, close gate A (91) before the arrival of rainstorms and flash floods to prevent the sand-carrying water from entering the lower reservoir (13), ensuring the normal operation of the pumped storage power station units. At the same time, open gate B (92) to allow the sand-carrying water to enter the bypass flood discharge channel (2) and eventually be discharged into the river channel downstream of the reservoir tail dam (1) through the discharge chute (3); C. Flood exceeding the design standard: When a flood exceeding the design standard occurs, the overflow dam section (4) with gates and the overflow dam section (5) without gates overflow as a whole, and the flood enters the lower reservoir (13) through the spillway; or, when the bypass flood discharge and sediment discharge channel (2) collects water exceeding the design standard, the flood enters the lower reservoir (13) through the concrete side weir (25) of the bypass flood discharge and sediment discharge channel (2). At this time, due to muddy water entering the lower reservoir (13), the pumped storage power station unit is shut down. Wait until the sediment sedimentation is stable and the sediment content in the water body reaches the standard before the pumped storage power station unit is turned on again.

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