Harnessing River Energy: A Comprehensive Guide to Dam-Type Hydroelectric Power Stations

Hydraulic Engineering & Renewable Energy Popular Science Series | Clean Energy Technology Insights

1. Fundamentals of Dam-Type Hydropower Development

Hydroelectric power is one of the most reliable and mature forms of renewable energy worldwide. In hydraulic engineering, the method of constructing a dam across a natural river channel to raise the upstream water level and establish a significant hydraulic head (the elevation difference between upstream and downstream water surfaces) is known as Dam-Type Hydropower Development (坝式水电开发). A hydropower station developed using this approach is designated as a Dam-Type Hydroelectric Station (坝式水电站).

The primary engineering advantages of dam-type development include:

· Flow Regulation & Water Management: Creates an artificial reservoir that stores excess seasonal runoff during flood periods and releases it during dry seasons, maximizing energy utilization efficiency.

· Multipurpose Water Resource Benefits: Beyond electricity generation, the impounded reservoir solves vital regional water conservancy challenges, including flood mitigation, agricultural irrigation, municipal water supply, navigation enhancement, and sediment scouring.

Depending on riverbed gradient, geological conditions, and hydraulic head, dam-type power stations are predominantly engineered into two primary architectural layouts:

· Run-of-River (Bed-Type) Power Stations: Powerhouse structure is directly integrated with the dam axis to jointly retain water, ideal for low-head, high-discharge river sections.

· Dam-Toe (Dam-Rear) Power Stations: A dedicated massive dam retains high hydrostatic pressure, with the powerhouse situated at the downstream toe of the dam, designed for medium-to-high head canyon environments.

2. Run-of-River (Bed-Type) Hydropower Stations

Run-of-river or bed-type power stations (河床式水电站) are commonly constructed on the middle and lower reaches of major rivers where the natural channel bed has a gentle gradient. In this configuration, the hydroelectric powerhouse and the non-overflow dam blocks form a continuous barrier across the river, jointly resisting upstream hydrostatic pressure.

Because the impounded water head is relatively low—typically around 10 to 25 meters in small-to-medium stations—power generation relies heavily on high discharge volume. Consequently, they are categorized as low-head, high-flow hydroelectric facilities.

Figure 1: Cross-sectional profile of a typical run-of-river powerhouse layout, detailing inlet flow, penstock, hydro turbine, generator, and draft tube.

The structural layout of a run-of-river power station typically places the overflow spillway gates in the central riverbed for flood discharge, while the generating powerhouse is positioned on one or both riverbanks.

Case Study 1: Xijin Hydropower Station (Guangxi, China)

The Xijin Hydropower Station (西津水电站) is a classic example of a large-scale run-of-river project in southern China. It features a total dam crest length of ~800 meters, a maximum dam height of 41 meters, and an average operating head of 20 meters.

· Left Section: Comprises an earthfill embankment and concrete gravity sections.

· Central Section: 112-meter-long overflow spillway section equipped with crest radial gates for discharging seasonal floods.

· Right Section: 132-meter-long bed-type powerhouse that simultaneously blocks river water and channels inlet flows through four Kaplan (axial-flow adjustable-blade) turbine-generator units, with a total installed capacity of 234.4 MW.

Figure 2: Overview of Xijin Hydropower Station showing the central spillway dam and the integrated run-of-river powerhouse.

Case Study 2: Gezhouba Water Control Project (Hubei, China)

The Gezhouba Water Control Project (葛洲坝水利枢纽) on the Yangtze River is one of the world's largest low-head run-of-river installations. The concrete gravity dam spans 2,595 meters in total length with a maximum height of 53.8 meters and a total reservoir storage capacity of 1.58 billion cubic meters.

From the right bank to the left bank, the project layout incorporates: Dajiang sediment flushing sluice, Ship Lock No. 1, Dajiang powerhouse, Erjiang spillway sluice, Erjiang powerhouse, Ship Lock No. 2, Sanjiang sediment flushing sluice, and Ship Lock No. 3.

Figure 3: Aerial configuration of the Gezhouba Project on the Yangtze River, showing powerhouses, silt flush sluices, and navigation locks.

The Erjiang spillway serves as the primary flood conveyance corridor, featuring an open flat-bottom sluice design with 9 gate bays and 27 gate orifices. The absence of upstream breast walls combined with flat discharge chutes maximizes flow capacity, greatly facilitating high-velocity flood discharge, sediment flushing, timber rafting, and ice clearance.

Gezhouba is equipped with giant low-head axial-flow turbines: 14 × 125 MW units in the Dajiang powerhouse, and 2 × 170 MW + 5 × 125 MW units in the Erjiang powerhouse, achieving a total installed capacity of 2,715 MW (2.715 GW).

3. Dam-Toe (Dam-Rear) Hydropower Stations

When river topography permits the construction of a tall dam to impound a large reservoir and harness high hydraulic heads, the immense upstream hydrostatic water pressure far exceeds the structural self-weight and stability limit of a powerhouse alone. Under such conditions, a dedicated, heavy water-retaining dam (such as a concrete gravity or arch dam) must be constructed, and the powerhouse is situated directly behind the downstream toe of the dam. This layout is designated as a Dam-Toe Hydropower Station (坝后式水电站).

Figure 4: Cross-sectional schematic diagram of a dam-toe power station, showing pressurized penstocks traversing the dam body into the powerhouse.

Dam-toe stations are commonly built in steep mountain gorges along the upper and middle reaches of major rivers, enabling power generation from medium-to-high hydraulic heads (50 to over 200 meters).

Global Benchmark: The Three Gorges Hydropower Station

The Three Gorges Hydropower Station (三峡水电站) on the Yangtze River is the world's largest power station by installed capacity (22,500 MW). It utilizes a monumental concrete gravity dam with a total crest length of 2,309.5 meters, a maximum height of 181 meters, and an operating head of approximately 110 meters.

Figure 5: Downstream perspective of the Three Gorges Dam, showing the central spillway section, flanking powerhouses, and non-overflow dam monoliths.

The Three Gorges Dam layout is organized into distinct functional zones:

· Central Spillway Section: 483 meters long, equipped with 22 surface crest spillway bays and 23 deep outlet sluices arranged alternately. Deep sluices effectively scour upstream silt deposits and flush heavy sediment under high pressure.

· Left & Right Powerhouse Sections: Flanking the central spillway on both sides, housing 26 giant 700 MW Francis hydro-generator units fed by individual steel penstocks embedded in the dam body.

· Non-Overflow Dam Sections: Houses navigation facilities, including a continuous multi-stage ship lock and a vertical ship lift.

Figure 6: Structural cross-section profiles of the Three Gorges Dam, comparing the powerhouse dam monolith (left) with the spillway monolith (right).

Figure 7: Deep sluice flood discharge and sediment scouring operations at the Three Gorges Dam.

Figure 8: Close-up layout of the Three Gorges Left Bank Dam, illustrating penstock alignment, gantry cranes, and the downstream powerhouse.

The power generation capacity of the Three Gorges Project is unprecedented:

· Left Powerhouse: 14 × 700 MW Francis turbine units.

· Right Powerhouse: 12 × 700 MW Francis turbine units.

· Right Bank Underground Powerhouse: Excavated inside Mount Baishijian on the right bank, housing 6 × 700 MW units.

· Total Capacity: 32 main units of 700 MW each plus two 50 MW plant-power units, totaling 22,500 MW (22.5 GW).

4. Underground Powerhouse Complexes in Dam-Type Projects

In deep mountain canyons with steep slopes or fragile geological abutments, placing a massive powerhouse on the surface at the downstream dam toe may be impractical due to space limitations or rockfall hazards. Under such conditions, engineers excavate an Underground Powerhouse Complex (地下厂房) inside the adjacent mountain rock mass.

An underground powerhouse typically comprises the main generating cavern, main transformer cavern, high-pressure water intake tunnels, tailrace discharge tunnels, ventilation shafts, cable galleries, and transportation tunnels.

Case Study 1: Xiangjiaba Hydropower Station (Jinsha River, China)

The Xiangjiaba Hydropower Station (向家坝水电站) is a major cascade development on the lower Jinsha River. It features a solid concrete gravity dam with a maximum height of 161 meters and a crest length of 937.5 meters.

In addition to a conventional dam-toe powerhouse on the left bank (4 × 800 MW units), Xiangjiaba features a massive underground powerhouse excavated inside the right-bank mountain (4 × 800 MW units), achieving a total installed capacity of 6,400 MW.

Figure 9: 3D cutaway schematic layout of Xiangjiaba Hydropower Station, revealing the underground powerhouse caverns and hydraulic tunnels inside the mountain.

Figure 10: Overall engineering photograph of Xiangjiaba Hydropower Station during final commissioning, showing the dam-toe and underground facilities.

Case Study 2: Ertan Hydropower Station (Yalong River, China)

The Ertan Hydropower Station (二滩水电站) on the lower Yalong River was the largest hydropower station built in China during the 20th century. Located in a steep, narrow V-shaped gorge, Ertan utilizes a 240-meter-high concrete double-curvature arch dam with a crest arc length of 775 meters.

Due to the canyon's extreme narrowness, the entire powerhouse is built underground inside the right-bank mountain, housing 6 × 550 MW Francis turbine units with a total capacity of 3,300 MW.

Figure 11: Ertan concrete double-curvature arch dam and high-velocity ski-jump spillway discharge.

5. Comprehensive Engineering Comparison

The table below summarizes the key engineering, hydraulic, and structural differences across the three major dam-type hydropower configurations:

6. Conclusion & Engineering Outlook

Dam-type hydroelectric power stations represent one of the most effective and durable solutions for large-scale renewable electricity generation and regional water resource security. By raising water levels and impounding seasonal flows, they provide dispatchable baseload and peaking power, stabilize power grids, prevent catastrophic downstream flooding, and secure freshwater supplies.

While dam projects require substantial upfront capital investment, comprehensive environmental impact mitigation, and careful ecological stewardship, their operational lifespan of over a century and near-zero carbon emissions make them indispensable cornerstones in the global transition toward clean, sustainable energy.