Upstream Slope Monitoring at Bala Hydropower Station

Background

Bala Hydropower Station is in Ma’erkang, Aba Prefecture, Sichuan, China. Its installed capacity is 746,000 kW, with a reservoir capacity of 133.8 million cubic meters and design annual generation of 2.553 billion kWh. Construction began in early 2021, followed by impoundment in early 2025.

Project detail	Monitoring record
Location	Ma’erkang, Sichuan, China
Asset	Upstream slope near Sejiang Village, Bala Hydropower Station
Instruments	GNSS and RT-1010 Array Displacement Meters
Period	June 26, 2025 through late July
Reported results	Deformation exceeded 1 m; the rate fell below 1 mm/day by late July, following reservoir release on July 8

Challenges

During impoundment in 2025, deformation accelerated on the upstream slope near Sejiang Village. A large landslide entering the river or reservoir could generate a surge, affect the dam and nearby communities, and reduce reservoir capacity through deposited material.

The project investigation associated the movement with sustained rainfall and rising reservoir levels. Infiltration and prolonged submergence can alter the weight and strength of slope materials; changing water pressure also affects the forces acting on the slope. The monitoring team considered these mechanisms when assessing the developing movement.

Surface movement and deformation at depth

The owner needed timely surface and subsurface measurements to assess the slope and inform reservoir management. Surface monitoring would track movement across the slope, while borehole profiles would show how deformation was distributed at depth.

Solution

GNSS and borehole displacement measurements

The automated system combined high-precision GNSS observations with Array Displacement Meters. GNSS tracked surface movement; the borehole arrays measured internal deformation along the monitored depth.

Remote transmission brought both sets of readings to the platform for near-real-time review. This reduced reliance on repeated manual readings at a site where deformation was changing rapidly.

Annotated aerial site plan showing GNSS surface monitoring points and inclinometer boreholes on slopes around Sejiang Village upstream of Bala Hydropower Station; original Chinese labels — Figure 3. GNSS monitoring points and borehole locations around Sejiang Village (Chinese labels).

Establishing the borehole direction reference

Field photographs record the instrument installation and an orientation reference at the borehole head. A documented measurement direction gives engineers a consistent basis for interpreting displacement profiles and comparing dates.

Direction reference and sensor assembly at a borehole head during Bala upstream slope monitoring installation — Figure 6. Borehole orientation reference photographed during installation.

Results

The published monitoring record runs from installation on June 26, 2025 through late July. Maximum reported deformation during this period exceeded 1 m. Successive depth profiles showed the development of movement within the slope, complementing the GNSS surface observations.

After reservoir release on July 8, the recorded rate of movement declined. The project report records a deformation rate below 1 mm/day by late July. These measurements helped the team assess the slope’s response following reservoir regulation.

Figure 7. Successive depth–displacement profiles from June–July 2025 (Chinese labels). View full-size chart.

Figure 8. A second depth–displacement profile series (Chinese labels). View full-size chart.

Reviewing GNSS observations alongside borehole profiles helped the team follow both surface movement and deformation at depth during reservoir operation. The records supported assessment of the slope’s response to reservoir regulation.