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SvenskaHow are hydropower plant structures inspected underwater?
Hydropower plant structures are inspected underwater using a combination of sonar-based surveys, remotely operated vehicles (ROVs), and diver-led visual inspections. These methods allow engineers to assess the condition of dams, turbine intakes, penstocks, spillways, and other submerged components without dewatering the structure, which would be costly and operationally disruptive.
Underwater inspections are essential for hydropower operators because submerged concrete, steel, and rock are continuously exposed to erosion, cavitation, and sediment loading. Project managers responsible for infrastructure maintenance need reliable, high-resolution data to prioritize repairs, satisfy regulatory requirements, and keep generation capacity online.
Below, we cover the core questions project managers ask when planning a hydropower structure inspection.
What methods are used to inspect hydropower structures underwater?
Hydropower structure inspections underwater rely on four primary methods: sonar-based acoustic surveys, remotely operated vehicle (ROV) inspections, diver-led visual and tactile assessments, and sediment profiling. Each method targets different structural elements and levels of detail, and most comprehensive underwater surveys combine at least two approaches to produce a complete picture of structural condition.
Sonar surveys, including multibeam echosounder (MBES) and side-scan sonar (SSS), generate high-resolution bathymetric models of the reservoir floor, dam face, and intake structures. These surveys are especially effective for detecting large-scale changes such as scour, sediment accumulation, and surface deformation across wide areas quickly and safely.
ROV inspections complement sonar data by providing close-range video and photographic documentation of specific areas of concern. ROVs can navigate into confined spaces such as intake tunnels and gate slots that are inaccessible to divers, and they can be equipped with sensors to measure crack widths, corrosion depth, or water quality parameters.
Diver inspections remain valuable when tactile assessment is needed, for example to test the integrity of grout seals, check anchor bolts, or clear debris from inspection targets. However, diver operations are depth-limited, weather-sensitive, and carry higher safety overhead than remote methods.
Sub-bottom profiling (SBP) and seismic surveys add a further layer of data by revealing sediment thickness and subsurface conditions beneath the reservoir floor, which is critical for understanding foundation stability. We offer all of these survey types as part of our underwater survey services, allowing project teams to select the right combination for their specific structure and inspection objective.
How does sonar technology work in hydropower inspections?
Sonar technology works in hydropower inspections by emitting acoustic pulses from a transducer and measuring the time it takes for those pulses to reflect back from submerged surfaces. The return signals are processed into precise depth measurements and surface models, enabling engineers to map dam faces, reservoir floors, and structural profiles with centimeter-level accuracy without physical contact.
Multibeam echosounder systems emit a fan-shaped array of acoustic beams simultaneously, capturing thousands of depth points per second across a wide swath. This makes MBES the preferred tool for producing full-coverage bathymetric models of large submerged areas such as dam aprons, stilling basins, and forebay floors. The resulting 3D point clouds can be compared against previous surveys or design drawings to identify material loss, scour holes, or unexpected deposition.
Side-scan sonar produces high-contrast acoustic imagery of the seabed or structure surface, making it effective for detecting surface anomalies such as cracks, displaced blocks, or debris fields. While side-scan sonar does not measure depth directly, it excels at identifying the location and extent of surface features that warrant closer investigation.
Sub-bottom profilers use lower-frequency acoustic signals that penetrate the sediment layer, revealing stratigraphy and the depth of buried structures or voids beneath the reservoir floor. This is particularly relevant for assessing conditions around dam foundations where sediment has accumulated over decades of operation.
When should a hydropower plant schedule an underwater inspection?
A hydropower plant should schedule an underwater inspection at regular intervals defined by its structural safety plan, typically every three to five years for routine condition monitoring, and immediately following any seismic event, flood, or operational incident that may have caused structural stress. Regulatory frameworks in most jurisdictions also mandate periodic dam safety inspections that include underwater components.
Beyond scheduled cycles, several specific triggers should prompt an unplanned inspection:
- Unusual vibration or noise from turbines or gates, which can indicate cavitation damage or debris impact on submerged components
- Visible changes in leakage rates or seepage patterns around the dam body or foundation
- Significant flood events that may have caused scour at the dam toe or deposited debris in intake structures
- Planned major maintenance or rehabilitation work, where baseline underwater data is needed before and after the intervention
- Changes in reservoir operating levels that expose previously submerged zones to new loading conditions
For project managers working on new hydropower construction or capacity upgrades, an underwater survey during the design and planning phase is equally important. Pre-construction surveys establish the baseline bathymetry, identify existing structures, and characterize sediment conditions that directly influence foundation design and construction methodology.
What structural issues can underwater inspections detect in hydropower plants?
Underwater inspections can detect a wide range of structural issues in hydropower plants, including concrete cracking and spalling, scour and erosion at dam foundations, sediment accumulation in intake channels, corrosion of steel gates and penstocks, joint failures, and displacement of rock or concrete armor blocks. Early detection of these defects is critical because underwater deterioration is invisible during surface inspections and can progress rapidly under hydraulic loading.
Concrete and masonry defects
Submerged concrete in dams, spillways, and stilling basins is subject to erosion from high-velocity water, freeze-thaw cycling in shallow zones, and long-term chemical attack from dissolved minerals. Underwater inspections identify surface erosion depth, crack patterns, delamination, and loss of aggregate that indicate advancing deterioration. ROV video and photogrammetry can document these defects with enough precision to support repair design.
Scour and foundation erosion
Scour at the dam toe and around foundation elements is one of the most serious risks in hydropower infrastructure. High-velocity discharge from spillways or bottom outlets can progressively excavate rock or soil from beneath the dam structure, undermining its stability. Multibeam sonar surveys are particularly effective at detecting scour because they produce accurate 3D models that can be compared against historical surveys to quantify material loss over time.
Steel components including gate frames, trashracks, and penstock linings are also vulnerable to corrosion and mechanical damage. Underwater inspections assess coating condition, pitting depth, and weld integrity, providing the data needed to plan targeted maintenance before a failure affects plant availability.
If you are planning a hydropower structure inspection and need to define the right survey scope, our team is ready to help. Contact us to discuss your project requirements.