6 perspectives to assess erosion risk at solar power plants using drone surveying

In solar power plants, when water flow concentrates on site slopes, drainage channels, access roads, around racking, stream channels, or collection areas, surface soil can be washed away and scouring and erosion can advance. Even if they appear as small rills or steps in the early stages, repeated rainfall can lead to reduced drainage capacity, impaired passage for maintenance vehicles, ground deformation around racking foundations, exposure of buried cables, and other problems. One way to detect such changes early is to conduct condition assessments using drone surveying.

Table of Contents

• The significance of assessing scour risk through drone surveying

• Consideration 1: Check for terrain that easily accumulates water and the flow of water

• Aspect 2: Check erosion tendencies on slope faces and at the edges of constructed fills.

• Inspection point 3 Check for abnormalities around drainage channels and transverse structures

• Aspect 4: Confirm changes in ground conditions around racking foundations and panel rows.

• Aspect 5: Check maintenance roads and work access routes for scour.

• Aspect 6: Check progress by comparing with past data

• Precautions when assessing scour risk using drone surveys

• Summary

The Importance of Assessing Scour Risk with Drone Surveying

Assessing erosion risk at a solar power plant is not something that can be determined simply by checking whether the ground has been slightly worn away. The plant is laid out over a wide site with panels, racking, access roads, drainage facilities, fences, cable routes, and so on, and how rainwater flows is also affected by site grading, drainage planning, the degree of surface compaction, and the presence or absence of vegetation. Walking the site to inspect it is important, but when you view a large area from the same eye level it can be difficult to grasp the overall slope of the terrain and the places where water tends to collect.

By using drone surveying, you can view the entire power plant from above, which makes it easier to organize not only the locations where scour is occurring but also the catchment directions and relationships with the surrounding terrain that tend to cause it. For example, a slight low line on a graded surface, the natural flow toward a drainage channel, the spot where water falls from the top of a slope, and watercourses crossing an access road can all be overlooked during inspections from the ground alone. By combining aerial photographs and three-dimensional data, you can link individual anomalies with the overall movement of water across the site and confirm them.

However, drone surveying is not a universal method that can automatically determine the presence or absence of scour. The appearance can vary depending on imaging conditions, ground vegetation height, shadows, muddiness after rain, overlapping features, and so on. Also, looseness within the ground or the support condition of foundations cannot be directly determined from images alone. Therefore, it is important to use drone surveying in combination with on-site inspections, inspections of drainage facilities, and, when necessary, ground surveys and specialized investigations.

In practice, rather than scrambling to investigate after scour occurs, it is more effective to regularly photograph under conditions as similar as possible so that you can compare changes. In particular, times when changes to the ground surface are easily visible include after heavy rain, after typhoons, during initial operation following completion of site development, after drainage channel repairs, and after grass cutting. By not treating drone surveys as a one-off check but accumulating them as maintenance records, it becomes easier to detect scour risks earlier.

Consideration 1: Identify terrain prone to collecting water and confirm water flow

Erosion is a phenomenon that tends to occur where water flows. Therefore, the first thing to check is the terrain connectivity within the solar power plant—where water collects and where it flows. On developed sites, surfaces that appear flat often have subtle gradients, and rainwater flows toward lower areas. Using terrain data and orthophotos produced by drone surveys makes it easier to get an overview of the site's overall slope, the valley-like lines where water tends to concentrate, and the directions of flow toward drainage channels.

Particular attention should be paid to locations where rainwater flows in from nearby mountainsides or unpaved slopes. Solar power plants are often installed on large development sites, and if water from outside the site enters more than expected, the capacity of the drainage facilities can become insufficient, making localized scour more likely to progress. When inspected from above with a drone, you may find flow paths near the site boundary, sediment accumulation along fences, and thin erosion lines extending down the lower parts of slopes. These locations need to be addressed not only as internal plant issues but also in relation to the surrounding terrain.

The arrangement of panel rows also affects water flow. If drips falling from the panels concentrate on the same spot, narrow grooves can form on the ground surface. Even if they are not noticeable during normal rainfall, if droplets continue to fall on the same spot over a long period, topsoil can be eroded and crushed stone can be displaced. In drone surveys, it is important to broadly inspect the downstream side of panel rows and the lines where drips tend to collect, and to check whether similar areas of deterioration occur in sequence.

When identifying terrain that readily collects water, don’t just look at low spots; also pay attention to places where water is likely to accelerate. At the lower end of long slopes, along lines running from the shoulder to the toe of a embankment, where maintenance-road side ditches end, and at bends in drainage channels, water can gain momentum and the force that erodes the surface can increase.

Check aerial photos for color differences, sediment streaks, lines of sparse vegetation, and subtle steps, and use those cues to narrow down the locations to prioritize for on-site inspection to be more efficient.

In practical work, it becomes easier to manage if you roughly subdivide catchment areas while reviewing the results of a drone survey. Rather than viewing the entire power plant as a single surface, clarify which drainage channels collect runoff from which areas, which maintenance roads are likely to act as water pathways, and which slopes are most susceptible to upstream influence. Once this organization is done, erosion sites become easier to treat not as mere point defects but as area-wide problems caused by water flow.

Aspect 2: Check the erosion tendencies of slopes and edges of fill

On sites for solar power plants, slopes are sometimes formed by cutting and filling. Slopes have steep surface gradients and are prone to increased rainwater flow velocity, making them susceptible to scouring and surface erosion. Especially on fill slopes, if surface protection is not functioning adequately or if heavy rain occurs before vegetation becomes established, rill-like erosion can progress. Drone surveys can observe the entire slope from directly in front or from obliquely above, making it easier to identify continuous deterioration that is difficult to discern by looking up from the ground.

Points to check on a slope face include narrow longitudinal rills, notching near the slope shoulder, sediment accumulation at the slope toe, scour around drainage outlets, and displacement of protective materials. Although each of these may look minor on its own, if multiple occurrences appear on the same slope face they may indicate concentrated water flow. Viewing the entire slope from drone imagery can often reveal connected start and end points of erosion, making it easier to estimate where water is entering.

The edges of constructed areas are also easy to overlook. Along the site's outer perimeter, by fences, at the ends of maintenance roads, and where they meet drainage channels, the terrain can change abruptly and the direction of drainage can shift. In such places, if steps or gaps form on the ground surface, water can concentrate and flow in, causing scouring to progress from the edges. In particular, areas along fences can be difficult to approach during inspections, and when grass has grown it becomes hard to confirm surface deformation. Using drone surveys makes it possible to continuously inspect the entire perimeter and more easily grasp the distribution of deformations.

When assessing the risk of scour on a slope, consider not only its current shape but also the conditions that make deterioration more likely. For example, if there is a large catchment area above the slope, the volume of water flowing down from above will increase. If there is no drainage treatment at the slope shoulder, water is more likely to fall directly onto the slope. If sediment has accumulated at the toe of the slope, it may indicate that material eroded from the upper part is being carried downward. Photographs and topographic data from drone surveys provide material for visually organizing these relationships.

However, slopes are often covered with grass or protective materials, and fine erosion of the ground surface can be difficult to capture in images. When grass is densely grown, it may appear stable at first glance, but small rills can form beneath it. Conversely, areas with sparse grass are not necessarily all dangerous. Appearance varies depending on sunlight exposure, soil properties, and maintenance conditions. When a potential anomaly is found in drone surveys, it is essential to check the condition underfoot, signs of soil movement, and traces of drainage on site.

Aspect 3: Inspect for deterioration around drainage channels and crossing structures

When assessing scour risk, inspecting drainage channels is extremely important. At solar power plants, it is common practice to plan to direct on-site rainwater into side ditches, unlined channels, catch basins, culverts, cross pipes, etc., and discharge it off-site. If these facilities function properly, surface runoff is easier to control. However, if there is sediment clogging, erosion at outlets, changes in slope, insufficient cross-sectional area, localized damage, or the like, water can overflow or flow to unintended locations, leading to scouring.

Drone surveying allows you to check the continuity of drainage channels over a wide area. During ground inspections, you may be able to tell whether the drain right in front of you is clogged, but it is time-consuming to simultaneously grasp the connections upstream and downstream. From above, you can view as a whole the locations of sediment buildup along the drain, traces where water has overflowed, the way surrounding vegetation has been knocked down, and the patterns of mud spread. Especially when filming after heavy rain, traces of where water actually flowed are often still visible, making it easier to identify weak points in the drainage.

Areas around crossing structures are also prone to scour. At culverts that carry water beneath maintenance roads, drainage channels that cross the road, and the inlets and outlets of catch basins, the flow of water is concentrated into a narrow cross section. When water jets out forcefully from an outlet, the downstream ground can be scoured away. If sediment or fallen leaves accumulate at an inlet, water can overflow onto the road and create a new flow path elsewhere. In drone imagery, sediment streaks formed upstream and downstream of the crossing structure and fan-shaped traces where water has overflowed are often easy to identify.

In inspections of drainage channels, it is important not only to look at their shape but also to examine their height relationship with the surrounding ground. If a drainage channel is located higher than the ground surface, the shoulder of a side ditch has collapsed, or water is escaping in another direction before entering the channel, the system may not be able to collect water effectively even if equipment is in place. By using three-dimensional data from drone surveys, it becomes easier to confirm the relative heights of the drainage channel and the surrounding ground, providing a basis for deciding where to re-measure on site.

Also, scouring around drainage channels is influenced by downstream conditions. If the drainage capacity at the downstream end is reduced, water can pond upstream and overflow more easily. When downstream channels have become shallower due to sediment or when the water level at the discharge point tends to rise, on-site drainage may not drain as expected. In drone surveys, it is desirable to check not only the site but also the conditions around the downstream end within permitted areas and to understand how the drainage connects.

Viewpoint 4 Check for changes in the ground around racking foundations and panel rows

At solar power plants, changes in the ground around rack foundations and rows of panels can lead to risks in equipment management. If the soil around a foundation is eroded, it can cause foundation exposure, subsidence of the surrounding ground, pooling of rainwater, and interference with mowing and inspection work. However, the safety and bearing condition of a foundation cannot be determined by appearance alone. In drone surveying, a practical approach is to broadly capture changes to the ground surface and signs of erosion, and to extract locations that require detailed inspection.

Around rows of panels, narrow grooves can form along the positions where raindrops fall. In particular, when rainwater falls repeatedly on the same spot from the lower edge of a panel, the crushed stone or topsoil on the ground surface can gradually move, producing band-like deformations along the row. When photographed from above, these may appear as color differences parallel to the panel rows or as streaky disturbances on the ground surface. If such deformations occur over a wide area, they should be checked not as individual inspection points but in terms of the relationship between panel layout and ground surface treatment.

What to pay attention to around racking foundations is whether the base of the foundations is lower than the surrounding ground, whether there are traces of soil having washed away, and whether depressions that tend to collect water have formed. Depending on the resolution and shooting angle of drone surveys, it may be difficult to discern the fine condition of individual foundations, but you can verify whether there is any bias in ground color or surface irregularities across the entire row. In particular, for rows of panels installed on slopes, water from upstream can flow around the foundations toward downstream, producing localized scour.

Attention is also required around cable routes and buried conduits. If the ground surface is eroded, burial depth can become shallower and protective materials or conduits may become exposed. Drone imagery does not allow you to confirm every cable itself, but locations with narrow, continuous grooves on the surface or where sediment has been washed away are worth checking on site to verify their position relative to the cable route. Exposure of equipment caused by scouring is not only a landscape concern but also affects maintenance and safety management, so early detection is important.

When inspecting around panel rows, plan flight paths to avoid the power generation equipment itself and maintain a safe distance and altitude. Flying lower makes details easier to see, but you must consider obstacles and wind effects, distance to electrical equipment, and worker safety. In practice, it is efficient to capture wide-area images under set conditions to extract anomaly candidates and then perform detailed on-site verification only where necessary.

Aspect 5 Confirm scour of access roads and work routes

In the operation and maintenance of solar power plants, the condition of access roads and work routes is also important. Even if the power generation equipment shows no major abnormalities, if access roads are eroded and become difficult for vehicles to pass, inspections, mowing, repairs, and emergency response can be impeded. Especially on unpaved roads and gravel-surfaced roads, rainwater flowing over the road surface can widen ruts and grooves and wash surface materials downstream. Drone surveying helps check the entire alignment of access roads and identify where water crosses the road and where the road surface is being eroded.

Erosion on management roads is most likely to occur on sections with steep longitudinal gradients, on the outside of curves, on stretches without side ditches, where roadside drainage is insufficient, and on low-lying parts of the pavement. When rainwater flows along the road for a long time, narrow rills can eventually develop into deep erosion. Drone images can reveal differences in pavement color, traces where crushed stone has been washed away, accumulations of mud, and locations where vehicle ruts and watercourses overlap. Based on this information, it becomes easier to assess on-site passability and the need for repairs.

Also, because maintenance roads often intersect drainage channels, it is important to focus inspections on the interfaces between the road and drainage facilities. If water crossing the road is not properly managed, shoulders can be eroded and steps can form at the crossings. Even small steps can interfere with the passage of inspection vehicles and work machinery. By using drone surveying to obtain an overhead view of the entire road, these problem locations can be organized by route, making it easier to prioritize repairs.

Erosion of work routes also affects the efficiency of routine inspections. If the pathways between panel rows, patrol routes along fences, or access roads to collection equipment and maintenance facilities become muddy or eroded, inspectors may be forced to detour, which can lead to missed checks. Regularly checking the condition of work routes with drone surveys allows you to identify hazardous or hard-to-pass areas before entering the site. This is especially useful as a pre-entry check for inspections after heavy rain.

However, judging whether vehicles can pass based solely on drone surveying is dangerous. The pavement's bearing capacity, the depth of mud, the degree of compaction of crushed stone, and the actual measurements of steps or irregularities all require on-site verification. Drone surveying is appropriate to use as information to understand where risks are likely to exist and to develop inspection routes and repair plans. Confirm the abnormalities visible in images on site, and by combining them with simple surveys or repair records as necessary, you can more easily apply the information to the maintenance and management of managed roads.

Perspective 6: Confirm progress by comparing with past data

Comparison with past data is particularly important for understanding scour risk. A single drone survey can detect anomalies, but it cannot tell whether those anomalies have existed previously or have recently progressed rapidly. Because scour often advances over time, regularly photographing the same location and comparing the amount and extent of change makes it easier to determine response priorities.

Data used for comparison should be organized at each management milestone, such as at completion of site development, at completion of construction, at the previous inspection, after heavy rainfall, and after repairs. In particular, topographic data taken immediately after completion of site development serves as a baseline for confirming subsequent changes. In the early post-construction stage, small settlements and movement of surface soil can occur until the ground surface stabilizes. Understanding this provides a basis for judging whether a change is within expected bounds or is a change that should be treated as erosion requiring attention.

When comparing with past data, it is important to match the image acquisition conditions as closely as possible. If flight altitude, imaging extent, the handling of ground control points and reference points, time of capture, whether grass was mowed, weather, or ground surface moisture differ significantly, the appearance and surveying results are likely to vary. It can be difficult to make conditions exactly the same, but if comparison is intended, you should record the surveying conditions each time so that differences can be checked later.

When checking differences, it is important not to judge by the numbers alone but to compare the images with on-site conditions. Places that appear to have lowered in the terrain data may in fact only look that way because mowing has made the ground surface more visible. Conversely, scour may appear smaller because it is hidden by vegetation. Treat the difference results only as a clue for further checks, and it is safer to confirm the situation through a field inspection.

Being able to confirm the degree of progression makes it easier to prioritize repairs. Even small scours can be a concern if they are expanding rapidly over a short period. Conversely, areas that have shown little change over time can sometimes be handled through monitoring and regular inspections. The strength of drone surveys lies in allowing these decisions to be recorded rather than relying solely on intuition. Because on-site personnel, management companies, designers, and repair contractors can discuss while looking at the same images and terrain data, sharing the situation becomes easier.

Points to Note When Assessing Scour Risk with Drone Surveys

When using drone surveying to assess scour risk, it is important to clarify the objectives before planning the imaging. Simply photographing the entire power plant may not be sufficient to confirm the subtle terrain changes related to scour. Organize in advance the features you want to inspect—such as intake areas, slopes, drainage channels, areas around support structure foundations, and access roads—and consider the resolution and shooting angles required for each. Because the appropriate imaging conditions differ for broad-area reconnaissance and detailed inspection, it is also necessary not to try to force everything into a single flight.

Before flight, safety management and coordination with stakeholders are also essential. Solar power plants contain electrical equipment, mounting structures, cables, fences, monitoring equipment, workers, vehicles, and the like. Confirm the flight area, takeoff and landing locations, working hours, access restrictions, and emergency procedures to avoid disrupting site operations. On windy days, in rain, or when visibility is poor, it is also important to decide to avoid attempting a flight. Inspections for scour or erosion are sometimes carried out after disasters or heavy rainfall, but those are precisely the times when the ground and access routes can be unstable, so prioritize safety, including for any ground work.

When handling data, be mindful of positional accuracy and reproducibility. To compare the progress of erosion, it is important that each dataset is organized according to the same standards. Properly managing ground control points and benchmarks and recording the imaging extent and processing conditions makes it easier to compare with past data. Conversely, data created with ambiguous standards make it difficult to determine whether observed changes are actual terrain changes or differences in surveying conditions. If you intend to use the outputs for maintenance management, it is desirable to standardize the data-creation procedures on site.

Be careful about how images appear. When vegetation is tall, the ground surface can be easily hidden and small erosion channels may not be visible. Strong sunlight can cast deep shadows, making surface irregularities appear larger than they actually are. Immediately after rain, puddles and wet soil stand out, so caution is needed to accurately interpret the shape of the ground surface. Conversely, in dry conditions the marks left by flowing water can become faint and traces may be hard to see. It is important to record the conditions at the time of imaging and not to make conclusive judgments from images alone.

In assessing scour risk, it is also important not to immediately assume that discovered anomalies are dangerous. Even small surface erosion may, depending on the location, be acceptable to monitor over time. On the other hand, at locations that are likely to affect equipment or safety—such as drainage outlets, around foundations, the upper parts of slopes, and the shoulders of maintenance roads—early inspection is required. Based on information obtained from drone surveys, conduct on-site inspections, photographic records, necessary measurements, and cross-checks with repair histories, and make a comprehensive assessment of the magnitude of the risk.

Also, it is important to organize the results of drone surveys in a way that can be communicated to stakeholders. Rather than having only the on-site staff look at the images and stop there, keep a single record that includes the locations of potential scour sites, the details of observed deterioration, changes over time, the results of on-site inspections, and the planned response measures. In a large power plant, relying on verbal explanations alone can lead to misunderstandings about locations. Indicating the inspected points on aerial photographs and organizing them with management numbers and dates makes it easier to link them to the next inspection or to repair requests.

Summary

The erosion risk at solar power plants arises from a complex interaction of stormwater flow, site grading, drainage facilities, slopes, access roads, and the ground conditions around the mounting racks. Even small rills or sediment washouts, if left unaddressed, can lead to poor drainage, impeded access, and ground deformation around equipment. Therefore, in addition to walking the site for inspection, it is effective to use drone surveying to obtain an aerial overview of the entire site and to understand the distribution of deformations and the flow of water.

When checking for scour (erosion) risk, organizing the inspection around six perspectives—terrain prone to water collection, slopes and fill edges, drainage channels and cross structures, racking foundations and areas around panel rows, access roads and work paths, and comparison with historical data—makes it easier to reduce oversights. The important point is to use drone surveying not merely as aerial photography but as material for maintenance and management decisions. By recording where water accumulates, where the ground surface is being eroded, and which deformations are progressing, it becomes easier to prioritize repairs and inspections.

On the other hand, drone surveying alone cannot determine subsurface conditions or the safety of facilities. The basic workflow is to use images and topographic data to identify candidate anomalies and, when necessary, carry out on-site verification or additional investigations. Because appearance can change with shooting conditions, vegetation height, shadows, and weather, it is also important to record survey conditions and keep the data in a state that allows comparison with past data.

In the operation and maintenance of solar power plants, early detection of erosion risk and continuous monitoring of drainage and changes to the ground surface contribute to stable operation. If you want to efficiently inspect a large site and organize data that can be used for on-site decision-making, consider an inspection system that utilizes drone surveying and use it in combination with field checks and maintenance management plans.