Over time, sediment accumulation at the bottom of reservoirs reduces their effective capacity, degrades water quality, and limits the reservoir’s usability. This can lead to decreased irrigation efficiency, interruptions in water supply, and reduced flood control capacity. To prevent such consequences and plan maintenance activities in a timely manner, precise mapping and regular monitoring of bottom deposits are essential.
In this example, our Swiss partner Pix4D demonstrated how modern photogrammetric technologies can significantly enhance the efficiency of such work. In a project carried out in Japan, combining aerial imagery from a drone with terrestrial scanning using PIX4Dcatch with RTK increased measurement accuracy by 70% compared to traditional approaches.
Project overview
The study was conducted at an agricultural reservoir in the mountainous area of Toyama Prefecture, Japan. Before starting the work, the reservoir was partially drained to expose the sediment accumulation zone and enable precise measurements.
The agricultural reservoir before draining, photographed by a drone, with obstructing trees
Data collection methodology
- Aerial imagery provided a comprehensive top-down view for most of the site. However, due to the presence of trees, certain areas remained inaccessible to drones.
- To capture data from these sections, PIX4Dcatch with an RTK device was used, enabling high-precision terrestrial scanning.
- Aerial and terrestrial images were processed separately and then merged in PIX4Dmatic to create a unified 3D model.
On the left is the project captured on the ground using PIX4Dcatch RTK, and on the right are captures from the sky with a drone
This combination made it possible to obtain the most complete and accurate representation of the reservoir bed’s topography.
Implementation highlights
- The coordinates of ground control points (GCPs) were determined using the single-point measurement function in PIX4Dcatch, eliminating the need for a total station or other specialized surveying equipment.
- By attaching an RTK device to a smartphone, the operator could collect accurate data simply while walking around the site.
- Processing was carried out in PIX4Dmatic — software that enables quick parameter setup and easy placement of control points.
3D model completed by merging terrestrial and drone data
Results
- Sediment measurement accuracy increased by 70% compared to the traditional method involving a surveyor and bulky equipment.
- Speed: Determining GCPs with PIX4Dcatch and RTK took 15 minutes instead of approximately 8 hours using conventional tools.
- Visualization quality: The resulting 3D model provided a detailed reproduction of the reservoir bed’s topography, offering far more insight than 2D drawings with points and lines.
- Reporting efficiency: Digital models make it easier to share information and help all stakeholders better understand the condition of the infrastructure.
Conclusion
The combination of PIX4Dcatch RTK and PIX4Dmatic for reservoir monitoring significantly improves measurement accuracy, reduces labor requirements, and ensures full coverage even in challenging environments with limited drone access.
This case demonstrates that modern photogrammetry is not only an alternative to traditional methods but also an effective tool for decision-making, maintenance planning, and optimizing the operation of engineering, agricultural, and environmental facilities.
