Case study by SPH Engineering · Hydrology · River monitoring
Drone hydrometry on a remote tropical river
In May 2025, researchers from the UAWOS project surveyed the Ouémé River in Benin with drone-mounted sensors, backed by selected ground measurements. Flying from boats, they captured water surface elevation, flow velocity and riverbed shape across all their planned cross sections in four days.
The background
The Ouémé River runs about 500 km from the Atakora Mountains to the Gulf of Guinea and is central to Benin's water system. Seasonal shifts between dry and wet periods shape the river and the fishing and sand extraction along it.
The survey covered two areas: a 6 km stretch around the Bonou gauging station, and the area near the Zou River inflow at Dasso. Each was split into ten cross sections.
The challenge
The survey ran during the change from the dry to the rainy season. The Zou inflow area was remote, with floodplains under vegetation all year that blocked ground access to the cross sections. Dense tropical growth and high temperatures added to the difficulty. Reaching sections on foot would have needed a lot of clearing, and carrying equipment through the floodplain was slow and tiring.
The solution
The UAWOS team flew its drones directly from boats. This made it quick to move between cross sections and cut exposure to heat and vegetation. The drones collected:
- orthophotos and LiDAR coverage of both areas;
- water surface elevation with a Geolux LX-80 radar altimeter;
- flow velocity with a Geolux RSS-2-AB Doppler radar;
- riverbed shape with SPH Engineering's integrated water-penetrating radar (WPR) system using the Zond Aero LF on a DJI M300.
For validation, the team also measured velocity with ADCP and Ott MF-Pro, bed shape with sonar, and used SWOT satellite altimetry as a water level reference.
The results
- All selected cross sections were surveyed within four days.
- Early processing shows strong agreement between drone and traditional measurements for velocity, bed shape and water surface elevation.
- The drone radar picked up small-scale changes in water level that satellite altimetry did not resolve.
Where this applies in India
Flying sensors from a boat or bank suits rivers where walking to each section is not practical:
- rivers with wide, vegetated floodplains;
- discharge and water level studies near gauging stations;
- river confluences and reservoir inflows;
- hydrology research at universities and research institutes.
SPH Engineering's bathymetry training is also available through HobiTech.
The equipment, available from HobiTech
| Water level | Geolux LX-80-AB water level measurement kit |
| Surface velocity | Geolux RSS-2-AB water surface velocity measurement kit |
| Water-penetrating radar | Radar Systems Zond Aero LF, as part of SPH Engineering's integrated system |
| Drone and mapping | DJI M300 was used, with orthophoto and LiDAR mapping. Ask us for current compatible drones. |
Case study by SPH Engineering, published December 2025. This page summarises it in our own words; the research was carried out by the UAWOS project team, not by HobiTech. Read the original case study on SPH Engineering ↗
Need river data from hard-to-reach sections?
Tell us the river, the number of sections and what you need to measure. We will specify the sensors, SkyHub and drone, quoted in rupees with a GST invoice.