Case study by SPH Engineering · Bathymetry · Water resources
Tracking reservoir volumes through a drought with drone bathymetry
Throughout 2024, Chile's Ministry of Public Works (MOP) surveyed four reservoirs in the drought-hit Coquimbo region with a drone-mounted echo sounder from SPH Engineering. Repeat surveys showed how storage changed with the seasonal rains and fed into water allocation decisions.
The challenge
The Coquimbo region has faced severe water shortages, and Chile declared a drought emergency there in both 2022 and 2023. Erratic rainfall and higher evaporation threaten farming, drinking water and ecosystems.
Reservoir monitoring had relied on manual methods that were slow, prone to error and produced little data. That made it hard to track water levels precisely, spot trends and manage drought and flood risk. The Ministry decided to move to SPH Engineering's drone-based echo sounder system.
The solution
The Ministry flew a DJI Matrice 300 RTK with a DJI D-RTK 2 base station for RTK corrections.
- Photogrammetric cameras produced orthomosaics and DEMs of the reservoirs and surrounding terrain.
- An ECT 400 echo sounder, run by SkyHub, recorded depths tied to precise GPS positions.
- Flight paths were planned in UgCS to cover the large reservoir areas efficiently.
- Hydromagic turned the data into detailed bathymetric maps and volume calculations.
The results
- Cogotí: 1.14 million m³ at a critical low in March 2024, rising to 16.46 million m³ by July after seasonal rains. The figures informed water distribution decisions for farming and towns.
- Puclaro: 9.9 million m³ in April, used for immediate allocation decisions.
- Recoleta: 7.1 million m³ in February, rising to 10.04 million m³ by July.
- La Paloma: updated volumes compared with an earlier survey, to help assess long-term storage and sedimentation trends.
Lessons learned
- Without earlier bathymetry, sediment build-up could not be measured precisely.
- Strong winds sometimes delayed flights, so schedules needed slack.
- Battery life meant several flights per reservoir, and base stations had to be moved often to keep accurate GPS.
- Small changes in method between surveys made direct comparison harder.
The Ministry now plans to standardise its drone survey method, build historical baselines and streamline processing.
Where this applies in India
India's reservoirs and tanks face the same need for regular, reliable storage figures. The workflow suits:
- capacity surveys of irrigation and drinking-water reservoirs;
- pre- and post-monsoon storage checks for water allocation;
- sedimentation studies to track loss of live storage over time;
- village tanks and check dams that are too small or shallow for survey boats.
SPH Engineering's bathymetry training is also available through HobiTech.
The equipment, available from HobiTech
| Echo sounder | EchoLogger ECT 400S (named ECT 400 in the source) |
| Onboard computer | SkyHub by SPH Engineering with the SkyHub echo sounder software |
| Flight planning | UgCS - Drone Flight Planning Software |
| Drone | DJI Matrice 300 RTK with a DJI D-RTK 2 base station was used in this project. Ask us for current compatible drones, such as the DJI Matrice 350 RTK. |
| Processing | Hydromagic (used in the project) |
Case study by SPH Engineering, published March 2025, citing the 2024 bathymetric reports for Embalse Cogotí, Puclaro, Recoleta and La Paloma by Chile's Dirección General de Aguas. This page summarises it in our own words; the surveys were carried out by Chile's Ministry of Public Works, not by HobiTech. Read the original case study on SPH Engineering ↗
Need reliable reservoir volumes?
Tell us the reservoirs, their size and how often you need figures. We will specify the drone, echo sounder, SkyHub and UgCS setup, quoted in rupees with a GST invoice.