Sediment surveys of 13 stormwater ponds with a drone echo sounder

The challenge

Stormwater ponds control runoff, reduce flood risk and trap sediment before it moves downstream. They only work if they keep enough storage, so municipalities check them from time to time against the design and decide whether dredging is due.

The 13 ponds in this project needed water depth, sediment thickness and total volume. Many were small, oddly shaped, ringed by thick vegetation or bordered by unstable banks with nowhere safe to enter the water. Crewed boats and USVs struggle here: there is little room to manoeuvre, launching is unsafe, and propellers foul on plants and debris.

The solution

Altomaxx flew a DJI Matrice 300 RTK carrying an EchoLogger ECT D052S echo sounder. It records returns at 50 kHz and 200 kHz, which lets the team separate water depth from the soft sediment layers below. The drone was flown manually to keep close control near vegetation and pond edges.

• Flight lines were spaced 2 m apart for dense coverage.
• An Emlid GNSS base with NTRIP corrections improved positioning.
• An Emlid rover recorded water-surface elevations, so depths could be turned into elevations.
• Hydromagic was used for GPS adjustment, noise filtering, TIN models and interpretation.

The results

• High-resolution bathymetric models for all 13 ponds.
• Most ponds held little sediment, in line with expected performance.
• One pond was heavily infilled: 7,512 m³ of sediment in a total volume of 10,477 m³.
• A "Delta Matrix", the difference between the low- and high-frequency surfaces, showed clearly where sediment had settled.
• Ponds that would take a full day by vessel were surveyed safely in a few hours.

The municipalities got models they can use for capacity checks, environmental planning and maintenance scheduling.

Where this applies in India

Indian cities and industrial estates rely on many small water bodies that silt up. The same workflow suits:

• stormwater detention and retention ponds in cities and townships;
• urban lakes and tanks before desilting work, to estimate volumes;
• sedimentation ponds at highway, airport and industrial sites;
• effluent and treatment ponds that need regular capacity checks.

SPH Engineering's bathymetry training is also available through HobiTech.

The equipment, available from HobiTech

Echo sounder	EchoLogger ECT D052S
Onboard computer	SPH Engineering's bathymetry kit runs on SkyHub by SPH Engineering with the SkyHub echo sounder software
Drone	DJI Matrice 300 RTK was used in this project. Ask us for current compatible drones, such as the DJI Matrice 350 RTK.
Positioning	Emlid GNSS base and rover with NTRIP (used in the project)
Processing	Hydromagic (used in the project)

Case study by SPH Engineering, published December 2025. This page summarises it in our own words; the surveys were carried out by Altomaxx Technologies, not by HobiTech. Read the original case study on SPH Engineering ↗