Water and sediment depth in a fast river, for a bridge expansion

The challenge

Alberta's worst recorded flood, in 2013, reshaped the banks of the Bow River and caused heavy erosion near an electrical substation south of the Ivor Strong Bridge. Temporary riprap was placed to stabilise the area. A planned bridge expansion now needed fresh bathymetry.

Engineers needed sediment depth as well as water depth, because the volume of riprap needed depends on how far the rock sinks into the riverbed. The site also made boat work difficult and unsafe:

• a fast, constant current;
• unstable riverbanks and few places to launch a vessel;
• the difficulty of keeping a sensor upright from a boat or USV in moving water.

The solution

Altomaxx flew a DJI Matrice 300 RTK carrying SPH Engineering's bathymetry kit with an EchoLogger ECT D052S dual-frequency echo sounder, connected through the SkyHub onboard computer. The two frequencies were captured at the same time:

• 200 kHz for water depth and the riverbed surface;
• 50 kHz to pass through soft sediment and map the structure below it.

The survey ran on 12 July 2024, from the bridge to about 200 m downstream. The pilot flew manually so the speed could be matched to the current and the echo sounder kept as upright as possible, with lines that covered the whole reach. This reduced geometric distortion and gaps in the data.

The data was processed in Hydromagic: noise was filtered, depths were aligned with GPS positions, and a depth matrix was interpolated into a TIN surface, giving a 3D model of the riverbed.

The results

• Water depth across the surveyed reach.
• The depth of soft sediment above more consolidated material.
• The position of the thalweg, the deepest line of the channel.
• Evidence of where the old riverbank had slumped into the river.

With this, engineers could estimate riprap volumes with more confidence and reduce the risk of over-ordering rock and paying to transport it. The survey took a few hours, and no one had to work on the unstable banks or in the current.

Where this applies in India

Fast rivers and soft riverbeds are common at Indian bridge and bank-protection sites. The same workflow suits:

• river surveys for new bridges and bridge widening on highways and railways;
• planning riprap, gabions and other bank protection after floods;
• scour checks near piers, intake structures and riverside substations;
• measuring sediment build-up upstream of weirs and barrages.

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

The equipment, available from HobiTech

Echo sounder	EchoLogger ECT D052S
Onboard computer	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.
Processing	Hydromagic (used in the project)

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