From a Waterfall to 1,000 Acres of River Corridor: A Year of UAV Survey Work in Nepal

There's a question we get asked at almost every industry event we attend: "Can drones really replace traditional survey methods in Nepal's terrain?"

The honest answer, after a year of project data, is: in most cases, yes. Faster, cheaper, and in many situations more accurate than ground-based alternatives — particularly in terrain that would take a survey crew days to traverse on foot.

Here's a look at the real survey work our team completed over the past year, what each project demanded, and what the data actually delivered.

Tinau Khola River Corridor — 1,000+ Acres

This was our largest survey of the year by area, and the one that pushed our flight planning systems hardest. The Tinau Khola river corridor required mapping over 1,000 acres of active floodplain — a mix of agricultural land, settlement areas, river channel, and unstable riverbank that's been eroding significantly in recent monsoons.

The client needed accurate cross-sectional data for flood modelling: how wide is the active channel? Where are the banks most vulnerable? What's the volumetric storage capacity of the floodplain during a 100-year flood event?

We flew the corridor in multiple strips with 80% frontal and 70% lateral overlap, using RTK-enabled positioning throughout. The resulting orthomosaic and digital terrain model gave the client the cross-section data they needed with centimetre-level accuracy in the channel bed — data that would have taken weeks of boat-based survey to collect at equivalent resolution.

Rupse Waterfall — UAV Survey and Photogrammetry

This one was unusual. Rupse waterfall is both a natural landmark and a site of active geological interest — the rock face around the falls has been showing signs of erosion and small rockfall events that concerned the local community.

The challenge: helicopters can't fly close enough to the face safely, and rope access teams would take weeks for a comprehensive survey. We flew a custom approach path that kept our UAV within 15 metres of the rock face during photogrammetry passes, capturing the geometry of the overhang, fracture lines, and erosion patterns in a 3D point cloud that the engineering team could analyse frame by frame.

The deliverable was a georeferenced 3D mesh of the entire fall face with 2cm/pixel resolution — more detail than any previous survey of the site. It identified three areas of active undercutting that weren't visible from the ground.

Bridge Construction Site — Structural Progress Survey

One of our most repeat-client projects: UAV surveys for bridge construction monitoring. The client needed weekly orthomosaics of the construction site to track earthworks progress, verify that embankment fills matched design volumes, and document site conditions for insurance and compliance.

Weekly flights of 20–30 minutes each. Deliverables processed and delivered within 24 hours. Volumetric comparison against the design model flagged two instances where the fill volume was below specification — catching the issue before it became a structural problem.

Survey for Zipline — Photogrammetry Corridor Mapping

Zipline installations need accurate catenary calculations — which means knowing the exact elevation of every anchor point and the terrain below the line with precision. A miscalculation means a rider hits the ground or an anchor pulls under load.

We flew the proposed zipline corridor and delivered a 3D terrain model, cross-sectional elevation profiles at 5-metre intervals, and a computed clearance map showing minimum ground clearance along the entire line at different load conditions. The design team used this data to adjust two anchor points before construction began.

Private Land Surveys — Cadastral Mapping

Several of our projects this year were private land cadastral surveys — landowners and developers needing accurate boundary demarcation and area calculation that stands up to legal scrutiny.

We completed a 15-acre private land survey and multiple smaller parcels across the year. For each, we combined RTK drone photogrammetry with DGPS ground control points to achieve boundary accuracy within 2–3cm — comparable to traditional total station survey at a fraction of the time and cost.

UAV + DGPS: When You Need Both

The Pokhata survey was our most technically demanding ground-truth project. The client required centimetre-level accuracy for a regulatory submission — the kind of precision that drone photogrammetry alone, without ground verification, doesn't always guarantee.

We deployed a combined UAV photogrammetry and Differential GPS (DGPS) ground survey: the drone for rapid area coverage, DGPS for precise point verification at critical locations. The combined dataset gave the client GPS-grade accuracy with UAV-grade speed and area coverage. CM-level accuracy, confirmed by independent verification at 14 checkpoints.

What This Year Proved

Nepal's terrain — river corridors, mountain faces, construction sites, forested cadastral boundaries — is almost designed to make traditional survey slow and expensive. UAV survey doesn't solve every problem, but for the categories of work we've been doing this year, it consistently delivers faster turnaround, lower cost, and comparable or better accuracy than ground-based alternatives.

The Tinau Khola alone would have taken a ground team 6–8 weeks. We flew it in 4 days.

If you have a survey project in Nepal — land mapping, construction monitoring, terrain modelling, infrastructure inspection — talk to us. We'll tell you honestly whether UAV is the right tool for your job. More often than not, it is.