Erosion rarely announces itself. A creek bank loses a few feet over a wet spring, a lake shoreline slumps after a high-water season, a fresh cut slope on a job site starts to rill after the first big storm. By the time someone notices from the ground, the question is no longer "is it moving?" but "how much, how fast, and since when?"
That's the question drone erosion monitoring answers well. A Part 107 pilot flies the same area on a schedule and turns each visit into a dated, measurable map, so you can compare one date to the next instead of relying on memory and a few phone photos. This guide is set up the way our clients usually ask about it: the questions first, then the answers that help you hire well.
What does a drone erosion monitoring job actually produce?
The core product is a set of matched surveys of the same footprint over time. A typical package includes:
- Dated orthomosaics. A sharp, georeferenced top-down image of the bank, slope or shoreline for each visit.
- Elevation surfaces. A surface model for each date, so changes in height can be measured, not just seen.
- Change maps. An elevation-difference map between two dates that shows where material was lost or deposited.
- Cross-sections and profiles. Lines drawn across the bank or slope at fixed stations so you can track the same profile visit after visit.
- Bank or shoreline edge lines. A traced top-of-bank or water-edge line per date, so retreat can be measured along the reach.
- A photo log. Oblique photos of washouts, undercut banks, failed silt fence, exposed roots or damaged structures, tied to locations on the map.
Who usually hires for this?
Landowners with a creek or pond eating into a pasture. Lake associations and marinas watching shoreline loss. Developers and contractors documenting erosion and sediment controls through construction. Road and utility owners checking embankments and crossings after storms. Conservation groups tracking restoration work. Engineers and surveyors who want repeat imagery between their own field visits.
Why does "repeat" matter so much?
One flight shows you what a site looks like. Two flights, done the same way, show you what changed. The value is in consistency, and that's the part to write into your hire:
- Same footprint every time. Ask the pilot to save the flight plan and reuse it.
- Same height and overlap. Changing them between visits changes the detail and can blur real change with noise.
- Fixed ground control. Permanent or re-occupiable control points (and a few checkpoints) are what let two maps line up closely enough to measure small changes.
- Similar conditions. Similar season, sun angle and, on shorelines, similar water level. Record the water level or gauge reading at flight time.
- A trigger plan. Scheduled visits (quarterly, seasonal) plus event flights after major storms or high water.
Is this the same as a drainage mapping job?
Close cousins, different questions. Drainage mapping asks where water flows and pools across a site. Erosion monitoring asks how the ground itself is changing over time, usually along banks, slopes and shorelines. If your main concern is runoff paths, ponding or culvert flow, read our guide to hiring a drone pilot for stormwater and drainage mapping first. Many projects need both, and one pilot can often fly them together.
How accurate does it need to be?
That depends on how small a change you care about. If you're documenting a bank that retreated several feet after a flood, a well-flown map with good control will show it clearly. If you need to detect a few inches of change on a gentle slope, you're asking for survey-level care: tight control, checkpoints and a pilot who reports accuracy honestly for each date.
If your project needs a stamped baseline or elevations you'll rely on for design, start with a proper topographic baseline. Our guide to hiring a drone pilot for a topographic survey walks through how that kind of job is scoped and who signs it.
What can't a drone see?
Be clear-eyed about the limits before you sign:
- Vegetation hides ground. Photo-based mapping sees the top of grass, brush and trees. Heavily vegetated banks may need leaf-off timing or a LiDAR sensor to measure the ground surface.
- Water is a blank. Moving or reflective water doesn't map well with photos, and a photo map doesn't measure underwater bank toe or scour.
- Undercuts are hidden. A top-down view can't see under an overhanging bank. Oblique photos help document it, but don't measure it.
- Steep faces need extra passes. Near-vertical bluffs and cut banks may need oblique flights in addition to the standard grid.
Who signs off on permits and designs?
Not the drone pilot. Imagery and change maps are evidence and documentation. Permit compliance sign-off, stabilization design, shoreline protection and any engineering judgment stay with the licensed engineer or surveyor on the project, and with whatever inspector your permit names. A good pilot will ask who that person is and deliver data in a format they can use.
What should go in your scope?
- Location and limits. A KMZ or marked map of the reach, slope or shoreline, plus a buffer.
- Purpose. Documentation, change tracking, construction controls, restoration monitoring, or input for an engineer.
- Schedule. Baseline date, repeat interval and event triggers (for example, after any storm above a set rainfall amount, or after high water).
- Deliverables per visit. Ortho, elevation surface, change map against the baseline and the previous visit, profiles, photo log.
- Accuracy and control. Whether you have existing control or need the pilot to set it, and the checkpoint report you expect.
- Formats. GeoTIFF, PDF, KMZ, CAD-ready files, or a browser link for people without GIS software.
- Access and airspace. Gates, landowner permissions, nearby airports, and whether the site sits in controlled airspace.
Questions to ask before you hire
- Can you show me a change map from a past repeat project?
- How do you keep flights consistent from visit to visit?
- How will you handle ground control so different dates line up?
- What accuracy do you report, and how is it checked?
- How do you handle vegetation and water on this site?
- What's your turnaround after an event flight?
- Do you hold a current Part 107 certificate and liability insurance?
Red flags
- Promising inch-level change detection without control or checkpoints.
- No plan for reusing the same flight between visits.
- Offering to "certify" erosion control compliance or design a fix.
- Delivering pretty pictures with no dates, coordinates or measurements.
What does it cost?
Pricing usually follows site size, how many visits you commit to, whether control has to be set, how many deliverables come with each visit, and how fast event flights must turn around. A recurring program often prices better per visit than one-off flights because the pilot can reuse the plan and control. Ask for the baseline visit and repeat visits to be priced separately so you can compare quotes fairly.
Next step
Write a short scope with the checklist above, bring in your engineer or surveyor if you have one, and send it to a few qualified Part 107 pilots. Ask each to describe how they'd keep visits consistent. Their answer will tell you most of what you need to know.