Royal River Dam Assessment: Drone LiDAR & Bathymetry Mapping in Maine

In 2025, Active Intelligence Drone Services completed one of Maine's most complex drone mapping projects: a comprehensive LiDAR, photogrammetry, and bathymetric survey of the Royal River in Yarmouth. Using advanced drone technology and hydrographic sonar, we delivered precision 3D data to support feasibility assessment for potential modifications to three historic dams—providing engineers and community stakeholders with accurate information to evaluate options for the river's future.

Project Overview

Project Stats:

Location: Royal River, Yarmouth, Maine (15 minutes north of Portland)
Survey Extent: One Mile river corridor from Yarmouth History Center to Bridge St.
Data Points Collected: Multiple million across integrated datasets
Accuracy Achieved: Sub-decimeter precision
Timeline: Spring - Early Summer 2025
Structures Mapped: 3 historic dam structures
Technologies Deployed: Aerial LiDAR, photogrammetry, drone bathymetry, RTK GNSS

A Brief History of the Royal River

Flowing from Sabbathday Lake in New Gloucester to its tidal mouth in Yarmouth, the Royal River has long been part of Maine's industrial and environmental story. In the 1800s, its steady current powered sawmills, tanneries, and textile mills, fueling Yarmouth's growth as a manufacturing hub. But with progress came infrastructure—dams, retaining walls, and channels—that permanently altered the river's natural flow.

Today, community discussions focus on the future of these aging structures and the river's role in Yarmouth's ecology and identity. Any potential changes to the three historic dams require careful study of environmental impacts, engineering feasibility, costs, and community input. Our drone mapping project was designed to provide the accurate baseline data necessary for informed decision-making—whatever direction the community ultimately chooses.

Our Mission: Drone LiDAR Mapping for Feasibility Assessment

Active Intelligence Drone Services was contracted to deliver a complete topographic and hydrographic model of the Royal River corridor through Yarmouth. Our mission was to provide engineers, environmental consultants, and municipal planners with a unified, high-accuracy 3D dataset to support feasibility studies examining options for the three historic dam structures.

This involved integrating aerial LiDAR scanning, high-resolution photogrammetry, and drone-based bathymetric sonar surveys, combined with manual GNSS control points collected using an RTK rover pole, to produce a seamless model of both land and underwater terrain. The resulting data allows stakeholders to model multiple scenarios—from maintenance and fish passage improvements to partial or full structure modifications—with engineering-grade precision.

[Image: SPH Engineering DC052S dual-frequency sonar towed 2 m below DJI M300 RTK for bathymetric mapping of Royal River] Caption: Drone-mounted DC052S echo sounder collecting bathymetry while maintaining altitude with a laser altimeter.

Advanced Drone Mapping Technology & Equipment

For this complex multi-sensor mapping effort in southern Maine, we deployed a combination of advanced systems and workflows:

Aerial LiDAR Scanning

DJI Matrice 300 RTK equipped with a LiDAR L2 sensor for high-density topographic scanning across forested and urban sections of the river corridor
Captured millions of elevation points through tree canopy and along structural features

High-Resolution Photogrammetry

DJI P1 45 MP camera, capturing ultra-detailed imagery for orthomosaic generation and surface modeling
Provides visual context and texture mapping for 3D models

Drone-Based Bathymetric Survey

SPH Engineering DC052S dual-frequency echo sounder mounted beneath the drone and towed slowly through the river on a 2-meter cable
Laser altimeter maintained precise elevation above the water surface
This configuration allowed accurate hydrographic survey even in confined or shallow sections where boat access was limited

Ground Control & Verification

Emlid RS3 GNSS rover to establish ground control points (GCPs) and verify elevations along banks, structures, and submerged reference locations
RTK positioning ensures centimeter-level accuracy throughout the survey area

[Image: Active Intelligence field crew collecting RTK shallow-water points with Emlid RS3 to bridge LiDAR and bathymetry datasets] Caption: Field technician collecting over 500 shallow-water manual points with Emlid RS3 GNSS rover.

Bridging Land and Water

In addition to numerous GCPs and independent checkpoints, our team collected over 500 additional manual survey points using the Emlid RS3 in shallow-water transition zones—areas too shallow for sonar but too deep for LiDAR returns. These manually measured points bridged the gap between aerial and aquatic datasets, ensuring continuous coverage and sub-decimeter accuracy throughout the entire corridor.

By combining airborne LiDAR, drone-towed bathymetric sonar, and manual GNSS measurements, we successfully mapped the entire Royal River corridor—from canopy to channel—under a single coordinate system.

Why Choose Drone-Based Bathymetry for River Surveys?

Traditional hydrographic surveys rely on boats with mounted sonar systems, which can be limited in shallow rivers or narrow corridors. Our drone bathymetry approach offered several advantages for the Royal River project:

Accessibility: Drones can access shallow, narrow, or obstructed waterways where boats cannot operate safely
Integration: Seamless combination of above-water LiDAR and underwater bathymetry in one coordinate system
Efficiency: Faster data collection than traditional boat surveys for linear river corridors
Safety: Reduced risk to personnel in areas with strong currents, debris, or limited access
Cost-Effectiveness: Lower mobilization costs and faster turnaround for complex river mapping projects in Maine
Precision: RTK-corrected positioning ensures accurate alignment between aerial and aquatic datasets

This integrated approach is ideal for dam feasibility studies, river restoration planning, flood modeling, and infrastructure assessment throughout New England.

[Image: High-resolution LiDAR and photogrammetry composite map of Royal River created in GIS and LiDAR software] Caption: Orthomosaic and LiDAR hillshade overlay of Royal River corridor.

Integrating Data into a Unified GIS Model

After field collection, all datasets were processed and merged within GIS & Lidar Software. Using classified LiDAR point clouds, high-resolution orthomosaics, bathymetric depth grids, and the RS3 shallow-water points, we created a comprehensive multi-surface 3D GIS deliverable capturing every key feature:

Riverbed contours and sediment composition
Large rock outcroppings and debris formations
Historical stone and timber retaining walls
The three existing dam structures and their foundations
Bridge foundations, abutments, and access points
Vegetation and canopy coverage along the corridor
Adjacent infrastructure and property boundaries

This unified GIS model enables the engineering team to:

Visualize current conditions with centimeter-level accuracy
Model hydraulic changes under various scenarios
Estimate sediment volumes and transport patterns
Design safe access routes for potential construction staging
Simulate post-modification river morphology
Support environmental impact assessments
Provide visual aids for community presentations and regulatory review

Project Challenges & Solutions

The Royal River drone mapping project presented a unique set of challenges that required innovative solutions:

Challenge: Narrow Flight Corridors

Dense tree canopy and urban infrastructure created confined aerial mapping conditions. Solution: Precise flight planning with the Matrice 300 RTK's obstacle avoidance and our LiDAR sensor's ability to penetrate vegetation

Challenge: Land-Water Transition Zones

The gap between LiDAR's water penetration limit and bathymetric sonar's minimum depth created data gaps. Solution: Over 500 manual survey points collected with the Emlid RS3 in shallow areas

Challenge: Data Alignment Precision

Every data layer—LiDAR, imagery, sonar, and GNSS—had to synchronize within tight horizontal and vertical tolerances to meet engineering-grade standards. Solution: Extensive ground control network and rigorous quality control procedures in post-processing

Through careful mission planning, equipment integration, and precise data fusion, we delivered a seamless, high-resolution 3D model that now serves as the foundation for feasibility studies, engineering analysis, and community discussions regarding the future of Yarmouth's historic dams.

[Image: Historic dam structure on Royal River in Yarmouth Maine captured by Active Intelligence aerial mapping] Caption: Historic dam structure on Royal River, captured via aerial mapping.

Deliverables & Applications

Active Intelligence provided the project team with a comprehensive suite of data products:

3D Point Clouds

Classified LiDAR data (ground, vegetation, structures, water)
Colorized point clouds from photogrammetry
Bathymetric point clouds with depth attributes

2D Mapping Products

High-resolution orthomosaic imagery (sub-inch ground resolution)
Digital elevation models (DEMs) for land surfaces
Bathymetric depth grids for underwater terrain
Contour maps at user-specified intervals

GIS-Ready Datasets

Shapefiles and geodatabases of key features
Dam structure models and dimensions
Cross-sectional profiles along the river corridor
Volumetric calculations for sediment and water storage

3D Visualization Models

Integrated terrain models viewable in CAD and GIS platforms
Fly-through animations for stakeholder presentations
Web-based 3D viewers for public engagement

These deliverables support a wide range of applications beyond dam feasibility assessment, including flood modeling, habitat restoration planning, recreational trail development, and long-term monitoring of river conditions in southern Maine.

Frequently Asked Questions

What is drone bathymetry? Drone bathymetry uses an echo sounder (sonar) system suspended beneath a drone to measure water depth. The drone flies slowly over the water surface while the sonar sends acoustic pulses to the riverbed and measures the return time. Combined with precise GPS positioning, this creates an underwater elevation map similar to aerial LiDAR for land.
How accurate is LiDAR for dam feasibility studies? Our integrated LiDAR, photogrammetry, and bathymetric approach achieves sub-decimeter (under 10 cm) vertical accuracy throughout the survey area. This exceeds the precision requirements for engineering design, hydraulic modeling, and environmental impact assessment. Ground control points and independent checkpoints verify accuracy at every stage.
Why use drones for hydrographic surveys instead of boats? Drones offer several advantages for river surveys: they can access shallow or narrow sections where boats cannot operate, they collect data faster along linear corridors, they integrate seamlessly with aerial LiDAR data, and they reduce safety risks to survey crews. For the Royal River's confined channels and variable depths, drone bathymetry was the optimal solution.
What other applications benefit from this type of drone mapping in Maine? Our integrated approach is valuable for coastal erosion monitoring, reservoir surveys, bridge inspections, flood risk assessment, environmental compliance documentation, aggregate mining operations, and waterfront development planning throughout New England. Any project requiring accurate elevation data both above and below the waterline benefits from this technology.

Closing Thoughts: The Future of Environmental Surveying

This project highlights how modern drone mapping technologies can transform environmental assessment and infrastructure planning. By combining LiDAR, photogrammetry, drone-towed bathymetry, and GNSS ground verification, Active Intelligence produced a dataset that bridges land, water, and structure with unmatched precision.

The Royal River survey demonstrates how integrated drone-based data collection and GIS modeling can support informed decision-making for complex infrastructure questions. Whether communities are evaluating dam modifications, planning river restoration, assessing flood risks, or documenting baseline conditions, accurate geospatial data is the foundation for smart, sustainable outcomes.

Located in southern Maine, Active Intelligence Drone Services specializes in precision mapping for environmental, engineering, and municipal applications across New England. Our expertise in LiDAR scanning, bathymetric surveys, and photogrammetry helps clients make data-driven decisions with confidence.

Ready to Plan Your River Survey or Dam Assessment Project?

If you're evaluating infrastructure options, planning environmental restoration, or need accurate terrain data for engineering analysis, Active Intelligence Drone Services can help. Our integrated drone mapping approach delivers the precision and comprehensive coverage your project requires.

Tags: drone LiDAR Maine, bathymetric survey, dam assessment, dam feasibility study, hydrographic survey drone, Royal River Yarmouth, photogrammetry services, drone mapping New England, RTK survey, environmental surveying, river restoration mapping