Drone-based inspection, digital defect mapping and precision aerial survey for one of the largest dams in NSW

Drone aerial survey and drone aerial inspection
Project Overview

One of the largest dams in NSW has a rock wall that is 747m long and 114m high, with a rock-fill embankment and clay core, and a 300m long concrete chute spillway located at the eastern end of the dam wall. Routine monitoring of the dam requires inspection of the spillway structure to identify the presence of any defects. Conventional inspection of the spillway involves personnel working at heights to manually map the location and extent of identified defects. Diodrone was engaged by WaterNSW to develop a digital engineering solution for inspection and defect mapping over the spillway structure.

Diodrone Solution

Diodrone developed a drone based reality capture solution which would provide a detailed defect map for the spillway structure, a precision aerial survey for the embankment to assist with routine displacement monitoring, and a reality model of stilling basin rock exposures to assist with geotechnical assessment.

Project Scope
Spillway Inspection
Spillway Inspection
Precision Aerial Survey
Precision Aerial Survey
3D Modelling
3D Modelling

The use of drone-based reality capture eliminated working at heights and created an inspection data set significantly better than conventionally available.

CAD and PDF defect mapping outputs for each concrete slab with linework for various classes of inspection and defect features

A small multirotor drone was used to capture RGB (visual) and thermal IR imagery over the extent of the spillway structure. Images were then processed in photogrammetry software to develop an ultra-high-resolution 3D model.

Photogrammetry processing achieved an average resolution of 2mm per pixel and an accuracy of 7mm RMSE when compared to a network of 5no. precise check points.

A digital inspection was then carried out, referencing the 3D model and thermal IR photographs, to develop a detailed defect map which marked out the extent of cracks, patch repairs, pitting, spalls, debris, vegetation, and thermal IR anomalies.

Each class of defect was presented as a separate layer in a web-based 3D GIS as well as detailed in a slab-by-slab defect report which included CAD and PDF defect maps.

  • Web-based 3D GIS
  • Vectors (linework) for various classes of inspection features
  • CAD and PDF outputs for each concrete slab including chute and training walls
  • Factual Inspection Report

Digital Inspection and Defect Mapping over 13,000m2 of concrete using ultra-high-resolution 3D modelling and thermal IR.

Dam defect mapping and thermal anomalies extracted for 3D model
Visible defects and thermal IR anomalies were extracted from the imagery and 3D model to produce a geo-referenced and scale accurate digital representation of the inspection results.
Thermal infrared identified thermal anomalies, possibly indicative of shallow sub-surface defects, used as part of the dam defect mapping output.
A thermal IR anomaly identified over one of the concrete slabs, possibly indicative of a shallow sub-surface defect.
Precision Aerial Survey

A small multirotor drone equipped with RTK direct georeferencing was utilised to capture imagery for a precision aerial survey over the dam embankment. Photogrammetry processing of the imagery achieved sub-pixel reprojection error and the resulting point cloud output achieved an accuracy of 15mm RMSE when compared to a network of 17no. check points established throughout the survey area.

The high-density point cloud was gridded into a digital elevation model (DEM) from which 1m contours were developed. With future surveys of the area, change detection analysis of the point cloud and DEM can be carried out to assist the WaterNSW survey team with modelling and monitoring displacements of the structure.

Photogrammetry outputs achieved an accuracy of 15mm RMSE when compared to a network of high-precision check points.

Photogrammetry derived 3D model
A network of ground control points and check points were established throughout the survey area using a total station to achieve the highest possible accuracy and precision for photogrammetry control and validation of achieved accuracy. 
photogrammetry developed a high density point cloud, digital elevation model and elevation contours of the dam embankment
Photogrammetry processing of direct georeferenced imagery, in conjunction with a network of precisely surveyed control points, was used to develop a high density point cloud, digital elevation model and elevation contours of the embankment.
3D Modelling

Imagery from the spillway inspection and the precision aerial survey was combined to form a data set of more than 10,000 photographs, which covered the entire dam structure at 20mm resolution or less. Extensive oblique photography was included in the data set to ensure steep, vertical, and overhanging surfaces were captured.

Photogrammetry software was then used to reconstruct a 3D model for the entire dam, which achieved an accuracy of 15mm RMSE when compared to a network of checkpoints established throughout the project area. The 3D model included an extremely high level of detail over rock exposures on the abutments and at the base of the spillway, for use in geological mapping and geotechnical assessment.

High-resolution 3D textured mesh of the site, suitable for digital inspection, geological modelling, and general site visualisation.

3d model of spillway structure, embankment, abutments and downstream areas of dam. Close visual inspection of the model allows for dam defect mapping.
Drone-based photography of the spillway structure, embankment, abutments and downstream areas was combined and processed in a single photogrammetry reconstruction to create a 3D model of the entire site.
High resolution 3d model of dam site
Ultra-high-resolution 3D modelling of the site, including rock exposures on the abutments and at the base of the spillway.