1. Using Drones to Undertake Inspections of Open Stormwater
Channels
Pramod Janardhanan
Asset Strategist, Sydney Water, NSW, Australia
E-mail: pramod.janardhanan@sydneywater.com.au
Masood Naqshbandi
Director and Co-Founder, Abyss Solutions Pty Ltd, NSW, Australia
E-mail: masood@abysssolutions.com.au
James Rennie
Director, Australian UAV, NSW, Australia
E-mail: james.rennie@auav.com.au
Abstract
As our population grows and the complexity of our environment increases, new technologies provide
water utilities opportunities to seek innovative ways to manage their assets. The traditional method of
inspecting open stormwater channels involved personnel entering these assets to photograph visual
defects, which increases the risk of working in live assets and requires significant prior planning to
mitigate these risks. This paper discuss a trial undertaken by Sydney Water to use aerial and aquatic
drones to undertake inspections of our open stormwater channels.
1. INTRODUCTION
Sydney Water owns and manages over 440 kilometres of major trunk stormwater drains in 71
stormwater systems throughout Sydney Water’s area of operations. Most of these systems were
constructed between 1890 and 1940 with one third of stormwater channels built during the Great
Depression (1930s). Over time these assets deteriorate, and require regular inspections to identify
maintenance works to achieve their expected life, and renewal works in advance of structural failure.
Failure of stormwater assets is likely to result in:
 damage to adjacent structures and utility infrastructure
 significant environmental impact
 risks to public safety
 breach of legislative requirements to maintain the structural stability of Sydney Water’s
stormwater assets
1.1. Current Inspection Program
These stormwater assets have been the subject of a rolling condition assessment program since the
mid-1990s, with each asset re-inspected every 10 years.
Inspections are carried out using a combination of closed circuit television (CCTV) devices and
physical inspection by people, due to the varying size of stormwater channels and the capability of
current technologies. The following table summarises the breakdown of these inspection
methodologies:

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Table 1: Inspection categories
Inspection type Asset type
CCTV inspection Enclosed channels with height <1.5 m
Person-entry
inspection
Open channels
Enclosed channels with height >1.5 m
Of these, 130km comprises of open stormwater channels. Traditional method of inspecting open
stormwater channels involved personnel entering these assets to photograph visual defects, which
increases the risk of working in live assets and requires significant prior planning to mitigate these
risks.
1.2. Drone Trial
As our population grows and the complexity of our environment increases, new technology provides
water utilities opportunities to seek innovative ways to manage our assets. The use of drones, both
Unmanned Aerial Vehicles (UAVs) referred to as aerial drones and Unmanned Underwater Vehicles
(UUVs), referred to as aquatic drones in this paper provides us with such an opportunity. Sydney
Water undertook a trial to use aerial and aquatic drones as an alternative approach to undertake
inspections of our open stormwater channels.
The objectives of the trial were
 Develop a more cost effective and efficient method of undertaking stormwater inspections
through the use of drones
 Be able to easily undertake inspection of sites that have high traffic volumes or inaccessible
 Improve safety outcomes through substitution of physical access through the use of drones
The trial was carried out at the following two locations:
 Cooks River, Croydon Park for the aerial drone and
 Alexandra Canal, Alexandria for the aquatic drone
1.3. Aerial Drone Trial
The aerial drone inspection was carried out at Cooks River. Cooks River is a 23km long waterway
located approximately 10km south west of Sydney CBD. The Cooks River catchment is approximately
102 km2
and covers portions of 13 local government areas. The catchment is highly urbanized and
serves as part of a stormwater system discharging flows into Botany Bay.
The inspection for the aerial drone involved flying along the length of the canal walls from Canterbury
Park Racecourse, Canterbury to Punchbowl Rd, Belfield, capturing photos at regular intervals. The
data is georeferenced and uploaded to an online portal and used to create a comprehensive 3D
inspection model of the site.
The processed data is available on the online portal the next business day and can be used straight
away for inspection and comparison.
The online portal allows specific inspection visualizations for the canal wall and these can be used to
quickly and conveniently check areas with the full resolution of the individual photos.

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Figure 1: Aerial drone
Figure 2: Aerial drone online portal
1.4. Aquatic Drone Trial
The aquatic drone trial was carried out at Alexandra Canal. Alexandra Canal is a 4km long canal
located south of the Sydney CBD. The Alexandra Canal catchment is approximately 17 km2
and
located within the City of Sydney and Marrickville local government areas. Alexandra Canal is a State
Listed Heritage owned and managed by Sydney Water. The canal is 60 metres wide, increasing to 80
metres at its mouth and is one of only two navigable canals constructed in New South Wales. It was
built in the 1880’s, servicing the industrial areas along its length was constructed from a natural tidal
watercourse known as Shea’s Creek that drained the South Sydney district into Botany Bay via the
Cooks River. It currently serves as a major conduit for stormwater drainage
The inspection for the aquatic drone was carried out by lowering the drone into the water body within
the open stormwater channel. The drone weighs 2.6kg and is 30cm long x 20cm wide x 15cm high.
The drone has a mounted HD pan tilt camera with 120 degree field of view and LEDs with brightness
of 200lm for imaging in poorly illuminated environments. Extra visual sensors were also mounted on
the drone for high-resolution imagery of the canal banks. The drone is tethered and remotely
controlled by a crew at the ground station away from the canal banks. Live video and position data

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was relayed continuously to the ground station. This capability allowed the team to acquire
georeferenced imagery - which enabled the spatial location of faults and other features of interest.
Figure 3: Aquatic drone front view
Figure 4: Aquatic drone rear view
The trial was divided into the following tasks, which will be conducted in the order listed below:
a. Determination of site locations - an initial inspection of the canal was carried to identify regions
containing faults of significant concern. The selection will seek to maintain continuity of
imaging where possible, a range of materials including sandstone blockwork, concrete
blockwork and shotcrete, and a variety of failures which may include missing block work,
grouting failure, shotcrete fracture, and, base, toe, face or crest failures, as well as failures of
adjacent assets such as blocked stormwater outlets and cracking of pavement at the crest of
the bank.
b. Imaging strategy - the aquatic drone is deployed at the site to image the fault. This will involve

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mounting a 14 MP high-resolution camera to collect optical imagery. The camera will be
mounted on the port side of the aquatic drone. The distance of the camera to the banks
determines the resolution of the images acquired, and thus the resolution of the final product -
photos of faults and 3D models of the banks. Capturing images at a greater distance from the
bank greatly increases the image footprint, which speeds up both image acquisition and
processing time, resulting in a lower overall cost. However, this comes at the expense of
image quality. On the contrary, images acquired closer to the bank are higher resolution but
take longer to collect and cost more to assemble into a 3D model of a fault. Data was
collected at different resolutions to present the range in image quality achievable, and to
choose the quality level most appropriate for future needs. The following table summarises the
specifications for different resolution that were captured.
Table 2: Trial Resolutions
Camera GoPro Hero
Black 7MP
GoPro Hero
Black 7MP
GoPro Hero
Black 7MP
GoPro Hero
Black 14MP
(wide angle
lense)
GoPro Hero Black
7MP
Image Foot Print
(m)
1.02 2.05 3.07 5.11 0.37
Image Capture
Frequency (/s)
2 2 2 2 2
Drone speed (m/s) 0.41 0.82 1.00 1.00 0.15
Time to image per
km (mins)
40.85 20.33 16.67 16.67 112.61
c. Engineering Assessment – The imagery collected is reviewed and for each fault identified the
following work is undertake:
1. Determine the exact location of the fault in terms of MGA coordinates using captured
georeference data,
2. Analyse the physical fabric of the fault region including the bank slope, water level, ground
level, materials, construction methods and structures on/in/near the bank using both high
resolutions imagery and site measurements,
3. Assess the condition of the fault region including the state of any blockwork, grouting,
shotcrete, concrete, slope, crest, toe and backfill of the bank determined.
4. Issue a condition grade of excellent, good, poor or failed according to the outcome of item
3,
5. Identify any assets in/near the fault region, including public reserves, pavements, fences,
stormwater outlets, bridge piers, jetties and private property, and assess the conditions of
such assets,
6. Determine whether any reparative work is necessary, and if so the nature of this work,
7. The urgency with which any reparative work determined in item 6 is to be undertaken,
categorised as immediate, within 6 months, 1 year, 5 years and 10 years, and,
8. Make any additional notes on features or issues relating to the fault and site which may be
of material importance.
d. Computational Processing - There are a few subtasks involved in this process
1. Geotagging of photos - A single GPS tag was carried out at the start of the inspection site
and the exact location of the fault will be tagged in conjunction with data coming in from
the Inertial Measurement Unit (IMU) based on dead reckoning.
2. Colour Correction - This was carried out on all the underwater images to remove the
effects of turbidity.
3. Mosaicking - This is the last task that will stitch the images together for each site into a
satellite style high-resolution map. An example of the processing pipeline and the 3D
model deliverable is given below for above water surface imaging

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Figure 5: Image processing
Figure 6: 3D model
Finally a full engineers report with geo-tagged and classified faults along with comprehensive 3D
maps for each section of the asset is uploaded on Google Earth for user-friendly interface.
1.5. Results
The outputs from the trial included:
 High resolution georeferenced images
 Comprehensive 3D inspection model of the site
 The aquatic trial inspection also provided a report with a description of the physical fabric,
catalogue of defects, condition grade and likely reparative works.
1.6. Conclusion
The use of drones enabled inspection of sites that have high traffic volumes or inaccessible, improve
work practices through reduced cost and time and being not dictated by water levels or tides and most
significantly improving safety for personnel as they are not accessing confined spaces or entering into
channels.
Drone technology has the potential to have a place in our regular asset inspection regime and be
expanded for defect identification and waterway health assessment.
2. ACKNOWLEDGMENTS
This work was conducted in collaboration with the Sydney Water, Abyss Solutions Pty Ltd, Propeller
Aero Pty Ltd and Australian UAV.

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3. REFERENCES
1. Sydney Water. (1999), Cooks River & Cup and Saucer Creek Capacity Assessment, Sydney
Water, Sydney
2. Sydney Water. (2003), Alexandra Canal Capacity Assessment, Sydney Water, Sydney
3. NSW Department of Commerce. (2004), Alexandra Canal Conservation Management Plan, NSW
Department of Commerce, Sydney