A vast network of sewers runs under our cities for the purpose of carrying wastewater and stormwater to the nearest wastewater treatment plant, where it undergoes purification to make it suitable for discharge into the receiving media. These sewers can be classified by whether or not they are accessible to the personnel charged with their maintenance and inspection. The smallest sewers, which carry a smaller flow of wastewater and where it is impossible for a person to enter, are inspected by robots fitted with wheels and one or more cameras to record the status of the sewer, which is subsequently evaluated by supervisory staff on viewing the video information.


However, sewers whose size enables the entrance of people cannot be inspected in the same way. This is because their size goes hand-in-hand with a greater wastewater flow and a higher flow rate, making the deployment of robots unfeasible. For this reason, such sewers are generally inspected and maintained by staff who walk, wherever possible, on the side platform (in dry weather, this platform is dry but in wet weather it becomes flooded). Such operations are carried out
in difficult conditions with respect to visibility and safety. The project described in this article will be carried out in “walkable” sewers such as these.

Canal de Isabel II manages over 15,000 kilometres of sewers in the Autonomous Community of Madrid. Over 2,400 kilometres of this network are walkable. These walkable sewers feature a number of characteristics that hamper the inspection work carried out by Canal staff. The smallest of them have a height of 1.7 metres and they can be located at depths of up to 25 metres. Added to this is the accumulation of substances that can be hazardous to health in large quantities (sludge, gas pockets…). Moreover, the environment is corrosive for the measuring instruments and electrical installations needed in the sewer. Maintenance of these types of installations requires on-site inspection in order to verify their status and make decisions regarding the prioritisation of actions required.

Canal de Isabel II, through Pre-Commercial Procurement, is promoting the design, manufacture and subsequent validation of an autonomous, self-flying drone to carry out inspections and improve the results of current inspections in a number of areas which will be outlined below:

This first improvement sought is increased safety for inspection staff. Walkable sewer inspections are currently carried out by field crews who periodically visit the network in search of cracks, obstructions and other anomalies. Field crews are made up of three workers, with two of them entering the sewer to carry out the inspection as such, while the third member of the crew remains overground.

Overground support staff play a vital role in the safety of the other two crew members, who are exposed to a polluted environment due to the presence of sludge. Moreover, the slippery conditions can even cause workers to enter into contact with the sewage.


Antonio Lastra de la Rubia
Coordinator of Network Innovation. Sub-directorate of R&D&i – Canal de Isabel II

Published in: Nº63 FuturENVIRO September 2019