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30-11-2021

Siphon inspection and maintenance. How do we do it?

Written by Karst Beens

    Inspecting a siphon with an ROV, that’s possible. Easy to say of course, “but can it also be done for a siphon that hasn’t been inspected for 100 years? We would like to show what drones are capable of when used properly, and demonstrate that even these types of difficult assets that cannot be inspected traditionally can be visualised.

    What are siphons?

    When we talk about a siphon, we do not mean the siphon found under your wash basin in the bathroom. No, we mean large siphons that connect small waterways under other objects.

    To give you a general idea, we have a comparison:
    Whereas an aqueduct is used to connect water via bridges, i.e. above the ground, siphons are used to connect water under the ground.

    Why do we use siphons in practice?

    Siphons are therefore used to maintain a waterway. Often, there is an obstruction that prevents the waterway from flowing properly, and it therefore has to be diverted. This can often be done under objects, so that, for example, a stream can continue to flow between meadows, even if there is a motorway between them.

    Especially around 1900, many siphons were constructed. This was because many large canals were dug (all by hand, of course). A large canal for shipping had a higher priority than a stream, so it was logical that it would be allowed to pass through in a straight path. However, the brooklet still had influence on its surroundings, and if it were to connect to the large canal, the water of the brooklet would flow over, and it would not remain separate from the large, new canal.

    De oplossing om het beekje toch volledig intact te laten, maar de grotere prioriteit (het kanaal) voorrang te geven is dus een sifon!

    What are the latest developments in siphons?

    For maintenance, siphons have never been the biggest priority. Bridges and dykes have a greater impact on the land, so of course they take priority.

    Siphons are regularly flushed, however, in order to flush out sludge and sediment. This ensures that a siphon always has sufficient flow.

    The condition can never be determined. Many have not been checked or inspected for over 70 years, so it is not clear whether it can be safe enough to send a diver in there. Apart from that, it is not nice for a diver to dive into a pipe that goes up and down, with little room to move. This means that many siphons have never been inspected for soundness, even though this is possible nowadays…

    Inspecting a siphon with an ROV:

    Below is a possible step-by-step plan of how we envisage such an inspection with an ROV:

    Starting with lowering an ROV into the pipe and ‘just’ cruising around if possible. This way, it can be determined how much flow there is in the pipe and whether it needs to be cleaned or blown through.
    If the pipe is clean enough, a report can be made of the top and side walls by means of sonar images, to determine the quality of the siphon.

    Below is a possible step-by-step plan of how we envisage such an inspection with an ROV:

    Starting with lowering an ROV into the pipe and ‘just’ cruising around if possible. This way, it can be determined how much flow there is in the pipe and whether it needs to be cleaned or blown through.
    If the pipe is clean enough, a report can be made of the top and side walls by means of sonar images, to determine the quality of the siphon.

    What can go wrong with a siphon?

    A siphon can be made of different materials, such as metal or concrete. In the event that something can go wrong, for example a leak or a collapse, this is often at a connection. These are therefore always checked for soundness. There may be a crack, for example, or a rubber between the connection may no longer be in place.

    Siphons run under constructions or other waterways, and can cause subsidence if things go wrong. This under a motorway, for example, is… not convenient.

    Small problems can have major consequences, so it’s always better to look at them preventively, to make sure nothing can go wrong. With today’s technology, siphons can finally be inspected, after years of not being properly deployed. So now you can book an inspection for this, to map out the state of service, and avoid major problems.


    Would you like to know more about inspections of a siphon or other water-related assets? Then contact one of our experienced employees here!

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