Aquasense ApS

Overflow monitoring of sewers and storm pipes

Monitoring overflows can be advanced, but you can benefit from a small setup.

Contact Aquasense

Why is there a focus on overflow now?

The Ministry of Environment and Food has initiated work to register and sanction overflows throughout Denmark. In order to be able to provide data, a desired minimum accuracy of +/- 50% of the actual flow has initially been set. This is a relatively large margin compared to the measurement methods we normally work with. But it must be seen in a much broader perspective. It is the total discharge that must be determined by 50%, not the individual outflow.

Aquasense therefore estimates that it would be possible to determine, for example, half of all discharge volumes with 100% accuracy and the rest with +/- 100% uncertainty, as this together gives 50% accuracy. In practice, it is difficult to achieve an accuracy of flow measurements much better than +/- 10%.

We have instruments that promise better than 2%, but that is under ideal conditions. And we find them very rarely.

If one could identify the most emitting buildings in the sewer system over the year, give them some good measurements and then equip some of the smaller ones with meters with less precision, then an estimate, or a short-term measurement could form the basis for an unmeasured estimate of the latter. In this way, one could overall reach the 50% average accuracy without equipping all overflows with measurements.

Aquasense therefore does not see a “one size fits all” strategy for discharge flow measurement. There will be places where it requires advanced equipment and maintenance to perform good measurements, and there will be places where far less advanced solutions can be used with advantage.

In the following, we have attempted to describe some of the many different solutions we offer for overflow measurements and emphasize that they are not exhaustive.

Contact Aquasense
Our Suppliers

Overflow edge

With a primary element that has a defined overflow area, an overflow edge and a level transmitter, overflow flow can be measured. The existing concrete overflow edge can be used as the primary element. Alternatively, a metal rail can be mounted on the side of the edge, which provides a more firmly defined area. Metal rails can be used that are designed in a stepped shape so that small flow volumes are followed in a limited area, and only when the level rises does the area expand.

Level measurement can be carried out with an ultrasonic level transmitter, a radar meter or a pressure transmitter. The advantage of the first two is that they are not exposed to the medium and are therefore not exposed to contamination and aggressive media. In addition, the operation over time and as a function of temperature fluctuations is often less compared to pressure transmitters.

  • It is easy and quick to install.
  • Ultrasound and radar are not affected by media and are therefore not exposed to contamination and aggressive media.
  • Radar is immediately less sensitive to condensing water on the instrument.
  • With a very low power consumption, an installation can run for at least 5 years without changing the battery.
  • The price for a complete installation can stay below DKK 25,000.

There is often not a large difference in level because the overflow edge is long in relation to the increase in height that occurs as a function of the flow. It is deliberately designed this way because, as is often the case, one tries to maximize the depth on the sewer side so that one can store as much water as possible, and is therefore not interested in a further increase in level. But with a wide edge, even a few millimeters of level at the overflow gives a large flow. The best level transmitters have an accuracy of +/- 2 mm.

Another significant disadvantage is that after an overflow, deposits in the form of paper, etc. often settle on the edge, which means that the edge at the next overflow no longer has the full area before the overflow itself has cleaned the edge. This can be solved by flushing from a sludge suction device between overflows, which is very resource-intensive.

Primary restriction, Palmer-Bowlus flumes

Another option for making a primary element is a Palmer-Bowlus flume restriction. Here, you make a rise at the bottom of the outlet pipe and measure the level before the rise. See sketch

It is usually easy and quick to install. It is significantly less sensitive to deposits between two overflows, as the flow velocity is relatively high even at low flow. Still a cheap installation.

The primary element is molded to the occasion and therefore more elaborate.

The space for the level gauge can be problematic, you have to pay attention to the blanking distance for an ultrasonic gauge.

Flow measurement with combined velocity measurement Microflow and level dBi

By combining the above solution with a velocity meter, a much better measurement is obtained. With a level transmitter it is possible to determine the water-bearing area with good accuracy and with a good velocity measurement, an accuracy of better than +/- 10% can be achieved. The installation costs do not increase, so only the investment in a level measurement changes.

Touch-free to avoid contamination. Relatively accurate measurements. Clear price package.

Requires physical space for installation. Requires free outlet with a slope.

Doppler flow, 2150 or Signature 350

The Doppler principle uses the speed of sound, which is constant in the same medium, to determine the speed and reflect sound. By sending out a sound wave, e.g. 500 kHz, and having a microphone that receives the echoes, you can determine the speed of the particles in a liquid. Combined with a level sensor and knowledge of the water-bearing profile, the water-bearing area can be determined. This determines the flow. According to the specifications, this can be done better than +/- 2%, in reality better than +/- 5% in practical installations.

Very high accuracy. Very stable operation.

A relatively expensive measurement that requires a relatively large amount of energy. Here it would be an advantage to have a fixed power supply. Sensitive to sludge deposits at the bottom of the channel, which will isolate the sounder/receiver.

Velocity measurement in pipes/channels Micro flow

A simplified measurement is to measure only the velocity in the outlet from the overflow. This gives a velocity of the surface water. However, there are a number of conditions that must be met for there to be an approximate relationship between surface velocity and flow. This requires a free outlet, a reasonable drop in the pipe/channel and a known cross-section. If these conditions are present, it is a good solution. In any case, a good indication is obtained of whether there is excess flow, and whether it is a lot or a little.

Easy and quick installation. The sensor is not exposed to the media. Cheap components.

Accuracy worse than +/- 20%.

Data presentation

Data presentation system from Aquasense collects data from all loggers easily and simply in one place. In addition, analysis work and graph displays of the logged data can be done directly on the portal. There are several different parameters and graphs that can be used. It is possible to get the overall overview, but at the same time you can get more detailed and advanced graphs with simple clicks.

It is also possible to make notes for the simple measurement campaigns, so that all data can be collected in the same place.

The system can be connected to everything from a Point Orange to an Oda H2S logger or the new DuraTracker. It actually only requires an online connection via SIM card, and then the application possibilities are almost endless!

Are you looking for a solution that creates an overview and can make everyday life more efficient? Then we would really like to have a non-binding chat with you about how you can utilize the data presentation system to release more resources!

About data presentation
Dataloggere gruppe billed

Datalogger, Point or Signalfire

Logging and securing data is actually the most important thing about a measurement or a measurement campaign. It is no use having perfect measurements if they cannot be stored or communicated further. It is therefore important to have confidence that the equipment you use can withstand the load, whether it is the amount of data or physical loads.

There are several different data protocols that you need to take into account when composing your application, but also whether you want to use telemetry. For example, the Point series from Metaspheere has the option of a SIM card, so that they can send data to a server with a pre-defined interval.

Today, almost anything is possible with data loggers. We could spend pages describing data loggers and what they can do. Instead, we would much rather come out and hear what your problem is and from there find the right solution.

Go to data loggers

Did you find what you where looking for?

My most important task is that you find what you are looking for, or the non-binding advice you need.
Therefore, you are more than welcome to contact me if you have any questions!

Søren T. Møller | Direktør

Tel. +45 42 42 50 80
Write to us at: info@aquasense.dk
Contact Aquasense

Fill out the form and we will get back to you as soon as possible.