I see that there are at least 4 options for sensors to measure water level. Radar, Lidar, Ultrasonic and pressure.
Does anyone know which works best for monitoring the height of a river? I want the most reliable and most robust sensor. Something that is as maintenance free as possible.
Thanks!
All these sensors have advantages and disadvantages, which must be selected according to the given environmental conditions.
What do you mean exactly - the depth (underwater) or the height (the water level relative to the something on the river bank or to the bridge, for example) ? These cases are different and require a different sensors.
Level can also be measured with a series of resistive sensors arrayed vertically. The sensors that are underwater will have a lower resistance than the ones above water.
Hi Richard,
Hydrographic Surveyor here!
The two most common methods would be pressure (underwater) or sonic/radar (above water). Lidar probably not, because other EM freqs would be more suitable.
If you are looking to install it permanently (like at a bridge / river bank), I would go with a radar/ultrasonic. Just bolt it on, easy to access, download / transmit data from.
Whether it is radar / sonic would depend on the range above the water and the power / freq of the trasmitter / echo sounder.
Radar obviously works better through air, but ultra-sonic is okay over short distances.
You would want to understand the max variation of the river height, so your system doesn't go under water, but equally not so high you need to much power to get a two-way return.
For underwater, there is a bit to consider, like how you convert pressure to depth (water density formula based on sality / temperature) - depending on accuracy needed.
To install underwater, you will obviously need to anchor it sufficently to the seabed (or fixed structure like bridge pier) and then have a method to recover it to download, or install a telemetry cable to the surface.
The issue with a seabed installation is avoiding silting / coverage over time and avoid it being washed away (particularly in a river).
The final consideration is how you link your measurements back to a "height" above something (ie: to know if a road is flooded).
For above water installation (or installation to a fixed object like a pier), that is pretty easy.
You can just run a tape to measure the vertical offset between the sensor Zero and the top of the road, or whatever your datum is.
For below water - the easiest method is to install the sensor, get a stable measurement on its depth below the surface, then measure from the surface (water line) to your datum and you have connection.
A final note: generally we would calculate the 'depth' (or height) based on the average of 60 obs over 1 minute. That helps smooth out ripples, waves, vibrations from cars over a bridge, etc.
I came across your question as I am looking to put sensors on my farm water tanks, and trigger solar pumps.
Thanks.
Depends if you really want to know the depth or to know if it is above a certain level. In which case there are tilt float switches that would do the job .
Thank you, matt the tinker. You will see many "measure the level inside a cistern" questions here... hope you stick around.
Either. Water pressure will give depth, as will distance from surface to sensor above in free air, if you know the distance to the bed of the river from the sensor.
Can you elaborate? What, for example, is the environmental condition that will adversely effect radar? I assume the surface codition of the water (still or waves) may reduce the effectiveness of ultrasonics?
Hi Matt, From what I can find on pressure sensors, they are usually installed vertically, sometimes in a tube, with the cable coming up to the control box. To get a reading on river height, they don't need to be at the bottom of the river, just deep enough to be covered in all river conditions. This may help avoid silting, plant growth etc.
To me, a non-contact sensorm in the air above the water seems the best approach, but pressure transducers seem to be used more often for some reason.
I may just test and evaluate all four types on one unit to see which works best in my location. IR range, ultrasonic, radar and pressure are all non-interfering so maybe that's what I'll try.
I am looking to measure the height of a small stream, less than 1 metre deep, about 1-2 metres across. Depth can vary from a few cm to maybe 150cm. Turbulance can vary from smooth and calm to quite turbulant during a storm.
The unit needs to be battery operated, compact and have a LoraWan radio in it.
Dragino make units like this with all of the sensors mentioned.
I want to know actual height/depth, checked at least hourly.
The simplest I have seen is a 'meter' stick on the side where you read it. Note this are large enough to read at a distance and long enough to cover the full range of the river fluctuations. A simple camera would let you basically read it anywhere in the world.
Water movement effects ultrasonics. You know, they are often used to measure flow rate in water pipes.
Hi Richard,
Based on what you have said, I would go with above water setup. That will make all your comms / power / access much easier.
A simple setup with IR would be to install a vertical tube (pvc down pipe) into the water, such that water can flood into the tube and find its level. Then have the sensor at the top.
The water in the tube will be less turbulent and protected from sunglare, etc. You should get a pretty solid return. If not, put a floating disc in the tube to act as the reflector to the sensor. That should give you a good solid setup and consistent readings.
Cheers,
Matt
That measures from 0 to 1.6 Mpa or 0 to 6429.83 inches of water. It doesn't appear to be sensitive for a few feet of water.
Really, one of the test is to blow on it..
But yeah, I do see we went from a river to a stream or brook..
~q
Does river flow not affect pressure and sonic sensors?
You would know!
When did weighted line fathom measures go out of use?
Hmmm, so I'd need a 4G webcam, a sim contract and someone to watch it and record the levels every hour...
I think an arduino and IR distance sensor and a LoraWan shield will be a better solution!
You just changed the requirement when you stated you wanted to record it every hour. Then the simplest solution is a pressure sensor, one that is sensitive enough. Check this link: https://new.abb.com/products/measurement-products/level/a-dozen-ways-to-measure-fluid-level
