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### Topic: Measuring the height of water during heavy rainfall event (Read 1 time)previous topic - next topic

#### Hiddenowl

##### Mar 21, 2017, 12:49 am
Hello! I'm new here but I do have a question for all you smart ones, I'm working on a project that wants to measure the change in water height during heavy rainfall occurrences. The height being looked at would be 0-2cm on flat pavement or tarmac with 0.25mm resolution. I have thought about using an ultrasonic sensor, send a continuous sine wave and  measure the phase shift change as water height changes to determine the height. Low budget would be ideal (like under 200). I think 66-70kHz ultrasonic sensor might work. I have thought of other methods such as laser, capacitive and resistive ideas but using an ultrasound will have minimal interference with data collection. So where could I get a 66-70kHz ultrasonic sensor that is able to send a continuous wave? Or is this idea feasible?

#### jremington

#1
##### Mar 21, 2017, 02:05 amLast Edit: Mar 21, 2017, 02:07 am by jremington
Not really feasible with ultrasonic, especially at that rather low frequency - the wavelength is far too long for 0.25 mm resolution.  340 kHz = 1 mm

#### allanhurst

#2
##### Mar 21, 2017, 02:16 amLast Edit: Mar 21, 2017, 02:21 am by allanhurst
Surely in heavy rainfall there will be severe disturbance of the water surface due to the raindrops...  and if the water is flowing, significant ripples.

So even if you achieved 0.25mm resolution by whatever method, what would it mean?

Allan

#### ardy_guy

#3
##### Mar 21, 2017, 04:26 am
So even if you achieved 0.25mm resolution by whatever method, what would it mean?
Yeah even if it was mirror smooth, I can't think why 1/4mm would be significant.

Adafruit have these
which do purport to have 1/4mm resolution.

Quote
Low budget would be ideal (like under 200).
You're the only one who knows the units of the 200 budget. Adafruit's USD40  may or may not be within that, who knows.
[irishAccent]Have you tried turning it off and on again?[/irishAccent]

#### TomGeorge

#4
##### Mar 21, 2017, 08:57 am
Hi,
Welcome to the forum.

What is the application?

Tom...
Everything runs on smoke, let the smoke out, it stops running....

#### Robin2

#5
##### Mar 21, 2017, 09:31 am
How about making a regular rain gauge. If you have a large area collector feeding into a narrow cylinder it will amplify the vertical scale for easier measurement. You could use a float inside the cylinder to move a transducer.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

#### ardy_guy

#6
##### Mar 21, 2017, 09:37 am
What is the application?
How about making a regular rain gauge.
The civil engineer in me is guessing this might be some kind of hydrological assessment of drainage rates vs the amount of rain.

[irishAccent]Have you tried turning it off and on again?[/irishAccent]

#### Robin2

#7
##### Mar 21, 2017, 11:26 am
The civil engineer in me is guessing this might be some kind of hydrological assessment of drainage rates vs the amount of rain.
That is not unreasonable.

But the idea of measuring the water depth on the ground in a rainstorm to a precision of 0.25mm suggests that the OP is not an engineer.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

#### ardy_guy

#8
##### Mar 21, 2017, 12:21 pm
I doubt even a pond on a perfectly still day would be still enough.

[irishAccent]Have you tried turning it off and on again?[/irishAccent]

#### Hiddenowl

#9
##### Mar 21, 2017, 04:59 pm
Not really feasible with ultrasonic, especially at that rather low frequency - the wavelength is far too long for 0.25 mm resolution.  340 kHz = 1 mm
would it be feasible if it were say 0.5mm or 1mm resolution instead?

Surely in heavy rainfall there will be severe disturbance of the water surface due to the raindrops...  and if the water is flowing, significant ripples.

So even if you achieved 0.25mm resolution by whatever method, what would it mean?

Allan
The idea is to measure the change in height and observe overland flow depth so  if you had 50 units you could study how 2D kinematic waves work at a small scale, if possible.

Yeah even if it was mirror smooth, I can't think why 1/4mm would be significant.

Adafruit have these
which do purport to have 1/4mm resolution.

You're the only one who knows the units of the 200 budget. Adafruit's USD40  may or may not be within that, who knows.

Yeah I have looked at the resistive tape as a potential option, looking at the datasheet it does not work well between 0 to 1 inch. I should clarify, my budget is \$200-300, forgot the unit

I'm trying to figure out a way that I could measure the change in overland sheet flow if possible. The interest in this is hydroplaning. If rainfall is sufficiently intense, water does not drain away quickly and cause appreciable depths to build up and cause accidents. The design including the sensor and everything else should only have little effect on the depth the sensor would be measuring. I'm going to keep looking to see if there is a way to get that 0.25mm resolution, if it definitely cant be feasible with that resolution, how about 0.5mm? Other than that, I know maxbotix has a line of sensors that have a resolution of 1mm.

But the idea of measuring the water depth on the ground in a rainstorm to a precision of 0.25mm suggests that the OP is not an engineer.

...R
I'm working on a project given by a professor in civil engineering.

#### ardy_guy

#10
##### Mar 21, 2017, 05:10 pm
I'm working on a project given by a professor in civil engineering.
That's as may be: it makes no sense to me (and I'm a civil engineer, although not a Professor....) to even think of measuring water flowing in the road to within even 10mm or so, I'd say. It's not a matter of the precision of the measuring device, but the fact that the water's height will be varying by that much except when it's a settled puddle. Just the natural movement of the water across a road with its surging and turbulence would make me think I'd be lucky to measure to 5mm at best. Regardless of my equipment.

Different in the hydraulics lab of course, but in a real road? Doubtful.

[irishAccent]Have you tried turning it off and on again?[/irishAccent]

#### Robin2

#11
##### Mar 21, 2017, 05:11 pmLast Edit: Mar 21, 2017, 05:14 pm by Robin2
If rainfall is sufficiently intense, water does not drain away quickly and cause appreciable depths to build up and cause accidents.
This sounds to me like something that would be much better studied in a laboratory. The concept seems simple enough. Deliver 100 litres (or 1000 litres) of water onto an area over a specified time period and see how quickly it disappears down the drain. If the surface it falls on is level and flat it can surely be assumed that the water will have a uniform depth for all practical purposes. The difference between the mass of water in the tank and the mass of water in the sump will be the mass of water on the surface - from which the depth can be calculated.

Trying to get useful data from a test outside the laboratory seems to me a waste of time because the data would be affected to such an extent by the local ground and weather conditions that it could not be assumed to apply at another location. For example wind blowing against the water flow will cause the water depth to build up - not to mention its effect in causing ripples or even waves.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

#### Hiddenowl

#12
##### Mar 21, 2017, 06:17 pm
That's as may be: it makes no sense to me (and I'm a civil engineer, although not a Professor....) to even think of measuring water flowing in the road to within even 10mm or so, I'd say. It's not a matter of the precision of the measuring device, but the fact that the water's height will be varying by that much except when it's a settled puddle. Just the natural movement of the water across a road with its surging and turbulence would make me think I'd be lucky to measure to 5mm at best. Regardless of my equipment.

Different in the hydraulics lab of course, but in a real road? Doubtful.

The professor knows that the certainty about the shallow depth would be much poorer than the certainty about 1-2cm depths. If any depth can be know to 0,25mm (if it can be achieve) the information at least would be useful, from listening to everyone's feedback right now, it seems that it is either going to be really hard to achieve or may not be feasable with ultrasonic. If it was say 0.5mm or 1mm resolution would that be feasable with a sensor like this one?:

https://www.adafruit.com/products/985 (for 1mm resolution)

I don't think currently there is a ultrasonic sensor with 0.5mm. But what about maybe using a laser since it has a shorter wavelength and have it reflect at an angle to a receiver?

#### jremington

#13
##### Mar 21, 2017, 08:28 pm
Quote
so  if you had 50 units you could study how 2D kinematic waves work at a small scale, if possible.
Utter nonsense.

#### Hiddenowl

#14
##### Mar 21, 2017, 08:53 pm
Utter nonsense.
It was something that the professor was thinking about if the design was cheap enough to be replicated

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