water level

Horizontal or vertical pipe?

What is the expected change in level?

What are the conditions of the air in the pipe above the water? Open to the atmosphere, sealed?

Can you drop a small tube down the pipe, blow a small amount of air through it and measure the pressure created by the water level above the tube's bottom?

In message , dated Sat,

I guess the Q of a 1/2 inch pipe 150 feet long might be a bit low?

Find the resonant frequency of the half-open pipe?

l = 4*L Where l = wavelength L = length of air column in the pipe.

f = v/l Where v = speed of sound in air in pipe ~ 340m/s

For a 150 foot pipe the resonant frequency will be around 1.8Hz.

The voice-tube system is a classic system, and it results in attenuation of sounds if the wavelength is more than about five radii of the tube (this relates to the first zero of the Bessel function... but that's for another group).

The lowest frequency that will work in a 1/2 inch pipe is about 10 kHz (lower frequencies, while they might resonate, are damped). You could use a kind of time-delay reflectometry with an ultrasonic transducer, OR

(2) you could just dump water into the pipe until it overflows, keeping track of the amount added, OR

(3) you could tape some Fizzies to the end of a plumber's snake and pay careful attention to the odors or gas quantity emitted at the input port while you push the snake

Could be.

Somebody always has to bring sex into it.

-- John