That sounds very good. I had similar plans to you!
So, you can definitely use that turbidity meter. The datasheet is a little bit weird (there’s a missing label, and I can’t find the Ground Pin!), but you know that you will have to measure voltage between pin 2 and Ground (I imagine this will be Pin 3 – may need some playing around!). I recommend you ask the manufacturer, or play around a bit.
Note, however, that this is a 5v sensor. If you operate on a 3.7V LiPo, you’ll have to boost the voltage for that particular sensor.
For simplicity, lets assume you’re using a 5V system, connect pin 1 to VCC, pin 3 to GND and Pin 2 to any analog pin on an Arduino-variant. Read the voltage off the Pin using analogRead(),which will output a number from 0 to 1023. Convert that to a voltage by dividing by 1023.
In a 3.3V system, it’ll be a little more complicated because you will have to boost your voltage, then use a ‘voltmeter circuit’ to measure the output voltage. There are tutorials online on how to do this simply-just google Arduino Voltmeter!
So, in this system, voltage will decrease (non-linearly) with increasing turbidity. You will probably have to create your own calibration curve.
For the distance sensor, what you intend to do should work. I was planning the same approach. Bear in mind, however, that that is not an outdoor sensor, and it may easily get damaged by environmental factors. You could look at something like thism though it is more expensive. However, if you’re really not concerned, or are confident that you can adequately protect your sensor, I guess you can always try :). Also, you may need a stilling well, as these sensors can be thrown off by wave action. You would need a fairly wide diameter pipe, as the sensor will otherwise read the pipe as its target!
Yes, stream flow and level are correlated for a particular point. However, the correlation is not particularly accurate (you have to know the rating curve of the point you’re measuring, and estimations won’t be precise). It really depends on what sort of accuracy you need here; if just stream level is good enough for your purposes, don’t go beyond that.
For accurate open-channel flow measurements, you would usually install a temporary weir or flume. This is quite a hassle, requires permission, etc.
I hope this helps! I look forward to seeing your results.