Lots of good ideas in this thread. I’ll add some of what I’ve been up to…
I’m primarily using the Maxbotix ultrasonic sensors for water depth (mounted above the water). I’ve got them tied to a Sodaq Mbili and GprsBee so that I’m getting the data every 30 minutes via the cellular network. You can read more about it here, including downloading the code that I’m using – http://mara.yale.edu/esa-2015.
The real hard part comes when you try to install something in the river (which is why most of my stations are only water depth using a non-contact method). I’ve also built a few water quality units using primarily the Atlas Scientific sensors and the Sodaq Mbili. I’ve been using the Sodaq Mbili for most of these stations as well. The biggest problem is with how you actually affix the station into the river/lake/stream. The best thing I have found is lots of concrete. 😉
I have used the Stalker in the past and stopped once I found the Sodaq Mbili. The Stalker just ended up causing me too many problems (memory, power, quality control of the build, etc).
In reference to Kevin’s earlier question about longevity, I’ve had stations working fine for up to a year with zero maintenance. Some stations crap out after a week. It all has to do with protecting the electronics from the elements (at least in my case).