I think Chris speaks with experience and it is very wise to do your home work when buying any type of flow monitors.
Has anyone tried the Sonic Sens from Radcom for Combined Storm Overflow monitoring. I have used it extensively in Scotland and it works well. The Sonic Sens uses SMS to transfer the data remotely and it has a 5year battery life when logging at 5min sample rates, so no worry on power requirements.
You can send it a txt message from a mobile phone to interogate it even when your miles away from the actual site.
The unit can also be used as a flow meter when used with a primary devise such as a flume or weir.
see link below
http://www.radcom.co.uk/c2/uploads/R...s20060929p.pdf