Hi,
I'm doing a flood monitoring system with GSM alerts for my project. Can i use ultra sonic sensor to messure water levels in an irrigation canal? Is ultra sonic sensor is suitable for this...would like to here your ideas.....Thanks! 
The standard ultrasonic distance measurers should work fine for this.
One thing I'd suggest is to mount the measurer at the top of a plastic (PVC) pipe with it's lower end in the water, to make it less affected by wave scatter etc.
Check this - http://mechanical.poly.edu/faculty/vkapila/ME3484/Readings/NV27-Measuring%20Water%20Level.pdf -
Really appreciate u guys!....
please let us know how your project continues, as water level measurement is a frequently seen project!
Your project might guide people in the future!
Defiantly, I'll update status of this...Also may need help & guidance for this!...Thnkx! 