You could use level loggers (e.g. http://www.onsetcomp.com/products/data-loggers/u20-001-04). You then could calibrate the measured water level by velocity measurements which is a common approach to monitor velocity in flowing waters. But then you would need a defined cross-section through the waterway, which might be feasable for small water but definitely not for bigger ones.

cool! thanks for the quick response! our streams are 0.3m to 5m in width, depth usually between 0.1 and 0.4m. in your experience with these loggers, are they accurate in very shallow water? thanks again

Hey,

generally there are different ways to measure water depth / velocity. To measure water level there are two alternatives. Either you can use ultrasonic or you use pressure sensors. Ultrasonic might be more accurate and the actual measurement time is faster but they are more sensible than pressure sensors. Ultrasonic sensors also need particles in the water to measure acurately which could be another problem when you want to measure in quite clear water. The accuracy of both kind of sensors is quite high. Besides the mentioned HOBO loggers, seba hydrometrie (http://www.seba-hydrometrie.com/index.php?id=132&L=1) or WAS (http://www.was-bs.de/Mobile-Water-Level-and-Flow-Monitoring,cms-58,en) might be also a good address.

Besides the indirect way to estimate velocity via water level and calibration with velocity measurements is to measure velocity directly via ultrasonic. Sensors like http://www.seba-hydrometrie.com/fileadmin/files/05_Hand_MobileGeraete/B06_AquaProfiler-M-Pro_mobile_e_S1-4_%26.pdf might be something one could use. However these sensors are more sensible than water level measurement via pressure sensors.

All the best,

Andreas

Dylan,

You can use pressure sensors to give you stage height logging.  You will need to be on-site to calibrate the pressure sensor at a range of flows (velocity profile of cross section at sensor), that way you can get Q from pressure.  You'll need two pressure sensors, one in the water for column height and one on shore for local barometric pressure (you can skip the latter if you have nearby weather station data).

Chris

this recent EPA Report covers methodologies and instrumentation for flow gaging using inexpensive pressure transducer technology http://www.treesearch.fs.fed.us/pubs/46926

Daniel/Chris: thanks for the super helpful advice and link to the EPA paper, it is really useful!

Andreas: thanks for the additional links.

Others here I have contacted recommended Solinst loggers as well in case anyone looking at this is shopping around:

http://www.solinst.com/products/dataloggers-and-telemetry/3001-levelogger-series/levelogger-edge/

they aren't cheap (I am getting quotes of about $600 CDN, albeit the CDN dollar sucks right now), but apparently their battery lasts several years and can store >100,000 readings, more than enough for our research needs!