I have to take water level measures in a river that in time of drought its 30 meters wide and in rainy weather its 100 meters wide. Max level its below 5 meters all the year.
I need an advice
I will going to use a Campbell datalogger but i cant find the adequate level sensor (we prefer to use a non contact sensor like radar, ultrasonic, or ?)
But :
1.- If we use an ultrasonic or radar sensor, how can we install it? if there isnt a bridge or any structure that cross the river
2.- If we use a pressure sensor or bubble sensor, how can we install it to avoid damage caused by the current of the river, or at least minimize it
3.- In the case of use a pressure sensor, bubble sensor or float sensor( if there is someone with similar installations) how can we avoid bad measures caused by river slit or mud? (there isnt people close to mantain clean the installation site)
4.- I find a laser sensor that measures distance, and it can be mounted in a pole at an angle. But we have the doubt if a laser can measure water level
5.- If there is another type of sensor that we can use in that river conditions
Installations tips are welcome
* Last updated by: bquintana on 5/31/2010 @ 10:57 PM *
bquintana,
I'll throw a few thoughts out.
*Laser level: You are right to be concerned. Generally laser rangers used for liquid measurements generally employ the use of a floating reflective/shiny target.
* Stilling well: Installation of a stilling well is very common in this situation. It is often resource intensive, but provides protection of your measurement device and often eliminates problems related to sediment between maintenance visits. Outside the main channel, install a vertical riser pipe (aka well) that extends above flood stage and below low flow. Then install a horizontal intake from the channel to the bottom of the vertical riser. This intake should have a slight slope so that water does not pool inside. You will have to auger horizontally from inside the channel to the riser or trench to the channel and drop in the intake. The water surface elevation inside the well will equal that of the river. The sensor should be installed in the well. During maintenance, remove and clean the sensor. Also, use a gallon jug to repeatedly flush the well of any sediment that has accumulated inside.
* Non-contact: Construct a span.
* Placing sensor on stream bed: If the majority of the sediment transported is silt or sand, you many be fine anchoring the sensor to the bottom (in PVC or EMC). A bubbler will "purge" before measuring. This will push much of the sediment away from the orifice before measuring. A PT should be able to measure the interstitial pressure.
The take home message though is that maintenance is a *must*. Especially in an unstable (incising or aggrading) system.