Hi Friends, I recently wrote the listserv asking for advice on measuring fluctuating water levels in wetlands that dry out from time to time. Thank you for all of the helpful responses and feedback. I wanted to share that advice with the listserv in case it might help others. I've pasted the information that I summarized below; however, I did create a pdf (could not submit to listserv), so just email me if you would like that too. I decided to leave the feedback anonymous. Thank you all very much! Kristy
Original question to Ecolog: "Tips or advice on equipment for measuring fluctuating water levels during storm events in wetlands that dryout from time to time during the growing season. In addition, has anyone used video equipment to monitor water level changes and if so, can you provide some equipment names, models, etc." Specific Types of Water Level Equipment Hobo water level loggers: http://www.onsetcomp.com/waterLevelVsCompetition http://www.onsetcomp.com/products/data-loggers/u20-001-01-ti Infinities USA, Inc. Data loggers: Reliable dataloggers ("...used these data loggers for ~15 years for a long term hydrological monitoring effort). Nice company, would "be happy to talk about needs". http://infinitiesusa.com/Site/Pressure_Water_Level_Data_Loggers.html Ultrasonic Level Sensors: e.g. http://automationwiki.com/images/a/ac/Ultrasonic_Level_Sensor.jpg Sutron Level Loggers: http://www.sutron.com/products/allwaterlevel.htm Pipe/Well Solutions * Levelloggers installed into a well pipe in the ground might be able to give you water level for a longer period of time. Depending upon the substrate, you may be able to drive a 1.25 or 1.5" well point and pipe with a post-driver, or you can auger a hole and use PVC pipe. * Place an ultrasonic level sensor head on the top of your peizometer and it will record distance to reflective surface (water level). A similar system is used for remote automated snow depth sensing -- the sensor is placed on a cross-arm attached to a tall post -- so these systems should be very weather hardy. * Bubblers tend to be more durable than pressure transducers. Being out of water or freezing seems to be hard on transducers. The transducers they put in the level logger type units seem a bit better. That's probably due to different applications rather than any differences in the equipment. Level loggers a couple feet below the ground surface in wells should work. Screen the entire length of the wells to get actual water or groundwater levels and make sure to calibrate the units to the ground surface and a good benchmark of some sort to allow for settling. As usual, use a second level logger above the water level to get barometric pressure compensation. Sutron is pretty good and their customer service is excellent. I haven't heard anything bad about any of the level loggers. * We monitor overwash on a barrier island washover fan by suspending a HOBO logger inside of a shallow (~1 m deep) well. The logger records the water level in the well, and when the well is overwashed there is an obvious signal in the record (it jumps up to the ground surface level or higher). We've deployed several of these wells, and depending on the elevation of the well location, sometimes they are influenced by groundwater and sometimes they are "high and dry" for most of the time... which actually just makes the signal easier to interpret. It is also possible to distinguish a rain signal from an overwash signal, which is nice for our work. (1see more detail below of integrating cameras) Other Water Level Solutions * At one field site (near a river), we're interested in how often an area is inundated and when it is, how high the water is in that spot. We've attached a HOBO data logger to rebar (driven into the ground) and suspended the logger above the ground surface, so when the area floods the pressure sensor reads how much water is over it. This method only measures inundation; it's not connected to the groundwater. * We use Hobo water level loggers to measure stream discharge. We have one logger in the stream and one on the bank measuring barometric pressure. We also directly measure stream discharge monthly, so we are able to create a relationship between discharge and barometric pressure corrected "height". Since we use the same loggers for the air and water pressure measurements, drying won't be a problem. * A standard pressure transducer (Onset HOBO U20 Water Level Data Logger (U20-001-01) encased within a 1" pipe, attached to a 25lbs gym weight) installed in streams to estimate discharge (our streams are gauged seasonally) in the main channel. In reaches that experience episodic hyporheic flow we also install time lapse game cameras (the cheapest Moultrie ones do the job) to verify drying and we spread out an array of iButton temperature loggers (very cheap, but need to be waterproofed) to measure the extent of drying. (2see more detail below under Video/Camera Solutions) Video/Camera Solutions * A staff gage installed on a t-post or 2x4 and then use a wildlife camera or other time lapse camera (gopro, etc.) (mounted on something) to take photos depending upon how fast you think the change will occur. * Plant cams were used during storms to visually measure levels. They are cheap and easy to use, but I'm not sure I'd deploy one for more than a few weeks without attention. Batteries may run out or the memory card may fill up. They are pretty adjustable, so you might figure out settings that would last longer. Then use a good staff gauge. Getting measurements at night might be tough. http://www.amazon.com/Wingscapes-WSCA04-Timelapse-Outdoor-PlantCam/dp/B002M2TLLI * Another researcher uses plantcams: They cost about $75 per camera and they will die if submerged for too long. In the past, we have purchased them from the swamp school, but recently we bought them on amazon. The price seems to be going up and up. I have them record the level of a staff -each hour. It has worked well enough. * 1To ground-truth what we were seeing in our wells, we deployed several Reconyx (HC500 HyperFire Semi-Covert IR) cameras and used the time-delay feature to take pictures every 5 minutes during daylight hours. We were only concerned with determining when an overwash event occurred, and distinguishing between overwash and rain (as opposed to getting a quantitative measure of the amount of water in the area). The cameras work very well... with the exception of the occasional foggy lens (usually resulting from extreme temp/humidity changes). Another nice feature is that the batteries last a long time. Even when taking pics every 5 minutes, I only need to switch the batteries every 1-2 months! * 2In reaches that experience episodic hyporheic flow we also install time lapse game cameras (the cheapest Moultrie ones do the job) to verify drying and we spread out an array of iButton temperature loggers (very cheap, but need to be waterproofed) to measure the extent of drying. Our system is extremely dynamic, from drought to flood in a couple days, but I found a reading/picture frequency of ~6 times a day was more than sufficient to get the trend, but it will depend on your conditions, The temperature profile generated form the iButtons can be used to correlate daily variance in temp with flow/no flow at a very fine scale. The challenge (we've had) is locating the instruments in a meaningful spot. We missed the thalweg a couple times. Because we are measuring fish passage through these areas, it was also a challenge to find the first location to go dry in the reach (blocking fish movement). Kristine N. Hopfensperger, Ph.D. Assistant Professor Department of Biological Sciences Northern Kentucky University 859-572-5305 hopfensp...@nku.edu<mailto:hopfensp...@nku.edu>
