Reply To: MayFly Data Logger During Winter

When we scout an area for a potential CTD sensor installation, one of the top deciding factors is whether that portion of the stream will freeze during extremely cold weather.  Almost all of our sensors are mounted in deep, continuously flowing water.   Most of the time our streams won’t freeze at all in the area around the sensor, or if they do, it’s only the top inch or two.  By installing the sensors at least 12 inches or more below the surface, they aren’t damaged by the ice. There’s a few small tributaries or streams with shallow or slow water that we have to monitor for a particular reason and can’t choose a deeper spot, so we just make sure to pay close attention to the site when extended cold weather is in the forecast.  We’ve got over 200 stations in the Delaware River watershed, and since we only see deep prolonged freezes a few times a year, if at all, our stations typically make it through the winter with no damage.  We’ve only had a few sensors be damaged by ice in the past 5 years, most were in the first year or two of the project before we got good at predicting ice formation areas.  If someone has a sensor in a stream that might freeze and isn’t sure whether or not it will survive some upcoming cold weather, it’s certainly safer to remove the sensor and place it on the streambank (dry it off thoroughly and either hang it somewhere off the ground and protected from rain that might later freeze, or wrap the sensor in a dry towel and place it in a ziploc bag on the shore (in a safe area that won’t be damaged in case of flooding resulting from future snow-melt). Note that freeze damage to pressure sensors is not covered by the manufacturers, so if your sensor is still under warranty and you think it will likely freeze, it’s up to you to decide what to do.  One of our biggest monitoring efforts right now is examining the effects of road salt in our waterways, so being able to measure water depth and conductivity during these winter months is extremely important and worth taking a gamble that we might lose one or two sensors out of 200.  If you are only interested in measuring temperature and conductivity and not depth, then a simpler sensor like Meter Group’s ES-2 conductivity-temperature sensor is a better choice than the CTD, because it doesn’t have the sensitive pressure sensor on it and the housing can be completely incased in ice without damage.