I have been doing QA/QC on hydrometric data for many years, and as part of my job I ensure that data being collected is as accurate as possible. This extends to the instruments collecting the data – today I’m going to talk about troubleshooting a tipping bucket rain gauge, and some of the tools I use within FlowWorks to do so.
If you use a tipping bucket rain gauge you may notice that from time to time the funnel can become clogged with dirt, mud, leaves and other forms of debris. Clearly a plugged rain gauge will not collect accurate rainfall or precipitation data!
The key is to be able to quickly identify a plugged rain gauge so it can be cleaned out without delay. There are two ways to do this – accessing your online data (like you could if you are a subscriber to FlowWorks), or manually checking the unit in the field. I’m going to review both of these options in this article.
Identifying A Plugged Rain Gauge Through Data Analysis
Identifying a plugged rain gauge can be easy when you know what to look for and if you have access to right analysis tools. If you are lucky enough to be receiving live data, you will be able to identify a plugged rain gauge as often as you check the data. Historical data is ok too because you will at least be able to identify data sets where the rain gauge was plugged and make sure to disregard that data during further analysis.
A Completely Plugged Rain Gauge
You can tell a rain gauge is completely plugged when there is no rainfall data being recorded when you clearly know that is raining. So if you are looking outside your window and its pouring rain and your live rain gauge isn’t showing any rainfall data, it is probably safe to assume that it’s plugged. Or if you can compare the data to another rain gauge in the same area they should show similar rainfall.
In the figure below, the data from two rain gauges located in close proximity are graphed using the FlowWorks graphing tool. The two rain gauges should show similar rainfall but during January 2, 2010, the top rain gauge basically became completely plugged.
Partially Plugged Rain Gauge
Sometimes a rain gauge is only partially plugged. If this is what has occurred then you would see ‘weird’ rainfall patterns. That is because during rainfall the gauge will start to fill with water and then the water will start to slowly trickle trough which looks like constant low rainfall and it will tend to continue long after the rainfall has stopped.
In the figure below, the data from two rain gauges located in close proximity are graphed using the FlowWorks graphing tool. The two rain gauges should show similar rainfall but during the last week of August 2008 the bottom rain gauge became partially plugged. The constant slow filtering of the rainfall is quite obvious and this is a common indicator that the rain gauge is plugged.
Identifying A Plugged Rain Gauge Through Inspection
The other way to check if a rain gauge is plugged is by pulling it apart on a site visit. You will either see the funnel clearly plugged or the collection cylinder may be full of water and not draining. Remove the cylinder to drain the water and make sure the funnel is completely clear of debris. If the cylinder is not full of water but you still have suspicion that it is plugged, you can pour some water slowly into the cylinder and if the water does not drain or drains very slowly then there may be a partial plug.