Texans are no strangers to severe weather events. Each year brings its challenges of potential droughts, fires, hurricanes, flash floods and more.
A heavy rain season brings additional challenges to the water team at the Texas Water Resources Institute (TWRI) and their monthly routine water quality sampling visits to water bodies around Texas. We talked with three of our research specialists to learn about those challenges.
Have you experienced high rain events?
Shay Postma (SP): Yes, usually after high rain events we’ll check the United States Geological Survey’s gauges first and find out what the flows are on that stream if the stream has them. If it looks really high, we can make a decision on whether we’re going to use our handheld Flow Tracker in the stream or need to use the M9 doppler boat.
Amanda Tague (AT): You have to be very, very flexible on days with high flow, so, during the entire rainy season really.
Ed Rhodes (ER): With rain, as long as we can do it safely, we sample it. Sometimes if the flow is too high and the banks are too steep, we might not.
How does that affect water quality monitoring?
AT: Our sampling is supposed to involve all types of events. We want to be sampling drier periods, higher flow events, and average days, to get the full picture of the stream. So, does it affect it? Yes. But in that, we get a fuller picture of the stream.
ER: Ideally you want to capture all kinds of events with sampling: drought, normal flow, high flow events.
Are the samples taken during high flow different from regular samples?
SP: When we get higher flow events, especially if we’ve had a long dry spell before, we tend to see a lot higher E. coli levels initially.
ER: Anything that’s on the ground when it rains is going to end up in the creek.
What do you do when you can’t safely measure the stream or the spot you used is gone?
SP: We can go to the bridge above it, usually our sites are at a road crossing or bridge, and we’ll drop a bucket over the bridge and use that to take our samples. That just means we can’t get a flow measurement, otherwise we can get all the data we need.
ER: The guidance from the Texas Commission of Environmental Quality is you can move about 400 meters from the location, you don’t have to sample in the exact spot. They recognize that streams move, erosion and other stuff happens.
Have you seen anything new this year compared to high rain events in years past?
SP: Yes, some of our creeks and streams get really, really high when we have a rain event. And that's just totally normal. But this summer we had a river that usually is in the hundreds of CFS that instead was flowing somewhere around 10,000 CFS upstream of where we sampled. We actually got to the site, and it was just a straight, steady stream of debris and logs floating down the river. That was one where we had a hard time accessing the edge of the river, because of the mud and the banks and the high flow. So, we did our sample off of the bridge. And we've had more of those situations this year than usual because we've been getting lots of rain.
AT: In addition to the creeks we sample being really high earlier this year, all of the rains spread out from here to North Texas caused the Brazos to swell. And so, what we had earlier this year that we really hadn’t faced in past years was, the Brazos was so high that it caused creeks to flow backward in some cases. One day at our Mill Creek site, we were trying to take a flow measurement, and sometimes it was flowing forward, and sometimes it was equally flowing backward. Trying to use that to get a representative sample is very difficult.
What do you do in situations like that?
SP: It depends. In this case, we were able to stick around, and we took around a dozen transects, and we finally did get four transects that were within 10% of each other, which is our usual rule. We want to get an average of four measurements that are close to each other for our overall streamflow measurement. But in this case, it was really interesting because the M9 Doppler boat gives us a 2D image of the transect of the stream, and it'll be color-coded according to the flow rate. And when we compare that with a typical 2D image of the transect, this one was really checkerboarded. So, it had some parts flowing really fast, some parts flowing really slow, and some parts were flowing negative. Whereas normally we see something that's a lot more even, and usually mostly flowing all in the same direction. So, it was a really unique day. And the creek was also 20 feet deep versus its usual 3 or 4.
Besides sample collection difficulties, what other challenges does heavy rain cause for monitoring?
SP: One of the other things we deal with a lot when we get these high-flow events is getting a ton of erosion. So, some of our monitoring sites changed really drastically, and where we might have had a nice solid bank to sample from before, it can be totally washed out the next month after a big rain.
ER: At Pond Creek, we used the Flow Tracker wading rod when we first started that project, because there was a gravel bar that we could walk out on, it sloped off, and there was a 10-foot-wide spot where all the flow was getting choked down. And so, we would do the Flow Tracker there. And then there was one massive rain, and when we came back the next month, that gravel bar was gone. So now we use the M9 Doppler boat a little further upstream.
Despite the challenges, the TWRI water team works hard, rain or shine, to get the samples needed for their projects. Adapting to what nature throws at them is just part of the job. Follow TWRI on Instagram for more behind-the-scenes looks at our water quality monitoring process.
