Shed a little light on your local stream
During the past couple of weeks I’ve been thinking about emergence. This is the time of year, as spring starts, that green is exploding out of every pore in the landscape. After winter, when so much is buried underground, the sudden flourish when sunlight reaches us is always a welcome shock.
On Nov. 12, 2021, a sudden, heavy rain caused waters to rise over a meter in Tan Brook in less than 15 minutes; in 30 minutes, water was flowing out and over Fearing Street in Amherst. An hour and a half after it had begun, streamflow was back to normal. Michelle Hosp.
This fall and winter, the town of Amherst requested my assistance measuring flow in Tan Brook, a little-known stream that flows right through the center of town. Like many small streams in places with numerous humans and lots of paved roads to get around on, Tan Brook was perhaps an inconvenience, crisscrossing the paths we wanted to travel, making places wet that we wanted dry.
Over time, it was pushed aside to put a road here, a school there; or buried completely under an apartment building, a house, or a parking lot. As we traveled and lived over it, we forgot about it. Tan Brook was removed from surface maps, since it didn’t flow on the surface much anymore.
As part of our investigation, my students and I decided first to find Tan Brook, and figure out where its waters were coming from and going to. We used detailed elevation maps and models of the land surface coupled with information about town sanitary sewer and drainage structures to map our best guess, then we went into the field to investigate on the ground.
We talked to the neighbors, who are passionate advocates for the remaining natural stretches of Tan Brook, flawed and messy as it is. These neighbors have not forgotten Tan Brook. Their combined observations of many decades painted a rich picture of the ebbs and flows of the brook, its wildlife and the neighborhood through which it runs.
We walked several open sections of the stream and appreciated its natural beauty and its wet floodplain. There were recurring reminders of human presence in the stream: loose bricks, drainage pipes of all ages, sizes and colors; pervasive bank erosion in places, bank armoring by all manner of things in others.
We measured stream flow in Tan Brook several times over the year to develop a rating curve — the relationship between water height and the volume of water passing by that point in time — and placed a data logger at a friendly neighbor’s house to measure water height when we weren’t around.
So what if the stream is underground? Does it really matter?
Tan Brook in Amherst drains a watershed of about half a square mile, and flows more than half of its length underground in culverts. Here, the stream disappears beneath the high school fields. CONTRIBUTED/CHRISTINE HATCH
There are a couple of things that make a really big difference to streams: One of these is impervious surfaces. An impervious surface is a waterproof material like asphalt, cement or a rooftop that is designed not to let any water through it. If you can’t go through it, you’ve got to go over it! And, since we don’t want to be walking or driving through the water, the goal is to get it off as quickly as possible, which is very effective — and it drains directly into the stream.
When I looked at water level data from November, I thought there was a problem with the data logger. Most of the variations I was seeing were on the order of millimeters to centimeters, but on Nov. 12, 2021, there was a sudden spike of almost 2 meters.
Recalling a sudden, heavy rain that day, and news reports of flooded cars, I looked more closely at the data. Rain had caused waters to rise over a meter in Tan Brook in less than 15 minutes; in 30 minutes, water was flowing out and over the road. An hour and a half after it had begun, streamflow was back to normal.
This is what impervious surfaces do, and this is a “flashy” stream. Depending on the time of year, if pavement is really hot, all of that heat (in addition to whatever chemicals might be on that surface) gets transported into the stream too, which can be really hard on aquatic organisms. Together, these kinds of ecological degradation have been defined since 2005 as “urban stream syndrome.”
Humans love water. We love to be next to water, to watch it flow and listen to it gurgling by. It’s enlivening to watch the creatures that enjoy it, how the seasons change the light on it.
And yet we cover it up. It’s ironic that the more of us there are, the more we tend to shunt away and bury our streams.
Hidden in between the culverts, beautiful naturally meandering sections of Tan Brook still exist, winding across the wetland floodplain. What if more of the brook looked like this? CONTRIBUTED/CHRISTINE HATCH
So much of what we saw on our sleuthing exercise to map Tan Brook seemed to be methods of “dealing” with it, rather than embracing it. There is a corner with two sharp right-angle bends that probably go neatly along the property lines, but require those same property owners to wage an endless battle with erosion using larger and larger rocks, but stormwater runoff gets faster and higher.
This may be changing, though: Some urban areas have been consciously “daylighting” formerly buried streams, bringing people back in touch with the natural world around them.
What would it look like if instead of burying this sweet little brook we allowed more of it to emerge? What if we let it meander through thoughtfully designed parks that flow beside and between the three schools, where students could observe nature and enjoy a little shade?
What if instead of hemming it into ever-narrower chutes, we let it spread out and wander across more of its natural floodplain, reducing the risks of flooding downstream?
Christine Hatch is research-extension liaison for the Center for Agriculture, Food and the Environment, and extension associate professor of Water Resources and Climate Change in the Geosciences Department at University of Massachusetts Amherst. She is a leader of the RiverSmart Communities project, supporting ecologically restorative flood prevention and remediation in New England.
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