Smith students walking by Paradise Pond might have noticed some changes in recent weeks. Almost overnight, the pond appeared to go from full to empty, leaving behind something that looked more like a mud pit than the familiar pond. For weeks, excavator trucks pushed the dirt around. Staff and students wore waders and took samples. The pond became a source of conversation — and confusion — for students who didn’t know what was going on. Then, just as quickly as it disappeared, the water returned and the pond was back to normal.
This happens every year. Paradise Pond is a section of the Mill River. As the Mill River flows, it picks up
and moves sediment. When it reaches Paradise Pond, it slows down considerably, which deposits the sediment. Because Paradise Pond was artificially constructed by damming the Mill River, the sediment accumulates instead of continuing to move downstream. This causes the pond to get gradually shallower. So, as part of the pond’s annual maintenance, the sediment that collects has to be dealt with.
Maintenance takes the form of sediment redistribution, not dredging, which is an important distinction. “Dredging is when the sediment is actually removed and hauled away in dump trucks,” said Ph.D. Laboratory Instructor in Biological Sciences Marney Pratt. The pond hasn’t been dredged since 2008; instead, since July 2016, sediment that accumulates in the pond has simply been moved. “The
pond is partially lowered in both cases, but dredging removes the sediment entirely from the system, while sediment redistribution just moves it within the system, from places where it builds up to places where it erodes, so we can move enough of it out of the pond.”
“All we want is a pond that you can have a canoe in without hitting the bottom,” said Gary Hartwell, the project manager for pond maintenance operations.
Sediment redistribution is key to that. “Not redistributing the sediment yearly would mean that sediment would build up in various parts of Paradise Pond that would add more islands and make it difficult, if not impossible, to navigate with boats,” said Pratt. “If we want to keep the dam and
keep Paradise Pond, then we will need to manage the sediment.”
Sediment hasn’t always been managed this way. Paradise Pond used to be dry dredged about every eight years, which means that the pond was fully drained and sediment was removed and transported by trucks to the Northampton landfill. The last instance of this was 1998; after that, the state
did not issue a permit for dry dredging. Smith then turned to hydraulic dredging, which was “an expensive failure,” according to Pratt. “Sediment redistribution is the best option that we can do in the current conditions.”
Sediment redistribution has many benefits. It is less expensive than dredging — Hartwell estimated that in 2008, it cost around $700,000 to dredge the pond, whereas this year’s redistribution operations will cost between $10,000 and $30,000. “It’s dramatically cheaper,” said Hartwell. It is also less labor-intensive and healthier for the river system, as it provides nourishment and habitat for
benthic life.
Sediment redistribution also gives professors and students the opportunity to study the health of the river by analyzing the sediment. Pratt focuses on macroinvertebrates — “animals without backbones that are large enough to see without a microscope” — to do this. “These organisms vary in how sensitive they are to pollution or disturbance. Thus, we can use their abundance and diversity as a way to assess how healthy a river ecosystem is,” she explained. “If there is a wide diversity of organisms, including many that are sensitive to pollution and disturbances, then that indicates a healthy ecosystem. On the other hand, if the river is dominated by relatively few kinds of organisms that are really tolerant to pollution and disturbance, then that could indicate an imbalance or unhealthy ecosystem.”
However, the project is not without its downsides. “When we drain the pond, the beavers don’t like it,” said Hartwell. Beavers are not the only wildlife in the pond; the otters, fish and mussels that live in the pond are also affected by the redistribution process, which Hartwell admitted was “mostly inconvenient and possibly deadly” to the animals. Still, “they’re never wiped out. They’re pretty robust.”
The sediment redistribution, especially compared to previous pond maintenance methods, “is the least
damaging we can be and still maintain Paradise Pond,” said Pratt. She also said that the shift to doing the redistribution in the winter has helped mitigate some of that potential damage, since the pond’s animal population is more dormant in the winter.
Redistributing the sediment in the pond is not the only option, though. Reid Bertone-Johnson, a lecturer in Landscape Studies, is in favor of removing the dam and returning to a natural river system. Letting the artificially-constructed pond become a river again “would be much more sustain-
able and ecologically sound,” he said. Currently, toxins and bacteria accumulate alongside the sediment, which fosters a view of the pond as unclean. Fast-moving river water would wash them downstream; then, said Berton-Johnson, “I actually believe that more people would engage with it dangle their feet in, wade in, you know, experience the river.”
It would also solve the problem of the sediment. “If we took the dam out, the sediment would not accumulate,” said Hartwell. By lowering the spillway to the level of the original bedrock, the river would “find its natural channel again [and] there would be no regular, on-going maintenance,” added
Bertone-Johnson. “The river upstream and downstream of the pond demonstrates that quite clearly.”
As for the ecological impact of such a dramatic change to the pond environment, “removing the dam would have a huge short-term impact on the macroinvertebrates and everything else downstream, but eventually it would just turn into river all the way along and the system would return to some kind of healthy stable state,” said Pratt.
It wouldn’t be a simple process; Smith would need to study how removing the spillway would impact flooding hazards in Northampton, which would then need to be approved by the Army Corps of Engineers. But Bertone-Johnson doesn’t think that’s impossible. “I think that Smith could make a bold move to align campus landscape management with stated environmental goals and remove the spillway to the dam,” he said. “I hold out hope that Smithies (current students and alumnae) could embrace a well-designed (or even natural) riverfront as being a valuable asset to the campus — especially when educated about the cost and ecological footprint of pond maintenance.”
“The pond is lovely. No doubt. It is also expensive and ecologically unsound to maintain it,” said Bertone-Johnson. “I think it is important to interrogate pond maintenance from a perspective of what values are revealed by how we handle it. Does doing what we do to maintain Paradise Pond reflect
the stated values of Smith College?”
