The Dredging Begins
It’s 10:20 on a sunny and hot July morning. The drawdown of Paradise Pond has begun. It’s the first step in a multi-week experiment to send unwanted, heavy sediment accumulations on their way downstream—restoring the pond to a healthy ecosystem.
Key professors, students and staff are busy checking equipment and hopping on and off a small boat—fondly referred to as the Maid of the Muck—while monitoring the flow of the pristine waters of Paradise Pond. The pond was formed by a dam on the Mill River that has in some form or another been altering the water’s flow since the mid-1700s.
On this day, a sluice gate has been opened at the side of the dam to allow water, and unwanted sediment, to pass through at a controlled flow. At first the waters move slowly downstream, draining the pond throughout the morning. By 2:30 p.m. the pond’s water level is down four feet. The water has drained down some 8 feet by evening, dwindling to a narrow natural channel for the Mill River. The sluice gate is then closed, and the pond’s bed left to dry.
Five days later, the smell of swamp and decomposition is overpowering. An excavator has arrived and now gathers sediment accumulated in the upstream sections of the pond bed and pushes it into a small river channel where the water currents will carry the sediment toward the dam. The displaced muck will eventually be flushed downstream through the sluice gate at the bottom of the dam during high-flow conditions (translated: heavy rain).
Testing the Waters
This is not the first time the 9.2-acre horseshoe-shaped Paradise Pond has been drained and dredged to allow for the removal of sediment left behind by the Mill River as it flows through the pond. Nor will it be the last.
The pond was dredged in 1974, 1982, 1990 and 1998 using both hydraulic dredging and mechanical removal of the sediment during drawdown. 1998 was the last time the pond was dredged using the traditional method under state Department of Environmental Protection guidelines, and the college used a permit to remove 15,000 cubic yards of sediment from the dry pond bottom and truck it to a nearby landfill. While the dredging was underway, Smith students and faculty conducted lab studies on samples they pulled from the sediment loads.
In recent years, Bob Newton, professor of geosciences and director of Smith’s Center for the Environment, Ecological Design and Sustainability, and students and faculty from Smith departments of geosciences, biological sciences and engineering have delved into research projects involving Paradise Pond. Their various studies have included analyzing the metal content of pond sediments as well as monitoring the health and diversity of the Mill River before and after the sluicing gates have been opened. (Read more about the project in the Grécourt Gate.)
The 2016 dredging technique is a departure from the previous operations, Newton says. It involves a unique management plan for the pond sediment—an experiment, really—which is an efficient procedure that should be carried out frequently, he says, to maintain a healthy ecosystem in Paradise Pond.
While this year’s dredging involved moving about 1,000 cubic yards of sediment, the hope is that next summer the college will be granted permits to move 10,000 more cubic yards of sediment.
Meanwhile, students will continue to work on the ecosystem of the pond. “This will be a permanent laboratory and a long-term project,” promises Newton.