With manmade openings at the Edgartown Great Pond a long-established practice, I would like to raise the question of whether the more recent practice of dredging near the openings constitutes sound environmental management.

It is my understanding that the scientific advice on managing the Great Pond is that we should maximize the exchange of water between ocean and pond. I assume that this flushing should take place during the bio-active months since the intent of the openings is to influence the bioactivity in the pond.

The pond rises to the height necessary to make an opening by the addition of fresh water. A fourth of this water comes from direct rainfall and three fourths come from groundwater flow. This is the annual fresh water budget, and it limits the amount of water available for pond recharge.

After an opening is cut, most of the pond’s water is exchanged in the first week of tidal flow. By the fourth day, more than half the pond’s water has been exchanged. The rate of exchange diminishes daily, and by the 12th day the exchange is negligible. Significant pond-ocean exchange will not occur again until after the next opening. This is the reason to close and recharge the pond as quickly as possible.

The dredge should be deployed only if the obstruction is such that an opening cannot be made using the traditional mechanical method: digging out the cut with an excavators, by hand or both. That does not seem to be the case here. It appears that we are being asked to dredge so that the duration of the opening is extended. This is the opposite of sensible water management. A long duration opening drains the reservoir of groundwater that is needed for the next opening. Not only is the date of the next opening postponed by delaying the start of the recharge, the duration of the recharge is prolonged by the loss of the groundwater that has been spent for negligible gain.

The Edgartown Great Pond is not a sea-level pond. Natural openings happen about every 20 years. During the decades between those events, if the town did not intervene, the pond would remain in its natural state; always closed, three feet higher than sea level, slightly brackish, and quite eutrophic. Hence the openings.

But these two things should not be confused. A natural opening cannot be used as the model that defines a successful, intentional opening. A natural opening is the small visible part of a much larger animal — a weather event that changes the sediment flow along the entire south-facing beach. It can take months for the beach and its offshore bars to settle into a new equilibrium after the extreme storms that open the pond.

By contrast, a deliberately cut opening will not change the fundamental integrity of the barrier beach or the balance of its offshore bars. It is a temporary structure and it has a specific purpose: exchange between ocean and pond. An opening’s service life is brief. By the 12th day it has ceased to be an instrument of ocean-pond exchange, and has become instead a pond-to-ocean drainage canal.

Beach cuts are a tool for managing a pond that is higher than sea level. They are not capable of transforming it into a pond that is sea level. The ecological spasms the Edgartown Great Pond has suffered in the last decade are the result of attempts to do exactly that. A long time ago, Hiram Jackson, the legendary late Edgartown shellfish warden who worked on the waterfront all his life, told me that people have the hardest time getting through their heads the fact that the Great Pond is higher than sea level.

The optimal duration of an opening is a question I would like to understand more accurately.

Dudley Levick lives in Edgartown.