Weweantic Revisited

Is it time to look into Weweantic with fresh eyes? What does Weweantic have to offer us? What do we, in 2005, have to offer Weweantic?

Come take a look with us into the area surrounding the Horseshoe Pond Dam. This man made boundary, is the key to the future of the largest river system in the Buzzards Bay Watershed, a key which if thoughtfully turned will open a door to reveal unexpected treasures. What might these treasures be? To find out we need only to look thoughtfully into this hidden gem of the Buzzards Bay Watershed.

Differentiating between looking "at" something and looking "into" something is a worthwhile exercise here at Weweantic. In the above paragraphs I specifically use the phrase "look into," rather than "look at", for a purpose. To often we look at things whether they are places or people, and come to conclusions based on outward appearances or preconceived notions. Looking thoughtfully "into" something is a different exercise.

My experience into this section of Weweantic began about ten years ago, in 1996, when a fishladder was proposed for the Horseshoe Pond Dam. At first glance it seemed a harmless plan. It would only require a notch to be cut in the concrete face of the dam and the addition of a few aluminum steep pass segments. Along with these minor alterations a new spill gate for the dam’s spillway would have to be installed to maintain enough of an impoundment for the fishladder to pass fish. The former spillgate had been removed by the dam owner thirty odd years ago, which allowed the impoundment to fluctuate as flow conditions dictate. Although this plan would have a favorable impact on the targeted specie, the alewife, it did not fully consider or look thoughtfully into the overall diversity of Weweantic.

It may sound strange but the future of Weweantic hinges on the three foot square hole where the dams spillgate once was.

From what I have gathered, Mr. Robbins, the dam’s late owner, removed the spillgate of the Horseshoe Pond Dam sometime in the 1960's. He did so to prevent flooding in the brook trout hatchery he established on Patterson Brook, a small spring stream at the upper reach of the Horseshoe Pond Dam impoundment. It was Mr. Robbins objection to a new spillgate being put on the dam that ended the 1996 fishladder effort.

When Mr. Robbins removed this spillgate, he opened a new chapter in the history of Weweantic. For the previous two hundred years, Weweantic above the dam had been an impoundment maintained for the sole purpose of turning the wheels of industry. Before the gates’ removal the dam had maintained a fairly constant water level in the impoundment. Water was impounded to the tree line of the surrounding woods, with no saltwater intrusion. What had been part of a diverse fluctuating upper estuary before the dams construction, became a freshwater impoundment with far less diverse habitat and species. When Mr. Robbins removed that spillgate, the impoundment above began to fluctuate again, breathing its first breaths of its estuary since the days of horse and buggies.

The value of fluctuating water levels and the resulting saltwater intrusion must not be overlooked here. It is no secret that the constantly fluctuating water levels of estuaries and free flowing systems create a diversity of habitats, followed naturally by a diversity of species.

Over these past ten years my children and I have spent countless hours looking into the environs of Weweantic, at and around the Horseshoe Pond Dam. Although we may lack the credentials to draw scientific conclusions, our observations leave no doubt that this is a very unique place, which presents us with unique restoration opportunities.

Our Observations

 

  • The Horseshoe Pond Dam is built some distance below tidal influence. It does cause significant tidal restriction to the upper estuary at Weweantic (Horseshoe Pond).

Low tide below dam

High tide below dam

 

  • Because there is no spillgate on the dam the impoundment fluctuates seasonally. This fluctuation creates habitats which are more diverse than impoundments which do not fluctuate. Diversity of habitat naturally increase species diversity. This is most visible in wading bird abundance. When high flows raise the impoundment to tree level there is no place for wading birds. When flows drop and the impoundment drains below the tree line, flocks of various wading birds appear.

Looking upstream from the Horseshoe Pond Dam August, 05 low flow.

Same view Sept 05, after rains raised the impoundment.

If the spillgate on the dam was replaced the water level would remain fairly constant at the level in the Sept 05 photo above. It is pretty enough to look at but offers little in diversity of habitat.

 

  • Saltwater intrusion through the dam occurs during periods of low flow and high lunar tide cycles. We have observed this often during summer low flow periods. When this takes place on late summer evenings, it is quite a spectacle. As the high tide approaches all sorts of estuarine species gather at the base of the dam, schools of juvenile menhaden, grass shrimp, jelly fish, blue crabs, small flounder, elvers and others. When the tide reaches the right level the current reverses sending its estuary soup upstream through the open spillgate into the pond above. This is likely an important transport route for the American eels upstream migration, during high flows they often languish at the base of the dam.

Looking upstream through the spillgate of the dam at high tide.

Questions

  • How can we maximize the potential of the Weweantic upper estuary (Horseshoe Pond). Bearing in mind the following.

 

  • Overall habitat and species diversity

 

  • The value of saltwater intrusion and water level fluctuation, both tidal and seasonal.

 

  • Fish Passage; The following anadromous and catadromous fish species migrate up Weweantic, Alewife, Blueback Herring, American Eel, Rainbow Smelt, Tom Cod, White Perch, Sea Lamprey. Anecdotal  accounts suggest American shad and Salter (sea run) Brook Trout migrated up Weweantic in the past. Presently only the alewife and blueback herring have reliable passage around the dam.

 

  • Waterfowl/Shorebirds; What would be most beneficial to the numerous bird species which visit this area? The current situation is probably not ideal. Because of the small size of the open spillgate the impoundment is prone to rapid flooding after heavy rains. While gradual, subtle changes in water level is good, rapid flooding of potential nesting areas, is not.

 

  • Above is just a snapshot of some of the questions which need to be answered in relation to some of our more recognizable species. 

Solutions

The Horseshoe Pond Dam is somewhat unique because it is built within the tidal zone. Using the benefit of these tides we can restore tidal flow, maintain seasonal water level fluctuations, allow easy passage of all sea run fish species, and still maintain enough of the impoundment to support a modest run of alewives. In other words, we can restore the upper estuary of Weweantic (Horseshoe Pond).

Follow the links to photo's to see how the tide works at the Horseshoe Pond Dam.

Page 1 rising tide

Page 2 Change

 

  • Fish passage is an interesting issue at this dam, although there is no fish ladder, fish do get upstream by other means. Lets look at them species by species.

Alewives

Alewives find their way above the pond by way of the channel which was used by the mill complex to power the mill. It is not an ideal set up. The entrance way to the channel is a couple hundred feet below the dam, therefore it can be difficult for them to locate. The alewives tend to follow the strongest flow which brings them to the base of the dam where they are vulnerable to the ever present poachers. Despite this draw back the channel functions fairly well as passage for alewives. Over the past several years we have observed a respectable run of adult alewives coming upstream. Spring of 2005 was an exception, as observed elsewhere adult alewife returns appeared quite low. We have also observed schools of juvenile alewives in the pond during summer months.

Alewives may also access the pond through the spillgate hole during periods of high spring tide cycles. Although there is no upstream flow above the dam during high spring flows, it appears high lunar tides stem the flow from the pond enough to allow alewives to swim through to the pond.

Photo's of bypass channel... HERE

Rainbow Smelt

Like the alewife, rainbow smelt are an anadromous fish, which spawn in freshwater and return to salt. Rainbow smelt spawn earlier than the alewife, in 2005 eggs were visible in late March and early April below the dam.

Because of the dam smelt have limited spawning habitat in Weweantic. The only area they lay their eggs is within a hundred feet downstream of the dam. The problem for the smelt here, is the tide. Smelt, by nature move up the river on the high tide to overcome swift water and obstructions. They also must spawn in fresh or low saline water. Because they cannot get past the dam they lay their eggs below it, within the the tidal zone, therefore at low tide their eggs are on dry ground. Under normal circumstances the smelt would move above tidal influence to spawn. After an evening spawn at Weweantic thousands of tiny smelt eggs can be seen lying dead among the rocks after the tide recedes.

Dead smelt eggs clustered on the stream bed at low tide April 05 Weweantic

 

 

 

 

Follow this link for additional Weweantic tidal info.... HERE