The Carlisle Mosquito Online

Friday, January 19, 2007


Beavers and humans — can we co-exist?

Note: This is part one of a two-part article.
Gabrielle Dockterman and Boomer (appropriately outfitted in his life jacket) kayak around their backyard pond. (Photo by Dot Kelly)

Did you know that:

• Beaver dams are more protected than beavers themselves? The fine for breaching a beaver dam without a permit can be up to $25,000 per day.

• Beavers show affection and mate for life.

• They have hand-like forepaws and eat the bark off of sticks like we would eat an ear of corn.

• In the 1970s a woman turned one of her bedrooms into a swimming tank for a family of pet beavers who lived with her.

These are just a few of the interesting facts I've learned since discovering that a family of beavers lives with us, too. Well, in our backyard, that is. In retrospect, they've been here a long time, though we didn't recognize the signs until recently.

Our house is situated on a point jutting into a wetland that used to be more like a swamp than a pond — but is now more like a lake! When we first moved to Carlisle 14 years ago, we could barely see the water through the woods except for certain wet times of year. It would look like a pond for a few weeks in the spring, and then turn scummy and mucky. A few summers ago it dried up completely, and lush, emerald green grass sprang up from the rich mud. Autumn rains always restored it to pond status for a few weeks before winter set in.

I can't recall which came first, our first beaver sighting or our purchase of kayaks, but now I realize they were related. My home office overlooks the pond, so from my desk I am often distracted and delighted by all sorts of visitors to the pond, mostly birds but also deer and fox. Some years ago, at dusk, I spotted something swimming very purposefully and swiftly in a line parallel to the water's edge. The wake was actually what I noticed first, its ripples reflecting the orange sky from the waning sunset. There was enough light left that I could tell this was not the usual duck or goose. I grabbed my binoculars to investigate further.

Muskrat or beaver sighting?

At the time I thought it was a muskrat, because I had seen muskrat lodges on the pond during an exploration on my ice skates one winter. Their huts are made of cattails and reeds piled together into a conical mound sticking up out of the ice. Though muskrats are smaller than beavers, they look similar when swimming. I learned later that usually only the beaver's head is visible, whereas the muskrat's head and back are partially above water. At the time I didn't think much of it, other than to add it to my mental list of reasons to enjoy living in the boondocks.

With the spring rains of 2003, the pond level rose so much that we decided to buy kayaks because we could literally kayak in our back yard. Oblivious to the real reason for the gradual change, we paddled around our property happily, thinking maybe with global warming we would have a nice pond for years to come.

Kayaks allowed us to explore the pond as never before. Visible on most maps of Carlisle, ours is one of the larger ponds in a chain of wetlands linked together by streams. Part of the Spencer Brook water system, it is actually considered a river. If you drive from the center of Carlisle down School Street, eventually on the left you will pass a wetland where the road is at a low point. Under the road a culvert allows the stream to cross the road and eventually feed our pond. The downstream border of our pond is actually a long rock wall. The water flows over this rock wall into a stream that feeds another pond a short distance away through the woods.

I had never put much thought into this geography until this past spring when we had a huge amount of rain. Suddenly there seemed to be an inordinate amount of water in the pond, flooding the woods and encroaching upon our house. Our wonderful pond was turning into a menace. Water started seeping up from under the basement floor. I began to think that something was wrong. We had been concerned about the position of two new houses on Russell Street, whose driveway could cause the runoff from Bellows Hill Road to run right down into our water system. But the town asked the builder to deal with the runoff, and a berm was installed to address the concern. Still, something wasn't right.

As soon as it stopped raining I got into my trusty kayak to investigate. On the downstream side of the pond, water was still flowing over the rock wall. There were sticks along the wall but I figured that was debris from the runoff. By then the flooding seemed to be a problem everywhere, so I grew less concerned about our situation being unique. I visited the Old North Bridge in Concord and saw the drastic flooding there. Instead of calling the Conservation Commission in a panic, I convinced myself that flooding was an issue everywhere. Our basement dried out and the water receded a little. I stopped drafting plans to build an ark.
The 250-foot rock wall at the right turned out to be the mud-and-debris beaver dam, nearly two feet high. (Courtesy photo)

Enjoying the pond

All summer long we enjoyed our new lakefront property. It was beautiful in every direction. Our little dog took up frog hunting along the water's edge and would accompany us with his little lifejacket on the kayak. From my desk I saw wildlife as never before. One afternoon three river otters swam along the water's edge. I grabbed my binoculars and watched them frolic upstream. One caught a huge bright green frog with its meaty legs flailing, and chomped it right down.

We assumed the water was high everywhere due to the record rainfall. In late summer, another odd thing happened: the trees bordering the pond turned their blazing fall colors early, starting in August. In the fall I returned to Old North Bridge, expecting to see high water. I was stunned to see that the water level there was back to normal. I realized then that we really did have a problem. That panicked call to ConsComm was in order after all.

Sylvia Willard, the ConsComm administrator, came to look at the pond and saw right away we had a big problem. She alerted me to another concern: the submerged trees in the flooded areas would likely die. In fact, they had turned colors early because they were stressed. She told me of some beaver activity nearby and suggested beavers might be causing the problem. "I've been all over the pond in my kayak," I replied (oh so confidently), "and I haven't seen any signs." Sylvia suggested I look online to learn about signs of beaver activity. In doing so, I realized I had a serious misconception about what beaver dams look like.

A shocking discovery

As I paddled downstream toward the rock wall that borders the downstream edge of the pond, I scanned the wall more carefully. At a distance, the roughly 250-foot long wall looked like the edge of an infinity pool, with water right up to the top, spilling a little over the brim. I had attributed this to the high water level, but it hadn't actually looked like that in years past. Why should it look like this? This old rock wall should look irregular. As I got closer, again I saw the sticks poking up that I thought were debris. They continued along the entire length of the wall. Then it occurred to me that I had only been looking at the wall from the water side. I pulled my kayak up to the edge and peered over. A massive blockade of mud and sticks had been piled up along the entire 250-foot wallthe engineering work of beavers!

They had built the wall up nearly two feet above the rocks! I don't recall my blood turning cold on this realization, though it was that kind of moment. Mostly the naturalist in me thought it was pretty cool and amazing. But the property owner in me, knew we had to do something, both to prevent future flooding of the basement, and because the edge of the pond was now a mere six feet away from our well head, possibly threatening our water supply.

Since the rising water posed a health threat, legally we could do something about it with the proper permits from the Board of Health and ConsComm. The question was, what?

Editor's note: What Gabrielle Dockterman did about her engineering beavers, and who came to Carlisle to film it, will be revealed in next week's Mosquito.

2007 The Carlisle Mosquito