Princeton's Mountain Lakes Dam Restoration Story

(Also posted at PrincetonPrimer.org)Quite a story will be told this Thursday, Nov. 15, 7pm, at the Princeton Library community room, about the reservoirs that once provided Princeton with ice in pre-refrigeration days. Engineers identified the need for restoration of the dams as far back as the 1970s, but only when an anonymous donor came forward with several million dollars (eventually totaling 3.5) was the project able to move forward, in 2010. (The donor had also helped to purchase Mountain Lakes back in the 1980s.)

Here's a description of Thursday's event:

"Created as an ice pond in 1884, Mountain Lake gradually filled in with sediment and the severe deterioration of its dams threatened to drain it altogether. Princeton Township engineering staff and consultants review Mountain Lake's ice harvesting history, archaeological discoveries, and the careful rehabilitation over the last two years that has restored the beauty of this National Register site and has preserved it for future generations."

The Mountain Lakes Preserve is one of Princeton's best-kept open secrets. Despite being in the middle of Princeton geographically, Mountain Lakes feels tucked away, accessed down a long driveway at 57 Mountain Ave, not far from town hall, across 206 from the Community Park fields.

You can access a pictorial and descriptive history of the restoration project at this link (scroll to the bottom and work your way up chronologically), but I'll show a few photos here.

The small wooden posts in the foreground of the above photo show where a ramp once conveyed big blocks of ice out of the lake and up into barns that once stood three stories high just below the dam. The barns, insulated with straw, could store ice for up to two years. The ice, of course, was delivered to people's homes to cool their ice boxes, in those more sustainable days before refrigeration became widespread in the 1930s or so.

Mountain Lakes House, built around 1950 and now used for weddings and other events, has a beautiful view of the upper lake and dam.

Dredging of the thick sediment (The 1600 truck loads were taken to a sod farm) during restoration apparently uncovered a rich seedbank of native wetland rushes, sedges and wildflowers that carpeted the lakebeds while the lakes remained drained. Friends of Princeton Open Space board member Tim Patrick-Miller led efforts to rescue some of these plants prior to refilling the lakes. They now make a fine native border along the upper lake.

Native woodland asters flourish along a lakeside trail in an area we cleared of invasive shrubs. All trails are open to the public.

This area too, just below the upper dam, is being managed for native species.

Though the restoration was primarily the work of Princeton township engineers, consultants and the very capable contractor who did the elaborate stonework (done primarily by a man named Wolfgang) and concrete reinforcement needed to restore the original beauty while bringing the dams up to current standards, I was able to contribute to the project in various ways.

As resource manager for Friends of Princeton Open Space, I helped correct some misperceptions about the lakes' original depth, made sure that areas near the dams with rare native plants remained undisturbed, and also pointed out the importance of restoring not only the two main dams, but also the smaller dams just upstream that had served to capture stream sediment before it could reach the two lakes.

Restoration of one of these upstream dams, built in 1950, was made possible by additional funds from the anonymous donor. Now cleaned of seven feet of sediment accumulated in its first 60 years, it should substantially increase the life of the two main lakes.

I also encouraged the township to dig several vernal pools nearby to serve the local frog population. State regulations may have bogged down those plans.

If you haven't been to Mountain Lakes, take a walk out there some day to see the award-winning dam restorations, an occasional great blue heron, "Devil's Cave" at the top of the boulder-strewn slopes of Witherspoon Woods, and maybe even hear the call of a pileated woodpecker. It's one of the finer meetings of nature and culture, wild and tamed, natural and man-made beauty.

Update on Dam Restoration at Mountain Lakes

I haven't heard anything official, but it looks like the lower dam at Mountain Lakes Preserve is nearly complete. The wooden posts in the foreground mark where a ramp once was located for hauling chunks of ice out of the pond and hoisting them into the 3-story ice barns that used to rise behind the dam to the right.

The ice operation closed down around 1930, as refrigerators became more widely available. The stone wall extending the length of the dam is completely new, designed to mimic the original wall that now lies buried under the expanded earthen portion of the dam. For safety reasons, the dam is now broader and several feet higher than previously.

At the other end of the dam stands the newly restored spillway. As far as I know, the informative signs that were there prior to restoration will be reinstalled, describing the decades during which Mountain Lakes supplied Princeton with ice for its iceboxes.

Meanwhile, upstream of the two Mountain Lakes is another dam that was added onto the project, funded by the same anonymous donor. I had long argued in favor of restoring this "upper settling pond", also known as North Pond--an argument that was going nowhere until funding became available. It's located on one of the two tributaries feeding the lakes, and was built in the 1950s by the Clarks, who also built Mountain Lakes House around the same time.

The pond is called a catchment basin for good reason. Water rushing downstream from Witherspoon Woods drops its sediment in this pond, thereby greatly reducing the amount of sediment that would otherwise have continued into the Mountain Lakes. It played this role very effectively, completely filling up over the past 50 years. There must be 8 feet of very rich sediment here, which this week is being trucked away, perhaps to a topsoil business.

With the catchment basin trapping sediment, at least on that one tributary, the upper Mountain Lake will last much longer before it once again will require dredging.

This is my favorite vista, standing at the northwest, upstream end of the lakes, looking down.

Dam Restoration at Mountain Lakes

For many years, Princeton township has been making plans to restore the historic dams at Mountain Lakes, which were originally built to collect ice for Princeton's ice boxes in the days before refrigerators.

Over the past century, the two dams have weakened, and the lakes have filled in with sediment. The upper lake, for instance, was originally 7 feet deep, but now has only a foot of water.

Only in the past year, when an anonymous donor offered to fund the $2 million project, has the restoration moved beyond the planning stage.In the photo, township engineers and historians meet on the lower spillway to discuss details of the restoration plan. The large boulders piled against the dam are temporary reinforcement for the buckling spillway.



Interpretive signs tell the history of the ice business that once included two 3-story barns to store blocks of ice just below the dam. Hay from nearby fields was used to insulate the barns, which could keep ice for up to two years.

The restoration will include a dredging of the two lakes, and is scheduled to begin in May, 2010.

Mountain Lakes Dam Restoration Update

 Work is proceeding apace on restoring the two historic dams at Mountain Lakes. The dams were originally built around 1900 as part of an ice harvesting operation that supplied Princeton with ice for several decades before refrigerators became available. An anonymous donor provided the nearly $3 million needed to fund the restoration and lake dredgings. In the photo, workers are rebuilding the stone facing of the upper dam.

Meanwhile, on the upstream side of the dam, new concrete is being added to reinforce the structure. The dirt access road on the right will be removed after restoration is complete. When the lake is allowed to fill up again, possibly as early as this December, the water will regain its original depth of eight feet. Prior to dredging, the lake was barely one foot deep, with seven feet of sediment under that.

Seen from the upper dam, the drained lower lake is an expanse of mud, with any remaining fish and turtles huddled in a small area where water remains. Snapping turtles with 2 foot wide shells (they get bigger with retelling) were frequently sighted in the lower lake, and one of them may still be lurking in the remaining water. Fish in the two lakes were removed prior to draining in July, and mostly relocated to Lake Carnegie.

Archeologists recently used metal detectors to find some century-old tools buried in mud in the lower lake, left over from the ice cutting era.

Mountain Lakes and the Panama Canal

A PBS documentary last night on the building of the Panama Canal offered a dramatic portrayal of the beginning of the 20th century, when the U.S. was emerging as a world power. Described at the time as "The greatest liberty ever taken with nature", the canal was gnawed out of swamps and mountains with a combination of dynamite, giant steam shovels (think Mike Mulligan), and brutal manual labor. Teddy Roosevelt started the project in 1904. After ten years and 5600 lives lost to landslides and epidemics of yellow fever and malaria, they blew up the last retaining dam, allowing water to fill the final segment of the canal.

Meanwhile, the pre-refrigeration age was all the rage in Princeton (why they didn't include this in the documentary I cannot say). Mountain Lakes Ice Company was harvesting blocks of ice from Mountain Lakes and distributing them to residents and businesses on carts pulled by mules. Small liberties had been taken with Mountain Brook some years prior, when the lower dam was built in 1884, and the upper dam added in 1902.

Steam power (the foundation and chimney are still visible in a thicket of invasive shrubs) was used to transfer the blocks of ice from the lake to the three-story insulated barns for storage.

Maybe this juxtaposition came to mind because just last week, a retaining dam (buried in snow to the left of the restored dam in the photo) built to protect the upper dam during its restoration was removed, albeit not with anything as exciting as dynamite. This spring, the upper dam will return to action, backing up water to refill the upper lake, now restored to its original size and depth.

While the Panama Canal represented a will to overcome nature's obstacles in the name of economic progress, a contrary movement to preserve the great American landscapes began at the same time, as Roosevelt set about protecting lands in 1902.

The Panama Canal happens to play a role in a pathbreaking drama about climate change that debuted last year at the McCarter Theater in Princeton. Called The Great Immensity, its story begins on an island in the middle of a lake created by the canal. Scientists have been conducting a longterm study there to better understand whether populations of wildlife can survive when they become isolated in small fragments of habitat, as has happened to much of New Jersey due to development.

Wouldn't it be nice if the two often conflicting drives--economic expansion and preservation of natural heritage--could converge into what's being called a green economy. Mountain Lakes Preserve is one place where a historical example of a sustainable economy (ice harvest) and land preservation find common ground.

Dam Restoration Update

Restoration of the historic upper dam at Princeton's Mountain Lakes Preserve is nearing completion, with refilling of the upper lake promised, or at least predicted, to come in March or April.

The broad spillway of the dam, capped with concrete, needs to be perfectly horizontal in order to prevent overflow from concentrating in one place. The apparent tilt of the wall has more to do with the camera lens than the actual dam.

Mountain Lakes Dam Restoration Begins

The official groundbreaking ceremony for the dam restoration at Mountain Lakes took place today. The photo includes township staff, elected officials, members of Friends of Princeton Open Space and the Princeton Historic Preservation Commission, consulting engineers, and the contractor who has agreed to take on all the work.

A Flurry of Activity at Mountain Lakes

Even before the snowstorms hit last week, this winter has been marked by a flurry of activity at Mountain Lakes, with a blizzard to follow, come summer.

Here, two FOPOS board members, Clark Lennon and Tim Patrick-Miller, are removing invasive shrubs from an area near the Mountain Lakes House, as part of a beautification of the grounds that's starting to gain some momentum.

A couple hundred yards southeast of the house, visitors to Mountain Lakes may have noticed some pink ribbons showing up in one area of the woods. The trees have been numbered, measured and mapped so that a location can be chosen for a clearing, to be used as a staging area for the dam restoration and lake dredging work scheduled to begin in July.

Much discussion has gone in to selecting an area that will disturb as few of the marked trees as possible. Township engineers have been working closely with FOPOS (Friends of Princeton Open Space), which holds the conservation easement on the property and has to approve various aspects of the proposed work.

For those interested, the township will present its plans for the dam restoration and dredging project, and accept public comment, on March 1st at 7pm in the Main Meeting Room of the Township Municipal Building.

PHS Students Study Fish at Mountain Lakes

Thanks to Tim Anderson, Princeton High School science teacher, who sent me these photos of his May 25 visit to Mountain Lakes with his students to study the lakes before they get drained this July as part of the upcoming dam restoration.

Tim has often used Mountain Lakes as a study area for his classes. This year, they sampled "fish, plankton, etc." In two seines of 80 feet of shoreline, they caught "a 22" large mouth bass (see below), hundreds of bluegill and pumpkinseed sunfish, one green sunfish, white suckers, golden shiners, and one 14" bullhead catfish."

22 inch largemouth bass. This may be the big one fishermen have told me they've seen in the lower lake.

Determining fish age

My understanding is that the fish will be rescued from the lakes during draining, and transported to Carnegie Lake. Though the lakes will be restocked after the restoration is complete, I've been told that it will take some years for fish populations to recover.

I had wondered whether there might be something genetically special about the fish in the lake, since the dams have effectively isolated them from the rest of the watershed for the past 110 years. But I was unable to find anyone who thought it worth looking into.

In any case, it's good to have some information about what lives in the lakes, before they get remade.

Revised Trail Map for Mountain Lakes

Hikers and joggers heading to Mountain Lakes Preserve can find a map showing which trails remain open during the dam restoration by going to
http://www.princetontwp.org/mountain_lakes_preserve.html and scrolling down.

Nature Walk This Sunday at Mountain Lakes, June 19, 2pm

After quality time with Dad, a nature walk this Sunday, June 19 around the back side of Mountain Lakes, with a look at progress on the lower dam restoration, including the recently unearthed ramp from the 1900 ice business, if they haven't covered it back up yet (see post earlier today). I'll be doing some plant inventorying along the way. All welcome.

Meet at Community Park North parking lot, on Mountain Avenue just off 206. Check this website for any last minute cancellation due to weather.

University Students Experience Mountain Lakes

Two weeks have flown since co-leading, with local writer and historian Clifford Zink, a tour of Mountain Lakes for a group of Princeton University students. All are taking a course taught by history professor Vera Candiani, who passionately believes that students need to break out of the academic bubble of campus and get acquainted with the world around them. Much of the university's emphasis in this regard has been to encourage students to study and experience distant continents. But Vera believes there is also a great deal to discover and perspective to be gained just a short walk or ride from campus.

On the premise that we leave our human legacy primarily through our "actions on matter", her students are learning to "'read' the material and landscape record that our species’ interaction with nature over time created."

"Actions on matter" at Mountain Lakes could include the double-walled ice houses built to store ice harvested from the lakes in the early decades of the 20th century. Or the pastures and plowed fields that had such a big impact on what plants grow there now, long after the fields grew up in trees.

While Clifford spoke about the dams and their restoration, I introduced the students to the aromas of spicebush and eastern red cedar, and explained how to crack the color codes of spring. A quick survey of red maples in the forest can be done by looking for the red hue they cast in spring, and woody species that evolved on other continents and climates can often be spotted as they green up earlier than most native shrubs and trees. This early greening can impact other species by preventing the spring ephemeral wildflowers beneath them from collecting enough solar energy to prepare for the following year. What looks like lush, healthy green, then, may actually be throwing a wrench in the ecological functioning of the landscape.

The students learned also to "read" the history of deer management in the growth pattern of a spicebush. I explained how the spicebush, now thriving in the preserve, had just 15 years ago been barely hanging on, as heavy deer browsing pressure prevented any new sprouts from growing up. Many spicebush shrubs held on through that era with only one stem high enough to escape the deer. When the town took action to fill the vital role of the absent wolves and other predators, by culling the deer, the spicebush were able to grow multiple stems up and beyond the reach of the deer. With these new "solar panels" in place, the shrubs quickly abandoned the old one--a once precious lifeline that was no longer needed. The photo shows one of those "heroic" old stems still standing in the middle of all the new ones.

A spigot sticking up in a floodplain meadow near Mountain Lake House hints at the prior existence of an olympic-sized pool, once used by the high school swim team for practices. Back when I worked for Friends of Princeton Open Space, we'd plant Hibiscus and other wildflowers in that field, finding shards of ornamental tile as we dug holes for the new plants.

Like pages torn out of what once was an epic poem, we saw a few scattered wildflowers--a trout lily near the path, or a Solomon's Seal hidden beneath a thick patch of winged euonymus. Call it a first step on a long return from the disruptions of the agricultural era a century ago. Though the students saw lots of areas where past plowing and pastures erased the native diversity, they also got to see the few spots that had somehow escaped those historic impacts, where otherwise rare species and lush native herbaceous growth has survived and prospered.

There was a pop quiz midway through to test the students' reading abilities. As Woody Guthrie says about a sign, "On the back side, it didn't say nothing."

Whenever I see the upper dam, I think of Clifford's insistence that the stone masons restore the dam's spillway to be as level as possible, so that water would spill evenly across its length.

It was a gorgeous day in a beautiful local preserve, with bright, inquisitive students who opened up to the peacefulness of the setting and all the stories it had to tell of past, present, and future, less than a mile from campus.

One idea Professor Candiani has, for expanding this connection of university students to the locale they call home for four years, is to make field trips like this a required part of the freshmen class's orientation, so that students can get to know each other and their new community at the same time.

Plant Rescue at Mountain Lakes

Now, that's strange. Seems to me there was a lake around here somewhere. The plug has been pulled, the 7 feet of fertile sediment accumulated over the past 100 years is being dug and hauled off to farms and topsoil makers, and the dam is being restored to its cerca 1900 appearance. Given the highly conducive weather thus far, the contractor is hoping to complete restoration of the upper lake and dam by December.

One of the streams that feeds the lakes enters back where the trees meet the mud in this photo, between the two backhoes. From an old aerial photo the engineers determined that the pond used to extend further up into that valley, and I was alerted that some more mud and associated plants would be coming out.

FOPOS board member Tim Patrick-Miller agreed to help me rescue some of the wetland species before the digging started. Much to my surprise, we found 4 species to add to the list of plants growing at Mountain Lakes.

In the wheelbarrow (our manual labors contrasted comically with the big machinery of the dredging operation) is pickerel weed, which is rarely found growing in the wild in Princeton. It likes shallow standing water at pond's edge.

Nearby was a little gravel streambed, away from the main current, that was clearly perfect habitat for three other species of plants also rarely encountered. This one, new to me, turned out to be ditch stonecrop. Not a pretty name, but it's true it was growing in something akin to a stony ditch.

Water plantain has oval leaves and tiny white flowers. It also needs a very stable hydrology, quickly perishing for lack of water.

Petals and branchings come in threes.

Bur Reed has leaves like an iris and seed capsules like those that fall from a sweet gum tree.

All four of these species only survive in locations that stay consistently wet throughout the summer. Though this continent once had abundant wetlands with much more stable hydrology, suggesting these plants were once abundant, the only places I find them now are in areas kept artificially wet, such as the edges of impoundments like Mountain Lakes, and the pump-enhanced marsh at Rogers Refuge.

Death of a Stream

During my visit to North Carolina last month, my friend Perry took me to see how erosion can destroy a creek. Just last year, there had been a healthy, shallow, narrow creek meandering through this section of a wooded valley. What we found on this visit was a ditch eight feet deep. Trees had fallen as erosion undermined their roots, the ground pulled out from under them. This land is protected--preserved for all time--and yet the stream appears to be self-destructing within the boundaries of this nature preserve.

How this happens is completely counterintuitive. There's no rogue backhoe tearing at the tree roots, no misguided government policy like the channelizations of streams that happened in the 1960s. Though we usually think of erosion as being a process that degrades a stream from the top downward, this demolition starts downstream and heads up. Furthermore, the valley upstream of this section is undeveloped beyond a few scattered homes.

The process at work can be seen in the lower left of this photo, where there appears to be a ledge, a sudden dropoff in the mud. That's what's called a "head cut". As water flows over that ledge, it erodes the face of the dropoff, causing the ledge to gradually shift upstream. The same process is at work on a much grander scale at Niagara Falls, which is slowly but steadily moving upstream from where it was millenia ago. It's like the streambed were a loaf of bread that someone has been cutting slices off of, slice after slice, heading upstream.

How did this process of destruction get started? On the map, there are two branches of a stream that flows northward (bottom to top on the map). At the lower right is I-85. Tens of thousands of people drive peacefully by every day, their ride made smooth and safe by that broad ribbon of carefully engineered concrete. Not one of them is aware that the road, a ribbon of impervious surface, sheds copious amounts of stormwater, which then barrels down the creek, creating enormous erosive pressure. Somewhere miles downstream, the bottom of the creek gives way. A headcut begins, which then "travels" upstream, back towards the source of the eroding stormwater, consuming and deepening the creekbed as it goes.

Though the little branch of the creek on the left of the map, the one we visited, isn't downstream of the freeway, the erosion of the main branch created a headcut that then headed up the smaller branch as well.

We looked at the soil. It was sandy rather than piedmont clay. At this point, Perry pointed out that the headcut was moving upstream so fast--we estimated 200 feet of creek consumed by erosion in the past year alone--because the soil it was cutting through had not been there a few hundred years ago. During the heyday of tobacco farming, the soil that washed off the fields accumulated in the valleys. The stream is actually cutting down through layers of silt deposited during the agricultural era.

This might suggest that the erosion is actually helping the creek return to its historical level, but the result will not be restoration. Even though the creek may end up down near its original level, the valley's vegetation is still perched high on all the silt. The creek has become disconnected from its floodplain. The water table in the valley drops to match the level of the creek, which makes the vegetation more susceptible to drought.

A healthy creek floods easily and often, in the process dissipating energy and watering the surrounding floodplain vegetation. A deeply incised creek floods rarely, so that all that weight and power of water puts erosive pressure on the creek banks, detaching the stream even further from its natural interaction with the floodplain. Aquatic life has a hard time of it when its home is being either eroded away or buried in silt.

Christmas ferns and witchhazel will still grow on the slopes of the valley. But the valley is changed. The headcut has reached a spot where a beaver dam had created a wetland. Chances are, the headcut will undermine the dam and drain the wetland. Yet another example in our world of how cause--the building of an interstate a half century prior--can be so distant in time and space from ultimate effect.