Washington Road Stream Restoration

Members of the Princeton Environmental Commission (that would be me) and the Planning Commission got a chance to tour the sight of an upcoming stream restoration in the valley between Washington Road and the new Princeton University chemistry building. In the shade of giant blackgums, oaks and beech trees, most of which will be saved, Randy, a specialist in stream restoration at Rutgers, explained the concept and the detail drawings.

The stream, which drains much of the campus, is very "flashy", meaning that the buildings, roads and well-trodden ground shed water quickly in a storm. The resulting powerful surges of runoff have been busy eroding the streambanks near Washington Road. A healthy stream tames and dissipates the power of storm runoff by overflowing its banks and spreading out into the floodplain. But an eroded stream eventually becomes too deep to overflow, meaning that all the runoff goes surging down the stream channel, dissipating its energy by causing even more erosion.

This is an upstream shot of a "headcut", which describes the process by which a stream burdened with unnatural doses of stormwater runoff cuts deeper and deeper into the ground. The headcut is the sudden dropoff--a transition to a new depth that starts at a downstream point and actually migrates up the stream channel until the whole length of the stream has become more deeply incised. As a stream cuts more deeply, it drains the surrounding groundwater, drying out the valley and stressing the plants. This stream is an example of how the town's "hardscape" of buildings and roads has been slowly transforming the local stream corridors.

The goal of the restoration is to prevent headcuts like this, re-establish a natural meander and a floodplain into which the stream can spread out and dissipate the energy from storm surges. Overall, the result should be a stable and naturalistic stream.

Though exotic plants in the stream corridor will be replaced with native species after the streambed is recontoured, there are exotic shrubs and trees on the upland slopes that need to be removed. I'm hoping to work with university staff to organize removal of these, and also rescue native wildflowers like horsebalm (photo) that would otherwise be bulldozed as part of the stream work.

Big Changes Come to a Hidden Valley

 There's a hidden valley in Princeton that everyone drives by but no one sees. Just over this ridge is Washington Rd, with athletic fields beyond. Down to the left is Faculty Road and Carnegie Lake.

Despite being sandwiched between a busy road and Jadwin Gym, the valley's rich soil sustains old oaks, tupelo, beech and ash that reach improbable heights.

This year, big changes have come to this long-hidden valley. Approached from Faculty Road, stacks of boulders and heavy equipment suggest some sort of road construction.

 A pile of stumps looks less than auspicious.

Further up the valley, more boulders, bales of hay, and orange fencing.

Giant trees, some a yard thick, have been cut down. How could this be anything but bad news? But wait, this post is getting depressing, so let's start from the top of the valley and work our way down.

The valley, which is to say the remnant of valley that was never developed as campus, begins at the new bridge over Washington Road. In the distance is the new chemistry building and the football stadium.

Looking downhill from the bridge, a lovely little stream meanders peacefully down the valley.

Starting farther up towards Nassau Street, the stream runs underground through campus, then emerges (or "daylights") from a big pipe just below the bridge.

The water immediately encounters what looks like an olympic luge track, attractively armored with stones.

 Further down, the narrow channel flows through a broad floodplain.

All of this--the pleasing meanders, the floodplain for stormwater to spread out into, the series of riffles and little waterfalls over stones--is manmade.

Why would anyone want to remake a stream? After a hundred or two years of flash floods caused by all the impervious surface on campus, the stream channel had eroded the ground around it, and was threatening to undercut Washington Road (beyond the green fence on the right) if nothing was done.

Here's a portion of the old streambed, broad and ill-defined. More photos of the old streambed can be found in a post one year ago when members of the Princeton Environmental Commission were given a tour of the proposed project.

A group from Rutgers developed the plans. In this photo, you can see the hoses used for pumping water around the section of stream being worked on. The "V" of stones at the left is called a "cross-vein". Water flowing over the rocks converges to scour out a pool just below them. Pools, riffles, and a narrow stream bed to focus flow are all characteristics of a healthy stream.

The stacks of boulders, then, are materials used to direct water in such a way that the streambank will survive the flash flooding coming from the hardened landscape of campus.

Lots of digging is required to form an adequate floodplain to accommodate the massive infusions of water during storms. The disturbed areas will be restocked with native plants, and though they had to take down some large trees, many were spared.

So that gets us back to the downed trees. This section of white ash is 36 inches in diameter. I counted roughly 200 annual rings, which are caused by the alternation of light-colored fast spring growth followed by a darker band of slower growth later in the season. The tree, and others in the valley, standing or cut, could well date back to the Revolutionary War. Visitors to Mount Vernon may remember the giant white ash trees in the circular drive approaching the house.

 About 160 years back, this ash began to grow very slowly, as can be seen from the very narrow rings on the left. Perhaps it was shaded heavily by another tree, which apparently fell 120 years ago when the rings began to spread out again.

It is unsettling that such old trees have been cut down, and all the more remarkable that few even know about it in a town that loves and protects its trees. But there are extenuating circumstances, tradeoffs made, factors that mitigate, at least partially, the loss. Erosion from campus has been undermining some of the majestic trees, and this project is meant to reduce that erosion.

Time will tell if the trees that were saved will survive all the disturbance around them. Tree roots are very sensitive. And the carefully designed channel is not necessarily immune from the powerful erosive forces of repeated floods.

One useful pursuit at this point would be to study the rings of the fallen trees to see what they might tell us of Princeton's past.

I had recommended a pre-construction rescue of rare native plants like horsebalm, but the idea probably got lost in the mix. Not everyone has learned to make a distinction between rare wildflowers that have survived for centuries in a valley, and whatever natives one can buy in pots at a nursery.

I had also encouraged them to remove the Norway Maples (mottled green/yellow in this photo and next) that have invaded the valley, since the invasive maples are competing with the old growth natives, and their dense shade will threaten the newly planted natives over time.

Overall, though, there's reason to believe this stream restoration--rare in New Jersey--will validate its good intentions. The project leader spoke excitedly last year during the tour about how he hopes students will find the valley an attractive place to visit, rather than merely serving as a traditional shortcut for athletes heading to practice.

This long-sheltered space, with so many stories to tell of past centuries, is beginning a new chapter worth reading.

PU's "Hidden Valley" Nature Trail

Make yourself like rainwater, follow Princeton University's slopes down to the graceful Streicker Bridge that straddles Washington Road, and there you will find a trail through what I call the Hidden Valley. The trail begins under the bridge, branching off from a paved bikepath that goes around the back of the Chemistry Building.

The valley's steep slopes and canopy of 200 year old trees give a sense of seclusion, despite being a stone's throw from Washington Road.  Okay, "stone's throw" is an old expression, and probably should come with a cautionary warning in this safety-conscious era. By accidentally using it, I didn't mean to encourage or condone the actual throwing of stones, particularly with the off chance of hitting two birds, or a car driving by.

It's a very stony valley, though, and when I was a boy, the impulse would definitely have been to toss a stone at the water in the stream, to get that satisfying kerplunk. The stream was restored to kerplunkable condition by the university. Bulldozers and backhoes lumbered up into the woods to carefully place boulders in the shape of "cross veins" which manipulate the scouring effect of the water to form a series of pools and riffles, which in turn make good aquatic habitat.

There's evidence that nature's been throwing stones--big ones. The same powerful stormwater runoff from the campus that had degraded the original stream has also pushed some of the carefully placed rocks out of position. That got my land manager's mind going, which is to say I started noticing all the little interventions that could make a big difference for this small gem of open space. Call it a passion for maintenance, which either turns this post into a timely call for action (university grounds supervisor, please read!) or makes me something of a rude guest in this Hidden Valley, pointing out the flaws.

A workday with some university students could get those stones back into place before surging stormwater pushes even more out of position.

And the white oak on the left, 200 years old if it's like others in the valley whose rings have been counted, is having to compete with a smaller but quickly growing Norway maple that has invaded the valley.

Norway maples are notorious for their aggressive root systems and a capacity to grow up in the shade, eventually outcompeting and displacing the native trees above them. The same slow drama is happening along the fencelines of people's backyards. Looking up, one sees the dense green leaves of Norway maple, not the oak's.

Here, one of the old giants has succumbed, perhaps from the trauma of Hurricane Sandy, or the soil trauma of the stream restoration project, or from the root competition of Norway maples. Maybe all three. It would be relatively easy to cut down all the invasive maples, which otherwise will expand their impact on native shrubs and old growth trees. If we're going to be active, we might as well be pro-active.

And porcelain berry, "kudzu of the north", has gotten a hold, here seen climbing over one of the witchhazels the university planted as part of the restoration.

The extensive replantings of forbs, shrubs and trees, by the way, was very successful, despite the tough work of planting into shale, and it would be a shame if it all gets overrun by invasive vine. I'm sure the university tries to instill the values of early intervention and followup in its students. No better place to get a hands-on experience with that than in this Hidden Valley. Muscles remember far better than the mind does.

This little foot bridge over the stream has an unfinished quality to it, unless it's designed to help athletes hone their sense of balance while walking between sports fields and boathouse to the west and the Jadwin Gym complex to the east.

The main trail ends at Faculty Road, with the big field and Carnegie Lake just to the left in the photo. It's a fine little trail, sustained mostly by hikers and deer, with a mowed branch that heads over to Jadwin Gym, and another across the unfinished mini-bridge to Washington Road. The university's intention, according to those who designed the stream restoration, was to make this little valley welcoming to students and the general public. With its towering old trees, lovely stream and sense of seclusion amidst the university's bustle, the valley is rewarding to visit now, and could be even more so with some periodic informed intervention.

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.

A Spring Walk Through Herrontown Woods

(This post from 2017)

Update: We had a wonderful spring nature walk at Herrontown Woods on Sunday, April 23. It was Earthday weekend, which is part of Earth Month, Year, Century, and miscellaneous millennia extending out beyond, towards infinite. Earth takes care of people day in and day out, so it's only fair that we return the favor.

Below is a virtual version of the walk along the red and yellow trails past vernal pools and boulder fields, all graced with wildflowers and the babble of brooks this time of year, then past the daffodil-strewn Veblen farmstead and over to the Veblen House grounds for refreshments.

Head down the parking lot to the Red Trail, and the first thing you encounter in spring is the vernal pools that form in the holes left by trees uprooted by storms. It's fun to search the banks of these pools for the well-disguised wood frogs.

It was a weird early spring, with summer-like heat followed by snow-come-lately, but some frogs managed to leave globs of eggs behind. Mosquito wigglers promise a good food source whenever the eggs get around to hatching.

It's proving to be an unusually good year for trout lilies--the yellow flowers with trout-like mottling on their leaves. Most years, one sees abundant leaves on the forest floor, but few actual flowers.

Spring beauty is a more dependable bloomer.

The Yellow Trail branches off from the Red Trail just past the stream crossing, then follows the stream up to a convergence. The opulent leaves of skunk cabbage make these streams a ribbon of green in spring. Take the stone stream crossing to stay on the Yellow Trail.

Here's an impressive lean-to someone built, using the crook of a tree to support the central beam.

Along the stream is some scouring rush (Equisetum), which we discovered on a walk with kids from the nearby Princeton Learning Cooperative. You can pull apart its segments, and use their abrasive silicon texture to sand a clarinet reed, or scour whatever needs scouring. It's a very primitive plant, and small compared to its tree-sized ancestors from the Carboniferous era.

Jack in the Pulpits are getting ready to preach.

Rue anemone lines some sections of trail, giving the impression that the edges of trails offer a particularly conducive habitat, where wildflowers are less impeded by the forest leaf cover.

We may also see wood anemones and Virginia pennyworts. I'm told that the pennyworts have an S2 designation in NJ, meaning S2, which means "imperiled because of rarity (6 to 20 occurrences)". This speaks to how important it is for us to carefully manage Herrontown Woods to protect its diversity.

As the Yellow Trail climbs the slope of the Princeton Ridge, you can see the surrounding understory turning green with, alas, winged Euonymus. That early green flush of species that evolved on other continents can shade out the native spring wildflowers, which depend on that sunlight streaming down unimpeded, to recharge their roots with enough energy to bloom the next year. Native trees and shrubs are slower to leaf out, and so give the native wildflowers the "window of opportunity" they need.

Along the trail, you'll see many of the winged Euonymus were cut. We're experimenting to see if the deer will follow up and eat the resprouts. 

It takes awhile to notice the subtle beauty of flowering sedges.

Mayapples are numerous, though relatively few can be found with flower buds.

Near the top of the yellow trail, before it swings over towards the quarry area and farmstead, is a favorite spot: the boulder field.

A stream flows through the boulders, with enough current this time of year to create a wonderful stereo effect with gurglings of various pitches. These sounds mix with birdsongs, the occasional small plane coming or going from Princeton Airport, and various rustlings of wind and wildlife to create that special seductive serenity of Herrontown Woods. I'd suggest that it was that serenity that drew Oswald and Elizabeth Veblen out to this part of town, and led ultimately to the land being preserved when the Veblens donated it all for public enjoyment.

Here's one of the native shrubs--spicebush--which make subtle, fleeting clouds of yellow in the understory. If the shrubs benefit from an opening in the tree canopy, they get enough energy to make bright red, lipid-right berries for the birds.

Here's the mystery Viburnum. Only a few specimens at Herrontown Woods. There are various natives--V. prunifolium, V. dentatum, and V. acerifolium--and the nonnative Linden Viburnum. But this is not any of those.

Update: Thanks to Henry Horn for putting me in touch with Michael Donoghue of Yale for an ID of this shrub: Tea Viburnum (V. setigerum), a Chinese species "that is escaping and becoming established in several areas in North America."

Part of the charm of Herrontown Woods is its farmstead (photo below), which includes a small red barn and corncrib, and the shingled 1875 farmhouse known as Veblen Cottage. Many people confuse the cottage with the Veblen House, which is a couple hundred feet away, through the high fence. These daffodils were either planted by Elizabeth Veblen or by one of the local garden clubs that showed their love for the Veblens and Herrontown Woods by caring for the gardens well after Elizabeth passed away in 1974. The daffodils went unnoticed until Friends of Herrontown Woods board member Sally Tazelaar removed all the multiflora rose that had grown over them.

The current owner of these buildings, Mercer County, has taken initial steps that, if not countered, would lead to their demolition. They are in fine shape and remind park visitors of Princeton's farming heritage. Our nonprofit, the Friends of Herrontown Woods, has submitted a proposal to acquire and maintain these buildings with the same love and commitment we have shown by taking care of Herrontown Woods for four years.

Update, April, 2021: The Friends of Herrontown Woods and its supporters convinced the town to take ownership of Herrontown Woods from the county, and lease the buildings to our nonprofit to begin repairs.

Learn more during the walk, and consider getting involved via our FOHW.org website.