Showing posts with label Flooding. Show all posts
Showing posts with label Flooding. Show all posts

Tuesday, March 06, 2012

Repairing the Towpath and Nature Along the D-R Canal

For years, the towpath was a given, a high quality crushed-stone pedestrian and bicycle thoroughfare stretching more miles than most anyone has time to explore, up and down the DR Canal. That changed last August as the unprecedented flooding of Hurricane Irene--tearful after having been downgraded to a tropical storm--deposited a thick layer of silt over the trail. The gift of fertility, reminiscent of the ancient Nile, would have been more welcome if the valley's investment was in agriculture rather than transport.

I inquired last fall and was surprised to hear that there were no funds available for repair, and if and when they become available, the northern portion's washouts, up towards New Brunswick, would get the first attention. Some repair in the Princeton area, by the water authority rather than state parks, has taken place. The photo shows a patch job just up from Turning Basin Park.

I called Stephanie Fox at DR Canal State Park today, and was told that more extensive repairs are waiting on FEMA money from the federal government. In addition to trail damage, some of the park's historic buildings were also damaged in the flood. Though the crushed stone surface is still intact in most places underneath the mud, repair will involve bringing in additional stone. Cost for repairing just one mile of minimally damaged trail could run $10,000, so overall cost will likely be very high.

Near Harrison Street, where the nature trail branches off, the towpath is in relatively good shape, at least when it is dry. The trail loop was built by parks personnel after I "discovered" the meadow there where the land between Carnegie Lake and the towpath broadens out. At the time, the park crews were mowing the meadow weekly during the summer. When I pointed out that they were mowing not grass but a field of beautiful native wildflowers, they agreed to limit mowing to once a year in late winter. Everyone was a winner with this arrangement: less work, more habitat, more flowers.

In winter, at the trailhead, the switchgrass leaves are an attractive legacy of last year's growth.
Word is that the bluebirds have hung around all winter, it being so mild.
One reward of exploring the nature trail this time of year is an encounter with fragrant honeysuckle (Lonicera fragrantissima), whose small white flowers live up to their name. This is the one exotic bush honeysuckle species that I've never seen spreading into wild areas. A line of the shrubs remains from maybe 40 years ago when that ribbon of land between the canal and Carnegie Lake was carefully tended as part of the grand entryway into the university.

Each year, with no assistance other than annual mowing, the meadows have become richer with wildflowers like joe-pye-weed, ironweed, tall meadowrue and cutleaf coneflower. It seemed time to relax, sit back and enjoy the fruits of less labor.

But a trained eye will see in this very plain-looking photo a web of vines. Porcelainberry, a grape-like exotic vine that has covered forest edges at Princeton Battlefield with stifling kudzu-like curtains of growth, has been spreading down the canal corridor. A light infestation noticed a few years ago is now exploding, threatening to permanently overwhelm the wildflower meadows.

Park crews are busy elsewhere along the canal, dealing with invasive Japanese knotweed and hops. We'll have to see if there's anything that can be done this year.

In the meantime, there are sweetgum balls serving as natural tree ornaments next to the trail,
the resident geese, and, if one can negotiate with the geese for access to the shore,

trout to be caught.

Monday, November 14, 2011

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.

Tuesday, September 06, 2011

Towpath Seeks Mule Team After Flood

Maybe the mules that once towed the boats along the canal could return to scrape all the mud off of the towpath. When I stopped by, three days after Hurricane Irene's deluge, a fine layer of goo had been deposited throughout the floodplain. Rivers have long deposited sediment in floodplains during floods,  enriching the soil. Hopefully, lighter rains will wash the mud off of the trail.
It was easy to see how deep the floodwaters had been--about knee-high along the towpath near Harrison Street.
Meanwhile, at Rogers Refuge, upstream from Alexander Road, floodwaters rose halfway up the kiosk.

Sunday, August 28, 2011

Princeton High School Floods Again

Yesterday, with Hurricane Irene headed our way, I stopped by the Princeton High School to check on preparations for the coming deluge. This part of the school had stormwater seep under the doors a week ago, and was most emphatically flooded two years prior when Hurricane Bill paid a visit. I've heard from several sources that the bill for Hurricane Bill included a new stage floor for the high school's performing arts center, which had become warped by flooding damage. Even if insurance paid for the replacement, one has to wonder if the district school's insurance rates took a jump afterwards.

Here's how the flooding happens: The retention basin in the photo (a.k.a. "ecolab", which we have planted with native wetland species), is surrounded on three sides by the high school and receives runoff from the high school roofs and also from nearby parking lots. The basin in turn drains into the system of stormwater pipes underneath Walnut Street. If it rains long enough and hard enough, however, the street's underground stormdrain system becomes filled to the brim, water has nowhere to go, and the basin overflows. At that point, pipes no longer matter and surface flow dictates where floodwater goes. Since water flows downhill, the only way to get rid of the water is for it to flow out to Walnut Street and safely away from the building. Unfortunately, Walnut Street is higher than the high school doorway thresholds. In these heavy rains, Walnut Street floods and becomes a river, and stormwater actually flows towards the high school rather than away.

The highschool has responded to this by placing sandbags in front of all the doorways during heavy rains. These help, but when I stopped by at 1am this morning, after Irene's fury had begun to ease, the music room and hallway into the performing arts center showed signs of having again been flooded. (These photos were taken this morning, after stormwater had receded.)

Exasperated school staff were trying to pump water out of the school. The custodians had just finished prepping all the floors for the return of students, and now they would have to do it all over again. The cafeteria had flooded, and it looked like utility rooms in the basement were now under water.

One staff member tried to blame the vegetation in the retention basin, but all around him was evidence that the vegetation had played no role in the flooding whatsoever.

The drain, photographed this morning, showed no signs of blockage, which is no surprise given that, when the street storm drains become overwhelmed, the water reverses flow and heads in to the retention basin from the street, rather than out.
At 1am this morning, this whole area was a lake.
A curb cut meant to carry surface water away from the retention basin was instead carrying water towards it.
The only solution I see is to lower the curb on the other side of Walnut Street so that the mighty Walnut Street River can flow into the field owned by Westminster Conservatory.

This, in fact, is what some water was doing last night, but to an insufficient extent.
A pond formed in this field last night, next to the Westminster parking lot. Last year, the field was declared by Westminster's own consultants to be a wetland that could not be developed. Since the conservatory uses the highschool performing arts center for some of its performances, utilizing this field more effectively to prevent flooding of the high school seems to be a solution that would benefit all involved.

What needs to be made clear to decision-makers is that the native plantings in the retention basin have no impact on flooding, lest this ecologically vibrant and educational planting become the victim of an invasion of red herring.

Hurricane Irene--A Reprise of Hurricane Bill's Flooding Two Years Prior

Most of these photos are from a post two years ago after Hurricane Bill paid a visit to Princeton. Hurricane Irene, because it passed through 'round midnight last night, was less photogenic, but the impact of the torrential rains was the same. The underground pipes designed to carry away stormwater get overwhelmed, the streets become rivers, and the flow of the water becomes dictated by the lay of the land (and streets).

In my part of town, these massive downpours cause water to flow from the high school and Westminster Conservatory onto Franklin Street. It then takes a right down Ewing before making an unfortunate left turn into the apartment parking lot.

The water then flows pell mell down to the bottom of the parking lot, (photo taken today, after flooding was over)

quickly overwhelms the stormdrain, then heads under the fence into people's backyards.

This is not good. The water came within one inch of the neighbor's threshold.

After flowing diagonally across the block through backyards and around foundations, it emerges across the street from me, spilling over the curb at Ewing and Harrison Street on its way down to the intersection with Hamilton, where it serves as a traffic calming device.

Back at the point where things go wrong on Ewing Street, this unfortunate foray of stormwater runoff into people's backyards could be avoided if the entryway to the apartment parking lot off Ewing Street was raised slightly so that the surface water would continue down Ewing rather than flow into the parking lot.

I proposed this solution to the borough engineer two years ago, to no avail. Reportedly, the borough has no control of the matter, and the apartment complex is within its rights to (unintentionally) "harvest" stormwater from a public street and divert it into the yards of neighbors.

All this seems strange. Since the needed modification is within the boundaries of the borough's street right of way (the street right of way actually includes the sidewalks), the borough would seem within its rights to intervene. In the meantime, history continues to repeat itself.