North Carolina’s valuable pile of sand

This land isn’t permanent, it moves. This whole pile of sand moves with every storm with sea level rise, and it’ll continue to move for hundreds of years. And we’ve tried to engineer it like it’s Raleigh, like it’s a rock, but it’s not. It’s sand.” — Stanley Riggs, former professor of marine and coastal geography. — Courier-Tribune, Sept. 15, 2018

The pile of sand Riggs is talking about is the Outer Banks, the 200 mile string of barrier islands off the coast of North Carolina. His concern is the continuing development on that long sand bank, and the general lack of interest in restricting it.

Map of North Carolina’s Outer Banks

Map of North Carolina’s Outer Banks. Image from U.S. National Parks Maps

Given that the Outer Banks consist of shifting sands, sit barely above sea level, and are located in a part of the world subject to violent ocean storms, why is there continuing development?

The developers know that building houses and roads on sand is asking for trouble. The difficulties associated with the stability of buildings have been researched for well over 2000 years. Matthew, a great authority on the subject, said: ”And everyone who hears these words of mine and does not do them will be like a foolish man who built his house on the sand. And the rain fell, and the floods came, and the winds blew and beat against that house, and it fell, and Great was the fall of it.“ — The guy knew what he was talking about.

Image of fallen house on Hatteras Island, North Carolina

fallen house, Hatteras Island, Outer Banks, North Carolina. Image: Steve Early/ Virginia Post

North Carolina’s Coastal Resources Commission studied the situation in 2010 and wrote a report predicting a 39 inch rise in sea level by the year 2100, enough to flood coastal towns and wash away the existing built environment on the Outer Banks. Advocates for economic development in twenty of the State’s coastal counties formed the NC-20 group to lobby against the report which, they said, was based on bad science. It would, they argued, scare away business and tourists. The Legislature agreed, passed a bill prohibiting scary predictions, and ordered the commission to write something acceptable to the economic development people. The result was a 2015 report predicting a sea level rise of 6 – 8 inches by the year 2045. What a relief.

As well as the thousands of year-round residents and summer-cottage owners, the Outer Banks attract several million tourists each year. It’s a big enterprise and an important tax generator. Of course government wants to support it, and they’ll continue to do so until the environmental situation becomes untenable. In the mean time, the real estate developers, estate, agents, house builders, private insurers, road contractors, shop owners, and rental accommodation suppliers, will all get paid. And the tourists will continue to enjoy fun in the sun.

What about the property owners? Well, in real estate, timing is everything. They’ll just have to watch the market and judge when to sell — that’s if they even care; purchasing beach-front property is not a poor man’s game. And if a hurricane happens to blow their stuff away, there’s always FEMA and the Feds (the American taxpayer) to help them rebuild their houses, on taller stilts if necessary.

Beach houses on Hatteras Island, August 2011 after Hurricane Irene

Beach houses on Hatteras Island, August 2011 after Hurricane Irene. Image: Telegraph/AP

If sea level rises faster and higher than the 6 – 8 inches currently mandated by North Carolina’s law makers, who will bare the cost? Probably the people living in towns along the State’s low lying mainland coast. The houses they live in are not summer homes or holiday rentals — it’s all they’ve got.

Map of North Carolina showing physical regions

North Carolina Physical Regions. Map image from NCPedia

 

Light Rail Transit – the right choice for Norfolk VA

Siemens S70 Light Rail vehicles at MacArthur Square, Norfolk VA

The Tide Light Rail vehicles at MacArthur Square, Norfolk VA. Image by Mega Anorak at Flickriver.com

It’s an eight minute ride on The Tide, from the Eastern Virginia Medical Center campus in Norfolk’s Ghent district to downtown Norfolk. The Tide is the city’s Light Rail Transit line. Opened in 2011, the line runs seven and a half miles from its eastern terminus at EVMC/Fort-Norfolk, through downtown Norfolk, to its western terminus at Newtown Road. From end to end, the ride takes 18 minutes, including brief stops at nine intermediate stations.

Map showing route of The Tide Light Rail Transit Line, Norfolk VA

Route of The Tide Light Rail Transit Line, Norfolk VA. Termini marked in blue and circled

The route to the west from Downtown Norfolk is far from scenic. It runs roughly parallel to Interstate-264, which means that the passing scene consists mostly of highway support structures  — underpasses, overpasses, level-crossings, and the like. Also on view are commercial buildings and parking lots. Many parking lots. Suburban residential areas along the the way appear like untamed nature by comparison. The ride is comfortable and entertaining. And it gives one an appreciation of the enormous amounts of concrete and blacktop used to sustain our automobile economy.

Interior view of Siemens S70 Light Rail Vehicle

Interior view of Siemens S70 Light Rail Vehicle. Wikimedia Commons

The Tide is presently equipped with nine Siemens S70 Light Rail Vehicles. These are double-ended cars with operating controls at both ends and doors on both sides. The same vehicles are in use or on order at nine or ten other US cities.

Diagram of the Siemens Light Rail Vehicle

Diagram of the Siemens S70 Light Rail Vehicle. Image from Wikipedia

According to the August 13, 2016 issue of the Virginia-Pilot, building the 7.4-mile line cost $318.5 (including $86 million in cost overruns). That year, weekday ridership had reached 4,800, and the operator, Hampton Roads Transit, declared the project a success. There’s been talk since then about extending the system into other parts of Norfolk and into Virginia Beach.

Investment in Light Rail Transit systems makes perfect sense. They are clean, quiet, safe, popular, and they do the job. But for Norfolk, the big question is this: Expand the transit system or Protect the city against the rising sea — which comes first?

The Tide Light Rail, Norfolk VA. View of EVMC/Fort-Norfolk terminus

The Tide Light Rail, Norfolk VA. View looking south-east from the EVMC/Fort-Norfolk Station. Image by Jon Bell

 

 

Norfolk VA – Retreat, Dig-In, or Both?

The Coastal Plain — the land bordering the Atlantic Coast from Florida to Cape Cod — was once sea bottom. It has low topographic relief and extensive areas of wet land and drowned valleys such as the Chesapeake, the Delaware, and Long Island Sound. From the air the plain looks as flat as a pancake. The part of the plain that extends eastward into the Atlantic, forms the continental shelf. Norfolk, Virginia, is located on the eastern edge of the plain, on land the sea now wants to reclaim as its own.

Water view of Norfolk VA

Norfolk VA viewed from across the Elizabeth River. Wiki Commons image

It’s a pleasantly warm November day in downtown Norfolk. The sun is shining on the Elizabeth River and there’s nothing to suggest to the casual visitor that the city is under threat from an encroaching ocean. But the Inhabitants of the city are well aware of the threat and are constantly reminded of it.

For example, here’s part of a memorandum from the administrators of the Eastern Virginia Medical School to its students, faculty, and staff, concerning campus safety:

[The school] is located in a low lying coastal area; Norfolk’s elevation and its proximity to several rivers make it susceptible to flooding. Nearly every year, and sometimes several times throughout the year during times of heavy rain, hurricanes or nor’easter storms, the EVMS Community is threatened with the potential of precipitation, tidal and/or wind-driven flooding and/or low-land flooding.

The memo goes on to offer safety tips: If advised to evacuate your home, do so immediately; If there is any possibility of a flash flood, move to higher ground; If possible, move essential items to an upper floor; Turn off utilities at the main switches or valves; Do not walk through moving water. As little as 6 inches of moving water can make you fall; Do not drive into flooded areas. If floodwaters rise around your car, abandon the car and move to higher ground if you can do so safely.

The EVMS campus is located a mile or so north-west of Norfolk’s downtown core, in the district called Ghent. But the threat of flooding is not restricted to any one area, it is a constant concern throughout the city. 

Norfolk VA storm surge map

Norfolk VA storm surge map. Virginia Dept. of Emergency Management

What the map tells us is that, under present sea level conditions, the surge from a category three hurricane would put most of the city under several feet of sea water. However, because the level of the sea is continuing to rise, the potential for catastrophic flooding will increase with time.

The grey area on the map at the north end of the city marks the location of Navel Station Norfolk, the nations largest navel base. The base is particularly vulnerable to storm surge. When a serious storm approaches, the fleet wisely heads out to sea.

Navel Base Norfolk from the air

Navel Base Norfolk. Wiki Commons image

So what can be done to protect the city?

The US Corps of Engineers – Norfolk District, has produced a 438-page report titled ‘Coastal Storm Risk Management Feasibility Study’ in which it proposes building — at a cost of $1.57 billion — a series of storm surge barriers and sea walls. The scheme is designed to protect the city from a 50-year storm, assuming a rise in sea level of 1.5 feet. However, since no one knows what level the sea will actually rise to, or how strong future storms will actually be, and considering the high cost of the plan, it’s unlikely the city will move on the recommendations any time soon.

The May 21, 2018 issue of Inside Climate News, quotes George Homewood, Norfolk’s planning director:

“I truly believe that technology will begin to address some of our climate issues and some of our sea level rise issues, . . . There are obviously some issues, but in theory, can we live with water? Can we make it so the water comes, the water goes, and we just keep on keepin’ on?”

In the same issue, the author, Nicholas Kusnetz, writes:

“Norfolk officials say they don’t know how exactly their city will cope in the long term if seas rise quickly. They voice an understandable, but ultimately troubling faith that someone, somehow, will figure out a solution. Homewood acknowledges that, on some level, it won’t be enough.”

The light at the end of the tunnel

My last post titled, ‘Help! The Hudson River Rail Tunnel is falling to bits’, elicited this question:

Is the tunnel as straight as the map suggests?

Map showing route of Hudson River Rail Tunnel from North Bergen, NJ to Penn Station, NYC

Map showing route of Hudson River Rail Tunnel from North Bergen, NJ to Penn Station, NYC. Image from Draft Environmental Statement, June 30, 2017; Hudson Tunnel Project.

The answer is yes, it is in reality as straight as a die, at least in plan view. tunneling is a costly business; the least expensive way to dig a tunnel is to keep it absolutely straight. The following YouTube video created by Konstantin Gorakine titled, ‘Tunnel ride under Hudson River to Penn Station, NYC’, will convince you. It convinced me.

You’re a visitor and you want to experience ‘authentic’ New York City life. To the millions of people who live and/or work in the city, there’s nothing more ‘real’ than the daily commute. About one hundred thousand commuters pour into the city through the Hudson River Rail Tunnel every weekday. And that’s just one of the entry points. Get a feel for what it’s like; take the same train ride. But there’s no need to punish yourself; avoid the rush hours.

The NJ Transit train ride from Penn Station, NYC to Penn Station, Newark, NY, makes for an enjoyable excursion — about 20 minutes travel time, each way. If you leave at about 10:30 in the morning, you can be back by noon. Navigating Penn Station is an authentic New York experience in itself.

Map showing location of Penn Sta., NYC in relation to Penn Sta., Newark andNorth Bergen Tunnel portal

Map showing locations of Penn Sta.,NYC, North Bergen Tunnel portal, and Penn Sta., Newark, NJ

Help! The Hudson River Rail Tunnel is falling to bits.

A few days ago, New York Governor, Andrew Cuomo, accompanied by a film crew, paid a late night visit to the Hudson River Rail Tunnel. His objective was to publicize the sorry state of the tunnel’s physical condition, and to thereby convince the Trump  administration that federal funding is urgently needed to help finance the construction of replacement tunnels. The New York Times called it a Hollywood stunt “ . . . designed solely to win over an audience of [the] one who sits in the Oval Office.” True or not, Mr. Cuomo’s efforts should be applauded. It’s encouraging to see a politician up to his elbows in honest dirt rather than mucking about in the sort politician’s usually wallow in. And apart from that, he does an excellent job of pointing out the tunnels’s defeciencies. Listen to Mr. Cuomo’s exposé on the following YouTube video and decide for yourself:

The tunnel (actually a pair of single-track tunnels), presently operates at or above capacity. About 450 trains pass through the tunnels each weekday (averaging one train every six minutes) carrying about 100,000 New Jersey commuters (plus Amtrack passengers) to Manhattan in the morning and back to NJ in the evening. Whenever the tunnel is shut down, those citizens have no other practical way to get to work because the tunnels and bridges for road and subway traffic are also at capacity.

Map showing route of Hudson River Rail Tunnel from North Bergen, NJ to Penn Station, NYC

Map showing route of Hudson River Rail Tunnel from North Bergen, NJ to Penn Station, NYC

The 14,575 foot tunnel has been in use for 108 years and shows it. The flooding that occurred during hurricane Sandy in 2012, entered the tunnel through the portals at its eastern (Manhattan) end. As Mr. Cuomo points out in his video, the corrosion caused by salt water has intensified the deterioration within the tunnel. In view of his other comments concerning, rotted steel, crumbling cement, exposed rebar, damaged electrical gear, leaking walls, it’s fair to wonder about risk to human life. Are the tunnels in danger of collapse?

The experts say no. Here’s why:

The tunnel was driven through solid rock except were it passes under the river through accumulated silt. That’s where it proved necessary to construct the tunnel using 23 foot diameter, cast iron rings, each weighing 22 tons. The 2.5 foot wide rings were bolted together, one after the other, to form the two tubes running under the river. The seams between the rings were caulked to make the tubes watertight. The tubes were then lined with concrete. The structural integrity of the tunnel depends on the cast iron shells, not on the crumbling concrete that lines them. That said, if the deterioration inside the tunnel continues to worsen, it will eventually become impossible for trains to pass through it.

The next image shows one of the cast iron rings used to construct part of the Hudson River Rail Tunnel. It was one of the exhibits at the 1907 Jamestown Exposition.

Cast Iron Tunnel Ring exhibited at 1907 Jamestown Exposition

New flood gates will keep NYC road tunnels dry next time the city’s streets are under water

New York City was struck by hurricane Sandy six years ago. Since then, while the city has updated its flood-risk maps, it hasn’t taken any concrete steps to prevent storm surges from entering the city. That’s not surprising; the city is rimmed by more than 580 miles of coastline, most of it at risk from storm surge.

Map of NYC flood-zones. Image from NYC Mayor’s Office

NYC flood-zones. Image from Mayor’s Office

Instead, city planners have focused on upgrading critical systems, such as: ‘hardening’ electrical systems; relocating backup generators; flood proofing subway openings; designating more emergency shelters for flood victims. Resilience is a word the city planners like to use these days. In other words, let the seas rise, we’ll deal with the water when it comes.

the most impressive example of this approach so far has been a $64 million project (now complete) to install flood gates on two of the city’s four road tunnels, namely: the 9,117 ft. Hugh L. Carey (Brooklyn-Battery) tunnel under the East River, and the 6,414 ft. Queens-Midtown tunnel, also under the East River. Both suffered serious damage during the Sandy flooding, the Hugh L. Carey tunnel, especially  so. The portals of both tunnels are located within zone-1 (first zone to flood).

18517B9F-3016-4BA7-AC8C-828DEBB399F3

Map showing location of tunnel flood gates

Eight steel flood gates have been installed, two at each tunnel end. The gates were manufactured by Walz & Krenzer, Inc., of Oxford CT. (“Watertight Closures for the Marine industry since 1939”), one of about 50 U.S. companies involved in the flood-control equipment business.

Each gate weighs 44,600 pounds (about 20 tons), and measures 29 ft. wide by 14 ft. high by 22 inches thick.

34E3624B-22C4-4293-A2F3-4DAC393F16F1

MTA Photo

The gate swings on two massive hinges. When parked in its open position, the free end rests on jacks.  Assuming  a two man crew, a machine such as a forklift is needed to help close it. In the event of a storm, the crew will first remove steel cover-plates from  a trough that stretches across the mouth of the portal. Once the gate is closed, the crew will latch it to the face of the portal and to attachments within the trough. Compression seals around the gate’s inner edge will make it watertight.

2E3DCDFC-A815-4DB5-9C21-414FF0976DA8

MTA photo

The only way to see these gates up close is to drive through the tunnels. You’ll get only a second or two of observation. Considering New York’s frantic traffic, stopping to gaze at the thing is something no prudent driver should attempt.

It’s just as difficult to get a good look at the gates while on foot. Barriers of one sort or another along the streets surrounding tunnel entrances inhibit pedestrians from peering over walls. The Morris Street footbridge will eventually provide a platform from which to observe the Hugh L. Carey flood gates at the tunnel’s Manhattan end, but that bridge is being renovated and will not be available for use this year.

 

Why did the I-35W Highway Bridge in Minneapolis fall down?

Several readers of the post titled ‘Smart Bridge across the Mississippi River’ have asked if the cause of the collapse of the old I-35W bridge has ever been officially determined. The answer is yes.

I-35W highway bridge which collapsed November 2008

Old I-35W Highway Bridge. Image from en.wikipedia.org

The National Transportation Safety Board is mandated by Congress to investigate transporation accidents and determine the probable causes. The NTSB issued its report (HAR0803) on the I-35W bridge collapse on November 14, 2008. It’s a detailed, 162-page, engineering study.  Here’s an excerpt from the report’s conclusions (the italics are mine):

[T]he probable cause of the collapse . . . was the inadequate load capacity (bridge was not strong enough), due to a design error by Sverdrup & Parcel and Associates (the bridge designers) of the gusset plates at the U10 nodes (specific places within the bridge structure described in the report), which failed under a combination of (1) substantial increases in the weight of the bridge which resulted from previous bridge modifications, and (2) the traffic and concentrated construction loads on the bridge on the day of the collapse.

What exactly are gusset plates?

The collapsed bridge belonged to a class of bridge called truss bridges. These are bridges assembled from straight pieces of steel — girders, beams, angles, etc. — that are connected together in the form of triangles, and whose ends are tied together by gusset plates. The NTSB report defines a gusset plate as “A metal plate used to unite multiple structural members of a truss.

Gusset plates on Old I-35W highway bridge in Minniapolis, MN

One of the bridge’s ‘nodes’ where structural members were joined together by gusset plates. Image from NTSB report.

The I-35W bridge had a total of 112 nodes. The gusset plates at each node were 1/2 inch thick steel. According to the NTSB report (page 128), they should have been 1 inch thick. That was the design error. Catastrophic failure of two or more gusset plates in the central region of the bridge initiated the sudden collapse.

As noted in the report’s conclusions, there were two contributing factors:

(1) The bridge was initially constructed with 1.5 inches of concrete as the deck surface. To combat corrosion of the underlying steel, the layer of concrete was eventually increased to an average of 8.7 inches by the time the bridge collapsed. The weight of the additional concrete increased the dead load on the bridge by 13.4 percent (page 23).

(2) On the day of the collapse, deck renovations were underway. The additional weight of construction equipment as well as piles of sand and gravel for making cement were concentrated on one side of the bridge.