Mississippi Basin Model construction and instruments

Regular readers may remember my earlier posts about the Mississippi Basin Model from early 2010, July 2010, and Dec. 2010. This was the most comprehensive hydraulic model ever built, meaning it covered the largest land extent of any model. The Corps of Engineers also built a Chesapeake Bay Model and one of San Francisco Bay. The Chesapeake model only had a full operational life of three years and is now gone.  But the San Francisco model still exists and is open to visitors in a warehouse in Sausalito.

Building a model like this is a complex project requiring precise scaling and ultra-precise shaping of the terrain. I found some photographs that help explain how a scale physical hydraulic model like this is constructed.

In the first photograph, metal templates that show the topography have been laid out across the soil at specified intervals. The templates usually have vertical exaggeration, such as 1:10, meaning vertical distance is scaled 10 times greater than the horizontal scale. Then the soil is moved and shaped to approximately match the templates.

At the Mississippi Basin Model, the original earth work, excavating canals, and installing piping was performed by German prisoners of war.  The Germans were repatriated in 1946, and civilian employees completed the rest of the model.  The template method of shaping the terrain was used between 1946 and approximately 1953. But the expansive soil in the area required a shift to the contour method of construction (not shown in these photographs).

In the second photograph, the workers are carefully pouring concrete and shaping the surface to exactly match the top of the templates. This is painstaking work requiring years of experience. The labor, time, and space requirements underscore why building physical models is so expensive.

This is an electronic water-level follower, meaning an instrument to measure water level. Notice that electronic circuits means vacuum tubes!

Finally, here is one of the Stevens chart recorders that plots the water level over time. As the paper drum turns, an ink pens moves up and down on the guide rails.

This is a January, 2010, photograph of one of the controls rooms at the Basin Model. Since then, all the Stevens recorders have been removed, probably stolen.

Historical black and white photographs courtesy of the Coastal and Hydraulics Laboratory, Engineer Research and Development Center, US Army Corps of Engineers.

Condemned Beach Houses at South Nags Head, North Carolina

Long-term readers may remember my 2010 article on the group of condemned beach houses at South Nags Head, North Carolina. In 2010, the surf zone was literally under the piles that supported the houses, and everyone assumed they would soon collapse. The City had condemned them because of exposed septic tanks.
To everyone's surprise, the houses are still standing. And now they are perched on a beautiful wide beach, courtesy of the recently-completed beach fill. I do not understand all the details, but the owners are suing the city to be allowed to re-access their properties so that they can fix them up and un-condemn them. Only in America....

The beach nourishment project was conducted between May 24 and October 27 of 2011. Hurricane Irene on August 27 interrupted the work. For safety, the dredging company moved their equipment to Norfolk, Virginia. Storm waves caused extensive adjustment of the nourished beach profile, but no loss of sand within the project area (Kana et al., 2012).  Adjustment means sand moved deeper on the profile and morphologic features like sand bars formed, but the overall volume of sand remained within the project boundaries. Because of delays in securing federal funds for a comprehensive Dare County beach nourishment project, the Town of Nags Head elected to fund an "interim" beach nourishment locally. Total sand placement amounted to 4,600,000 cubic yards. This may be the largest locally-funded beach nourishment project completed in the United States.
Some notes on beach projects:

When confronted with severe beach erosion, local, county, and Federal authorities can choose four broad classes of technical and management alternatives (Coastal Engineering Manual, 2008, Part V.3):

1. No action
2. Controlled and strategic retreat
3. Hold the line and refuse to retreat
4. Replicate or augment the natural sediment supply to the region with artificial beach nourishment.

1. The first option is often followed on undeveloped coasts, such as in National Seashores. But even the National Park Service is now selecting to add sand to some of their eroding parks.

2. The second option, strategic retreat, is politically difficult because property owners lobby their politicians to "do something" to protect their valuable beach-front property. And, towns and municipalities derive major tax revenue from beach property, whose owners are often wealthy and often only occupy the premises temporarily.

Nevertheless, in the face of rising sea level, many communities are confronting the previously unthinkable fact that some areas will be impossible to protect and maintain. Also, taxpayers from inland areas complain that wealthy beach residents voluntarily purchased their properties in hazardous geographic locations. Why should general taxpayer revenues pay for storm recovery to let wealthy people live at the beach and profit from the appreciation of their houses (i.e., capitalism for the profit, but socialize the risk)?

3. The third option, "hold the line," was popular in the early-mid 20th century. It consists of building massive sea walls or shore-front stone revetments to mark the permanent position of the shoreline. One side is ocean, the other is city. The 1900-vintage Galveston Seawall is an example of this type of project. Seawalls have many disadvantages. They:

• Are difficult to design and expensive to construct.
• Have aesthetic issues
• Require maintenance and are vulnerable to major storms.
• Are environmentally troublesome (there is little habitat in front of a concrete wall).
• Offer only limited recreational opportunities.

Because of cost, environmental, and permitting issues, we will probably not see new major seawall construction in the United States.

4. The fourth option is more and more popular around the world. A beach nourishment project has as its intent to replace sand onto a shoreface from where sand was lost over the years due to natural and man-made reasons. Most beaches around the United States are far from "natural" any more, and most are sediment-deficient because of various man-made reasons. These include:

• Dam-construction on rivers
• Sediment trapping by jetties at inlets
• Sand lost offshore due to harbor and channel dredging, followed by deep-water disposal.
• Sand-mining from beaches
• Loss of sand sources due to paving and urbanization
• Armoring of bluffs and banks

The concept of a beach fill is to pump sand onto the beach from an offshore deposit or bring in sand using trucks. The South Nags Head project is an example of hydraulic pumping from an offshore deposit.

Many critics state that a beach fill is fundamentally a failure because eventually the sand will wash away. Of course it will - that is the function of a beach! The beach serves as a flexible and sacrificial buffer to dissipate storm wave energy and protect upland development. Regular maintenance is one of the costs of living at the beach. The cost of periodic renourishment is low compared to the economic activity generated by wide recreation beaches. Think of the alternative: who comes to the coast to look at a seawall?
This is a view of the barrier island at Duck, about 25 miles north of South Nags Head. Unlike Nags Head, Duck has been relatively stable and has not suffered net beach erosion over the last half century. In this view, the Atlantic ocean is to the left and Currituck Sound to the right. The undeveloped land in the foreground belongs to the U.S. Army Corps of Engineers and is used for their Field Research Facility. It was originally a bombing range in World War II and reverted to the Corps of Engineers in the late 1960s. It is obvious where commercial property begins beyond the Army property. Much of the island has been so thickly developed, it is essentially urban.

On the Federal land, the first row of sand dunes is thickly vegetated. The frontal dune all along the Outer Banks was built by the Civilian Conservation Corps during the 1930s - another example that the beaches are not "natural." This is a photograph from the 43-m (120 ft) observation tower, which is used for experiments and continuous video imaging.
This is a view of the research pier.  Long-period swells are approaching almost perpendicular to the shore. This is the best view in Duck other than from an airplane!

The view north from the tower shows some palatial vacation "bungalows."
This photograph shows workers planting grass on a beach restoration project. The date and location were not recorded, but the scene is likely the Outer Banks. The National Park Service and other Federal agencies sponsored many dune and beach restoration during the late 1930s. These also served as work relief efforts during the Great Depression. Photograph from the Beach Erosion Board Archives, U.S. Army Corps of Engineers (from the Coastal Engineering Manual, Part I, Chapter 3).  For more information on dune construction, see Schroeder, Dolan, and Haden (1976).

References:

Coastal Engineering Manual. 2008. Shore Protection Projects, Part V, Chapter 3. Engineer Manual EM-1110-2-1100, US Army Corps of Engineers, Washington, DC (avail. online, http://publications.usace.army.mil/publications/eng-manuals/EM_1110-2-1100_vol/PartV/Part_V-Chap_3.pdf, accessed 22 June 2012).

Kana, T.W., Kaczkowski, H.L., Traynum, S.B., and McKee, P.A. 2012. Impact of Hurricane Irene during the Nags Head Beach Nourishment Project. Shore & Beach, Vol. 80, No. 2, pp. 6-18.

Schroeder, P.M., Dolan, R., and Hayden, B.P.  1976.  Barrier-dune construction on the Outer Banks of North Carolina.  Environmental Management, Vol. 1, No. 2, pp. 105-114.

Demolition of Hangar 3 at the Waterways Experiment Station, Vicksburg, Mississippi

Hangar 3 was one of four aircraft-type hangars acquired by the Waterways Experiment Station (WES) sometime in the late-1940s or early-1950s. When complete, it covered 58,700 square feet. Recall that WES is the research and development laboratory operated by the US Army Corps of Engineers in Vicksburg, Misissippi. After World War II, a lot of surplus military equipment and infrastructure was available, and I assume WES acquired these hangars from the Army Air Force or equivalent for free or at low cost.
Two of the hangars were used as shelters to cover hydraulic models. Hangar 3 was transferred to the Coastal Engineering Research Center (CERC) in 1983. CERC has now been incorporated into the Coastal and Hydraulics Laboratory (CHL). As the years go by, fewer and fewer physical hydraulic models are used due to high construction cost, water use, and time. Therefore, there is no need for some of the hangar space.
Not much is left in this interior photograph. But you can see why a hangar is a brilliant design: the strong arch allows a vast floor space to exist without the need for central pillars or supports. I assume originally these hangars could be lengthened as needed by simply adding more arch girders and roof panels.
The blue woven matting was used for wave dampening in hydraulic models.
The hangars were equipped with serious electrical supply (for pumps) and bright lights. During tests, paper confetti was thrown into the water and photographed with time-lapse photography. The cameras were mounted on walkways suspended way above the models.
It does not take long for a commercial demolition crew to tear down the metal panels with a cutting machine. So sad...

April 9, 2012 update: My wife informed me that the roof is totally down.

All photographs taken with a Fuji F31fd compact digital camera.

June 2015 update: Hangar 4 has also been demolished to make way for the new headquarters building.

On the Beach, South Nags Head, North Carolina - 2010

East Seagull Drive, South Nags Head, North Carolina

South Nags Head is a summer playground of sun, surf, beer, and jolly good times. It's also an area of uncontrolled overbuilding on the rapidly eroding barrier island. These cottages on East Seagull Drive have been condemned because they are in imminent danger of collapsing into the surf. The view above is looking to the north, with the Atlantic Ocean to the right.The dune line is well landwards of the cottages.

The cottages were originally built on piles because in this environment, occasional flooding is inevitable. But as you can see in the photograph above, the beach has eroded so severely, the original piles were undermined. To keep the houses from collapsing, extension piles were added below the original ones. The bags are geotubes filled with sand to protect the houses. North Carolina law only allows such bags when a house is threatened. Also, North Carolina no longer allows any hard structures like rock seawalls to be erected as shore protection devices (Update: this may no longer be true as of 2020). I wish other states would follow this example.

Exposed septic tanks, South Nags Head, North Carolina

When the septic tanks are exposed (the concrete tubs above), the town or county condemns property. But then a major problem arises: what to do with the structures? FEMA formerly funded removal of houses, but I was told that the program ended. The town is taking legal action against the homeowners to remove them, but the town will not pay any of the costs. If the owners walk away and the structures collapse, the town would have to foot the bill for hazardous debris removal, not a trivial issue in the marine environment. Consider also that taking over the properties would not yield a salable commodity for the town. The town might do a beach nourishment to add enough sand to un-condemn the houses. Then they would be back on the tax rolls and generate revenue. It is an odd twist of logic.

Notice that even though only five years have passed since the disaster of Hurricane Katrina, we still are politically too cowardly to ask serious questions about whether people should live in hazardous locations, and whether municipalities have a responsibility to provide protection and services to residents of these hazardous areas. 

• Should developers be restricted by means of setback lines? 
• Why don't building codes require highly robust construction, thereby thwarting the quick buck artists who build shoddy homes and move on after selling to naive buyers? 
• Should the buyer beware? 
• Is uncontrolled building "capitalism," while spreading the rebuilding risk throughout the town/county is not considered "socialism"? 

These are all troubling questions.
The scene above shows swells from Hurricane Danielle on August 29, 2010. I took this photograph from the U.S Army Corps of Engineers' Field Research Facility (FRF) pier at Duck, NC. They are about 9-10 second period and approaching the coast at an unusually steep angle. The FRF has an excellent web page with live cameras, wave statistics, and other oceanographic data:

http://www.frf.usace.army.mil/