Of berms and bacteria - a few updates

As discussions of these issues gather momentum, more resources become apparent, and this is simply a post with a few more links and recommendations. The Federal Government has now approved the berm building, to be paid for by BP. However, there remains much confusion around the project, some of it reasonable, some not. For example, the image at the head of this post is from the Times Picayune, under the headline “Obama orders BP to build $360 million barrier islands.” No, this is not what this project is about – what are planned are emphatically not barrier islands, but simply walls of sand; this error is, of course, politically valuable, and recurs in many different contexts.

Now, the Deepwater Horizon Unified Command has held a meeting “to discuss the barrier island berm proposal” (there it is again). The meeting was held last Tuesday afternoon with time for comments closed at the end of the following day. The link can take you to the agenda for the meeting and the responses – all 174 pages of them – can be viewed here. They are, understandably, overwhelmingly in favour of the project. However, they are also hugely varied, some long and thoughtful, some short and emotional, many are anonymous, and at least one is in Russian. From a random sampling, I selected two: first, one of the few in opposition, “This insanely useless stopgap will cause more damage than it would supposedly prevent. I liken it to treating a man for snakebite by applying a tourniquet to his neck.” Second, one of more terse and blunt ones: “Dredge now!!!! What are you waiting for? Your delays are costing us our coastal wetlands.” It’s worth noting that the latter is not anonymous, being from one “P.J.Hahn.” Whose name rang a bell – yes, the Director of Coastal Zone Management for Plaquemines Parish has again expressed his views.

On the bacteria question, there is still not much around – a piece in USA Today (probably the one that Jules referred to in his comment) reviews all the reasons against this approach – some of which seem to directly contradict what the microbiologists at Bangor University were saying, as I reported in my previous post. The question seriously has to be asked “isn’t this worth at least trying, in a test area to begin with?” Christopher Gertler, one of the Bangor Scientists, has just been interviewed on BBC radio, and reported no progress in getting an audience.

So, back to the berms. I would thoroughly recommend a piece at Yale’s environment360 blog by Rob Young, professor of coastal ecology at Western Carolina University and director of the Program for the Study of Developed Shorelines. He concludes with the following:

The BP oil spill will be with us for years, not days. In order to move forward in a sensible way, the administration should set up a scientific review panel to vet all proposals for large-scale coastal engineering in response to the spill. The panel should include experts from science agencies like the U.S. Geological Survey and the National Oceanic and Atmospheric Administration, as well as leading academics. The review panel should still be charged with responding very quickly to permit applications, but the public needs to have a higher level of confidence that the best science is being brought to bear on this problem. At the moment, that is simply not the case.

And then there has been the fascinating contact, through this blog, and linked on the posts, with Dallon Weathers, a coastal geologist based at the Pontchartrain Institute for Environmental Resources, Department of Earth and Environmental Sciences Coastal Research Lab at the University of New Orleans. It was this group who conducted, with the USGS, the comprehensive study that I have referred to and used extensively. It’s refreshing to read the views of an intimately involved professional. I have linked to his open letter to Admiral Allen, but will here take the liberty of reproducing in its entirety an earlier one of his pieces – it’s full of thoughtful observations and information, ideal weekend reading!

Since the Deepwater Horizon platform sank April 20th, the Gulf of Mexico surrounding Louisiana has been experiencing an oil leak that is releasing a significant amount of oil into the gulf, and that amount is increasing each day. This oil slick has a very high chance of moving ashore throughout coastal Louisiana, and a swift, effective plan of action is certainly required to mitigate the impacts to our shoreline, and especially our coastal wetlands.
Several days ago, Gov. Jindal and Plaquimines Parish President Nungesser floated an emergency spill response plan that calls for mobilizing a fleet of dredges to immediately begin moving sediment and build a temporary protection berm. This emergency berm is intended to act as a sand boom to keep the spill from oiling the coastline and especially to block it from entering the coastal wetlands. At times, this project has been referred to as barrier island building and has been advertised to having an extra benefit of coastal restoration. Nothing could be further from the truth. This project is not a viable oil protection strategy nor will its implementation build barrier islands or provide any restoration benefits. If this berm is built to the design specifications, there is potential to cause detrimental, long-term physical impacts to the coastal system, to misuse valuable off-shore sand resources, and, through perceived failure and waste, negatively impact the way restoration is viewed by the federal government, as well as the rest of the country.
The location of the proposed berm east of the Mississippi River would front the Chandeleur Islands, Breton Island, and also create a sand levee in the expanse of open water between them. West of the river, it would extend east of Grand Isle from Grand Terre eastward, ending near Empire at Sandy Point. The design specifies that the berm crest will be 6 feet above the mean water line and 20 feet wide. The base will be 300 feet wide at the water line. The material used to make this berm will come from one of two suggested borrow-areas. One borrow-area is a 500 foot wide band located 1 mile off-shore and will follow the extent of the proposed berm along its entire length (about 90 miles). This is approximately the 15-18 foot depth contour. This region of the seafloor is rife with pipelines that could easily be ruptured in the dredging process, which could further add to spilled oil in the Gulf. The other borrow-areas are from identified sand bodies near the river mouth, as well as other sand deposits off-shore on the inner continental shelf.
This project is on a fast track, and it is skirting all standard permitting procedures and environmental impact studies. While the design specifications are very precise, it is clear that there has been no input from any coastal geologist. Let us now discuss this plan as coastal geologists. I present the following discussion to illustrate how this plan is doomed to fail, have long lasting negative impacts on our coastline, and imperil future restoration. The sections that follow will discuss: sediments, waves, and tidal inlets, as well as other potential hazards/effects.
Sediments
Per the design, the volume of sediment required to the build the proposed berm is, at a minimum, 1240 cubic feet per foot alongshore. As the base of the berm at the water line is to be 300 feet, its footprint, and sediment required to build it, will increase with depth of placement. If this material were dredged from 1 mile offshore, it would leave a 500 ft wide by 2.5 ft deep trench extending up to 90 miles. The forecast trench depth is based on the assumption that the dredged material would be nearly 100% sand, and this assumption is false. One mile offshore, in 18 feet of water, much of the seafloor sediment is muddy with low sand content. A larger dredge cut than is assumed by project planners will be required in order to generate enough sediment to build the proposed berm to specifications. This will set back the assumed quick (one or two months) time frame for project completion. Another more important result of a larger dredge cut (greater than 2.5 ft) is a deeper trench in the active beach profile. Dredging operations will liberate a large volume of muddy sediment that will quickly be transported out of the near-shore beach profile under the forcing of waves and currents. The resulting trench will be a void in the near-shore that represents a deficit in the local sediment budget. It will also act as a geometric disruption to the beach profile which will adjust in order to find a new equilibrium shape. As a result, the beach profile, the shoreline, and with it the entire barrier island will move backward. The other borrow plan that calls for mining known sandy shoals is also problematic.
Several of our offshore shoals (St. Bernard off of the Chandeleur Islands, Ship off the Timbalier Islands) contain clean, beach quality sand. These shoals occur farther away from the proposed location of the berm and would require more time to dredge, transport, and put in place. This cumbersome process will increase the timetable of project completion. In addition to this logistical issue, it would be a poor use of our natural sand resources to use these deposits of beach quality sand for a temporary feature. Processes of erosion will scatter the sand across the near-shore seabed where it will mix with muddy sediment, preventing this resource from future use in designs whose goal would be to restore the shoreline. The following section will discuss how waves will interact both with the proposed berm and also the dredge trench in the offshore zone.
Waves
The proposed placement of the berm is in the near-shore and at an angle that is ten times steeper than the natural beach profile. As a result, two things will happen. First, a much greater percentage of wave energy will act directly on the berm, as there is no gently sloping shore face to dissipate it. Second, the waves will tend to reflect off of the steep berm, and act to scour at the base of it twice per wave. As such, sediment will erode from this feature swiftly and the berm will not last long.
Let us now change the focus to the offshore the trench left by dredging. The borrow pit will be at least 2.5 ft deep by 500 ft across and extend for as many as 90 miles. A feature such as this on the seafloor in 18 feet of water will do one thing for sure: modify the wave climate. But how? We could run wave models with existing bathymetry, and then modify the seafloor with a virtual berm and digitally dredged trench, and compare the results. The Jindal-Nungesser plan does not have a provision for such a study. As Gov. Jindal has repeatedly intonated, “The time for studies and waiting is over”. Without a detailed study, we do know that as waves move across the inner shelf, they interact with the seafloor, changing direction and size until they break at the shoreline. Dredging will introduce a perturbation to the near-shore sea floor. Several studies have shown that offshore dredge pits interact with incoming waves and focus wave energy at certain spots such that they experience enhanced erosion. Focused waves would first act on the proposed berm to wash away more swiftly. However, the lingering wave focal mechanism, the dredged trench, would exist for years and continue to focus wave energy on the coastlines of our barrier islands.
Tidal Inlets
In addition to building a berm in front of the barrier islands, the project calls for closing off or severely constricting tidal inlets and passes in order to block the oily water from entering the marshes that lie landward of the barrier islands. As a result, there will not be adequate openings for tidal passage.
In the case of small ephemeral cuts in barrier islands that form during storms, infilling poses little harm, as it is speeding up a natural beach healing process. The natural time scale of these small cuts is as short as days or weeks, or up to a few years, depending on storm frequency and intensity. There are many of these along the Louisiana coast in various stages of self repair as waves push the sand near a barrier island onto shore. I will concede that plugging these small cuts would help decrease potential conduits for oil to enter the marsh. However, inlets that have existed on the order of decades persist for an entirely different reason, and to constrict or close these off would be a bad idea.
Tidal inlets serve one sole purpose. They convey the tide from the Gulf of Mexico to the estuaries which are comprised of inland marshes and bays. Marine life and estuarine health have evolved with this exchange as a necessary process. The volume of water that passes through an inlet during one half of a tidal cycle (high tide to low tide, or vice versa) is referred to as the tidal prism, which is defined quantitatively as the tide range multiplied by the surface area of the estuary. There is a well established relationship where the total cross sectional area of an inlet (depth multiplied by width) is directly proportional to the tidal prism of the estuary that it serves. The larger the tidal prism, the greater the cross sectional area required to accommodate the tide waters. A plan to either block tidal inlets or constrict their flow with a berm, without regard for the necessary amount and type of water passages needed to accommodate the natural tidal prism, is a plan predisposed to failure.
Furthermore, putting sand in an inlet to ‘fix it’ because ‘there is a lack of sediment’ is an incorrect assumption in regards to restoring a viable coastline. This will fix nothing. As discussed, the occurrence and size of inlets is related to the tidal prism (a function of tidal range and estuarine surface area) not sediment supply. The occurrence and distribution of tidal inlets is governed by forces (the tide) that are more powerful than an engineered berm can handle. Plugging a tidal inlet or building a levee to block its flow is a futile endeavor. Swift tidal currents will cause the berm to erode as sediment placement occurs, and thus extend the project completion timeline. If blocking or constricting tidal flow at any inlets is completed, an imbalance in the tidal prism exchange per the relationships described above would unceasingly work towards equilibrium, resulting in new inlet breaches or increased scouring at tidal existing passages.
Other consequences of inlet closure are ecological in nature and include: disrupting of salinity gradients within the estuaries; interfering with the transfer of the movement of nutrients back and forth from the estuaries and gulf; and impeding the inshore/offshore migrations of marine life. Instead of plugging these inlets, there are booming techniques and oil collection strategies at inlets that are well documented in the literature, as well as NOAA technical reports and manuals directly related to oil spill response.
Conclusions
Apart from the overarching likelihood that the logistical setbacks described above will prevent berm completion on the time scale of this spill, this project, if built to specifications, will have several negative outcomes. First, it will leave an offshore trench that will become a persistent wave modifier focusing wave energy and enhancing erosion. It will upset the beach profile equilibrium and cause shoreline retreat, and it will act as a sediment sink that will rob sediment from the coastal system until it is refilled. Bear in mind this trench has the potential to extend along the entire length of the project area (about 90 miles). Second, the project plans to utilize scarce natural resources (our offshore sand) in a poorly designed scheme that will leave good, beach quality sand to be cast about the seafloor, making it a less useful resource for future restoration. Third, attempts to significantly constrict tidal flow are unwise, as the forces at work are on too large a scale to control. Any change to the existing configuration, size, or distribution of tidal inlets would cause scouring at existing inlets or even the creation of new inlets at unforeseen locations. Another hazard of dredging in the near-shore is the possibility that one of the dredges would cut a pipeline and cause another spill. Failures realized with this project could impact the future of how we are able to manage our coast in Louisiana. Coastal restoration is expensive and benchmarks for success are difficult to package. Many people, including the federal government, are skeptical of coastal restoration efforts, thinking they are ineffective and not worth the cost. Although this project is not a restoration project, there is a public perception that it is. The failures of this project will cast doubt on coastal restoration in Louisiana as a viable endeavor. This sentiment, that coastal restoration is nothing more than pork barrel spending, could carry into the future and affect future planned restoration.

And if, after all this, readers find themselves in need of a little amusement, they can always consult the latest wise words of Sarah Palin.

Comments

[searoemer]

At first glance the notion of berms appears to be a bad idea. But we need to know what effect a temporary barrier will have on the oil. If we need to survive one or two waves of oil the berm looks like a good bet---but if we need to prepare for prolonged oil baths berms will not help.

[Dave]

As to the use of Hesco barriers in the sand berms and whether they would change the hydrology, a couple of photos of Hesco barriers is worth a thousand words:
http://northshorejournal.org/hesco-barriers-a-photo-primer

[Sandglass]

Worth a thousand words, indeed! Emphatically not a contribution to a "restoration project" and not even a berm in the normal sense of the word.

There are also suggestions, although I couldn't possibly comment further, that there is an element of political and commercial cosiness with respect to the use of Hesco baskets.....

[suvrat]

great lesson in coastal dynamics!

[seo training in urdu]

thanks for sharing information about coastal dynamics.