Holdfast Training Services Trial Blog

Poplar Island

So, I’m actually on site now doing some engineery type things!  However, for obvious reasons taking photos is proving to be a bit problematic.  In order maintain some sort of presence on the blog, welcome to my new two part mini-series, which I’ve catchily decided to call “interesting things that USACE do that the Royal Engineers don’t do”!  Location one:  Poplar Island.

Poplar Island was/is an island in the middle of the Chesapeake Bay, approximately 18 miles south-east of Annapolis.  Historically it was settled in the 1630s, and had a permanent population all the way up until around 1920.  However, due to a number of reasons, mainly human mismanagement, but also natural erosion, the island shank from approximately 1000 acres in the 1840s to less than 5 acres by 1990, and was set to disappear altogether had someone clever not decided to do something about it.  A vast amount of material is dredged out of the Chesapeake Bay each year in order to keep the shipping route to Baltimore open, and some other clever person decided it might be a good idea to use this material to try and stabilise and rebuild the island.

Poplar Island During Construction (bottom photo is probably 2 or 3 years old)

What has been achieved since then is one of the best examples of ‘environmental’ engineering that I’ve ever come across.  Since 1998 USACE have created 1140 acres of ‘new’ wildlife reserve in the middle the Chesapeake Bay.  The technique they use is to create a series of waterproof bunds that divide the ‘island’ up into manageable ‘cells’.  They then pump millions of litres of sediment rich slurry into the cell they are working on, allow the slurry to dry out, then repeat the process for as many times as is necessary to build up the amount of material required for the habitat they are trying to create.  The two habitats being created on Poplar Island are ‘tidal wetlands’ and ‘upland woodland’ in about a 50:50 ratio.  When we visited last month a number of the tidal wetland cells had been completed, but all of the uplands cells were still ‘work in progress’ because they require the ‘finished floor level’ to be significantly higher!

Completed ‘Tidal Wetland’ Cell

Whilst generally successful the tidal wetland cells that have been completed so far provided some challenges, mainly for the biologists creating the habitats.  Initially the channels linking the ‘inland’ water and marshes to the bay were too small and discouraged the large predator fish species from entering which led to an unbalanced ecology.  Subsequent cells have been designed with larger openings and have been more successful.

So far the island is frequented by around 175 different species of birds, including ospreys, and terns.  The terns are interesting; despite having over 1000 acres to choose from, they are habitual, and so return every year to the same tiny section of the island that they have always used!  The biologists are hoping they’ll eventually get the idea, but so far they seem happy on their little patch of mud.  The ospreys are currently living on ready-made posts, but the plan is for them to move into the trees once the woodland sections of the island are far enough advanced.  A significant colony of terrapins has also established itself on the island which the staff are particularly happy about!

Local Inhabitants (Osprey)!

From an engineering point of view project is interesting, but really relies on the sheer volume of material for success.  Now that the techniques have been tried and tested there is little in the way of complicated problems to be solved, and the process is very repetitive.  The one issue the project did have was when one of the bunds was breached/overtopped during a particularly bad storm early in construction.  This led to a significant amount of material being washed away and the bund having to be reconstructed before work could re-commence.

Henry’s Head (and the pumping station from where dredged material is pumped to the cells)

The total cost of the project is set to be around $800m, of which 75% comes from the Federal Government and 25% from Maryland State.  The scheme has proved to be so successful that plans are well advanced to add a 575 acre expansion to the north of the island which would take the total area to approximately 1700 acres.  The ‘construction’ phase is currently due to be completed in 2029, however significant management would be required beyond this date.  If only the Royal Engineers were trusted to deliver something like this!

Other News

I’ve inherited three Officer Cadets!  They were recently sent out on a two day ‘recon’ to gather ‘intel’ on some local critical national infrastructure!  I very much enjoyed listening to their backbriefs and grilling them ‘Warfare Wing style.  The next “interesting things that USACE do that the Royal Engineers don’t do” blog will be on the Raystown Dam and reservoir, an equally colossal project!

Hello folks, just a short, sharp snip it of some interesting bits going on in the design office here in Sydney’ M4 East motorway project.  Clearly, those two terms are rarely linked but today I think they make the cut.

“Info Only” – Interesting proposal by AEH (AECom & Hyder JV)…Clear lack of comms…

Attached below are two images.  1.  Plan of mainline tunnel with surface loads indicated.  2.  A screen shot showing the proposed AEH foundation design within a section of mainline tunnel I was analysing for crown loads and canopy tube design.  The confliction with our 4m rock bolts emanating out from the tunnel lining is not show.

AEH released their package today for various permanent M&E structures to be installed above the tunnel.  I’m in the process of assessing the shotcrete lining thickness and elephant foot dimensions based upon surface loads, overburden, relaxation, ground water etc… The original idea was to install a raft foundation which we were more than happy with (10.5m above).  The fact that they now wish to terminate their piles 2m above the crown of the Westbound mainline tunnel is one thing… the fact that they only put Macmillen Jacob Associates (MJA) down as “INFO ONLY” on the cross discipline review form is another!  Unbelievable…

Presumed next step..Cost analysis to compare the additional excavation + lining thickness + time+programming required to support new proposal vs an reconsidered AEH foundation design.   Interesting stuff but clearly not my main priority at the min…