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Giacomini Wetland Restoration Project: Summary of Construction Under Phase I and II: What Aspects of Construction Substantially Differed From What We Expected?

 

Careful planning paid off for this project in that there were very few "surprises" during construction (other than accidental levee breaches!). However, some aspects that differed from what was anticipated during final design included:

  • Ditches Proverbial "Black Holes" In Terms of Fill Volume: Drainage ditches took an estimated 50% more material than expected, because of the highly unconsolidated nature of the ditch soils (Mark Cederborg, Hanford ARC, pers. comm.), while the borrow ditch north of the West Pasture took less.
  • Dry Areas Not Necessarily "Dry": Shallow groundwater table interfered more with on-site hauling than expected in both the West and East Pastures, even in areas that were seemingly "dry." Changes in hauling conditions even differed depending on the tide despite the fact that the site was not tidal, because hydraulic pressure on the groundwater table during high tides elevated the shallow groundwater table in the pasture.
  • High Tides Even Higher than Expected: Tides were amplified substantially this year relative to the predicted tides at Inverness. The strong winds this summer amplified tides relative to predicted tides in Inverness by as much as 0.2 to 0.8 feet (Mark Cederborg, Hanford ARC, pers. comm.), which increased the difficulty of keeping tides out of the construction site and exacerbated the tendency of "thinned" levees to erode or breach.
  • Abundant Wildlife: There was a lot more wildlife present than might have been expected with the amount of construction activity ongoing. Download the Construction Critters: Wildlife during Construction poster (191 KB PDF) for some photos and discussion of species observed.

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