West Marsh Water Conveyance: Project Update #3 (Prepping for Precast Concrete)

A shot from above for scale -- Jason and Mike are setting pins to establish the bottom elevation of the new structure

Much of this past week at the project site has involved clean-up of the demolition debris, hauling to an off-site recycling center, and preparation for the precast concrete structures that will serve as housing for many of the water management components featured in our new design.

A few yards of concrete below the precast structures
are extra insurance for long-term stability

While work at the site never stopped, we also spent a good part of the week waiting for final confirmation from the geotechnical and structural engineering team to be sure that the soils could support (a) more than 70,000-lbs of precast concrete over a ~10 x 12' area, and (b) our associated sheet pile "flume" design -- which will extend from the precast on the marsh side of the structure, more or less north to the Bay.

The sheet pile component is further complicated by the fact that we need to design for a dike crossing that typically will only need to accommodate a pickup truck (or MULE), but periodically will need to accommodate a tri-axle dump truck loaded to 75,000-lbs large limestone (for protection from the destructive forces of wind and waves on the bay).

Mud on mud -- the mud mat from above

While deemed to be marginal based on soil borings and related geotechnical analysis (not a huge shocker), the substrate was ultimately determined to be suitable. A big relief.

Our contractor still decided to add extra insurance and install a 5-6" thick "mudmat" of concrete to serve as a stabilizing foundation beneath the precast. Four discrete concrete segments will be installed as two stacks of two structures -- tied together to form one large rectangle that is split into two chambers.

This is really the heart of the new design. Not only will it house a new pump, it will also be equipped with screw gates, flap screw gates, stop logs, and debris/carp screens. I will get further into what all of these components are and what they are designed to do later, but for now, suffice it to say we're laying the groundwork for increased water conveyance between the bay and the marsh, with much more capacity to provide that connection in a fish and wildlife-friendly way. In many ways, the new system will act much like the old. But our new design will be much wider, much more attractive to migratory fish, and generally much more versatile from a water management perspective. It's really exciting.

The reinforced and reinforcing "mud mat" being poured and leveled in place

A 35-ton crane set to position the first of four precast segments

The first precast segment in place; the next will rest along side it (where Jason is standing) -- the third and fourth
will be stacked on the bottom two, tied, and sealed together

Weather kept us on our toes yesterday and kept us from working today. We probably picked up 3/4" of rain so far -- not ideal when working in these conditions. We're keeping our fingers crossed that we'll weather the next 12 hours or so without too much more rain because we are forecast to dry out tomorrow and remain dry for the balance of the week. If everything plays out as we hope, we may have the precast all in place by the end of the week. Then it's on to the sheet pile steel!