Dam Construction Update for June 16 – June 20, 2014

From Pat Colgan

Week of June 16 to June 20…

As I sit here looking out my window Friday afternoon, June 20, 2014, watching the flooding, debris filled Maquoketa River roaring by our cabin at a flow rate of 8000 cubic feet per second (cfs), I think back only to yesterday when the river was at 600 cfs and then to Monday afternoon when the the river was at 80 cfs. Average river flow for this week is 350 cfs. Depending on which day I wrote this update this week my report would be remarkably different. This week offers a vivid reminder that our river is a uniquely “flashy” river where flooding waters can occur quickly and sometimes severely.

As of last Monday, June 16, our rebuild  project had just experienced 3 wee ks of excellent construction weather and low river flows which allowed significant progress in Phase 1 work. By Thursday afternoon this work progress was continuing with many significant tasks being achieved even though the river was rising rapidly. Upstream and downstream cofferdams protected the work in progress. Around 3:00 pm that day a line of storms forced work to suspend mainly due to lightening. The storm lasted for an hour or so effectively ending work for the day.

More rain Thursday evening. When I went to bed at 11:00 pm, the river was at 1000 cfs. When I got up at 4:30 am on Friday, it had increased to 4500 cfs. I went to the dam and took pictures when it was light enough, about 5:30 am.

Even though the cofferdams are sound all of the work on the upstream side and downstream side was flooded. Despite all this, the contractor Lunda, was able to work on higher ground to install some sheet piling needed to be able to excavate more material on the north upstream end of the concrete structure on Friday.

By Friday afternoon the rive flow had risen to 8000 cfs.

Barring more rain, the river flows will fall over the weekend and early next week we will be able to determine when the work areas can be pumped out and areas cleaned up to resume the great work that had occurred over the last three weeks.

So when I am asked when will the lake be ready, I wonder will we have more days like Monday, 80 cfs, or like Friday, 8000 cfs, over the next year or so? That will tell us when the project will be complete.

General Project Information

As has been discussed, the rebuild plan will be accomplished in two parts, Phase 1 and Phase 2.

Phase 1 will restore the concrete portion of the dam on the north side of the river. Phase 2 work will follow later this summer will restore the earthen dike on the south side of the river including a new large concrete labyrinth overflow spillway.

 

The important critical goal of Phase 1 work is to complete enough refurbishing work on the concrete structure to allow river water flow to be diverted through it from the current river bed flowing through the breeched dike area.

Current Project Progress and Status in last 10 days, June 10 to June 20, 2014

The important DNR permit allowing the entire project to be constructed including Phase 2 has been received.

Phase 2 work is now ready to be bid and awarded. The timing of the Phase 2 bidding will depend on being confident that Phase 1 work will be substantially complete by October allowing for the river to be diverted through the refurbished concrete structure. Right now in looks like Phase 2 work will be bid in July 2014 for an August 2014 contract mobilization to begin this work.

Project completion date is heavily dependent several factors including river flows being average or below (not this past week), minimal weather extremes in the next 12 months, selecting a quality contractor for Phase 2 and sufficient flow in the river at available at the time needed to refill the lake.

Specific Progress by Lunda on Phase 1 work through June 20, 2014 includes:

Work Progress from June 10, 2014, to June 20, 2014

Excavation for the Rock Anchor Block is 90% complete.

Lunda has finished assembling scaffolding and placing it on top of spillways for pier nose removal.

Lunda continues a daily vigilance of making the work site safe.

Eastern Iowa Concrete Sawing has begun sawing on existing Pier Noses for removal.

Lunda has finished preparing upstream face of dam for Rock Anchor Block by roughening the concrete wall where the Block will be in contact with it.

Lunda will continue to drill holes for rebar anchorage into face of dam at Rock Anchor Block elevation.

Lunda has poured a mud slab to level the bedrock at the ends of the upstream side of the dam.

B&J will continue pumping ground water from Stilling Basin.

Downstream Silt removal is complete.

Next Dam Construction Report – Tuesday, July 3, 2014

Pat Colgan

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