Cook Lake Spillway Reconstruction

Cook Lake is on Bearlodge Ranger District, Crook County, Wyoming. The lake's spillway was reconstructed in 2019 and 2020. The project included demolition of the previous spillway and construction of a new spillway, embankment, stilling basin, and bridge.  

 

August 28, 2020

Hydroseeding was conducted today. The project is nearly complete.  

 

July 13, 2020

Crews continue to backfill and shape the embankments. Work has begun on the emergency spillway.

 

May 8, 2020

 

May 1, 2020

 

November 21, 2019

Work has ended for the winter. The crew placed additional fill, graded the upstream face of the dam, and added riprap in the outlet area of the stilling basin. 

 

November 7, 2019

The crew stripped forms from the upstream wingwalls and downstream chute walls. They then began backfilling along the walls and bridge, but more snowstorms slowed progress. Backfill was achieved to the top of the bridge and crest elevation of the dam.

Dam and bridge after backfill

 

Compacting the backfill on the left side of the bridge

 

Completed bridge and chute

 

October 24, 2019

Bridge sections and a crane for installing them arrived at the site early last week. The crane lifted the bridge arch sections into place on the cast-in-place footing/slab. Three arch sections were set, followed by the upstream and downstream headwalls. The install was complete by the end of the day on Tuesday.

After the bridge was set, the crew formed up the upstream wingwalls and downstream chute walls. The last concrete placement was completed this week. A total of 536 cubic yards of concrete were placed during spillway construction.

Wingwall formwork, ready for concrete

 

Securing the upstream headwalls to the bridge arch

 

Preparing to set the first arch section

 

October 10, 2019

The final part of the spillway floor has been poured. The crew partly installed formwork for the upper wingwalls and the downstream chute walls. The last of the six-foot culverts was removed to make room for the crane that will install the bridge.

View looking up the spillway chute after removal of the final culvert

 

Wall formwork and completed spillway floor

 

September 30, 2019

The crew installed wall forms for the center section of the spillway and formed the uppermost section of floor slab and the bridge footing. Concrete was placed in the forms on Sept. 20 and 25. The spillway and stilling basin drains were also installed and plumbed.

Placement of bridge foundation slab

 

Rebar mat for bridge foundation

 

September 16, 2019

Wall forms were stripped from the stilling basin walls. The crew placed another section of the spillway floor, constructed forms for another section of the spillway walls, and formed the dentates. Concrete for the walls, dentates, and spillway floor was placed on September 9 and 11. 

Dentates and baffle blocks in spillway chute

 

Stilling basin with forms removed from walls

 

August 29, 2019

The crew installed and tied rebar in the floor slab, formed the baffle blocks and stilling basin walls, added formwork, and tied and braced the forms. Concrete for the chute slab and stilling basin walls was placed on August 28.

Placing concrete into the wall forms

 

Spillway formwork done and braced, ready for concrete

 

August 15, 2019

Part of the crew spent the first few days of the shift cutting and bending rebar for the stilling basin floor and walls. The rest prepared the subgrade for the stilling basin floor, excavating wet clay and placing a gravel filter. The concrete cap over the filter was formed and placed on Friday, August 9.

Spillway slab placement nearly completed

 

Formwork for the concrete slab over the sand/gravel filter drain

 

Cleaning out the stilling basin footprint

 

August 9, 2019

Lake drawdown was completed on August 8

 

July 30, 2019

The lake level has dropped significantly

 

Three of the four culverts have been removed and excavation for the new spillway floor has begun

 

July 18, 2019

The crew installed pumps to drain the lake. They removed gabion blankets and riprap from beneath the culvert discharge and excavated a portion of the embankment. The lake level dropped by about three feet before a storm brought it part way back up, and another storm hit the area on July 17.

Pump draining lake

 

Embankment below culverts, partially removed

 

July 11, 2019

Staging equipment and preparing to draw down the lake prior to spillway demolition

 

The log mat that dissipated outflow below the culverts has been removed