Outlet structure needs to be replaced- Aug 27

Before we jump into the issue of the outlet structure and more specifically the outlet drain/catch basin, which had to be addressed on the 27th, we wanted to share one more picture taken by Colin on the evening of the 26th. He just posted this photo on the Thurston Nature Center Facebook page!

View from above – from top left hand corner of the photo one can follow outlet channel (consisting of the outlet structure, pipes and valves) sediment forebay, deep habitat pool, the two off-shoot channels, and the Nesting Island

View from above – from top left hand corner of the photo one can follow outlet channel (consisting of the outlet structure, pipes and valves) sediment forebay, deep habitat pool, the two off-shoot channels, and the Nesting Island

On-site conditions, which were not possible to confirm before the construction work on the outlet channel, caused us to make some changes to our outlet beehive drain/structure/catch basin. The floor of the existing outlet structure had concrete that sloped up from the invert toward the pond side of the structure. This concrete prevented the outlet pipe we had just placed in the outlet channel from being installed at the required lower elevation. Because of the critical nature of this elevation, it was agreed that the existing structure would need to be replaced and the proper elevation of the pipe would need to be re-established.

Perhaps some further explanation and definition is needed…..

Many of the terms used to describe the various components (i.e. outlet structure, drain, beehive drain, catch basin, etc..) are confusing because they frequently provide more than one function. Therefore, the terms are often “interchanged”.

In the case of our pond at the TNC, the water discharged from the pond, goes through an outlet structure (by the Pond Circle Trail), and into the AAPS stormwater pipe before being introduced into the city stormwater pipe at Prairie Street.

The outlet structure is at the outlet of the channel and provides a transition between the water flowing from the pond (though the channel and outlet pipe) and the inlet to the AAPS stormwater pipe. Sometimes you might have heard us call it a beehive drain. The drain has a specific grate that sits on top of the drain which is referred to as a beehive grate. Therefore, the term beehive drain is sometimes used.

The ECT and Anglin Civil team discovered this issue and resolved it in a timely and efficient manner. Unfortunately, it cost us one day and additional funds, which fortunately were previously allocated in a contingency budget.

Sal (Anglin) & Alice (ECT) verifying and checking elevations

Sal (Anglin) & Alice (ECT) verifying and checking elevations

Sal (Anglin) & Alice (ECT) - - only way to check things out

Sal (Anglin) & Alice (ECT) – – only way to check things out

Outlet channel has to be dug-up

Outlet channel has to be dug-up

Pipes and valves needed to be removed

Pipes and valves needed to be removed

Pipes removed

Pipes removed

Gate valve removed

Gate valve removed

Extra effort-whatever it takes

Extra effort-whatever it takes

New outlet structured is delivered to site

New outlet structure is delivered to site

Holes are cut in new outlet structure for pipe

Holes are cut in new outlet structure for pipe

Existing outlet structure torn apart and removed

Existing outlet structure torn apart and removed

Concrete of existing structure has to be cut

Concrete of existing structure has to be cut

A lot of work

A lot of work

Making hole for new outlet structure

Making hole for new outlet structure

Measurements verified

Measurements verified

New outlet structure ready to be placed in hole

New outlet structure ready to be placed in hole

Put into hole

Put into hole

Proper placement and positioning is critical

Proper placement and positioning is critical

Concrete pipe added to new structure

Concrete pipe added to new structure

Pipe in structure

Pipe in structure

Pipe is connected to AAPS stormwater inlet pipe for drainage of water

Pipe is connected to AAPS stormwater inlet pipe for drainage of water

Channel re-dug and prepped for re-installation of outlet pipes and valves

Channel re-dug and prepped for re-installation of outlet pipes and valves

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