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!
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.