[240dl]

In addition to the main chamber there are several pits that also store lots of water. Here's a photo I took on the tour that might show it better: https://static1.squarespace.com/static/5265796de4b0bacb22141...

Unfortunately I don't remember the tour specifics well enough to confirm the exact use case of the system.

[kweks]

From what I remember (and similar to other designs), the pits take the brunt of the flash flooding, before releasing into the chamber. The reservoir can hold the water for as long as required before dispatching it.