i still dont see how that applies to the parking lot area. But dont try explaining further just for my sake.Watch the youtube video with the sound on and listen. Around 30 seconds in, it is described as a "safety plug, a soft plug" purposefully built in. One that would purposefully erode away in a sacrificial manner. Continue watching the video to see how such a weak spot can be used to safely release water before the flows increased dramatically hours later. Those hours give precious time for evacuations.