Quote:
Originally Posted by BlackArcher101
Except in this case I believe they designed it (storage and pumps) to handle a much greater rainfall rate than has fallen so far and the pumps should have handled it. Might have been a temporary pump control issue with some kinks being worked out. If I recall, these were just commissioned recently.
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As long as the volume of water flowing into the tank is bigger than the volume of water getting pumped out, the tank could overflow. There is quite a large area that drains into that stormwater tank. I have no idea about the size of the pumps, but it's not unreasonable to think that a moderate rain for an extended period of time could completely fill the storm tank, meaning extra water would pool in the tunnel.
For the simple fact that the tunnel is sunken into the ground, there is nowhere else to bring the water but to the storage tank, where it can be pumped higher. The drainage areas, for the sake of a visualization, are 400m long and 100m wide on each end of the tunnel, so let's say 80,000 square metres. 10mm of rain falling on that area means that you have 800 cubic metres of rain water to deal with. Obviously, one storm event can bring a lot more than 10mm of rain.
If the tunnel area gets hit with a storm like hit in June 2007, with 75mm in an hour and a half, the tunnel might be flooded with 10 feet or more of water. That rainfall would bring more than a cubic metre of water into the stormwater tank every SECOND.