The spillways can only transport so much water. If inflow is greater than that, you can build up above that point. Even a fast moving channel 10 feet deep is dw

The spillways can only transport so much water. If inflow is greater than that, you can build up above that point. Even a fast moving channel 10 feet deep is dwarfed by the flux of water that can be deposited by a heavy storm over a large area. Edit: for some concrete numbers, the reservoir was rising 0.5 ft/hr!! For reference, it appears the Addicks Reservoir has an area of 26,000 acres around this depth. That's 157,300 ft^3/s of inflow. Outflow was only 4,000 ft^3/s! Edit 2: Here's a visualization: http://i.imgur.com/usZAici.jpg http://i.imgur.com/usZAici.jpg