Gobs.
Let’s say that 2 inches of rain falls on an average neighborhood block in one hour. During that storm, about 130,000 gallons of rainwater will wind up in the storm sewers.
To picture this, imagine a line of 130,000 milk jugs filled with water. THAT’S OVER 12 MILES WORTH OF MILK JUGS! And that’s how much rain would go through the sewers after a 2-inch rain on one block.
By the way, if 2 inches of rain fell in one hour, it would be a really heavy rainfall.
A lot of rainwater is carried underground by storm sewers. But some stormwater is carried aboveground in channels like you see here.
Photo: USDA NRCS