About 132,398,214 gallons of water fell on Forest Park in February of this year. How do I know this? The National Weather Service, which keeps track of things such as this, informs me that we had a rainfall of 3.56 inches for that month. While that doesn’t sound like a lot, it is about 1.6 times the monthly norm. This past Saturday we had 1.28 inches of rain, which, while not a one day record for March (3.59 inches on March 24, 1913), is more than a third of the previous month’s rainfall. To calculate rainfall per square mile, Forest Park is approximately 2 square miles (2.14 square miles counting the part covered by highway), we multiply the number of square inches in a square mile (4,014,489,599), times 2.14 (8,591,007,741.86), by the number of inches of rain for the month (3.56 - one inch of rain is one cubic inch) for the total number of cubic inches of water (30,583,987,561), divided by 231 (number of cubic inches in a gallon) and we have 132,398,214 gallons of water falling on the park in February of this year. This is equivalent to almost 83 seconds of the average flow of the Mississippi river (1,600,000 gallons per second). It’s a good good thing it didn’t wash through all at one time!
On a more practical note, however, the park gets a lot of water and has to somehow deal with it. The runoff from the storm sewers goes directly into the River DesPeres, which flows through the park in a huge culvert, deep under the buildings and waterways of the park, but in periods of heavy rain, the artificial waterways of the park (supplied by city water) carry a lot of water to their drains and into the depths of the underground river.
Walking through the park after a heavy rain reveals just how many low places there are, with puddles ranging from an inch or so deep to some that might come up to your shins. The park managements efforts to control all of this water are met with varying degrees of success. Pipes and culverts make their efforts to direct streams of water to their desired destination, but water flows where gravity and opportunity dictate, and erosion can be a difficult problem to solve.