# How Many Bath Tubs?

And the Rain will Fall.....

Every winter Meerkerk experiences a tremendous amount of surface water drainage. This year we have been proactive in installing additional swales, improving culverts, and upgrading french drains to help move the water through the gardens to protect plants and facility structures.

We thought it would be interesting to calculate the total amount of water and convert the total drainage to bathtubs to help visualize the millions of gallons of surface water that Meerkerk has to manage each year.

Thanks to Meerkerk’s Special Projects Manager Barton Cole for providing the calculations for this demonstration.

So here it goes.....

Assume 20 acres of watershed.

Assume 24" of annual rainfall

thus, 40 acre-feet of water falls to the ground

(One acre-foot equals about 326,000 gallons, or enough water to cover an acre of land, about the size of a football field, one foot deep.).

That equals 13,000,000 gallons of rainfall - WOW!

Assume 80% evaporates/transpires/infiltrates.

Therefore 20% of annual rainfall becomes surface water for Meerkerk to manage.

13,000,000 x.2 = 2,600,000 gallons of surface water - WOW Again!

So how many bathtubs is that?

Average Bathtub holds 40 gallons of water and is 5 feet long.

2,600,000 divided by 40 = 65,000 bath tubs.

Here's the Visual:

Place the bathtubs end to end = 61.55 miles (Whidbey Island  is 51 miles long).

For those who are familiar with the Alderwood Mall: If it takes 7 bathtubs to fit into one parking lot space at the Seattle Alderwood Mall then 65,000 bathtubs would fill 9,285 parking spaces. The Alderwood Mall only has 6,300 spaces.

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