Swale Holding Capacity

To determine how much water a swale can hold,  first find its volume in cubic feet.  Total cubic feet is then multiplied by 7.48 (the number of gallons in a cubic foot), to determine how many gallons of water the swale can retain.

Because the shape of a swale  is basically half an oval cylinder we plug its dimensions into the formula for the volume of an oval cylinder and take half of that number (divide by two).   *Note:  if the width and depth of the swale are the same, use the formula for volume of a regular cylinder).


The formula for volume of an oval cylinder is:

Pi  x  length/2  x  width/2  x  height


*length= Swale’s Width,    width = Swale’s Depth x 2,     and height = Swale’s Length

Next, because the swale is actually only half of an oval cylinder, you would divide by 2; your answer is in cubic feet.

Multiply your answer by 7.48 (the number of gallons held by 1 cubic ft).  This will give you the total gallons of water your swale can hold.

Click here for a specific step by step example.


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