How do you calculate the gradient of groundwater? - Answers

Groundwater gradient is calculated by the equation: i=dh/dl Where: i= groundwater gradient d= the change in, or Delta h= groundwater head l= length of casing in the well Using this you would take two wells, use the well log to determine the length (ie. depth) of each well, and subtract the first from the second. That's dl. On a particular date or time (must be the same time/date for both wells), you determine the groundwater elevations in the two wells and subtract the first from the second. That's dh. Divide dh by dl, the answer is your gradient. The gradient is dimensionless, if it's positive groundwater is flowing upward (vertically) in the direction of the first well to the second well, if it's negative, groundwater is flowing downward (vertically) in the direction of the first well to the second well.