If the drains in Problem 17.7 are located on the impervious surface, determine the spacing of the drains so that the water table does not rise more than 2 ft above the drains.

Problem 17.7

The following conditions were observed for an agricultural drainage system.

1. Vertical distance from impervious layer to drains = 30 ft

2. Maximum water table above drains = 6 ft

3. Average hydraulic conductivity = 7.5 in./hr

4. Infiltration rate = 3 in./hr

5. Runoff = 40%

6. Irrigation schedule as per the following table

Determine the drain spacing so that the water table does not build up more than 1 foot above the drain.