There are two types of drainage for infield mixes that I typically see during my travels. 1. subsurface drainage 2. surface drainage
First up, let’s talk subsurface drainage, which is drainage tile installed under the surface. Typically the trenches are backfilled with stone and then capped with infield mix. Simple enough, though there are two primary concerns.
One, basic soil science tells us that finer textured soil should not be placed over courser soil. Why? The finer textured soil must become fully hydrated before water moves to a larger textured soil.
Two, if the infield is compacted correctly during construction/renovation and it contains the correct sand/silt/clay ratio, the infield is too firm to percolate any moisture. I have seen numerous examples of infield projects gone wrong when the local earthwork contractor attempts to install subsurface drainage on an infield.
Often, drain tiles are installed when what the infield needed was more infield mix to bring the infield to the correct grade. Another issue with drain tile installation on an existing infield is that the infield mix will most likely become contaminated with gravel from the drain installation.
The second drainage option is surface drainage. For me, this is the way to drain an infield. From the front edge to the back arc, .5% grade is all that is needed for an infield surface. 1% is too much as the topdressing on the infield tends to run off into the outfield grass during heavy rain events.
For softball, from the pitching rubber in all directions, .4% grade is all that is needed. Why the difference? Any grade more than .4% will provide a surface that appears to have a mound. As we all know, softball players do not like mounds on their fields. Another note on softball fields, .4% has to be consistent across the infield. I have fielded numerous calls on infield mixes and topdressing running off of infields an into dugouts/seating areas. One field in particular had a .4% around the mound, which is correct, but a 1% from the foul lines to the dugouts. It is the 1% that is causing the runoff during heavy rains.
As you can tell, a little variation in surface drainage can cause big problems. So, how do you ensure the correct surface drainage? Laser grading is the answer. Under ALL circumstances lasers should be used. The technology is the industry standard, do not accept anything less. Depending on your site, a conical or dual plane laser will be the tool of choice.
My advice? Forget all the subsurface drainage and make sure that your infield is laser graded frequently to .5% for baseball and .4% for softball.