SPORTS FIELD DRAINAGE

I gave some tips on sports field irrigation and this month I focus on irrigation’s twin sister, drainage. It may not be the most exciting subject to review, but there is no aspect to sports field quality more important than good drainage. Whether you work in a wet or dry climate, your field’s drainage is critical because managing soil moisture is a key aspect of Sports Surface Management. Managing your soil moisture means understanding and effectively managing irrigation and drainage. A poorly draining field, grass or turf, will eventually fail due to poor grass health, destruction of the surface due to play in saturated soils, and infill floatation/runoff issues on a synthetic turf field.

Drainage addresses how well water from irrigation and natural precipitation moves off and through your field playing surface. The two basic types of sports field drainage are surface drainage and internal drainage.

Sports Field Surface Drainage:

Surface drainage is about moving excess water flowing off the playing surface, like after a strong thunderstorm. This is typically addressed with field sloping and contouring to get water to move off the important areas and into the less critical areas where safely placed surface drains can move the water into a storm-drain system. Your field’s slope percentages and contours need to be designed by a professional to work correctly during large rain storms and snowmelt. A quality field, with good internal and surface drainage, doesn’t have to have a huge crown or strong slope to achieve adequate surface drainage. Depending on the circumstances and how far the excess water has to flow to get off the field, a slope of less than 2% is generally effective and reasonable to play at some levels, and 1% or less can work on certain fields, in my opinion.

That’s all great if you are designing a new field from scratch, but most sports field managers and facility owner/operators have to deal with existing fields and how they can improve surface drainage. Re-grading an existing field is difficult to impossible without a major renovation of the surface. On a large scale, you pretty much have to live with the surface drainage you have. But there are some things you can do to help.

Note: Surface drains need maintenance. Many have some kind of filter-screen or catch basin similar to typical drain pipes underneath a kitchen sink. These need to be regularly inspected and cleaned as needed for the system to work.

On a smaller scale, you can repair any smaller low spots in the field that tend to collect water. A skinned area on a baseball or softball field has to be brought up to grade with correct and matching base and top layer composition and construction as the rest of the infield. You can’t just dump some sand or other soil amendment into a low area and expect it to perform correctly. On a grass area you might be able to topdress-up the low spot to meet grade, but be careful not to dump too much material on at a time. Do about ¼-ich at a time at most, allowing plenty of time between topdressings for the grass to grow up and develop into the newly applied soil before adding the next layer of topdressing. With spot topdressing, repairing a low spot on a grassed area takes time, depending on how much elevation gain you need. A quicker option is to sod-cut out the grass if it is in good shape, correctly reconstruct the soil profile to proper grade and re-sod with grass you cut out or newly purchased sod of appropriate specifications. This is difficult to do by eye alone, but can be achieved with experience. It’s best to use a simple surveyor’s transit from a rental store to check your elevations, or maybe contract out a report to a reputable surveyor.

Turf Tips 101: Sports Field Internal Drainage:

Your field’s internal drainage capacity is more complex than your surface drainage issues, but there is also more you can do to an existing field to aid internal drainage. Simply put, internal drainage involves water moving into and through your soil profile. This is done by optimizing both your field’s infiltration and percolation rates.

Infiltration: Water moving into your field soil profile.

If you poor water onto any flat surface, it will either sit there or penetrate into the surface and your field needs to do the latter to perform well. A surface that does not absorb water is often said to be “sealed-off”. This is often due to a relatively thin layer on the surface that keeps water from penetrating into the soil. This could be surface compaction from maintenance vehicles and play on the field. It could be a thin slimy layer of accumulated organic material from the grass has sealed off the surface. It could be the sod you installed in the last few years has a slightly different texture or particle size distribution than your underlying rootzone soil and your water table is essentially “perched” at the surface.

Your playing field infiltration rate can be measured with a simple double-ringed infiltrometer (there are several types and sizes of infiltrometer available). You can see it how it is used in this video.

Note how this test is done in a non-saturated soil. To me, this is a good indicator of how your field will deal with typical rain events and irrigation. Soil percolation (described below) looks at how water moves through the soil once it is saturated, like might be the case during a prolonged rain event.

I’d love to see fields have a 2 inch/hour infiltration rate, but that is rarely practical on a densely turfed soil that has routine traffic like a sports field. But a heavy rain is considered to be 2 inches/hour or more so that would be the ideal infiltration rate. Realistically, a good infiltration rate on a heavily used field is probably more like .5-1.0 inches/hour and maybe less. The first step is to measure your rate in several different parts of the field.

Note: Your field infiltration rate has to be less than your irrigation system precipitation rate (discussed in last month’s Tips from the Pros). Otherwise you waste water with runoff and create soggy turf.

A sealed-off surface usually needs to be sliced, verti-cut or aerified (core or solid tine) deeper than the sealing layer to open the surface and let water in.

These techniques are generally non-invasive, requiring little or no recovery time on the field before play can commence. They are usually a temporary relief measure, to varying extents, and may need to be done routinely to be effective. You can also manage an organic accumulation that is sealing off the surface by diluting the organic material with light and frequent topdressing using an appropriate soil in combination with your chosen cultural practices. Fraze mowing, as I described in my February 2016 Tips from the pros blog, may help tremendously with poor infiltration if you go deeper than the sealing layer.

Percolation: Water moving through your soil profile.

Once the water has infiltrated into the soil and essentially saturated it, the rate at which it will move vertically down through the soil and eventually into the ground water table or some type of drainage system is called the percolation rate, often referred to as Saturated Hydraulic Conductivity” or “Ksat”. Percolation and infiltration are both critical. Having one good and not the other doesn’t work. If you can’t get water into the soil (poor infiltration-sealed surface), it doesn’t really matter how good your percolation rate is. On the other hand if you can’t move water very well vertically down through the saturated soil profile of your field, then it doesn’t really matter if you have good infiltration during long-duration rain events. You want and need both.

So how can you measure your field percolation rate? To a certain extent, you can run your infiltrometer tests in a saturated soil to get an idea. There are limitations to this, especially if you have any layers in your soil profile. An undisturbed soil core can be laboratory tested for a more accurate assessment of Ksat, as the water is forced to only move vertically through the entire soil profile. Using an infiltrometer to measure your perc rate when saturated may allow for some horizontal movement of water and not really give a good indication of how your field will react during the long duration rains.

As a field manager, you will generally know when your field has poor infiltration and percolation rates by simply observing how your field reacts to smaller rain and irrigation events as well as how it performs in terms of drainage during longer duration/high precipitation rate events.

Aside from changing to a better textured soil, what can you do to an existing field to effectively improve its percolation rate? There are several technologies available these days to deal with a poorly percolating soil.

Maybe the most popular way is deep tine aerification of your field or problem areas of the field. Metal tines of 8-12 inch length or more are driven into the soil to a specified depth. The tines can be solid or coring tines and typically articulate in some fashion so as to fracture and slightly heave the soil, creating a deep channel in the soil with little surface disruption. See video of deep-tine (solid) process on a field.

Other technologies include machines that will inject sand or other appropriate soil amendments into the holes that are actually drilled deep into the soil, or at least past the offending layer. This process is often called drill-and-fill and can be very effective at longer term relief of poorly draining soils on an athletic field. See a video here of a drill-and-fill process on a golf green. A similar process involves cutting a slit deep into the soil that is then filled with a clean sand in a pattern designed to intercept any surface runoff. See a sand-slit installation process video here.

New ideas also include fracturing the soil with a high pressure injection of water, or more recently compressed air. See a video of the Air2G2 aeration machine here.

A recycling dresser, seen in this video, cuts a deep groove in the soil and re-dresses the excavated soil on the surface as a topdressing.

Finally, if you can’t achieve a high level of surface or internal drainage on your field (think baseball skinned areas), or even if you do enjoy good internal drainage, a quality waterproof field tarp cover or raincover can be your best bet at managing your soil moisture levels for play. Careful use of raincovers can be the most cost effective way to solve a poorly-draining turf field, but they won’t help for rain events during the game. For that, you will want to optimize your field drainage overall.

Resources of the Month

The Sports Turf Managers Association (STMA) has a good bulletin on athletic field drainage with some conceptual drawings.

Read the chapter on Drainage at Google Books from the seminal book Sports Fields: A Manual for Design, Construction and Maintenance.Note: Second edition updated in 2010.

End Quote

“There is an eagle in me that wants to soar, and there is a hippopotamus in me that wants to wallow in the mud.” Carl Sandburg