One of the most important aspects for sports field construction is designing the field for maximum drainage to remove excess moisture from rainfall prior to and/or during an event. Unfortunately, too many sports fields are constructed without any type of installed internal drainage system. They do not have an adequate crown to remove excess moisture from the field rapidly.
Drainage in Sports Fields
Overwatering
Once the topsoil on a sports field becomes saturated, the water will do one of two things, pond or run-off. In this case, the water starts pooling because there is no crown on the field. Playing games when the soil is saturated will cause severe damage to the field and will increase the amount of soil compaction. This will only make the drainage problem with the field worse.
Thoughts for the Design
Over the years of working with sports field construction, I have always been amazed at how little attention is given to this critical phase for sports field construction. Or, how many times at the last minute, the internal drainage system was removed from the original design specifications to try and save money.
Key factors to consider when designing drainage systems for a sports field include; movement of water onto the field from surrounding areas, type of soil and soil depth, ability to remove excess water away from the field ( storm sewer, creek, etc.) and weather factors such as rainfall. In areas of east Texas were average rainfall is 55 to 60 inches per year, proper drainage is going to be more critical than in areas of west Texas were average rainfall is 10 to 11 inches per year.
One of the first steps in assuring that a proper drainage system will be designed for a new sports field, is to hire an architectural firm and/or contractor that has extensive experience in the construction of sports fields. Just because someone knows how to run a grader, doesn’t mean they can build a sports field. During the design phase, it is important to hire someone such as an experienced sports field consultant or an experienced architect to develop a very detailed set of specifications for the new sports field to be constructed.
I am also amazed at how many sports fields are built without any design specifications for soil type and depth, drainage system, irrigation, etc. Then, when a problem arises with the field, the school or city that contracted to have the field built have no recourse to have the problem corrected.
Draining a Field
Excess moisture is generally removed from the playing surface of a sports field in one of two ways; surface run-off and/or through an installed internal drainage system. Sports fields built out of a native soil or an amended native soil, surface drainage is going to be the main means for removal of excess moisture from the field. For football fields, the general guidelines is to provide a 12 to 18 inch crown in the center of the field with a continuous grade from the center of the field to and past the sideline areas of the field.
In sandy loam to loam soils, a 12 inch crown is normally sufficient grade (slope) to remove excess moisture. And for fields built with clay type soils, it is recommended to construct an 18 inch crown in the center of the field with a continuous grade from the center of the field to and past the sideline areas of the field. It is important to install some type of drainage system on the sideline areas of the field to remove the excess moisture from these areas of the field.
Football Fields
Note, many high school football and city park fields are also being used for soccer following the football season. If this is the case, then the slope for the field needs to extend well beyond the normal sideline area of the football field. If this is not done, then the sideline areas of the football field were the players stand during games becomes torn up and this will make a very poor playing surface for the soccer games.
Soccer Fields
For soccer fields built out of native soils, the recommendation is to provide for a 6 to 12 inch crown. While a 6 inch crown is preferred by most soccer players, they also don’t like playing in a quagmire. If an internal drainage system cannot be included in the design of the soccer field then it would be best to use a 12 inch crown for the soccer field to insure good surface drainage.
Layout of the Field
Adding a Crown
While a crown in the center of football and/or soccer field is the most effective method to provide for surface drainage, it should be recognized that for some fields, surface drainage can be provided for by sloping the entire field from sideline to sideling or from endzone to end zone. However, the further the surface water has to flow to get off the field, the less effective the surface drainage becomes.
For sports fields built with a proper sand mix, a six inch crown is generally the recommended guideline. Providing a continuous, uniform grade on the field is just as important as providing the correct height for the crown. Any low areas in the grade will disrupt the flow of surface water from the field. Improper grading and settling of the topsoil are the two main reasons for low areas occurring in the final grade.
Considering the Grade
Baseball Fields
For baseball fields, the high point of the field should be the pitchers mound, which is normally 10 inches higher than home plate. Then the field should be sloped in all four directions away from the mound at a 1.0 to to 1.5 % slope. As with football and soccer fields, this slope needs to continue to the sideline areas of the field and then some type of drainage system installed to remove excess moisture from this area of the field.
Also, for baseball fields it is very important that this 1 to 1.5% slope continue across the skinned portions of the baseball field and into the outfield. If constructed correctly, there will be very little movement of water down through the soil profile in the skinned area of the field. Surface drainage is the main method to remove excess water from this portion of the baseball field.
Another problem that often occurs on baseball fields is the build up of lips on the grass areas next to the skinned area. These lips will prevent water from flowing off the skinned area and into the grass portions of the field. Regular maintenance practices should be used to prevent the occurrence of lips around the skinned portion of the field. From the skinned area, the field is then sloped at a 1 to 1.5% slope to the outfield fence.
Softball Fields
For softball fields their are a couple of common ways to grade the field. The most common grade is to slope the entire field, starting at the back stop and going toward the outfield fences at a 0.6 to 1.0% slope. A second method is to provide a level crown through the center of the softball field going from home plate to the pitchers mound through second base and then to center field. Then the field is sloped at a 1 to 1.5% grade from the center of the field toward the right sideline and from the center of the field to the left sideline. The advantage of this design is that home plate and the pitchers mound are at the same height, which for fast pitch softball is important.
Moisture in the Soil
With the exception of sand based fields, assuming that the correct sand is selected, the movement of water into the soil profile (infiltration) and then down through the profile (percolation) is very slow. Movement of water into and through a soil profile is generally determined by the amount of pore space and type of pore space in the soil.
Determining the Pore Size
Macro-pores (large pores) provide for good drainage and good aeration, but provide for very little moisture retention. On the other hand, the micro-pores (small pores) provide for good moisture retention, but provide very little drainage and aeration.
Sands used for sports field construction generally have more macro-pores and fewer micro-pores. While these soils provide for excellent internal drainage of excess moisture, they generally require more inputs of supplemental irrigation and fertilization to maintain a healthy stand of turfgrass.
On the other hand, native soils high in clay and/or silt content have a larger number of micro-pores and fewer macro-pores. Internal drainage of excess water on these type fields is very slow. Providing a crown for good surface drainage is a must for these type fields.
Testing the Soil
Before selecting a particular soil for use in the construction of a sports field, the soil should be sent to a certified soil testing lab and tested for factors such as texture analysis, porosity, saturated hydraulic conductivity and compressibility. This step is not an option, but is a must. While testing for physical characteristics of a soil is considerably more expensive than chemical analysis, the fee for these tests is a drop in the bucket compared to the overall costs of constructing a sports field.
Another step in sports field drainage that is often overlooked by the inexperienced contractors, is removal of the excess moisture from the subgrade. Movement of water into the subgrade of the field can only occur once the topsoil profile becomes saturated.
Then, drainage of the field occurs at the rate of water percolation down through the subgrade, which as a rule is much slower than the percolation rate for the topsoil. If means are not provided to assist in the removal of excess water once it hits the subgrade, then the field will tend to hold water at the interface between the subgrade and the topsoil. During periods of heavy rainfall, the field then acts like a bathtub and fills up with water, thus dramatically increasing the amount of time required for the field to drain.
Compacting the Soil
On native soil fields, it is very important that the subgrade not be heavily compacted prior to placing the topsoil mix over the subgrade. This is often one of the big mistake inexperienced contractors make in building a sports field. Compaction of the subgrade will further reduce the flow of water from the topsoil profile down into the subgrade, thus increasing the time required for removal of excess moisture from the topsoil.
While you do need a firm subgrade to prevent excess settling of the subgrade, do not heavily compact the subgrade prior to placement of topsoil over the subgrade. For sand based fields, it is necessary to stabilize the subgrade with compaction. However, it is also important to install an internal drainage system in the field to remove excess water from the subgrade area of the field.
Note, installation of a internal drainage system on fields built using native soils will also help in the removal of excess moisture from the subgrade, just not as well as a sand based field.
Trenches and Drainage
Correct installation of the drain lines in a new sports field is critical to the successful removal of excess moisture from the field during heavy rainfall periods. Spacing for the trenches should be at a 15 to 20 foot spacing for sand based fields. However, on native soil fields I would recommend a maximum of 10 to 15 foot spacing.
The grade on the trench should have a minimum positive slope of 0.5% with 1.0% grade preferred. Note, use of trenchers with a laser attachment can insure that a uniform, continuous grade occurs in the base of the trench. If any low areas occur in these trenches, this will impede the flow of water through the drain lines and thus allow the fine soil particles, silt and clay, to settle out in the bottom of the drain lines and eventually plug up the drain lines.
In most cases, it is recommended to line the drainage trench with a plastic layer in order to keep the silt and clay soil particles found in the subgrade from moving into the trenches and thus slowing down the movement of water into the drainage pipe.
Adding in the Gravel
Next, place a 1 to 2 inch layer of fine gravel, % to 318 inch gravel, in the base of the trench. Place the plastic pipe used for drainage on top of the gravel layer and then top off the pipe with a l to 2 inch layer of the same fine gravel. For most sports fields, a sand layer is then placed over the gravel to the top of the drainage trench in the sub-grade.
Again, remember that it is just as important to send samples of the gravel and sand used in the drainage trenches as the soil for topsoil to a certified lab for physical analysis. Most sports fields today use the corrugated plastic pipe with fine slits in the plastic for the drainage system. However, if PVC pipe with a single row of holes in the pipe is used, it is very important to place the holes on the bottom of the trench to encourage faster movement of water in the trench into the PVC pipe.
Determining the Proper Trench Size
Note, the common size for drainage trenches in the sub-grade of sports fields is a six inch width with a minimum eight inch depth. The key is to make sure that .the pipe is placed deep enough in the field so that aerification with a deep tine aerifier will not pierce the pipe. You night be surprised how often this actually happens.
For most new football and soccer fields, the drain lines are installed lengthwise in the field. This requires much less trenching and also allows for maximum interception of water flowing from the center of the field toward the sideline areas of the field.
Recently, I have been involved with the construction of a couple of sand based baseball fields that used the flat corrugated pipe for drainage instead of the four inch round corrugated drainage pipe. Instead of digging trenches in the subgrade for this flat corrugated pipe, they laid this pipe flat on the surface of the subgrade and then covered the pipe with a four inch layer of fine gravel and then placed the sand topsoil mix over the gravel.
The drainage of these fields to date has been excellent. The key to this system is the installation of a uniform, continuous subgrade surface with no low areas. The slope should be a minimum of 1% with a 1.5% grade preferred. It is also critical that a layer of fine gravel be used to cover the pipe. Also, spacing for the drainage pipe should be placed at a 10 to 15 foot spacing for best results. Note, I would not recommend using this type of drainage system for sport fields constructed using native soils and/or amended native soils.
Keys to achieving a successful drainage system:
1. Select an architect and/or contractor with experience in building sports fields.
2. Send the soil, sand, and gravel to be used in construction of the field to a certified lab for physical analysis.
3. Construct a uniform grade on surface of the field to provide maximum surface drainage from the playing surface. Critical for native soil fields.
4. Prevent any low areas from occurring in the surface of the field.
5. Install an internal drainage system for the field.
6. Prior to construction, survey the site to determine any movement of water onto the field from neighboring sites. If this is a potential problem, then install interceptor drainage lines around the field to prevent movement of water from neighboring sites onto the new field.
7. Make sure excess water can be easily moved away from the field through storm sewers or natural areas such as a creek.
Written by Jim McAfee, TAMU
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