Spring and early summer months bring warm sunshine, blooming flowers. Sometimes those “April showers” bring damaging rainfall and flooding events that devastate turf grass and sports fields. Here’s what you need to know in order to recover from springtime flooding.
Factors that Impact Turfgrass Survivability
Every turfgrass species differs in its ability to tolerate and survive flooding events. A few variables impact the survivability of each species.
Water temperature is a significant factor. Turfgrass tends to survive better when the floodwater and air temperatures are cooler. Turfgrass can survive up to 60 days submerged under floodwaters when the water is around 50 degrees. But if the water temperatures are 86 degrees or warmer the grasses tend to die within 24 hours.
Floodwater depth is another major survival factor. If even a little bit of the leaf tissue is above the water line, the grass will probably survive. Plants that are completely submerged in water can die from oxygen and light depravation in the rootzone.
Once the turf is submerged under water it doesn’t take long for soil oxygen levels to be depleted. When the oxygen levels decline, the root hairs begin to die and the grass cannot absorb nutrients, water, and oxygen.
Standing floodwater also allows sediment to collect on the grass blades, leading to turfgrass injury. For this reason, slow-moving floodwater is often less damaging to turfgrass than stagnant floodwaters.
Soil erosion may also occur either from flowing rivers or streams that left their banks or from floodwaters draining quickly in channels across fields. These flowing waters can leave silt, sand, clay, and other debris along the way.
Relative Submersion Tolerance Rating
Each species of turfgrass is different in its ability to survive flooding. While there are no hard, fast numbers regarding their survivability, each species is assigned a “relative submersion tolerance” rating.
Creeping Bentgrass, for example, has an excellent relative submersion tolerance rating. It is often seen floating on the edges or growing in the middle of ponds and lakes. Kentucky blue grass and tall fescue receive a “medium” rating. Poa annua and perennial ryegrass are “fair”, and red fescue brings up the rear with a “poor” relative submersion tolerance rating.
Cleaning turfgrass after a flood
Nothing can be done for the cleanup effort until the soil is dry enough to support equipment without rutting or causing compaction. It is best to stay off the fields until then.
Assess submersion injury to turf grass
To assess floodwater damage to turfgrass, collect several plants from the flood area and cut horizontally through the crown. If the crown is brown and soft, the grass has died. If the crown is white and firm, the grass is still viable.
Remove debris and sediment
The first step in the cleanup process is to remove large debris then the sediment. It is very difficult to remove all traces of sediment, so it is best to use a variety of methods to break up the sediment layer and encourage root recovery.
If large amounts of silt, soil, sand, or clay are left behind, remove as much as possible with a flat-bladed shovel or rake it across the turf. You should not till the silt or sediment into the rootzone.
Slicing or hollow or solid tine aeration can help with the drying process, improve the condition of the soil, and increase oxygenation to the rootzone.
Sediment layers that are less than an inch thick can be very difficult to remove. After the layer completely dries, a drag mat will break up the sediment. Follow the drag mat with aggressive hollow tine aeration and topdressing to prevent the sediment from clogging the rootzone.
Evaluate the soil and grass
Once the debris and sediment are removed, begin assessing the damage. Fields that suffered extensive damage may need to be tilled, re-graded, and reseeded or sodded. Fields with less damage may only need some soil cultivation to return to normal.
After you core cultivate, topdressing will level the turf surface and help dilute any remaining sediment. It also helps improve the rootzone. Make sure the topdressing material matches or is slightly coarser than the particle size of the existing rootzone.
Flooding causes nutrients like nitrogen, lime, phosphorus, and potassium to leach out of the soil. Conduct soil tests and create a fertilization plan. Fertilizing after a flood is important to promote turf grass growth and recovery.
Nitrogen and phosphorus stimulate recovery and improve overall stress tolerance in the turf. Use a quick-release form of nitrogen. Phosphorus will help with seedling growth.
Replant, seed, or sod
Depending on the extent of the damage, some fields may need to be replanted to facilitate growth and recovery. Fields with minimal damage may only need a spot-seeding or light over-seeding.
Fields that suffer moderate to major damage may need seedbed preparation and heavy over-seeding. Areas with the most severe flood damage may need to be sodded. If properly installed, sod can allow for play within weeks or a few months.
In the summer months, if flood damage occurs to a game field during the playing season, choose thick-cut sod for the fastest recovery time. Thick cut sod allows for the field to be playable within hours instead of weeks or months.
Prevent weeds and disease
Floodwaters often deposit weed seeds on turf fields. If the fields only suffered minimal damage, apply pre-emergent or post-emergent herbicide to control weed infestation.
Hot humid weather and saturated soils are the perfect environment for diseases to develop in turfgrass. Keep an eye out for developing diseases and use the proper fungicides as needed.
Synthetic turf cleaning
While synthetic turf fields are not directly damaged when submerged under floodwater for long periods of time, floods can cause carpet displacement, infill displacement or loss, contamination, and debris and sediment deposits.
Some sediment is easier to remove when wet and other types are easier to remove when dry. Clean the sediment as quickly as possible and practical.
Severe flooding may cause the synthetic turf to wrinkle. The fabric needs to be stretched and repositioned. Restore the infill to the proper levels and perform a Gmax analysis to ensure the field is safe for play.
Flooding can cause contamination of artificial fields, particularly if the flood included “grey water”. Use proper topical sprays to decontaminate the field and prevent bacteria from growing.