Too much water is sometimes worse than not enough water.
Besides causing major structural damage to homes and buildings, it also causes problems to your landscape. It accelerates soil erosion, deposits soil, sand, salt and debris on the turf and causes direct submersion injury. The extent of submersion injury is dependent on the type of grass, duration, depth, environmental conditions and health of the plant.
Common sense would tell you to pick up any debris, such as wood, glass, stones, nails and other metal objects, deposited on lawn areas. This debris is a safety hazard to operators and can damage power mowers or other equipment used on the lawn. Remove leaves or any other material that smothers grass.
Turfgrass in flooded conditions declines from lack of oxygen and light. Substantial turf loss can be expected after 4 days of continued submersion. Other factors associated with flooding also damage turfgrass, i.e. silt/sand cover, water contaminated with petroleum or pesticides, high water temperature and algae scum.
Fast-moving water adjacent to muddy rivers can leave silt and sand deposits in excess of 2'. Soil deposits greater than 1" should be scraped or washed from the lawn surface before renovation. It is best to remove deposits of soil and debris since the level of contamination from petroleum products and pesticides is not usually known. If removal is not possible, till the area to thoroughly mix the flood deposits with the previous grass and soil. When tilling, be sure to break up the old sod layer. Soil deposits of less than 1" can be spread and dragged into the grass surface as a beneficial layer of topdressing.
Core aerifying, slicing or verticutting can help dry out the surface and break up a 1" layer of crusty soil and algae left from flooding. If lawns were flooded for less than 4 days, the soil temperature remained below 60 degrees F and water was moving to supply oxygen, the lawn has a good chance of recovering.
As flood waters recede, sun and high temperatures can literally cook the turf in its soggy surroundings. If there is a positive side to summer flooding, it is that the dead lawns can be prepared for the perfect time to re-plant - August 25 through September 15. Planting early in the fall ensures a good stand of grass going into the winter. Cool-season grasses should be seeded no later than October 15.
Silted lawns— 1" or less Lawns submerged less than 4 days and covered with an inch or less of silt have a good chance to recover.
To assist recovery:
If water use is unrestricted in your area, use a garden hose to wash as much silt as possible from the lawn.
To encourage root development, keep the remaining silt crust broken throughout the growing season or until grass is well established. Use a steel tooth garden rake.
Silted lawns - more than 1"
Lawns covered with more than 1" of silt may be heavily damaged, with only a slight chance of recovery. Degree of recovery will vary with grass species and depth of silt. Re-establish the lawn as follows:
Remove as much silt as possible, especially if silt accumulation exceeds 3", as soon as possible after water recedes.
If silt is less than 3" or has been removed to this depth, till the area, making sure silt is mixed thoroughly and uniformly in the top 4" — 6" of original soil.
Re-seed or re-plant the areas as you would to establish a new lawn.
Flooded lawns (not silted)
Degree of injury will depend on duration of submergence, water depth, temperature, grass species, light intensity and the condition of grass prior to flooding. Grass will not survive as long at water temperatures above 60 degrees F as at lower temperatures.
Ryegrass and red fescue have poor tolerance to submergence. Bermudagrass, zoysia and some buffalograss varieties have excellent tolerance to submergence. Kentucky bluegrass, tall fescue and bentgrass are intermediate in tolerance.
Most grasses will survive 4 — 6 days submergence at normal summer temperatures. Aerate and lightly fertilize flooded areas as soon as possible after water recedes. Areas submerged more than 4 to 6 days may not survive and will require complete re-establishment as previously noted.
Loss of topsoil and eroded areas
Where topsoil has been greatly eroded, replace it to a depth of 4" — 6".
If topsoil is unavailable or too expensive, improve existing soil by adding organic matter such as peat, manure or other organic materials, along with sand. Do not use sand alone. Apply these materials at the rate of 3 cubic yards per 1,000 square feet of lawn area and work materials into the top 4" of subsoil. If you are able to till deeper, the amount of the amendments can be increased accordingly. A temporary lawn, established immediately and later worked into the subsoil, can also be a source of organic matter.