Answer: You have quite a job on your hands. Here are the recommendations I have been able to find:
Lawns submerged for less than 4 days and covered with an inch or less of silt have a good chance of recovery.
To assist recovery: If water use is unrestricted in your area, wash as much silt as possible from the lawn using a garden hose.
To encourage root development, keep the remaining silt crust broken throughout the growing season, or until grass has become well-established. Use a steel tooth garden rake, a mechanical aerator, or spiking equipment to break up the silt crust.
Apply a nitrogen fertilizer to the lawn. Use whatever grade fertilizer you can obtain, applied at a rate of 1 pound nitrogen per 1000 square feet of lawn area.
Have a soil sample tested as soon as possible to determine lime, phosphorous and potassium requirements of soil. Follow the recommendations given with test report.
If lawn recovery is spotty or generally thin, mechanically aerate the lawn four to six times in late summer or early spring. Then overseed with a desirable permanent seed mixture.
If your lawn is covered with more than 1 inch of silt it may be heavily damaged, with only a slight chance of recovery. The 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 inches. If you can't rake or hose it off, you may have to simply till things all together and then reseed or resod the area.
Best wishes with the renovation of your lawn!
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