It's only a little grass in the street, what harm could that cause? As it starts out, not much, but add tens and hundreds of areas and it quickly becomes a major issue. Grass in the curb will block the stormwater from getting to the catch basin. The drainage at the blocked area will push the water out into the travel lanes of the street and potentially cause ponding of water.
Once the grass gets wet, it tends to stick together and start to decompose. It is almost like creating compost in the street. This problem perpetuates the previous issue, as more and more grass gets caught up in the blockage with each mowing.
Sometimes the grass makes it all the way down to the catch basin. Catch basins are designed to accept a certain amount of drainage. Storm sewer systems are engineered to reduce flooding in the street and private property. When the catch basins become blocked with grass, the capacity is taken away from accepting water. Ponding occurs around the catch basin, which can lead to localized flooding and possibly property damage. The Village might be able to sweep it up, but that could be months away. It takes the Village street sweeper approximately 2-3 weeks to go through the Village one time. There are over 130 curb miles to sweep in the Village.
What happens after the stormwater gets into the catch basin? The stormwater travels through a series of progressively larger pipes until it outlets into a ditch, stream, river, or pond. It does not take much for a twig or small tree branch to enter the catch basin and attempt to travel downstream. Sometimes stones or other material get caught in the pipes which act as a dam and additional debris catcher for grass. The grass begins to compost, and release pollutants like phosphorus or nitrogen into the stormwater every time it rains. The capacity of the pipe to convey water is reduced as well, until water backs up onto the street or yard drains.
The Village has over 90 miles of pipes and over 1,200 catch basins installed throughout the community. We manage to clean and maintain only a small fraction of those every year. When hazardous weather approaches, it there is not enough time for our staff to make sure every catch basin is cleared off and all debris (grass/leaves) are cleared out of the curb to prevent potential flooding. We need your help to make sure the systems operate efficiently by not mowing grass into the curb. Please take the time to sweep or blow the street grass back onto the lawn. If you have catch basins in your neighborhood, take the time to make sure it is cleared off before rainfalls come.
The Village does have ordinances prohibiting discharging grass into the street. Please help to protect the environment and your community from the damage that grass clippings can inflict!