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, 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.
So what starts out as not such a big deal for one person can leads to a big deal impacting thousands of people traveling along the roadway each day. It might blow away, but it might not. The Village might be able to sweep it up, but that could be a month away. It takes the sweeper 2.5 weeks to go through the Village one time. There are over 130 curb miles to sweep and our stormwater permit madates we sweep the streets at least once a month. It would be nice to get flash flood warnings scheduled a month out so we can take care of any debris in the street, but that does not happen.
The previous paragraphs address what happens to the surface, but 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 down stream. 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 1200 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. That is why 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.
Every little bit helps. Spread the word to your neighbors and make an impact one person at a time. The Village has ordinances prohibiting discharging grass into the street. No one wants to endure the embarrassment of having a Village official issue a warning or citation for "just a little grass". Please help to protect the environment and your community from the damage that grass clippings can inflict!