Different Types of Flooding
Elmhurst residents, generally, can experience flooding in 5 different ways:
- Street Flooding that Rises and Threatens Property
Overland Flooding (large amounts of water flowing to properties from the neighborhood)
Sanitary Sewer Backup
Street flooding occurs when the City’s storm sewer system’s ability to take in and convey water is exceeded. Like all drainage systems, Elmhurst storm sewers have a limited capacity. A level of protection was chosen years ago to balance impacts and costs.
Occasionally, intense storms exceed the capacity of the system and water sits in the streets and yards for a period of time. The City has developed detention areas designed to store water during these events. Notably the most vulnerable property to this type of flooding is the home with a “down sloped” driveway.
The amount of street flooding that may occur in any given storm is also impacted by the amount of debris that may be in the street. The debris can clog inlets and greatly reduce their ability to take water. In order to reduce the time water sits in the street, the City aggressively cleans its streets of the debris that may clog inlets and pipes. The City also proactively sweeps areas within the City that are prone to this type of problem prior to the arrival of a known storm. The limitations of this are, of course, the storm has to be predicted accurately in advance and even though the area is swept, if the storm is strong enough it knocks the leaves right off of the trees negating the sweeping efforts. The City also does request residents help with clearing inlets during a storm.
Overland flooding can be a damaging and even scary occurrence. Due to the somewhat flat topography of northeastern Illinois, it is sometimes difficult to discern that one is at the bottom of a very large, albeit not steep, hill. Water sits in low spots in private yards from time to time. The City offers a program to assist property owners who want to drain low spots of their land to the public storm sewer system.
For example, upon close examination of contour maps it was discovered that an area of 395 acres drained directly to a point right between a set of homes in the City. These 395 acres had approximately 40 feet of fall across it. Unfortunately, there is no “fix” to this situation, the topography cannot be changed and there is not a structure or system that could be constructed to redirect or absorb that amount of flow. In these cases the City works with the property owner to help them protect their home from large events. The land will go under water; the goal is to flood proof the home.
For information on the program that the City offers to assist property owners who experience flooding, please click here.
Sanitary sewer back up occurs when the sanitary sewer is surcharged. A sanitary sewer system is designed and sized to carry waste water away from a residence to the City's wastewater treatment plant, where it is treated and the effluent pumped into Salt Creek.
What causes a sanitary sewer to surcharge is clean water getting into the system via inflow (such as illegally hooked up sump pumps) and infiltration (small cracks and open joints in the pipe). This is more commonly referred to as “I and I”. The City has aggressively sought to reduce sources of I and I through numerous programs, including nearly $1 million annually on sanitary sewer lining. No matter how much of this work occurs, a home that is directly connected to the sanitary system without some mechanism to prevent back flow will always be at risk.
The best mechanism to prevent back up is the installation of an overhead sewer. This type of plumbing basically insures that no sanitary water can backup into a house. An overhead sewer is a passive system – meaning it takes no human intervention for it to work. The City offers up to a 50% cost share with the homeowner (up to $5,000). For more information, please see "Overhead Sewer Program."
Seepage occurs when water infiltrations the home through a variety of means such as cracks or holes in the foundations, a gap between the foundation and the wall, or a window opening that is not sealed correctly.
Salt Creek Overbank Flooding
Overbank flooding is when a stream's capacity to carry water is exceeded and the water profile rises to a point where the stream leaves its banks and flows into the surrounding area. This area is known as the flood plain.
The levee runs for over a mile and protects over 1,400 homes. The quarry holds 8,300 acre-feet of water, an amount equal to the volume of the entire 1987 event. The City did not incur any overbank flooding during recent heavy rain events.