Why Flooding Sometimes Occurs
in South Holland

Over-bank Flooding

South Holland is subject to over-bank flooding from three sources: the Little Calumet River, Thorn Creek, and the Calumet Union Drainage Ditch. The Little Calumet River flows through the Village from east to west. The Little Calumet drains northeastern Illinois and northwestern Indiana via several tributaries. At South Holland, the river’s watershed is over 200 square miles. A small tributary, Thorn Ditch, drains the central part of South Holland. Its over-bank flooding is caused by backwater from the Little Calumet.

Thorn Creek flows from the south and joins the Little Calumet on the southeast side of town. Thorn Creek collects water from Deer, North, and Butterfield Creeks, and Lansing Ditch. The Thorn Creek basin drains over 100 square miles, accounting for over half of the water that enters the Little Calumet at South Holland.

The third stream is the Calumet Union Drainage Ditch, a man-made ditch that drains 18 square miles of the Markham and Harvey areas to the west. It joins the Little Calumet River in the west part of the Village.

Most of the Village’s over-bank flooding problem is in the Little Calumet River’s floodplain. Because the area is so flat, the flooding of one stream is accompanied by flooding on the other two. Therefore, while there are three sources of over-bank flooding, the problem is treated as one floodplain.

Flooding History

Flooding has occurred in South Holland’s streams since the last glacier left Illinois. Early settlers avoided building too close to the rivers. As late as the 1940s, large areas of the south suburbs remained vacant, primarily because it was too marshy to build on. These areas were used by the rivers to carry and hold excess rain runoff and snow melt.

Beginning in the late 1940s, this scene changed as the Chicago area population expanded to the south. Urban development put pressure on the vacant land along the rivers. The floodplains were built up during the 1950s and 60s, primarily with single-family housing. It was not until the 1970s that local governments passed floodplain management regulations to require the elevation of new buildings in the floodplain. Since then, floodplain development has slowed down, but developers still fill flood prone areas for new homes or commercial properties.

In the 1920s, the Calumet-Sag channel was completed and the Little Calumet received an additional outlet. Instead of flowing into the Grand Calumet and Lake Michigan, most of its water now flows west through the Cal-Sag to the Des Plaines River. There are locks on both the Cal-Sag and the Grand Calumet to control low flows.

At the other end, Burns Ditch was connected to Lake Michigan in the 1920s. During high flows, the Indiana portion of the Little Cal drains west. These two diversions mark the northwest and eastern limits of the Little Calumet River’s watershed.

With post-war growth to the south of Chicago, farmlands were replaced with roofs, parking lots, streets, gutters, storm sewers, and more ditches. Under urban development, more rainwater ran off the land and into the rivers and it ran off faster. As with floodplain regulations, it was not until the 1970s that communities began storm water management regulations that require developments to restrict runoff.

In short, while the rivers of the Little Calumet basin flooded in the past, the problem has escalated since the 1940s. Until 1981, the worst flood on record for all three streams was in July 1957. Heavy summer storms caused widespread flooding in northeastern Illinois. The subsequent flood on the nearby Kankakee river was estimated at being a 750-year flood.

The 1957 flood was exceeded in 1981 by another flood caused by summer storms. While there was not as much rain as in 1957, the 1981 flood caused much more damage because there was more development. Because so many homes and businesses were affected, the June 1981 flood resulted in a Presidential Disaster Declaration for the area. Another presidential declaration followed the December 1982 flood.

One of South Holland’s worst floods on record occurred in late November 1990. Heavy local storms caused the Little Calumet and its tributaries to rise higher than before, over half a foot higher than the 1981 record.

Flood Data

Flood heights have been recorded since 1947 on a river gauge that is currently located at the Cottage Grove Avenue bridge over the Little Calumet. Recorded flood heights can be shown in stage or in elevation. Stage is measured in feet above an arbitrary starting point that was set when the gauge was first installed. Elevations are in feet above sea level.

“Flood stage” is the elevation where the river leaves its banks. There is no official “flood stage” for the Little Calumet. Yards and parks are flooded when the river reaches an elevation of approximately 590 feet above sea level. Buildings are affected at approximately 593 feet.

The 100-year flood at Cottage Grove would reach an elevation of 598.0. The 500-year flood is predicted to crest at an elevation of 601.5, 3 1/2 feet higher than the 100-year flood. As the river flows from east to west, flood elevations are higher in the east and lower in the west. The 10, 100, and 500-year flood elevations for various locations are shown below:

Projected Flood Elevations

Village Flood Services

The Code Enforcement office at 16240 Wausau Avenue (210-2915) provides the following:

• Information on whether a property is in a mapped floodplain, and related flood insurance rate map data
• General records of past flooding throughout the Village, but not for specific parcels
• Advice on how to protect a building from water problems
• Guidance on the laws that govern construction and property improvements
• Site visit (when a lot is part of a flood rebate program and after receipt of at least two estimates from waterproofing companies) to view the cause and suggest possible solutions to a problem

Flood maps and flood protection references are also available at the South Holland Public Library.