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How flood control in Armstrong Park is supposed to work

August 4, 2010

It’s worth taking some time to try to understand how Carol Stream’s flood systems are supposed to work, and how people believe the system is failing.

1.) When rain first falls, it is collected into retention ponds, until they are filled to capacity. Each of these ponds can hold a certain volume of water, and in stormwater management, that volume is measured in “acre-feet”. An acre-foot of water is equivalent to one acre of land covered in one foot of water. It’s much easier to measure in acre-feet, because even though most people measure water in gallons, “one acre-foot” is easier to say than “325,851 gallons”.

I do not have measurements for how many acre-feet any of these first-level retention ponds can hold; DuPage County likely knows what that value is, because stormwater engineers there have done rainfall modeling for our watershed. The Gary-Kehoe reservoir can hold 140 acre-feet, or about 45,619,140 gallons of water at full capacity.

2.) Lake George is the primary destination for runoff from a relatively large area. As it fills to capacity, Lake George overflows into another detention basin to the north, which effectively doubles (or more) Lake George’s capacity. Located at the eastern end of this basin is a lift pump. Village engineers use this lift pump to pump water out of the basin back into Klein Creek when the threat of flooding has passed.

From 5 years of observation, it takes about 1.5″-2.5″ of rain (depending on how saturated the ground is) for this northern basin to begin to fill.

3.) After about 3-4″ of rain (surprisingly, we have only had one storm in 5 years drop less than 7 inches but more than 3 inches of rain), the flood pool overtops the northern detention pond and begins to fill the rest of the park; this continues until the water level reaches the southeastern portion of the park, near the library, and spills into Klein Creek.

4.) However, if more than 5″ of rain has fallen, runoff from Mitchell Lake will cause Klein Creek will reach that point before the floodpool in Armstrong Park does, causing water to flow into Armstrong Park from Klein Creek. This is a particularly bad sign; it means that runoff has already brought the creek to flood stage, and that additional runoff that will flow into Armstrong Park will serve merely to increase the floodwater level.

5.) Occasionally, a great deal of rain falls in a very short period of time (3-4″ in 2 hours). This can cause creek levels to fluctuate wildly: the creek will rise to a high level from the initial runoff, then fall back to a lower level as excess water runs into Armstrong Park, then rise again as Armstrong Park fills from the bottom and begins to spill back into the creek.

In short, the system works great… until more than a certain amount of rain (probably 5″) falls. Expanding the system to accommodate more rain is difficult, and the alternatives will be covered in later posts.

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2 Comments leave one →
  1. Bruce MacPherson permalink
    June 30, 2011 7:45 am

    Is there any plan to deepen or widen Kline Creek? Or create more detention ponds further south that Kline Creek could flow into in case of extreme flooding conditions? Might such renovation even exclude the need to do such costly proposed renovation at Armstrong Park?

    Our house (642 Adobe Ct.) doesn’t flood, but could very easily do so. We help near neighbors who have been less fortunate. We appreciate the concerted and combined effort being put forth to resolve this huge problem.

    • lpangelrob permalink*
      June 30, 2011 9:47 am

      Bruce,

      Thanks for commenting. There are no current plans to deepen or widen Kline Creek. Most flood ordinances throughout the country prevent municipalities from doing, likely for two reasons: 1.) It’s obscenely expensive (DuPage River thorium removal project: $100 million, 77,000 yards) 2.) It needs to be done every few years to remain effective, and 3.) municipalities aren’t allowed to relieve their current flooding problems by causing problems downstream, except some cases, see below.

      Surprisingly, detention ponds anywhere south of Thunderbird Trail would do nothing to relieve flood problems upstream. This is because there is a local topographical “choke point” that only lets a certain amount of water through. As the water level gets higher, this area can convey more water downstream, but in cases of severe flooding, the amount of water entering this choke point far exceeds the amount of water able to leave. The current solution would allow for a diversion sewer increase the flow of water from Armstrong Park to Kline Creek, further downstream.

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