Is There a Flood Control Problem?? Flood April 2013

Yesterday, maintenance, management and a board member became aware of a situation with the Lake #4 Retention Pond. This resulted in a flurry of activity which eventually made it's way to the Chicago news stations. As is the case with most of these situations, this was merely the tip of the iceberg. There was a flurry of activity which preceded placing sand bags near a manhole on the south side of the lake.

There have been questions raised about the County flood control system. I raised some of those questions, as did others during recent COD expansion hearings. However, finger pointing is not the purpose of this post. What needs to be determined is simply if the existing flood control system for this part of DuPage County is adequate. This storm was not the worst in this area (See Note 1:  July 17-18, 1996 Wheaton received 9.52 inches). However, it has been reported that on April 18-19  the East Branch of the DuPage River rose 10 feet above the pre-storm level and reached a height 2 feet above the all-time record.

Recent videos I've taken show large water outflow from the College of DuPage to the Lake #3 and #4. They also show overflow of Lake #3 which created a river running from the North to the South and into Lake #4. That river bypassed the restrictors in this flood control system, and resulted in uncontrolled flow to retention Lake #4.

However, the discharge of Lake #4 is restricted! This high flow upstream of Lake #4 may have caused the high levels of that lake and the overrun of the berms on the south side of the lake. Residents of South Wheaton need to ask this question "Are the County of DuPage flood control systems adequate?"

Allowing unrestricted flow into Lake #4 while restricting outflow may jeopardize south Wheaton. This association pointed this out to County and COD officials as part of the concern of BLMH residents about the ambitious construction programs at that college. Yes, with only 6 inches of rainfall in a 24 hour period, we were surrounded by water on three sides for two days, with the flood runoff from the north and east literally "lapping at our doors."

These concerns had been raised with the County and the College of DuPage and the larger, redesigned COD retention/detention pond was supposed to alleviate this situation. However, the videos posted here in recent days indicate that these efforts were INADEQUATE. Throughout this entire episode the college was "high and dry" as it has successfully created a system which, in my opinion, drains it's runoff into the neighboring communities.

It's my opinion the current situation was avoidable, and the water retention system at the College of DuPage is flawed. It may also be that the County flood control system is also flawed!

Temporarily, sand bags were used to stabilize a possible breach of the retention pond wall after water levels had already overrun the banks. However, the water in that pond reached almost to the top of the pond discharge and the overflow point. It reached a height sufficient to run over the berm on the south side of the retention pond and the wetlands.

I'm sure the County will step in and tell others to "fix this." But as I stated to a resident of South Wheaton, just how high are these berm walls to be built? It's impractical to contain the flow of water from upstream retention ponds #1, #2, #3 and the College of DuPage in a single retention pond.

This was a close call for about a thousand homes. Nearby residents told me they were unawares of the situation. Was this a wake-up call?

Notes:

Note 1. This added April 28. I originally listed 1993 has having a higher rainfall. it was 1996. Here are some recent statistics for "24-hour rainfall depth, inches":

August 13-14, 1987; 7.26" rainfall according to DuPage County

July 17-18, 1996; 9.52" rainfall according to DuPage County

September 12-13, 2008; 5.27" rainfall according to DuPage County.

Note 2. There are different methods in use for reviewing maximum rainfalls. Here are a few:

• Rolling 24-Hour Totals  - Picks up storms that straddle over two calendar days 
• Calendar Day - Totals for a specific day
• Annual Duration - The Largest Event in Each Calendar Year.

Note 3. The term "100 year" rainfall is used to describe a rainfall that has a 1% chance of occurring.  The problem is, when designs are based upon such rainfall data, as is true with many things, it all depends upon the data used. A "100 year rainfall" could mean 7.25 inches of rain in a 24-hour period, or 8.68 inches. The recent rainfall did not reach these levels according to the National Weather Service.

What does a "100 year" rainfall mean? If there is a 1% chance of such a rainfall each year, then such an event could occur with a frequency of once each hundred years. However, that's a description, not a fact. The facts are, Wheaton is getting a "100 year" rainfall about every 10 years! How can that be? Let's just say that if we think a 100 year event will happen only once in 100 years, then we are mistaken and we are gambling. The biggest gambling myth is that an event that has not happened recently becomes overdue and more likely to occur. This is known as the “gambler’s fallacy.” The opposite is also true. Simply because a "100 year" or 1% rainfall occurred last month, does not mean that it cannot occur next month. In fact, such a rainfall could occur every year. 

As a design criteria, a 1% rainfall is useful for determining how much rain might occur in a 24 hour period; that provides engineers with some idea of how much water their retention designs must accommodate  However, it's useless for determining how frequent such a rainfall can or will occur. What this means for those living in the area immediately to the southwest of the College of DuPage is simply this. If a 1% rain causes that area to flood, it will flood each and every time such a rainfall occurs. Assuming that this event will happen only "once every 100 years" is a grave mistake.

There are also other possibilities, including 5-year, 10-year and 25-year rainfalls.  So what would those rainfall totals be? There are different methods of using the data available.

Here is a list of 24 inch rainfall depths for Wheaton, using the "Gumbel extreme distribution" method. This provides some smoothing of the data:

• 5-year, 24 hour rainfall = 4.29 inches. 
• 10-year, 24-hour rainfall = 5.03 inches. 
• 25-year, 24 -hour rainfall = 5.96 inches.
• 50-year, 24-hour rainfall = 6.66 inches.
• 100-year, 24-hour rainfall = 7.35 inches. 

Here is a list of 24 inch rainfall depths for Wheaton, using the "Log Pearson Type 3" analysis:

• 5-year, 24 hour rainfall = 3.89 inches. 
• 10-year, 24-hour rainfall = 4.71 inches. 
• 25-year, 24 -hour rainfall = 6.03 inches.
• 50-year, 24-hour rainfall = 7.24 inches.
• 100-year, 24-hour rainfall = 8.68 inches. 

Note 4. It's probably worthy of a separate post on this data and what it may mean for Wheaton.  The above  Gumbel and Log Pearson data is from a report prepared by Megan Elberts which was entitled "How Recent Rainfall Events Compare to Bulletin 70," which was presented at the 2012 IAFSM Conference.   "Bulletin 70" was data published in 1989 regarding heavy rainfalls  in Illinois. 

Note 5. Natural Disasters in DuPage County. (http://www.city-data.com/city/Wheaton-Illinois.html)
 According to city-data.com the number of natural disasters in DuPage County was 13. Here's a list, but some incidents may be assigned to more than one category:

Major Disasters (Presidential) Declared: 9 
Emergencies Declared: 4
Causes of natural disasters: 

• Storms: 7,
• Floods: 6
• Snowstorms: 2
• Blizzard: 1
• Snow: 1
• Tornado: 1
• Winter Storm: 1
• Flood: 1
• Hurricane: 1
• Tornado: 1
• Winter Storm: 1 

Note 6. I  once posted here that our association was in "no man's land" between Wheaton and the College of DuPage/Glen Ellyn. I think that is true. In fact, here's a link to a neighborhood map of Wheaton. We don't exist in any recognized neighborhood!

http://www.city-data.com/nbmaps/neigh-Wheaton-Illinois.html

Note 7. How much water falls on the College of DuPage in a 1% rainfall event? This depends upon how one measures a "1% rainfall event." Let's assume such an event covers the 273 acres of COD with 7.25 inches of water. Here's one number to think about: 56,000,000 gallons. Yes, that's right. COD doesn't retain but a very small portion of the rainfall that hits the campus. So about 56 million gallons have to be "dispensed" via their drainage systems into the nearby water rainfall drainage systems. When those systems are filled, the excess flows elsewhere, such as the "wetlands" on the [southwest] corner of the college, and from there into retention lake #4.  In fact, some of COD's rainfall drainage systems carry the water just far enough to dump it in the "wetlands" thereby assuring that it will continue to flow downhill into retention lake #4.

If the volume of the "wetlands" and retention lake #4 can't handle the water directed to it, then it simply flows downhill into the homes in that part of Wheaton! As far as the College is concerned, this is a good system because the college is high and dry. As for everyone else downstream? I guess that's "their problem." That, by the way, accurately describes the situation since the 1987 "flood." What's been done about this? COD has constructed more parking and better and larger (higher capacity) underground systems to drain the college property and protect it. Oh, and one small retention pond (pond 9) was recently built. But where is the water conveyed by these systems? Oh, that's someone else's problem!

Press Releases
Here are the City Press Releases on this issue, with the most recent at the top:

PRESS RELEASE - City Of Wheaton

4/22/2013

Briarcliffe Lake 4 Status Update

WHEATON, Ill. – Lake 4 of the Briarcliffe subdivision has returned to normal water levels and continues to be stable. Wheaton’s Public Works Department has sandbags in the area to use if necessary. The City will continue to monitor the lake. Updates will be posted as they are available.

People who want to sign up to receive press releases by email as they are issued may use the City’s email notification system here: http://www.wheaton.il.us/emailupdates, and choose the "Press Release" option at the bottom.

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PRESS RELEASE - City of Wheaton

4/21/2013

UPDATE: Briarcliffe Evacuation

Emergency personnel have stabilized the Lake 4 retention pond with sandbags and residents from the immediate are have been evacuated. The situation is ongoing and will be continually monitored throughout the evening and morning hours. A full assessment will be made early Sunday, April 21 and updates will be posted to the City's website.

Further information will be posted to the City’s website or will be available by calling the Wheaton Police Department at 630-260-2161. 

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PRESS RELEASE - City of Wheaton

4/21/2013

UPDATE 2 - Briarcliffe Evacuation

WHEATON, Ill. – This morning members of the City of Wheaton’s engineering and public works personnel assessed the Lake 4 retention pond breach and determined it to be stable. Residents who evacuated their homes can return.  The City will continue to regularly monitor the situation throughout the day and consult with experts as time progresses.

 For any residents who have had utilities turned off:  If their natural gas service was shut off, they are advised to call Nicor to check appliances and reestablish service. If electrical power was turned off due to flooding, a qualified electrician should be contacted to evaluate their system before restoring power.  

 Ongoing information will be posted to the City’s website or will be available by calling the Wheaton Police Department at 630-260-2161.  People who want to sign up to receive press releases by email as they are issued may use the City’s email may use the City’s email notification system here: http://www.wheaton.il.us/emailupdates, and choose the Press Release option at the bottom.

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PRESS RELEASE - City Of Wheaton

4/20/2013

Evacuation Recommended for Homes Near Lake 4 Retention Pond

WHEATON, Ill. – The Lake 4 retention pond to the north of Brentwood Lane in the Briarcliffe subdivision is currently leaking but stable, causing the potential for the berm to breach. Homes in the immediate area could experience flooding if this occurs.

The City is recommending evacuation of residences in the area bounded by:

• Brentwood Lane to the north
• Nottingham to the west
• Windsor to the south, and
• Cheshire to the east.

Residents in this area have been contacted by the City of Wheaton’s reverse 9-1-1 system alerting them of this condition. This evacuation is recommended until further notice. Anyone needing temporary shelter can go to the emergency shelter at the Krasa Center at Benedictine University, 5700 College Road in Lisle.

Further information will be posted to the City’s website or will be available by calling the Wheaton Police Department at 630-260-2161.

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