Fourmile Creek Floodplain & Floodway Updates

A public meeting was held on Tuesday, November 20, 2007, on Des Moines’ east side to talk about the revised floodplain and floodway maps around Fourmile Creek. The maps were updated recently thanks to a survey by the U.S. Army Corps of Engineers and compilation of data from storm events. The Federal Emergency Management Agency (FEMA) last updated the zones in 1987. I was unable to attend the meeting, but I did talk with employees in the city’s community development and engineering departments.

One of the many questions I had was about the proper name for the waterway. I have seen it spelled as one word, as two words, and with a numeral. The single-word version is what the city uses officially. The creek starts in Boone County, runs for 26 miles, and has a drainage area of 92.7 miles. In the graphic to the right, Fourmile Creek is shown in orange. The creek curves down from the northwest (not shown), starting at a point roughly north of the arm jutting off of Saylorville Lake. As the creek heads towards the Des Moines River, it runs through Pleasant Hill from University to Scott Avenue.

Both of the city employees with whom I spoke stressed the large size of the creek’s drainage area when talking about flood control. Planning Administrator Mike Ludwig pointed out that Des Moines has authority over only a small part of the creek’s route. Development decisions made by other municipalities and county governments impact how much water runs into the creek and how quickly it enters the waterway. I talked to people who know the east side area and they thought the city had spent money on flood control about five to ten years ago. However, according to a city engineer who deals with storm water and sewers, a storm basin and related work was not connected to any flooding of Fourmile Creek.

The current map revisions, according to the city employees, came about when residents who live near the creek complained in 2000 or 2001 that their properties were being flooded. Apparently, the 1987 maps did not include those properties in the floodway or in the flooplain. The city received grant money to help pay for an updated study. The Army Corps of Engineers was already in the city doing analysis on the Des Moines River.

FEMA manages the National Flood Insurance Program (NFIP), which has three parts: flood insurance, floodplain management, and flood hazard mapping. The FEMA web site has an interactive tool to determine how much flood insurance would cost depending on the risk (low to moderate, with and without prior flood claims; high; and, coastal high). Insurance may be bought for either ground or contents separately or for both together. Prices for combined insurance covering $250,000 and $100,000 in ground and content damage, respectively, range from $317 annually for low to moderate risk without prior flood claims to $5,358 per year for a high risk coastal residence. Separate $500 dollar deductibles apply to ground and to content damage even when combined insurance is bought. Some mortgage lenders may require homeowners in a floodplain or a in floodway to buy flood insurance.

A floodway is defined as the channel of the creek plus the adjacent land that is needed to spread the flood waters without raising the elevation of the water’s surface more than a foot. A floodplain is the relatively level land on either side of the creek’s banks that is subject to flooding. The 100-year floodplain is the area around a waterway that is expected to flood once every hundred years. Just glancing at the new maps it appears that, in general, the floodway has been reduced slightly but the floodplain has been expanded by several blocks. However, any given piece of property along the course of the river may have a different type or degree of change as the adjacent land.

The revised maps will not help to provide relief from flooding. Instead, being included in one of the designated areas may allow homeowners, renters, and businesses to obtain flood insurance under the NFIP. In addition, the designations will not limit development but certain requirements, such as the height of living space above flood levels and inclusion of retention ponds, may apply.

The Army Corps of Engineers applies a cost-benefit analysis to flood control measures. According to the storm water engineer, there is a negative cost benefit assigned to Fourmile Creek. In contrast, the value of some businesses along the Des Moines River means there is a high benefit compared to cost for changes along that waterway. Residents living near Fourmile creek believe the cost of insurance should be included in the cost analysis done by the Corps. Flood analyses were also done for the Raccoon River and Walnut Creek.

M.R. Field is editor of Leading Voices: Iowa.

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