State doing re-evaluation of Smoky Hill watersheds

May 17--With all of the rain that has fallen on the Kansas prairies since February, one concern that inevitably follows is the possibility of flooding.

Dane Bailey, a floodplain mapping coordinator with the Kansas Department of Agriculture, has been collecting data for the newest Federal Emergency Management Agency (FEMA) floodplain maps since the fall of 2016.

The goal of floodplain mapping for the Lower Smoky Hill River valley is to digitize the new information and revise the current maps which are only available in paper copies.

Dickinson County is one of 15 Kansas counties where the maps on record are only available on paper. The goal Bailey has for the study in progress is to digitize the data for the future so it is available everywhere and can be updated any time. These paper maps date as far back as the 1970s and only reflect studies done in the mid-1980s with few revisions.

To do this, engineers from Bailey's department use a remote sensing method called LIDAR (light detection and ranging) to map out the area. Bailey said the LIDAR measurements taken from low-flying aircraft are accurate down to a tenth of a foot. This new method of mapping is better than the traditional method of using contour maps, he said, because the contours are spaced 10 feet apart.

As a part of this study, Bailey's crews mapped the local watersheds, evaluating the ever-changing landscape and checking to see which creeks have dried up and what the flood of record is for water sources. They studied the contours of the creek and riverbeds and used data from long-term gauge records to model the amount of water flow (both normal and at peak levels). The normal and peak water levels are determined both by existing data and a statistical analysis of what has actually occurred in the past.

"We are modeling major flooding so the maps will reflect that," Bailey said. "This summer is still the point we expect to be able to begin providing initial draft data to communities."

When it comes to mapping floodplains, engineers are estimating the occurrence of a flood based on previously recorded water levels and an equation that predicts the likelihood of flooding. These water level measurements and flood tables are used to help insurance companies determine the risk and severity of potential flooding.

It also helps consumers buy flood insurance for their homes based on if they live in a floodplain. The cost of flood insurance is determined by the interval of flooding that occurs where the house is and the likelihood of a complete loss that may result.

Determining what types of watersheds are present also determines the types of zoning cities are allowed to make, whether it is for a residence or for a business district.

For Abilene residents, the flood of record for the Smoky Hill River is the flood of 1951. The river crested at 34 feet, July 14, 1951, and inundated the south side of Abilene, causing more than $.5 million in property damage and losses.

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