City of Prairie Village, Kansas
When Overland Park, Kansas, resident Keith Carr found himself traveling east rather than west on an unfamiliar stretch of rainy 83rd Street the night of Aug. 29, 2016, he made a quick left onto the next side street he encountered in order to turn around: Delmar Lane.
Meanwhile, a few miles to the north, emergency crews were busy rescuing stranded motorists from high water left by the 25-year storm event that had just passed.
Straining through the rain hammering his windshield to spot the next cross street, Carr traveled less than a block before missing the warning sign and running full into the low-water crossing that by this time was swollen by several feet of rushing water. His Ford Mustang suddenly spun 180 degrees by the current, Carr found himself floating off the roadway. He pushed the door open and swam for the bank, where, holding tight to a tree limb, he watched the tail lights disappear downstream until his car came to rest against the double culvert passing under Somerset.
Carr had encountered a problem the City of Prairie Village had struggled with for years. One neighbor told the Shawnee Mission Post he could recall at least two other similar incidents, including a 16-year-old who had to be rescued in 2001. “What I want to see is that nobody dies there,” he told the news site, “and someone will one day.”
The Delmar Lane low-water crossing, along with another upstream at Fontana, had regularly flooded at less than the 20 percent annual occurrence flood event. In addition, seven homes on Delmar Lane and Somerset Drive were threatened by the 1 percent annual occurrence flood event and had flooded in the past. In particular, significant flooding occurred on Oct. 4, 1998.
Over the course of the years, Prairie Village had asked other engineering firms to evaluate the situation and recommend alternatives. While many alternatives had been developed and studied, none were ever proven to solve the problem cost-effectively.
The most recent round, in 2011, estimated the solution at between $4.6 million and $5.9 million — a solution that Water Resources Solutions, when asked by Prairie Village for an evaluation, discovered would not protect homes and travelers sufficiently to qualify for funding from the county’s stormwater projects fund. WRS employed its hydraulic and hydrologic modeling expertise to evaluate the validity of the flood-elevation reduction. WRS’s study demonstrated the updated Northeast Johnson County Watershed Study modeling indicated three of the seven identified houses would still flood after the project was completed using the suggested alternatives. With only four houses taken out of the flooding, the project would not receive a ranking high enough to make it funding eligible.
Based on its analysis, including use of three-dimensional computational flow dynamic hydraulic modeling of the project reach, WRS advised the city instead to consider altering the channel to lower the flood elevation, and to construct a triple-cell culvert running north of the Chateau Condominiums. That elegant solution successfully removed all but one of the seven houses from flooding, allowed both dangerous low-water crossings to be replaced by culverts, and created the added benefit of avoiding the impact to utilities and the roadways that the previously suggested bypass system would create.
At the same time, WRS solved the aesthetic problem of using hammerhead cul-de-sacs, which was considered by most of the residents to be an objectionable alteration to the quality and culture of the neighborhood. By altering the channel, WRS was able to design culverts to replace the low-water crossings and keep Delmar and Fontana through streets, without significantly sacrificing stormwater handling capacity, providing capacity to convey the 1 percent annual occurrence flood under the roadway. WRS engineers worked closely with residents, the city and construction vendors to design the culverts at Delmar Lane and Fontana Street to fit with the character of the neighborhood. And the cost to do so was only 3.8 percent more than the original project cost to include cul-de-sacs, a solution the city was so satisfied with that it chose to absorb the additional cost itself.
Construction began on the project in early summer 2019, at a final estimated cost of $4.8 million, with a completed solution to this vexing problem accomplished in winter of 2019.