As the area around the Rock Chalk Park sports complex develops, a group of drainage leaders is predicting flooding along the Kansas River will become more frequent, unless the city changes future development regulations.

Leaders of the Kaw Valley Drainage District persuaded Douglas County commissioners Wednesday to support a study of how development in northwest Lawrence will affect flooding along the Baldwin Creek tributary and portions of the Kansas River.

At risk are thousands of acres of farmland and dozens of residences along the south banks of the Kansas River west of Lawrence, said Charles Taylor, president of the Douglas County Kaw Valley Drainage District.

“We know that these areas are naturally going to flood from time to time, but we don’t think the city should be doing things to flood us more often,” Taylor said.

County commissioners at their Wednesday evening meeting unanimously agreed to craft the letter asking the Lawrence City Commission to jointly study drainage issues in and around northwest Lawrence. The county is proposing to pay for 40 percent of the cost of the estimated $75,000 study. It hopes the city will pay for 40 percent and the drainage district would pay for the other 20 percent.

The area to be studied is the Baldwin Creek drainage basin, which basically is an area south of the Kansas River, west of Wakarusa Drive, north of Sixth Street and extending into the county to a point known as Kanwaka Corner, which is about two miles west of Lawrence on U.S. Highway 40.

The study will provide data about how much water various creeks and tributaries can handle. But drainage leaders are hopeful the study will be the first step in the city tightening its stormwater regulations.

Taylor said the need for stronger stormwater regulations came into focus with the development of the Rock Chalk Park sports complex at Sixth Street and the South Lawrence Trafficway.

An engineer hired by the drainage district estimates the detention ponds for the Rock Chalk Park complex need to be about 50 percent larger to ensure that property downstream won’t be negatively impacted by heavy rains.

Taylor said the drainage district knows it is too late now to change the requirements for Rock Chalk Park, but he said the city can still act to improve the regulations for future development.

The city does have stormwater regulations that require developments to control the peak amount of stormwater that can come off a developed site. But Vic Robbins, an engineer with King & Associates in Holton, said the city regulations do not pay enough attention to the total volume of stormwater that can run off a developed site, and that regulations don’t do enough to control when detained stormwater can be released.

Development creates larger volumes of stormwater runoff because of the buildings, parking lots and other impervious surfaces it creates. Robbins said by focusing only on the peak flows of stormwater, the city is allowing development that can still overwhelm existing creeks, drainage ways and portions of the Kansas River at times.

Robbins said larger and deeper detention ponds for development may be part of a future solution, or, he said, developers may want to combine their resources to build small lakes of several acres that could retain water for multiple properties in the region.

County commissioners did not weigh in on any of those potential regulation changes, but rather said that a study would be a good first step in assessing potential drainage problems in the area.

The county and the drainage district expect to present a letter to city commissioners asking them to consider the study in the next several days.

In other news, county commissioners:

• Accepted a new set of estimates for bridge work on Douglas County Route 1055 south of Lawrence. Commissioners previously had been told it would cost about $100,000 to make concrete repairs to the Wakarusa River bridge on County Route 1055, which is about a mile south of 31st and Haskell. But commissioners were told further evaluation of the bridge has increased the estimated cost to about $356,000. Commissioners were told the county had the necessary funds in a capital improvement fund. Work likely will begin next summer, and it will reduce traffic to one lane on the bridge during the project.

• Unanimously agreed to to allow dirt work to begin at the Penny Sand Pit at N. 1500 Road and E 1850 Road between Lawrence and Eudora. Originally, earth-moving work was not approved to begin until a contract had been approved for county road improvements near the site. But design work for those road improvements has been delayed, and the project is not expected to start until this spring.

Officials with Penny want to do dirt-moving at the sand pit site prior to spring. Commissioners agreed to the change in conditions after officials for the project assured commissioners that the dirt work would not create any extra truck traffic on the county roads. Commissioners kept in place a condition that sand mining at the site can’t begin until the county road improvements are completed.