Lawrence city commissioners hinted Thursday they might adopt more restrictive floodplain regulations than recommended by the Lawrence-Douglas County Planning Commission.

During a study session on the issue, officials said the floodplain was expanding as the city grew. It might not make sense, they said, to approve regulations that don’t take that into account.

“We’re already dealing with (floodplain) maps that are 5 years old,” city planner Bryan Dyer said. “The city has added streets and impervious surface that don’t show up on this map.”

Next month, the city commission will have two versions of floodplain regulations to approve. Both would require builders to do a hydrological study showing their development wouldn’t expand the floodplain.

The version recommended by the planning commission applies only to properties already designated by the Federal Emergency Management Agency as part of the 100-year floodplain.

A second version, advocated by planning staffers but not recommended by the planning commission, would make those rules also apply in a bigger “Drainage Protection Overlay District.” That district includes all the areas, more than 1,000 pieces of property, that would be covered if the FEMA floodplain were expanded by 2 feet  an area also known as “freeboard.”

During the study session, Commissioner Marty Kennedy noted the FEMA floodplain is based on 1996 data. Development since then had probably made the floodplain bigger, he said.

“The freeboard brings us back closer to what the FEMA map would be at this point in time,” Kennedy said. “In fact, the FEMA floodplain might be larger than the freeboard.”

Commissioners are scheduled to decide which version of regulations to adopt at their meeting at 6:30 p.m. in City Hall, Sixth and Massachusetts streets.