The Howard County Council is considering a measure that would temporarily halt commercial and residential development around Ellicott City after July's deadly flash flood in the historic mill town.

Councilman Jon Weinstein, who represents Ellicott City, said he proposed the building freeze so that the county could critically examine whether development “poses additional threats to the safety of people, businesses and property.”

His proposal would stop new development in the Tiber-Hudson watershed for nine months. The Tiber and Hudson streams, which feed into the Patapsco River, overflowed during the flood.

Andy Barth, spokesman for County Executive Allan Kittleman, declined to take a position on the bill, saying the administration is reviewing it.

“We'll need to study more to come to a determination,” Barth said.

Meanwhile, Howard County officials are looking at the impact of development on the area's waterways. The county is conducting hydraulic studies of the watershed and other analyses that will also examine how flooding is affected by development.

Weinstein said he believes development contributed to the July 30 flood, which killed two people, affected nearly 90 businesses and displaced 190 residents. With development, stormwater runoff rushes off roofs and parking lots rather than being absorbed into the ground.

The proposed moratorium would apply to the approval of building and grading permits but exempt permits for reconstruction needed after a natural disaster, such as flooding.

Valdis Lazdins, director of the Howard County Department of Planning and Zoning, said the administration hasn't determined how many projects would be affected.

Developers have submitted more than 100 proposals to build homes, shopping centers and other buildings in less than three square miles around Ellicott City since 2001, and most applications have been approved. Dozens of those developments are near the Tiber and Hudson streams.

Barth noted that any new development would be subject to various stormwater controls requirements.

“The county will need to determine through the studies underway the contribution to flooding by older development versus newer development,” Barth said.

Howard County officials and others, including Weinstein, say no amount of flood management could have stopped the storm's effects.

“We can't stop six-and-a-half inches of rain falling from the sky in two hours,” Weinstein said. “Water will go where water will go.”

But many residents have raised concerns about the pace of development in the area. The river town was designed in 1772 to support a flour mill by speeding up the flow of water that courses under the low-lying district's buildings.

Compared to other jurisdictions in the state, Howard County has a high portion of land dedicated for development. According to studies by the Maryland Department of Planning, nearly 51 percent of the land in the county is developed.

The area targeted for the moratorium extends south of Bonnie Branch Road, north of Interstate 70 and west of U.S. 29 in some places, bordered by the Patapsco River to the east, according to a map attached to the legislation.

Several projects have submitted new applications for subdivisions or development since July 1.

One proposal that lies within the zone outlined in the bill — to create 13 new single-family lots on Church Road in the Ellicott City historic district — is slated to go before the Planning Board next week. Engineer and landscape architect Stephanie Tuite, a partner at a consulting firm involved in the project, said it's too early to tell if the legislation would affect the site's development timeline, which is still far from construction-ready.

“It is a concern but it's not an immediate concern for us,” said Tuite, of the firm Fisher, Collins and Carter Inc.

Tuite added that while she also worries about flooding, she's not sure about the bill. “I know what they're trying to achieve, but I don't know that it will achieve what they're trying to achieve,” she said.

Katie Maloney, chief lobbyist for the Maryland Building Industry Association, said she has not read the legislation but that the organization is generally concerned about moratoriums, which create backlogs and can be costly for developers.

New construction often must follow stricter stormwater restrictions implemented in recent years, which she said helps to address the problem.

“We believe it's counterproductive to halt development just for the sake of trying to resolve a flooding issue,” she said. “We think the problem is much deeper.”

But a temporary halt to new construction could give officials time to assess the magnitude of the problem and the adequacy of current stormwater rules, said Bob Smith, a Columbia-based principal at the NAI KLNB real estate brokerage, who focuses on commercial and industrial properties.

“A moratorium based on new development within the watershed is probably a rational approach,” he said.

By design and topography, Ellicott City is prone to flooding.

Twice in the past five years, the streams that feed into the Patapsco River have overflowed, raising concerns about stormwater runoff from development in and around the Tiber-Hudson watershed.

But stormwater runoff from new development is only part of the challenge.

Older developments were built at a time when state and federal regulations required little to no stormwater management, studies show.

Twenty years ago, state and federal regulations focused on managing the quantity, not the quality, of runoff.

That approach used a curb and gutter system to move stormwater off of streets and buildings as quickly as possible, discharging runoff into water bodies, according to studies by the Chesapeake Bay Foundation.

Since then, the state has shifted to requiring larger stormwater controls like ponds and man-made structures designed to catch and hold water.

The unique challenge in the historic district is that stormwater management must extend outside the flood-prone area. “The work has to be done outside the district if we want to catch the rain and keep it there,” Weinstein said. “We have to follow the tributaries along the way.”

Officials have acknowledged the county's approach to handling stormwater runoff has been piecemeal in some parts of the county.

As it works on long-term solutions, Barth said the county is installing temporary curb and gutter structures and expanding storm drains to reduce the impact of storms in the area.

Earlier this year, Weinstein and Kittleman established a work group to explore ways to encourage businesses to manage stormwater runoff.

Kittleman also established a workgroup to examine flood control tactics in historic Ellicott City. That group's recommendations, submitted late last year, will guide the county's future strategy, Barth said.

He added that much of the county's flood-mitigation work will depend on whether or not the county receives federal disaster aid.

While the county has already begun research into the flow of water draining from the watershed, Weinstein hopes a moratorium would allow for even more study.

“A moratorium now allows us to take a step back and look at this issue more comprehensively,” he said.

The council will hear testimony on the bill during its Sept. 19 meeting in the George Howard building in Ellicott City.

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Baltimore Sun reporter Natalie Sherman contributed to this article.