Houston-area developers, engineers and real estate professionals were among the most vocal supporters of last summer’s $2.5 billion Harris County flood bond, the largest storm infrastructure investment in county history.

They contributed to a political action committee established by bond backers and helped shepherd the initiative to passage on the one-year anniversary of Hurricane Harvey, the devastating 2017 storm that flooded more than 204,000 homes and apartments in Harris County.

For the past several months, however, many of those players quietly have lobbied Houston and Harris County officials to delay implementation of new building rules developers say will increase housing costs but county engineers insist are needed to protect neighborhoods from future storms.

The changes under consideration would expand the area subject to flood-related building restrictions by roughly 65 percent in areas of the county outside the city of Houston, and would require developers to devote a larger share of their properties to holding back stormwater, among other changes.

Pressure from the development community already has delayed a Commissioners Court vote on the regulations by five weeks, though builders’ pleas for even more time have not prevented the Harris County Flood Control District from asking the court to approve the new rules on Tuesday.

The city of Houston — despite an initial plan to have the city and county jointly adopt the rules in early June — has no set date on which it will adopt similar changes, said Houston Public Works Director Carol Haddock, though she hopes city council will vote before Harvey’s second anniversary in late August. The changes would take effect sometime in 2020, she said, to give builders time to submit plans already in progress.

Nonetheless, the resistance by county leaders to further delay or change the proposed rules illustrates how the influence of developers long accustomed to getting their way may be waning as the city and county grapple with a post-Harvey reality in which residents clamor for better protection.

“We’ve never had this moment, where you have a disaster that could be laid back to decisions that were made in the past that had to do with development,” said Jerry Wood, a former city planner under three Houston mayors. “You’ve got people energized about this subject in a way they never have before.”

Flood maps outdated

The new rules would incorporate the most recent rainfall data compiled by the federal government, called Atlas 14, into city and county policies. Higher rainfall totals from more frequent and intense storms in recent years suggest the so-called “100-year” storm — the weather event on which most drainage rules are based — has been understated by 30 percent.

The new numbers mean a larger area is at risk of flooding than previously thought, and that more water must be detained each time builders replace grass with pavement to prevent stormwater runoff from overwhelming drains and bayous.

For many county projects, the minimum detention rate will increase 18 percent. If the city follows suit, its minimum detention rate on sites of more than an acre would increase by 30 percent.

Flood control district leaders say waiting until new flood maps are complete in 2021 poses too much of a public safety risk. They have proposed to use the current 500-year floodplain as a proxy for what likely will become the new 100-year map. City council narrowly voted to make a similar change last year after a contentious fight.

As a result, an additional 162 square miles — an area larger than Philadelphia — will fall under Harris County’s floodplain development rules outside the city of Houston, which have strict home elevation mandates.

“It’s really to ensure that the new development doesn’t unintentionally flood any downstream or adjacent developments,” said Craig Maske, the flood control district’s planning director. “It’s not about (developers). It’s about everybody else.”

A group of developers, builders and engineers urged the county to delay the new rules in a May 24 letter to County Judge Lina Hidalgo. Of the nine signers, seven of the organizations — the American Council of Engineering Companies, Greater Houston Builders Association, Greater Houston Partnership, Houston Association of Realtors, Houston Real Estate Council, Katy Area Economic Development Council and West Houston Association — backed the flood bond.

West Houston Association president Auggie Campbell, the author of the letter, warned the new rules could increase housing costs without providing tangible benefits, discourage investment and harm the county’s bond rating and long-term fiscal health. In private meetings and phone calls since March, members of the development community have urged Hidalgo to weaken the rules or delay their approval, her office said.

Hidalgo said the county has a “moral responsibility” to act on the latest data to ensure new development does not contribute to flooding.

Precinct 3 Commissioner Steve Radack said he has little patience for a “whisper campaign” and said developers and builders who wish to delay the new rules should make their case before Commissioners Court.

“If you’re not prepared to say something that’s wrong with the plan, you better get ready for my vote for the plan,” Radack said.

In interviews, developers acknowledged stricter floodplain development rules are needed, though they said the flood control district has rushed the process this time around. The group raised particular concern about using the 500-year floodplain as a stand-in while the new 100-year model is being built.

Campbell said that because the Atlas 14 data only measures rainfall, it may be inadequate to predict flooding, which also depends on topography and existing stormwater infrastructure.

“Our modeling isn’t that good yet and our data isn’t that good yet,” Campbell said. “What we’re saying is, you should model what you know, but you shouldn’t model what you don’t know.”

Houston Association of Realtors board member Bill Baldwin said the county must focus on developing “smart policy” and advocated for a three-month delay implementing the new rules. He lamented that a group of stakeholders, a mix of city and county officials, developers and engineers, had met just twice since the flood control district proposed the rule changes in March.

“I sure would like to get it right, and I would tell you two meetings isn’t enough,” he said.

Maske, of the flood control district, conceded the county is moving more aggressively to approve this set of development rules than in past updates. He said Harvey, however, shook policymakers to act with more urgency.

Maske said the county approached developers with a prepared proposal and a timeline for implementing it, “not necessarily asking ‘gee, what do you think about this?’ but rather, ‘this is what has to happen; what do you think?”

Almost three-quarters of homes damaged by the storm were outside of floodplains, exposing likely significant inaccuracies in the county’s floodplain maps. As soon as the flood control district had data that could be used to predict boundaries of the new floodplain, Maske said engineers had to act.

“We don’t have the luxury of not modeling what we don’t know,” Maske said. “We have to use the best estimates using the best data that we have, in order to protect the people of Harris County.”

Linda Wilshire, who lives about 500 yards from Cypress Creek in northwest Harris County, said she anxiously watches the construction of an apartment building near the bayou’s north bank at Cutten Road. The project, approved in February, straddles the 100- and 500-year floodplain.

“They have that detention pond in place; I look at it and can’t believe it’s going to hold enough water,” Wilshire said.

Wilshire said she worries development puts neighbors in Prestonwood at greater risk of flooding and welcomes stiffer floodplain building rules that aim to protect adjacent and downstream properties.

City waits

Mayor Sylvester Turner’s administration asked county officials to join the city in delaying the new rules until January, and some participants in the county-led discussions this year said a lack of updates from the city led them to conclude that Houston was unlikely to act until after this fall’s municipal election.

Haddock, the city Public Works director, said she had suggested the two governments align the rules’ effective dates, but never sought to punt the policy discussion until January.

This round of changes, Haddock added, is following the same pattern as the last one: The county mandated higher building elevations in floodplains roughly three months after Harvey, with immediate effect; the city acted five months later and gave builders — who strenuously opposed the changes — a five-month grace period.

“We can’t adopt something Wednesday and then Thursday say, ‘Too bad, you’re going to have to throw out that year’s worth of design and start over,’” Haddock said. “We don’t want to hurt someone’s business.”

Haddock said Public Works plans to use the new rainfall data to study its detention rules in more detail in the coming months, noting that city and county development patterns differ. She was unsure how the city would change its approach to the small lots that make up the bulk of redevelopment projects in the city, however.

The detention rate required on tracts of less than an acre inside city limits is less than half that required on larger lots, and would be less than a third as stringent as the new standard the city and county plan to adopt. City lots smaller than 15,000 square feet also are presumed to be 65 percent paved even if they are not, further reducing required detention.

zach.despart@chron.com

mike.morris@chron.com