Stormwater, zoning guard from disaster
As Houston and other parts of Texas, Louisiana, Tennessee and Kentucky try to recover in the aftermath of Hurricane Harvey, local jurisdictions are wondering if they, too, can handle a severe rain event of the same magnitude.
“You’re never going to convey that much water off of the streets and put it back into rivers and tributaries that are already swelled,” said Calvert County Planning and Zoning Director Mark Willis, referring to the reported 33 trillion gallons of water that fell along the Gulf of Mexico during Hurricane Harvey.
“I think Mother Nature took her gloves off on this one and
she said ‘I’ll show you who’s in charge,’” added Willis.
Post-Harvey, there were several suggestions that wild growth due to poor planning and zoning, as well as stormwater management deficiencies, made Houston’s flooding worse.
“They are married. They cannot be separate. They have to go together,” stressed Willis, referring to zoning and stormwater management regulations. “[You] don’t have a choice.”
Willis said zoning is the law of how people use your land, once they get permission to build something within the planning process, and that zoning is important in mitigating future disasters by determining what construction is allowed within certain areas.
Willis, who previously served as deputy director of enterprise fund operations under the Department of Public Works with some purview over stormwater management, explained stormwater management is the technique used to direct the water elsewhere.
When developing a parcel of property into an apartment building, with asphalt parking lots and sidewalks — impermeable surfaces that will not absorb water — a developer must engineer systems to direct water elsewhere, said Willis. Stormwater management would be required for a house being built on a hill and other structures on various elevations because the land was changed and there is less land to absorb water.
“You want to be able to convey water away in the most efficient way possible,” Willis said.
The planning head said he took a look at Houston’s stormwater management regulations and liked what he read. He believes the regs would have worked 99.9 percent of time, but not with the amount of rain from the hurricane.
“With Harvey, [Houston] wasn’t going to win that. I don’t care what stormwater management they put into place — they still are going to have flooded streets,” said Willis.
Public Works Department Deputy Director of Engineering and Highways Danielle Conrow said proper zoning and stormwater management practices can help lessen the impact of flooding or heavy rain events, but concurred with Willis that no jurisdiction is prepared for the amount of precipitation Houston experienced. In some areas of Texas, nearly 40 to 53 inches of rain fell over a period of four days during Harvey.
“Calvert County’s roads are designed today to convey stormwater up to a rate of 5.3 inches over a 24-hour period. In some cases, aging infrastructure may convey stormwater at a slower rate,” reported Conrow, who explained the amount of manageable rainfall per hour depends on a combination of factors, including recent weather, the soil type for the area, surrounding slopes, land elevation and the design standards of the stormwater management infrastructure at the time of construction.
“Keep in mind when the first 10 inches of rain falls on day one, the ground is now saturated and runoff is still seeping into conveyance structures. That means the next 10 inches of rain has a greater impact — followed by day three and day four,” explained Willis, suggesting that the wind shear that is possibly pushing the Chesapeake Bay waters landward causing flooding without rain would also have to be taken into consideration.
Willis believes that with 10 inches of rain, there would be flooding on many roads and properties during the actual rain event, but the county could still be accessed cautiously in most areas. Conrow added that ground saturation contributes to the stormwater runoff as well.
Planning for density, vulnerabilities
“We are in no way ever going to reach the density of Houston, obviously … and any development that we do, whether it’s an individual residence or it’s a commercial building, here all of them have to address stormwater management,” stressed Willis.
He said zoning is import- ant in mitigating future disasters by determining what construction is allowed within certain areas. Part that requires using environmental regulations to provide guidance on the allowable density in floodprone areas.
Conrow said any area with low-lying and flat land is vulnerable to heavy rain events due to rising water levels. High water levels not only cause flooding directly, but also prevent storm drain systems from conveying stormwater properly until the water level lowers.
“Calvert is more vulnerable on the shores. You don’t even need Harvey to cause that,” said Willis, adding that a heavy wind during a high tide could flood out the critical areas, those within 1,000 feet of the water.
Right now in Calvert there are several areas identified as flood prone, for which the county has completed or begun studies, and completed or drafted policies: Cove Point, Broomes Island, Neeld Estates/Breezy Point, Chesapeake Beach/North Beach and Solomons Island.
There are 17,123 parcels of land in the critical area, according to Willis. Roughly 8,144 have structures built on them. Willis stressed that the critical area may not be damaged by water, but may be damaged by wind or wind-borne objects. “Either way, a hurricane like Harvey could cause this damage and no amount of zoning could prevent that,” said Willis.
However, there are ways to mitigate.
Willis said people have to be very careful about how they situate houses in those areas. For those who want to build in floodprone areas in the county, they will have to build their house in an “elevated status” that will allow flood waters to pass through and around the bottom section of the home.
Willis said in areas where it is “financially tough” to save homes, houses are either elevated or demolished with the use of grants from the Federal Emergency Management Agency. The demolition is to physically remove those structures from the floodprone areas so their debris is not a hazard to other homes and residents.
To date, the county has raised three homes and demolished one home within critical area using the FEMA grants. With a new grant waiting, there are plans to elevate four more houses and demolish three more, subsequent to approval from FEMA.
Participation in such efforts is purely voluntary and many people elect not to participate because they have to bear 25 percent of the cost. The grant covers the other 75 percent.
In addition to shouldering the cost, people have to be willing to accept a change in what their residence looks like and how they access it, which may be problematic for someone with a disability. The county will not force homeowners to raise or demolish their homes. However, any new construction, even for existing homeowners who may have lost their house to a disaster, would have to adhere to new regulations requiring homes be elevated.
For the areas in the county not prone to flooding, Willis said “all bets of off” in a Hurricane Harvey-type event, but said that the county won’t experience completely submerged buildings because of Calvert’s elevation, which is not flat like Houston.
“If we got a heavy rain, can we convey the water? Yes,” Willis confidently responded, referring to a possible rain event not of biblical proportions. “I guess it’s unique for us because [we] can’t do that in Broomes Island, but we can in Prince Frederick.”
Planning and zoning, in concert with the county’s Department of Public Safety, Emergency Management Division, is working on a countywide flood mitigation plan and hazard mitigation plan to improve Calvert’s resistance to natural hazards, to include flooding.