Designing an Effective Flood-Protection System

The Alley Theatre in downtown Houston includes “barely there” flood barriers such as glass that could handle water loads as well as a 10- by 12-foot steel-panel flood gate at the stage door and loading docks. (Walter P Moore)

Collaboration and Communication Are Key

For decades, scientists have warned about extreme weather. Droughts, wildfires, oppressive heat and floods are frequently sweeping the globe. Such extreme weather is impacting communities in a major way from damage to properties as well as infrastructure.

Floods alone have cost U.S. taxpayers more than $850 billion since 2000 and are responsible for two-thirds of the cost of all natural disasters, according to Flood Defenders, a nonprofit organization with the goal to make flood protection a top priority for elected officials.

To help mitigate flooding and other natural disasters, the $1.2 trillion Infrastructure Investment and Jobs Act is designed to make the nation’s infrastructure resistant against the impacts of climate change and extreme weather events. So far, the funds trickling down for actual flood-related projects have been slow, and there are preventive measures that can be implemented now—design and planning—as they relate to infrastructure as well as structures.

Although each have their own distinctive needs regarding flood protection, a properly designed and installed flood-protection system can prevent floodwaters from causing severe damage. The time to start planning for a flood is now—not after disaster strikes.

Determining Flood Risk

First, it’s critical the design team and owner work together to create a system that ensures the proper flood protection. After the owner is informed about potential flood risks for their property, a flood-protection system must be designed to meet current needs, and it must be upgradeable to meet any future needs as conditions change.

Defining the flood risk for a site contains many different considerations the owner must weigh to define the level of acceptable risk which, in turn, starts to define elevations and extent of protection. Risk is measured in the probability of flooding recurrence, cost of protection vs. cost of recovery, impacts to operations and reputation of a facility that experiences a flood, cost of insurance for a facility prone to flooding, and the emotional impacts of surviving a flood. If the cost includes potential loss of life, then the risk rises to an even higher level. Flood risk includes, but is not limited to, the property being mapped in a Federal Emergency Management Agency (FEMA)-effective flood zone. The analysis includes how often and how high it floods. It also looks at other flooding source risks not identified in floodplain maps. This information is explained as part of an initial analysis that identifies flood exposure.

Each property has unique flood risks based on a multitude of flooding sources, including natural and man-made occurrences. Understanding how water drains to and from a property is important in determining these risks. It’s helpful to know the history of flooding and how to look for information that may indicate risk, and every region has its own unique ways to handle and quantify drainage.

Flood risk is one of the most-difficult things to comprehend; water damage can be devastating and demoralizing. Ultimately, the owner should be provided the proper information to assess whether investment in flood mitigation is warranted.

When an owner determines flood protection is necessary, the protection plan is developed from the initial designs based on a feasibility study conducted at the project’s onset. The study further identifies points of exposure to floodwaters, identifies potential levels of floodwaters, determines the protection system to address current and future points of exposure, and works through any other related issues with the system. The latter may include code requirements, agency interface requirements, anticipated costs, impacts to operation and project schedule. After issues are addressed in the feasibility study, the flood-protection system is moved to the design phase.

The design phase, based on owner decisions, advances concept development from the feasibility study. Following the proof of concept, the design evolves to include schematic design, design development and construction process. Concurrently, the budget must be tracked and any design changes vetted with the owner.

Kingwood High School in Kingwood, Texas, has automatic flood gates at the entrances as part of an extensive flood protection project that necessitates 8 feet of protection in the front and 3.5 feet of protection in the rear of the structure. (Aaron Bielish & Walter P Moore)

Alignment Among Partners

A proactive owner can address flood risk by assembling a cohesive team that understands the specific flooding concerns of the facility and infrastructure to be protected to deliver a properly executed project.

“The correct partners are important when defining and planning solutions, developing the design, and constructing the flood-protection project,” says Ray Drexler, a principal and project manager in Walter P Moore’s Diagnostics Group. “A diverse team for any flood-protection project is essential, as there are several different facets that must be addressed.”

For example, in addition to knowing flood-protection design, team members must have a strong understanding of potential funding mechanisms, insurance impacts, flood risk to the surrounding community, and the impact of flooding on the infrastructure and surrounding areas. It’s also important to have the ability to address code issues, architectural design elements, MEP design requirements and, where warranted, landscape architecture.

After the team is selected, there should be alignment among all parties: a team leader is chosen, and each role must be clearly defined. Frequent communication among all team members, including the owner, leads to a better-defined, priced and executed project.

A flood-protection system must address myriad features, consider the various requirements for implementation, and provide requirements to keep the flood-protection system operational and maintained. In addition, if government funding is involved, the system should be designed and implemented with a FEMA consultant to meet any regulatory requirements.

“A critical group beyond the owner and design team includes FEMA consultants as well as FEMA representatives themselves,” says Drexler. “FEMA and their consultants must be included from the onset of the project so they may be able to voice any concerns to the design team and owner.”

A FEMA consultant’s feedback is critical to the design team because it may impact financial or regulatory issues. Regular meetings between FEMA and the design team are necessary early in the project to verify approaches and funding streams. A good FEMA consultant can help navigate some of the various bureaucratic processes to ensure reimbursement isn’t jeopardized by not correctly following procedures.

Savings and Resilience

Resilience is related to the ability of a property and infrastructure to absorb flood damage and return to operational within a limited amount of time—it can play a significant role in determining how to approach flood mitigation.

The owners must consider whether the cost of recovery is less impactful than the funds invested to protect against a potential flood. Costs include installation as well as maintenance and the ability to implement the system when needed.

Flood events that infiltrate a building or overwhelm the infrastructure are disruptive and costly to owners and the local community. Flood events have a significant impact due to lost revenue and operations, costs of cleanup and repairs, and loss of patronage. By determining flood resiliency, a good understanding of risk-associated costs can be provided to the owner.

Innovative Engineering Solutions

Kingwood High School in Kingwood, Texas, suffered severe damage from three separate floods within two years, destroying much of the campus and gymnasium and other portions each time. As a result, the school required a comprehensive flood-protection system to guard against future flood events.

To ensure components of the flood-protection system being proposed for Kingwood could be demonstrated, site visits to other flood-protection systems were conducted throughout the Houston area with school representatives, FEMA consultants and the design team. The site walks provided Kingwood representatives the opportunity to hear testimonials from owners of the systems.

“The design team also walked the perimeter of Kingwood High School with the client to ensure we understood their needs,” says Keith Gaynor, team director of civil engineering services at Walter P Moore. “We then held design charettes in the office, producing multiple options for each flood vulnerability while providing the pros and cons.”

Following an evaluation by the design team, several flood-protection options as well as the specific design details and cost options were presented to the Humble ISD and the FEMA consultant in a feasibility study. The FEMA consultant recommended a design that aligned with FEMA flood-protection requirements and cost $14 million, well below initial estimates that exceeded $30 million.

Due to topography at Kingwood, the existing buildings required more than 8 feet of flood protection in the front and 3.5 feet in the back. The building’s front has float-up gates that connect to the external walls and flood-rated glass. The back required several different custom flood-protection components be tailored into the overall system to ensure the structure doesn’t flood.

“At the end of the day, the client knew what to expect and was extremely happy with how the design team kept them involved throughout the design process,” adds Gaynor.

Another custom flood-protection system was designed for the Alley Theatre in downtown Houston after a disaster struck in 2017 when Hurricane Harvey dumped the greatest rainfall event in U.S. history on the Greater Houston area. The hurricane inundated the theater with 17 feet of floodwater, causing $18 million in damages.

At the time of the hurricane, the theater was protected against water infiltration pathways that devastated the basement with 14 feet of water from Tropical Storm Allison in 2001. The flood-protection system secured connection tunnels to a nearby underground parking structure. However, this system hadn’t been breached during Hurricane Harvey, so an emergency-assessment team was deployed to identify the new flood vulnerabilities.

To meet the client’s vision, the existing structure was retrofitted with a new flood-protection scheme featuring creative uses for existing technologies, such as employing fiber-reinforced polymer (FRP) strengthening to resist potential floodwaters in place of constructing new reinforced concrete walls. Plain glass panels in the lobby atrium were replaced with flood-rated alternatives to achieve the goal of “barely there” flood barriers that protect the building beyond the devasting power of future floods and hurricanes.

YES Prep, a Houston public charter school located in a repurposed commercial office building, was retrofitted to include overhead drop-down gate system hidden above the ceiling. The system can be manually operated in the event of a power outage. (Slyworks Photography)

“We hid everything so most patrons would not even notice there was a flood-protection system,” says Jared Wood, partner, Studio RED Architects. “We changed out the glass to new glass that could handle water loads, we hid gates in the sidewalk and built walk-off matts into the surface to hide them. We also changed the regular doors to flood doors. Where FRP had to be added to strengthen walls, we found ways to hide it behind finishes.”

Furthermore, several custom flood-protection aspects were retrofit into the building’s makeup, including a 10- by 12-foot steel-panel flood gate at the stage door and loading docks; a tracked, vertical lift door at the loading dock; and a redesigned, subgrade venting system with flood louvers for the electrical vault.

As another project example, when YES Prep, a Houston public charter school, purchased an existing commercial office building to house its Yorktown campus, it was initially unaware that repurposing the building from commercial to institutional would change its requirements for flood protection.

The facility met the floodplain development criteria as an office building, but because it was being renovated as a school, it had to meet city criteria for a “critical” facility. It was required to be protected 12 inches above the 500-year flood elevation instead of 12 inches above the 100-year flood elevation. The building was about 14 inches shy of meeting that requirement, so YES Prep’s initial plans to renovate the space into a school were rejected by the floodplain management office.

With hurricane season approaching and an opening date that wasn’t flexible, YES Prep’s director of operations wanted a flood-protection system that was simple and cost-efficient.

A feasibility study resulted in a flood-protection system that included an 18-inch poured-concrete curb within the wall cavity around the entire structure. An overhead drop-down gate system also was included in the design to meet YES Prep’s campus needs while concurrently preserving aesthetics of the updated building.

The overhead door system was designed to be unobtrusive and easy to deploy and operate, and it worked within their budget. The gate is a flood log attached to a guiderail concealed within the door jam. The gate, when open, is hidden above the ceiling. The doors are manually operated and can still be operational in the event of a power outage.

Collaboration and Engagement

Regardless of project scope, a flood-protection team must tailor its design to the owner’s specific needs based on a feasibility study and necessitated thorough communication and collaboration. Critical team members, including FEMA consultants, local authorities and funding entities, should participate in discussions to ensure alignment and address concerns.

Understanding the owner’s operations, capabilities and limitations is crucial for effectively integrating flood-protection systems. The team must engage the owner’s staff to assess operational impacts and costs, presenting alternative solutions for informed decision-making.

Determining the level of owner involvement and identifying key decision-makers during the initial phases of the project is essential. Project leadership requires open-minded collaboration and early engagement with all team members for any flood-protection design.

About Doug Coenen

Doug Coenen is a principal in Walter P Moore’s Civil Engineering Group; email: dcoenen@walterpmoore.com.

The post Designing an Effective Flood-Protection System first appeared on Informed Infrastructure.

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