An Introduction to Flood Protection: Understanding Flooding Concerns and Three Steps to Address Flood Protection

An Introduction to Flood Protection: Understanding Flooding Concerns and Three Steps to Address Flood Protection

November 16, 2021

As part of a series of posts related to An Introduction to Flood Protection: What Owners Need to Know to Protect Their Properties by Doug Coenen and Ray Drexler, this article examines why owners need to understand the flooding concerns related to their facility as well as the first three steps related to flood protection project continuum.

Feasibility Study Frames Scope Options

Proactive owners address flood risks by assembling a cohesive team that understands the specific flooding concerns of the facility to be protected to deliver a well thought out and properly executed project. The initial phase should be a feasibility study or scoping to set the project parameters. The feasibility study is designed to identify the points of exposure to the facility, determine the optimum protection system that can address all points of exposure, and work through the issues associated with the system including code requirements, agency interface requirements, anticipated costs, impacts to operations, and project schedule. Based on the feasibility study, the decision can be made to proceed with the design phase.

Flood Protection Process

The design phase starts with further development of the concept from the feasibility study. The feasibility study identifies relevant inputs such as design flood protection elevation and relevant constraints such as property line setbacks, wetlands, architectural requirements, accessibility, etc., in order to generate potential solutions. After proof of concept, the design phases are schematic design, design development, and construction documents. Throughout this process the budget is tracked and the design elements are vetted with the operations of the facility.

Once the project is sufficiently defined, an early set of drawings can be developed for the Authority Having Jurisdiction (AHJ) to review. The construction documents, typically drawings and specifications, should address comments and concerns from the AHJ, local flood control district, FEMA, and others that may have a vested interest in the project. The next step is bidding, followed by construction, which should include system commissioning, testing, and training on how to operate and maintain the system. The final step is regular maintenance and exercising of the protection system(s). Below is a brief breakout of what each step should include:

1. Scoping

Choosing the right team is especially important in defining, planning solutions, developing the design, and constructing flood protection/mitigation projects. Because of the different facets of flood protection projects, a strong understanding of potential funding mechanisms, insurance impacts, flood risk… the list goes on and on and each item is important. Choose wisely and make sure that all roles are covered.

After selecting the team members, definition of their roles (prime, support, etc.), the establishment of project communication/direction procedures occur. The first step in scoping is deciding on team member responsibilities and selecting a team leader. The next step in the scoping process is listening: owner needs, wants, desires, limitations, operational/logistical freedoms, and/or constraints, financial status (non-profit, public, private), etc.; AHJ as well as FEMA and/or state Department of Emergency Management (DEM) expectations, requirements, procedures, prohibitions, etc.; individual design team member’s experience, strengths, weaknesses, creativity, etc.

Experience proves that open and frequent communication between all team members (including the owner, as well as bidders and contractor) leads to a better-defined, priced, and executed project. The owner’s risk tolerance to flood damage may be greater or less than the budget tolerance; therefore, it is important to establish expectations early on with respect to protection level(s), budget certainty, schedule, and other project metrics. When walking the site to understand and define the project, it is typically easy to point out many potential vulnerabilities, such as sanitary drains without check valves. Other vulnerabilities are not so obvious and require various amounts of investigation. For example, whether the electrical conduits enter the building above or below the desired flood protection elevation. Similarly, research is required to determine the design flood elevation as well as what types of protection may or may not be allowed by the AHJ. This must be followed up by determining if the AHJ is open to alternatives based on site history, updated hydrology, future site usage, etc.

Ultimately, flood protection elevation is determined based upon the flood risk—flash flood or floodplain—and owner’s risk tolerance balanced by their budget. The intended ownership duration and/or ownership financial structure—non-profit, public, private—may have a significant impact on project scope and/or budget as well as how the project is procured. Non-profits are typically grant process driven, while public and private institutions typically have a very long-term view and employ comprehensive and durable solutions but use differing financial and procurement methods. An additional question to ask: Is it more important for the flood protection to be invisible or obvious to show the facility is flood protected?

2. Assessment

The assessment of the facility forms the basis of what is and is not feasible or practical in terms of flood mitigation options with respect to constructability and finances. The assessment needs to determine the appropriate level of flood protection required. This requires retrieving data and information from the owner, FEMA, the municipality/authority having jurisdiction, etc.

Before performing a physical site survey, the civil/hydraulics and hydrology team must determine both the FEMA 100-year and 500-year flood elevations as well as any local municipality requirements that influence the recommended flood protection elevation. This involves reviewing topographic surveys, as-built drawings, researching the FEMA floodplain models, determining elements that predict flooding, expected water elevation(s), geographic limit(s) of flooding, and interviewing the local facility manager to understand the site’s history of flooding and/or high-water experiences. Understanding the meteorology, the watershed, and the critical zones—often flood elevations for specific locations—helps determine how to provide flood protection.

After determining the appropriate floodplain elevations, the team must perform a site assessment to locate known and potential vulnerabilities at or below these different elevations. This involves looking for above-grade building envelope penetrations such as windows, air intake/exhausts, hose bibs, electrical feeds, as well as below-grade penetrations such as sewer discharge, sump and/or ejector pumps, underground tunnels/connections, etc., to determine the locations of all penetrations/potential vulnerabilities.

At this point, the owner risk tolerance needs exploring—how high is high enough for flood protection? Local code requirements and site history are obviously important, but the owner budget, schedule, and insurance profile can also influence the desired flood protection elevation (FPE).

After determining the target FPE, the ability of the existing structure to resist the flood waters needs evaluating. This requires record drawings and/or detailed site assessment information if no drawings are available or critical information is missing. This may involve nondestructive or destructive testing and/or explorations of the structure and/or site. The condition of various penetrations, such as hose bibs, require evaluation as do the windows and seals to determine if they have the structural integrity to hold back the desired FPE loads. The assessment must also address building envelope porosity. Brick masonry construction—even with damp proofing—is typically considered porous while cast-in-place concrete is considered impervious, even without a vapor barrier. Tiltwall/precast construction is most vulnerable at the seals between panels for lower levels of flood loading. Water can also enter the building from below-grade penetrations and joints, especially if the site has sand lenses and high storm-driven ground water issues. At this stage it may be important to know the hydraulic properties of the soil if no geotechnical reports are available.

Typically, the most desired approach is to minimize the amount of new construction, followed by minimizing the amount of strengthening. However, in some instances, a free-standing flood protection system may be more desirable due to schedule, economics, or occupant disruption. Finally, each discipline—architect, civil engineer, MEP engineer, and structural engineer—is now responsible for formulating potential flood mitigation approaches for discussion with the team and owner before moving into design development.

3. Design

The assessment phase discovers all necessary design data, which is then discussed amongst each discipline (team member) to develop multiple feasible flood protection options. After several options are determined, they can be presented to the owner for review. The team’s design members should address redundancy of protection level(s), if any, and other salient owner concerns. The team’s construction contractor should address rough order of magnitude construction costs, durations, disruptions, and potential impacts on facility ingress/egress during construction for the various options. Flood protection design is site specific and is discussed within this paper in broad terms only.

The design team develops flood protection options in accordance with the desired FPE; local, state, and federal codes; and AHJ, DEM, and FEMA requirements. During discussions with the owner, the flood protection options are reviewed, and the desired option is selected for design.

The technical design requires coordination between the entire design team: geotechnical, MEP, civil, and structural engineers as well as architectural and life safety consultants. Other disciplines may be needed, site and constraint dependent. The design team must maintain regular communication with the owner during the design. Various unexpected conditions may arise that could significantly impact the surrounding area as a result of the construction and must be resolved before proceeding to the next design phase. Additionally, regular communication is recommended with manufacturers of flood doors and flood gates. The engineers drive the flood protection system requirements and designs while the architect guides the aesthetic improvements focusing on the appearance of the finished product while maintaining constructability and function.

At this point in time, a construction contractor may develop the initial construction cost estimate and anticipated schedule for construction. The design team works with the contractor in relation to any constructability issues or other areas of potential improvement. Before the drawings are finalized, the owner reviews them for present and future operational compatibility and any other concerns. Upon owner’s approval, the team finalizes the construction documents for permitting. In some cases, the schedule dictates the need for an early package submittal to allow contractor mobilization. The contractor can then begin rough grading and other utility work prior to the main design package completion. Some items such as flood doors and barriers have long lead times, which must be properly accounted for in the schedule. Commissioning/proof testing of these element installations is strongly encouraged.

Download An Introduction to Flood Protection: What Owners Need to Know to Protect Their Properties.

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Doug Coenen, PE is a Principal and the Civil Engineering Business Development Manager in Walter P Moore’s Infrastructure Group. He can be reached at dcoenen@walterpmoore.com.

Ray Drexler, PE is a Principal and Senior Project Manager in Walter P Moore’s Diagnostics Group. He can be reached at rdrexler@walterpmoore.com.