What is the principal technical challenge in effectively implementing dry floodproofing for a building in a flood-prone area?

Dry floodproofing is the process of making a building or portions of it completely impermeable to water up to a specific flood elevation, ensuring no water enters the structure. The principal technical challenge in effectively implementing dry floodproofing for a building in a flood-prone area is maintaining a continuous, durable, and fully effective watertight seal across all building components and openings below the design flood elevation against significant hydrostatic pressure. Hydrostatic pressure is the force exerted by standing water due to its weight, which increases with water depth. For example, just one foot of floodwater exerts over 62 pounds of pressure per square foot against a building's exterior, significantly stressing any barrier designed to keep water out. Buildings inherently have numerous potential points of water entry. These include the main structural elements like foundation walls, which can be porous or develop cracks, and their critical joints with the building's slab. More significantly, all openings such as doors and windows present inherent weak points. Standard doors and windows are not designed to withstand hydrostatic pressure, requiring specialized flood-resistant doors, windows, or temporary barriers that must form a perfect, pressure-resistant seal with the existing structure. Furthermore, every utility penetration through the building's envelope below the flood elevation—pipes for water, sewer, and gas, electrical conduits, and HVAC ducts—must be meticulously sealed to prevent water ingress. The challenge lies in the absolute requirement for continuity: any single flaw, no matter how small, in the seal around any of these components or at their interfaces, will allow water to bypass the entire system under pressure. This necessitates not only robust materials and precise construction techniques but also careful consideration of long-term durability against weathering, building movement, and material degradation. For temporary floodproofing measures, such as deployable flood barriers, the additional technical challenge includes ensuring correct and timely installation, complete sealing, and reliable performance during an actual flood event, often under adverse conditions.