47.5 MB - The Whole Building Design Guide

Earthen levee: Earthen levees are engineered structures that are designedto keep water away from land area and buildings. Hydraulicanalyses and geotechnical investigations are required to determinetheir feasibility and effectiveness. For existing sites, constraints includethe availability of land (levees have a large “footprint” andrequire large land areas), cost (including availability of suitable fillmaterial and long-term maintenance), and difficulties with site access.Levees are rarely used to protect a single site, although theymay offer a reasonable solution for a group of buildings. Locatinglevees and floodwalls within a designated floodway is generallynot allowed. Rapid onset flooding makes it impractical to design aflood levee with access points that require installation of a closuresystem. Earthen levees may also be subject to high velocity flowsthat cause erosion and affect their stability.Permanent floodwall: Floodwalls are freestanding, permanent engineeredstructures that are designed to prevent encroachment offloodwaters. Typically, a floodwall is located some distance from abuilding, so that structural modification of the existing buildingis not required. Floodwalls may protect only the low side of a site(in which case they must “tie” into high ground) or completelysurround a site (which may affect access because special closurestructures are required and must be installed before the onset offlooding, see Figure 2-32).Figure 2-32:A masonry floodwallwith multiple engineeredopenings protected theOak Grove LutheranSchool in Fargo, ND fromflooding in 2001.SOURCE: Flood CentralAmerica, LLC2-80 MAKING CRITICAL FACILITIES SAFE FROM Flooding