47.5 MB - The Whole Building Design Guide

2.2.2.1 Site DamageThe degree of site damage associated with flooding is a functionof several variables related to the characteristics of the flood, aswell as the site itself.Erosion and scour: All parts of a site subject to flooding by fastmoving water could experience erosion, and local scour couldoccur around any permanent obstructions to flow. Gradedareas, filled areas, and cut or fill slopes are especially susceptible.Stream and channel bank erosion, and erosion ofcoastal shorelines, are natural phenomena that may, over time,threaten site improvements and buildings.Debris and sediment removal: Even when buildings are not subjectto water damage, floods can produce large quantities of debrisand sediment that can damage a site and be expensive toremove.Landscaping: Grass, trees, and plants suffer after floods, especiallylong-duration flooding that prevents oxygen uptake, andcoastal flooding that stresses plants that are not salt-tolerant.Fast-moving floodwaters and waves also can uproot plants andtrees.Fences: Some types of fences that are relatively solid can significantlyrestrict the free flow of floodwaters and trap floatingdebris. Fences can be damaged by flowing water, and can beknocked down under pressure of flowing water or if the buildupof debris results in significant loads (see Figure 2-12).Accessory structures: Accessory structures can sustain both structuraland nonstructural damage. In some locations, suchstructures can be designed and built using techniques thatminimize damage potential, without requiring elevation abovethe DFE.Access roads: Access roads that extend across flood-prone areasmay be damaged by erosion, washout of drainage culverts,failure of fill and bedding materials, and loss of surface (seeFigure 2-13). Road damage could prevent uninterrupted accessto a facility and thus impair its functionality.2-42 MAKING CRITICAL FACILITIES SAFE FROM Flooding