47.5 MB - The Whole Building Design Guide

minimize those risks, some State or local regulatory authorities requirethat access roads be designed so that the driving surface isno more than 1 to 2 feet below the DFE. To maximize evacuationsafety, two separate accesses to different feeder roads are recommended.In some circumstances, especially long-duration floodingwhere a critical facility is built on fill, dry access may allow continuedoperations.Floodplain impacts: Engineering analyses may be required to documentthe effects on flood elevations and flow patterns if largevolumes of fill are required to elevate a road to minimize or eliminateflooding above the driving surface.Drainage structure and road surface design: The placement of multipledrainage culverts, even if not needed for local drainage, can facilitatethe passage of floodwaters and minimize the potential fora road embankment to act as a dam. Alternatively, an access roadcan be designed with a low section over which high water can flowwithout causing damage. Embankments should be designed to remainstable during high water and as waters recede. They should besloped and protected to resist erosion and scour. Similarly, the surfaceand shoulders of roads that are intended to flood should bedesigned to resist erosion. The increased resistance to erosion maybe accomplished by increasing the thickness of the road base.2.3.5.2 Utility InstallationsUtilities associated with new critical facilities in flood hazard areasmust be protected either by elevation or special design and installationmeasures. Utilities subject to this provision include allsystems, equipment, and fixtures, including mechanical, electrical,plumbing, heating, ventilating, and air conditioning. Potablewater systems (wellheads and distribution lines) and wastewatercollection lines are addressed in Section 2.3.5.3.Utility systems and equipment are best protected when elevatedabove the DFE (plus freeboard, if required). In somecases, equipment can be located inside protective floodproofedenclosures, although it must be recognized that flooding that exceedsthe design level of such an enclosure will adversely affectthe equipment (see Figure 2-31). Designers should pay partic-2-74 MAKING CRITICAL FACILITIES SAFE FROM Flooding