T.F. Green Airport Improvement Program - FEIS Chapters - PVD

T.F. Green Airport Improvement ProgramEnvironmental Impact Statement and Final Section 4(f) Evaluation5.14.1 Regulatory ContextExecutive Order 11988, Floodplain Management, requires each federal agency to provide leadership and takeaction to reduce the risk of flood loss, to minimize the impact of floods on human safety, health, and welfare,and to restore and preserve the natural and beneficial values served by floodplains when managing federalfacilities. 425 Actions that may impact floods include filling floodplains, which may cause displacement of floodstorage and increase flood height or duration. USDOT Order 5650.2, Floodplain Management and Protection,contains USDOT policies and procedures for implementing Executive Order 11988. According to USDOT Order5650.2, floodplains or base floodplains are the lowlands and relatively flat areas adjoining inland and coastalwaters including flood prone areas of offshore islands, at a minimum, that are prone to the 100-year flood.When used in this section, the 100-year flood is understood to mean a flood which inundates an area with a onepercent likelihood of occurrence in any given year and is equivalent to the 1 percent Annual Chance Flood asdefined by the Federal Emergency Management Agency (FEMA) and depicted on the Flood Insurance RateMaps (FIRMs). 426 The 100-year storm event is the storm with precipitation depth that has a one percentlikelihood of occurrence in any given year. The 100-year flood may result from storms that generateprecipitation depths greater or less than the 100-year storm event, depending on various environmental factorsincluding antecedent moisture conditions and tide, as well as wind and whether or not the ground is frozen.USDOT Order 5650.2 section 6(1) states that “A Flood Insurance Rate Map or Flood Insurance Study shall be consultedfirst” to determine base floodplain limits in a Project Area. There are current FIRM and a Flood Insurance RateStudy that cover the Project Area.At the state level, the Rules and Regulations Governing the Administration and Enforcement of the Fresh WaterWetlands Act 427 (RIDEM Rules) regulates the 100-year floodplain and floodway as freshwater wetland.According to section 2-1-20(3) of the Fresh Water Wetlands Act 428 , floodplain is defined as that land area adjacentto a river or stream or other flowing body of water that is, on average, likely to be covered with flood watersresulting from a 100-year frequency storm. A storm of this nature is one that is to be expected to be equaled orexceeded once in 100 years, and hence may be said to have a one percent probability of being equaled orexceeded in any given year. Rainfall intensity data for such a storm are those established for New Englandlocations by the National Weather Service (formerly the U.S. Weather Bureau).The RIDEM Rules require the use of a 100-year storm event for the purposes of flood modeling to evaluatefloodplain extents and impacts caused by any modifications to the floodplain. The flood modeling that wascompleted is intended to supplement FEMA mapping and to provide a relative comparison of conditions beforeand after floodplain filling and mitigation and to ultimately show that the fill has been appropriately mitigatedby new storage provided in created wetland areas, and that no increase in the floodplain results. Real-liferainfall events are of varied duration and intensity and therefore the selection of a design storm, such as the100-year storm event, will approximate the conditions that would occur during a flood event of this recurrenceinterval.425 Federal Executive Order 11988, Floodplain Management, 42 F.R. 26951, May 24, 1977.426 Flood Insurance Rate Map, Kent County Rhode Island, Map Numbers: 44003C0113G, 44003C0131G, 44003C0129G, and 44003C0127G. FEMA.Effective Date December 3, 2010427 RIDEM. December 2010.428 The Fresh Water Wetlands Act refers to sections 2-1-18 through 2-1-25, inclusive, of the Rhode Island General Laws.Chapter 5 - Environmental Consequences 5-243 July 2011\\mawatr\ev\09228.00\reports\FEIS_Final_July_2011\PVD_CH05_Environmental_Cons_JUL_2011.doc