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

T.F. Green Airport Improvement ProgramEnvironmental Impact Statement and Final Section 4(f) Evaluation5.14.2 Significance ThresholdsAccording to FAA Order 1050.1E, a significant impact to floodplains occurs when notable adverse impacts onnatural and beneficial floodplain values occur. In determining significance, the FAA must decide if a“significant floodplain encroachment” would occur.5.14.2.1 Finding: Significant Floodplain ImpactFloodplain impacts associated with Alternatives B2 and B4 would be significant as Alternative B2 would fill0.5 acres of FEMA-delineated floodplain and Alternative B4 2.3 acres of FEMA-delineated floodplain.Unmitigated, both Alternatives B2 and B4 would result in notable adverse impacts on natural and beneficialfloodplain values. USDOT Order 5650.2 section 4.k. defines natural and beneficial floodplain values to includebut not limited to: natural moderation of floods, water quality maintenance, groundwater recharge, fish,wildlife, plants, open space, natural beauty, scientific study, outdoor recreation, agriculture, aquaculture, andforestry. Analysis of the Improvement Program indicates the action would not have a high probability of loss ofhuman life and would not result in substantial encroachment-associated cost of damage including interruptingaircraft service or loss of a vital transportation facility. Alternatives B2 and B4 would, however, constitute a“significant encroachment” since they would cause adverse impacts on natural and beneficial floodplain values,specifically flood storage, water quality maintenance and groundwater recharge. Importantly, these impacts canbe mitigated, as described in Chapter 6, Mitigation.5.14.3 MethodologyThe evaluation of impacts to floodplains includes direct impacts, indirect impacts, and cumulative impacts, asdescribed below.Since the existing FEMA floodplain mapping for this area is based on an estimate and there was no model inexistence that could be used to evaluate the impacts of the fill in relation to any increase in water surfaceelevations at specific locations within the floodplains it was necessary to develop a detailed floodplain model toevaluate impacts to state-regulated floodplain. Appendix L, Floodplains, describes the floodplain analysis of theBuckeye Brook watershed upstream of Warwick Avenue that was prepared in order to evaluate any direct orindirect impacts at detailed cross sections as a result of the fill proposed in the state-regulated floodplain asdefined in the RIDEM Rules.The foot by foot analysis of fill and mitigation plan as described in this chapter is based on the FEMA-delineatedfloodplain presented in the current and accepted FIRM map.5.14.3.1 Direct Impacts MethodologyDirect impacts are effects caused by the action and occur at the same time and place. Indirect impacts are effectsthat occur later in time or are further removed in distance.Direct impacts to floodplains in the Project Area were evaluated by overlaying each 30-percent designalternative footprint onto floodplain mapping based on the available topographic data and the base floodelevation provided in the FIRM, to determine:Chapter 5 - Environmental Consequences 5-244 July 2011\\mawatr\ev\09228.00\reports\FEIS_Final_July_2011\PVD_CH05_Environmental_Cons_JUL_2011.doc