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Floodplain Information Sheet No. 2 <br />Floodplain Management Series <br />iEE11PlE11 BI What are the Floodway and the Flood Fringe? <br />Illllil 1FSIIISES <br />For regulatory purposes, the floodplain is divided into Floodway and Flood <br />Fringe: <br />• Floodway is the channel of the river or stream and the adjacent land <br />that must remain free from obstruction so that the 100 -year flood can <br />be conveyed downstream. <br />• Flood Fringe is the remaining portion of the floodplain. FEMA and state <br />regulations permit communities to allow the flood fringe to be <br />obstructed and developed if standards (i.e., elevating and floodproofing <br />structures) are met. <br />When the FEMA floodplain maps are initially developed, the community works with <br />state and FEMA representatives to determine which portion of the floodplain will be <br />floodway versus flood fringe. Detailed engineering models are run to determine the <br />effect of filling in (or developing) all the flood fringe areas. The filling that would be <br />Figure 1. view of floodway and <br />flood fringe on a river. <br />allowed in the flood fringe generally cannot: <br />• Increase the 100 -year flood elevation more than % foot above the natural unobstructed condition, or <br />• Increase the 100 -year flood elevation if the filling would negatively impact existing floodplain development (even the <br />increase would be less than % foot. <br />Development in the floodplain is regulated by local (i.e., city, county or township) ordinances. Development within the <br />floodway is very restricted. The type of development allowed in the flood fringe (i.e., residential, industrial, etc.) depends on <br />the local zoning, but must meet minimum elevation or flood proofing standards. <br />Figure 2. Cross-section of river showing <br />floodplain before obstructions or filling. <br />What is the General Floodplain? <br />If no detailed hydraulic model has been developed to delineate <br />the floodplain and approximate methods are used, the <br />floodplain is designated as General Floodplain. When <br />development is proposed in a general floodplain area, the <br />permit applicant is responsible to pay for the hydraulic studies <br />that identify floodway versus flood fringe areas. <br />100 YEAR <br />FLOODPLAIN <br />FLOOD <br />FRINGE FLOODWAY <br />i <br />(FF) <br />SURCHARGE t 0.5 R <br />Figure 3. Cross-section of river showing <br />floodplain with filling in flood fringe. <br />FLOOD FRNGE <br />Ft,rx>«r WAV <br />ROOD FRIOM <br />IJ - <br />co <br />R -i Reeldentlai <br />�. <br />Gi con,�,tet�lal <br />_�.. .� <br />R -i jFF] Residential <br />Fle FHnV* EJ <br />4 77. _ <br />n . I <br />C-1 to F FINN <br />Fw pie n <br />Figure 4. Local zoning map showing flood fringe <br />and floodway overlay districts. <br />Contact: DNR Ecological & Water Resources in St. Paul (651) 259-5100 <br />htlp://.nmdnr.gov/waters <br />Page 1 <br />July 2014 <br />