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NoNo--Impact: Hydraulic ModelingImpact: Hydraulic Modeling

Risk MAPNo-Impact/ No-Rise

A Document Used to show that a proposed project will result in “no impact” in the 1% annual chance floodresult in “no-impact” in the 1% annual chance flood and floodway elevations or floodway widths and locations

See RIV Guidance Document

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Risk MAPGeneral OverviewNo-Rise Conditions

Section 60.3 (d) (3) of the National Flood Insurance Program (NFIP) regulations states that a community g ( ) g yshall “prohibit encroachments, including fill, new construction, substantial improvements, and other developments within the adopted regulatory floodwaydevelopments within the adopted regulatory floodway unless it has been demonstrated through hydrologic and hydraulic analyses performed in accordance with t d d i i ti th t th dstandard engineering practice that the proposed

encroachment would not result in any increase in flood levels within the community during the occurrence of y gthe base (100-year) flood discharge.”

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Risk MAPGeneral OverviewNo-Rise Conditions (Continued)

Prior to issuing any building grading or development permits involving activities in adevelopment permits involving activities in a regulatory floodway, the community must:• obtain a certification stating the proposed g p pdevelopment will not impact the pre-project base flood elevations, floodway elevations, or floodway d t idthdata widths.

• The certification should be obtained from the permittee and signed and sealed by a professionalpermittee and signed and sealed by a professional engineer.

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Risk MAPGeneral ConditionsNo-Rise Conditions (Continued)

The engineering or “no-rise” certification must be supported by technical databe supported by technical data. • Based upon the standard step-backwater computer model utilized to develop the 100-year floodway p y yshown on the community’s effective Flood Insurance Rate Map (FIRM) or Flood Boundary and Floodway Map (FBFM)Map (FBFM)

• and the results tabulated in the community’s Flood Insurance Study (FIS).su a ce S udy ( S)

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Risk MAPNo-Impact

“No Rise” “No Impact”“No-Rise” = “No-Impact”

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ExampleExample

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Risk MAPProposed Project

Proposed road in the floodway and floodplain Cut and fill along a river

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Risk MAPEffective FIRM

Risk MAP9Two New Cross Sections Between G and H

Risk MAPCross Sections14650 and 14850

Added to the effective model to create pre-project conditions modelM difi d i th j t diti d l t fl t Modified in the pre-project conditions model to reflect the proposed project cut and fill conditions

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Risk MAPCross Section 14650

Cut and Fill

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Risk MAPCross Section 14850

Cut and Fill

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Risk MAPEffective Conditions HEC-2 Input- found in warehousep

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Effective ConditionsHEC-2 Input

G

H

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Pre-Project GR Data

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Risk MAPPost-Project GR Data

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Risk MAPWhat to Look For . . .

Water-surface elevation increases Floodway elevation increases Floodway width increases Floodway width increases Surcharges that exceed 1.0 Negative surcharges Changes to Manning’s “n” values Reach lengths

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Risk MAPPre-ProjectConditions Output

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Risk MAPPost-ProjectConditions Output

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Risk MAPPre-ProjectConditions Output

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Risk MAPOutput Table 200

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Risk MAPThree (3) Computer Runs

Effective

Pre-Project

Post Project

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Output Comparisonp p

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Output Comparisonp p

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Risk MAPCommon Problems

Changes in Manning’s “n” values Changes to the floodway Surcharge values outside 0.0 to 1.0 Incorrect reach lengths

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Risk MAPNo-Impact

Project cause increases in • flood levels • floodway velocitiesfloodway velocities • floodway widths

Not a “No-Rise” andM t t S ti 65 12 (CLOMR) Must meet Section 65.12 (CLOMR)

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No-ImpactHydraulic ModelingHydraulic Modeling

Questions?

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