FLOOD06840

• County: Statewide
• Basin: Statewide
• Title: Development of Technical Criteria for Effects of Works on Channel Stability
• Date: 1/1/1992
• Floodplain - Doc Type: Educational/Technical/Reference Information

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APPLICATION OF
EROSION RISK IN
FLOODPLAIN
MAPPING

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Peter F. Lagasse, Ph.D., P.F.
James D. Schall, Ph.D., P.F.
Ayres Associates
(rormerly ReE)

OUTLINE OF ANALYSIS
.-APPROACH
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. Erosion and Flood Risk

fTRISK ASSOCIATED WITH
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. In a 10 year period:
- 90 percent certainity will not occur...
- calculated risk of 10 percent in a 10 year
period.
. In a 25 year period:
- 78 percent certainity will Dot occur...
- calculated risk of 22 percent in a 25 year
period.

IT INTRODUCTION/.
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. Origin of Methodology
- AMAFCA
- Calabacillas Arroyo
. Purpose of Methodology
- establish flooding and erosion risk houndary
- facilitate multi-use opportunities

ITpRUDENT L~EP?NGEPT
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. "Prudent Line" adopted to describe the
erosion boundary
. Relating "prudent" to an acceptable degree
of risk in an urban setting

IT SINGLE EVENT .VS.
I CUMULATIVKEVBNTS
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. lOO-yr flood defines short term flooding
and erosion risk.
. Erosion can also be cumulative over long
term...what is long term?