8-1. 8-2 8-3 8-4 8-5 8-6 Alluvial Fan 8-7 Delta

8-1

8-2

8-3

8-4

8-5

8-6

Alluvial Fan

8-7

Delta

8-8

Which stream is more likely to be “Seasonal”?

8-9

8-10

8-11

8-12

8-13

8-14

8-15

8-16

8-17

8-18

Insurance Companies & HomeownersStudy historical “Peak Discharge”

Discharge determines area to be floodedUse Recurrence Interval Equation

Allows you to “predict” floodingWhy is it getting worse?

8-19

Recurrence Interval (RI) = (N+1)/MN= number of years of dataM=magnitude of the event

This equation allows you to predict frequency of flooding events

8-20

8-21

8-22

8-23

Type of Precipitation eventGround ConditionsVegetation Cover

8-24

Removal of VegetationDestruction of WetlandsConstruction ActivityUrbanization

8-25

Flash Floods (Upstream Floods)Smaller StreamsSteeper SlopesShorter “Lag Time”Little or No Warning

8-26

8-27

Downstream FloodsWider valley and larger floodplainRegional water from higher in drainage basinSignificant “Lag Time”Time for WarningCovers larger area

8-28

8-29

Build Dams

8-30

8-31Channelization

8-32

Retention Basins

8-33

Erosion Control

8-34Floodplain Management & Wetlands Restoration

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8-36