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 & Homeowners  Study historical “Peak Discharge”  Discharge determines area to be flooded  Use Recurrence Interval Equation  Allows you to “predict” flooding  Why is it getting worse?

8-19  Recurrence Interval (RI) = (N+1)/M  N= number of years of data  M=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 event  Ground Conditions  Vegetation Cover

8-24  Removal of Vegetation  Destruction of Wetlands  Construction Activity  Urbanization

8-25  Flash Floods (Upstream Floods)  Smaller Streams  Steeper Slopes  Shorter “Lag Time”  Little or No Warning

8-26

8-27  Downstream Floods  Wider valley and larger floodplain  Regional water from higher in drainage basin  Significant “Lag Time”  Time for Warning  Covers larger area

8-28

8-29 Build Dams

8-30

8-31 Channelization

8-32 Retention Basins

8-33 Erosion Control

8-34 Floodplain Management & Wetlands Restoration

8-35

8-36