ENVI 485 02/15/07

1. ENVI 485 02/15/07 • INTRO. TO NATURAL HAZARDS & DISASTERS • STEAMS AND FLOODING • Case Study 1

2. Phase 1: Emergency(days) • Normal activities stop • Search and rescue • Emergency shelter/feeding • Capital damaged or destroyed

3. Phase 2: Restoration(weeks-months) • Normal activities return but at minimal levels • Restoration of urban services • Return of refugees • Capital patched

4. Phases 3 & 4: Reconstruction I & II(months-years) • Normal activities return to predisaster levels • Capital rebuilt (replaced) • Activities improved and developed • Capital improved beyond predisaster levels • Disaster preparedness & response improved

6. Effects of Selected Hazards in the U.S.

7. Effects of Selected Hazards in the U.S.

8. Rivers and floods Stream/river any body of water that flows in a channel Floods any high flow of surface waters that overtops normal confinements or covers land normally dry most devastating of all geologic agents -in loss of life

9. Extent of a floodplain

12. Longitudinal Profile & Gadient

13. Drainage basin and cross sections at the headwater and near base level

15. Show animation

16. Factors in Stream flow • Several basic factors control the way a stream behaves: • Gradient [h/x] (expressed in meters per kilometers) • Stream-cross-sectional area [A] • (width * average depth, expressed in square meters) • Average velocity of water flow [v] • (expressed in meters per second) • Discharge [Q] (expressed in cubic meters per second) • Load (expressed in kilograms per cubic meter) • Dissolved matter generally does not affect stream behavior

17. Discharge, Velocity, & Channel Shape • The relationship of discharge, velocity, and channel shape for a stream can be expressed by the equation: Q = A * V Discharge Cross-sectional Average (m3/s) area of stream velocity (width x average (m/s) depth) (m2)

19. Flood stage • The elevation (in meters, feet, etc.) of the water above normal at the highest point in the flood

20. Stream Gage • USGS: 7000 nationwide • Measures water level (gage height) every 15 minutes • Sends data via satellite every 4 hours • “rating curve” converts gage height to discharge • Rating curve modifed after technition measures streamflow on site every 6 weeks

21. Measuring Stream Velocity

22. Calculating Discharge from a Stream GageVelocity X Area = Q

23. Rating curve

24. USGS National Streamflow Program http://water.usgs.gov http://waterdata.usgs.gov/ca/nwis/uv?11023000

27. San Diego River Watershed • Two USGS stream gages • Fashion Valley: 429 sq. mi

28. Santee Stream Gage

29. 482 Stream gages in CA

36. 1927 Flood • Photo taken on February 2, 1927 shows the Old Town railroad bridge washed out by the flood. This rail right-of-way still exists - you can see it looking east from I-5; Friars Rd. runs underneath it.

37. San Diego River • 1852 - Since San Diego Bay was a deeper harbor, and the San Diego River carried heavy silt deposits, it was decided to deflect the San Diego River into False Bay (Mission Bay) • The project was completed in two years by Indian laborers who reportedly hauled building materials in baskets. The Darby dike washed out one year after its completion and the San Diego River returned to its old course.

38. San Diego River • 1862 – Possibly the largest flood in the history of the San Diego River occurred (almost 100,000 cfs). • 1875- New dike constructed (cobblestone face two to three feet thick). A small channel was constructed on the north side of the dike that the river was diverted into the eastern part of Mission Bay.

40. Meandering River, showing forms and processes

41. Meander on the Colorado River

42. Erosion

43. Koyakuk River, Alaska, showing meander bends, point bar, and cut bank

44. Show animation

46. Braided channels in Granada, southern Spain with multiple channels, steep gradient, and coarse gravel

50. Floods In The US