1. Flooding

2. 2 / 80 Hydrologic Cycle Hydrologic Cycle

3. 3 / 80 The Three Fates of Precipitation 1. Infiltration 2. Runoff 3. Evapotranspiration

4. 4 / 80 Infiltration capacity of the soil is controlled by: 1. Intensity and duration of rainfall 2. Soil saturation 3. Soil texture 4. Slope of the land 5. Nature of the vegetative cover

5. 5 / 80 The Function of Rivers 1. Move runoff away from land and out to the sea (or lake) 2. Transport sediments (erosion)

6. 6 / 80 The Function of Rivers Erosion = transportation of sediments 1. Dissolved load 2. Suspended load 3. Bed load Streambed sediments = Alluvium

7. 7 / 80 The Function of Rivers Load is related to a stream's Load is related to a stream's Competence - maximum particle size Competence - maximum particle size Capacity - maximum load Capacity - maximum load Discharge Discharge volume of water flowing in the stream (generally expresses as cubic feet per second) volume of water flowing in the stream (generally expresses as cubic feet per second) Capacity is related to discharge Capacity is related to discharge

8. 8 / 80 Rivers – Profile

9. 9 / 80 A River’s Journey... Erosion – Mountains Vertical erosion Valleys are narrow & V-Shaped Arroyo Seco in the San Gabriel Mountains, Angeles Crest Highway looking towards La Canada & Los Angeles Photo by S. Leyva © 2006

10. 10 / 80 A River’s Journey... Erosion – Mountains Smaller channel = Smaller discharge = Higher velocity Higher velocity = higher energy = greater competence Riverbeds typically contain large boulders Sturveyant Falls Trail, San Gabriel Mountains Photo by S. Leyva © 2001

11. 11 / 80 A River’s Journey... Erosion – Foothills Stream velocity decreases Decreased velocity = decreased competence = deposition of load alluvial fans, braided streams, & sinuosity Source: Hyndman & Hyndman’s Natural Hazards & Disasters (http://earthscience.brookscole.com/hyndman)http://earthscience.brookscole.com/hyndman

12. 12 / 80 A River’s Journey... Erosion – Flatlands Larger channel = Larger discharge = Lower velocity Lower velocity = lower energy = decreased competence Riverbeds typically contain sands and gravels

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14. 14 / 80 Rivers Deposition Deposition Decreased velocity = decreased competence = deposition of load Decreased velocity = decreased competence = deposition of load Alluvium Alluvium Alluvial fans Alluvial fans Floodplains Floodplains Deltas Deltas

15. 15 / 80 Lena RiverLena River Delta, Siberia http://veimages.gsfc.nasa.gov//3451/landsat_art_lena_lrg.jpg

16. 16 / 80 The Mississippi River Delta

17. 17 / 80 Floods: The Worst Geological Hazard They are the most costly in terms of life, property, and land They can occur almost anywhere

18. 18 / 80 Types of Floods RegionalFlashUrban Storm surge / coastal Dam inundation

19. 19 / 80 Flood damage is caused by: 1. Erosion by flood waters 2. Impact of water on structures 3. Sediment deposition 4. Contamination of surface waters

20. 20 / 80 Factors which Have Increased Erosion 1. Deforestation – results in increased erosion 2. Overgrazing – also increased erosion 3. Urbanization More rapid discharge to streams causes: More rapid discharge to streams causes: More frequent floods, Higher flood peaks More frequent floods, Higher flood peaks Urban runoff is highly toxic Urban runoff is highly toxic

21. 21 / 80 Urbanization and Erosion Both natural and urban landscapes have low erosion rates Construction as natural lands are urbanized causes high erosion rates

22. 22 / 80 Recurrence Interval Time between floods of the same magnitude Time between floods of the same magnitude Example: there is 1 in 100 chance that a peak flow of a certain amount (say, 30,000 cf/s) can occur on a river. Example: there is 1 in 100 chance that a peak flow of a certain amount (say, 30,000 cf/s) can occur on a river. Thus, that river is said to have a 100-year interval Thus, that river is said to have a 100-year interval

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25. 25 / 80 Recurrence Interval Engineers design for particular recurrence intervals Engineers design for particular recurrence intervals Streets 2-5 years Streets 2-5 years Debris dams 5 – 25 years Debris dams 5 – 25 years Upper valley dams 100 years Upper valley dams 100 years Levees 100 yrs Levees 100 yrs Large dams 1000+ years Large dams 1000+ years

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27. 27 / 80 Societal Responses to Floods Hard Responses Hard Responses Dams Dams Levees Levees Sandbagging Sandbagging Soft Responses Soft Responses Watershed Management Watershed Management Zoning and Land Use Zoning and Land Use Insurance Insurance Erosion Control Erosion Control Forecasting Forecasting

28. 28 / 80 “Hard” Responses Dams and Reservoirs Dams and Reservoirs Los Angeles County Drainage Area (LACDA) Projects, CA Los Angeles County Drainage Area (LACDA) Projects, CA Sepulveda Dam Sepulveda Dam Sepulveda Dam Sepulveda Dam Hansen Dam Hansen Dam Hansen Dam Hansen Dam Lopez Dam Lopez Dam Lopez Dam Lopez Dam Santa Fe Dam Santa Fe Dam Santa Fe Dam Santa Fe Dam Whittier Narrows Dam Whittier Narrows Dam Whittier Narrows Dam Whittier Narrows Dam Brea Dam Brea Dam Brea Dam Brea Dam Fullerton Dam Fullerton Dam Fullerton Dam Fullerton Dam

29. 29 / 80 “Hard” Responses Dams and Reservoirs Dams and Reservoirs Santa Ana River Drainage Basin, CA Santa Ana River Drainage Basin, CA Seven Oaks Dam Seven Oaks Dam Seven Oaks Dam Seven Oaks Dam San Antonio Dam San Antonio Dam San Antonio Dam San Antonio Dam Prado Dam Prado Dam Prado Dam Prado Dam Carbon Canyon Dam Carbon Canyon Dam Carbon Canyon Dam Carbon Canyon Dam

30. 30 / 80 “Soft” Responses Flood Plain Management Flood Plain Management Flood Plain Zoning Flood Plain Zoning Flood inundation maps are easy to prepare for zoning purposes Flood inundation maps are easy to prepare for zoning purposes Zoning is hard to do because of extensive flood plain development Zoning is hard to do because of extensive flood plain development Urban development is the worst use of flood plains Urban development is the worst use of flood plains Farming, recreation, and natural areas are best Farming, recreation, and natural areas are best

31. 31 / 80 “Soft” Responses Federal Flood Disaster Protection Act of 1973 Federal Flood Disaster Protection Act of 1973 Provides flood insurance at affordable rates Provides flood insurance at affordable rates But it also requires: But it also requires: Stringent control on new construction in flood plains Stringent control on new construction in flood plains Comprehensive flood management plans Comprehensive flood management plans

32. 32 / 80 “Soft” Responses FEMA Flood Insurance Rate Maps (FIRMS) FEMA Flood Insurance Rate Maps (FIRMS) Cartographers map Special Flood Hazard Areas (SFHAs) on maps Cartographers map Special Flood Hazard Areas (SFHAs) on maps SFHAs are areas that are subject to inundation by a 100-year flood SFHAs are areas that are subject to inundation by a 100-year flood The Santa Clarita Valley is the only area in L.A. County to be affected by FIRMS. The Santa Clarita Valley is the only area in L.A. County to be affected by FIRMS.

33. 33 / 80 “Soft” Responses Flood Plain Management Flood Plain Management Flood forecasting - Function of the River & Flood Service of the US National Weather Service Flood forecasting - Function of the River & Flood Service of the US National Weather Service

34. 34 / 80 Determination of Flood Hazard Floodplains Floodplains Paleoevents Paleoevents Historic Records Historic Records

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36. 36 / 80 Determination of Past Events

37. 37 / 80 Examples Regional - Mississippi river, Santa Ana River & LA River Regional - Mississippi river, Santa Ana River & LA River Flash - La Cañada Flash - La Cañada Urban - Storm surge / coastal - Hurricane Katrina Urban - Storm surge / coastal - Hurricane Katrina Dam inundation - St. Francis Dam inundation - St. Francis

38. 38 / 80 Regional Flooding – Southern CA Santa Ana River has the largest CA river basin south of the Sierra Nevada Santa Ana River has the largest CA river basin south of the Sierra Nevada River has breached its levees many times River has breached its levees many times 1862 – large flood, small population 1862 – large flood, small population 1938 – smaller flood, larger population 1938 – smaller flood, larger population

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42. 42 / 80 Regional Flooding – Southern CA Rainy season – October through April

43. 43 / 80 Regional Flooding – Southern CA Reasons for heavy rainfall amounts Reasons for heavy rainfall amounts El Niño / La Niña / other oscillations El Niño / La Niña / other oscillations Orographic Lifting - Storms moving inland must rise over rugged mountains Orographic Lifting - Storms moving inland must rise over rugged mountains Record storms in the San Gabriel Mtns Record storms in the San Gabriel Mtns 26” in 24 hours January, 1943 26” in 24 hours January, 1943 1” in 1 minute April 5, 1926 1” in 1 minute April 5, 1926 Debris flows and mudflows are generated and dump their deposits on the alluvial fans Debris flows and mudflows are generated and dump their deposits on the alluvial fans

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45. 45 / 80 Regional Flooding – Southern CA Fatal Storms Fatal Storms 1914, 1916, 1921, 1926, 1927, 1934, 1938, 1943, 1952, 1962, 1969, 1976, 1978, 1983 1914, 1916, 1921, 1926, 1927, 1934, 1938, 1943, 1952, 1962, 1969, 1976, 1978, 1983 1914 1914 Los Angeles Basin population ~700,000 Los Angeles Basin population ~700,000 19+ inches of rain in four days in the San Gabriel Mountains 19+ inches of rain in four days in the San Gabriel Mountains Resulted in floods causing $10 million in damage. Resulted in floods causing $10 million in damage.

46. 46 / 80 Regional Flooding – Southern CA Fatal Storms Fatal Storms 1934 1934 "New Year's Day Flood" in the La Canada Valley "New Year's Day Flood" in the La Canada Valley 40+ people died 40+ people died 400 houses destroyed & damaged streets, bridges, and highways 400 houses destroyed & damaged streets, bridges, and highways Causes: Causes: fire and lack of heavy rainstorms in the years before the flood fire and lack of heavy rainstorms in the years before the flood

47. 47 / 80 Regional Flooding – Southern CA Fatal Storms Fatal Storms The 1938 storms were the greatest in 70 previous years The 1938 storms were the greatest in 70 previous years Hit entire area from SD to SB with 36” rain in 6 days Hit entire area from SD to SB with 36” rain in 6 days 1000 cfs/sq mile of runoff 1000 cfs/sq mile of runoff 87 lives and $78 million 87 lives and $78 million Data gathered is the basis of our flood control program Data gathered is the basis of our flood control program El Niño year and possibly due to a hurricane! El Niño year and possibly due to a hurricane!

48. 48 / 80 Regional Flooding – Southern CA Department of Public Works of Los Angeles County Department of Public Works of Los Angeles County WEB Page: http://ladpw.org/services/water/ WEB Page: http://ladpw.org/services/water/http://ladpw.org/services/water/ Flood control is their responsibility Flood control is their responsibility The LA County Flood Control District first formed in 1915 The LA County Flood Control District first formed in 1915 After the fires of 1913 and the floods of 1914 After the fires of 1913 and the floods of 1914

49. 49 / 80 Flood Control – Southern CA Dams Paved River Channels Storm Drains Other areas may use: channel dredging, alteration, diversion or stabilization; dike and levees

50. 50 / 80 Southern California Dams (over 40,000 acre feet)

51. 51 / 80 Flood Control – Southern CA Dams – Mountains Dams – Mountains The basic control is construction of flood control dams within the mountain ranges The basic control is construction of flood control dams within the mountain ranges Uncontrolled Mountain Runoff Uncontrolled Mountain Runoff Dams are designed to take instant peak water flow Dams are designed to take instant peak water flow They conserve storm water for public use They conserve storm water for public use Example: Big Tujunga Dam Example: Big Tujunga Dam

52. 52 / 80 Flood Control – Southern CA Dams – Debris Flow Dams – Debris Flow Debris flows formed below the dams that could come from canyon mouths into urban areas are controlled with debris dams Debris flows formed below the dams that could come from canyon mouths into urban areas are controlled with debris dams 354 debris dams in LA County 354 debris dams in LA County Designed to catch large amounts of sediment Designed to catch large amounts of sediment Must be cleaned out when 25% full Must be cleaned out when 25% full Fire a common cause of debris flows Fire a common cause of debris flows

53. 53 / 80 Flood Control – Southern CA Dams - Debris flows (continued) Dams - Debris flows (continued) Factors determining the type and magnitude of debris flows Factors determining the type and magnitude of debris flows Drainage area characteristics Drainage area characteristics Canyon slopes and stream gradients Canyon slopes and stream gradients Type and degree of rock weathering Type and degree of rock weathering Type and density of ground cover Type and density of ground cover Duration and intensity of the storm Duration and intensity of the storm

54. 54 / 80 Rubio Canyon Debris Flow Basin, Altadena, CA

55. 55 / 80 Rubio Canyon Debris Flow Basin, Altadena, CA Photo by S. Leyva © 2006

56. 56 / 80 Flood Control – Southern CA Dams – Upper Valley Dams – Upper Valley Flood regulating reservoirs serve 2 purposes Flood regulating reservoirs serve 2 purposes 1. Catch and control runoff from rain falling downstream from mountain controls 2. Store water released from the mountains These reservoirs often help recharge groundwater supplies These reservoirs often help recharge groundwater supplies Example: Hanson Dam Example: Hanson Dam

57. 57 / 80 Flood Control – Southern CA Flood Control Channels Flood Control Channels fully lined reinforced concrete fully lined reinforced concrete Controls high velocity flow Controls high velocity flow Prevents scour Prevents scour Also prevents sediments from reaching the coast Also prevents sediments from reaching the coast

58. 58 / 80 City of Calabasas Stream Restoration Before Photos courtesy of Dr. Barry Hibbs, CSULA Hydrology

59. 59 / 80 City of Calabasas Stream Restoration After – looking downstream Photos courtesy of Dr. Barry Hibbs, CSULA Hydrology

60. 60 / 80 City of Calabasas Stream Restoration After – looking downstream Photos courtesy of Dr. Barry Hibbs, CSULA Hydrology

61. 61 / 80 City of Calabasas Stream Restoration After – looking downstream Photos courtesy of Dr. Barry Hibbs, CSULA Hydrology

62. 62 / 80 City of Calabasas Stream Restoration After – looking upstream Photos courtesy of Dr. Barry Hibbs, CSULA Hydrology

63. 63 / 80 City of Calabasas Stream Restoration After – looking upstream Photos courtesy of Dr. Barry Hibbs, CSULA Hydrology

64. 64 / 80 Flood Control – Southern CA Storm Drains Storm Drains Storm drains and tunnels connect to major flood control facilities Storm drains and tunnels connect to major flood control facilities Not all areas have them Not all areas have them The total length of all LA County channels of all types is ~ 2500 miles The total length of all LA County channels of all types is ~ 2500 miles

65. 65 / 80 Flood Control – Southern CA It probably can not handle a 100 year flood It probably can not handle a 100 year flood Public should be as concerned about this as a great Earthquake Public should be as concerned about this as a great Earthquake

66. 66 / 80 Santa Ana River Flood Control Project Project Protects 90 miles along Santa Ana River Project Protects 90 miles along Santa Ana River Will handle a worst in 170 years flood Will handle a worst in 170 years flood This area is regarded by the Army Corp of Engineers as the worst flood hazard west of the Mississippi This area is regarded by the Army Corp of Engineers as the worst flood hazard west of the Mississippi Serious flood could cause 3000 deaths Serious flood could cause 3000 deaths Could cause $14 billion damage in Orange County alone Could cause $14 billion damage in Orange County alone

67. 67 / 80 Santa Ana River Flood Control Project Project includes: Project includes: 550' long Earthfill dam 4 miles above Mentone 550' long Earthfill dam 4 miles above Mentone Raise the Prado Dam 30 feet Raise the Prado Dam 30 feet

68. 68 / 80 Dam inundation - St. Francis Dam 3/12/28 3/12/28 Dream of William Mulholland Dream of William Mulholland 200 ft high curved concrete gravity dam 200 ft high curved concrete gravity dam Failed catastrophically at midnight upon first filling Failed catastrophically at midnight upon first filling 420-500 killed 420-500 killed

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70. 70 / 80 Walking across the top of the St. Francis Dam, looking west, sometime between 1926 and 1928. St. Francis Dam shortly before its March 12, 1928, collapse. It is said that this photograph was taken at noon on March 12, 1928. However, the caption on the back of the original photo reads: "Taken March 9, 1928, by E.B. (Al) Louden." In any case it is believed to be the last photograph of the St. Francis Dam before it broke at 3 1/2 minutes before midnight on March 12.

71. 71 / 80 This colorized photo shows the St. Francis Dam on its day of formal dedication in May of 1926, almost two years before the failure. http://web.umr.edu/~rogersda/st_francis_dam/

72. 72 / 80 Photo, looking north, shows what was left of the St. Francis Dam shortly after it failed on March 12, 1928.

73. 73 / 80 This colorized photo was taken the day after St. Francis Dam failed.

74. 74 / 80 This picture, taken just after the 1928 disaster,looks towards the southwest. The San Francisquito Fault dips to the northwest.

75. 75 / 80 March 11, 2001: Ruins at the base of the former St. Francis Dam in San Francisquito Canyon. The red speck in the center is a person.

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77. 77 / 80 Dam inundation - St. Francis Dam Cause of failure complex Cause of failure complex Sespe formation prone to “slaking” Sespe formation prone to “slaking” excessive titling when fully loaded excessive titling when fully loaded an absence of seepage relief in the dam's sloping abutments an absence of seepage relief in the dam's sloping abutments and the partial reactivating of underlying paleo mega-slides within the Pelona Schist. and the partial reactivating of underlying paleo mega-slides within the Pelona Schist.

78. 78 / 80 Dam inundation - St. Francis Dam Some of the most important consequences included Some of the most important consequences included the formulation of the world's first dam safety agency the formulation of the world's first dam safety agency normalization of uniform engineering criteria for testing of compacted earthen materials normalization of uniform engineering criteria for testing of compacted earthen materials A reassessment of all LADWP dams and reservoirs A reassessment of all LADWP dams and reservoirs the formulation of a state-mandated process for arbitration of wrongful death suits the formulation of a state-mandated process for arbitration of wrongful death suits

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