Floods: The Worst Geological Hazard
Flood Styles: Coastal Flood
Flooding in coastal areas is often caused by storm surges, but can also be produced by seismic sea waves called tsunami.
Flood Styles: Urban Flood
Roads and parking lots prevent infiltration of water. Urbanization increases runoff 2 to 6 times over what would occur on natural terrain. Streets can become swift moving rivers, can flood homes and businesses.
Flood Styles: Ice Jams
Floating ice can accumulate at a natural or man-made obstruction and stop the flow of water.
Flood Styles: Dam Failure
The St. Francis Dam - This dam was the dream of William Mulholland. It was a 200 ft high curved concrete gravity dam that failed catastrophically at midnight upon the first filling. An estimated 420-500 people were killed
| PRESENT STATUS OF DEATH & INJURY CASES ST. FRANCIS DAM DISASTER 15-Jul-29 |
|
| Total Number of Persons Killed | 306 |
| This number includes the identified and missing dead on which claims were presented, and a few who were known to be killed but left no heirs. It does not include the unidentified bodies, of which there are ... | 64 |
| Number of Persons Injured | 66 |
| Number of Settled Death & Injury Claims | 352 |
| Number of Unsettled Death & Injury Claims | 38 |
| Total Amount of Death & Injury Claims | $3,674,207.56 |
| Amount of Settlement of Above Claims | $915,751.74 |
| Total Amount of Unsettled Death & Injury Claims | $1,376,251.35 |
| The above amount was filed by 12 claimants, and covers 21 deaths and 4 injuries. |
|
| Number of Claims which have gone into Litigation | 35 |
| The above claims were filed by 10 claimants. |
|
| Entire Families Wiped Out | 20 |
| Number of persons reported missing, but on whom no inquiries were received or claims filed | 67 |
Roster of St. Francis Dam Victims Compiled by Ann Stansell
One of the last photos of the dam before it's failure. The photo was taken on 3/9/28.
Image Source: St. Francis Dam Disaster: An Extended Timeline Compiled by Alan Pollack
Photo No. 2 from The Newhall Land and Farming Co.'s March 24, 1928 report on the March 12-13 St. Francis Dam Disaster. Caption reads "The Dam as it now appears from inside."
From: Report on St. Francis Dam Flood. For The Newhall Land & Farming Company. By A.M. and GEO. A. NEWHALL JR.
What caused the dam to fail? The cause of failure complex, and it was due to may factors.
- Sespe formation prone to "slaking"
- Excessive titling when fully loaded
- An absence of seepage relief in the dam's sloping abutments
- And the partial reactivating of underlying paleo mega-slides within the Pelona Schist.
"Photo, looking north, shows what was left of the St. Francis Dam shortly after it failed on March 12, 1928." Note the landslides to the right of what is left of the dam, and another one further upstream. Image source: St. Francis Dam Failure / San Francisquito Canyon
This picture, taken just after the 1928 disaster,looks towards the southwest. The San Francisquito Fault dips to the northwest. Image from: http://seis.natsci.csulb.edu/VIRTUAL_FIELD/Francesquito_Dam/franmayn.htm
The fallout from this disaster was immense. William Mullholland never truly recovered from the failure. Entire families were lost and some bodies never recovered. However, some good did come out of the bad. Some of the most important outcomes included:
- The formulation of the world's first dam safety agency
- Normalization of uniform engineering criteria for testing of compacted earthen materials
- A reassessment of all LADWP dams and reservoirs
- The formulation of a state-mandated process for arbitration of wrongful death suits
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