The Santa Barbara County 1/9 Debris Flows of 2018 Extreme Runoff Response to Extreme Precipitation

Southwest Extreme Precipitation Symposium Scripps Institute CW3E, La Jolla California March 29, 2018 ------Jeremy Lancaster – Sup. Engineering Geologist California Geological Survey Nina Oakley – Ph.D. Candidate DRI-WRCC 2017 Wildfires – Historic Context

California Wildfires Years over 1 million acres since 1987 Year Fires Acres 2017 9,133 1,248,606 2008 6,255 1,593,690 2007 6,043 1,520,362 1999 11,125 1,172,850 1987-2016 average: 555,700 acres Source: CALFIRE

http://www.cnrfc.noaa.gov/radarArchive.php 63 Fires Notable Fires with PFDF • Coyote • Romero • Jesusita • Sherpa • Thomas Thomas Fire Debris Flow Hazards

Source: landslides.usgs.gov/hazards/postfire_debrisflow/ Santa Barbara Coastal: Empirical Intensity-Durations 80

No Debris Flow 70 Gap and Jesusita Fires Debris Flow 60 Jesusita Fire

50

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30 22.4mm/h

20 Precipitation Intensity mm/h Intensity Precipitation 10

0 0 10 20 30 40 50 60 Duration in Minutes

Source: USGS OFR 16-1106 Santa Barbara Coastal: Empirical Intensity-Durations

80 No Debris Flow Gap and Jesusita Fires 70 Debris Flow Gap and Jesusita Fires 60 Debris Flow Sherpa Fire 50

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20 Precipitation Intensity mm/h Intensity Precipitation

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0 0 10 20 30 40 50 60 Duration in Minutes

Source: USGS OFR 16-1106 Sherpa Fire –El Capitan PFDF Jan 20, 2017

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0 0 10 20 30 40 50 60

Santa Barbara Coastal: Empirical Intensity-Durations 90 No Debris Flow 80 Gap and Jesusita Fires Debris Flow 70 Jesusita Fire Debris Flow 60 Sherpa Fire Debris Flow 50 Thomas Fire

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20 Precipitation Intensity mm/h Intensity Precipitation 10

0 0 10 20 30 40 50 60 Duration in Minutes 5-minute burst! Santa Barbara Coastal: Empirical Intensity-Durations 160 No Debris Flow 140 Gap and Jesusita Fires Debris Flow

120 Jesusita Fire Debris Flow Sherpa Fire 100 Debris Flow Thomas Fire 80

60

40 Precipitation Intensity mm/h Intensity Precipitation 20

0 0 10 20 30 40 50 60 Duration in Minutes 1/9 Post-Fire Debris Flows and Precipitation Frequency Threshold precipitation rate known to trigger debris flows: Intensity NOAA Atlas 14 Gage Name • Thomas Fire: 24 mm/hr for 15 i15 (mm) Return Period minutes (USGS) KTYD 76.2 25-year Observed on 1/9: Montecito 67.1 50-year Daulton Tunnel 80.3 25-year • 15 min: 36.6-80.3 mm/hr Summerland 52.8 5-10 year • This is more than 1.5x-3.2x Edison Trail 58.9 5-year thresholds Carpenteria 53.8 5-year La Conchita 65 25-year • 5 minute rates were extreme, in Old Man Mountain 36.6 1-year some cases record-setting! Record at Jameson Dam Tied Record at Carpenteria FS 1/9 Debris Flow Magnitude Comparisons

# of Debris Max Estimated Debris Flow Estimate of Debris Flow Magnitude Classification Fire Name Area Storm Date Flows Depth (m) Volume Innundation Area (Jakob, 2005)

Montecito, Hot Springs, Coyote Cold Springs, San Ysidro, 11/1/1964 >5 6.1 Unkown >2 Km^2(est.) 5 Mission Creek Romero, Toro Canyon, Garrapata, Santa Romero 12/27/1971 >6 N/A Unkown >2 Km^2(est.) 5 Monica, Franklin, and Carpenteria Creek Jesusita Gibraltar Road 2/27/2010 1 N/A Unkown N/A 1 Jesusita JS 3/3/2010 1 N/A Unkown N/A 1 Sherpa El Capitan 1/20/2017 1 >3 >20,000 Cubic Meters <0.5 Km^2 4 Santa Thomas 1/9/2018 >20 >6 >1.0 Million Cubic Meters 3-4 Km^2 7 Barbara/Carpenteria

Pickens La Cresenta 1/1/1934 >15 6.1 >0.5 Million Cubic Meters 8 Km^2 7 Rancho Cucamonga/San Gran Prix - Old 12/25/2003 41 N/A 3.7 Million Cubic Meters N/A 7 bernardino Inyo Complex Independence 7/12/2008 3 3.9m 1.5 Million Cubic Meters 3 Km^2 7

Were precipitation rates unprecedented?

All Time 5 min UCSB: 0.72 in (1998) Jameson Dam (s. 1965) All Time 15 min 5 min: 0.6 (0.53 1997/98) San Marcos Pass: 1.39 in (1998) 15 min: 0.99 (0.96 1997/98) Stanwood FS (s. 1953) Preliminary Assessment: 5 min: 0.42 (0.52 2014/15) Precipitation rates EXTREME 15 min: 0.55 (1.19 1983/84) Edison Trail (s. 1993) but not UNPRECEDENTED 5 min: 0.35 (0.49 2004/05) 15 min: 0.78 (0.91 2004/05)

El Deseo (s. 1969) 5 min: 0.46 (0.49 2004/05) 15 min: 0.64 (0.91 2004/05) Doulton Tunnel (s. 1965) 5 min: 0.45 (0.5 2014/15) 15 min: 0.85 (0.99 2014/15) Carpinteria FS (s. 1964) 5 min: 0.36 (0.36 1968/69) 15 min: 0.86 (0.66 1974/75)

Western Regional Climate Center Providing climate services since Data Source: SB County Public Works 1986