California Alluvial Fans: Regional Differences, Fan Identification and Hazards

A Scientific Approach to Managing RISK: Joint Arid Regions Committee & FMA Symposium Management Association – Annual Conference September 8, 2015 ------Jeremy T. Lancaster California Geological Survey Introduction

• Alluvial Fans Differ with… • California Geography/Geology and Fan Types • Hazards Present – Examples • Regional Mapping – Surficial Geology • Hazards – Pre -type Identification – Examples Alluvial fans differ with geographic location…

• Watershed: – Geology – Tectonic History – Size – Relief – Hydroclimatic Setting – Vegetation – Soils – Land use – Fire frequency – Drainage complexity Alluvial fans differ with geographic location…

• These affect fan formation and fan geomorphic expression – Depositional landforms – Incising landforms – Abandoned and relict fans • Fan Similarities – Fan shape – Radial topography – drainage patterns – Definable apex, lateral boundaries and toe California Physiography and Geology California Climate Streamflow Fans

Drainage Basin Name Pushwalla Area (square miles) 19.5 Mean Slope (%) 36.6 Max Elevation (ft) 5,215 Annual Precip (in) 10.4 Relief Ratio 0.075 Watershed Geology Granite/Gneiss Composite Fans

Drainage Basin Name Oak Creek Area (square miles) 24.3 Mean Slope (%) 52.9 Max Elevation (ft) 13,218 Annual Precip (in) 20.5 Relief Ratio 0.17 Watershed Geology Granite Composite Fans

Drainage Basin Name Hanes Area (square miles) 0.9 Mean Slope (%) 48.7 Max Elevation (ft) 2,176 Annual Precip (in) 19.8 Relief Ratio 0.14 Watershed Geology Shale/Sst Side Fans

• Side canyon/ junction fans • Fan Deltas Alluvial Fan Mapping Preliminary Hazards Debris Flow Hazards

Google Earth Pro Imagery

Source Canyon San Jacinto Mountains

Active Firebreak View South toward Soboba Road

Abandoned Golden Era Productions Buildings Abandoned Buildings View Apartments Golden Era Productions and Hemecinto Temple Soboba Road San Jacinto

Drainage Basin Name San Jacinto New Debris Flow Area (square miles) 0.3 Debris Initially Deposited Mean Slope (%) 47.7 Along Pre-Flow Drainage Alluvial Fan Max Elevation (ft) 3,681 Annual Precip (in) 17.7 Relief Ratio 0.39 Watershed Geology Granite View Southeast of Debris Flow Deposits Debris Flow Hazards (pre-typing) • Identification Methods Debris Flow Hazards (pre-typing) Watershed Morphometric Factors – Relief Ratio – Meltons # – Meltons # + Plannimetric Length

Watershed Factors used in USGS Debris Flow Models (sounthern Cal) Gartner et al. (2014) Mean Min Max Meltons # 0.51 0.12 1.03 Relief Ratio 0.24 0.05 0.71 Mean Slope (%) 57.8 18.7 84.8 Watershed (%) 81.7 5 100

Wilford (2005) Non-Fire Meltons # >0.30 Meltons # and Plannimetric Length >0.60 and ≥ 2.7km

Bovis and Jakob (1999) Non-fire Meltons # >0.52

(R = Meltons#, WL = Plannimetric Length; Welsh and Davies, 2011) Debris flow hazards: Watershed Specific

• availability – Supply limited Event Frequency – Supply unlimited Supply unlimited + Transport unlimited High Supply limited + Transport Limited Low • Hydroclimate – Transport limited – Transport unlimited • Slope processes – Landslides – Colluvium • Channel reach morphology – Constrictions/confinement – Plunge pools – Broad gentle reaches – Bedrock presence Camarillo Springs Oct./Dec. 2014

• May 2013 Springs fire – 24,250 acres – 22 Structures Camarillo Springs Oct./Dec. 2014

Drainage Basin Name Camarillo Springs Area (square miles) 0.09 Mean Slope (%) 61.7 Max Elevation (ft) 1,777 Annual Precip (in) 15.8 Relief Ratio 0.55 Meltons # 0.99 Plannimetric Length (km) 1 Watershed Geology Granite/Volcanics Dibblee, 1990 Camarillo Springs Oct./Dec. 2014

– October 31, 2014: .55in in 2hrs; .29in @ 9pm and .26in @10pm – December 12, 2014: 1.75 inches in 9hrs; 1in/hr @ 2am; 1.2 in b/w 2 and 4 am Drainage Basin Name Clark Area (square miles) 0.1 Mean Slope (%) 73.6 Max Elevation (ft) 3,123 Annual Precip (in) 8.39 Relief Ratio 0.61 Meltons # 2.97 Plannimetric Length (km) 0.86 Watershed Geology Granite