Emergency Assessment of Post-Fire Debris-Flow Hazards 

for the 2013 Powerhouse Fire, Southern California

By Dennis M. Staley, Greg M. Smoczyk, and Ryan R. Reeves

Open-File Report 2013–1248

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013 

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment—visit 

http://www.usgs.gov or call 1–888–ASK–USGS

For an overview of USGS information products, including maps, imagery, and publications,

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Suggested citation:

Staley, D.M., Smoczyk, G.M., and Reeves, R.R., 2013, Emergency assessment of post-fire

 debris-flow hazards for the 2013 Powerhouse fire, southern California: U.S. Geological Survey 

Open-File Report 2013–1248, 13 p., 3 plates, http://pubs.usgs.gov/of/2013/1248/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

Although this information product, for the most part, is in the public domain, it also may contain

copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be 

secured from the copyright owner. 
iii

Contents

Abstract ......................................................................................................................................................................... 1

Introduction.................................................................................................................................................................... 1

Physical Setting of the Powerhouse Burn Area ............................................................................................................. 2

Methods Used To Estimate Debris-Flow Hazards ......................................................................................................... 5

Debris-Flow Hazard Assessment................................................................................................................................... 6

Debris-Flow Probability Estimates ............................................................................................................................10

Debris-Flow Volume Estimates .................................................................................................................................10

Combined Relative Debris-Flow Hazard Rankings ...................................................................................................10

Limitations of Hazard Assessments ..........................................................................................................................10

Summary and Conclusions...........................................................................................................................................11

References Cited..........................................................................................................................................................11

Figures

Figure 1. Overview map of the Powerhouse fire burn area near Lancaster, California, USA.................................... 3

Figure 2. Burned Area Reflectance Classification (BARC) burn severity map of the Powerhouse fire burn 

area near Lancaster, California, USA............................................................................................................................ 4

Table

Table 1. Basin outlet locations (UTM Zone 11 NAD83, Meters), morphometric variables, rainfall characteristics 

and model predictions for the 73 defined watersheds in the Powerhouse burn area..................................................... 7

Plates

Plate 1. Estimated probability of post-fire debris flows in the area burned by the 2013 Powerhouse fire, 

southern California.....................................................................................................................................................link

Plate 2. Estimated volume of post-fire debris flows in the area burned by the 2013 Powerhouse fire, 

southern California.....................................................................................................................................................link

Plate 3. Combined post-fire debris-flow hazard in the area burned by the 2013 Powerhouse fire, 

southern California.....................................................................................................................................................link
iv

Conversion Factors and Datums

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

hectare (ha) 2.471 acre

square kilometer (km2) 247.1 acre

square kilometer (km2) 0.3861 square mile (mi2)

square meter (m2) 10.76 square foot (ft2) 

Volume

cubic meter (m3) 35.31 cubic foot (ft3)

Flow rate

millimeter per hour (mm/h) 0.03937 inch per hour (in/h)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
Emergency Assessment of Post-Fire Debris-Flow Hazards 

for the 2013 Powerhouse Fire, Southern California

By Dennis M. Staley, Greg M. Smoczyk, and Ryan R. Reeves

Abstract

Wildfire dramatically alters the hydrologic response of a watershed such that even modest 

rainstorms can produce dangerous flash floods and debris flows. Existing empirical models were used 

to predict the probability and magnitude of debris-flow occurrence in response to a 10-year recurrence 

interval rainstorm for the 2013 Powerhouse fire near Lancaster, California. Overall, the models predict 

a relatively low probability for debris-flow occurrence in response to the design storm. However, 

volumetric predictions suggest that debris flows that occur may entrain a significant volume of 

material, with 44 of the 73 basins identified as having potential debris-flow volumes between 10,000

and 100,000 cubic meters. These results suggest that even though the likelihood of debris flow is 

relatively low, the consequences of post-fire debris-flow initiation within the burn area may be 

significant for downstream populations, infrastructure, and wildlife and water resources. Given these 

findings, we recommend that residents, emergency managers, and public works departments pay close 

attention to weather forecasts and National-Weather-Service-issued Debris Flow and Flash Flood 

Outlooks, Watches, and Warnings and that residents adhere to any evacuation orders.

Introduction

The occurrence of debris flows in response to high-intensity rainfall is well documented in 

recently burned areas of southern California (for example, Eaton, 1935; Campbell, 1975; McPhee,

1989; Cannon and others, 2008; 2010; 2011; Cannon and DeGraff, 2009; Kean and others, 2011;

Staley and others, in press). Two recent examples highlight the destructive nature of post-fire debris 

flows. On December 25, 2003, a high-intensity rainstorm initiated debris flows within the Grand Prix 

and Old burn areas and killed 16 people near San Bernardino, California (Calif.). On February 6, 2010, 

debris flows produced in the Station burn area overtopped sediment-retention basins and damaged or 

destroyed 46 homes in La Crescenta, Calif. These events provide sobering examples of the threat that 

post-fire debris flows pose to lives, properties, infrastructure, and important natural resources within 

and downstream of recently burned steeplands. 

Wildfire causes numerous changes to the vegetative characteristics and physical and chemical 

properties of the soil within a burn area. Reduction in vegetation cover on hillslopes increases the 

likelihood of soil erosion during rainfall and runoff. Wildfire has also been demonstrated to increase 

the rate of runoff production by enhancing hydrophobicity in soils through chemical changes and by 

introducing ash into the soil column (Shakesby and Doerr, 2006; Gabet and Sternberg, 2008; Larsen 

and others, 2009). These changes ultimately contribute to increases in the rate of runoff and sediment 

production during rainfall. The enhanced runoff response initiates floods and debris flows even during 

relatively minor rainstorms (Shakesby and Doerr, 2006; Cannon and others, 2008). Post-fire debrisflow hazards further increase in likelihood when the physical and chemical changes introduced during 
2

wildfire are combined with steep slopes and an abundant supply of sediment. Given the relatively steep 

terrain, severity of the wildfire, and proximity of local population and infrastructure, there is an 

elevated risk of post-fire debris-flow hazards within and downstream of the Powerhouse fire burn area.

The purpose of this report is to provide a preliminary assessment of the likelihood and potential 

magnitude of post-fire debris flows in the area burned by the 2013 Powerhouse fire in Los Angeles 

County, Calif. We use empirical methods that have been previously applied in this region of southern 

California (for example, Cannon and others, 2007; 2009) to estimate (1) the probability of debris-flow 

occurrence in response to a storm of a given duration and intensity, (2) the predicted volume of 

material transported and deposited by a debris flow in response to a storm with a 10-year (yr)

recurrence interval, and (3) a combined relative hazard ranking that incorporates the results of the 

probability and volume models.

Physical Setting of the Powerhouse Burn Area

The Powerhouse fire burned 122.5 square kilometers (km2) (30,275 acres) of mountainous 

terrain in northern Los Angeles County near Lancaster, Calif. (inciweb.org, 2013) from May 30th 

through June 10th, 2013 (fig. 1). The communities most affected by this event include the towns of 

Elizabeth Lake and Lake Hughes and private properties within Elizabeth Lake Canyon, such as the 

Cottonwood Campground and the Canyon Creek Sports Camp. The Powerhouse fire damaged or 

destroyed 24 homes, all of which were located near Lake Hughes.

The Powerhouse burn area occupies mostly mountainous terrain, where elevations range from 

630 meters (m) to 1,410 m, with an average slope of 32 percent. The rock type in the burn area is 

predominantly gneiss and granodiorite, with some sandstone and alluvium units (Jennings and Strand, 

1969). These lithologies weather to produce coarse sandy loam soils. The burn area also contains 

numerous faults, including approximately 5 kilometers (km) of the San Andreas fault zone, along 

which the towns of Elizabeth Lake and Lake Hughes are situated. A majority of the area was burned at 

moderate (56 percent) and high (10 percent) severity (fig. 2) (Remote Sensing Applications Center,

2013). Areas of moderate and high burn severities fall primarily in the southern portion of the burn 

area where the topography contains steeper slopes and more dense vegetation. The northern extent of 

the burn area, which contains portions of the Portal Ridge hills, the San Andreas fault zone, and the 

Antelope Valley, was burned primarily at moderate or low severity.

The Powerhouse burn area is located in inland Los Angeles County and has lesser rainfall than 

other debris-flow prone locations, such as the San Gabriel, San Bernardino or Santa Monica 

mountains. Precipitation frequency estimates for the burn area indicate that there is 10-percent

likelihood in any given year (that is, a 10-yr storm event) that 30-minute (min) rainfall accumulations 

within the burn area will range between 13.6 and 21.2 millimeters (mm) (0.5 and 0.8 inches [in]) 

(Bonnin and others, 2006). These estimates suggest that it would take a relatively large rainstorm (that 

is, greater than a 10-yr recurrence interval) to produce rainfall rates that have been observed to initiate 

post-fire debris flows in the region (Cannon and others, 2008; Staley and others, in press).
3

Figure 1. Overview map of the Powerhouse fire burn area near Lancaster, California.
4

Figure 2. Burned Area Reflectance Classification (BARC) burn severity map of the Powerhouse fire burn area 

near Lancaster, California, USA.
5

Methods Used To Estimate Debris-Flow Hazards

The preliminary hazard assessment relies upon two empirical models to estimate the 

probability, volume, and combined relative hazard ranking of debris flows for selected drainage basins 

within the Powerhouse fire burn area in response to a design storm. In this case, we use a rainstorm 

with a 10-yr recurrence interval for the design storm. We selected this storm frequency and magnitude 

as it represents a relatively large magnitude (in terms of total accumulation and peak storm intensities), 

but still somewhat common rainstorm. The empirical models are based upon historical debris-flow 

occurrence data, rainfall storm conditions, terrain and soils information and burn severity data from 

recently burned areas in southern California. The database consists of 1,748 records from 20 burn areas 

from the years 2003–2010.

In this study, the drainage basin scale was used to calculate post-fire debris-flow probability, 

volume, and combined hazards. Here, 73 basins were defined by analyzing elevation data from 10 m 

USGS digital elevation models (DEMs). Measures of the soil K-Factor within each basin were 

obtained from the State Soil Geographic (STATSGO) database (Schwartz and Alexander, 1995). The 

soil K-Factor represents a relative index of the susceptibility of bare soil to particle detachment and 

transport by rainfall (Schwartz and Alexander, 1995). If more than one soil unit occurred within a 

given basin, a spatially weighted average of the soil variable values was calculated. The K-Factor of 

soils in basins burned by the Powerhouse covered a narrow range from 0.18–0.29.

The probability estimates are based upon a logistic regression model derived from a southernCalifornia-specific database (Rupert and others, 2008), updated in 2011 to include basin-response 

information from the fires of 2007–2010 (Susan Cannon, 2011, unpublished data). This model is 

designed to predict the probability of debris-flow occurrence at a basin outlet in response to a given 

storm by combining the following two equations:

P = e x /(1 + e x

), (1) 

where:

P is the probability of debris-flow occurrence in fractional form and 

e x is the exponential function where e represents the mathematical constant 2.718. 

Equation 2 is used to calculate x:

x = −5.8 + (0.002 × ElevRange) + (0.022 × pctB50) + �0.028 × pcthigh� +

(7.017 × Kfact) + (0.017 × r30) (2)

where:

ElevRange is the range (maximum elevation–minimum elevation) within the watershed (in meters), 

pctB50 is the percentage of the watershed that was burned and has slope values in excess of 50 percent

(in percent), 

pcthigh is the percent of the drainage basin area burned at high severity (in percent), 

Kfact is the dimensionless erosivity index for the soils in the basin obtained from STATSGO data 

(Schwartz and Alexander, 1995), and 

r30 is the 30-min rainfall accumulation for the design storm, in this case we use the 30-min rainfall 

intensity for a 10-yr recurrence interval storm (in mm).

Probabilities predicted by the equation potentially range from 0 (least likely) to 100 percent (most 

likely). The predicted probabilities are assigned to one of five equal (20 percent) interval classes for 

cartographic display.

Debris-flow volumes are predicted using a multiple linear regression model (Gartner and 

others, 2008) which have been applied in nearby southern California burn areas between 2007 and 

2009 (for example, Cannon and others, 2007; 2009). This model is used to estimate the volume of 

material that could issue from the mouth of the defined drainage basin in response to a storm of a given 
6

rainfall intensity. This model was based upon volume estimates from 53 debris-flow-producing 

drainage basins in seven burn areas in southern California and follows the equation:

lnV = 3.41 + �0.485 × �i15� + (0.298 × log(hm50km)) + (0.173 × �ElevRange

where: 

ElevRange is the range (maximum elevation–minimum elevation) within the watershed (in meters), 

hm50km is the area of the watershed that was burned at high or moderate severity and has slope values 

in excess of 50 percent (in km2

), and

i15 is the peak 15-min rainfall intensity for the design storm; in this case we use the 15-min rainfall 

intensity for a 10-yr recurrence interval storm (in mm).

Volume estimates were classified in order of magnitude scale ranges 0–1,000 cubic meters (m3);

1,000–10,000 m3; 10,000–100,000 m3;and greater than 100,000 m3 for cartographic display.

Debris-Flow Hazard Assessment

We calculated the probability, predicted volume and combined hazard at the outlet of 73 

drainage basins located within the Powerhouse burn area. Drainage basin areas range from 0.11–7.8 

km2

. Basin outlet locations, morphometric variables, rainfall characteristics and model predictions are 

listed in table 1. Debris-flow probability, predicted volume, and combined hazard represent the 

estimates at the outlet of each drainage basin.
7

Table 1. Basin outlet locations (UTM Zone 11 NAD83, Meters), morphometric variables, rainfall characteristics and model predictions for the 73 defined 

watersheds in the Powerhouse burn area. 

Basin 

ID

Basin 

area 

(km2) 

Basin

outlet

easting

(m)

Basin

outlet 

northing

(m)

Elevation

range

(m)

Percent of 

basin burned 

with slopes 

greater than

= 50 percent

Area of 

moderate 

or high 

severity 

(km2) 

Percent of 

basin 

burned at 

high 

severity

Average 

K-factor

10-year 

peak 15-

minute 

intensity 

(mm/hr)

10-year

30-minute 

rainfall 

accumulation 

(mm)

Probability 

of debris 

flow

Predicted

volume

(m3) 

Combined

Relative

Hazard

Ranking

(1 = Low,

5 = High)

1 7.14 369158 3841871 326 0.3 0.00 0.0 0.21 51 18 3.3 1,000–10,000 3

2 4.21 369039 3845731 200 0.5 0.00 0.0 0.29 41 14 4.2 1,000–10,000 3

3 7.81 368079 3845821 480 1.4 0.12 1.5 0.22 49 17 4.9 10,000–100,000 4

4 1.21 366700 3845212 206 2.1 0.00 0.0 0.23 45 16 3.0 1,000–10,000 3

5 2.29 371340 3845237 175 0.0 0.00 0.0 0.29 41 14 4.0 0–1,000 2

6 4.45 364859 3844052 421 4.6 0.01 0.2 0.18 53 19 3.6 10,000–100,000 4

7 5.82 370629 3840791 311 1.2 0.02 0.3 0.18 51 18 2.7 1,000–10,000 3

8 4.83 372529 3840431 348 0.7 0.01 0.2 0.20 48 17 3.2 1,000–10,000 3

9 1.61 373089 3838961 263 4.6 0.00 0.0 0.18 48 17 2.6 1,000–10,000 3

10 0.78 373769 3838850 217 6.7 0.00 0.0 0.18 47 17 2.5 1,000–10,000 3

11 0.44 374179 3838561 255 4.9 0.00 0.0 0.18 47 16 2.5 1,000–10,000 3

12 0.44 374599 3838641 264 3.4 0.00 0.0 0.18 45 16 2.5 1,000–10,000 3

13 0.69 374838 3838649 323 5.6 0.00 0.0 0.19 45 16 3.0 1,000–10,000 3

14 0.45 364739 3839719 193 22.3 0.01 1.2 0.18 56 20 3.5 1,000–10,000 3

15 1.19 366280 3838251 396 18.7 0.17 14.5 0.18 57 20 6.9 10,000–100,000 4

16 0.34 368648 3837411 193 10.0 0.02 6.2 0.18 55 19 3.1 1,000–10,000 3

17 0.52 369348 3837042 217 9.3 0.05 8.7 0.18 55 19 3.4 1,000–10,000 3

18 2.32 369738 3836961 366 3.3 0.04 1.6 0.18 55 19 3.3 10,000–100,000 4

19 0.32 370239 3836891 207 8.3 0.11 32.9 0.18 55 19 6.3 1,000–10,000 3

20 0.64 373197 3836551 167 0.2 0.00 0.0 0.18 49 17 1.9 0–1,000 2

21 0.78 366238 3836361 349 36.9 0.04 5.0 0.18 57 20 7.2 10,000–100,000 4

22 3.18 366659 3836571 432 18.9 0.40 12.7 0.18 56 20 7.0 10,000–100,000 4

23 1.28 366057 3836021 452 39.0 0.37 29.3 0.18 56 20 16.3 10,000–100,000 4

24 1.74 365669 3835663 465 46.8 0.64 36.6 0.18 56 20 22.6 10,000–100,000 5

25 0.72 364958 3835611 380 48.6 0.02 2.6 0.18 57 20 9.1 10,000–100,000 4

26 0.38 364688 3835681 331 42.1 0.01 2.2 0.18 57 20 7.2 10,000–100,000 4

27 1.25 364698 3835461 483 55.4 0.43 34.6 0.18 57 20 25.8 10,000–100,000 5

28 3.78 363768 3835111 537 52.4 0.19 5.1 0.18 59 21 13.8 10,000–100,000 4
8

Table 1. Basin outlet locations (UTM Zone 11 NAD83, Meters), morphometric variables, rainfall characteristics and model predictions for the 73 defined 

watersheds in the Powerhouse burn area.—Continued

Basin 

ID

Basin 

area 

(km2)

Basin

outlet

easting

(m)

Basin

outlet 

northing

(m)

Elevation

range

(m)

Percent of 

basin burned 

with slopes 

greater than = 

50 percent

Area of 

moderate 

or high 

severity 

(km2)

Percent of 

basin 

burned at 

high 

severity

Average 

K-factor

10-year 

peak 15-

minute 

intensity 

(mm/hr)

10-year

30-minute 

rainfall 

accumulation 

(mm)

Probability 

of debris 

flow

Predicted

volume

(m3)

Combined

Relative

Hazard

Ranking

(1 = Low,

5 = High)

29 1.08 363369 3834581 445 60.9 0.35 32.6 0.18 57 20 25.6 10,000–100,000 5

30 0.39 363269 3834522 423 39.4 0.21 54.4 0.18 57 20 27.5 10,000–100,000 5

31 0.43 362779 3834261 423 47.4 0.13 30.2 0.18 57 20 18.7 10,000–100,000 4

32 0.74 362288 3834131 411 50.6 0.30 40.7 0.18 57 20 24.4 10,000–100,000 5

33 0.38 362180 3834151 298 58.2 0.09 24.2 0.18 58 20 16.2 10,000–100,000 4

34 1.98 359944 3833751 475 23.7 0.36 17.9 0.18 58 20 9.7 10,000–100,000 4

35 0.21 359768 3833280 361 42.6 0.00 0.4 0.18 58 20 7.4 10,000–100,000 4

36 2.57 359356 3833117 486 39.4 0.42 16.3 0.18 57 20 12.9 10,000–100,000 4

37 2.28 357657 3830520 500 3.0 0.05 2.0 0.18 57 20 4.4 10,000–100,000 4

38 0.26 359410 3829964 400 30.9 0.11 42.0 0.18 55 19 17.3 10,000–100,000 4

39 2.35 361667 3829264 303 10.0 0.25 10.6 0.18 53 19 4.3 10,000–100,000 4

40 0.54 361128 3829469 438 29.9 0.20 37.1 0.18 54 19 16.1 10,000–100,000 4

41 0.13 361049 3829670 214 27.9 0.01 9.8 0.18 55 19 5.2 1,000–10,000 3

42 0.82 360238 3829991 416 21.8 0.07 8.0 0.18 55 20 6.4 10,000–100,000 4

43 1.01 359868 3830051 496 33.1 0.33 32.6 0.18 54 19 17.0 10,000–100,000 4

44 0.25 359698 3830010 314 12.6 0.00 0.7 0.18 55 20 3.6 10,000–100,000 4

45 1.34 358898 3830241 469 25.6 0.05 3.4 0.18 56 20 6.8 10,000–100,000 4

46 3.67 362219 3830913 489 21.0 1.71 46.7 0.18 54 19 18.6 10,000–100,000 4

47 7.83 362218 3830952 514 18.5 1.73 22.1 0.18 56 20 10.3 10,000–100,000 4

48 1.43 362108 3830930 376 26.9 0.13 9.1 0.18 56 20 6.8 10,000–100,000 4

49 0.78 361668 3830451 326 27.6 0.13 16.3 0.18 56 20 7.6 10,000–100,000 4

50 1.00 364071 3828870 337 18.0 0.05 4.8 0.18 52 18 4.6 10,000– 100,000 4

51 2.27 364290 3828901 582 25.1 0.17 7.6 0.18 53 19 9.1 10,000–100,000 4

52 0.19 364917 3828791 298 24.4 0.00 0.0 0.18 51 18 4.3 1,000–10,000 3

53 2.09 365819 3828641 674 30.2 0.05 2.3 0.18 51 18 10.3 10,000–100,000 4

54 0.50 366308 3828792 350 18.0 0.00 0.2 0.18 50 17 4.1 10,000–100,000 4

55 0.34 367259 3829580 304 32.8 0.02 5.2 0.18 50 18 5.9 10,000–100,000 4

56 1.33 367451 3830300 565 30.5 0.27 20.4 0.18 52 18 13.4 10,000–100,000 4
9

Table 1. Basin outlet locations (UTM Zone 11 NAD83, Meters), morphometric variables, rainfall characteristics and model predictions for the 73 defined 

watersheds in the Powerhouse burn area.—Continued

Basin 

ID

Basin 

area 

(km2)

Basin

outlet

easting

(m)

Basin

outlet 

northing

(m)

Elevation

range

(m)

Percent of 

basin burned 

with slopes 

greater than = 

50 percent

Area of 

moderate 

or high 

severity 

(km2)

Percent of 

basin 

burned at 

high 

severity

Average 

K-factor

10-year 

peak 15-

minute 

intensity 

(mm/hr)

10-year

30-minute 

rainfall 

accumulation 

(mm)

Probability 

of debris 

flow

Predicted

volume

(m3)

Combined

Relative

Hazard

Ranking

(1 = Low,

5 = High)

57 0.13 367409 3830011 249 25.0 0.00 0.0 0.18 51 18 3.9 1,000–10,000 3

58 0.63 367648 3830359 395 11.3 0.04 6.4 0.18 52 18 4.7 10,000–100,000 4

59 1.61 367768 3831711 534 34.9 0.75 46.6 0.18 54 19 25.2 10,000–100,000 5

60 0.60 360779 3829702 467 46.1 0.21 35.1 0.18 54 19 21.5 10,000–100,000 5

61 0.39 361407 3829410 317 8.8 0.04 11.1 0.18 54 19 4.4 10,000–100,000 4

62 0.24 368908 3837772 176 14.9 0.00 0.0 0.18 54 19 2.8 1,000–10,000 3

63 0.21 369030 3837712 167 11.6 0.00 0.0 0.18 54 19 2.6 1,000–10,000 3

64 0.55 369609 3837469 196 6.6 0.00 0.0 0.18 53 19 2.4 1,000–10,000 3

65 0.50 371149 3836432 227 0.6 0.03 5.2 0.18 54 19 2.6 1,000–10,000 3

66 0.52 370939 3836901 227 2.7 0.06 11.5 0.19 54 19 3.4 1,000–10,000 3

67 0.11 369018 3837361 203 13.3 0.01 10.7 0.18 55 19 3.8 1,000–10,000 3

68 0.20 368558 3837661 148 9.0 0.01 6.4 0.18 55 19 2.8 1,000–10,000 3

69 0.13 368118 3837771 149 4.7 0.00 3.6 0.18 55 19 2.4 1,000–10,000 3

70 0.28 366838 3837581 172 10.1 0.02 7.3 0.18 55 19 3.1 1,000–10,000 3

71 0.18 366348 3836500 262 37.5 0.00 0.5 0.18 56 20 5.5 10,000–100,000 4

72 0.21 365938 3835921 280 25.5 0.00 0.0 0.18 57 20 4.4 10,000–100,000 4

73 0.23 358199 3830221 274 36.7 0.00 0.0 0.18 56 20 5.4 1,000–10,000 3
10

Debris-Flow Probability Estimates

Overall the model predicts relatively low probabilities of debris flow in response to a 10-yr,

30-min rainstorm (plate 1). Seven of the 73 defined basins were identified as having a 20–40 percent

likelihood of debris flow during the design storm. Five of these basins (Basins 24, 27, 29, 30, and 32) 

were located along Lake Hughes Road within Lake Canyon. Basin 59 (located in South Portal Canyon 

above the South Portal Truck Trail) and Basin 60 (located in Ruby Canyon) were also identified as 

having a 20–40 percent probability of debris flow in response to the design storm. All other basins were 

identified as having less than 20 percent probability of debris flow in response to the design storm.

Debris-Flow Volume Estimates

While the models predict a relatively low likelihood of debris flow, the consequences of debrisflow occurrence are quite high (plate 2). The volume model estimated that 44 of the 73 basins were 

capable of producing debris flows with potential volumes ranging from 10,000–100,000 m3

. These 

basins were located primarily in Lake Canyon along Lake Hughes Road and in Ruby Canyon and South 

Portal Canyon above the South Portal Truck Trail. Twenty-seven of the 73 basins were identified as 

having debris flows with volumes ranging from 1,000–10,000 m3. These basins were located mainly 

within Pine Canyon above Elizabeth Lake Road and on the northeastern portion of the burn area 

draining towards Lancaster. Only one of the basins (Basin 5) was identified as having a predicted 

debris-flow volume less than 1,000 m3.

Combined Relative Debris-Flow Hazard Rankings

We combined the results of the probability and the volume maps following the methods of 

Cannon and others (2010) to obtain an estimate of the combined relative hazard of the drainage basins 

defined for the Powerhouse fire (plate 3). Forty-four of the 73 defined basins were identified as having a 

moderate hazard ranking. Within the moderate class, the higher scores (a score of 5 out of a possible 9) 

were identified for seven of the 73 defined basins. These basins coincided with those that were predicted 

to have the highest probabilities of debris flow, including Basins 24, 27, 29, 30, and 32 in Lake Canyon, 

Basin 59 in South Portal Canyon, and Basin 60 in Ruby Canyon. Thirty-seven of the basins were 

identified as having the second-highest combined hazard score (score of 4 out of a possible 9). These

basins are located in the central and southwestern portion of the burn area, many of which drain directly 

onto Lake Hughes Road.

Low hazard rankings were identified for 29 of the defined basins. Within this class, 27 of the 

defined basin were found to have a moderate combined relative hazard ranking (a score of 3 out of a 

possible 9). These basins were situated above Lake Hughes and Lake Elizabeth and the communities in 

Pine Canyon. The remaining two basins (Basins 5 and 20) had the lowest combined score (a score of 2 

out of a possible 9).

Limitations of Hazard Assessments 

This assessment used a 10-yr recurrence interval storm to predict the probability, volume, and 

combined relative hazard of debris flows in basins burned by the 2013 Powerhouse fire in Los Angeles 

County, Calif. Differences in model predictions and actual debris-flow occurrence will arise with 

differences in actual storm duration and intensity. In addition, this study relies upon readily available 

geospatial data, the accuracy and precision of which may influence the estimated likelihood and 

magnitude of post-fire debris flows. However, local conditions, such as debris supply, certainly 
11

influence both the probability and volume of debris flows. Unfortunately, locally specific data is not 

presently available at the spatial scale of the post-fire debris-flow hazard assessment. As such, local 

conditions that are not constrained by the model may serve to dramatically increase or decrease the 

probability and(or) volume of a debris flow at a basin outlet. The input geospatial data are also subject 

to error based upon mapping resolution, elevation interpolation techniques and mapping and/or 

classification methods. Finally, this assessment is specific to debris-flow hazards; hazards from flashflooding are not described in this study and may be significant.

This assessment also characterizes potential debris-flow hazards at a static point in time 

immediately following wildfire. Studies of post-fire debris flows in southern California and the 

intermountain western United States have indicated that debris-flow activity in recently burned areas 

typically occurs within 2 yr of wildfire (Cannon and Gartner, 2005; Cannon and others, 2008; Gartner 

and others, 2008; Cannon and others, 2009). As vegetation cover and soil properties return to pre-fire 

conditions, the threat of debris-flow activity decreases with the amount of time elapsed since a wildfire.

However, the hazards from flash-flooding may persist for several years after wildfire.

Finally, this work is preliminary and is subject to revision. It is being provided due to the need 

for timely “best science” information. The assessment is provided on the condition that neither the U.S. 

Geological Survey nor the Unites States Government may be held liable for any damages resulting from 

the authorized or unauthorized use of the assessment. 

Summary and Conclusions

This assessment characterizes the post-fire debris-flow hazards that may exist within and below 

the 2013 Powerhouse fire near Lancaster, Calif. We use geospatial data related to basin morphometry, 

burn severity, soil properties, and rainfall characteristics to estimate the probability and predicted 

volume of debris flows that may occur in response to a 10-yr recurrence interval rainstorm. We have 

identified that probabilities of debris-flow occurrence in response to the design rainstorm are relatively 

low, with only 7 of the 73 defined basins having a probability of debris-flow greater than 20 percent.

Despite low probabilities, the predicted volume of potential debris flows may be large: 44 of the 73 

basins were identified as capable of producing debris flows with volumes ranging from 10,000–100,000

m3. Combining the probability and volume models into a combined-hazard ranking indicates that 7

basins were of the greatest threat of post-fire debris-flow activity, obtaining a score of 5 out of possible 

9. We have identified that Lake Canyon, Pine Canyon, Ruby Canyon, and South Portal Canyon are at 

greatest risk for hazards associated with post-fire debris flows. Moderate combined hazard rankings in 

the basins upstream of these locations indicate a significant possibility of debris-flow impact to homes, 

building, roads, bridges, culverts, and reservoirs located within and downstream of the burn area. We 

recommend that residents remain vigilant and take responsible actions to prevent injury or loss of life 

from post-fire debris flows and flash floods that may occur in response to high-intensity rainfall during 

short-lived summer convective thunderstorms and longer duration winter storms. 

References Cited

Bonnin, G.M., Martin, D., Lin, B., Parzybok, T., Yekta, M., and Riley, D., 2006, Precipitation 

frequency atlas of the United States: Silver Spring, Md., National Weather Service, National Oceanic 

and Atmospheric Administration atlas 14, v. 1, version 5, accessed July 30, 2013, at 

http://hdsc.nws.noaa.gov/hdsc/pfds/.

Campbell, R.H, 1975, Soil slips, debris flows, and rainstorms in the Santa Monica mountains and 

vicinity, southern California: U.S. Geological Survey Professional Paper 851, 55 p.
12

Cannon, S.H., Boldt, E.M., Laber, J.L., Kean, J.W., and Staley, D.M., 2011, Rainfall intensity–duration 

thresholds for postfire debris-flow emergency-response planning: Natural Hazards, v. 59, no. 1, 

p. 209–236.

Cannon, S.H., Boldt, E.M., Kean, J.W., Laber, J.L., and Staley, D.M., 2010, Relations between rainfall 

and postfire debris-flow and flood magnitudes for emergency-response planning, San Gabriel 

Mountains, southern California: U.S. Geological Survey Open File Report 2010–1039, 31 p.

Cannon, S.H., and DeGraff, J., 2009, The increasing wildfire and post-fire debris-flow threat in Western 

USA, and implications for consequences of climate change, chap. 9 of Sassa, K., and Canuti, P., eds., 

Landslides—Disaster Risk Reduction: Berlin, Springer, p. 177–190.

Cannon, S.H., and Gartner, J.E., 2005, Wildfire-related debris flow from a hazards perspective, chap. 15 

of Jakob, M., and Hungr, O., eds., Debris-flow hazards and related phenomena: Chichester, U.K., 

Springer–Praxis Books in Geophysical Sciences, p. 321–344.

Cannon, S.H., Gartner, J.E., Michael, J.A., Bauer, M.A., Stitt, S.C., Knifong, D.L., MCnamara, B.J., 

and Roque, Y.M., 2007, Emergency assessment of debris-flow hazards from basins burned by the 

2007 Buckweed Fire, Los Angeles County, Southern California: U.S. Geological Survey Open-File 

Report 2007–1414,1 sheet.

Cannon, S.H., Gartner, J.E., Rupert, M.G., Michael, J.A., Staley, D.M., and Worstell, B.B., 2009, 

Emergency assessment of postfire debris-flow hazards for the 2009 Station Fire, San Gabriel 

Mountains, southern California: U.S. Geological Survey Open File Report 2009–1227, 20 p. (Revised 

April 2010)

Cannon, S.H., Gartner, J.E., Wilson, R., Bowers, J., and Laber, J., 2008, Storm rainfall conditions for 

floods and debris flows from recently burned areas in southwestern Colorado and southern California: 

Geomorphology v. 96, no. 3-4, p. 250–269.

Eaton, E.C., 1935, Flood and erosion control problems and their solution: Proceedings of the American 

Society of Civil Engineers, v. 62, no. 8, p. 1302–1362.

Gabet, E., and Sternberg, P., 2008, The effects of vegetative ash on infiltration capacity, sediment 

transport, and the generation of progressively bulked debris flows: Geomorphology v. 10, no. 4, 

p, 666–673.

Gartner, J.E., Cannon, S.H., Santi, P., and Dewolfe, V., 2008, Empirical models to predict the volumes 

of debris flows generated by recently burned basins in the western U.S.: Geomorphology, v., 96, 

no. 3-4, p. 339–354.

inciweb.org, 2013, Mountain fire: InciWeb, accessed July 2013, at 

http://www.inciweb.org/incident/3516/#.

Jennings, C.W., and Strand, R.G., 1969, Geologic map of California: Los Angeles Sheet, California 

Division of Mines and Geology, 1:250,000.

Kean, J.W., Staley, D.M., and Cannon, S.H., 2011, In situ measurements of post-fire debris flows in 

southern California—Comparisons of the timing and magnitude of 24 debris-flow events with rainfall 

and soil moisture conditions: Journal of Geophysical Research, v. 116, F4:F04019.

Larsen, I.J., MacDonald, L.H., Brown, E., Rough, D., Welsh, M.J., Pietraszek, J.H., Libohova, Z., de 

Dios Benavides-Solorio, J., and Schaffrath, K., 2009, Causes of post-fire runoff and erosion: 

Water Repellency, Cover, or Soil Sealing?: Soil Science Society of America Journal, v. 73, no. 4,

p. 1393–1407.

McPhee, J.A., 1989, The control of nature: New York, Farrar, Straus and Giroux. 272p.

Remote Sensing Applications Center, 2013, BAER imagery support data download, USFS Region 5: 

U.S. Department of Agriculture Forest Service, accessed July 2013 at 

http://activefiremaps.fs.fed.us/baer/download.php.
13

Rupert, M.G., Cannon, S.H., Gartner, J.E., Michael, J.A., and Helsel, D.R., 2008, Using logistic 

regression to predict the probability of debris flows in areas burned by wildfires, southern California, 

2003–2006: U.S. Geological Survey Open File Report 2008–1370, 20 p. 

Schwartz, G.E., and Alexander, R.B., 1995, Soils data for the conterminous United States derived from 

the NRCS State Soil Geographic (STATSGO) Database: U.S. Geological Survey Open-File Report 

95–449, accessed July 2013 at http://water.usgs.gov/GIS/metadata/usgswrd/XML/ussoils.xml.

Shakesby, R., and Doerr, S., 2006, Wildfire as a hydrological and geomorphological agent: EarthScience Reviews, v. 74, no. 3-4, p. 269–307.

Staley, D.M., Kean, J.W., Cannon, S.H., Schmidt, K.M., and Laber, J.L., in press, Objective definition 

of rainfall intensity–duration thresholds for the initiation of post-fire debris flows in southern 

California: Landslides, p. 1–16.