Prepared in cooperation with U.S. Department of Agriculture Forest Service,

Estimated Probability of Postwildfire Debris Flows in the 2012 Whitewater–Baldy Fire Burn Area, Southwestern

Open-File Report 2012–1188

U.S. Department of the Interior U.S. Geological Survey Cover: Left, The Sandy Point staging area for aerial mulching, Gila National Forest, N. Mex. (photograph by U.S. Forest Service). Right, Crews clearing log jam in Copper Creek, Gila National Forest, N. Mex. (photograph by U.S. Forest Service). Background, View of the Whitewater–Baldy Complex oriented east from U.S. Route 180, May 23, 2012, Gila National Forest, N. Mex. (photograph by U.S. Forest Service). Estimated Probability of Postwildfire Debris Flows in the 2012 Whitewater– Baldy Fire Burn Area, Southwestern New Mexico

By Anne C. Tillery, Anne Marie Matherne, and Kristine L. Verdin

Prepared in cooperation with U.S. Department of Agriculture Forest Service, Gila National Forest

Open-File Report 2012–1188

U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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Suggested citation: Tillery, A.C., Matherne, A.M., and Verdin K.L., 2012, Estimated probability of postwildfire debris flows in the 2012 Whitewater–Baldy Fire burn area, southwestern New Mexico: U.S. Geological Survey Open-File Report 2012–1188, 11 p., 3 pls. iii

Contents

Abstract ...... 1 Introduction ...... 1 Methods Used To Estimate Debris-Flow Hazards ...... 2 Model Application ...... 4 Debris-Flow Hazard Assessment ...... 4 Debris-Flow Probability Estimates ...... 4 Debris-Flow Volume Estimates ...... 8 Combined Relative Debris-Flow Hazard Rankings ...... 8 Limitations of Hazard Assessments ...... 8 Summary ...... 9 References Cited ...... 9

Table

1. Estimated debris-flow probabilities and volumes for the 2012 Whitewater–Baldy Fire, Gila National Forest, New Mexico ...... 5

Plates

(Available online at http://pubs.usgs.gov/of/2012/1188/.) 1. Estimated Probability of Postwildfire Debris Flows in the 2012 Whitewater–Baldy Fire Burn Area, Southwestern New Mexico 2. Estimated Volumes of Postwildfire Debris Flows in the 2012 Whitewater–Baldy Fire Burn Area, Southwestern New Mexico 3. Combined Probability and Volume Relative Hazard Ranking of Potential Postwildfire Debris Flows in the 2012 Whitewater–Baldy Fire Burn Area, Southwestern New Mexico 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). Estimated Probability of Postwildfire Debris Flows in the 2012 Whitewater–Baldy Fire Burn Area, Southwestern New Mexico

By Anne C. Tillery, Anne Marie Matherne, and Kristine L. Verdin

Abstract also include tributaries to Deep Creek, Mineral Creek, Gilita Creek, West Fork Gila River, Mogollon Creek, and Turkey Creek, among others. Basins with the highest combined In May and June 2012, the Whitewater–Baldy Fire probability and volume relative hazard rankings for the burned approximately 1,200 square kilometers (300,000 acres) 25-year-recurrence rainfall include tributaries to Whitewater of the Gila National Forest, in southwestern New Mexico. The Creek, Mineral Creek, Willow Creek, West Fork Gila River, burned landscape is now at risk of damage from postwildfire West Fork Mogollon Creek, and Turkey Creek. Debris flows erosion, such as that caused by debris flows and flash floods. from Whitewater, Mineral, and Willow Creeks could affect the This report presents a preliminary hazard assessment of southwestern New Mexico communities of Glenwood, Alma, the debris-flow potential from 128 basins burned by the and Willow Creek. Whitewater–Baldy Fire. A pair of empirical hazard-assessment The maps presented herein may be used to prioritize models developed by using data from recently burned basins areas where emergency erosion mitigation or other protective throughout the intermountain Western United States was measures may be necessary within a 2- to 3-year period of used to estimate the probability of debris-flow occurrence vulnerability following the Whitewater–Baldy Fire. This work and volume of debris flows along the burned area drainage is preliminary and is subject to revision. It is being provided network and for selected drainage basins within the burned because of the need for timely “best science” information. The area. The models incorporate measures of areal burned extent assessment herein is provided on the condition that neither and severity, topography, soils, and storm rainfall intensity to the U.S. Geological Survey nor the U.S. Government may be estimate the probability and volume of debris flows following held liable for any damages resulting from the authorized or the fire. unauthorized use of the assessment. In response to the 2-year-recurrence, 30-minute-duration rainfall, modeling indicated that four basins have high probabilities of debris-flow occurrence (greater than or equal to 80 percent). For the 10-year-recurrence, 30-minute-duration Introduction rainfall, an additional 14 basins are included, and for the 25-year-recurrence, 30-minute-duration rainfall, an additional Debris flows have been documented after many fires in eight basins, 20 percent of the total, have high probabilities the Western United States (Cannon and others, 2007, 2010; of debris-flow occurrence. In addition, probability analysis DeGraff and others, 2011). Rainfall on burned areas can result along the stream segments can identify specific reaches in transport and deposition of large volumes of sediment, of greatest concern for debris flows within a basin. Basins both within and down-channel from burned areas. The rapid with a high probability of debris-flow occurrence were transport of large amounts of material makes debris flows concentrated in the west and central parts of the burned area, particularly dangerous. In addition, debris flows following a including tributaries to Whitewater Creek, Mineral Creek, wildfire can occur in places where flooding or sedimentation and Willow Creek. Estimated debris-flow volumes ranged has not been observed in the past and can be generated in from about 3,000–4,000 cubic meters (m3) to greater than response to low-magnitude rainfall (Cannon and others, 2007, 500,000 m3 for all design storms modeled. Drainage basins 2010; DeGraff and others, 2011). with estimated volumes greater than 500,000 m3 included Under unburned conditions, the vegetation canopy, tributaries to Whitewater Creek, Willow Creek, Iron Creek, soil-mantling litter and duff, and soil serve to capture and and West Fork Mogollon Creek. Drainage basins with store rainfall, which results in relatively little or no runoff. estimated debris-flow volumes greater than 100,000 m³ for the Postwildfire hydrologic response is affected by a decrease 25-year-recurrence event, 24 percent of the basins modeled, in vegetation cover and altered soil properties. Wildfires can 2 Estimated Probability of Postwildfire Debris Flows in the 2012 Whitewater–Baldy Fire Burn Area consume rainfall-intercepting canopy, litter, and duff (Moody Service, 2012). The geology of the area is primarily an and Martin, 2001a, 2001b; Meyer, 2002; Cannon and Gartner, assemblage of Tertiary volcanic rocks, composed of welded 2005). Water-repellent qualities in some soils can be enhanced and ash-flow tuffs, volcaniclastic deposits, and layered or induced by the intense heat of a wildfire (DeBano, 1981; andesite, rhyolite, and basalt (Ratté and Gaskill, 1975; Ratté, Doerr and others, 2000; Letey, 2001; Woods and others, 2006), 2008; Mack and others, 2008). Soils vary in clay content from and increased overland flow and erosion can occur (Wells, about 16 to 40 percent (Schwartz and Alexander, 1995). 1987; Moody and Martin, 2001a, 2001b). The presence of The area burned by the Whitewater–Baldy Fire is now fine ash, which may expand when wetted, can block soil pore at risk of substantial postwildfire erosion, such as that caused spaces and further reduce infiltration of water (Romkens by debris flows and flash floods. The purpose of this report is and others, 1990; Woods and others, 2006). After a wildfire, to present a preliminary hazard assessment of the debris-flow the watershed response to rainfall events shifts, in general potential for basins burned by the 2012 Whitewater–Baldy terms, from an infiltration-dominated to a runoff-dominated Fire. response (Cannon and others, 2010). Because of reduced soil infiltration, rainfall on wildfire burn scars can run off almost immediately as overland flow. This runoff in low-order channels can erode surficial materials, and with flow through Methods Used To Estimate Debris-Flow the drainage network, rainfall can generate runoff that is rich Hazards in ash, soil, boulders, and dislodged vegetation. As additional sediment is entrained, sediment-laden flow in channels can For this preliminary hazard assessment, a pair of progressively transition into debris flows that can affect lives, empirical models was used to estimate the probability, property, infrastructure, aquatic habitats, and water supplies volume, and combined relative hazard ranking of debris (Cannon and Gartner, 2005). Debris flows are most frequent flows along the drainage network and for selected drainage within 2–3 years after wildfires, when vegetative cover is basins in response to a given storm event in the Gila National absent or reduced and abundant materials are available for Forest. The model for predicting debris-flow probability was erosion and transport (Cannon and Gartner, 2005; Cannon and developed by Cannon and others (2010) by using logistic others, 2010). multiple-regression analyses of data from 388 basins in 15 In May and June 2012, the Whitewater–Baldy Fire burned areas in the intermountain Western United States. burned approximately 1,200 square kilometers (km²) Conditions in each basin were quantified by using readily (300,000 acres) of the Gila National Forest, including the Gila obtained measures of areal burned extent and severity, Wilderness, in southwestern New Mexico (plate 1) (Inciweb, basin gradient, soil properties, and storm rainfall. Statistical Incident Information System, 2012). The fire started as two analyses were used to identify the variables that most strongly separate lightning-strike fires—one near Peak influenced debris-flow occurrence and to build the predictive and one in the headwaters of Whitewater Creek in the Gila model. Equation 1 is used to calculate debris-flow probability Wilderness east of Glenwood, N. Mex. (U.S. Department of (Cannon and others, 2010): Agriculture Forest Service, 2012). The two fires joined to form the Whitewater–Baldy Complex. The fire severely burned a P = e x /(1 + e x), (1) tract of land across the Gila National Forest, including the headwaters of Whitewater Creek, Mineral Creek, and Willow where Creek. These three creeks drain into the southwestern New P is the probability of debris-flow occurrence in Mexico communities of Glenwood, Alma, and Willow Creek, fractional form; and respectively. (Willow Creek is unincorporated private land e x is the exponential function where e represents within the national forest.) The Gila National Forest directly or the mathematical constant 2.718. indirectly contributes to the economy of the surrounding area, primarily through wildlife and recreation visits and ranching Equation 2 is used to calculate x: (University of New Mexico Bureau of Business and Economic Research, 2007). The Gila National Forest contains hundreds x = –0.7 + 0.03(%SG30) – 1.6(R) of miles of recreational trails including the Catwalk National + 0.06(%AB) + 0.07(I) + 0.2(%C) – 0.4(LL), (2) Recreation Trail, a popular tourist destination that follows the narrow gorge of Whitewater Creek. where The Gila National Forest is mountainous, with steep, %SG30 is the percent of the drainage basin area with narrow canyons and elevations as high as 3,321 meters (m) slopes equal to or greater than 30 percent; (10,895 feet [ft]). The Whitewater–Baldy Fire perimeter was R is drainage basin ruggedness, the change complex and irregular in outline, with inclusion of unburned in drainage basin elevation (in meters) areas extending into and within the burned area (plate 1, divided by the square root of the drainage inset). About 26 percent of the burned area was moderately basin area (in square meters) (Melton, to severely burned (U.S. Department of Agriculture Forest 1965); Methods Used To Estimate Debris-Flow Hazards 3

%AB is the percentage of drainage basin area analysis. The technique used here allows for a synoptic view burned at moderate and high severities; of conditions throughout the study area, which can be used I is average storm intensity (the total storm to identify specific 10-m pixels or stream reaches that might rainfall divided by the storm duration, in pose a higher risk of debris flows; the technique also aids in millimeters per hour); sampling design and monitoring-site selection. %C is the percent clay content of the soil; and The base layer upon which the continuous-parameteri­ LL is the liquid limit of the soil (the percent zation layers are built is the 1/3-arc-second National Elevation of soil moisture by weight at which soil Dataset (Gesch and others, 2002). This digital elevation model begins to behave as a liquid). (DEM) was transformed into a projection system appropriate to western New Mexico (Universal Transverse Mercator, A second statistical model was used to estimate the Zone 12) and processed by using standard DEM-conditioning volume of material that could issue from the basin mouth tools in ArcGIS (Environmental Systems Research Institute, of a recently burned drainage basin in response to a given Inc., 2009) and RiverTools (Rivix, LLC, 2012). Once the magnitude storm. This model was developed by using overland flow structure was derived (in the form of a flow- multiple linear-regression analyses of data compiled from 56 direction matrix) by using the DEM, the independent variables debris-flow-producing basins burned by eight fires (Cannon driving the probability and volume equations were evaluated and others, 2010). Debris-flow volume measurements were for every grid cell within the extent of the DEM. Because of derived from records of the amount of material removed from orographic effects of the mountainous terrain and the size of sediment-retention basins and from field measurements of the burned area, input rainfall totals and rainfall intensities the amount of material eroded from the main channels within will vary over the extent of the burned area. For this study, a burned drainage basin. Statistical analyses were used to however, the maximum rainfall amounts for each storm identify the variables that most strongly influenced debris- were assumed to be uniform over the entire burned area, flow volume. The model provides estimates of the volume providing the most conservative estimate of the probability of material that may pass through a drainage-basin outlet and volumes of potential debris flows. Values for all of the in response to a single rainstorm event. The model has the other independent variables driving the debris-flow probability following form: and volume equations were obtained by using the continuous- parameterization approach. The independent-variable values Ln(V)= 7.2 + 0.6(Ln(SG30)) can be represented as forming continuous surfaces over the + 0.7(AB)0.5 + 0.2(T)0.5 + 0.3, (3) burned area. Once the surfaces of the independent variables were developed, the probability and volume equations were where solved by using map algebra for each grid cell along the Ln is the natural log function; drainage network, thus deriving the probability and volume V is the debris-flow volume (in cubic meters); surfaces. Identification of the probability or volume of a debris SG30 is the area of drainage basin with slopes equal flow at locations within the study area can be obtained by to or greater than 30 percent (in square querying the derived surfaces. kilometers); Debris-flow hazards from a given basin can also be AB is the drainage basin area burned at moderate represented by a combined relative debris-flow hazard and high severities (in square kilometers); ranking that is based on a combination of both probability T is the total storm rainfall (in millimeters); and of occurrence and volume (Cannon and others, 2010). For 0.3 is a bias-correction factor that changes the example, the most hazardous basins will have both the predicted estimate from a median to a highest probabilities of occurrence and the largest estimated mean value (Helsel and Hirsch, 2002; volumes of material. Slightly less hazardous would be basins Cannon and others, 2010). that show a combination of either low probabilities and larger Values for both probability and volume were volume estimates or high probabilities and smaller volume obtained along drainage networks by using the continuous estimates. parameterization technique (Verdin and Greenlee, 2003; For this assessment, the estimated values of debris-flow Verdin and Worstell, 2008). With this technique, estimates probability and volume are categorized into relatively ranked of debris-flow probability and volume (Cannon and others, classes, and these classes are added together to calculate a 2010) were obtained for every 10-m pixel along the drainage combined probability and volume relative hazard ranking network (plates 1 and 2) as a function of conditions in the (plate 3). This combined ranking identifies a possible range drainage basin upstream from each pixel. This technique of responses from basins with the highest probabilities of was developed as an alternative to basin-characterization producing debris flows with the largest volumes to basins with approaches used in the past (for example, Cannon and the lowest probabilities of producing debris flows with the others, 2010), which require definition of outlets (pour smallest volumes (Cannon and others, 2010). points) and their corresponding basins at the beginning of the 4 Estimated Probability of Postwildfire Debris Flows in the 2012 Whitewater–Baldy Fire Burn Area

Model Application high-intensity rainfall events. Cannon and others (2008) found that most debris flows occur in response to storms with The two models were implemented for the Whitewater– short recurrence intervals (from 2 to 10 years), and Kean Baldy Fire by first calculating the debris-flow probabilities and others (2011) demonstrated that intense rain in periods and volumes along the drainage networks and then 128 basins of less than 30 minutes generated postwildfire debris flows. within the burned perimeter were delineated for further To characterize the effects of these rainfall conditions, the evaluation. The basins were delineated by analyzing elevation probability that a given basin could produce debris flows and data derived from 10-m DEMs (U.S. Geological Survey, the volume of a possible debris flow at the basin outlet were 2011) with geographic information system (GIS) hydrological estimated for three design storms: (1) a 2-year-recurrence, tools. Debris-flow probability and volume were estimated for 30-minute-duration rainfall of 22 millimeters (mm) (a 50 every 10-m pixel along drainage networks of the burned area percent chance of occurrence in any given year); (2) a 10-year- as a function of conditions in the drainage basin above each recurrence, 30-minute-duration rainfall of 33 mm (a 10 percent pixel (Verdin and Greenlee, 2003; Verdin and Worstell, 2008). chance of occurrence in any given year); and (3) a 25-year- Basins were delineated so that the area of the basin at the recurrence, 30-minute-duration rainfall of 39 mm (a 4 percent farthest downstream pixel modeled was within the size range chance of occurrence in any given year). Precipitation data for which the models were developed, 0.01–103 km² for the used were from Bonnin and others (2006) for a weather station probability model and 0.01–27.9 km² for the volume model at Glenwood. Results for the 25-year-recurrence rainfall are (Cannon and others, 2010). Drainage basins with a total area presented in plates 1 through 3. While the point precipitation exceeding the range of the volume model, such as Mogollon data used to establish the 25-year rainfall event may indicate Creek, were subdivided into side tributaries. Stream reaches that the chance of occurrence at a given point is uncommon, draining the large basins are highlighted on plates 1 through because of the large area encompassed by the fire, the chance 3 as “drainages within burned areas that can be affected by that a storm of this magnitude will occur somewhere in the the combined effects of debris flows generated from side burn area in the next several years is increased (Kerry Jones, tributaries.” These large basins fall within the size range of National Weather Service, oral commun., 2011). the probability model, and probability estimates are indicated along the streamline by segment, but no basin number is assigned for the combined basin, and no relative hazard Debris-Flow Hazard Assessment ranking is calculated. Areas for basins analyzed for volume and relative hazard ranking averaged 7.7 km2 and ranged from The hazards of debris flows from basins burned by 1.3 km2 to 33.4 km2. the Whitewater–Baldy Fire were assessed by estimating Measures of the physical properties of soils within the probability of occurrence, by estimating the volume of each basin were obtained from the State Soil Geographic potential debris flows, and by combining the probability and (STATSGO) database (Schwartz and Alexander, 1995). If volume into a relative hazard ranking. more than one soil unit occurred within a given basin, a spatially weighted average of the soil variable values was calculated. In basins burned by the Whitewater–Baldy Fire, Debris-Flow Probability Estimates clay content of soil ranged from about 16 to 40 percent, and liquid limit of soils ranged from about 25 to 45 percent. In response to the 2-year-recurrence, 30-minute-duration The Burned Area Emergency Response (BAER) rainfall, modeling indicated that four basins (40, 90, 92, Image Support Team of the U.S. Geological Survey and 93) have high probabilities of debris-flow occurrence Earth Observation and Science Center (EROS) and the (greater than or equal to 80 percent) (table 1). For the 10-year- U.S. Department of Agriculture Forest Service Remote recurrence rainfall, an additional 14 basins (12, 41, 74, 91, Sensing Applications Center provided a map of Burned 95, 96, 98, 99, 100, 105, 106, 107, 108, and 110) have high Area Reflectance Classification (BARC), which was used probabilities of debris-flow occurrence, and for the 25-year- as an indicator of the distribution of burn severity within recurrence rainfall, and an additional 8 basins (49, 57, 58, the fire perimeter (U.S. Department of Agriculture Forest 86, 87, 88, 89, and 109), representing together 20 percent of Service, written commun., 2012). The BARC map for the the total, have high probabilities of debris-flow occurrence Whitewater–Baldy fire indicates that the moderate and high (plate 1; table 1). In addition, probability analysis along the burn-severity areas totaled about 316 km2 (78,000 acres), stream segments can identify specific reaches of greatest which is 26 percent of the total burned area of about 1,200 km2 concern for debris flows within a basin. For example, in (300,000 acres). The basins selected for modeling included the basin 17 (plate 1), probability analysis by stream segment moderate and high burn-severity areas where slope, watershed indicates that debris-flow probability increases from the configuration, and topographic setting indicated susceptibility headwaters (20–39 percent) to the midbasin (80–99 percent) to debris-flow processes or where proximity to development and then decreases towards the basin outlet (40–59 percent). indicated a vulnerability to hazards presented by debris flows. The overall basin color (plate 1) represents the debris-flow Postwildfire debris flows in the intermountain Western probability of 40–59 percent at the outlet, or pour point, of the United States often occur in response to short-duration, basin. Debris-Flow Hazard Assessment 5 - 1 1 1 1 1 2 1 1 1 1 1 4 3 1 1 1 3 2 1 1 1 1 1 2 2 2 1 2 1 1 1 1 2 1 1 1 1 1 1 4 4 2 2 ard ranking Combined haz

39 mm 9,800 6,100 5,400 4,400 6,600 4,600 9,700 (m³) 11,000 11,000 31,000 25,000 23,000 22,000 21,000 62,000 26,000 99,000 97,000 25,000 18,000 67,000 27,000 23,000 13,000 27,000 20,000 13,000 14,000 13,000 53,000 17,000 56,000 26,000 17,000 13,000 36,000 34,000 Volume Volume 180,000 140,000 190,000 320,000 >500,000 >500,000

25-year, 30-minute rainfall 25-year, 2 9 5 2 4 8 6 1 8 8 6 11 11 53 14 20 14 96 41 55 34 10 23 53 26 20 12 12 34 18 13 98 97 57 20 <1 <1 <1 <1 <1 <1 <1 <1 (%) Probability - 1 1 1 1 1 2 1 1 1 1 1 4 2 1 1 1 2 2 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 4 4 2 1 ard ranking Combined haz

33 mm (m³) 8,500 5,300 4,600 3,800 5,800 4,000 9,700 9,300 8,400 11,000 11,000 22,000 20,000 19,000 18,000 54,000 23,000 86,000 84,000 22,000 15,000 58,000 24,000 20,000 12,000 24,000 17,000 12,000 12,000 46,000 15,000 48,000 23,000 15,000 31,000 29,000 27,000 Volume 160,000 120,000 160,000 280,000 >500,000 >500,000

10-year, 30-minute rainfall 10-year, 4 2 5 5 7 7 2 4 4 3 5 5 4 8 6 4 3 11 32 10 90 23 34 18 33 13 10 18 95 94 36 10 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 (%) Probability - 1 1 1 1 1 1 1 1 1 1 3 2 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 4 3 1 1 1 ard ranking Combined haz

22 mm 6,300 3,900 3,400 2,800 4,300 3,000 7,200 6,900 8,600 8,500 9,000 8,600 8,200 6,200 (m³) 11,000 11,000 16,000 15,000 14,000 14,000 40,000 17,000 64,000 63,000 16,000 90,000 12,000 43,000 17,000 15,000 18,000 13,000 34,000 36,000 17,000 23,000 22,000 20,000 Volume 120,000 380,000 120,000 210,000 >500,000

2-year, 30-minute rainfall 2-year, 1 9 1 1 2 2 6 4 3 9 3 2 1 1 5 2 1 2 11 66 10 81 77 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 (%) Probability

- 2.51 4.63 4.38 3.56 1.87 8.72 3.14 9.57 5.07 2.76 2.43 4.04 1.28 8.76 8.45 5.67 4.87 4.09 4.74 7.08 2.74 4.64 2.25 7.89 8.28 5.85 3.15 8.10 3.52 5.86 age area (km²) 11.25 11.95 11.92 33.44 20.23 14.09 26.11 10.29 18.03 15.40 18.68 10.45 18.60 Drain Description Estimated debris-flow probabilities and volumes for the 2012 Whitewater–Baldy Fire, Gila National Forest, New Mexico.—Continued Tributary to Negrito Creek Tributary to Negrito Creek Tributary to Negrito Creek Tributary to Negrito Creek Tributary to Negrito Creek Tributary to Negrito Creek Tributary to Negrito Creek Tributary to Negrito Creek Tributary to Negrito Creek Tributary Quaking Aspen Creek Creek Willow Creek Turkey Little to Gilita Creek Tributary to Gilita Creek Tributary to Gilita Creek Tributary to Iron Creek Tributary to Iron Creek Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Canyon Creek Tributary to Canyon Creek Tributary to Indian Creek Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary to Middle Fork Gila River Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Tributary to Negrito Creek Tributary Estimated debris-flow probabilities and volumes for the 2012 Whitewater–Baldy Fire, Gila National Forest, New Mexico.

2 3 4 5 6 7 8 9 1 11 10 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 basin Selected Table 1. Table [mm, millimeters; km², square kilometers; %, percent; m³, cubic meters; <, less than; >, greater than] Table 1. Table [mm, millimeters; km², square kilometers; %, percent; m³, cubic meters; <, less than; >, greater than] 6 Estimated Probability of Postwildfire Debris Flows in the 2012 Whitewater–Baldy Fire Burn Area - 2 1 3 1 2 4 1 1 2 2 1 2 3 3 4 3 3 2 1 1 1 3 3 2 1 3 2 3 2 2 4 3 2 3 3 3 1 2 1 2 3 3 3 ard ranking Combined haz

39 mm 8,100 (m³) 32,000 52,000 91,000 16,000 23,000 27,000 22,000 16,000 79,000 19,000 24,000 19,000 19,000 42,000 34,000 39,000 26,000 32,000 27,000 58,000 98,000 64,000 81,000 90,000 97,000 72,000 24,000 Volume Volume 110,000 110,000 270,000 210,000 230,000 120,000 180,000 120,000 170,000 450,000 130,000 140,000 160,000 100,000 >500,000

25-year, 30-minute rainfall 25-year, 3 5 2 6 5 7 53 65 10 34 84 33 26 15 56 76 80 90 61 67 59 17 68 68 31 15 42 10 48 42 39 96 71 22 61 79 65 10 18 26 42 70 80 (%) Probability - 2 1 3 1 2 3 1 1 1 1 1 2 3 3 3 2 2 2 1 1 1 2 2 1 1 2 1 2 2 2 4 2 1 2 3 2 1 2 1 2 2 2 3 ard ranking Combined haz

33 mm (m³) 7,000 45,000 79,000 14,000 20,000 23,000 19,000 14,000 69,000 16,000 20,000 17,000 17,000 36,000 30,000 33,000 22,000 28,000 24,000 98,000 50,000 85,000 55,000 70,000 78,000 84,000 62,000 21,000 92,000 91,000 28,000 Volume 110,000 240,000 180,000 200,000 100,000 160,000 100,000 150,000 390,000 500,000 120,000 140,000

10-year, 30-minute rainfall 10-year, 1 5 2 7 2 8 2 7 4 5 8 3 11 45 18 69 17 13 35 57 63 79 40 47 38 47 47 16 23 28 23 21 90 51 40 62 44 13 23 50 63 32 <1 (%) Probability - 1 2 1 2 2 1 1 1 1 1 1 2 2 3 1 1 1 1 1 1 1 1 1 1 1 1 2 1 2 3 1 1 1 2 1 1 1 1 1 2 1 2 1 ard ranking Combined haz

22 mm 5,200 (m³) 33,000 58,000 10,000 15,000 17,000 14,000 10,000 76,000 51,000 12,000 15,000 12,000 12,000 27,000 22,000 25,000 17,000 21,000 17,000 77,000 73,000 37,000 63,000 41,000 52,000 58,000 62,000 46,000 84,000 16,000 91,000 68,000 67,000 20,000 Volume 110,000 180,000 140,000 150,000 120,000 290,000 370,000 100,000

2-year, 30-minute rainfall 2-year, 1 5 4 3 2 2 4 2 6 8 6 5 2 1 2 3 6 9 15 33 10 22 27 45 13 16 12 16 16 67 18 13 26 14 18 27 <1 <1 <1 <1 <1 <1 <1 (%) Probability

- 2.11 9.09 9.29 6.49 7.58 5.80 1.96 7.62 2.84 4.22 2.39 1.80 3.48 4.31 7.80 4.13 4.80 3.63 7.82 9.67 3.87 5.06 4.96 4.91 4.39 5.06 8.12 9.13 9.21 9.17 4.86 age area (km²) 16.41 17.24 13.71 23.41 18.88 13.10 13.45 19.95 14.92 12.69 10.51 10.51 Drain Description Estimated debris-flow probabilities and volumes for the 2012 Whitewater–Baldy Fire, Gila National Forest, New Mexico.—Continued Tributary to West Fork Gila River West to Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Fork Gila River West to Tributary Creek Turkey to Tributary Creek Turkey to Tributary Creek Turkey to Tributary Creek Turkey to Tributary Creek Turkey to Tributary Creek Turkey to Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary to Mogollon Creek Tributary Fork Mogollon Creek West to Tributary Fork Mogollon Creek West to Tributary to Rain Creek Tributary to Rain Creek Tributary to Rain Creek Tributary to Rain Creek Tributary to Sacaton Creek Tributary to Sacaton Creek Tributary Duck Creek to Little Dry Creek Tributary to Big Dry Creek Tributary to Big Dry Creek Tributary to Big Dry Creek Tributary Tributary to West Fork Gila River West to Tributary

45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 44 basin Selected Table 1. Table [mm, millimeters; km², square kilometers; %, percent; m³, cubic meters; <, less than; >, greater than] Debris-Flow Hazard Assessment 7 - 3 3 3 4 4 4 4 3 3 3 3 3 3 3 1 3 3 3 3 3 4 3 4 3 2 2 1 3 2 2 2 2 2 1 2 2 1 1 1 1 1 1 ard ranking Combined haz

39 mm 8,000 (m³) 87,000 72,000 45,000 27,000 31,000 39,000 36,000 33,000 23,000 26,000 26,000 74,000 46,000 29,000 40,000 61,000 81,000 15,000 23,000 42,000 22,000 40,000 15,000 85,000 35,000 24,000 13,000 90,000 17,000 22,000 15,000 Volume Volume 110,000 150,000 100,000 120,000 130,000 100,000 170,000 100,000 >500,000 >500,000

25-year, 30-minute rainfall 25-year, 4 6 3 2 1 83 85 88 98 93 98 99 70 95 91 71 96 97 97 16 78 76 69 91 96 97 97 84 95 45 59 47 50 51 53 31 25 31 26 14 14 <1 (%) Probability - 3 3 3 4 4 3 4 2 3 3 2 3 3 3 1 3 2 3 3 3 3 3 3 3 2 2 1 2 2 2 2 1 1 1 1 1 1 1 1 1 1 1 ard ranking Combined haz

33 mm (m³) 7,000 11,000 62,000 39,000 90,000 23,000 27,000 34,000 31,000 28,000 20,000 22,000 22,000 64,000 40,000 25,000 87,000 35,000 95,000 53,000 70,000 13,000 20,000 36,000 19,000 35,000 13,000 74,000 30,000 89,000 20,000 78,000 15,000 19,000 13,000 75,000 Volume 110,000 130,000 470,000 120,000 140,000 >500,000

10-year, 30-minute rainfall 10-year, 8 2 3 6 6 1 71 76 96 85 96 97 49 90 80 51 91 93 94 60 58 49 81 90 93 92 69 90 26 38 28 30 31 32 16 12 16 13 68 <1 <1 <1 (%) Probability - 2 2 3 3 3 4 1 3 2 1 3 3 3 1 2 2 1 2 3 3 3 2 3 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 ard ranking Combined haz

22 mm 9,000 8,000 9,500 5,300 (m³) 11,000 46,000 29,000 96,000 67,000 17,000 20,000 25,000 23,000 21,000 15,000 17,000 16,000 80,000 47,000 86,000 29,000 19,000 65,000 26,000 71,000 39,000 52,000 10,000 15,000 27,000 14,000 26,000 55,000 23,000 66,000 15,000 58,000 14,000 56,000 Volume 110,000 350,000 >500,000

2-year, 30-minute rainfall 2-year, 2 7 8 8 9 9 4 3 4 3 1 1 11 34 41 83 55 85 88 17 65 47 18 68 74 77 24 23 17 48 66 74 72 32 65 31 <1 <1 <1 <1 <1 <1 (%) Probability

- 6.95 3.91 7.80 4.72 1.87 1.69 2.61 2.65 1.96 1.42 1.58 3.19 5.14 8.14 2.81 1.79 5.17 2.21 6.02 4.14 7.93 1.61 4.10 4.63 2.08 3.75 1.74 9.22 9.03 2.18 1.69 6.45 3.19 2.55 1.29 7.39 age area (km²) 11.48 27.96 17.95 20.11 10.65 17.73 Drain Description Estimated debris-flow probabilities and volumes for the 2012 Whitewater–Baldy Fire, Gila National Forest, New Mexico.—Continued Tributary to Big Dry Creek Tributary to San Francisco River Tributary Whitewater Little Creek Whitewater Creek to Tributary Whitewater Creek to Tributary Whitewater Creek to Tributary Whitewater Creek to Tributary Whitewater Creek to Tributary Whitewater Creek to Tributary Whitewater Creek to Tributary Whitewater Creek to Tributary Whitewater Creek to Tributary Whitewater Creek to Tributary to Silver Creek Tributary to Silver Creek Tributary to Mineral Creek Tributary to Mineral Creek Tributary to Mineral Creek Tributary to Mineral Creek Tributary to Mineral Creek Tributary to Mineral Creek Tributary to Mineral Creek Tributary to Mineral Creek Tributary to Mineral Creek Tributary to Mineral Creek Tributary to Mineral Creek Tributary Copper Creek to Deep Creek Tributary to Deep Creek Tributary to Deep Creek Tributary to Deep Creek Tributary to Deep Creek Tributary to Deep Creek Tributary to Deep Creek Tributary to Deep Creek Tributary to Deep Creek Tributary to Devils Creek Tributary to North Fork Devils Creek Tributary to North Fork Devils Creek Tributary to North Fork Devils Creek Tributary to North Fork Devils Creek Tributary Tributary to Big Dry Creek Tributary

88 89 90 91 92 93 94 95 96 97 98 99 87 111 110 112 113 114 115 116 117 118 119 100 101 102 103 104 105 106 107 108 109 120 121 122 123 124 125 126 127 128 basin Selected Table 1. Table [mm, millimeters; km², square kilometers; %, percent; m³, cubic meters; <, less than; >, greater than] 8 Estimated Probability of Postwildfire Debris Flows in the 2012 Whitewater–Baldy Fire Burn Area

Basins with a high probability of debris-flow occurrence five basins (49, 58, 92, 107, and 109), representing together 9 were primarily located in the west and central parts of the percent of the total, were modeled with the highest combined burned area, including tributaries to Whitewater Creek, hazard ranking (plate 3). Basins with the highest combined Mineral Creek, and Willow Creek. Tributaries to the West probability and volume relative hazard ranking for the Fork Gila River, Mogollon Creek, and Turkey Creek also 25-year-recurrence rainfall include tributaries to Whitewater included basins with high probabilities of debris-flow Creek, Mineral Creek, Willow Creek, West Fork Gila River, occurrence. These high probabilities reflect the combined West Fork Mogollon Creek, and Turkey Creek. Debris flows effects of these basins being nearly completely burned at from Whitewater, Mineral, and Willow Creeks could affect the high and moderate severities and having steep slopes. Debris communities of Glenwood, Alma, and Willow Creek. flows generated from these basins may directly affect the communities of Glenwood, Alma, and Willow Creek. Limitations of Hazard Assessments Debris-Flow Volume Estimates This assessment provides estimates of debris-flow probability, volume, and combined relative hazard ranking The debris-flow volumes estimated in this assessment for drainage basins burned by the Whitewater–Baldy Fire are independent of the estimated debris-flow probabilities. As in response to 30-minute-duration design storms with a 2-, a result, basins with high predicted debris-flow probabilities 10-, and 25-year-recurrence probability. Larger, less frequent present a range of high to low threats to areas downstream, storms (for example, a 50-year-recurrence storm) are likely to depending on the predicted volume of material mobilized in produce larger debris flows, and smaller storms (for example, a debris flow. Estimated debris-flow volumes can vary by a 1-year-recurrence storm) could also trigger debris flows. stream segment along a drainage network; basin color on Higher probabilities of debris flow than those shown on plate 2 reflects the volume class at the basin outlet. Estimated plate 1 may exist within any part of the basins. Because not debris-flow volumes ranged from about 3,000–4,000 cubic all rainstorms will be large enough to affect the entire burned meters (m3) to greater than 500,000 m3 for all design storms area, debris flows may not be produced from all basins during modeled (table 1). Drainage basins with estimated debris-flow a given storm. volumes greater than 500,000 m³ included basins 12 and 93 It is important to note that the maps shown in plates 1, for the 2-year-recurrence rainfall, an additional basin (17) for 2, and 3 do not identify those areas that can be affected by the 10-year-recurrence rainfall, and an additional two basins debris flows as the material moves downstream from the (74 and 91) for the 25-year-recurrence rainfall and include basin outlets (Cannon and others, 2010). Additionally, further tributaries to Whitewater Creek, Willow Creek, Iron Creek, investigation is needed to assess the potential for debris flows and West Fork Mogollon Creek (plate 2). Drainage basins with to affect structures at or downstream from basin outlets and estimated debris-flow volumes greater than 100,000 m³ for the to increase the threat of flooding downstream by damaging or 25-year-recurrence event, 24 percent of the basins modeled, blocking bridges or flood-mitigation structures. also include tributaries to Deep Creek, Mineral Creek, Gilita The variables included in the models and used in this Creek, West Fork Gila River, Mogollon Creek, and Turkey assessment are considered to directly affect debris-flow Creek, among others (plate 2). It is not known if the estimated generation in the intermountain Western United States. volumes of material are sufficient to dam watercourses or Conditions other than those used in the models (for example, cause flooding, which could affect resources in the valleys the amount of sediment stored in a canyon) could also affect downstream from the basins evaluated. debris-flow production. Data necessary to evaluate such effects, however, are not readily available. The potential for debris-flow activity decreases with time as revegetation stabilizes hillslopes and the supply of Combined Relative Debris-Flow Hazard erodible material decreases in the canyons. If dry conditions Rankings prevent sufficient regrowth of vegetation, however, this recovery period will be longer. In contrast, if rainfall events Combined probability and volume relative hazard for the first year are mild, recovery and stabilization of soil rankings of postwildfire debris flows are produced by with vegetation may occur rapidly and diminish debris-flow summing the estimated probability and volume ranking to hazards the following year. The assessment given herein illustrate those areas with the highest potential occurrence of is estimated to be applicable for 2–3 years after the fire, debris flows with the largest volumes. Rankings are shown depending on precipitation distribution (Cannon and others, for the 25-year-recurrence rainfall (plate 3). The highest 2010). combined hazard ranking is predicted for two basins, 40 and The maps in this report may be used to prioritize areas 93, for the 2-year-recurrence rainfall (table 1). For the 10-year- where emergency erosion mitigation or other protective recurrence rainfall, an additional five basins (12, 41, 74, 90, measures may be needed prior to rainstorms within these and 91) were modeled with the highest combined hazard basins, their outlets, or areas downstream from these basins ranking, and for the 25-year-recurrence rainfall, an additional within the 2- to 3-year period of vulnerability following the References Cited 9

Whitewater–Baldy Fire. This assessment evaluates only Creek, and West Fork Mogollon Creek. Drainage basins with postwildfire debris flows and does not consider hazards estimated debris-flow volumes greater than 100,000 m³ for the associated with flash floods; such hazards may remain for 25-year-recurrence event, 24 percent of the basins modeled, many years after a fire. also include tributaries to Deep Creek, Mineral Creek, Gilita This work is preliminary and is subject to revision. It is Creek, West Fork Gila River, Mogollon Creek, and Turkey being provided because of the need for timely “best science” Creek, among others. Basins with the highest combined information. The assessment herein is provided on the probability and volume relative hazard rankings for the condition that neither the U.S. Geological Survey nor the U.S. 25-year-recurrence rainfall include tributaries to Whitewater Government may be held liable for any damages resulting Creek, Mineral Creek, Willow Creek, West Fork Gila River, from the authorized or unauthorized use of the assessment. West Fork Mogollon Creek, and Turkey Creek. Debris flows from Whitewater, Mineral, and Willow Creeks could affect the communities of Glenwood, Alma, and Willow Creek. The maps presented herein may be used to prioritize Summary areas where emergency erosion mitigation or other protective measures may be needed prior to rainstorms within these In May and June 2012, the Whitewater–Baldy Fire basins, their outlets, or areas downstream from these basins burned approximately 1,200 square kilometers (300,000 acres) within the 2- to 3-year window of vulnerability. of the Gila National Forest, in southwestern New Mexico. This work is preliminary and is subject to revision. It is About 26 percent of the burned area was moderately or being provided because of the need for timely “best science” severely burned. The fire severely burned a tract of land across information. The assessment herein is provided on the the Gila National Forest and the , including the condition that neither the U.S. Geological Survey nor the U.S. headwaters of Whitewater Creek, Mineral Creek, and Willow Government may be held liable for any damages resulting Creek, which drains into Gilita Creek. These three creeks drain from the authorized or unauthorized use of the assessment. into the southwestern New Mexico communities of Glenwood, Alma, and Willow Creek, respectively. These communities are now at risk of damage from postwildfire erosion hazards such as those associated with debris flows and flash floods. This References Cited report presents a preliminary hazard assessment of the debris- flow potential from 128 basins burned by the Whitewater– Bonnin, G.M., Martin, Deborah, Lin, Binghang, Parzybok, Baldy Fire. Tye, Yekta, Michael, and Riley, David, 2006, Precipitation- A pair of empirical hazard-assessment models developed frequency atlas of the United States: Silver Spring, from data collected in recently burned basins throughout the Md., National Weather Service, National Oceanic and intermountain Western United States was used to estimate the Atmospheric Administration (NOAA) atlas 14, v. 1, probability of occurrence and volume of debris flows along version 5, accessed July 25, 2012, at http://hdsc.nws.noaa. the burned area drainage network and for selected drainage gov/hdsc/pfds/. basins within the Whitewater–Baldy Fire burned area in response to 30-minute-duration design storms of 2-, 10-, and Cannon, S.H., and Gartner, J.E., 2005, Wildfire-related 25-year-recurrence intervals. The models incorporate measures debris flow from a hazards perspective, chap. 15of Jakob, of areal burned extent and severity, topography, soils, and Matthias, and Hungr, Oldrich, eds., Debris-flow hazards storm rainfall intensity to estimate the probability and volume and related phenomena: Chichester, U.K., Springer–Praxis of debris flows following the fire. Books in Geophysical Sciences, p. 321–344. Probabilities of debris flow greater than 80 percent were identified for 20 percent of the basins modeled for the 25-year- Cannon, S.H., Gartner, J.E., and Michael, J.A., 2007, Methods recurrence rainfall. In addition, probability analysis along for the emergency assessment of debris-flow hazards from the stream segments can identify specific reaches of greatest basins burned by the fires of 2007, southern California: U.S. concern for debris flows within a basin. Basins with a high Geological Survey Open-File Report 2007–1384, 10 p. probability of debris-flow occurrence were concentrated in the Cannon, S.H., Gartner, J.E., Rupert, M.G., Michael, J.A., west and central parts of the burned area, including tributaries Rea, A.H., and Parrett, Charles, 2010, Predicting the to Whitewater Creek, Mineral Creek, and Willow Creek. probability and volume of postwildfire debris flows in the Tributaries to the West Fork Gila River, Mogollon Creek and intermountain Western United States: Geological Society of Turkey Creek also included basins with high probabilities America Bulletin, v. 122, p. 127–144. of debris-flow occurrence. Estimated debris-flow volumes ranged from about 3,000–4,000 cubic meters (m3) to greater Cannon, S.H., Gartner, J.E., Wilson, R.C., and Laber, J.L., than 500,000 m3 for all design storms modeled. Drainage 2008, Storm rainfall conditions for floods and debris flows basins with estimated volumes greater than 500,000 m³ from recently burned areas in southwestern Colorado and included tributaries to Whitewater Creek, Willow Creek, Iron southern California: Geomorphology, v. 96, p. 250–269. 10 Estimated Probability of Postwildfire Debris Flows in the 2012 Whitewater–Baldy Fire Burn Area

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