Variations in Soil Detachment Rates after Wildfire as a 

Function of Soil Depth, Flow Properties and Root Properties

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012–5233
COVER. Looking down a hillslope in the Sunday Creek Catchment in Victoria, Australia about 50 km 

north of Melbourne after the wildfires of February 2009 (photo taken in April 2009 by Petter Nyman).
Variations in Soil Detachment Rates after 

Wildfire as a Function of Soil Depth, Flow 

Properties and Root Properties

By John A. Moody and Petter Nyman

Scientific Investigations Report 2012–5233

U.S. Department of the Interior

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

KEN SALAZAR, 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

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.

Suggested citation:

Moody, J.A., and Nyman, P., 2013, Variations in soil detachment rates after wildfire as a function of soil depth, flow 

properties, and root properties: U.S. Geological Survey Scientific Investigations Report 2012–5233, 40 p.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................2

Soil Sampling..................................................................................................................................................2

Site Characteristics.......................................................................................................................................2

Field Sampling Methods ...............................................................................................................................3

Laboratory Methods......................................................................................................................................4

Soil Physical Properties.......................................................................................................................4

Soil Organic Content ............................................................................................................................4

Root Properties......................................................................................................................................4

Flume Properties...................................................................................................................................9

Boundary Shear Stress...............................................................................................................9

Stream Power.............................................................................................................................11

Soil Detachment Measurements .....................................................................................................12

Results and Discussion...............................................................................................................................25

Soil Properties.....................................................................................................................................25

Root Properties....................................................................................................................................26

Soil Detachment Rates ......................................................................................................................27

Non-Uniform Shear Stress and Root-length Density...........................................................28

Non-Uniform Unit Stream Power and Root-length Density ................................................30

Multiple Regressions using Flow and Root Variables .........................................................31

Soil Erodibility.............................................................................................................................35

Summary........................................................................................................................................................38

Acknowledgments.......................................................................................................................................38

References Cited..........................................................................................................................................38

Figures 

1. A, Upper section shows the location for collecting cluster samples (A, B, 

 and C) along transects (T1, T2, and T3) from one sample site called 

 Fourmile Canyon South. B, Lower section shows the details of the method 

 of collecting subsamples of the soil core.................................................................................3

2. Extracted roots from 3–5 cm below the soil surface from burned sites..............................8

3. Calibration of the grid method of measuring root length outlined by 

 Tennant (1975) by comparing the root lengths measured manually using metric 

calipers...........................................................................................................................................9

4. Diagram of shallow-water tilting flume and circulation system.........................................10

5. Relations between water discharge and water depth, at different slopes, 

 for the shallow-water tilting flume...........................................................................................11

6. Comparison of non-uniform shear stress measured for the tilting flume 

 with a smooth bed conditions and with a soil core in place...............................................25

7. Mean bulk density of soil for three sites based on three replicates for 

 each cluster.................................................................................................................................26
iv

8. Loss on ignition (LOI) of soil for three sites based on three replicates for each 

cluster...........................................................................................................................................27

9. Percent silt and clay (less than 0.063 mm) in soil for three sites based on three 

replicates for each cluster........................................................................................................28

10. Root density as a function of depth in the soil for three sites based on three 

replicates for each cluster........................................................................................................29

11. Root-length density as a function of depth in the soil for three sites based on one 

replicate for each cluster..........................................................................................................30

12. Relations between root-length density and root density.....................................................31

13. Comparison of the goodness-of-fit as measured by the coefficient of 

determination for power law relations between the detachment rate and the 

non-uniform shear stress or the root-length density............................................................32

14. Exponents of the independent variables used in multiple regressions of log 

transformed data in which detachment rate for greater than 0.063 mm size 

fraction is the dependent variable...........................................................................................34

15. Multiple regression model for detachment rates using all shear stress, stream 

power, and root-length density data for clusters collected in burned areas...................35

16. Relations between detachment rate for all data and A, Non-uniform shear 

stress and B, Non-uniform stream power..............................................................................36

17. Photographs of the appearance of the surface of the soil core in the tilting flume........37

Tables

1. Soil and root properties for Fourmile Canyon South site.......................................................5

2. Soil and root properties for Fourmile Canyon North site .......................................................6

3. Soil and root properties for Pozo South site ............................................................................7

4. Hydrologic parameters and sedimentologic results for soil core samples 

collected at the Fourmile Canyon South site .........................................................................13

5. Hydrologic parameters and sedimentologic results for soil core samples 

collected at the Fourmile Canyon North site..........................................................................17

6. Hydrologic parameters and sedimentologic results for soil core samples 

collected at the Pozo South site...............................................................................................21

7. Multiple regression information for the detachment rate as a function of 

root-length density and either non-uniform shear stress or non-uniform stream 

power............................................................................................................................................33
v

Multiply By To obtain

Length

millimeters (mm) 0.0393701 inch (in.)

centimeter (cm) 0.393701 inch (in.) 

square centimeter (cm2

) 0.155000 square inch (in.2)

centimeter per second (cm s-1) 0.032808 foot per second (ft s-1)

milliliters per second (mL s-1) 0.000035315 cubic foot per second (ft3

 s-1)

 Weight

milligram (mg) 0.000035274 ounces (oz)

gram (g) 0.0022046 pound (lb)

gram per cubic centimeter (g cm-3) 62.42796 pounds per cubic foot (lb ft-3) 

dyne 0.000035969 ounce-force (oz)

dyne 0.0000022481 pound-force (lb)

dyne per square centimeter (dyne cm-2) 0.0000145038 pound per square inch (lb in.-2)

erg per second (erg s-1) 0.0002655 foot-pound per hour (ft-lb h-1)

Soil erodibility

metric ton-hectare-hour per hectaremegajoule-millimeter (t-ha-h 

(ha-MJ-mm)-1

7.593 ton-acre-hour per hundreds of 

acre-foot-tonf-inch

Abbreviations

+ Plus and minus

< Less than

> Greater than

~ Approximately

FMC Fourmile Canyon

RD Root density

RLD Root-length density

Conversion Factors and Abbreviations

SI to Inch/Pounds

Units of Measure Used in This Report

cm centimeter

dyne cm-2 dynes per square centimeter

erg s-1 cm-2 erg per second per square centimeter

mm millimeter

g s–1cm–2 grams per second per square centimeter

s second

Variations in Soil Detachment Rates after Wildfire as 

a Function of Soil Depth, Flow Properties, and Root 

Properties

By John A. Moody1 and Petter Nyman2

Abstract

Wildfire affects hillslope erosion through increased surface runoff and increased sediment availability, both of which 

contribute to large post-fire erosion events. Relations between 

soil detachment rate, soil depth, flow and root properties, and 

fire impacts are poorly understood and not represented explicitly in commonly used post-fire erosion models. Detachment 

rates were measured on intact soil cores using a modified tilting flume. The cores were mounted flush with the flume-bed 

and a measurement was made on the surface of the core. The 

core was extruded upward, cut off, and another measurement 

was repeated at a different depth below the original surface of 

the core. Intact cores were collected from one site burned by 

the 2010 Fourmile Canyon (FMC) fire in Colorado and from 

one site burned by the 2010 Pozo fire in California. Each site 

contained contrasting vegetation and soil types. Additional soil 

samples were collected alongside the intact cores and were 

analyzed in the laboratory for soil properties (organic matter, 

bulk density, particle-size distribution) and for root properties 

(root density and root-length density).

Particle-size distribution and root properties were different between sites, but sites were similar in terms of bulk 

density and organic matter. Soil detachment rates had similar 

relations with non-uniform shear stress and non-uniform unit 

stream power. Detachment rates within single sampling units 

displayed a relatively weak and inconsistent relation to flow 

variables. When averaged across all clusters, the detachment 

rate displayed a linear relation to shear stress, but variability in 

soil properties meant that the shear stress accounted for only a 

small proportion of the overall variability in detachment rates 

(R2

 = 0.23; R2 is the coefficient of determination). Detachment 

rate was related to root-length density in some clusters (R2 values up to 0.91) and unrelated in others (R2 values <0.1). The 

overall R2 value improved and the range of exponents became 

narrower by applying a multivariate regression model where 

boundary shear stress and root-length density were included 

as explanatory variables. This suggests that an erodibility 

parameter which incorporates the effects of both flow and root 

properties on detachment could improve the representation of 

sediment availability after wildfire.

Introduction

Sediment availability is a critical, but relatively unknown 

variable needed to predict post-wildfire sediment erosion and 

transport as well as debris flow propagation in mountainous 

terrain (Moody and Martin, 2009; Nyman and others, 2011). 

Soils on unburned forested hillslopes in mountainous terrains 

generally have three layers: (1) a litter layer of loosely interwoven organic material, (2) a duff (or humus) layer consisting 

of partially to completely decomposed litter material that is 

more rigid and compressed than the litter layer, and (3) a cohesive soil layer with some organic material (DeBano and Neary, 

2005; DeBano and others, 2005). The upper two layers protect 

the underlying cohesive soil layer from erosion. Wildfires 

alter this structure in severely burned areas by combusting the 

organics and mixing in (by thermally driven winds) mineral 

soil particles with the combustion products to produce a layer 

of non-cohesive material consisting of ash, charcoal, and soil 

mineral that overlays the cohesive soil matrix. In less severely 

burned soils, an intact duff layer (that portion of the duff that 

did not burn) may be sandwiched between the top non-cohesive layer and the soil cohesive layer. Soil detachment rates 

would be expected to vary between such different soil layers. 

Detachment rates for particles within the non-cohesive 

layer have been determined by flow properties (such as shear 

stress or stream power) and particle properties (such as the 

critical shear stress or stream power) for initiation of motion 

and represent a “transport-limited case” (Foster and Meyer, 

1975; Hairsine and Rose, 1992). For the cohesive soil matrix 

layer, detachment rates for a given shear stress depend on the 

cohesive properties of the matrix as a whole, which are controlled by cohesive bonds of clay particles forming soil aggregates (Blake and others, 2007) and adhesive bonds of roots 

that hold the soil (Gyssels and others, 2005; De Baets and 

others, 2007; Grabowski and others, 2011) and produce the 

“detachment-limited case” (Foster and Meyer, 1975; Hairsine 

1

 U.S. Geological Survey, USA

2 University of Melbourne, Australia
2 Variations in Soil Detachment Rates after Wildfire

and Rose, 1992). In addition to the cohesive properties, other 

variables can possibly affect detachment rates, such as armoring by larger particles and roots (or scouring around these 

elements) and the degree of water repellency. Water repellency can be relatively high in the organic component of soils 

unaffected by wildfire, and can be elevated by the combustion 

process in soils affected by wildfire (DeBano, 2000).

The thickness of the post-wildfire erodible surface layer 

depends on the fuel load in the O-horizon/duff and A-horizon 

and on the soil burn severity, which determines the thickness of ash. The soil burn severity also changes the cohesive 

properties of the B-horizon by altering root strength (Busse 

and DeBano, 2005) and weakening organic bonds (Giovanni 

and others, 1988), which in turn affect the critical shear stress 

for the detachment mineral soil particles (Moody and others, 

2005). Thus, the total thickness of this erodible surface layer 

and the associated erodibility are the data that are needed to 

determine sediment availability.

There is a large volume of literature on the erodibility of 

agricultural soils from measurements made in the field (Elliot 

and others, 1989). However, less data is available for soils 

typical of mountainous regions susceptible to wildfire 

(Robichaud and others, 2010; Sheridan and others, 2007; 

Al-Hamdan and others, 2011), and most erodibility parameters 

have been calculated for surface material and not as a function 

of depths below the soil surface, which becomes a logistical 

problem in the field and better explored in a laboratory flume 

(Nachtergaele and Poesen, 2002). Erodibility does not have 

a consistent definition in the literature, because the detachment rate [g s-1 cm-2] is normalized by different flow variables 

(Moody and others, 2005; Grabowski and others, 2011) or 

detachment rate is expressed as a ratio of the actual rate to a 

rate expected for non-cohesive single-size sediment (Hairsine 

and Rose, 1992). 

Purpose and Scope 

This report presents the results of a set of laboratory 

flume experiments designed to measure the detachment 

rates for non-cohesive and cohesive soils as a function of 

depth below the soil surface. Soil cores were collected from 

unburned and burned hillslopes in two different precipitationwildfire regimes: one in Colorado and one in California. Soil 

detachment rates in this report are linked to corresponding 

measurements of soil properties as a function of depth (soil 

bulk density, particle-size distributions, organic matter content), root properties (root mass and root-length density), and 

to the hydraulic variables (water depth, discharge, shear stress, 

and stream power) such that the reader can investigate detachment rates in burned soils or use the data to calculate a desired 

erodibility parameter. 

Relations between detachment rate and hydraulic 

variables and root properties as a function of soil depth are 

presented. Power law relations are determined for replicate 

samples from the two different precipitation-fire regimes in 

order to assess the natural variability of soil erodibility after 

wildfire. 

Soil Sampling

Detachment of sediment particles from soil depends 

primarily on the degree of cohesion holding particles together, 

which can be a function of the particle size and distribution of 

vegetative roots in the soil profile. Thus, the sampling strategy 

was designed to collect soil samples from recently burned 

areas with contrasting geology, soil-particle size, and vegetative characteristics. One area had been burned by the 2010 

Fourmile Canyon fire in September 2010, and typically had 

sandy-gravelly soils with different types of coniferous vegetation on different aspects. A second area had been burned by 

the 2010 Pozo fire in August 2010, and typically had clayey 

soils and chaparral vegetation. 

Site Characteristics 

The area burned by the 2010 Fourmile Canyon fire was in 

the Front Range of the Rocky Mountains near Boulder, Colorado. This area has a Continental climate (Pepin, 2000) where 

the precipitation is primarily a mix of cyclonic storms in the 

spring and fall, convective storms in the summer, and snowstorms in late fall through early spring. Mean annual precipitation (map) from nearby Gross Reservoir consists of rain (346 

millimeters (mm)) during the late spring, summer, and early fall 

(April–September) and snow during the remainder of the year 

(175 mm) or total annual precipitation of 521 mm (National 

Oceanic and Atmospheric Administration, 2000). Cores were 

collected at elevations between 2,350 and 2,450 m on a northand on a south-facing site with hillslope lengths on the order of 

200–400 meters (m) and slopes of 20–30°. The Fourmile Canyon fire burned through primarily ponderosa pine (Pinus pondersosa) and Rocky Mountain juniper (Juniperus scopulorum) 

on south-facing slopes and primarily Douglas fir (Pseudotsuga 

menziesii subspecies glauca) and limber pine (Pinus flexilis) 

on north-facing slopes. Soils on the south-facing site are stony 

and gravelly sandy loams described by the U.S. Department 

of Agriculture (USDA) Survey Staff (2011) as frigid Lithic 

Haplustolls with relatively high mica content and derived from 

granitic bedrock (Gable, 1980). Soils on the north-facing site 

are derived from granodiorite and are primarily coarse to fine 

sandy-gravelly soils and classified as frigid Lamellic or Typic 

Haplustalfs (Gable, 1980; U.S. Department of Agriculture 

Survey Staff, 2011). The USDA database lists these soils as 

having a RUSLE2 surface soil erodibility factor, Kf

 [cm-1], of 

0.026 t-ha-h (ha-MJ-mm)-1 on south-facing hillslopes and 

0.037 t-ha-h (ha-MJ-mm)-1 on north-facing hillslopes.

The area burned by the 2010 Pozo fire was in the La 

Panza Mountains, which are part of the central California 

Coastal Mountains near San Luis Obispo, California. The 
Field Sampling Methods 3

mountains are inland and partly in the rain shadow from the 

Santa Lucia and Garcia Mountains closest to the coast (map = 

817 mm; Santa Margarita Boost; National Oceanic and Atmospheric Administration, 2000) and the average annual precipitation is 570 mm, which falls primarily in the winter months of 

December–March (Salinas Dam; National Oceanic and Atmospheric Administration, 2000). This rainfall pattern is typical 

of a Mediterranean climate. At this site, cores were collected at 

elevations between 500 and 580 m on short (50–100 m), steep 

(20–40°) south-facing hillslopes. The Pozo fire burned through 

chaparral vegetation consisting of scattered blue oak (Quercus 

douglasii), manzanita (Arctostaphylos sp.), chamise (Adenostoma sp.), and white sage (Salvia apiana). Soils are fine clay 

loams classified as thermic Mollic Haploxeralfs, and at lower 

elevations, these soils grade into fine, smectitic, thermic Typic 

Haploxererts (U.S. Department of Agriculture Survey Staff, 

2011) that are mostly derived from bedrock geology consisting 

of marine sedimentary rocks (U.S. Forest Service, 2011). Soils 

at higher elevations have values of Kf

 of 0.057 t-ha-h (ha-MJmm)-1 and soils at lower elevations have values ranging from 

0.026-0.032 t-ha-h (ha-MJ-mm)-1.

Field Sampling Methods

To obtain representative samples, soil cores were collected along transects starting near a ridge line and extending 

down the hillslope. In the Fourmile Canyon area, there were 

two sites. The first site was on south-facing hillslopes (FMCSouth) with three 80-m transects on a burned hillslope and 

one 80-m transect on an unburned hillslope. The second site 

was on north-facing hillslopes (FMC-North) with three 80-m 

transects on a burned hillslope and one 80-m transect on an 

unburned hillslope. In the Pozo area, there was one site on 

south-facing hillslopes (Pozo-South) with three 40-m transects on burned south-facing hillslopes and one 40-m transect 

on an unburned hillslope. Soil cores were collected at nine 

equally spaced locations along each transect. The first three, 

the middle three, and the last three locations were combined 

to form three separate composite transect samples that would 

characterize particle size and root properties of the burned 

hillslope. The three composite transect samples were archived 

for later analysis by any interested researchers.

At one location (judged to be the most representative) 

along each of three transects, 11 additional soil cores were 

collected (fig. 1A). Five were collected to measure soil detachment rates in a shallow water, tilting laboratory flume, three 

replicate soil cores were collected, within about a 1-m 

diameter area, to characterize the particle size and organic 

matter, and three replicate soil cores were collected to characterize root properties of the soil cores used in the flume 

(fig. 1B). This group of 11 cores is called a cluster in this 

report, and thus, there were three clusters (A, B, and C) for 

each site on a burned hillslope, one cluster for each unburned 

site, and a total of 12 clusters from the three different sites 

(FMC-South, FMC-North, and Pozo-South). Only the data 

from the cluster samples are given in this report.

Each soil core was divided into five subsamples 

representing different depths below the surface. Soil cores 

(4.7-cm diameter) collected for particle size and root properties were 10-cm long, and those cores for soil detachment 

measurements in the flume were 7.5-cm long. The core tubes 

were driven into the ground with a mallet, excavated by 

using a flat trowel slid under the bottom of the core tube, and 

subsamples were extruded from the core using a solid plastic 

cylinder mounted on a flat base at the following depth intervals: 0–1 cm, 1–3 cm, 3–5 cm, 5–7.5 cm, and 7.5–10 cm. In 

some cases, the core hit a pebble or rock, the core edge was 

re-sharpened or a spare core was used, and a new location 

was tried until a complete core was obtained. It was easier 

to obtain a full, intact core using the 7.5-cm long cores than 

using the 10-cm long cores. 

Each subsample was placed in a separate zip-lock bag 

and taken back to the laboratory for analysis (fig. 1). Soil 

cores for soil detachment measurements were excavated by 

 5 Depths

 6 soil samples

(0-10 cm) 5 intact cores

(0-7.5 cm)

PSA & OM

 3 

ROOT

3

Zip lock

Extruder

Stainless

steel core 

Holes for stop

pin 

Spatula

Retaining

annulus 

A

B

C

T1 T2 T3

Site:

Transects:

Fourmile Canyon South 

Clusters:

A

B

Figure 1. A, upper section shows the location for 

collecting cluster samples (A, B, and C) along transects 

(T1, T2, and T3) from one sample site called Fourmile 

Canyon South. B, lower section shows the details of the 

method of collecting subsamples of the soil core. Stainless 

steel pins are inserted into a series of holes in a solid 

plastic cylinder to provide stops as the core is slid down 

the extruding cylinder mounted to a base. At each stop, the 

protruding soil is retained inside a plastic annulus and then 

sliced at the bottom of the annulus by using the spatula to 

separate a subsample, which is put in labeled “zip-lock” 

sample bags.
4 Variations in Soil Detachment Rates after Wildfire

using the flat trowel, but then each end of the core was capped 

tightly to prevent shifting of the core inside the core tube. 

Core tubes were labeled and were brought back to the laboratory and refrigerated until they were used in the flume. At each 

sampling location, notes were made on the general characteristics of the location such as the proximity to trees and other 

plants or shrubs. The site itself was further characterized in 

terms of plant species, the density of plants (stems per hectare, 

stems ha-1), size of trees (basal area and diameter at breast 

height), and shrubby vegetation and ground cover. Visual 

observations of root structure were made in the field and some 

photographs were obtained of root networks that were exposed 

either in a trench or by removing topsoil using a jet of water 

(data on file at U.S. Geological Survey Office in Boulder, 

Colorado).

Laboratory Methods

Soil and root properties were analyzed at the fixed depth 

intervals corresponding to the depth intervals of the subsamples collected in the field, whereas the soil detachment 

measurements were made at five depths approximately equal 

to the midpoint of each depth interval. Soil properties were 

bulk density [g cm-3], particle size distribution, and organic 

content; and root properties were root density [mg cm-3] and 

root-length density [cm cm-3]. Soil detachment measurements 

include: flume properties, hydraulic properties (slope, water 

depth [mm], and discharge [mL s-1), shear stress [dynes cm-2], 

stream power [erg s-1 cm-2], soil detachment rates [g cm-2 s-1], 

and eroded sediment particle-size distributions.

Soil Physical Properties

Each cluster had three replicate soil samples of the source 

material collected at five different depths. Each of the 15 

samples was processed for particle size by using standard sieving methods (Guy, 1977). A sample was dried at 105°C for 24 

hours (hr), weighed to determine the total mass, and split into 

two parts: one part was used for particle-size analysis and one 

part was used for soil organic content analysis. The mass of 

these splits ranged from 5–50 grams (g), so they were processed through a set of standard 3-inch diameter sieves to give 

10 size classes (<0.063, 0.063–0.125, 0.125–0.250, 0.250–

0.500, 0.5–1.0, 1–2, 2–4, 4–8, 8–16, and 16–32 mm). Bulk 

density was computed from the total mass, thickness (which 

depended on the depth interval, and diameter of the core equal 

to 4.7 cm). Field observations indicated that samples from the 

area burned by the Pozo fire had more clay and possibly more 

aggregates than the samples from the area burned by the Fourmile Canyon fire. Therefore, to ensure consistent treatment 

and to break up possible aggregates into their fundamental 

particle size, all samples were processed by vibrating, shaking, and gently abrading the soil in each sieve by hand rather 

than by using a mechanical sieve shaker. Sieved samples were 

weighed to nearest 0.001 g and the mass lost in processing the 

samples was typically less than 0.5 percent. The average of the 

three replicates for bulk density and percent of the total sample 

in each size class is listed in tables 1, 2, and 3 for each site.

Detached soil was transported as sediment during the 

flume experiments. This eroded sediment (> 0.063 mm) was 

collected, dried at 105°C for 24 hr, and reweighed. The sample 

was processed through the same set of 3-inch diameter sieves 

(without the 4-, 8-, and 16-mm sieves) to give 7 size classes. 

For these samples it was desired not to break up the aggregates, which represented the natural detachment form, and so 

the samples were not processed by hand, but by running them 

in a RoTap (Model RX-29, W.S.Tyler, Mentor, Ohio) sieve 

shaker for 10 minutes (min).

Soil Organic Content

Organic content was measured as loss on ignition (LOI) 

for the split (half of the total sample) of each of three replicates (Heiri and others, 2001). Each split sample (~5–50 g) 

was put in pre-weighed porcelain crucibles and reweighed. 

Samples were placed in a pre-heated muffle furnace at 500°C, 

removed after 2 hr, cooled in a desiccator, and reweighed 

to nearest 0.001 g. The average loss of mass for the three 

replicates is reported as an average percent of the total loss on 

ignition of each split in tables 1, 2, and 3 for each site.

Root Properties

Three replicate soil samples containing roots were collected at five different depths for each cluster. Each of the 15 

samples was air dried in an open sample bag in the laboratory. 

The dried sample was put in a 2-mm sieve and the visible 

roots were removed and placed in a small plastic jar. The 

gravel fraction > 2 mm was weighed. Soil aggregates containing a network of fine roots were placed in a jar with water 

so that the aggregates could soak up water. A lid was put on 

the jar and it was gently shaken, in order to separate most of 

the fine roots from the soil aggregates. Roots floated to the 

surface and were extracted. The fraction < 2 mm fraction was 

wet sieved through a 0.5-mm sieve. Material retained in the 

0.5-mm sieve was transferred to a white enamel tray with a 

5-mm×5-mm grid drawn onto the base of the tray. Water was 

added to a depth of about 1cm, and the sample was spread 

uniformly across the tray. A squirt bottle was used to wash the 

roots off the sides and onto the water surface. A few drops of 

soap in the squirt bottle lowered the surface tension of water 

and helped reduce the clustering of roots along the edge of 

tray. Roots were manually extracted by using tweezers and a 

10X magnifying lens. In some cases, it was difficult to distinguish between roots and other organic matter. All organic fragments that had a cylindrical shape with a length >1 mm were 

treated as roots. When roots were abundant and when there 

was little other floating material, the roots could be extracted 

using a suction pipette. 
Laboratory Methods 5

Table 1. Soil and root properties for Fourmile Canyon South site.

[vcs, very coarse sand; cs, coarse sand; ms, medium sand; fs, fine sand; vfs, very fine sand; mm, millimeter; cm centimeter; g, gram; mg, milligram; cm3, 

cubic centimeters; %, percent; <, less than; no, not obtained]

Pebbles Granule vcs cs ms fs vfs

Silt 

and 

clay

32-16 16-8 8-4 4-2 2-1 1-0.500 0.500-

0.250

0.250-

0.125

0.125-

0.063 <0.063

Large 

organics

Average 

depth

Bulk 

density

Loss on 

ignition

Root 

density

Root 

length 

density

 mm mm mm mm mm mm mm mm mm mm

(cm) (g cm-3) (%) (mg 

cm-3)

(cm 

cm-3) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%)

Fourmile Canyon-South Unburned

0.5 0.46 43.8 9.71 28.7 0.0 0.0 7.4 2.9 5.7 6.4 8.4 7.9 6.9 5.8 48.6

2.0 0.51 28.1 11.52 12.6 0.0 0.0 1.6 6.7 8.0 11.0 14.2 11.6 10.3 11.9 24.7

4.0 1.27 4.8 8.95 8.60 20.2 0.9 13.1 10.6 11.0 11.9 10.5 7.7 5.0 7.5 1.6

6.3 1.28 2.6 8.07 5.00 16.4 20.0 10.2 10.1 9.9 8.6 8.8 6.1 3.7 5.7 0.4

8.8 1.69 2.4 no no 13.1 24.1 8.9 11.0 10.2 9.1 8.9 5.9 3.6 4.9 0.3

Fourmile Canyon-South Burned—Cluster A

0.5 1.06 6.8 3.97 17.9 0.0 4.6 11.4 11.1 14.2 17.4 16.6 9.7 5.4 7.6 2.0

2.0 1.58 3.8 8.02 17.3 9.0 11.8 8.4 7.6 11.0 14.2 14.8 9.7 5.2 6.5 1.7

4.0 1.78 3.0 5.79 7.57 15.8 12.5 7.7 10.0 11.3 12.7 12.7 7.9 4.3 4.8 0.3

6.3 1.46 3.1 3.62 4.52 0.0 14.0 15.2 10.9 11.9 13.3 13.9 9.4 5.3 5.6 0.5

8.8 1.28 2.6 2.83 3.98 34.1 9.5 7.8 7.4 8.5 8.8 9.5 6.5 3.9 3.7 0.3

Fourmile Canyon-South Burned—Cluster B

0.5 1.13 6.8 0.28 1.59 0.0 8.0 9.6 13.4 16.1 14.8 14.2 9.3 5.7 8.4 0.5

2.0 1.31 6.1 0.32 1.45 0.0 20.4 7.6 8.2 11.3 12.6 13.2 10.1 7.4 8.9 0.3

4.0 1.52 3.9 3.44 9.19 0.0 9.2 9.1 8.3 11.6 13.4 16.2 13.3 8.9 9.7 0.4

6.3 1.36 3.4 3.65 5.36 16.9 6.3 12.5 10.0 10.9 10.5 11.3 9.4 5.6 6.1 0.5

8.8 1.22 3.5 4.00 6.15 0.0 13.8 17.4 15.3 12.3 10.2 11.3 8.3 5.5 5.6 0.3

Fourmile Canyon-South Burned—Cluster C

0.5 0.92 9.2 2.71 5.98 0.0 0.0 5.8 10.9 15.6 19.4 15.5 10.8 8.7 7.9 5.4

2.0 1.19 5.8 11.54 23.8 0.0 18.1 7.1 5.6 10.9 13.4 14.9 11.0 8.7 8.2 2.2

4.0 1.41 4.4 6.65 19.2 0.0 21.3 7.0 7.8 11.4 12.6 13.4 10.0 6.9 8.6 1.1

6.3 1.32 3.2 6.12 13.6 0.0 14.2 9.3 10.8 12.0 11.6 14.4 11.5 7.9 8.3 0.0

8.8 1.54 3.2 no no 0.0 20.2 11.4 13.0 13.0 10.9 11.5 8.4 5.3 6.1 0.1
6 Variations in Soil Detachment Rates after Wildfire

Table 2. Soil and root properties for Fourmile Canyon North site.

[vcs, very coarse sand; cs, coarse sand; ms, medium sand; fs, fine sand; vfs, very fine sand; mm, millimeter; cm centimeter; g, gram; mg, milligram; 

cm3, cubic centimeters; %, percent; <, less than; no, not obtained]

Pebbles Granule vcs cs ms fs vfs

Silt 

and 

clay

32-16 16-8 8-4 4-2 2-1 1-0.500 0.500-

0.250

0.250-

0.125

0.125-

0.063 <0.063 Large organics

Average 

depth

Bulk 

density

Loss on 

ignition

Root 

density

Root 

length 

density

 mm mm mm mm mm mm mm mm mm mm

(cm) (g cm-3) (%) (mg 

cm-3)

(cm 

cm-3) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%)

Fourmile Canyon-South Unburned

0.5 1.32 4.9 17.04 30.0 0.0 2.2 7.6 12.7 15.8 13.3 13.3 9.7 6.7 9.3 9.3

2.0 1.50 3.9 8.24 12.7 0.0 12.2 10.7 12.7 13.5 12.2 12.4 9.8 6.3 8.1 2.0

4.0 1.48 2.9 11.12 7.8 0.0 1.4 18.5 14.8 14.0 13.5 12.7 10.1 6.2 7.7 1.0

6.3 1.49 3.2 6.83 7.1 0.0 6.7 18.3 15.0 13.4 11.8 12.8 9.6 5.9 6.3 0.4

8.8 1.38 2.0 no no 0.0 12.8 15.8 17.3 13.2 10.7 11.7 8.4 4.8 4.9 0.4

Fourmile Canyon-South Burned—Cluster A

0.5 0.84 9.8 1.00 3.8 0.0 6.6 6.9 19.1 15.5 9.8 6.9 6.0 5.0 17.5 6.8

2.0 0.99 8.4 11.68 13.0 0.0 2.1 11.9 15.2 14.9 10.4 9.4 7.5 6.1 15.3 7.4

4.0 1.27 7.9 16.71 10.5 0.0 3.6 8.1 13.5 13.1 12.1 11.6 8.7 7.2 14.3 7.6

6.3 1.29 3.3 8.99 6.5 0.0 14.7 3.9 9.7 13.8 15.7 15.5 10.6 6.8 8.1 1.0

8.8 1.16 3.0 4.17 4.5 22.0 0.0 4.7 13.6 12.2 10.6 10.9 8.5 6.6 10.1 0.9

Fourmile Canyon-South Burned—Cluster B

0.5 1.24 3.2 7.30 11.5 0.0 0.0 10.0 9.9 10.9 13.7 19.0 15.4 11.2 9.2 0.7

2.0 1.33 3.4 11.48 10.9 0.0 3.7 5.8 8.9 12.8 15.3 22.4 13.7 10.3 6.5 0.6

4.0 1.37 3.4 16.04 12.7 6.8 5.8 4.5 8.8 11.7 14.9 18.2 14.2 9.1 5.5 0.4

6.3 1.21 3.4 6.77 5.7 4.5 1.8 8.5 10.6 12.7 14.4 19.4 13.2 8.6 5.5 0.8

8.8 1.26 2.7 no no 16.0 7.1 3.2 9.8 11.2 12.8 16.5 11.4 6.9 5.0 0.2

Fourmile Canyon-South Burned—Cluster C

0.5 1.13 5.1 5.88 13.4 0.0 0.0 4.2 12.9 16.8 15.4 14.1 10.6 7.4 16.5 2.0

2.0 1.31 4.6 6.21 8.7 0.0 11.1 4.8 11.9 12.8 12.5 13.0 11.5 7.9 12.6 1.9

4.0 1.20 5.4 7.72 6.5 11.5 6.5 5.7 12.2 12.5 11.7 10.9 9.7 6.9 10.5 1.9

6.3 1.34 4.8 7.72 6.0 12.4 5.4 6.7 12.2 11.9 11.3 11.4 9.6 7.3 10.0 1.7

8.8 no 6.2 5.30 3.9 45.7 8.8 4.1 4.3 6.1 6.8 6.5 5.9 4.3 7.0 0.6
Laboratory Methods 7

Table 3. Soil and root properties for Pozo South site.

[vcs, very coarse sand; cs, coarse sand; ms, medium sand; fs, fine sand; vfs, very fine sand; mm, millimeter; cm centimeter; g, gram; mg, milligram; 

cm3, cubic centimeters; %, percent; <, less than; no, not obtained]

Pebbles Granule vcs cs ms fs vfs

Silt 

and 

clay

32-16 16-8 8-4 4-2 2-1 1-0.500 0.500-

0.250

0.250-

0.125

0.125-

0.063 <0.063 Large organics

Average 

depth

Bulk 

density

Loss on 

ignition

Root 

density

Root 

length 

density

 mm mm mm mm mm mm mm mm mm mm

(cm) (g cm-3) (%) (mg 

cm-3) (cm cm-3) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%)

Fourmile Canyon-South Unburned

0.5 1.18 6.0 0.52 3.3 0.0 10.3 15.1 13.8 10.0 11.8 8.1 9.0 9.5 10.6 1.7

2.0 1.19 3.2 1.35 7.2 0.0 13.1 7.9 8.1 8.5 7.8 11.0 13.4 14.0 15.9 0.2

4.0 1.21 2.3 5.18 15.2 0.0 10.8 11.0 11.3 8.2 7.2 10.5 12.7 13.3 14.8 0.1

6.3 1.41 2.0 5.89 18.4 0.0 16.4 8.9 10.2 8.4 7.0 10.1 12.9 12.7 13.5 0.0

8.8 1.50 2.4 no no 0.0 7.4 11.9 9.0 8.0 7.4 11.2 15.5 14.6 14.9 0.1

Fourmile Canyon-South Burned—Cluster A

0.5 1.33 3.2 0.10 0.7 0.0 2.1 3.1 9.1 8.3 11.2 13.4 14.7 15.5 22.3 0.2

2.0 1.05 3.4 1.32 5.0 0.0 0.0 4.1 4.7 6.8 11.6 14.6 18.0 17.6 22.7 0.0

4.0 1.16 3.7 2.96 9.2 0.0 1.1 5.9 5.1 7.0 11.2 14.8 17.5 16.6 20.7 0.2

6.3 1.28 3.4 2.86 8.1 0.0 5.3 3.2 5.1 5.9 10.6 16.9 17.8 15.8 19.2 0.2

8.8 1.59 2.9 no no 0.0 8.7 6.1 5.4 6.4 8.8 14.4 19.5 14.4 16.2 0.2

Fourmile Canyon-South Burned—Cluster B

0.5 1.19 5.3 0.04 0.2 0.0 0.0 4.7 5.2 8.1 10.4 12.2 14.8 15.7 28.9 0.0

2.0 0.88 5.9 2.59 3.5 0.0 0.0 5.2 9.2 9.4 10.5 10.6 15.0 16.4 23.7 0.1

4.0 1.13 5.0 3.30 7.0 0.0 2.2 8.4 7.0 7.5 7.7 10.9 15.0 15.5 25.4 0.3

6.3 1.26 4.1 8.08 10.4 0.0 7.5 4.0 5.1 5.9 8.3 12.7 15.8 16.9 23.5 0.2

8.8 1.59 4.1 no no 0.0 3.6 5.2 6.8 6.3 9.5 11.5 16.9 16.3 23.6 0.3

Fourmile Canyon-South Burned—Cluster C

0.5 1.24 4.1 1.24 7.6 0.0 0.0 10.4 16.7 12.7 9.7 9.6 10.5 11.6 18.9 0.0

2.0 1.07 4.6 1.63 8.6 0.0 0.0 6.7 11.4 12.9 9.0 10.2 12.4 14.8 22.7 0.0

4.0 1.25 3.5 5.36 17.9 0.0 9.9 8.3 10.7 9.0 7.8 9.5 11.4 12.1 21.3 0.0

6.3 1.39 3.3 3.84 13.7 0.0 5.6 8.9 9.8 9.1 8.0 11.0 12.7 14.9 19.8 0.1

8.8 1.57 3.0 6.12 16.2 0.0 5.3 11.8 7.4 9.0 7.7 11.6 13.0 15.4 18.5 0.2
8 Variations in Soil Detachment Rates after Wildfire

At each grid element, roots and water were sucked into 

the pipette, discharged from the pipette onto a small piece 

(2 cm×1.5 cm) of fine (approximately 1 mm×1 mm) mesh 

attached to a handle, and then submerged under water in the 

root sample jar to release the extracted roots. This method 

was more time efficient but was not suitable for samples with 

abundant organic material which would contaminate the root 

sample and become a source of error in the root-mass measurements. Dead and live roots were not distinguished. However, some roots were visibly charred and possibly weakened 

by the fire. We rubbed the roots between our fingers and if 

the root rubbed onto the skin as charred material, the root was 

considered to be ineffective and excluded. 

Root density and root-length density were measured as 

a function of soil depth for each site. Roots were dried in an 

oven at 65°C for 48 hr, cooled, and weighed to measure the 

root density (RD) [mg cm-3] (tables 1, 2, and 3). Root-length 

density, (RLD) [cm cm-3], was measured by following the 

procedure outlined by Tennant (1975) using a grid method 

(fig. 2). The accuracy of the procedure was evaluated by 

comparing the grid estimation method developed by Tennant 

(1975) with manual root-length measurements made by using 

calipers. The grid-based root-length estimation performed well 

(coefficient of determination, R2 = 0.998) when compared to 

manual measurements of root lengths (fig. 3). RLD data in this 

report are based on the grid method (tables 1, 2, and 3).

A B

C

Figure 2. Extracted roots from 3–5 cm below the soil surface from burned sites. A, Fourmile Canyon-North. 

B, Fourmile Canyon-South. C, Pozo. The tray is 22 cm wide by 30 cm long and each grid cell is 5 mm×5 mm.
Laboratory Methods 9

Flume Properties

The flume used to measure soil detachment rates from 

soil cores was a shallow-water, tilting flume. It was made of 

aluminum and was 10 cm wide and 50 cm long, with a maximum depth of 2.5 cm (fig. 4). A 5.1-cm diameter hole was 

cut into the 1-cm thick aluminum bed of the flume to permit 

insertion of the 4.7-cm diameter soil core (5.1-cm outside 

diameter), which was held in place by an extruder with piston 

mounted underneath the flume bed (fig. 4). The center of the 

core was 39.5 cm downstream from the outlet of the flow 

diffuser, 10.5 cm from the end of the flume, and 4.7 cm from 

each side wall. At the beginning of each measurement run the 

surface of the core could be adjusted using the extruder piston 

to be approximately flush with the flume bottom.

Water was not recirculated in this flume so that only 

clear water flowed across the soil core; thus, all the associated 

detachment measurements in this report are for clear water 

conditions. Clear water from a laboratory supply line was run 

into a supply tank and water was pumped from the supply 

tank (fig. 4C) through a 3.2-cm diameter semi-flexible plastic 

tubing into the head box of the flume. Discharge could be 

manually controlled by an inline butterfly valve from 0.02–

1.2 L s-1. Water left the head box through a diffuser, flowed 

down the flume, across the soil core, fell off the flume bottom 

into a 115-L sump tank, and the water with any sediment was 

pumped out of the sump tank into a drain.

Flow depth was controlled by the discharge and slope of 

the flume bed. The flume was mounted on a box frame such 

that it could be tilted (by using a screw jack inside the box 

frame) from a horizontal to a maximum slope of about 0.80 

(~40°). Flow depth was measured before each run by using 

a point gage (accuracy: 0.005 cm) mounted 7.5 cm upstream 

from the center of the core, and sometimes flow depth was 

measured after the run with a second point gage (accuracy: 

0.005 cm) mounted 7.5 cm downstream from the center of 

the core. Discharge was computed from the measured volume 

(~4 L with an accuracy of + 10 mL) collected in a bucket and 

the corresponding time (accuracy + 0.01 s) to fill the bucket. 

Discharge in this type of flume is not a linear function of depth 

at all slopes (fig. 5). The relation is non-linear for slopes less 

than < 0.08 and linear for slopes > 0.08. Slopes used in the 

detachment experiments ranged from 0.053–0.177 (tables 4–6; 

between solid black lines in fig. 5). Typical flow conditions 

in the flume (with a smooth plug inserted in the hole for the 

soil cores) were supercritical with Froude number (Dingman, 

1984) increasing with slope from about 1 to 4, Reynolds number (Dingman, 1984) ranging from about 1.8×102

 to 1.2×104, 

and Darcy-Weisbach friction factor (Dingman, 1984) ranging 

from 0.05–0.4.

Boundary Shear Stress 

While the flow in the flume was steady, it was not uniform. Generally, the water accelerated down the flume without 

any soil cores in place and varied between accelerating and 

decelerating with a soil core in place depending on the surface 

roughness of the soil. For uniform flow the shear stress, τ 

[dynes cm-2] would simply be the product of water depth, h

[cm], and flume slope, S [non-dimensional] or 

 τ = rghS (1)

where 

 r [g cm-3] is density of water, and 

 g is acceleration of gravity 

 (980 cm s-2). 

For accelerated flow, two terms must be added that 

represent the shear stress caused by change in mean velocity and change in pressure between two points (Julien, 1998). 

If h1

[cm], h2 [cm], U1 [cm s-1], and U2

 [cm s-1] are the water 

depths and mean cross-sectional velocities at points 1 and 2 

separated by a distance, d [cm], then the non-uniform shear 

stress is given by:

 τN = rh [gS + (U1

+U2)/2)(U1-U2)/d + (h1+h2)/2)(h1-h2)/d] (2)

Non-uniform shear stresses were measured for smooth 

flume conditions and compared to non-uniform values corresponding to many different soil surface conditions. Initially, 

a suitable range of target shear stresses (16, 31, 95, and 182 

dynes cm-2) were selected for the flume experiments and combinations of flume slope and water depth were calculated that 

would give these values of uniform shear stresses (0.053, 0.30 

cm; 0.053, 0.60 cm; 0.088, 0.110 cm; and 0.177; 0.105 cm; 

see tables 4–6). The flume (with a smooth plug in the hole for 

the soil core) was run with these combinations to determine 

the non-uniform shear stresses (22, 63, 144, and 421 dynes 

Figure 3. Calibration of the grid method of measuring root

length outlined by Tennant (1975) by comparing the root 

lengths measured manually using metric calipers. The red 

line is a 1: 1 line.

Measured = 0.954 estimated

R2 = 0.998 

0

50

100

150

200

250

300

0 50 100 150 200 250 300

Root length measure by

using a ruler, centimeter 

Root length estimated by

using the grid method, centimeter 
10 Variations in Soil Detachment Rates after Wildfire

A Diffuser

1st point gage

Laser level

Hinge

B 

Center line for 2nd point gage

1-cm thick aluminum flume bed

Box frame

on 4 adjustable

pads

Control valve 

To flume To drain 

115 L sump

115 L supply tank

Main water

supply 

Submersible

supply pump 

Drain pump

supply pump

C 

Head box

Wheel

to adjust

slope

Flume base

(1-cm aluminum plate)

Soil core 

Piston head

Core holder 

and extruder

10 cm

Clamp to hold soil 

core to aluminum plate

Figure 4. A, Diagram of shallow-water tilting flume and circulation system. B, Core attachment. C, water circulation system. 

Diagrams prepared by Graeme Scheuber.
Laboratory Methods 11

cm-2) under smooth conditions. The non-uniform shear stress 

was then periodically checked during actual conditions with 

different soil cores in the flume. Water depth was always set 

to a predetermined depth at the upstream point gage before 

each experimental run, but it was not possible to measure the 

water depth at the downstream point gage while collecting the 

sediment during the actual experimental run. Therefore, after a 

set of 3 runs (for a given depth below the surface of the core) 

a separate run was made without collecting sediment and the 

second depth was measured. 

Mean velocities were computed from the two depths, 

width of the flume (10 cm), and the measured discharge, 

and τN was computed for the condition with a soil core in 

place. The range of τN measured in the flume with different 

roughness conditions of the soil surface bracketed the values 

measured for the smooth flume conditions (fig. 6). There were 

42, 40, 39, and 37 measurements corresponding to 22, 63, 144, 

and 421 dynes cm-2, respectively.Linear regression of the average shear stress values for rough conditions with a soil core 

in place,τN

r

, versus those for smooth conditions, τN

s

, gave τN

r

= 0.98τN

s

 (R2=0.99) with coefficient of variations for the four 

shear stresses (22, 63, 144, and 421 dynes cm-2) used in the 

experiments that were 0.21, 0.27, 0.25, and 0.18, respectively.

Stream Power

Stream power can be expressed as either a power per 

unit bed area or power per unit weight. Stream power is the 

rate that energy or work is supplied to the flow by converting 

potential energy into kinetic energy (Bagnold, 1966; Yang, 

1972). For a unit length of flow, l [cm], the decrease in height 

is lS [cm], the force per unit time is rgQ [dyne s-1 or erg cm-1

s-1], and the stream power per unit length, Ω [erg s-1cm-1], was 

given by Bagnold (1966) as:

 Ω = rgQS (3)

Stream power per unit area or unit stream power, 

 wa

 [erg s-1 cm-2], is Ω divided by the flow width or

 wa = rgdUS = tU (4)

where 

U is the cross-sectional mean velocity. 

Unit stream power can also be expressed as power per unit 

weight of water if the flow is assumed to be steady and 

Q = 0.0028h2.2

R2 = 0.95

Q = 0.024h1.5

R2 = 0.99

Q = 0.029h1.5

R2 = 1.00

Q = 0.11(h-1.08) 

R2

 = 1.00

Q = 0.11(h-1.05) 

R2

 = 1.00

Q = 0.11(h-0.96) 

R2

 = 1.00

Q = 0.12(h-0.78) 

R2

 = 1.00

Slope = 0.016

Slope = 0.053

Slope = 0.069

Slope = 0.088

Slope = 0.132

Slope = 0.177

Slope = 0.226

EXPLANATION

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 5 10 15

Discharge, Q, liter second-1

Water depth, h, in millimeters

Figure 5. Relations between water discharge and water depth, at different slopes, for the shallow-water tilting flume.
12 Variations in Soil Detachment Rates after Wildfire

uniform (Yang, 1972). The equation for this unit stream power, 

ww [cm s-1] was given by Yang (1972) as:

 ww = US (5)

Flow in the tilting flume is non-uniform, so values of wa

are listed in tables 4–6 as non-uniform unit stream power.

Soil Detachment Measurements

Each individual core provided five measurements for 

one value of shear stress at five different depths, which corresponded approximately to the midpoint of soil sampling 

intervals (0.5, 2, 4, and 6.25 cm). A second core was used for 

measurements for a different shear-stress value at five depths. 

Thus, soil detachment was measured at all four shear stresses 

by using four cores from a cluster. The fifth core collected in 

a cluster was archived in a refrigerator. Each burned site had 

three clusters, which provided three replicate measurements 

for each shear stress. 

Two types of experimental runs were carried out to 

measure the soil detachment as a function of depth below the 

surface of the soil—a short run and a long run. For both runs, 

a soil core was mounted in the extruder (fig. 4B), and then 

attached to the underside of the flume so that the soil surface 

in the core was flush with the bed of the flume, which was set 

to the desired slope. Water drops were placed on the surface 

to qualitatively assess the water repellency, other physical and 

visual characteristics were recorded, and then the soil core was 

covered with a protective cover (piece of sheet metal) to prevent erosion while the desired flow depth (that would produce 

the required shear stress) was established by using the manual 

control valve (fig. 4C). 

For a short run, once flow conditions were steady, the 

protective cover was removed and a bucket was simultaneously placed under the water falling off the end of the flume 

and a timer was started. Approximately 4 L of water was 

collected in the bucket and the timer was stopped as was the 

flow in the flume. The water in the bucket was poured through 

a 0.063-mm sieve, set inside a funnel, with the funnel’s spout 

inside a 4-L graduated cylinder to measure the volume. The 

volume was recorded and then poured into a churn splitter 

(14-L, Bel-Arts Products, Wayne, New Jersey). The piston 

was advanced until 50 percent of the soil surface topography 

was again flush with the bed of the flume, the depth below 

the surface of the soil was recorded, the protective cover was 

replaced, and the flow restarted. The process was then repeated 

two more times to give a composite sample consisting of three 

short runs. After the third short run, the sediment in the 0.063-

mm sieve was transferred into pre-weighed aluminum tray, 

dried at 105°C for 24 hr, and reweighed (accuracy 0.001 g) to 

determine the mass of the > 0.063-mm fraction. A subsample 

(400-500 mL) of water and sediment was withdrawn from the 

churn splitter, filtered through two, pre-weighed 0.45-micrometer (mm) membrane filters (HAWP04700, Millipore Ireland 

Ltd., Billerica, Massachusetts), dried at 105°C for one hour, 

and reweighed (after being in a desiccator for 15 min) to determine the mass of the < 0.063-mm fraction. 

If the soil was non-cohesive and could be eroded, then 

the flowing water was used to erode the core down to the next 

desired depth and the process for three short runs described 

above was repeated. If the water could not erode the soil 

material, then the core was advanced by using the piston until 

just below the desired depth, and the core was cut manually 

by using scissors to cut root material and a thin piece of sheet 

metal to slice through the soil material. The soil surface was 

flushed twice with approximately 400 mL surge of water 

lasting 1–2 s, and then extruded a short distance until the 

surface topography was flush with the flume bed. Because the 

soil had been disturbed by cutting, a series of two short runs 

followed by a separate long run was used to measure the soil 

detachment. 

A long run was carried out after collecting separate 

composite samples (> 0.063-mm and < 0.063-mm fractions) 

consisting of two short runs described above. For the long run, 

after removing the protective cover, a 0.063-mm sieve was 

inserted into the flow for 1 min, and at some point during this 

time interval, the bucket was held briefly (3–20 s) under the 

water coming through the sieve to collect ~ 4 L of sediment 

and water in order to determine the discharge and to obtain 

a sample of sediment < 0.063 mm. This sample was poured 

directly into a 4-L churn splitter (4-L, Bel-Arts Products), 

subsampled (~ 400–500 mL), and filtered through another 

set of two, pre-weighed 0.45-mm membrane filters to determine a mass of the < 0.063-mm fraction for the long run. The 

> 0.063-mm fraction, in the 0.063-mm sieve, was processed 

as described above, but was put in a separate aluminum tray 

and labeled as a long run. The long run is thought to be a better measurement of the soil detachment after the disturbance 

caused by cutting the core. 

For the initial experiments, the short runs were physically 

combined with the long runs and then weighed to determine 

the total detachment rate (values in italics in tables 4–6). For 

later experiments, the short and long runs were weighed separately, the detachment rates were calculated separately, and 

then combined mathematically to determine the total detachment rate. To estimate the detachment rates for the initial long 

runs in the initial experiments, correlation equations were 

developed for the > 0.063 mm and the < 0.063 mm fractions 

by plotting the values for long run from the later experiments 

(values in bold font in tables 4–6) versus the mathematically 

combined short and long runs for the same experiments. 

Power laws were found to be the best fit for the >0.063-mm 

data because equal weight was given to small and large values 

that spanned 3–4 orders of magnitude. Linear relations with 

intercept equal to zero were found to best fit for the <0.063-mm 

data because the range of values was less than those for the 

>0.063-mm fraction, and there were numerous zero values 

(essentially below the resolution of the measurement method), 

which the >0.063-mm fraction did not have, and thus, the 

<0.063-mm data could not be fitted to a power law. The 
Laboratory Methods 13

Table 4. Hydrologic parameters and sedimentologic results for soil core samples collected at the Fourmile Canyon South site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Hydraulic Shear stress Non-uniform

unit stream

power

(erg s–1 cm–2)

Water

depth

upstream

(mm)

Water 

depth 

downstream

(mm)

Slope

flume bed

x 10-2

Slope

over core

x 10-2

Total slope 

x 10-2

Discharge

(mL s-1)

Uniform Non-uniform Measured 

(dynes cm–2)

Fourmile Canyon-South Unburned

0.1 3.0 2.4 5.3 0.4 5.7 145 16 22 29 752

0.9 3.0 2.8 5.3 0.1 5.4 140 16 22 19 727

2.0 3.0 2.5 5.3 0.3 5.6 136 16 22 25 709

4.0 3.0 2.2 5.3 0.5 5.8 130 16 22 31 677

6.0 3.0 2.8 5.3 0.1 5.4 126 16 22 19 655

0.1 6.0 4.4 5.3 1.1 6.4 346 31 63 87 1,799

1.6 6.0 4.8 5.3 0.8 6.1 367 31 63 74 1,906

2.5 6.0 4.7 5.3 0.9 6.2 361 31 63 77 1,875

3.9 6.0 4.4 5.3 1.1 6.4 346 31 63 86 1,797

5.9 6.0 4.2 5.3 1.2 6.5 357 31 63 100 1,853

0.1 11.0 11.4 8.8 –0.3 8.5 1,094 95 144 66 9,437

0.4 11.0 10.2 8.8 0.5 9.3 1,111 95 144 160 9,579

1.9 11.0 10.2 8.8 0.5 9.3 1,098 95 144 158 9,466

3.9 11.0 9.8 8.8 0.8 9.6 1,078 95 144 190 9,298

6.0 11.0 9.8 8.8 0.8 9.6 1,089 95 144 192 9,392

0.2 10.5 nm 17.7 nm nm 1,174 182 421 nm 20,357

0.4 10.5 7.9 17.7 1.7 19.4 1,171 182 421 492 20,314

2.0 10.5 8.9 17.7 1.1 18.8 1,186 182 421 355 20,574

4.6 10.5 nm 17.7 nm nm 1,252 182 421 nm 21,712

6.0 10.5 nm 17.7 nm nm 1,230 182 421 nm 21,334

Fourmile Canyon-South Burned—Cluster A

0.4 3.0 nm 5.3 nm nm 152 16 22 nm 791

0.7 3.0 nm 5.3 nm nm 131 16 22 nm 682

2.0 3.0 2.7 5.3 0.2 5.5 145 16 22 21 753

4.0 3.0 2.3 5.3 0.5 5.8 129 16 22 28 671

5.9 3.0 2.7 5.3 0.2 5.5 139 16 22 21 722

0.3 6.0 nm 5.3 nm nm 404 31 63 nm 2,097

0.9 6.0 4.2 5.3 1.2 6.5 345 31 63 96 1,793

2.0 6.0 4.7 5.3 0.9 6.2 354 31 63 75 1,838

4.0 6.0 4.5 5.3 1.0 6.3 349 31 63 83 1,811

5.9 6.0 4.9 5.3 0.7 6.0 350 31 63 66 1,818

0.2 11.0 nm 8.8 nm nm 1,128 95 144 nm 9,730

0.4 11.0 9.7 8.8 0.9 9.7 1,153 95 144 213 9,941

2.0 11.0 10.1 8.8 0.6 9.4 1,139 95 144 172 9,825

3.8 11.0 10.2 8.8 0.5 9.3 1,111 95 144 160 9,585

6.1 11.0 nm 8.8 nm nm 1,149 95 144 nm 9,909

0.2 10.5 nm 17.7 nm nm 1,173 182 421 nm 20,342

0.7 10.5 7.8 17.7 1.8 19.5 1,156 182 421 500 20,045

2.1 10.5 nm 17.7 nm nm 1,191 182 421 nm 20,650

3.9 10.5 10.0 17.7 0.3 18.0 1,170 182 421 229 20,297

5.9 10.5 8.6 17.7 1.3 19.0 1,178 182 421 392 20,427
14 Variations in Soil Detachment Rates after Wildfire

Table 4. Hydrologic parameters and sedimentologic results for soil core samples collected at the Fourmile Canyon South site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Detachment rate x 1,000 Total

short runs

or total

long run

Eroded Particles >0.063 mm short and long runs

>0.063 mm

short runs

>0.063 mm

short runs 

or long run

<0.063 mm

short runs

<0.063 mm

short runs

or long run

Total

short

runs

>2 mm 2–1 mm 1–

0.500 mm

0.500–

0.250 mm

0.250–

0.125 mm

0.125–

0.063 mm <0.063 mm

(g cm–2 s–1) (g cm–2 s–1)

Fourmile Canyon-South Unburned

0.1 0.41 0.41 0.41 0.41 0.83 0.83 0.12 0.073 0.12 0.058 0.028 0.008 0.0

0.9 0.042 0.042 0.042 0.04 0.084 0.084 0.005 0.005 0.011 0.010 0.007 0.003 0.0

2.0 0.33 0.33 0.33 0.33 0.66 0.66 Core sliced @ 18mm.; composite of 3 short runs

4.0 0.68 0.21 0.10 0.020 0.78 0.23 SB 106 and SB107 were combined

6.0 0.75 0.29 0.052 0.001 0.77 0.29 SB 104 and SB105 were combined

0.1 1.43 1.43 0.12 0.12 1.55 1.55 0.028 0.25 0.45 0.38 0.22 0.089 0.010

1.6 0.52 0.52 0.060 0.060 0.58 0.58 0.00 0.10 0.12 0.15 0.11 0.040 0.0

2.5 1.18 1.18 0.08 0.077 1.25 1.25 Core sliced @ 24mm; composite of 3 short runs 

3.9 2.45 0.44 0.25 0.045 2.70 0.49 SB 113 and SB114 were combined

5.9 16.0 2.98 1.23 0.20 17.2 3.17 SB 111 and SB112 were combined

0.1 10.6 10.6 0.96 0.96 11.6 11.6 1.32 1.32 2.60 2.13 1.56 1.48 0.22

0.4 3.22 3.22 0.42 0.42 3.65 3.65 0.16 0.35 0.72 0.81 0.69 0.43 0.054

1.9 2.10 0.18 0.11 0.030 2.21 0.21 SB117 (2 short runs) combined with SB118 (1 long run) 

3.9 10.2 0.15 0.41 0.031 10.6 0.18 SB 119 and SB120 were combined

6.0 11.0 0.89 0.66 0.066 11.7 0.96 SB 121 and SB122 were combined

0.2 3.83 3.83 0.46 0.46 4.29 4.29 0.33 0.56 0.77 0.86 0.71 0.53 0.072

0.4 2.15 2.15 0.34 0.34 2.49 2.49 0.11 0.19 0.47 0.49 0.54 0.30 0.047

2.0 13.3 0.88 0.56 0.10 13.8 1.0 SB125 (2 short runs) combined with SB126 (1 long run) 

4.6 220 220 6.62 6.62 227 227 112 23.4 26.1 26.6 19.2 9.64 3.09

6.0 197 197 13.4 13.4 210 210 87.0 23.4 25.3 28.8 20.1 9.66 2.49

Fourmile Canyon-South Burned—Cluster A

0.4 13.0 13.0 0.46 0.46 13.4 13.4 2.73 2.14 2.92 2.41 1.65 0.89 0.23

0.7 0.74 0.74 0.034 0.034 0.78 0.78 0.088 0.22 0.17 0.13 0.082 0.036 0.008

2.0 0.33 0.045 0.015 0.005 0.35 0.050 SB72 (2 short runs) combined with SB73(1 long run) 

4.0 0.24 0.071 0.028 0.0 0.27 0.071 SB74 (2 short runs) combined with SB75(1 long run) 

5.9 0.50 0.045 0.030 0.010 0.53 0.056 SB76 (2 short runs) combined with SB77(1 long run) 

0.3 39.2 39.2 2.22 2.22 41.4 41.4 3.93 5.56 9.27 9.73 6.21 2.28 2.21

0.9 3.73 3.73 0.13 0.13 3.86 3.86 0.25 0.57 1.01 0.95 0.59 0.18 0.19

2.0 0.53 0.058 0.032 0.0 0.56 0.058 SB80 (2 short runs) combined with SB81(1 long run) 

4.0 1.47 0.11 0.13 0.0 1.59 0.11 SB84 (2 short runs) combined with SB85(1 long run) 

5.9 3.50 0.32 0.26 0.0 3.76 0.32 SB82 (2 short runs) combined with SB83(1 long run) 

0.2 79.8 79.8 3.26 3.26 83.0 83.0 11.4 11.0 21.1 18.7 11.6 5.21 0.66

0.4 6.37 6.37 0.36 0.36 6.73 6.73 1.05 1.19 1.67 1.26 0.73 0.27 0.19

2.0 22.1 22.1 1.21 1.21 23.3 23.3 composite 3 short runs after slicing

3.8 35.5 0.96 1.58 0.13 37.1 1.09 SB89 (2 short runs) combined with SB90(1 long run) 

6.1 58.2 19.6 2.43 1.27 60.6 20.9 SB91 (2 short runs) combined with SB92(1 long run) 

0.2 64.1 64.1 3.71 3.71 67.8 67.8 23.9 9.79 10.6 9.71 6.08 2.84 1.16

0.7 13.6 13.6 0.53 0.53 14.1 14.1 1.44 2.31 3.15 3.31 2.29 0.99 0.12

2.1 45.2 11.0 1.95 0.43 47.2 11.4 SB95 (2 short runs) combined with SB96(1 long run) 

3.9 40.8 2.13 2.34 0.52 43.1 2.65 SB97 (2 short runs) combined with SB98(1 long run) 

5.9 53.3 1.68 2.15 0.38 55.4 2.06 SB99 (2 short runs) combined with SB100(1 long run) 
Laboratory Methods 15

Table 4. Hydrologic parameters and sedimentologic results for soil core samples collected at the Fourmile Canyon South site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Hydraulic Shear stress Non-uniform

unit stream

power

(erg s–1 cm–2)

Water

depth

upstream

(mm)

Water 

depth 

downstream

(mm)

Slope

flume bed

x 10-2

Slope

over core

x 10-2

Total slope 

x 10-2

Discharge

(mL s

Uniform Non-uniform Measured 

(dynes cm–2)

Fourmile Canyon-South Burned—Cluster B

0.5 3.0 nm 5.3 nm nm 149 16 22 nm 773

1.4 3.0 nm 5.3 nm nm 135 16 22 nm 701

2.2 3.0 nm 5.3 nm nm 141 16 22 nm 733

4.1 3.0 nm 5.3 nm nm 145 16 22 nm 754

6.1 3.0 nm 5.3 nm nm 139 16 22 nm 720

0.5 6.0 nm 5.3 nm nm 379 31 63 nm 1,971

1.2 6.0 nm 5.3 nm nm 350 31 63 nm 1,818

2.1 6.0 nm 5.3 nm nm 347 31 63 nm 1,800

3.9 6.0 nm 5.3 nm nm 353 31 63 nm 1,833

6.2 6.0 nm 5.3 nm nm 365 31 63 nm 1,895

0.4 11.0 nm 8.8 nm nm 1,091 95 144 nm 9,405

1.6 11.0 nm 8.8 nm nm 1,081 95 144 nm 9,325

1.9 11.0 nm 8.8 nm nm 1,073 95 144 nm 9,253

 4.0 11.0 nm 8.8 nm nm 1,116 95 144 nm 9,624

 6.1 11.0 nm 8.8 nm nm 1,114 95 144 nm 9,604

 0.4 10.5 nm 17.7 nm nm 1,273 182 421 nm 22,081

 1.0 10.5 nm 17.7 nm nm 1,215 182 421 nm 21,069

 1.8 10.5 nm 17.7 nm nm 1,177 182 421 nm 20,418

 3.9 10.5 nm 17.7 nm nm 1,226 182 421 nm 21,272

 6.0 10.5 nm 17.7 nm nm 1,175 182 421 nm 20,378

Fourmile Canyon-South Burned—Cluster C

 0.1 3.0 2.5 5.3 0.3 5.6 151 16 22 27 783

 0.7 3.0 2.5 5.3 0.3 5.6 148 16 22 26 770

 1.6 3.0 2.8 5.3 0.1 5.4 158 16 22 20 823

 3.8 3.0 2.4 5.3 0.4 5.7 144 16 22 28 750

 5.8 3.0 2.6 5.3 0.3 5.6 152 16 22 24 791

 0.2 6.0 5.4 5.3 0.4 5.7 387 31 63 52 2,011

 0.7 6.0 nm 5.3 nm nm 379 31 63 nm 1,966

 1.2 6.0 5.5 5.3 0.3 5.6 384 31 63 48 1,994

 3.6 6.0 4.9 5.3 0.7 6.0 375 31 63 71 1,946

 5.5 6.0 4.9 5.3 0.7 6.0 377 31 63 71 1,960

 0.2 11.0 10.0 8.8 0.7 9.5 1,121 95 144 179 9,666

 0.8 11.0 9.7 8.8 0.9 9.7 1,115 95 144 206 9,612

 1.5 11.0 9.7 8.8 0.9 9.7 1,088 95 144 201 9,381

 3.8 11.0 10.0 8.8 0.7 9.5 1,080 95 144 173 9,312

 5.5 Large stone filled entire space

 0.3 10.5 nm 17.7 nm nm 1,213 182 421 nm 21,038

 0.7 10.5 9.1 17.7 0.9 18.6 1,276 182 421 352 22,134

 1.7 10.5 8.7 17.7 1.2 18.9 1,216 182 421 391 21,091

 3.6 10.5 8.6 17.7 1.3 19.0 1,219 182 421 406 21,137

 5.7 10.5 nm 17.7 nm nm 1,185 182 421 nm 20,550
16 Variations in Soil Detachment Rates after Wildfire

Table 4. Hydrologic parameters and sedimentologic results for soil core samples collected at the Fourmile Canyon South site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Detachment rate x 1,000 Total

short runs

or total

long run

Eroded Particles >0.063 mm short and long runs

>0.063 mm

short runs

>0.063 mm

short runs 

or long run

<0.063 mm

short runs

<0.063 mm

short runs

or long run

Total

short

runs

>2 mm 2–1 mm 1–

0.500 mm

0.500–

0.250 mm

0.250–

0.125 mm

0.125–

0.063 mm <0.063 mm

(g cm–2 s–1) (g cm–2 s–1)

Fourmile Canyon-South Burned—Cluster B

0.5 52.8 52.8 2.51 2.51 55.3 55.3 7.70 10.6 12.3 10.2 6.80 3.84 1.24

1.4 4.54 4.54 0.26 0.26 4.8 4.80 0.67 0.74 1.04 0.91 0.67 0.39 0.13

2.2 0.45 0.16 0.035 0.022 0.49 0.18 composite 2 short + 1 long runs no cutting mentioned

4.1 1.32 0.48 0.10 0.063 1.42 0.54 composite 2 short + 1 long runs no cutting mentioned

6.1 1.03 0.37 0.11 0.070 1.14 0.44 composite 2 short + 1 long runs no cutting mentioned

0.5 75.9 75.9 2.84 2.84 78.8 78.8 34.6 9.17 9.41 9.66 7.40 3.41 2.26

1.2 10.21 10.21 0.97 0.97 11.2 11.18 0.41 1.16 2.02 2.53 2.33 1.25 0.52

2.1 1.45 0.53 0.14 0.087 1.59 0.61 composite 2 short + 1 long runs no cutting mentioned

3.9 0.81 0.29 0.13 0.085 0.94 0.37 composite 2 short + 1 long runs no cutting mentioned

6.2 4.57 1.74 0.63 0.394 5.20 2.13 composite 2 short + 1 long runs no cutting mentioned

0.4 112 112 4.17 4.17 116 116 23.4 18.6 24.6 21.2 15.3 7.94 0.79

1.6 51.4 51.4 2.26 2.26 53.6 53.6 20.2 6.72 7.12 7.60 5.69 2.75 1.35

1.9 0.59 0.59 0.23 0.23 0.8 0.82 composite 2 short + 1 long runs no cutting mentioned

4.0 71.2 30.2 4.13 2.60 75.4 32.8 composite of 3 short runs; no slicing mentioned

6.1 142 61.9 5.47 3.45 148 65.4 composite of 3 short runs; sliced at 58 mm

0.4 122 122 3.26 3.26 125 125 13.0 27.8 32.2 22.1 17.6 8.18 0.61

1.0 1.72 1.72 0.43 0.43 2.1 2.15 0.55 0.19 0.27 0.31 0.25 0.11 0.05

1.8 0.37 0.13 0.025 0.016 0.39 0.14 composite 2 short + 1 long runs, sliced at ~ 20 mm

3.9 10.2 4.00 0.69 0.44 10.9 4.44 composite 2 short + 1 long runs, sliced at ~ 20 mm

6.0 229 102 8.02 5.05 238 107 composite 2 short + 1 long runs, no slicing mentioned

Fourmile Canyon-South Burned—Cluster C

0.1 3.74 3.74 0.062 0.062 3.81 3.81 1.31 0.91 0.71 0.46 0.25 0.08 0.035

0.7 1.57 1.57 0.10 0.10 1.66 1.66 0.25 0.26 0.32 0.28 0.24 0.17 0.034

1.6 0.93 0.93 0.071 0.071 1.00 1.00 0.24 0.11 0.18 0.19 0.11 0.067 0.016

3.8 0.89 0.39 0.10 0.041 0.99 0.43 0.11 0.018 0.050 0.10 0.081 0.037 0.002

5.8 2.04 0.56 0.11 0.049 2.15 0.61 0.10 0.12 0.074 0.10 0.090 0.044 0.027

0.2 15.3 15.3 0.31 0.31 15.6 15.6 3.27 3.80 3.36 2.45 1.42 0.58 0.38

0.7 8.97 8.97 0.35 0.35 9.32 9.32 2.70 1.03 1.40 1.62 1.23 0.71 0.28

1.2 5.11 0.41 0.45 0.035 5.56 0.44 0.011 0.063 0.076 0.092 0.094 0.060 0.011

3.6 14.7 0.55 0.98 0.057 15.73 0.61 0.029 0.087 0.10 0.14 0.11 0.060 0.027

5.5 9.93 1.38 0.60 0.17 10.53 1.55 0.49 0.15 0.18 0.24 0.21 0.11 0.016

0.2 30.8 30.8 0.64 0.64 31.5 31.5 10.79 5.62 5.95 4.66 2.40 0.68 0.72

0.8 2.10 2.10 0.40 0.40 2.49 2.49 0.08 0.36 0.57 0.55 0.36 0.18 0.00

1.5 3.41 0.18 0.24 0.0 3.65 0.18 0.022 0.019 0.053 0.039 0.031 0.014 0.003

3.8 3.99 0.19 0.26 0.0 4.26 0.19 0.0 0.025 0.036 0.058 0.051 0.021 0.002

5.5 Large stone filled entire space

0.3 56.2 56.2 1.15 1.1 57.3 57.3 14.5 12.9 12.0 8.8 5.3 2.3 0.4

0.7 17.7 17.7 0.60 0.60 18.3 18.3 6.7 2.7 2.5 2.6 1.8 1.1 0.4

1.7 5.18 0.39 0.35 0.0 5.53 0.39 0.0 0.024 0.073 0.12 0.10 0.061 0.007

3.6 10.0 0.74 0.17 0.0 10.20 0.74 0.085 0.050 0.15 0.21 0.15 0.066 0.031

5.7 318 3.53 322 No long run, pebble dislodged creating severe scour
Laboratory Methods 17

Table 5. Hydrologic parameters and sedimentologic results for soil core samples collected at the Fourmile Canyon North site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Hydraulic Shear stress Non-uniform

unit stream

power

(erg s–1 cm–2)

Water

depth

upstream

(mm)

Water

depth

downstream

(mm)

Slope

flume bed

x 10–2

Slope

over core

x 10–2

Total slope

x 10–2

Discharge

(mL s–1)

Uniform Non-uniform Measured

(dynes cm–2)

Fourmile Canyon-North Unburned

0.1 3.0 2.1 5.3 0.6 5.9 156 16 22 41 811

0.7 3.0 2.5 5.3 0.3 5.6 148 16 22 26 769

1.9 3.0 2.3 5.3 0.5 5.8 146 16 22 32 757

3.9 3.0 2.7 5.3 0.2 5.5 147 16 22 22 766

5.8 3.0 2.8 5.3 0.1 5.4 154 16 22 20 800

0.1 6.0 5.7 5.3 0.2 5.5 377 31 63 41 1,958

0.7 6.0 4.4 5.3 1.1 6.4 392 31 63 101 2,038

1.9 6.0 5 5.3 0.7 6.0 382 31 63 68 1,983

4.5 6.0 5.1 5.3 0.6 5.9 411 31 63 68 2,134

6.0 6.0 5.6 5.3 0.3 5.6 400 31 63 46 2,079

0.1 11.0 9.2 8.8 1.2 10.0 1,089 95 144 249 9,388

0.7 11.0 nm 8.8 nm nm 1,076 95 144 nm 9,277

1.8 11.0 9.5 8.8 1.0 9.8 1,069 95 144 216 9,217

4.1 11.0 10.2 8.8 0.5 9.3 1,108 95 144 159 9,556

6.0 11.0 10.2 8.8 0.5 9.3 1,141 95 144 163 9,841

0.1 10.5 8.5 17.7 1.3 19.0 1,182 182 421 407 20,509

0.8 10.5 8.4 17.7 1.4 19.1 1,177 182 421 419 20,410

2.1 10.5 7.9 17.7 1.7 19.4 1,154 182 421 483 20,009

4.1 10.5 7.9 17.7 1.7 19.4 1,157 182 421 485 20,072

5.81 10.5 10.4 17.7 0.1 17.8 1,208 182 421 192 20,957

Fourmile Canyon-North Burned—Cluster A

0.3 3.0 nm 5.3 nm nm 132 16 22 nm 686

0.6 3.0 2.6 5.3 0.3 5.6 136 16 22 23 708

2.4 3.0 2.5 5.3 0.3 5.6 135 16 22 25 699

4.0 3.0 2.6 5.3 0.3 5.6 135 16 22 23 700

6.1 3.0 2.5 5.3 0.3 5.6 134 16 22 25 695

0.6 6.0 nm 5.3 nm nm 378 31 63 nm 1,966

1.3 6.0 5.5 5.3 0.3 5.6 371 31 63 47 1,927

1.9 6.0 5.4 5.3 0.4 5.7 356 31 63 49 1,848

3.9 6.0 5.0 5.3 0.7 6.0 353 31 63 63 1,834

6.0 6.0 5.3 5.3 0.5 5.8 367 31 63 54 1,909

0.2 11.0 nm 8.8 nm nm 1,102 95 144 nm 9,508

0.4 11.0 9.9 8.8 0.7 9.5 1,140 95 144 191 9,833

1.9 11.0 10 8.8 0.7 9.5 1,138 95 144 181 9,812

4.1 11.0 9.8 8.8 0.8 9.6 1,135 95 144 200 9,791

6.5 11.0 nm 8.8 nm nm 1,124 95 144 nm 9,692

0.1 10.5 8.3 17.7 1.5 19.2 1,249 182 421 464 21,657

0.6 10.5 8.1 17.7 1.6 19.3 1,198 182 421 473 20,772

2.0 10.5 8.1 17.7 1.6 19.3 1,209 182 421 478 20,971

4.2 10.5 8.5 17.7 1.3 19.0 1,177 182 421 405 20,417

6.1 10.5 nm 17.7 nm nm 1,204 182 421 nm 20,876
18 Variations in Soil Detachment Rates after Wildfire

Table 5. Hydrologic parameters and sedimentologic results for soil core samples collected at the Fourmile Canyon North site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Detachment rate x 1,000 Total

short runs

or total

long run

(g cm–2 s–1)

Eroded Particles >0.063 mm short and long runs

>0.063 mm

 short runs

>0.063 mm

short runs

or long run

<0.063 mm

short runs

<0.063 mm

short runs

or long run

Total

short

runs

>2 mm 2–

1 mm

1–

0.500 mm

0.500–

0.250 mm

0.250–

0.125 mm

0.125–

0.063 mm <0.063 mm

(g cm–2 s–1) (g cm–2 s–1)

Fourmile Canyon-North Unburned

0.1 0.18 0.18 0.039 0.039 0.21 0.21 0.069 0.029 0.044 0.016 0.013 0.005 0.0

0.7 0.075 0.027 0.0 0.018 0.075 0.045 0.0 0.004 0.008 0.010 0.005 0.0 0.0

1.9 0.11 0.015 0.0 0.0 0.11 0.0 0.000 0.004 0.005 0.003 0.004 0.000 0.000

3.9 0.066 0.087 0.0 0.0 0.07 0.087 0.040 0.0 0.016 0.013 0.013 0.005 0.001

5.8 0.72 0.19 0.064 0.0 0.79 0.19 0.10 0.014 0.017 0.029 0.019 0.007 0.002

0.1 0.018 0.018 0.0 0.0 0.018 0.018 0.003 0.002 0.004 0.003 0.003 0.002 0.001

0.7 1.33 0.056 0.075 0.0 1.41 0.056 0.002 0.005 0.011 0.018 0.013 0.007 0.0

1.9 0.69 0.060 0.044 0.0 0.73 0.060 0.0 0.019 0.021 0.013 0.008 0.0 0.0

4.5 11.2 1.26 0.43 0.065 11.67 1.33 0.20 0.20 0.28 0.29 0.19 0.071 0.027

6.0 17.4 3.93 1.19 0.16 18.62 4.1 0.78 0.68 0.72 0.83 0.63 0.26 0.04

0.1 1.86 1.86 0.21 0.21 2.07 2.07 0.90 0.39 0.38 0.12 0.067 0.0 0.0

0.7 0.92 0.056 0.14 0.0 1.06 0.056 0.004 0.009 0.016 0.016 0.011 0.0 0.0

1.8 12.8 1.33 0.26 0.052 13.10 1.38 0.62 0.15 0.16 0.18 0.14 0.065 0.009

4.1 67.6 16.1 2.09 0.22 69.74 16.3 6.12 1.82 2.16 2.69 2.11 0.96 0.22

6.0 74.2 74.2 3.42 3.42 77.6 77.6 25.5 10.2 10.0 12.2 9.71 4.94 1.63

0.1 1.09 1.09 0.23 0.23 1.32 1.32 0.46 0.16 0.34 0.088 0.041 0.0 0.0

0.8 1.06 0.12 0.032 0.017 1.09 0.14 0.0 0.019 0.027 0.032 0.026 0.013 0.0

2.1 16.0 0.88 0.95 0.037 16.9 0.92 0.23 0.11 0.14 0.17 0.14 0.061 0.031

4.1 114 14.6 4.04 0.54 118 15.2 4.78 2.28 2.32 2.45 1.72 0.66 0.42

5.81 168 168 7.67 7.67 176 176 54.1 23.2 24.6 29.4 22.1 9.97 4.91

Fourmile Canyon-North Burned—Cluster A

0.3 2.50 2.50 0.54 0.54 3.03 3.03 0.47 0.36 0.38 0.41 0.37 0.28 0.23

0.6 1.01 1.01 0.16 0.16 1.17 1.17 0.20 0.16 0.16 0.16 0.16 0.13 0.04

2.4 0.12 0.027 0.0 0.0 0.12 0.027 0.0 0.0 0.009 0.009 0.007 0.001 0.0

4.0 0.23 0.048 0.003 0.0 0.23 0.048 0.00 0.00 0.02 0.01 0.01 0.00 0.00

6.1 0.35 0.067 0.020 0.0 0.37 0.067 0.0 0.010 0.013 0.022 0.015 0.006 0.001

0.6 17.2 17.2 3.10 3.10 20.3 20.3 1.17 1.78 3.15 3.73 3.45 2.08 1.81

1.3 8.01 8.01 0.43 0.43 8.44 8.44 1.46 1.63 1.63 1.64 1.18 0.43 0.037

1.9 4.85 4.85 0.24 0.24 5.09 5.09 0.63 0.95 0.89 0.86 0.70 0.48 0.34

3.9 3.51 0.96 0.16 0.0 3.67 0.96 0.28 0.14 0.17 0.17 0.11 0.05 0.04

6.0 13.0 0.98 0.65 0.042 13.65 1.02 0.17 0.23 0.20 0.17 0.12 0.062 0.031

0.2 16.4 16.4 1.19 1.19 17.6 17.6 5.52 3.81 2.08 1.65 1.44 0.89 0.99

0.4 7.75 7.75 0.12 0.12 7.87 7.87 3.08 1.83 1.16 0.70 0.52 0.34 0.11

1.9 1.48 0.026 0.0 0.19 1.48 0.21 0.00 0.00 0.008 0.010 0.008 0.00 0.00

4.1 1.13 0.56 0.06 0.0 1.19 0.56 0.32 0.038 0.044 0.068 0.065 0.026 0.004

6.5 100 nm 6.66 nm 107 nm only 1 short run then bottomed out

0.1 8.10 8.10 0.48 0.48 8.58 8.58 1.49 1.79 1.59 1.29 0.97 0.51 0.46

0.6 3.14 0.60 0.20 0.0 3.34 0.60 0.40 0.05 0.05 0.04 0.03 0.02 0.01

2.0 1.40 0.040 0.0 0.0 1.40 0.04 0.0 0.002 0.015 0.014 0.008 0.0 0.0

4.2 1.92 0.37 0.07 0.0 1.99 0.37 0.093 0.067 0.064 0.070 0.053 0.018 0.008

6.1 105 105 3.45 3.45 108 108 only 2 short runs then bottomed out
Laboratory Methods 19

Table 5. Hydrologic parameters and sedimentologic results for soil core samples collected at the Fourmile Canyon North site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Hydraulic Shear stress Non-uniform

unit stream

power

(erg s–1 cm–2)

Water

depth

upstream

(mm)

Water

depth

downstream

(mm)

Slope

flume bed

x 10–2

Slope

over core

x 10–2

Total slope

x 10–2

Discharge

(mL s–1)

Uniform Non-uniform Measured

(dynes cm–2)

Fourmile Canyon-North Burned—Cluster B

0.1 3.0 2.5 5.3 0.3 5.6 149 16 22 26 771

0.7 3.0 2.1 5.3 0.6 5.9 149 16 22 39 776

1.4 3.0 2.5 5.3 0.3 5.6 143 16 22 26 740

3.5 3.0 2.6 5.3 0.3 5.6 146 16 22 24 760

5.5 3.0 2.7 5.3 0.2 5.5 148 16 22 22 770

0.3 6.0 nm 5.3 nm nm 389 31 63 nm 2,018

0.6 6.0 5.1 5.3 0.6 5.9 387 31 63 64 2,008

1.7 6.0 4.9 5.3 0.7 6.0 393 31 63 74 2,044

3.9 6.0 5.4 5.3 0.4 5.7 389 31 63 52 2,021

5.9 6.0 5.7 5.3 0.2 5.5 401 31 63 42 2,084

0.3 11.0 9.5 8.8 1.0 9.8 1,129 95 144 228 9,734

0.7 11.0 9.7 8.8 0.9 9.7 1,104 95 144 204 9,524

1.6 11.0 10.4 8.8 0.4 9.2 1,094 95 144 141 9,435

3.7 11.0 10.8 8.8 0.1 8.9 1,067 95 144 109 9,198

5.1 11.0 10.8 8.8 0.1 8.9 1,089 95 144 110 9,389

0.2 10.5 9.2 17.7 0.9 18.6 1,211 182 421 324 21,009

0.7 10.5 8.5 17.7 1.3 19.0 1,212 182 421 418 21,025

1.6 10.5 8.3 17.7 1.5 19.2 1,239 182 421 459 21,488

3.7 10.5 8.5 17.7 1.3 19.0 1,200 182 421 414 20,811

5.7 10.5 nm 17.7 nm nm 1,187 182 421 nm 20,589

Fourmile Canyon-North Burned—Cluster C

0.3 3.0 nm 5.3 nm nm 151 16 22 nm 785

0.9 3.0 nm 5.3 nm nm 149 16 22 nm 772

1.9 3.0 nm 5.3 nm nm 141 16 22 nm 733

4.0 3.0 nm 5.3 nm nm 142 16 22 nm 736

5.7 3.0 nm 5.3 nm nm 133 16 22 nm 691

0.2 6.0 nm 5.3 nm nm 337 31 63 nm 1,753

0.8 6.0 nm 5.3 nm nm 345 31 63 nm 1,793

1.8 6.0 nm 5.3 nm nm 338 31 63 nm 1,753

3.8 6.0 nm 5.3 nm nm 351 31 63 nm 1,825

5.6 6.0 nm 5.3 nm nm 342 31 63 nm 1,774

0.4 11.0 nm 8.8 nm nm 1,116 95 144 nm 9,623

0.7 11.0 nm 8.8 nm nm 1,075 95 144 nm 9,270

1.9 11.0 nm 8.8 nm nm 1,099 95 144 nm 9,474

3.4 11.0 nm 8.8 nm nm 1,078 95 144 nm 9,298

5.7 11.0 nm 8.8 nm nm 1,100 95 144 nm 9,482

0.2 10.5 nm 17.7 nm nm 1,211 182 421 nm 21,004

0.6 10.5 nm 17.7 nm nm 1,145 182 421 nm 19,867

1.8 10.5 nm 17.7 nm nm 1,235 182 421 nm 21,421

4.0 10.5 nm 17.7 nm nm 1,202 182 421 nm 20,844

5.9 10.5 nm 17.7 nm nm 1,236 182 421 nm 21,446
20 Variations in Soil Detachment Rates after Wildfire

Table 5. Hydrologic parameters and sedimentologic results for soil core samples collected at the Fourmile Canyon North site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Detachment rate x 1,000 Total

short runs

or total

long run

(g cm–2 s–1)

Eroded Particles >0.063 mm short and long runs

>0.063 mm

 short runs

>0.063 mm

short runs

or long run

<0.063 mm

short runs

<0.063 mm

short runs

or long run

Total

short

runs

>2 mm 2–

1 mm

1–

0.500 mm

0.500–

0.250 mm

0.250–

0.125 mm

0.125–

0.063 mm <0.063 mm

(g cm–2 s–1) (g cm–2 s–1)

Fourmile Canyon-North Burned—Cluster B

0.1 1.56 1.56 0.12 0.12 1.68 1.68 0.25 0.21 0.25 0.33 0.34 0.17 0.01

0.7 1.63 1.63 0.13 0.13 1.76 1.76 0.30 0.16 0.21 0.32 0.35 0.16 0.13

1.4 0.48 0.082 0.092 0.0 0.57 0.082 0.0 0.012 0.015 0.020 0.023 0.012 0.0

3.5 1.34 0.38 0.11 0.003 1.44 0.38 0.119 0.032 0.059 0.076 0.065 0.023 0.003

5.5 3.64 0.58 0.23 0.025 3.87 0.61 0.034 0.066 0.11 0.15 0.14 0.068 0.010

0.3 13.4 13.4 0.98 0.98 14.4 14.4 2.61 1.88 2.27 2.64 2.48 1.36 0.19

0.6 2.34 2.34 0.41 0.41 2.75 2.75 0.26 0.27 0.36 0.51 0.54 0.35 0.05

1.7 1.13 0.082 0.26 0.13 1.39 0.22 0.0 0.006 0.016 0.023 0.023 0.010 0.005

3.9 2.95 0.26 0.33 0.060 3.28 0.32 0.038 0.025 0.051 0.063 0.053 0.022 0.008

5.9 15.4 1.53 1.04 0.27 16.44 1.81 0.20 0.21 0.27 0.34 0.30 0.13 0.078

0.3 17.6 17.6 1.18 1.18 18.7 18.7 4.04 2.45 2.80 3.50 3.05 1.49 0.21

0.7 10.0 10.0 0.57 0.57 10.6 10.6 6.15 0.46 0.67 1.06 0.98 0.24 0.48

1.6 14.3 14.3 0.54 0.54 14.8 14.8 3.02 1.33 2.25 3.39 2.75 1.21 0.35

3.7 25.7 2.90 1.52 0.34 27.2 3.24 0.72 0.34 0.40 0.60 0.53 0.26 0.05

5.1 54.1 4.95 3.46 0.55 57.5 5.49 1.87 0.49 0.60 0.80 0.75 0.37 0.061

0.2 32.8 32.8 1.58 1.58 34.4 34.4 13.5 3.35 3.88 4.71 4.44 2.54 0.43

0.7 11.6 11.6 0.86 0.86 12.5 12.5 4.01 1.21 1.60 1.89 1.58 0.71 0.65

1.6 6.26 6.26 0.42 0.42 6.68 6.68 0.37 0.67 1.09 1.55 1.44 0.61 0.54

3.7 31.7 3.31 2.51 0.41 34.2 3.72 0.48 0.33 0.61 0.77 0.65 0.34 0.14

5.7 164 nm 10.3 nm 174.3 nm only 2 short runs; no long run; no information on slicing

Fourmile Canyon-North Burned—Cluster C

0.3 12.2 12.2 0.80 0.80 13.0 13.0 2.44 2.01 2.19 2.20 1.77 1.04 0.54

0.9 0.59 0.59 0.088 0.088 0.68 0.68 0.03 0.09 0.12 0.14 0.12 0.06 0.02

1.9 0.060 0.022 0.0 0.00 0.060 0.022 composite of 2 short runs + 1 long run

4.0 0.14 0.051 0.006 0.001 0.14 0.05 composite of 2 short runs + 1 long run

5.7 0.63 0.25 0.051 0.011 0.68 0.26 composite of 2 short runs + 1 long run

0.2 16.5 16.5 1.73 1.73 18.3 18.3 2.71 3.31 3.09 2.92 2.34 1.29 0.88

0.8 13.1 13.1 1.03 1.03 14.1 14.1 3.31 2.08 2.21 2.19 1.77 0.90 0.68

1.8 0.29 0.11 0.044 0.010 0.34 0.12 composite of 2 short runs + 1 long run

3.8 0.27 0.11 0.00 0.001 0.28 0.11 composite of 2 short runs + 1 long run

5.6 1.65 0.68 0.16 0.035 1.81 0.72 composite of 2 short runs + 1 long run

0.4 66.2 66.2 3.21 3.21 69.4 69.4 8.71 12.0 14.7 13.0 9.49 5.99 2.26

0.7 0.97 0.97 0.77 0.77 1.7 1.7 0.04 0.11 0.20 0.22 0.22 0.15 0.04

1.9 2.98 1.26 0.24 0.051 3.22 1.31 composite of 2 short runs + 1 long run

3.4 3.87 1.65 0.40 0.085 4.27 1.74 composite of 2 short runs + 1 long run

5.7 1.95 0.81 1.25 0.27 3.20 1.08 composite of 2 short runs + 1 long run

0.2 73.4 73.4 6.30 6.30 79.7 79.7 11.3 10.1 12.0 14.5 13.0 7.31 5.24

0.6 1.73 1.73 0.86 0.86 2.59 2.59 0.35 0.21 0.23 0.32 0.36 0.21 0.05

1.8 1.15 0.47 0.41 0.088 1.56 0.56 composite of 2 short runs + 1 long run

4.0 2.17 0.91 0.88 0.19 3.05 1.10 composite of 2 short runs + 1 long run

5.9 2.91 1.23 1.19 0.26 4.11 1.49 composite of 2 short runs + 1 long run

1

Not cut, no long run.
Laboratory Methods 21

Table 6. Hydrologic parameters and sedimentologic results for soil core samples collected at the Pozo South site.

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Hydraulic Shear stress Non-uniform

unit stream

power

(erg s–1 cm–2)

Water

depth

upstream

(mm)

Water

depth

downstream

(mm)

Slope

flume bed

x 10–2

Slope

over core

x 10–2

Total slope

x 10–2

Discharge

(mL s–1)

Uniform Non-uniform Measured

(dynes cm–2)

Pozo South Unburned

0.1 3.0 2.6 5.3 0.3 5.6 135 16 22 23 699

1.4 3.0 2.5 5.3 0.3 5.6 133 16 22 25 693

2.3 3.0 2.7 5.3 0.2 5.5 134 16 22 21 696

4.0 3.0 2.7 5.3 0.2 5.5 133 16 22 21 691

6.0 3.0 2.9 5.3 0.1 5.4 139 16 22 17 723

0.2 6.0 5.2 5.3 0.5 5.8 385 31 63 60 2,002

0.5 6.0 4.8 5.3 0.8 6.1 370 31 63 76 1,922

2.0 6.0 5.2 5.3 0.5 5.8 374 31 63 59 1,944

4.0 6.0 5.0 5.3 0.7 6.0 373 31 63 65 1,935

5.9 6.0 5.3 5.3 0.5 5.8 378 31 63 57 1,966

0.4 11.0 11.1 8.8 –0.1 8.7 1,151 95 144 86 9,922

0.8 11.0 11.0 8.8 0.0 8.8 1,160 95 144 97 10,000

2.3 11.0 nm 8.8 nm nm 1,104 95 144 nm 9,525

4.4 11.0 nm 8.8 nm nm 1,133 95 144 nm 9,771

6.3 11.0 nm 8.8 nm nm 1,169 95 144 nm 10,081

0.4 10.5 nm 17.7 nm nm 1,257 182 421 nm 21,804

0.8 10.5 8.9 17.7 1.1 18.8 1,203 182 421 363 20,867

2.1 10.5 9.3 17.7 0.8 18.5 1,251 182 421 322 21,706

4.3 10.5 8.6 17.7 1.3 19.0 1,234 182 421 415 21,411

6.0 10.5 7.7 17.7 1.9 19.6 1,243 182 421 568 21,555

Pozo South Burned—Cluster A

0.4 3.0 nm 5.3 nm nm 149 16 22 nm 773

0.9 3.0 nm 5.3 nm nm 135 16 22 nm 701

1.9 3.0 nm 5.3 nm nm 154 16 22 nm 799

3.9 3.0 nm 5.3 nm nm 142 16 22 nm 737

5.8 3.0 nm 5.3 nm nm 148 16 22 nm 768

0.4 6.0 nm 5.3 nm nm 379 31 63 nm 1,967

1.2 6.0 nm 5.3 nm nm 354 31 63 nm 1,838

2.3 6.0 nm 5.3 nm nm 359 31 63 nm 1,866

3.8 6.0 nm 5.3 nm nm 356 31 63 nm 1,852

5.9 6.0 nm 5.3 nm nm 362 31 63 nm 1,881

0.2 11.0 nm 8.8 nm nm 1,132 95 144 nm 9,764

0.9 11.0 nm 8.8 nm nm 1,098 95 144 nm 9,472

1.9 11.0 nm 8.8 nm nm 1,124 95 144 nm 9,694

3.9 11.0 nm 8.8 nm nm 1,070 95 144 nm 9,229

5.8 11.0 nm 8.8 nm nm 1,110 95 144 nm 9,569

0.5 10.5 nm 17.7 nm nm 1,176 182 421 nm 20,402

1.3 10.5 nm 17.7 nm nm 1,218 182 421 nm 21,125

1.8 10.5 nm 17.7 nm nm 1,159 182 421 nm 20,100

3.8 10.5 nm 17.7 nm nm 1,164 182 421 nm 20,188

6.0 10.5 nm 17.7 nm nm 1,182 182 421 nm 20,509
22 Variations in Soil Detachment Rates after Wildfire

Table 6. Hydrologic parameters and sedimentologic results for soil core samples collected at the Pozo South site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Detachment rate x 1,000 Total

short runs

or long run

(g cm–2 s–1)

Eroded Particles >0.063 mm short and long runs

>0.063 mm

 short runs

>0.063 mm

short runs

or long run

<0.063 mm

short runs

<0.063 mm

short runs

or long run

Total

short

runs

>2 mm 2–1 mm 1–

0.500 mm

0.500–

0.250 mm

0.250–

0.125 mm

0.125–

0.063 mm <0.063 mm

(g cm–2 s–1) (g cm–2 s–1)

Pozo South Unburned

0.1 1.23 1.23 0.12 0.12 1.35 1.35 0.39 0.18 0.21 0.17 0.13 0.080 0.073

1.4 0.081 0.040 0.018 0.0 0.10 0.040 0.0 0.0 0.010 0.008 0.015 0.007 0.00

2.3 0.33 0.081 0.031 0.0 0.36 0.08 0.0 0.013 0.012 0.021 0.023 0.011 0.003

4.0 0.24 0.17 0.051 0.008 0.29 0.17 0.034 0.032 0.018 0.029 0.034 0.016 0.00

6.0 0.28 0.51 0.043 0.022 0.33 0.53 0.17 0.054 0.061 0.071 0.080 0.019 0.050

0.2 13.4 13.4 0.79 0.79 14.1 14.1 7.40 1.13 1.33 1.30 1.17 0.84 0.19

0.5 3.52 3.52 0.19 0.19 3.70 3.70 1.89 0.21 0.31 0.43 0.37 0.068 0.23

2.0 2.51 0.24 0.24 0.008 2.76 0.24 0.038 0.037 0.031 0.047 0.048 0.008 0.026

4.0 3.30 0.34 0.14 0.0 3.44 0.34 0.0 0.030 0.057 0.086 0.096 0.018 0.053

5.9 7.78 0.59 0.91 0.12 8.68 0.71 0.050 0.083 0.083 0.12 0.15 0.093 0.011

0.4 48.5 48.5 1.80 1.80 50.3 50.3 15.0 9.08 11.9 5.27 3.82 2.74 0.68

0.8 14.3 14.3 0.46 0.46 14.7 14.7 4.67 2.80 3.20 1.70 1.01 0.23 0.64

2.3 87.1 5.38 1.47 0.28 88.5 5.66 0.38 0.38 0.90 1.40 1.45 0.73 0.12

4.4 110 57.6 5.52 1.97 115 59.6 24.8 3.55 4.29 7.35 9.66 6.65 1.31

6.3 55.3 22.8 7.89 2.71 63.2 25.5 5.94 3.13 2.84 3.27 3.46 3.10 1.00

0.4 72.9 72.9 4.75 4.75 77.6 77.6 32.7 5.51 7.68 8.91 9.39 6.67 2.04

0.8 26.2 26.2 2.59 2.59 28.8 28.8 7.15 2.39 3.21 4.30 4.33 2.47 2.34

2.1 39.8 39.8 2.05 2.05 41.9 41.9 8.69 4.43 5.78 7.11 6.85 3.60 3.36

4.3 54.4 54.4 3.97 3.97 58.3 58.3 17.7 6.43 6.81 8.20 7.63 4.96 2.65

6.0 24.0 24.0 2.14 2.14 26.1 26.1 6.89 2.75 2.96 3.84 4.27 2.73 0.52

Pozo South Burned—Cluster A

0.4 12.7 12.7 0.94 0.94 13.6 13.6 3.40 1.34 2.20 2.16 1.62 0.94 1.02

0.9 2.77 2.77 0.22 0.22 3.00 3.00 0.72 0.36 0.46 0.46 0.36 0.22 0.18

1.9 0.30 0.12 0.012 0.004 0.32 0.13 composite of 2 short runs + long run

3.9 0.15 0.061 0.059 0.020 0.21 0.081 composite of 2 short runs + long run

5.8 0.37 0.15 0.15 0.051 0.52 0.20 composite of 2 short runs + long run

0.4 53.8 53.8 3.7 3.7 57.5 57.5 12.3 7.35 9.16 9.44 8.75 5.22 1.65

1.2 27.9 27.9 1.7 1.7 29.6 29.6 5.92 2.79 4.53 4.91 5.16 3.23 1.24

2.3 12.6 5.27 0.88 0.29 13.5 5.56 composite of 2 short runs + long run

3.8 0.67 0.27 0.15 0.049 0.81 0.32 composite of 2 short runs + long run

5.9 0.71 0.29 0.37 0.12 1.08 0.41 composite of 2 short runs + long run

0.2 75.9 75.9 4.39 4.39 80.2 80.2 30.0 11.17 10.47 8.19 7.10 4.04 4.94

0.9 3.64 3.64 1.03 1.03 4.7 4.7 1.06 0.57 0.64 0.46 0.45 0.31 0.13

1.9 0.47 0.19 0.010 0.003 0.48 0.19 composite of 3 short runs

3.9 0.85 0.35 1.12 0.37 1.97 0.72 composite of 2 short runs + long run

5.8 1.45 0.59 1.94 0.64 3.39 1.24 composite of 2 short runs + long run

0.5 147 147 11.11 11.11 158 158 42.0 21.5 24.6 21.2 17.8 11.2 9.01

1.3 26.8 26.8 1.30 1.30 28.1 28.1 8.37 3.37 4.92 3.91 3.37 2.03 0.80

1.8 2.74 0.031 0.14 0.091 2.88 0.12 SB64 was combined with SB 65

3.8 2.54 0.11 0.37 0.34 2.91 0.45 SB66 was combined with SB 67

6.0 7.18 1.23 2.52 0.086 9.70 1.31 SB68 was combined with SB 69
Laboratory Methods 23

Table 6. Hydrologic parameters and sedimentologic results for soil core samples collected at the Pozo South site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Hydraulic Shear stress Non-uniform

unit stream

power

(erg s–1 cm–2)

Water

depth

upstream

(mm)

Water

depth

downstream

(mm)

Slope

flume bed

x 10–2

Slope

over core

x 10–2

Total slope

x 10–2

Discharge

(mL s–1)

Uniform Non-uniform Measured

(dynes cm–2)

Pozo South Burned—Cluster B

0.1 3.0 nm 5.3 nm nm 135 16 22 nm 700

0.6 3.0 nm 5.3 nm nm 139 16 22 nm 721

1.9 3.0 nm 5.3 nm nm 134 16 22 nm 693

3.9 3.0 nm 5.3 nm nm 154 16 22 nm 798

5.9 3.0 nm 5.3 nm nm 135 16 22 nm 701

0.3 6.0 nm 5.3 nm nm 372 31 63 nm 1,935

0.7 6.0 nm 5.3 nm nm 366 31 63 nm 1,902

1.8 6.0 nm 5.3 nm nm 365 31 63 nm 1,895

3.9 6.0 nm 5.3 nm nm 357 31 63 nm 1,854

5.9 6.0 nm 5.3 nm nm 362 31 63 nm 1,881

0.2 11.0 nm 8.8 nm nm 1,120 95 144 nm 9,662

0.4 11.0 nm 8.8 nm nm 1,118 95 144 nm 9,640

2.1 11.0 nm 8.8 nm nm 1,095 95 144 nm 9,443

4.1 11.0 nm 8.8 nm nm 1,086 95 144 nm 9,362

6.0 11.0 nm 8.8 nm nm 1,139 95 144 nm 9,826

0.3 10.5 nm 17.7 nm nm 1,206 182 421 nm 20,924

0.7 10.5 nm 17.7 nm nm 1,230 182 421 nm 21,331

2.2 10.5 nm 17.7 nm nm 1,246 182 421 nm 21,618

4.4 10.5 nm 17.7 nm nm 1,277 182 421 nm 22,144

6.3 10.5 nm 17.7 nm nm 1,184 182 421 nm 20,534

Pozo South Burned—Cluster C

0.1 3.0 1.9 5.3 0.7 6.0 142 16 22 43 736

1.0 3.0 2.5 5.3 0.3 5.6 139 16 22 24 720

2.1 3.0 2.6 5.3 0.2 5.5 147 16 22 23 765

3.1 3.0 2.5 5.3 0.3 5.6 148 16 22 25 769

5.8 3.0 2.6 5.3 0.3 5.6 149 16 22 24 773

0.2 6.0 5.1 5.3 0.6 5.9 404 31 63 65 2,096

1.2 6.0 5.1 5.3 0.6 5.9 369 31 63 62 1,917

2.5 6.0 5.2 5.3 0.6 5.9 375 31 63 60 1,946

4.0 6.0 5.5 5.3 0.4 5.7 371 31 63 48 1,925

5.8 6.0 6.2 5.3 -0.1 5.2 388 31 63 25 2,013

0.3 11.0 nm 8.8 nm nm 1,116 95 144 nm 9,627

0.6 11.0 9.7 8.8 0.8 9.6 1,115 95 144 202 9,614

1.6 11.0 9.8 8.8 0.8 9.6 1,080 95 144 187 9,317

3.8 11.0 10.2 8.8 0.5 9.3 1,100 95 144 157 9,483

5.9 11.0 10.2 8.8 0.5 9.3 1,086 95 144 154 9,368

0.2 10.5 nm 17.7 nm nm 1,212 182 421 nm 21,024

0.4 10.5 8.1 17.7 1.6 19.3 1,209 182 421 479 20,967

1.7 10.5 8.7 17.7 1.2 18.9 1,214 182 421 388 21,062

3.9 10.5 8.3 17.7 1.5 19.2 1,183 182 421 435 20,521

5.9 10.5 8.3 17.7 1.5 19.2 1,174 182 421 439 20,367
24 Variations in Soil Detachment Rates after Wildfire

Table 6. Hydrologic parameters and sedimentologic results for soil core samples collected at the Pozo South site.—Continued

[Diameter of core = 4.7 cm; width of flume = 10 cm; distance between upstream and downstream water depths = 14.9 cm; distance downstream was only 

measured on 3rd run at a given core depth after a long run; italics, short runs were combined with a long run and then weighed; bold, long run; bold italics, long 

run was estimated from regression equations 6–11 given in the text; s, seconds; cm, centimeter; mm, millimeter; cm–2, square centimeter; mL, milliliter; g, gram; 

>, greater than; < less than; SB, sample code; nm, not measured]

Core

depth

(cm)

Detachment rate x 1,000 Total

short runs

or long run

(g cm–2 s–1)

Eroded Particles >0.063 mm short and long runs

>0.063 mm

 short runs

>0.063 mm

short runs

or long run

<0.063 mm

short runs

<0.063 mm

short runs

or long run

Total

short

runs

>2 mm 2–1 mm 1–

0.500 mm

0.500–

0.250 mm

0.250–

0.125 mm

0.125–

0.063 mm <0.063 mm

(g cm–2 s–1) (g cm–2 s–1)

Pozo South Burned—Cluster B

0.1 0.41 0.41 0.030 0.030 0.44 0.44 0.11 0.10 0.070 0.050 0.036 0.019 0.023

0.6 0.24 0.24 0.016 0.016 0.26 0.26 0.009 0.053 0.077 0.048 0.029 0.003 0.022

1.9 0.35 0.12 0.009 0.030 0.36 0.15 0.0 0.013 0.029 0.034 0.029 0.012 0.002

3.9 0.36 0.27 0.056 0.027 0.42 0.30 0.15 0.030 0.028 0.024 0.024 0.013 0.0

5.9 0.58 0.14 0.16 0.025 0.75 0.16 0.0 0.024 0.027 0.036 0.032 0.010 0.008

0.3 16.8 16.8 1.20 1.20 18.0 18.0 5.69 2.17 2.68 2.38 1.82 1.17 0.87

0.7 2.86 2.86 0.23 0.23 3.10 3.10 0.49 0.47 0.55 0.53 0.39 0.24 0.15

1.8 0.44 0.082 0.067 0.022 0.50 0.10 0.000 0.022 0.014 0.021 0.019 0.002 0.004

3.9 1.79 0.18 0.44 0.10 2.23 0.28 0.012 0.024 0.033 0.038 0.037 0.009 0.031

5.9 2.90 0.51 1.07 0.18 3.97 0.69 0.11 0.044 0.055 0.10 0.111 0.084 0.010

0.2 29.7 29.7 1.85 1.85 31.6 31.6 8.35 3.53 5.14 4.90 3.76 2.16 1.88

0.4 4.99 4.99 0.32 0.32 5.31 5.31 1.34 0.50 0.98 0.93 0.71 0.41 0.12

2.1 3.32 0.092 0.17 0.0 3.49 0.092 0.000 0.027 0.022 0.021 0.016 0.006 0.000

4.1 23.6 0.29 1.38 0.0 25.0 0.29 0.0 0.030 0.065 0.071 0.068 0.044 0.008

6.0 4.92 0.43 1.44 0.10 6.36 0.53 0.045 0.052 0.067 0.090 0.093 0.059 0.023

0.3 35.8 35.8 1.69 1.69 37.5 37.5 9.06 6.10 6.22 5.39 4.35 3.00 1.69

0.7 12.6 12.6 0.56 0.56 13.2 13.2 3.59 1.73 2.06 2.06 1.83 1.00 0.37

2.2 6.40 0.65 0.43 0.25 6.84 0.89 0.24 0.093 0.064 0.085 0.085 0.037 0.044

4.4 30.9 1.72 4.72 0.49 35.6 2.21 0.20 0.18 0.26 0.31 0.34 0.24 0.19

6.3 32.5 5.92 5.52 0.82 38.0 6.73 1.80 0.49 0.70 0.90 1.02 0.82 0.19

Pozo South Burned—Cluster C

0.1 0.75 0.75 0.037 0.037 0.79 0.79 0.23 0.13 0.12 0.10 0.080 0.053 0.034

1.0 0.23 0.065 0.020 0.024 0.25 0.089 0.0 0.010 0.007 0.014 0.015 0.007 0.012

2.1 0.49 0.044 0.034 0.013 0.53 0.057 0.0 0.0 0.010 0.018 0.016 0.0 0.0

3.1 0.37 0.11 0.057 0.0 0.42 0.11 0.0 0.009 0.024 0.025 0.027 0.007 0.021

5.8 1.35 0.19 0.19 0.017 1.55 0.21 0.020 0.019 0.026 0.037 0.045 0.027 0.017

0.2 10.3 10.3 0.29 0.29 10.62 10.6 6.25 1.01 0.76 0.77 0.87 0.59 0.092

1.2 1.06 0.059 0.16 0.008 1.22 0.067 0.0 0.010 0.010 0.010 0.015 0.006 0.004

2.5 1.68 0.78 0.22 0.057 1.90 0.83 0.35 0.075 0.092 0.084 0.086 0.039 0.048

4.0 2.69 0.90 0.49 0.16 3.18 1.06 0.51 0.066 0.063 0.078 0.10 0.078 0.011

5.8 3.17 0.63 0.85 0.20 4.02 0.83 0.076 0.11 0.087 0.114 0.132 0.092 0.015

0.3 60.1 60.1 3.70 3.70 63.8 63.8 35.6 4.44 5.09 4.71 5.06 3.92 1.32

0.6 17.5 17.5 1.21 1.21 18.7 18.7 8.62 0.85 1.81 2.06 2.01 1.42 0.78

1.6 5.77 0.65 0.84 0.0 6.61 0.65 0.056 0.085 0.13 0.13 0.14 0.095 0.013

3.8 26.1 0.87 1.79 0.16 27.9 1.03 0.16 0.14 0.15 0.13 0.14 0.11 0.038

5.9 11.7 0.93 1.17 0.24 12.9 1.17 0.28 0.082 0.13 0.14 0.14 0.09 0.05

0.2 39.1 39.1 1.45 1.45 40.5 40.5 13.3 4.60 5.29 4.87 4.98 3.99 2.00

0.4 13.1 13.1 1.11 1.11 14.2 14.2 4.62 1.41 1.74 1.69 1.67 0.81 1.13

1.7 10.7 0.60 0.75 0.20 11.4 0.81 0.10 0.068 0.10 0.11 0.11 0.080 0.040

3.9 17.7 1.81 1.73 0.31 19.5 2.12 0.70 0.13 0.21 0.27 0.29 0.19 0.027

5.9 35.3 2.74 3.95 0.88 39.2 3.63 0.90 0.26 0.35 0.41 0.44 0.31 0.063
Results and Discussion 25

following correlation equations were then used to estimate 

the detachment rate for the long runs for the initial experiments (values in bold italics in tables 4–6). For >0.063-mm 

size fraction, the equations are:

 Fourmile Canyon South: L = 0.357 (LS)1.04, R2

 =0.92 (6)

 Fourmile Canyon North: L = 0.405 (LS)1.04, R2

 =0.95 (7)

 Pozo South: L = 0.407 (LS)1.01, R2

 =0.89 (8)

where 

 L is the long run detachment rate in g cm-2 s-1, and 

 LS is the combined long and short run detachment 

 rate in g cm-2 s-1. 

 For <0.063-mm size fraction, the equations are:

 Fourmile Canyon South: L = 0.630 (LS), R2

 =0.73 (9)

 Fourmile Canyon North: L = 0.215 (LS), R2

 =0.75 (10)

 Pozo South: L = 0.331 (LS), R2

 =0.82 (11)

Results and Discussion 

Two types of data were collected from three different 

sites and are presented in this report. The first type of data 

describes the soil and root properties, and the second type is 

associated with the flume experiments to measure soil detachment. Results are presented in the order FMC-South, FMCNorth, and Pozo-South unless otherwise noted. Mean values of 

all properties represent the average of three replicates for each 

of three clusters from the burned areas or nine samples, and 

the average of three samples (one cluster) from the unburned 

area. 

Soil Properties

Bulk density generally increased with depth below the 

surface of the soil. Bulk density for each unburned area was 

affected by the amount of organic matter in the surface samples. The FMC-South site had the largest amount of organic 

material and thus the lowest bulk density (dashed blue line in 

fig. 7) at the surface. This effect decreased with depth such 

that the mean bulk densities at 6.3 cm were 1.28, 1.49, and 

1.41 g cm-3 for the soils from FMC-South, FMC-North, and 

Pozo-South. Mean values for soils from the burned area 

at the surface (0.5 cm) were essentially the same (1.04 and 

1.07 g cm-3) for the FMC-South and FMC-North sites, but the 

mean value at the Pozo-South site was greater (1.25 g cm-3) 

than the two FMC sites (tables 1–3). Corresponding mean 

values at 6.3 cm were 1.38, 1.28, and 1.31 g cm-3. Values at the 

deepest depth (8.8 cm) were more variable; due to their location at the end of the core, it was difficult to always obtain a 

sample exactly 2.5 cm thick. Thus, the volume used in 

the bulk density calculation had more uncertainty than at 

shallower depths. 

Figure 6. Comparison of non-uniform shear stress measured for the tilting 

flume with a smooth bed conditions and with a soil core in place. 

0

100

200

300

400

500

600

0 100 200 300 400 500 600

Non-uniform shear stress for smooth bed conditions, dynes centimeter-2

Non-uniform shear stress with soil core in place,

dyness centimeter-2

FMC-SOUTH

FMC-NORTH

POZO-SOUTH

1:1 line

EXPLANATION
26 Variations in Soil Detachment Rates after Wildfire

Organic matter in the soil, as measured by loss on ignition, generally decreased with depth below the surface of the 

soil. Samples from the FMC-South site had the most organic 

matter incorporated into in the surface soil (43.8 percent), 

those from the FMC-North site had the least organic matter 

(4.9 percent), and those from the Pozo site had 6.0 percent. 

Burning this organic matter generally reduced the mean values 

for soils in the burned area so that at the surface (0.5 cm) they 

were 7.2 percent, 6.1 percent, and 4.2 percent. The exception 

is the mean value for the FMC-North site, which had some 

residual unburned duff material that the other sites did not 

have. The three clusters collected in the FMC-North site also 

had more variability than the other sites with values ranging 

from 3.2 percent (less than the unburned value) to 9.8 percent 

(table 2). Mean values of organic matter at the deepest depth 

(8.8 cm) in the burn areas were essentially minimum values 

at all sites and were 3.1 percent, 4.0 percent, and 3.4 percent, 

respectively (fig. 8). 

Percent of silt and clay (<0.063 mm) differed more 

between the three sites than did the bulk density or the amount 

of organic matter. Silt and clay percentages of the surface 

soils (0.5 cm) from the unburned area in the FMC-South (5.8 

percent ) and FMC-North (9.3 percent) sites were less than at 

the Pozo site (10.6 percent), which had a thin veneer of fine 

gravel on the surface; this created a minimum value of silt and 

clay at the surface (tables 1, 2, and 3). Below the surface, the 

percent of silt and clay decreased with depth (fig. 9). A rain 

storm caused some runoff after the Pozo fire and before we 

collected samples in January, 2011. This runoff removed some 

of the veneer of fine gravel and the percent silt and clay at the 

surface was greater in the burned area than in the unburned 

area. Samples from the burned area in the Pozo site had the 

largest percentage at all depths with the mean values decreasing from 23.4 percent (0.5 cm) to 19.4 percent (8.8 cm). Similar percentages for the burned area in the FMC-North site were 

substantially less (ranging from 14.4 percent to 7.3 percent), 

and the lowest percentages were in the FMC-South (ranging 

from 8.0 percent to 5.1 percent) (fig. 9).

Root Properties

The root density RD and root-length density RLD varied 

between sites. The RD and RLD measurements near the soil 

surface (0–1cm) in unburned clusters at Fourmile Canyon 

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

0.0 0.5 1.0 1.5 2.0

Depth, cm

Bulk density, g cm -3

FMC_SBA

FMC_SBB

FMC_SBC

FMC_SUB

FMC_SB

FMC_NBA

FMC_NBB

FMC_NBC

FMC_NUB

FMC_NB

Pozo_SBA

Pozo_SBB

Pozo_SBC

Pozo_SUB

Pozo_SB

thickness of interval probably < 2.5 cm

58% Large Organics

42% Large Organics

14% Large Organics

FMC_SBA

FMC_SBB

FMC_SBC

FMC_SUB

FMC_SB

FMC_NBA

FMC_NBB

FMC_NBC

FMC_NUB

FMC_NB

Pozo_SBA

Pozo_SBB

Pozo_SBC

Pozo_SUB

Pozo_SB

EXPLANATION

58% Large organics

42% Large organics

14% Large organics

Bulk density, in gram centimeter-3

Thickness of interval probably < 2.5 centimeters

Depth, in centimeters

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

0.0 0.5 1.0 1.5 2.0

Figure 7. Mean bulk density of soil for three sites based on three replicates for each cluster. Each cluster (A, B, 

and C at the end of the three-letter code following the site name) from a burned (B) area is plotted separately, and 

the mean values of the three clusters are connected by a solid line. The mean values for the single cluster (three 

replicates) from the unburned (UB) area are connected by a dashed line. (FMC, Fourmile Canyon site; S, south 

aspect; N, north aspect) 
Results and Discussion 27

were consistently higher than the burned clusters. At Pozo, 

there was no difference between the burned and unburned 

clusters. At FMC-South and FMC-North, the RD and RLD

had maximum values between 2 and 5 cm below the surface, 

whereas at the Pozo site these root properties increased monotonically with depth (fig. 10). RD and RLD were generally 

lower in the soils from the Pozo site than from the Fourmile 

Canyon site (figs. 10 and 11). RD and RLD were more variable 

near the surface above 4 cm and less variable below 4 cm. 

Overall, RD was more variable at FMC-North, and less variable at Pozo than RLD. At FMC-South, the overall variability 

in the two root properties were similar. 

RD and RLD are related. However, the relation between 

the two root properties is weak (fig. 12), as expected given 

that root density is highly influenced by short and thick roots, 

whereas RLD is strongly influenced by fine roots which have 

low mass but may be very long (for example, mycorrhizas). 

A steeper slope in (fig. 12) indicates more root length per 

unit mass of root. Abundant mycorrhizas were found in some 

samples from Fourmile Canyon usually at depths above 3 

cm. Mycorrhizal associations are commonly reported in roots 

systems of Douglas Fir stands in both near surface organics 

and in mineral soil (Kluber and others, 2010). 

Soil Detachment Rates

The detached soil was separated into two fractions 

(>0.063 mm and <0.063 mm) during each experimental run. 

The > 0.063mm eroded sediment was further separated into 

seven size classes (tables 4–6) after drying (see “Laboratory 

Methods” section above). One of the size classes was <0.063 

mm, but this class represents those aggregates that broke during the sieve analysis. The five cores composing a cluster were 

collected within a 1-m radius, so that we assumed they were 

similar and a different core could be used for each shear stress. 

However, the clusters themselves were separated by distances 

on the order of 50–500 m, so that there may be substantial 

differences in soil properties; therefore, data were analyzed 

for each separate cluster. This separation was warranted for 

other reasons. For example, the FMC-North Cluster A was 

unique because these cores were collected from under a tarp, 

which had been put in place about 2 weeks (mid-September, 

Figure 8. Loss on ignition (LOI) of soil for three sites based on three replicates for each cluster. Each cluster (A, B, and 

C at the end of the three-letter code following the site name) from a burned (B) area is plotted separately, and the mean 

values of the three clusters are connected by a solid line. The mean values for the single cluster (three replicates) from the 

unburned (UB) area are connected by a dashed line. The value for FMC-south in the unburned area at the surface 

(-0.5 cm) not shown on the figure is 43.8 percent. (FMC, Fourmile Canyon site; S, south aspect; N, north aspect)

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

0 5 10 15 20

Loss on ignition, in percent

Depth, in centimeters

FMC_SBA

FMC_SBB

FMC_SBC

FMC_SUB

FMC_SB

FMC_NBA

FMC_NBB

FMC_NBC

FMC_NUB

FMC_NB

Pozo_SBA

Pozo_SBB

Pozo_SBC

Pozo_SUB

Pozo_SB

EXPLANATION
28 Variations in Soil Detachment Rates after Wildfire

2010) after the 2010 Fourmile Canyon fire was contained in 

order to preserve the ash layer on the surface. The FMC-North 

Cluster B cores were also unique in that they were collected 

1 year (yr) after the wildfire (in October, 2011), and during 

the intervening time, wind and water erosion had altered the 

surface. Additionally, there was only a single cluster from each 

unburned site.

Non-Uniform Shear Stress and Root-Length 

Density

Detachment rates and transport rates have often been 

related to the variables of boundary shear stress or stream 

power. Both variables are frequently expressed as the excess 

shear stress or excess stream power that is greater than some 

critical shear stress or critical stream power. The range of critical shear stress values for particle diameters from 0.063 mm to 

1.0 mm is 2–8 dynes cm-2 (Wiberg and Smith, 1987; Moody 

and others, 2005), and these are much smaller than the shear 

stress (22–421 dynes cm-2) used in these experiments. It is 

unlikely that we could determine the critical shear stress or 

critical unit stream power values. Thus, as a first step, we 

determined the relations between the detachment rate and the 

non-uniform shear stress for the >0.063 mm and <0.063-mm 

size fractions of the eroded sediment. For non-cohesive sediment in streams, the literature (Meyer-Peter and Müller, 1948; 

Roberts and others, 1998; Yang, 2006) indicates that the relation between detachment rate or transport rate and shear stress 

is generally a power law with exponent >1 and often equal 

to 1.5. 

Some literature for soils and cohesive sediments (Foster, 

1982; Lane and others, 1987; Elliot and others, 1989; Foster 

and others, 1995; Nachtergaele and Poesen, 2002; Huang and 

others, 2006) indicates that the exponent of the power law 

may be < 1. So, as an initial investigation, a power law was fit 

to the data for non-uniform shear stress, τN , and non-uniform 

unit stream power, waN. Deviations from the power-law form 

of the relation may indicate some type of cohesive or root 

effects. For some samples of the < 0.063 mm fraction, there 

was a trace amount of sediment, and these values are listed in 

tables 4, 5, and 6 as “0.0.” Zero cannot be used when fitting a 

power law, so that for depths with “0.0” a linear relation passing through (0,0) was computed (see “Laboratory Method” 

section above and tables 4, 5, and 6).

Figure 9. Percent silt and clay (less than 0.063 mm) in soil for three sites based on three replicates for each cluster. Each 

cluster (A, B, and C at the end of the three-letter code following the site name) from a burned (B) area is plotted separately, 

and the mean values of the three clusters are connected by a solid line. The mean values for the single cluster (three 

replicates) from the unburned (UB) area are connected by a dashed line. (FMC, Fourmile Canyon site; S, south aspect; N, 

north aspect) 

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

0 10 20 30

Depth, in centimeters

Silt and clay, in percent

FMC_SBA

FMC_SBB

FMC_SBC

FMC_SUB

FMC_SB

FMC_NBA

FMC_NBB2

FMC_NBC

FMC_NUB

FMC_NB

Pozo_SBA

Pozo_SBB

Pozo_SBC

Pozo_SUB

Pozo_SB

EXPLANATION
Results and Discussion 29

Detachment rates could also depend on root and cohesive properties of the soils. Therefore, as a second step, we 

determined the power-law relation between detachment rates 

and root-length density for the > 0.063-mm and <0.063-mm 

size fractions. Values of RLD were not extracted for each core 

measured in the flume, but were the average for specific depth 

intervals (0–1, 1–3, 3–5, 5–7.5, and 7.5–10 cm) from the three 

replicate cores collected from the same site. These values were 

interpolated to determine values of RLD at the specific depths 

of the detachment measurements, and were extrapolated to the 

surface by using two different assumptions. The first assumption was that RLD at the soil surface was zero and RLD values 

were interpolated values between 0 and 0.5 cm, and the second 

assumption was that RLD was a constant between the soil surface and 0.5 cm, and the value was constant and equal to the 

value of RLD at 0.5 cm. Power laws for τN and waN were fit 

to four values of shear stress or stream power (applied to four 

different cores) for five depth ranges (depths were not exactly 

the same for each core), whereas the power laws for RLD were 

fit to four values of RLD within the same core having the same 

non-uniform shear stress or stream power. 

The coefficient of determination, R2

, was used to indicate the goodness-of-fit to the power law relations between 

the detachment rate and the τN or the root-length density. Five 

value of R2 (one for each depth) for the power law fits using 

τN or waN for each cluster were averaged. Similarly, the four 

values of R2

 (one for each value of τN) for the power law fits 

using RLD were averaged for each cluster. How the RLD

was extrapolated to the surface made little difference, so R2

values are given here for the first assumption (RLD=0 at the 

soil surface). For the >0.063 mm fraction, the R2

 values for all 

clusters ranged from 0.33 to 0.86 for τN and from 0.07 to 0.91 

for RLD (fig. 13A) indicating a wide range of spatial variability. Spatial variability between sites is certainly expected, but 

the spatial variability between clusters within each site was 

surprising. For example, two very different clusters (Cluster B 

from FMC-North collected 1 yr after the wildfire and the Pozo 

unburned) had the highest R2

-values for τN and the lowest for 

RLD (fig. 13A). 

However, the FMC-North cluster A collected under 

the tarp with the ash layer intact had the combined lowest 

R2

-values for τN (0.33) and RLD (0.56). The highest R2-values 

for RLD were again from two different sites: the FMC-South 

Cluster C (0.91) with relatively constant exponents (-1.1 to 

-2.7) and Pozo Cluster A (0.85) with approximately constant 

exponents (-2.1 to -2.8). The exponent of the power law for 

Figure 10. Root density as a function of depth in the soil for three sites based on three replicates for each cluster. 

Each cluster (A, B, and C at the end of the three-letter code following the site name) from a burned (B) area is plotted 

separately, and the mean values of the three clusters are connected by a solid line. The mean values for the single 

cluster (three replicates) from the unburned (UB) area are connected by a dashed line. (FMC, Fourmile Canyon site; S, 

south aspect; N, north aspect) 

0.0

2.0

4.0

6.0

8.0

10.0

0 5 10 15 20

Root density, in milligram centimeter-3

Depth, in centimeters

FMC_SBA

FMC_SBB

FMC_SBC

FMC_SUB

FMC_SB

FMC_NBA

FMC_NBB2

FMC_NBC

FMC_NUB

FMC_NB

Pozo_SBA

Pozo_SBB

Pozo_SBC

Pozo_SUB

Pozo_SB

EXPLANATION
30 Variations in Soil Detachment Rates after Wildfire

RLD varied from -9.5 to 5.3 and the exponent of the power 

law for τN ranged from -0.34 to 2.5. No clusters showed any 

consistent pattern with depth. This wide variability of goodness-of-fit and the value of the exponent for the power laws 

indicated that a multiple regression including both variables 

was justified. 

 For the <0.063 mm size fraction, only two clusters had 

R2

 values for RLD > 0.60. These were the FMC-South Cluster 

C (R2

=0.65), which was noted in the field to have many cacti 

roots and has a distinct maximum at 2 cm depth for the RLD

(fig. 8), and Pozo Cluster A (R2

=0.63), which also had a high 

R2

-value (0.85) for the >0.063 mm size fraction. Only 4 of the 

12 clusters had R2

 values for τN greater than 0.60 compared 

to seven clusters for the >0.063 mm size fraction (fig. 13B). 

These results suggest that the detachment rate for the <0.063 

mm size fraction is generally not dependent on τN or RLD. 

Based on the low R2

-values for <0.063 mm size, no multipleregression analysis was done for the <0.063 mm size fraction.

Non-Uniform Unit Stream Power and Root-length 

Density

The results based on the non-uniform unit stream power 

were almost the same as those based on the non-uniform shear 

stress. On average the R2

-values were slightly greater (0.03), 

but were not statistically significant (p=0.085; paired t-test). 

The slight improvement is probably because waN was calculated by using the measured discharge, which varied slightly 

for the five experimental runs for a given core, whereas τN was 

constant for the five runs. The measured τN also may provide 

improved goodness-of-fits. Unfortunately, there are only 20 

runs out of the total of 60 runs for all sites that had measured 

τN values for all four shear stresses, and 45 percent of these did 

indicate slight improvements in the goodness-of-fit similar to 

the data for waN.

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

0 10 20 30

Depth, in centimeters

Root-length density, in centimeter centimeter-3

FMC_SBA

FMC_SBB

FMC_SBC

FMC_SUB

FMC_SB

FMC_NBA

FMC_NBB2

FMC_NBC

FMC_NUB

FMC_NB

Pozo_SBA

Pozo_SBB

Pozo_SBC

Pozo_SUB

Pozo_SB

EXPLANATION

Figure 11. Root-length density as a function of depth in the soil for three sites based on one replicate for each cluster. 

Each cluster (A, B, and C at the end of the three-letter code following the site name) from a burned (B) area is plotted 

separately and the mean values of the three clusters are connected by a solid line. The mean values for the single cluster 

(three replicates) from the unburned (UB) area are connected by a dashed line. (FMC, Fourmile Canyon site; S, south 

aspect; N, north aspect).
Results and Discussion 31

Multiple Regressions using Flow and Root 

Variables

Multiple regression analysis was done for just the 

>0.063 mm size fraction using the root-length density and the 

non-uniform shear stress or the non-uniform stream power as 

independent variables. The general form of the relation for the 

detachment rate, E [g cm-2 s-1] is:

 E = b1 t

N

b2RLDb3, (12) 

 

where 

b1 is a constant and 

b2 and 

b3 are exponents determined by the multiple 

 regression analysis (table 7.)

The first assumption relative to extrapolating RLD to the 

surface (RLD=0 cm cm-3 at 0 cm) was used, and all data were 

log transformed. Regression models (Brown, 2009) for each 

cluster were run separately (table 7), and all the data were 

combined rather than separating by depth (as done for the 

initial regression for τN and waN) or by shear stress (as done 

for the initial regression for root-length density). Because the 

data were log transformed, another measure of goodness-of-fit, 

the log RMSE (table 7), was used for these multiple regression models. This measure is the square root of the mean of 

the square values of the natural logarithm of the ratio of the 

predicted value divided by the measured value (Kroll and Stedinger, 1996). The goodness-of-fit as indicated by the R2

-value 

was higher (minimum R2

=0.11) for these multiple regression 

models than for the single variable regression models (minimum R2

=0.0014) discussed in the previous section. However, 

there was still a wide range of values for the exponents (b2

and b3, table 7) for the independent variables. 

Exponents for the RLD were mostly negative (fig. 14; 

except for FMC-SA and FMC-NC); this indicates that the 

detachment rate decreased with an increase in RLD. Exponents 

for the τN (or waN) were always positive (fig. 14) and had a narrower range of values equal to 0.34 to 1.96 (0.11 to 1.29) compared to those for the initial single regression models, which 

were -0.34 to 2.5 (-0.73 to 2.1). Exponents for τN were always 

greater than those for waN and averaged 1.01 and 0.83, respectively, based on all data from burned and unburned areas. This 

is probably due to the fact that the stream power is the shear 

stress multiplied by the mean velocity (related to energy or 

power). Overall the multiple regression models predicted the 

detachment rates for the Pozo soils best with R2

-values ranging from 0.60-0.79 using τN and from 0.63 to 0.84 using waN. 

Average values (for all clusters from all burned areas) were b1

= –1.80, b2 = 0.82 and b3 = -0.88. Similar results were found 

using the non-uniform stream power (b1=-3.62, b2=0.67, and 

0

5

10

15

20

25

30

35

0 5 10 15 20

Root density, in milligram centimeter-3

C

0

5

10

15

20

25

30

35

0 5 10 15 20

t

Root density, in milligram centimeter-3

A

0

5

10

15

20

25

30

35

0 5 10 15 20

B

Root-length density

(centimeter centimeter-3) Root-length density (centimeter centimeter-3) Root-length density (centimeter centimeter-3) 

Root density, in milligram centimeter-3

Figure 12. Relations between root-length density and root 

density. A, Fourmile Canyon-North; B, Fourmile Canyon-South; 

C, Pozo. Red points indicate samples where mycorrhizas were 

present and included as part of root-length density estimates. 
32 Variations in Soil Detachment Rates after Wildfire

Figure 13. Comparison of the goodness-of-fit as measured by the coefficient of determination 

for power law relations between the detachment rate and the non-uniform shear stress or the 

root-length density. A, greater than 0.063 mm size fraction. B, less than 0.063 mm size fraction. 

The red lines are drawn at an arbitrary value of R2

=0.60 (coefficient of determination) to 

separate those correlations that may be physically realistic from those that are probably not.

FMC_SUB

FMC-SA

FMC-SB

FMC-SC

FMC-NUB

FMC-NA

FMC-NB

FMC-NC

Pozo-SUB

Pozo-SA

Pozo-SB

Pozo-SC

EXPLANATION

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0

<0.063 mm

Average R2 for root-length density 

power law for 4 shear stresses 

Average R2 for shear stress power law for 5 depths

B

>0.063 mm

Average R2 for root-length density 

power law for 4 shear stresses 

FMC_SUB

FMC-SA

FMC-SB

FMC-SC

FMC-NUB

FMC-NA

FMC-NB

FMC-NC

Pozo-SUB

Pozo-SA

Pozo-SB

Pozo-SC

EXPLANATION

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0

A

Average R2 for shear stress power law for 5 depths
Results and Discussion 33

 Non-uniform shear stress b1 b2 b3 Maximum

 error R2 log  RMSE

 Constant

 Exponent for 

 non-uniform 

 shear stress

 Exponent 

 for root 

 length density

Fourmile Canyon South Unburned -2.27 1.36 -1.62 2.88 0.58 1.38

Fourmile Canyon South--Cluster A -7.17 1.34 0.77 3.53 0.35 2.00

Fourmile Canyon South--Cluster B -0.75 0.62 -0.47 4.91 0.11 2.27

Fourmile Canyon South--Cluster C 1.65 0.41 -1.42 1.71 0.70 0.96

Fourmile Canyon North Unburned -1.59 1.42 -2.31 4.18 0.57 1.80

Fourmile Canyon North--Cluster A 1.03 0.41 -1.62 4.27 0.32 1.97

Fourmile Canyon North--Cluster B -1.32 1.19 -1.43 2.68 0.57 1.13

Fourmile Canyon North--Cluster C -3.42 0.73 0.13 3.70 0.13 2.01

Pozo-South Unburned -6.54 1.96 -0.56 2.40 0.79 1.12

Pozo South Burned--Cluster A 1.16 0.34 -1.90 3.85 0.67 1.48

Pozo South Burned--Cluster B -4.64 1.07 -0.65 2.24 0.69 1.09

Pozo South Burned--Cluster C -2.72 1.27 -1.38 2.60 0.60 1.30

All Clusters from burned areas -1.80 0.82 -0.88 3.28 0.46 1.58

 Non-uniform stream power b1 b2 b3 Maximum

 error R2 log 

 RMSE

 Constant

 Exponent for 

 non-uniform 

 stream power

 Exponent for 

root length 

density

Fourmile Canyon South Unburned -4.70 1.04 -1.62 3.20 0.52 1.47

Fourmile Canyon South--Cluster A -11.20 1.21 0.82 3.67 0.42 1.90

Fourmile Canyon South--Cluster B -2.97 0.61 -0.46 4.96 0.14 2.23

Fourmile Canyon South--Cluster C 1.14 0.28 -1.41 1.88 0.66 0.99

Fourmile Canyon North Unburned -5.86 1.29 -2.30 3.79 0.61 1.66

Fourmile Canyon North--Cluster A 0.81 0.25 -1.62 4.46 0.31 1.99

Fourmile Canyon North--Cluster B -4.54 1.04 -1.46 2.42 0.63 1.05

Fourmile Canyon North--Cluster C -4.96 0.61 0.023 3.49 0.14 2.00

Pozo-South Unburned -11.23 1.65 -0.59 1.80 0.84 0.96

Pozo South Burned--Cluster A 1.78 0.11 -1.90 3.51 0.65 1.51

Pozo South Burned--Cluster B -6.62 0.83 -0.64 2.50 0.65 1.15

Pozo South Burned--Cluster C -6.00 1.09 -1.38 2.42 0.63 1.26

All Clusters from burned areas -3.62 0.67 -0.89 3.26 0.47 1.56

Table 7. Multiple regression information for the detachment rate as a function of root-length density and either non-uniform shear 

stress or non-uniform stream power.

[FMC, Fourmile Canyon; UB, unburned; S, South; N, North; b1 is a constant, b2 and b3 are exponents in the equation E = b1τ b2

N RLDb3 where τN is the 

non-uniform shear stress and RLD is the root-length density; R2, coefficient of determination; log RMSE, error statistic equal to the root mean square of the 

logrithm of the predicted value divided by the observed value]
34 Variations in Soil Detachment Rates after Wildfire

Exponent for non-uniform shear stress

Exponent for non-uniform stream power

Exponent for root-length density Exponent for root-length density

FMC_SUB

FMC-SA

FMC-SB

FMC-SC

FMC-NUB

FMC-NA

FMC-NB

FMC-NC

Pozo-SUB

Pozo-SA

Pozo-SB

Pozo-SC

EXPLANATION

B

A

FMC_SUB

FMC-SA

FMC-SB

FMC-SC

FMC-NUB

FMC-NA

FMC-NB

FMC-NC

Pozo-SUB

Pozo-SA

Pozo-SB

Pozo-SC

EXPLANATION

1.0

0.5

0.0

-0.5

-1.0

-1.5

0.5 1.0 1.5 2.0

-2.0

-2.5

0.0 2.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

0.5 1.0 1.5 2.0

-2.0

-2.5

0.0 2.5

Figure 14. Exponents of the independent variables used in multiple regressions of log 

transformed data in which detachment rate for greater than 0.063 mm size fraction is the 

dependent variable. A, Root-length density and non-uniform shear stress. B, Root-length 

density and non-uniform stream power.
Results and Discussion 35

b3=-0.88; table 7). These results indicate that the erodibility 

parameters for soil within burned areas need to include depth 

and root properties.

The wide variation in multiple regression models for the 

detachment rate from the multiple clusters and sites suggest 

that there is not a single model. A single model for nonuniform shear stress and a single model for non-uniform unit 

stream power were tested by using all the data from just the 

nine clusters collected from the burned sites (176 values) to 

determine two models. The goodness-of-fit for these models is 

low (R2 ~ 0.25; log RMSE ~ 1.94), over predicts detachment 

ranges at the low end, and under predicts detachment rates at 

the high end of the measured detachment rates (fig. 15).

Soil Erodibility

If the detachment rate, E, is a linear relation of some 

flow variable, X, then the erodibility can be simply defined as 

K=E/X, which makes the implicit assumption that the erodibility is a constant property of a given soil. Results from 

this study measured a wide range of exponents for the flow 

variables τN and waN for each cluster. These exponents were not 

equal to 1 (table 7), which suggests some form of non-linear 

relation is appropriate. However, the range was even wider 

for the single variable regressions but decreased considerably when the root-length density parameter was included in 

the multiple regressions. This implies that K is not a constant 

property of the soil but also a function of root properties. If n

in the relation E=KXn

 is not equal to 1, then the meaning of 

K becomes hard to define. Interestingly, the average values of 

all 12 exponents (table 7) determined for τN was 1.00 + 0.50 

(+ standard deviation), and for waN, the average was 0.85 +

0.47, which suggests τN might be the appropriate flow variable 

to use when computing erodibility (fig. 16). However, this 

changes when the exponents for the unburned and burned data 

are separated. The average value for the unburned sites are τN

=1.58 + 0.33 (similar to the exponent used for some sediment 

transport laws; Meyer-Peter and Müller, 1948; Roberts and 

others, 1998; Yang, 2006) and waN =1.33 + 0.31, whereas for 

the burned sites the averages are 0.82 + 0.40 and 0.67 + 0.40, 

respectively making the decision on how to define K more 

uncertain. 

Including the RLD variable as an explicit part of K made 

the exponents of the flow variable less diverse and closer to 

1. It is possible that by including other types of soil variables 

(physical, chemical, biological, and burn severity; Busse 

and DeBano, 2005; DeBano and others, 2005; Knoepp and 

DeBano, 2005), such as soil moisture (Bryan, 2000; Nachtergaele and Poesen, 2002) or a particle-size parameter, would 

help to decrease the variability more and the erodibility would 

become a linear function of one of the flow variables. However, this is beyond the immediate objective of this report. 

Soil moisture changes with time and other properties may also 

change (Bryan, 2000). This is highlighted by the results for the 

FMC-NB cluster, which was collected 1 yr after the wildfire 

in 2011. During this time, the Fourmile Canyon burned area 

was affected by snow cover during the winter and by spring 

melt and later by cyclonic and convective rainstorms during 

the spring, summer, and fall; all types of precipitation likely 

eroded some of the surface material. Soil erodibility results for 

this cluster were quite different than those for the FMC-NC 

cluster (collected soon after the wildfire in 2010); this suggests 

changes in K with time.

Better measurements of the actual shear stress and stream 

power values experienced by the soil particles at the surface of 

the core would most likely improve the detachment relations. 

This would require being able to subtract out from the total 

boundary shear stress, for example, the shear stress associated 

with the drag on the protruding roots tips or stems (fig. 17A) 

and small particles on the order of 0.2–1.0 mm (fig. 17B). 

Both represent a substantial drag (Smith, 2004) for shallow 

flows on the order of 3–11 mm deep, which were used in 

these experiments and are certainly typical of overland flows 

on burned hillslopes. As the surface evolved during the flow, 

numerous pits developed that affect the flow and hence the 

shear stress and stream power available to erode sediment. 

Additionally, we observed air films that developed (usually 

on highly repellent surfaces) between the surface of the core 

and the water (fig. 17C). These air films have been observed 

by others (Moody and others, 2005) in flume studies and 

prevented any erosion of the surface until air escaped in bursts 

from beneath the soil surface; this movement detached soil 

particles and aggregates. The exact areal distribution of air 

film during overland flow in the field has not been determined, 

but might be considered in future research.

Measured detachment rate, 

gram centimeter-2 second-1

Predicted detachment rate, 

gram centimeter-2 second-1

1,000

100

10

1

0.1

0.01

0.01 0.1 1 10 100 1,000

Non-uniform shear stress

Non-uniform stream power

EXPLANATION

Figure 15. Multiple regression model for detachment rates 

using all shear stress, stream power, and root-length density 

data for clusters collected in burned areas. R2

-value (coefficient 

of determination) is roughly 0.25.
36 Variations in Soil Detachment Rates after Wildfire

1,000

100

10

1

0.1

0.01

0 100 200 300 400 500

Detachment rate, E

(gram centimeter-2 second-1)

E =0.019 τN

1.00; R2

=0.23

Non-uniform shear stress, dyne centimeter-2

Detachment rate, E

(gram centimeter-2 second-1)

Non-uniform stream power, ωaN erg second-1 centimeter-2

1,000

100

10

1

0.1

0.01

0 5,000 10,000 15,000 20,000 25,000

E =0.0016ωaN

0.85;R2

=0.24

A

B

Figure 16. Relations between detachment rate for all data and A, Non-uniform shear stress. 

B, Non-uniform stream power. 
Results and Discussion 37

Figure 17. Photographs of the appearance of the surface of the soil core in 

the tilting flume. A, View looking upstream along the bed of the tilting flume 

showing some protruding roots and pits filled with water. The tip of point gage 

extends from the top of the photo, and the dark gray grid in the background is 

the diffuser. The diameter of the inside of the core is 4.7 cm. B, View looking 

upstream along the bed of the tilting flume showing some protruding sand and 

fine gravel particles. C, Oblique view across the soil core showing the air films 

(whitish gray objects at end of blue arrows) attached to the soil surface. Flow is 

from right to left.

A

B

C
38 Variations in Soil Detachment Rates after Wildfire

Summary

The heat released during wildfires affects sediment availability through soil heating and the combustion of vegetation, 

litter, and organic material within the soil. This can result in 

a temporary or permanent change in erodibility of soils, such 

that detachment and transport by overland flow is easier. This 

study aimed to quantify the erodibility of burned soil at different depths and relate variability in detachment rate to different 

flow and soil properties. Soil cores were collected (to measure 

erodibility using a shallow, tilting flume and to measure soil 

and root properties) from two different burned areas (2010 

Fourmile Canyon fire in Colorado and 2010 Pozo fire area in 

California) with contrasting geology, soil-particle size, and 

vegetative characteristics. 

Soil properties (bulk density, organic matter, and amount 

of silt and clay) and root properties (root density (RD) and 

root-length density (RLD)) showed distinct trends with soil 

depth. All sites displayed an increase in bulk density with 

depth and a slight decrease in organic matter (loss on ignition) 

and percent of silt and clay with depth below the surface. Bulk 

density and soil organic matter were relatively similar across 

the three sites, but percent silt and clay was generally higher 

in the Pozo site than in the FMC sites. At all sites, the RD

and RLD were lowest near the soil surface. At the two sites in 

Fourmile Canyon, the root properties had maxima between 2 

and 5 cm below the soil surface, whereas at Pozo, the RD and 

RLD increased monotonically with depth.

Detachment rates for burned and unburned soils were 

measured using a tilting flume which was modified so that the 

cylindrical cores could be inserted, attached below the flume 

bed (so that they were flush with the flume bed), and then could 

be extruded to exposed different depths below the soil surface. 

The detachment rate of burned soil cores decreased by up to 1–2 

orders of magnitude between surface and subsurface soils in the 

top 2 cm of the soil profile. Subsurface soils from the Pozo site 

had lower variability in detachment rates than soils from the 

Fourmile Canyon site.

The relation between detachment rate and flow variables 

was a power law for each depth in individual clusters, but the 

exponent was quite variable. The depth-averaged exponent for 

each cluster varied from 0.34 to 1.34 across all burned sites. 

Additional variability in detachment rates of burned soil could 

be linked to RLD. A multivariate regression indicated that the 

detachment rate of burned soils E [g cm-2 s-1] was a function of 

the flow variable,τN [dyne cm-2], and the root variable, RLD [cm 

cm-3]. The general form of the relation for the detachment rate, 

E was:

 E = b1 t

N

b2RLDb3 

 

where 

the average values (for all clusters from all burned areas) 

were b1 = –1.80, b2 = 0.82 and b3 = -0.88. Similar results 

were found using the non-uniform stream power (b1=-3.62, 

b2=0.67, and b3=-0.89). These results indicate that the 

erodibility parameters for soil within burned areas need to 

include depth and root properties. 

Acknowledgments 

Soil cores for this study were collected on Bureau of 

Land Management (BLM) and U.S. Forest Service (USFS) 

property in the area burned by the 2010 Fourmile Canyon Fire. 

John Smeins (BLM) and Erin Watkins (BLM) expedited the 

process of obtaining permission to collect the samples, and 

Eric Schroder (USFS, Arapaho/Roosevelt National Forest) 

made repeated trips to the field site to help identify sites. Melody Fountain (USFS, Los Padres National Forest) gave us a 

guided tour into the area burned by the 2010 Pozo Fire in California, which saved an enormous amount of time dedicated 

to finding and deciding on a representative site. Dick Martin 

(Martin Enterprises, Lakewood, Colorado) was instrumental 

in making changes to the tilting flume to accommodate the 

soil cores and in designing and fabricating the core holder and 

extruding device. The diagrams in Figure 6 were prepared by 

Graeme Scheuber. Pierce Martin stepped in at a crucial time to 

finish much of the soil particle-size analysis that is essential, 

but often tedious to complete. 

The project was partially funded by eWater Cooperative 

Research Centre and Melbourne Water. The second author was 

funded by a post-graduate travel scholarship from The University of Melbourne. Reviews by Brian Ebel and Christoph 

Langhans improved the report.

References Cited

Al-Hamdan, O.Z., Pierson, F.B., Williams, C.J., Nearing, 

M.A., Stone, J.J., Kormos, P.R., Boll, Jan, and Weltz, M.A., 

2011, Estimating concentrated flow erodibility parameters 

from pre- and post-fire rangeland field data for physicallybased erosion modeling: American Geophysical Union, 

AGU Poster H31B-1141.

Bagnold, R.A., 1966, An approach to the sediment transport 

problem from general physics: U.S. Geological Survey 

Professional Paper 422-I, 37 p.

Blake, W.H., Droppo, I.G., Humphreys, G.S., Doerr, 

S.H., Shakesby, R.A. and Wallbrink, P.J., 2007, Structural characteristics and behavior of fire-modified soil 

aggregates: Journal of Geophysical Research, v. 112, 

doi:10.1029/2006JF000660.

Brown, S.H., 2009, Multiple linear regression analysis—A 

matrix approach with MATLAB: Alabama Journal of Mathematics, Spring/Fall 2009, p. 1–3.

Bryan, R.B., 2000, Soil erodibility and processes of water 

erosion on hillslope: Geomorphology, v. 32, p. 385–415.
References Cited 39

Busse, M.D., and DeBano, L.F., 2005, Chapter 4—Soil Biology, in Neary, D.G., Ryan, K.E., and DeBano, L.F., eds., 

Wildland fire in ecosystems, effects of fire on soil and 

water: Ogden, Utah, U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station, General Technical Report RMRS-GTR-42-vol.4., p. 73–91.

DeBano, L.F., 2000, The role of fire and soil heating on water 

repellency in wildland environments—A review: Journal of 

Hydrology, v. 231/232, p. 195–206.

DeBano, L.F., and Neary, D.G., 2005, Part A—The soil 

resource—Its importance, characteristics, and general 

responses to fire, in Neary, D.G., Ryan, K.E., and DeBano, 

L.F., eds., Wildland fire in ecosystems, effects of fire on soil 

and water: Ogden, Utah, U.S. Department of Agriculture, 

Forest Service, Rocky Mountain Research Station General 

Technical Report RMRS-GTR-42-vol.4., p. 21–27.

DeBano, L.F., Neary, D.G., and Ffolliott, P.F. 2005, Chapter 

2—The soil physical properties, in Neary, D.G., Ryan, K.E., 

and DeBano, L.F., eds., Wildland fire in ecosystems, effects 

of fire on soil and water: Ogden, Utah, U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Research 

Station, General Technical Report RMRS-GTR-42-vol.4, 

p. 29–51.

De Baets, S. Poesen, J., Kanapen, A., and Galindo, P. 2007, 

Impact of root architecture on the erosion-reducing potential 

of roots during concentrated flow: Earth Surface Processes 

and Landforms, v. 32, p. 1323–1345.

Dingman, S.L., 1984, Fluvial Hydrology, W.H. Freeman and 

Company, New York, 383 p.

Elliot,W.J., Liebenow, A.M., Laflen, J.M. and Kohl, K.D., 

1989, A compendium of soil erodibility data from WEPP 

cropland soil field erodibility experiments 1987 and 1988: 

National Science and Engineering Research Laboratory 

(NSERL) Report No. 3, The Ohio State University and 

USDA Agricultural Research Service, 23 p, with multiple 

tables, accessed December 22, 2011, at http://www.ars.usda.

gov/SP2UserFiles/ad_hoc/36021500WEPP/weppbiblio.pdf. 

Foster, G.R., Meyer, L.D., 1975, Mathematical simulation of 

upland erosion using fundamental erosion mechanics, in

Present and prospective technology for predicting sediment yields and sources, Oxford, Miss., 1972, Proceedings: 

USDA Sedimentation Laboratory, Sediment-Yield Workshop, U.S. Agricultural Research Service (Rep) ARS-S-40, 

p. 190–207. 

Foster, G.R., 1982, Modeling the erosion process, chap. 8 of

Haan, C.T., ed., Hydrologic modeling of small watersheds: 

St. Joseph, Mich., American Society of Agricultural Engineers, ASAE Monograph No. 5, p. 297–360.

Foster, G.R., Flanagan, D.C., Nearing, M.A., Lane, L.J., 

Risse, L.M., and Finkner, S.C., 1995, Hillslope erosion 

component, chap. 11 of Flanagan, D.C. and Nearing, M.A., 

eds., USDA Water Erosion Prediction Project, NSERL 

Report No. 10: West Lafayette, Ind., National Soil Erosion 

Research Laboratory, p. 11.1–11.10. 

Gable, D.J., 1980, Geologic map of the Gold Hill quadrangle, 

Boulder County, Colorado: U.S. Geological Survey, Geologic Quadrangle Map GQ-1525, scale 1:24,000.

Giovannini, Giacomo, Lucchesi, S., and Giachetti, M., 1988, 

Effect of heating on some physical and chemical parameters 

related to soil aggregation and erodibility: Soil Science, 

v. 146, no. 4, p. 255–261.

Grabowski, R.C., Droppo, I.G., and Wharton, G., 2011, Erodibility of cohesive sediments—The importance of sediment 

properties: Earth-Science Reviews, v. 105, p. 101–120. 

Guy, H.P. 1977, Laboratory theory and methods for sediment 

analysis: Techniques of Water-Resources Investigations of 

the United States Geological Survey, Chap. C1, Book 5, 

58 p.

Gyssels, G., Poesen, J., Bochet, E., and Li, Y., 2005, Impacts 

of plant roots on the resistance of soils to erosion by 

water—A review: Progress in Physical Geography, v. 29, 

p. 189–217.

Hairsine, P.B., and Rose, C.W., 1992, Modeling water erosion 

due to overland flow using physical principles, 1. Sheet 

flow: Water Resources Research, v. 28, no. 1, p. 237–243.

Heiri, O., Lotter, A.F., and Lemcke, G., 2001, Loss on ignition 

as a method for estimating organic and carbonate content in 

sediments—Reproducibility and comparability of results: 

Journal of Paleolimnology, v. 25, p. 101–110.

Huang, Jianchun, Hilldale, R.C., and Greimann, B.P., 2006, 

Cohesive sediment transport, chap. 4 of Erosion and sedimentation manual: U.S. Bureau of Reclamation, 

p. 4-1–4-54.

Julien, P.Y., 1998, Erosion and sedimentation: New York, 

N.Y., Cambridge University Press, 280 p.

Kluber, L.A., Tinnes, K.M., Caldwell, B.A., Dunham, S.M., 

Yarwood, R.R., Bottomley, P.J., Myrold, D.D., 2010, 

Ectomycorrhizal mats alter forest soil biogeochemistry: Soil 

Biology and Biochemistry, v. 42, no. 9, p. 1607–1613.

Knoepp, J.D., and DeBano, L.F., 2005, Chapter 3—Soil 

chemistry, in Neary, D.G., Ryan, K.E., and DeBano, L.F., 

eds., Wildland fire in ecosystems, effects of fire on soil and 

water: Ogden, Utah, U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station, General Technical Report RMRS-GTR-42-vol.4, p. 53–71.
40 Variations in Soil Detachment Rates after Wildfire

Kroll, C.N., and Stedinger, J.R., 1996, Estimation of moments 

and quantiles using censored data: Water Resources 

Research, no. 32, v. 4, p. 1005–1012.

Lane, L.J., Foster, G.R., and Nicks, A.D., 1987, Use of fundamental erosion mechanics in erosion prediction: St. Joseph, 

Miss., ASAE, Paper No. 87-2540, 10 p.

Meyer-Peter, E., and Müller, R., 1948, Formulas for bed-load 

transport: International Association of Hydraulic Structures 

Research, Stockholm, 7–9 June 1948, p. 39–64.

Moody, J.A., Smith, J.D., and Ragan, B.W., 2005, Critical shear stress for erosion of cohesive soils subjected to 

temperatures typical of wildfires: Journal of Geophysical 

Research, v. 110, doi 10.1029/2004JF000141.

Moody, J.A., and Martin, D.A., 2009, Forest fire effects on 

geomorphic processes, chap. 2 of Cerdà, A., and Robichaud, 

P.R., eds., Fire effects on soils and restoration strategies, 

Volume 5—Land and reconstruction and management: 

Enfield, N.H., Science Publishers, p. 41–79.

Nachtergaele, Jeroen, and Poesen, Jean, 2002, Spatial and 

temporal variations in resistance of loess-derived soils to 

ephemeral gully erosion: European Journal of Soil Science, 

v. 53, p. 449–463. 

National Oceanic and Atmospheric Administration, 2000, 

Climatography of the United States No. 81, Monthly station normal of temperature, precipitation, and heating and 

cooling degree days 1971–2000, 04 California (73 p) and 

05 Colorado (40. P): Asheville, N.C., National Oceanic and 

Atmospheric Administration. 

Nyman, Peter, Sheridan, G.J., Smith, H.G., and Lane, P.N.J., 

2011, Evidence of debris flow occurrence after wildfire in 

upland catchments of south-east Australia: Geomorphology, 

v. 125, p. 383-401.

Pepin, N., 2000, Twentieth-century change in the climate 

record for the Front Range, Colorado, U.S.A.: Arctic, 

Antarctic, and Alpine Research, v. 32, no. 2, p. 135–146.

Roberts, Jesse, Jepsen, Rich, Gotthard, Doug, and Lick, 

Wilbert, 1998, Effect of particle size and bulk density on 

erosion of quartz particles: Journal of Hydraulic Engineering, v. 124, p. 1261–1267.

Robichaud, P.R., Wagenbrenner, J.W., and Brown, R.E., 

2010, Rill erosion in natural and disturbed forests—1. 

Measurements: Water Resources Research, v. 46, W10506, 

doi:10.1029/2009WR008314, 14 p.

Sheridan, G.J., Lane, P.N.J, and Noske, P.J., 2007, Quantification of hillslope runoff and erosion processes before 

and after wildfire in a wet Eucalyptus forest: Journal of 

Hydrology, v. 343, no. 1-2, p. 12–28.

Smith, J.D., 2004, The role of riparian shrubs in preventing 

floodplain unraveling along the Clark Fork of the Columbia 

River in the Deer Lodge Valley, Montana: American Geophysical Union, Riparian Vegetation and Fluvial Geomorphology, Water Science and Application 8, p. 77–85.

Tennant, D., 1975, A test of a modified line intersect method 

of estimating root length: Journal of Ecology, v. 63, 

p. 995-1001.

U.S. Department of Agriculture Soil Survey Staff, 2011, 

Natural Resource Conservation Service: U.S. Department of 

Agriculture, Web Soil Survey, accessed December 22, 2012, 

at http://websoilsurvey.nrcs.usda.gov/ and https://soilseries.

sc.egov.usda.gov. 

U.S. Forest Service, 2011, Forest geology of Los Padres 

National Forest: U.S. Forest Service, accessed December 

22, 2011, at http://www.fs.usda.gov/wps/portal/

fsinternet/!ut/p/c4/04_SB8K8xLLM9MSSzPy8xBz9CP0os3g

jAwhwtDDw9_AI8zPyhQoY6BdkOyoCAGixyPg!/?ss=1105

07&navtype=BROWSEBYSUBJECT&cid=fsm9_034082&n

avid=150130000000000&pnavid=150000000000000&pos

ition=Not Yet Determined.Html&ttype=detail&pname=Los 

Padres National Forest- Nature & Science.

Wiberg, P.L., and Smith, J.D.,1987, Calculations of the critical 

shear stress for motion of uniform and heterogeneous 

sediments: Water Resources Research, v. 23, p. 1471–1480.

Yang, C.T., 1972, Unit stream power and sediment transport: 

Journal of the Hydraulic Division, American Society of 

Civil Engineers, v. 98, no. 10, p. 1805–1826.

Yang, C.T., 2006, Noncohesive sediment transport, chap. 3 of

Erosion and Sedimentation Manual: U.S. Bureau of Reclamation, p. 3-1–3-111.

Publishing support provided by: 

Denver Publishing Service Center

For more information concerning this publication, contact:

Chief, Branch of Regional Research, Central Region

U.S. Geological Survey

Box 25046, Mail Stop 418

Denver, CO 80225

(303) 236-5021

Or visit the USGS National Research Program Web site at:

http://water.usgs.gov/nrp/
Moody and Neiman—Variations in Soil Detachment Rates after Wildfire—Scientific Investigations Report 2012–5233