Map of Debris Flows Caused by Rainfall During 

1996 in Parts of the Reedsport and Deer Head Point 

Quadrangles, Douglas County, Southern Coast 

Range, Oregon

By Jeffrey A. Coe, John A. Michael, and Marianela Mercado Burgos 

Pamphlet accompanies map

Open-File Report 2011–1150

U.S. Department of the Interior

U.S. Geological Survey
Cover: Aerial photographs of a debris fan taken before and after a debris flow in the map area. Photograph 

on the left was taken on July 29, 1992. Photograph on the right was taken May 17, 1997. The horozontal distance between the two buildings is about 200 m. The debris fan is located along the right edge of the map, 

just north of the Umpqua River. Photographs by the U.S. Bureau of Land Management.
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia 2011

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

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resources, natural hazards, and the environment:

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Suggested citation:

Coe, J.A., Michael, J.A., and Burgos, M.M., 2011, Map of debris flows caused by rainfall during 1996 in parts of 

the Reedsport and Deer Head Point quadrangles, Douglas County, southern Coast Range, Oregon: U.S. Geological Survey Open File Report 2011–1150, 9 p. pamphlet, 1 sheet, scale 1:12,000.

Any use of trade, product, or firm 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 contains copyrighted material as noted in the text. Permission to reproduce copyrighted items for other than personal use must be secured 

from the copyright owner.
Contents

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

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

Setting .............................................................................................................................................................2

Rainfall in November, 1996 ...........................................................................................................................3

Map Description.............................................................................................................................................3

Mapping Debris Flows .........................................................................................................................3

Subdivision of Debris Flows.......................................................................................................5

Field Checking .......................................................................................................................................5

Debris-Flow Polygons ..........................................................................................................................5

Digital Data......................................................................................................................................................6

Acknowlegments ...........................................................................................................................................7

References......................................................................................................................................................7 

Figures

1. Location of the map area with respect to the Reedsport and Deer Head Point

 1:24,000-scale quadrangles......................................................................................................................2

2. (A) Cumulative precipitation during 1996 and 1997, and (B) cumulative hourly precipitation

 during the Nov. 17–19 rain storm.............................................................................................................4

3. Example of a 1:12,000-scale aerial photograph used for mapping....................................................6

Table

1. Rain-gage station information .................................................................................................................3

Map

1. Debris flows caused by rainfall during 1996 in parts of Reedsport and Deer Head Point

 quadrangles.......................................................................................................................................... Link 

 iv
Conversion Factors

SI Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi) 

Area

square kilometer (km2

) 0.3861 square mile (mi2)

square meter (m2

) 0.0002471 acre

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

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83), HARN

Elevation, as used in this report, refers to distance above the vertical datum.

 v
Map of Debris Flows Caused by Rainfall During 

1996 in Parts of the Reedsport and Deer Head Point 

Quadrangles, Douglas County, Southern Coast 

Range, Oregon

By Jeffrey A. Coe,1 John A. Michael,1 and Marianela Mercado Burgos2

1

U.S. Geological Survey, MS 966, Denver Federal Center, Denver, Colo. 80225

2

University of Puerto Rico, Mayagüez, Puerto Rico

Abstract

This 1:12,000-scale map shows an inventory of debris 

flows caused by rainfall during 1996 in a 94.4 km2

 area of 

the southern Coast Range of Oregon. This map and associated digital data are part of a larger U.S. Geological Survey 

study of debris flows in the southern Coast Range. Available 

evidence indicates that the flows were triggered by a rain 

storm that occurred between November 17 and 19. The closest 

rain gage in the Coast Range (Goodwin Peak) recorded 245 

mm during the storm. Maximum rainfall intensity during the 

storm was 13.2 mm/hr on November 18. Debris flows were 

photogrammetrically mapped from 1:12,000-scale aerial 

photographs flown in May 1997. The inventory is presented 

on imagery derived from LiDAR data acquired in 2008. We 

classified mapped debris flows into four categories based on 

the type of debris-flow activity: (1) discrete slide source areas, 

(2) predominantly erosion, (3) predominantly transport or 

mixed erosion and deposition, and (4) predominantly deposition. Locations of woody-debris jams are also shown on the 

map. The area encompassed by debris flows is 2.1 percent of 

the 94.4 km2

 map area. 

Introduction

In the Coast Range of Oregon, nearly all drainage basins 

periodically generate debris flows (for example, see May and 

Gresswell, 2004). These flows often affect natural resources 

and roads and structures both within, and at the mouths of 

basins (Hofmeister, 2000; Squier and Harvey, 2000; Mills 

and Hinkle, 2001). During 1996, two major storms, one in 

February and one in November, produced widespread debris 

flows in the Coast Range. In the southern Coast Range, most 

debris-flow activity in 1996 was triggered by the November 

storm (Robison and others, 1999; Wiley, 2000). Two debris 

flows in November caused five fatalities (Mills and Hinkle, 

2001). Two additional storms affected southern Oregon in 

December 1996, and January, 1997, but the debris-flow effects 

from these storms were minimal in the southern Coast Range 

(Wiley, 2000). 

The Oregon State Highway 38 corridor through the 

southern Coast Range is one of the most hazardous debrisflow areas in Oregon, yet much previous debris-flow mapping in the area was limited to point data along the highway 

(Hofmeister, 2000), which is not particularly well-suited for 

debris-flow process studies or as “ground truth” for predictive 

maps of debris-flow hazard. Work by the Oregon Department 

of Forestry following debris flows in 1996 was an exception to 

this statement (Robison and others, 1999). Work by Robison 

and others consisted of detailed field mapping of debris-flow 

source areas and effects on channels in two areas south of 

Scottsburg, Oregon. Griswold and Iverson (2007) used part 

of this mapping to estimate debris-flow travel distances and 

effects on debris fans using the debris-flow modeling program 

LAHARZ (Schilling, 1998; Iverson and others, 1998). 
2 Debris Flows Caused by Rainfall in Parts of Douglas County, Southern Coast Range, Oregon

Our work expands on this previous work by providing 

detailed debris-flow mapping in a 94.4 square kilometer (km2

) 

area along Highway 38 between Reedsport and Scottsburg 

(fig. 1 and map). Our mapping identifies debris-flow source 

areas, areas of predominantly erosion, transport or mixed erosion and deposition, and areas of deposition. We used newly 

available (2009), high resolution (0.91 m cells (3 ft.)), airborne 

Light Detection And Ranging (LiDAR) data from the Oregon 

Department of Geology and Mineral Industries (DOGAMI) as 

the topographic base for our mapping. 

Setting

The map area is between Reedsport and Scottsburg, 

Oregon, and is transected by the Umpqua River and Highway 

38. Elevations in the map area range from about 2 m above sea 

level along the Umpqua River to about 490 m at the summit of 

Deer Head Point (see map). The area has a maritime climate 

with wet winters and dry summers. Average annual precipitation ranges from about 1,520 to 2,540 mm (PRISM Climate 

Figure 1. Index map showing the location of the map area with respect to the 

Reedsport and Deer Head Point 1:24,000-scale USGS topographic quadrangles.

Mapped 

area

Umpqua River

Smith River

Loon

Lake

Coos

Bay

PACIFIC OCEAN

Elkton

Reedsport

Dunes City

Deer Head

Point Reedsport Scottsburg

North

Bend

43°45’

124°00’

Elkton

Gardiner

Goodwin

Peak

101

101

38

OREGON

Portland

Salem

Eugene Study Area

0

0 5

5

10 KILOMETERS

10 MILES

EXPLANATION

USGS quadrangle name

Town

Rain gage

Reedsport
Setting 3

Group, 2006). The wet and relatively warm climate results in a 

coastal forest dominated by Douglas fir, western hemlock, red 

alder, and a variety of understory shrubs. Trees are harvested 

throughout the map area, usually by commercial clear-cut 

operations.

Tertiary marine sandstones and siltstones of the Tyee 

Formation (Niem and Niem, 1990; Walker and MacLeod, 

1991) underlie the area. The drainage network is dense, 

with a dendritic pattern that has often been characterized as 

highly dissected (for example, Benda, 1990). Hillslopes are 

short, steep, and typically mantled by 0.5 to 3 m of colluvial 

soil (Dietrich and Dunne, 1978; Reneau and Dietrich, 1991; 

Montgomery and others, 2002). Debris flows typically 

mobilize from small slides in concave hillslope areas and 

increase in volume by erosion and entrainment of downslope 

channel sediment before depositing material in higher order 

drainage channels and on fans (Benda and Cundy, 1990). 

Woody debris is often incorporated into debris flows, and 

woody-debris jams often influence the locations of debris-flow 

deposition (Montgomery and others, 2003). 

Rainfall in November, 1996

Four rain gages were operating in the vicinity of the 

study area in 1996 (figs. 1 and 2). Three gages, Gardiner, 

North Bend, and Elkton, were located at National Weather 

Service (NWS) Cooperative Network stations, and the 

fourth, Goodwin Peak, was at a U.S. Forest Service Remote 

Automatic Weather Station (RAWS). The Gardiner and North 

Bend stations were along the Pacific coast at elevations of 9 m 

and 2 m, respectively. The Goodwin Peak gage was within the 

Coast Range at an elevation of 557 m. The Elkton gage was 

on the eastern (leeward) flank of the Coast Range at an elevation 

of 37 m. 

Cumulative rainfall in 1996 was greatest at Goodwin 

Peak (3,232 mm, fig. 2A) and lowest at Elkton (2,163 mm). 

Cumulative rainfall at Gardiner and North Bend was 2,418 mm 

and 2,182 mm, respectively. Seasonal antecedent rainfall from 

the beginning of the fall/winter wet season on October 1, 1996, 

to the start of the November 17–19 storm was 441 mm, 232 

mm, 256 mm, and 201 mm at Goodwin Peak, Gardiner, North 

Bend, and Elkton, respectively. With the exception of Elkton 

rainfall, all of these rainfall values exceed the antecedent rainfall threshold of 203 mm defined by Wiley (2000) as necessary 

for debris-flow occurrence in Oregon.

The November 17–19 storm was the result of an extensive system of moist subtropical air that originated over the 

tropical Pacific and spread from south to north across Oregon 

(George Taylor, Oregon Climate Service, unpublished data, 

1997). More recent terms used to describe this type of weather 

system are “Pineapple Express” or “Atmospheric River” (for 

example, see Junker and others, 2009). Total rainfall during 

the 3-day storm was 245 mm, 254 mm, 231 mm, and 143 mm 

at Goodwin Peak, Gardiner, North Bend, and Elkton, respectively. Hourly rainfall during the storm was collected at the 

Goodwin Peak and Elkton gages (fig. 2B). The storm had a 

mean intensity of 4.9 mm/hr for 47 hours at Goodwin Peak 

and 3.4 mm/hr for 39 hours at Elkton. Maximum rainfall 

intensity was almost two times greater at Goodwin Peak (13.2 

mm/hr for one hour on November 18) than at Elkton (7.4 

mm/hr for two hours on the 18th). Based on the comparable 

positions of the Goodwin Peak gage and the map area within 

the core of the Coast Range, rainfall within the map area was 

probably most similar to that at Goodwin Peak.

Map Description

Mapping Debris Flows

Initially, we mapped debris flows from 1:12,000-scale, 

color, stereo aerial photographs onto a topographic base map 

using a Kern PG–2 photogrammetric plotter (Pillmore, 1989). 

The PG–2 had 5×, 10×, and 20× zoom magnification capabilities. The topographic base map used on the PG–2 was 

created by plotting digital versions of the Deer Head Point 

and Reedsport U.S. Geological Survey (USGS) 7.5-minute 

quadrangles at 1:12,000 scale. The aerial photographs were 

flown in May 1997. The 1:12,000 scale of the photography 

allowed us to accurately identify debris-flow features as small 

as about 1 m in clear-cut areas. For areas under trees, our 

ability to identify debris-flow features was highly variable and 

poorly constrained. Debris flows were mapped if their features 

were fresh, that is, they had a lighter tone than their surroundings (fig. 3). Many parts of the study area had dense tree cover 

making it difficult to see complete paths affected by debris 

flows. We extended mapped debris flows through these areas 

if we saw obvious evidence for debris flows in upstream and 

downstream locations. 

Table 1. Rain-gage station information

Gage name National Weather 

Service (NWS) ID

Latitude1 Longitude1 Elevation

(m)

Goodwin Peak 352545 43°55'41" 123°53'25" 557

Gardiner 353193 43°45'00" 124°07'00" 9

North Bend 356073 43°25'00" 124°15'00" 2

Elkton 352633 43°36'00" 123°35'00" 37 1 Latitude and longitude locations are approximate
4 Debris Flows Caused by Rainfall in Parts of Douglas County, Southern Coast Range, Oregon

Elkton 

Goodwin Peak

EXPLANATION

0

50

100

150

200

250

12:00

0:00

12:00

0:00

12:00

0:00

12:00

0:00

12:00

0:00

12:00

Cumulative Rainfall (mm)

Date/Time 

Maximum Intensity: 13.2 mm/hr 

11/18 21:00–21:59

Mean Intensity: 4.9 mm/hr 

11/17 17:00 to 11/19 16:00

Mean Intensity: 3.4 mm/hr 

11/17 23:00 to 11/19 14:00

Maximum Intensity: 

7.4 mm/hr 

11/18 13:00–14:59

B

Nov. 16

Nov. 17

Nov. 17

Nov. 18

Nov. 18Nov. 19

Nov. 19Nov. 20Nov. 20

Nov. 21

Nov. 21

1996

Goodwin Peak

North Bend

Gardiner

Elkton

EXPLANATION

Acquisition of 

aerial photographs

0.0

500.0

1,000.0

1,500.0

2,000.0

2,500.0

3,000.0

3,500.0

4,000.0

4,500.0

5,000.0

5,500.0

1/1/19963/1/19965/1/19967/1/1996

9/1/1996

11/1/1996

1/1/1997

3/1/19975/1/19977/1/19979/1/1997

11/1/1997

1/1/1998

Cumulative Precipitation (mm)

Date

A

Figure 2. Diagram showing A, cumulative precipitation during 1996 and 1997, and B, cumulative 

hourly rainfall during the November 17–19 rainstorm. See figure 1 for rain gage locations.
Map Description 5

Work by Brardinoni and others (2003) and Robison and 

others (1999) indicates that most (up to 85 percent and greater 

than 95 percent, respectively) landslides (or debris flows) 

may be missed by conventional aerial photographic interpretation in mature forested areas of the Pacific Northwest. 

Conventional aerial photographic interpretation and mapping 

consists of landslide identification using a desktop stereoscope 

(typically with 3× to 8× magnification) and manual transfer of 

identified landslides to a topographic base map. Even though 

our photogrammetric methods utilized more sophisticated 

equipment with higher magnification, we acknowledge that 

fewer debris flows are shown on the map compared to the 

unknown actual number of flows that occurred in 1996. 

Subdivision of Debris Flows 

During mapping, debris flows were subdivided into 

discrete slide source areas, areas dominated by erosion, those 

dominated by transport or mixed erosion and deposition, and 

areas dominated by deposition. We follow Varnes (1978) 

terminology and define “slide” as a displaced mass where 

movement has occurred by shear displacement along one or 

more surfaces. Discrete slides were mapped where we could 

see or interpret both the upslope and downslope extent of failures. Areas mapped as discrete slides included both evacuated 

areas (scars) and deposits. The downslope extent of discrete 

slides could often be defined as the location where the width 

of the failure narrowed and became channelized. At the heads 

of many mapped debris flows, we observed a headscarp and 

downslope erosion, but no indicator of the downslope extent 

of failure. These areas were mapped as eroded areas with no 

discrete landslide source area. Eroded areas were devoid of 

vegetation, topographically concave, very light in color, and 

exhibited sharp tonal contrast compared to vegetated surroundings (fig. 3). Areas dominated by deposition tended to 

have topographically convex or planar surface morphologies 

that were more jumbled (rougher) than eroded areas. Remnants of in-situ vegetation (for example, standing trees) were 

sporadically present in some deposition areas. In areas mapped 

as transport zones or as areas of mixed erosion and deposition, pre-flow topographic surfaces were visible, or surfaces 

exhibited features suggestive of both erosion and deposition 

(described above). Woody-debris jams were mapped in locations where we observed topographically convex bumps in 

channels that contained large tree trunks. Sediment deposition 

was often located upstream from these jams.

Based on the prevalence of debris flows in the southern 

Coast Range in 1996 (Robinson and others, 1999; Hofmeister, 

2000; Squier and Harvey, 2000; Wiley, 2000), we infer that 

debris flows were responsible for creating the areas of erosion, 

transport, and deposition shown on the map. However, as 

debris flows and water-dominated flows (floods) can often 

occur together on the west coast of the United States (for 

example, Ellen and Wieczorek, 1988), it is possible that 

flooding also contributed to the formation of features in 

the mapped areas. Also, modification of mapped features 

by running water or additional debris flows between the 

November 1996 storm and the May 1997 acquisition of aerial 

photography is also possible. We could not account for these 

possibilities in our mapping. 

Once mapped, debris flows were digitized from the 

1:12,000-scale, quadrangle-based maps into the Environmental 

Systems Research Institute, Inc. (ESRI®) ArcGIS® and then 

transferred to a LiDAR-derived, shaded-relief base map. The 

LiDAR data were acquired in 2008 and became available to us 

in August 2009. The shaded-relief base map has 0.91 m (3.00 

ft) cells and is illuminated from an azimuth of 315 degrees 

and a vertical angle of 45 degrees. The process of transferring 

mapped debris flows to the LiDAR map was difficult because 

the topographic details visible in the LiDAR were often 

not visible in, or were different from, the more generalized 

topography onto which the debris flows were initially mapped. 

When we transferred the debris flows, we attempted to retain 

their original shapes and sizes as much as possible. In general, 

travel distance lengths were not affected during the transfer 

process, and debris flow widths were minimally affected. 

However, in many instances, the debris-flow polygons, 

particularly in steep channel areas, had to be moved laterally 

by about 25 m (about 2 mm at 1:12,000-scale) to properly fit 

the LiDAR topography. Steep channels were the typical areas 

where this was a problem. There, large portions of debrisflow travel paths mapped onto the USGS quads often did not 

occupy channel bottoms on the LiDAR map, but rather were 

located entirely on side slopes of channels. In order to correct 

this situation, debris flows were moved laterally until they 

were positioned within channel bottoms on the LiDAR map. 

Field Checking

We did not systematically field check our mapping 

because most areas that were affected by debris flows in 1996 

were covered by vegetation in 2008 and 2009 when we did 

our mapping from aerial photographs. Based on the sporadic 

field observations that we did make, we found that it was difficult to differentiate 1996 scars and deposits from pre- and 

post-1996 scars and deposits from field observations alone. 

Additionally, we observed that many (most?) of our mapped 

debris flows from 1996 could not be identified using the 2008 

LiDAR data alone. This observation indicated that it would be 

difficult to use LiDAR alone, without any supplemental information from aerial photographs, satellite images, or field work 

to map the relatively small, shallow debris flows that are common in heavily forested areas of the Pacific Northwest. This 

assertion is similar to that made by Burns and others (2010) in 

the northern Coast Range of Oregon.

Debris-Flow Polygons

The area encompassed by all types of debris-flow 

polygons (slide, erosion, transport, and deposition) was 2.0 

km2

, which is 2.1 percent of the 94.4 km2 map area. For 
6 Debris Flows Caused by Rainfall in Parts of Douglas County, Southern Coast Range, Oregon

the 155 discrete slide source areas mapped, the minimum, 

maximum, and mean sizes were 17 m2

, 1,685 m2, and 370 

m2

, respectively. Thus far, the map data have been used for 

evaluating predictions of debris-flow source areas (Baum and 

others, 2011), developing models for estimating debris-flow 

travel distances (Coe and others, 2011), and for estimating 

volumes of sediment eroded and entrained into debris flows 

for accurate predictions of debris-flow volumes expected 

in channels and at the mouths of drainage basins (Coe and 

Michael, 2009).

Digital Data

Digital data included with this map report include a 

polygon showing the extent of mapping, debris-flow polygons, 

woody-debris jam locations, and the bare-earth LiDAR data 

used for the base map. Data are available as ESRI® shape and 

grid files within a single zipped archive file. Debris-flow polygon data are not intended for use at scales larger than 1:12,000 

(for example, 1:6,000). 

Image from U.S. Bureau of Land Management,

Coos Bay District Office, North Bend, Oreg.

43°40’40”

123°56’00”

2000 FEET

500 METERS

0

0

500 1000 1500

100 200 300 400

Figure 3. Example of a 1:12,000-scale aerial photograph used for mapping. Area covered by the photograph 

is shown on map.
Acknowlegments 7

Acknowledgments 

The authors thank Frank Price of the U.S. Bureau of Land 

Management in Coos Bay, Oregon, for lending us the aerial 

photographs used in this study. John Seward and Jason Hinkle 

of the Oregon Department of Forestry, and Bill Schulz and 

Jonathan Godt of the U.S. Geological Survey provided suggestions that improved the clarity of the report. Editing support 

provided by Lisa Binder, Denver Publishing Science Network.

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8 Debris Flows Caused by Rainfall in Parts of Douglas County, Southern Coast Range, Oregon

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