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Landslide-Induced Flooding at Ophir Creek, 

Washoe County, Western Nevada, 

May 30,1983

By Patrick A. Glancy, U.S. Geological Survey, and John W. Bell, 

Nevada Bureau of Mines and Geology

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1617

Prepared in cooperation with the

NEVADA BUREAU OF MINES AND GEOLOGY

Carson City, Nevada 

2000
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

CHARLES G. GROAT, Director

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government

Library of Congress Cataloging in Publication Data

Glancy, Patrick A.

Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30, 

1983 / by Patrick A. Glancy and John W. Bell; prepared in cooperation with the Nevada 

Bureau of Mines and Geology.

p. cm.—(U.S. Geological Survey Professional Paper; 1617)

ISBN 0-607-93988-5

1. Floods-Nevada-Ophir Creek Valley (Washoe County) 2.

Landslides-Nevada-Ophir Creek Valley (Washoe County) I. Bell, John W. II. Nevada

Bureau of Mines and Geology. III. Title IV. Series.

GB1399.4.N3G552000 

551.48'9'0979355-dc21

00-026435

For sale by U.S. Geological Survey, Information Services, 

Box 25286, Federal Center, Denver, CO 80225
Frontispiece. Panoramic aerial view of Ophir Creek and Slide Mountain, western Nevada, looking northwest. 

Mount Rose at upper right. Photographed from airliner by A.S. Van Denburgh, U.S. Geological Survey, 

August5, 1983.

CONTENTS

Abstract .....................................................................................................................................................................^ 1

Introduction ................................................................................. 2

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

Acknowledgments ..................................................................................................................................................... 6

The Setting ....................................................................._ 6

Basin Geologic Characteristics ................................................................................................................................. 9

The Drainageway ...................................................................................................................................................... 10

Price Lakes ..................................................................................................................................................... 10

Ophir Creek ................................................................................................................................................... 10

Summary of Landslide and Flood History ............................................................................................................................ 15

Landslides ................................................................................................................................................................. 15

Roods ................................................................................. 16

Antecedent Weather Conditions ............................................................................................................................................ 18

The Landslide .....................................................................................................................................................^ 22

Lithologic Character and Structure of Slide Mountain ............................................................................................. 22

The Landslide of May 30, 1983 ................................................................................................................................ 22

Possible Causes of the Landslide .............................................................................................................................. 24

Effects of the Orientation of Bedrock Joints ............................................................................................................. 25

The Flood .....................................................................................................................................................^ 26

The Expulsion of Price Lakes ................................................................................................................................... 27

The Torrent in the Canyons of Ophir Creek .............................................................................................................. 29

Flow on the Alluvial Fan ........................................................................................................................................... 33

Flow Rates and Velocities ......................................................................................................................................... 39

Average Rates and Velocities ......................................................................................................................... 42

Rates Associated With Expulsion of Price Lakes .......................................................................................... 44

Rates in the Canyons ..................................................................................................................................... 47

Slope-Area Measurement.................................................................................................................... 48

Flow-Around-A-Bend Measurement.................................................................................................. 50

Rates on the Alluvial Fan .............................................................................................................................. 51

Discussion ............................................................................._ 53

Debris Movement ................................................................................................................................................................. 53

Landslide Debris ....................................................................................................................................................... 53

Canyon Debris ........................................................................................................................................................... 53

Erosion ................................................................................. 55

Sediment Deposition ................................................................................................................................................. 55

Volume ........................................................................................................................................................... 56

Intercanyon Reach .............................................................................................................................. 56

Alluvial Fan ........................................................................................................................................ 56

Total ................................................................................................................................................... 56

Sediment Particle-Size Characteristics .......................................................................................................... 58

Flood Volume and Water Sources ......................................................................................................................................... 62

Volume ............................................................................................................................................................^ 62

Sources ...................................................................................................................................................................... 65

Source 1 ......................................................................................................................................................... 65

Source 2 ....................................................................................................................................................... 69

Source 3 ......................................................................................................................................................... 69

Source 4 ......................................................................................................................................................... 69

SourceS ................................................................................................................................................^^^^^ 70

Source 6 ......................................................................................................................................................... 70

Source 7 ........................................................................................................................................................^ 73

Descriptions, Discussions, and Interpretations of Floodflow Dynamics .............................................................................. 74

CONTENTS V
The Canyon Reach .................................................................................................................................................... 74

Proximal Segment of the Ophir Creek Fan ............................................................................................................... 76

Medial Segment of the Ophir Creek Fan .................................................................................................................. 77

Distal Segment of the Ophir Creek Fan .................................................................................................................... 80

Variation in the Water-Sediment Mixture Over Time................................................................................................ 80

Summary ..................................................................................................................................................................^ 82

Flood Damage ........................................................................ 83

The 1983 Flood—A Test of Flood-Hazards Prediction ........................................................................................................ 83

After the Flood ................................................................ 84

Summary and Conclusions ................................................................................................................................................... 88

References Cited ............................................................................................................................................................^ 92

Appendix A: Landslide, Flood, and Weather History ........................................................................................................... A-l

Previous Landslides.................................................................................................................................................... A-2

Previous Floods.......................................................................................................................................................... A-3

Floods Caused by Winter Storms ................................................................................................................... A-3

January 1874....................................................................................................................................... A-3

November 1875................................................................................................................................... A-3

July 1890................................................................_

March 1907......................................................................................................................................... A-7

December 1937................................................................................................................................... A-7

January 1943....................................................................................................................................... A-8

November 1950................................................................................................................................... A-8

January-February 1963 ....................................................................................................................... A-9

Weather Data and History.......................................................................................................................................... A-9

Appendix B: Eyewitness Accounts of the Landslide and Flood ........................................................................................... B-l

Ronald P Mentgen..................................................................................................................................................... B-2

Douglas R. Cook..........................................._ B-2

James Schumacher..................................................................................................................................................... B-3

Mark Bridgewater...................................................................................................................................................... B-3

William and Elizabeth Willets.................................................................................................................................... B-4

Tom Reed and Others................................................................................................................................................. B-4

Anne Ogilvy............................................................................................................................................................... B-6

Kathleen Thompson................................................................................................................................................... B-6

GregStafford.....................................................^ B-6

ShMey Stafford ....................................... B-7

VicStafford...................................................^ B-7

Kathleen ''Katy' 1 Cline..........................................^ B-7

Patricia Sommers ....................................................................................................................................................... B-8

Susan S. Graves.......................................................................................................................................................... B-9

Kenneth Julian.....................................................................................................^ B-9

ReedWDopf..............................................,...............^

Charles McQueny......................................................._

Mrs. E.H. Thorn ..................................................................................................................^

Appendix C: Particle-Size Distribution of Samples and Equations Used in Calculations.................................................... C-l

Equations Used in Calculating Statistics of Particle-Size Distributions.................................................................... C-2

VI Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
FIGURES

Frontispiece. Photograph showing panoramic aerial view of Ophir Creek and Slide Mountain, western Nevada, August 5, 1983. 

1-2. Maps showing:

1. Ophir Creek Basin, western Nevada, and nearby geographic features............................................................ 3

2. Locations of selected eyewitnesses and other features during the May 30, 1983, flood................................. 4

3. Photographs showing preflood and postflood views of Ophir Creek alluvial fan, July 15, 1977, and

June 6, 1983.........................................................» 7

4. Map showing areal extent of landslide and fluvial deposits prior to the May 30, 1983, flood................................. 8

5. Aerial photograph showing upper canyon of Ophir Creek downstream from Lower Price Lake, May 31, 1983 .... 11

6. Graph showing topographic gradients for Ophir Creek............................................................................................ 12

7-11. Photographs showing:

7. Two views of upper canyon of Ophir Creek, severely gouged and scoured by the high-energy flow

of the 1983 flood................................................................................................................................... 13

8. Heavily eroded Ophir Creek channel the day after the flood .......................................................................... 14

9. Downstream view of Ophir Creek just below mouth of lower canyon............................................................ 15

10. Oblique, aerial westward view of Ophir Creek alluvial fan, the major site of sediment deposition

bythe!983flood............................................._ 16

11. Views of Price Lakes and upper canyon of Ophir Creek before and after the flood, July 15, 1977,

and June 6, 1983.......................................................................................................................................... 17

12-13. Graphs showing:

12. Daily mean air temperature at Carson City, Nevada, April 1-June 28, 1983................................................... 20

13. Snowpack moisture and average daily temperature in late May and early June 1983,

Mount Rose Ski Area snow-survey station................................................................................................. 22

14. Map of 1983 Ophir Creek landslide features from preflood and postflood aerial photographs............................... 23

15-18. Photographs showing:

15. North-westward view of Ophir Creek landslide, May 31, 1983...................................................................... 24

16. One of the largest granitic blocks involved in rockfall-avalanche phase of Ophir Creek landslide ................ 25

17. Bottom sediments of Upper Price Lake, deformed and uplifted by 1983 landslide........................................ 26

18. Downslope dip of j oint surfaces and rockf all-avalanche zone of Ophir Creek landslide................................ 26

19. Stereographic plot of bedrock joint-set orientations in area of the 1983 Ophir Creek landslide.............................. 27

20. Photograph showing terminus of 1983 landslide and point of origin of flood ......................................................... 28

21. Profile of high-water surface of Upper Price Lake when expelled by the landslide................................................. 29

22-26. Photographs showing:

22. Two views of Price Lakes on June 3, 1983...................................................................................................... 29

23. Floodflow of Ophir Creek in upper canyon, downstream from Lower Price Lake, May 30, 1983................. 30

24. Northward view of flood downstream from mouth of upper canyon, May 30, 1983 ...................................... 31

25. Two views of coarse-grained deposits on broad flood plain between upper and lower canyons

of Ophir Creek, July 1983........................................................................................................................... 32

26. Two views of boulder berm on northern edge of flood plain of Ophir Creek at mouth

of lower canyon, July 1983 ......................................................................................................................... 34

27. Map showing flood-related reference sites on Ophir Creek alluvial fan .................................................................. 35

28-35. Photographs showing:

28. Three aerial views of effects of peak-flow surge on north terrace of Ophir Creek downstream

from lower canyon mouth ........................................................................................................................... 36

29. Northeastward route of mud-laden matrix fluid that swept away Linda Reed after it overflowed

the north-bank terrace of the Ophir Creek fan ............................................................................................ 37

30. Jeffrey pine abraded by the flood along the north bank of Ophir Creek about 100 yards

upstream from Old Highway 395................................................................................................................ 38

31. Downstream extent of boulder deposition on the Ophir Creek fan resulting from 1983 flood....................... 39

32. Two views of flood damage to Stafford home, June 1, 1983........................................................................... 40

33. Two views of flood damage to Cline home, June 1, 1983 ............................................................................... 41

34. Downstream view of Cline house buried in flood deposits, afternoon of May 30, 1983 ................................ 42

35. Two views of flood-damaged Turek home, June 1, 1983 ................................................................................ 43

CONTENTS VII
36. Photograph and cross section diagram of outlet of Lower Price Lake after flood.................................................... 45

37. Diagrammatic cross sections of Ophir Creek channel near lower canyon mouth before and after 1983 flood........ 49

38. Graph showing envelope curves for maximum measured floods in relation to 1983 Ophir Creek flood................. 51

39-41. Photographs showing:

39. Viscous, organic-laden leading edge of floodflow from Ophir Creek parallel to U.S. Highway 395

freeway, May 30, 1983................................................................................................................................ 52

40. Largest boulder known to have been moved by the 1983 flood....................................................................... 55

41. Unstratified and unsorted debris deposited by 1983 flood on broad flood plain between

upper and lower canyons of Ophir Creek.................................................................................................... 56

42. Map showing major areas of sediment deposition by 1983 flood on Ophir Creek alluvial fan................................ 57

43. Map showing locations of sediment sampling sites and histograms of particle-size distributions

of sediment sampled............................................................................................................................................ 59

44-46. Photographs showing:

44. Freshly exhumed debris deposits of 1983 flood on Stafford property just downstream from

Old Highway 395 ........................................................................................................................................ 60

45. Collection site of sediment sample 5 ............................................................................................................... 61

46. Collection site of sediment sample 6............................................................................................................... 61

47. Graph showing cumulative distribution of particle sizes for samples of sediment deposits ..................................... 62

48-49. Photographs showing:

48. Northeastward view of boulder- and tree-laden sediment deposits between Old Highway 395

and Tureck and Cline homes, afternoon of May 30, 1983.......................................................................... 64

49. Receding floodflow on Ophir Creek alluvial fan, May 31, 1983..................................................................... 66

50. Synthesized hydrograph of 1983 Ophir Creek flood................................................................................................. 67

51-53. Photographs showing:

51. Two aerial views of the freshly drained bed of Upper Price Lake................................................................... 68

52. Mud-coated north-bank terrace of Ophir Creek just downstream from lower canyon mouth, June 3, 1983... 77

53. Oblique aerial views of Ophir Creek flood early during flood recession........................................................ 81

54. Maps showing fluvial-debris hazards on the Ophir Creek alluvial fan as predicted in the 1970's and

as realized in 1983 ............................................................................................................................................... 85

55-57. Photographs showing:

55. Similar upstream views of Ophir Creek alluvial fan from U.S. Highway 395 freeway on different dates ..... 86

56. Debris deposited on Stafford property by Ophir Creek flood. Deposits are being excavated and

size sorted for commercial use, June 1992.................................................................................................. 89

57. Old fluvial deposits near the lower canyon mouth of Ophir Creek, which were exhumed 

by the 1983 flood........................................................^^

TABLES

1. Summary of winter, or winter-related, floods of Ophir Creek, western Nevada............................................................ 18

2. Summary of known summer floods during recent history in the Carson Range near Ophir Creek............................... 18

3. Precipitation at Reno during October-May of years with historically wet winters........................................................ 19

4. April 1 water content of snowpack near Ophir Creek for highest years of record ......................................................... 19

5. Maximum and minimum daily temperatures at Carson City, Glenbrook, and Reno, during May 1983........................ 21

6. Summary of estimated flow rates and velocities of the May 30, 1983, peak-flow surge in Ophir Creek...................... 52

7. Estimated areas and volumes of sediment deposited by the May 30, 1983, Ophir Creek flood.................................... 56

8. Summary of particle-size data from sediment deposits.................................................................................................. 58

9. Statistics for particle-size data from sediment deposits.................................................................................................. 63

10. Estimated floodflow volume on alluvial fan, 1983 Ophir Creek flood.......................................................................... 67

11. Summary of model results for ground-water discharge to Ophir Creek caused by flood-induced channel incision..... 72

12. Simulated ground-water discharge during duration of the flood as the result of channel incision ................................ 73

13. Damage caused by the May 30, 1983, Ophir Creek flood.............................................................................................. 84

VIII Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
CONVERSION FACTORS, VERTICAL DATUM, AND PARTICLE-SIZE UNITS

Multiply

acre

acre-foot (acre-ft)

cubic foot per second (ft3/s)

cubic yard (yd3 )

foot per foot (ft/ft)

foot (ft)

foot per mile (ft/mi)

foot per second (ft/s)

inch (in.)

mile (mi)

mile per hour (mi/h)

square foot (ft2 )

square mile (mi2 )

yard (yd)

By

0.4047

0.001233

0.02832

0.7646

0.3048

0.3048

0.1894

0.3048

25.4

1.609

1.609

0.09290

2.590

0.9144

To obtain

square hectometer

cubic hectometer

cubic meter per second

cubic meter

meter per meter

meter

meter per kilometer

meter per second

millimeter

kilometer

kilometer per hour

square meter

square kilometer

meter

Temperature: Degrees Fahrenheit can be converted to degrees Celsius by using the formula °C = 0.556(°F-32)

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, formerly called "Sea-Level 

Datum of 1929"), which is derived from a general adjustment of the first-order leveling networks of the United States and Canada.

Particle-size units are expressed in millimeters (mm) and phi ((])) units.

CONTENTS IX

Landslide-Induced Flooding at Ophir Creek, 

Washoe County, Western Nevada, 

May 30,1983

By Patrick A. Glancy, U.S. Geological Survey, and John W. Bell, Nevada Bureau of Mines 

and Geology

ABSTRACT

Ophir Creek, a small stream on the eastern 

slopes of the Sierra Nevada, western Nevada, flooded 

severely on May 30, 1983. Flooding began at mid-day 

during clear, hot weather devoid of recent storm activity. It killed one person, seriously injured four others, 

and caused over $2 million damages.

The flood was abruptly triggered by a landslide 

from the slopes of, appropriately named, Slide Mountain. The slide was the combined product of gravity, 

favorable geostructural orientations of bedrock, and 

sudden hydraulic imbalances. The aberrant hydraulics 

resulted from intensive melting and infiltration of 

heavy snowpack during several days of unseasonably 

hot weather. About 1,400,000 cubic yards of rock 

material plummeted into small Upper Price Lake, 

a pond astraddle the creek, on the upper flank of 

Slide Mountain. The force of the slide entering the 

lake quickly expelled about 20 acre-feet of mostly 

water. About 2 more acre-feet were incorporated 

downstream as nearby Lower Price Lake was, in turn, 

emptied by the sudden flow surge.

Expelled water initially flowed at probable rates 

of 13,000-20,000 cubic feet per second. Flow raced 

0.6 mile down the steep upper canyon of Ophir Creek, 

gouging easily erodible channel materials. Flow compounded as it further incorporated snow, eroded debris, 

and additional water. It deposited about 50 acre-feet 

of debris just downstream of the upper canyon. The 

debris-charged flow then surged 1.06 miles through the 

lower canyon of Ophir Creek, eroding and incorporating more debris from the flatter lower canyon. Peak 

flood discharge of the leading flood surge progressively 

increased to about 50,000 cubic feet per second near 

the lower canyon mouth.

The leading debris-flow front overtopped the normal channel downstream from the lower canyon mouth 

and overran two homes, killing one person and injuring

three who were fleeing the 20 to 30-foot-high, 200- 

foot-wide surge. The leading front arrived at Old Highway 395, about 2.9 miles downstream from Upper 

Price Lake, 8 to 9 minutes after it began, after travelling 

at an average velocity of 19 to 22 miles per hour (28 to 

32 feet per second). Upstream of the roadway, flow 

largely bypassed a manmade, diversionary channel. 

Instead, it flowed straightforwardly down the axis of 

the Ophir Creek alluvial fan, where lateral channel 

confinement decreased. The flood plain quickly widened and flattened causing spreading and slowing of 

the leading flow surge. This flow transformation 

resulted in the start of widespread debris deposition. 

Three more homes were damaged or destroyed and 

another person seriously injured downstream from 

Old Highway 395.

Hydraulic dynamics of the flood were complex 

and variable over time and enroute. The dilute peakflow surge from Lower Price Lake quickly transformed 

to boulder- and vegetation-laden flow through severe 

erosive bulking within the canyons. At the lower canyon mouth, the surge was a watery debris flow of a dual 

character: (1) A coarse component consisting of boulders, cobbles, gravel, sand, and trees intermixed with 

(2) a fine-grained, matrix-fluid component of low 

clay and mud content and of low cohesion and yield 

strength. These components tended to separate at 

sites of velocity drops wherein the turbid fluid matrix 

flowed faster and beyond deposits of the coarsegrained fraction. Flow of the turbid fluid matrix 

beyond the terminus of boulder deposits displayed 

mixed hydraulic characteristics that prevented confident classification as either hyperconcentrated flow or 

debris flow.

Total sediment deposits of the flood were about 

450 acre-feet. Sediment was only a component of the 

total floodflow, but resultant bulk volume of sediment 

deposits was more than 20 times the volume of Price 

Lakes, where the flood originated. Total floodflow

ABSTRACT
(water and debris) reaching the Ophir Creek alluvial 

fan was about 800 acre-feet, more than 36 times the initial volume of Price Lakes. Other contributing sources 

of water included snowmelt from upstream of the landslide, ground water draining from the slide mass and 

scar, existing streamflow overrun in the channel, tributary inflow downstream from Lower Price Lake, 

ground water in pores of debris eroded from the channel, ground water stored in the streambed and banks of 

Ophir Creek that drained to the channel following 

severe scour by the leading, boulder-laden flood surge, 

and snowpack atop the slide mass and in the canyons.

Stratigraphic and particle-size distribution 

characteristics of sediment deposits indicate that the 

coarse-grained sediments on the Ophir Creek fan were 

deposited by debris flows and infer that a prolonged 

debris-flow phase of progressively decreasing magnitude followed the leading peak-flow surge. Photographic evidence documented the progressive return to 

Newtonian streamflow conditions during early hours of 

the flood recession, which continued for several days.

INTRODUCTION

About noon on the hot, sunny Monday of May 30, 

1983, Tom Reed, his wife, and three companions were 

finishing the interior of Reed's newly built home on the 

west side of Washoe Valley in western Nevada (figs. 1 

and 2). The Reeds had constructed their house on the 

north-bank terrace of Ophir Creek less than a quarter of 

a mile downstream from the mouth of the lower canyon 

of Ophir Creek (fig. 2), just outside of the estimated 

100-year flood plain. Suddenly, a member of Reed's 

group commented about the abnormally loud noise the 

creek seemed to be making. Simultaneously, others 

glanced upstream and saw a wall of boulders, mud, and 

trees about 30 ft high and over 100 ft wide, cascading 

rapidly toward them from the canyon mouth. Instinctively, all five scrambled desperately in a race for life 

that only four of the group won. Reed's house and that 

of a nearby neighbor were the farthest upstream (fig. 2), 

and, thus, the first to be overrun by the 1983 "Memorial 

Day flood."

The origin of this flood was different from most 

floods in western Nevada, but its effects were similar to 

those of destructive flash floods that commonly occur 

almost yearly throughout Nevada, the Great Basin, and 

other parts of the arid West. Normally, desert flash 

floods are triggered by rainfall and therefore are 

accompanied by cloudy skies and unstable air currents.

People threatened by these "normal" floods are generally attuned to the impending hazards by blustery and 

unstable weather conditions, a warning that allows 

them to be on guard and seek safety when threatened. 

In contrast, this flood was triggered during and by the 

results of hot, clear, and calm weather, and the victims 

were struck immediately after a warning that consisted 

only of the sight and sound of the approaching deluge.

The unseasonably hot weather, which also had 

re vailed during several previous days, accelerated melting of an abnormally heavy snowpack. The snowmelt 

infiltrated the fracture system of the structurally unstable, steeply sloping, bedrock mass of Slide Mountain, 

which extends to the Ophir Creek channel several miles 

upstream from the area of human development. Apparently, the rapid infiltration of snowmelt increased 

hydraulic pressures within the bedrock fracture system 

sufficiently to unbalance the static forces that had been 

maintaining stability of the mountain slope. The destabilizing hydraulic forces and the force of gravity 

caused rapid failure of a portion of the steeply sloping 

bedrock mass and its overlying regolith, which triggered a rapid sequence of events that quickly culminated in disaster for the inhabited areas downstream. 

The destabilized mass slid downward into Upper Price 

Lake, a small reservoir. The force of its abrupt plunge 

into the lake rapidly expelled the lake contents into and 

through smaller Lower Price Lake, about 0.1 mi downstream. The combined contents of both lakes then cascaded downstream through two steep, narrow canyons 

and vigorously eroded the unstable channel bed and 

canyon walls enroute. This flood surge gathered mass 

and momentum as it progressively incorporated debris 

along about 2-3/4 mi of transit. When it reached the 

lower canyon mouth, the debris-laden flow disgorged 

its contents on unsuspecting inhabitants near the juncture of the mountain slopes and the valley floor (frontispiece).

Purpose and Scope

The landslide-induced flood at Ophir Creek on 

May 30,1983, provided an opportunity to scientifically 

document an important hydrogeological event. The 

rapid expulsion of Price Lakes by the landslide initiated 

a chain of events that was witnessed by many. Resultant 

scientific data were more plentiful than usual for severe 

floods in sparsely populated areas. The available data 

facilitated a major objective of this investigation by 

allowing quantification of several hydrogeological

Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
120°00' 119°45'

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- —f-x/tfz-# v^-fz&f •, *

L*^-:i--* i. i^*«rs?r/ -• %.«

Base from U.S. Geological Survey digital data, 1:100,000,1979-80; 

Universal Transverse Mercator projection, Zone 11. Shaded-relief base

Base from U.S. Geological Survey digital data, 1:100,000,1979-80 

Universal Transverse Mercator projection, Zone 11. Shaded-relief I 

from 1:24,000-scale Digital Elevation Model; sun illumination from 

northwest at 30 degrees above horizon

EXPLANATION

| ' J Ophir Creek Basin

Figure 1. Ophir Creek Basin, Western Nevada, and nearby geographic features.

0 5 MILES

I I I I I I

IPiI I I

0 5 KILOMETERS

INTRODUCTION
39°17'30" 390 18'30"

119° 52'30"

119° 50'

, " Slide " Mountain" ~ 0

IX •vT^Bowers.Mansion 

County-Park

0 1/2 KILOMETER

Contour interval, 200 feet

Datum is sea level.

__________I '"***.

Base from U.S. Geological Survey, 1:24,000 quadrangles: 

Mt. Rose, Nev., 1968 and Washoe City, Nev., 1974

Figure 2. Locations of selected eyewitnesses and other features during the May 30, 1983, flood of 

Ophir Creek, Nevada.

Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
EXPLANATION

—— • • —— Boundary of Ophir Creek Basin

c• Homes referred to in text

A Ogilvy

B Reed

C Thompson

D Stafford (originally Price)

E Cline

F Turek

G Graves

Approximate locations of eyewitnesses 

during flood (appendix B)

(jT) Ronald Mentgen (possible location)

(•) Doug Cook (approximate hanglider route)

(A) James Schumacher (approximate upstream location 

and extent of downstream retreat)

(4) Mark Bridgewater (location uncertain)

(5} William and Elizabeth Willets (approximate 

location)

(5/ Tom Reed. John Burruel, and Tim Miller

(7y Anne Ogilvy

(8J Kathleen Thompson

(£) Greg Stafford

® Shirley Stafford

<Q) Vie Stafford

\\2) Kathleen "Katy" Cline (swept to freeway by flood)

(K3) Patricia Sommers (abandoned car)

^4) Susan Graves

^5) Kenneth Julian

(jW) Reed Dopf (moving)

@ Charles McQuerry

~*^—— Arrows show approximate travel routes of 

eyewitnesses during the duration of 

their observation

Figure 2. Continued.

characteristics to add to our understanding of hazardous flood processes, specifically those associated with 

rapid releases of water in fragile and easily erodible 

environments. Another purpose of this documentation 

is to improve general understanding and awareness of 

hydrogeological hazards and their potential consequences in a high-risk area that is experiencing rapid 

human encroachment and development.

The benefit of having eyewitnesses strategically 

located throughout a drainage basin during a flash 

flood is uncommon, particularly in the sparsely populated Great Basin. This flood was witnessed by at least 

20 people who inadvertently were positioned fortuitously and were later able to vividly recount their 

observations and experiences. The sunny and warm 

weather that prevailed during the flood allowed witnesses to observe and note events without the distracting discomfort of inclement weather. Their 

observations were not obscured or distorted by wind, 

rain, poor visibility, or other discomforts common during floods. As a result of these factors, eyewitness 

accounts of high quality spanned the full duration of 

the landsliding and flooding. These accounts are 

included in this report (app. B) to provide both a broad 

overview and scientifically important details of the 

disaster from its beginning to its conclusion. Additionally, the eyewitness accounts provide detailed and varied perspectives on human reactions and responses to a 

natural disaster by those directly threatened and 

affected. Although catastrophic floods caused by reservoir spillage are not an everyday occurrence, neither 

are they extremely rare. Commonly, reservoirs drain 

rapidly during dam failures if their impounded volumes 

of water are small and if the dam fails quickly and completely; drainage can occur within a time period ranging from a few minutes to possibly half an hour, 

depending on characteristics of the small reservoirs and 

the nature of the failures. In contrast, the forceful and 

nearly instantaneous expulsion of a reservoir's contents, as occurred at Upper Price Lake during this 

event, is a rare phenomenon. The hydraulic-energy 

release for a given quantity of water may be on the 

order of one to several orders of magnitude greater in 

such cases of nearly instantaneous spilling. The downstream effects that follow such an intense energyrelease rate can be devastating, as demonstrated by the 

effects of this flood.

In addition to documenting the 1983 event, this 

report summarizes information on historical floods and 

prehistoric landslides and debris flows within the Ophir 

Creek Basin (app. A). The report compares the subject 

flood with predictions of flood hazards made about a 

decade earlier, and it documents some of the natural 

landscape-healing processes that have occurred during 

the decade following the flood. The report also summarizes damages caused directly by the flood. Last, it 

includes conclusions regarding the potential for future 

hydrogeologic hazards within the lower part of the 

Ophir Creek Basin, an area of continually accelerating 

human development.

INTRODUCTION
Acknowledgments

Many individuals and organizations contributed 

to the preparation of this report. Information that was 

used directly in the text, figures, or tables is credited at 

appropriate places. The authors also offer their gratitude to the many people and organizations that are 

not cited or mentioned directly, but who assisted in 

the investigation and shared their knowledge with us 

and the readers. The authors are especially grateful to 

Steven Ellen, Jon Major, Michael Nolan, and David 

Prudic of the U.S. Geological Survey, for critical 

reviews of the report and numerous helpful suggestions.

THE SETTING

Ophir Creek is a small, elongate drainage of about

o

4.5 mi that drains east-southeastward down the steep, 

east-facing slopes of the Carson Range of the Sierra 

Nevada. It heads on the southeastward flank of Mount 

Rose (upper part, fig. 1), includes the southward-draining slope of Slide Mountain, and empties into Washoe 

Lake (lower part, fig. 1). The lake occupies a natural 

land-surface depression; its surface outflow (Steamboat Creek) is ultimately tributary to the Truckee River, 

about 14 mi to the northeast. The Ophir Creek Basin is 

about 16 mi southwest of downtown Reno, Nev., and 

about 10 mi northwest of downtown Carson City. Ophir 

Creek is one of many small streams that drain eastward 

from the Sierra Nevada into a rapidly developing, 

mixed urban-suburban corridor that parallels the eastern flank of the range for about 65 mi southward from 

Reno.

The 1983 flood did not involve the entire 7-mi 

length of the Ophir Creek drainage basin, but rather 

was limited to the lower 3 mi of the channel (figs. 1 

and 2). The peak flood surge originated mainly from 

two small, adjacent point sources. These point sources 

of stored water were Upper and Lower Price Lakes, 

located about 3 mi upstream from the creek's mouth 

and juncture with Washoe Lake.

The Ophir Creek drainage (fig. 1) is currently 

(1990's) inhabited only along its lower 1-1/2 mi length. 

Although many people travel the upper part of the basin 

on Nevada State Highway 431, commonly called the 

Mount Rose Highway, most residents occupy the 

mountain-front alluvial fan that was constructed by 

numerous past Ophir Creek floods. The fan, as well as 

many other features described here, are collectively 

shown in the photographs of figure 3, the maps of figures 2 and 4, and the drainage profile of figure 6. U.S. 

Highway 395, a four-lane divided freeway, the primary 

transportation link between Reno and Carson City, 

crosses the distal extremity of the Ophir Creek fan 

diagonally on a southeasterly alignment. The old Virginia and Truckee Railroad grade, abandoned in 1950, 

also crosses the fan diagonally along a southwesterly 

alignment, a short distance upgradient from the freeway. The freeway and railroad grade cross irrigated 

pastures growing on fine-grained alluvial sediments 

that underlie the gently sloping distal part of the fan 

(figs. 3, 4, and 6). Ophir Creek joins Washoe Lake 

downstream from the freeway at a distance that varies 

with the stage of the lake and the varying position of its 

shoreline. Nevada State Route 429, better known as 

Old Highway 395, traverses the fan, roughly along its 

topographic contour, a short distance upstream from 

the abandoned railroad grade. This highway, which 

now serves mainly local residents, is situated along 

the more steeply sloping medial part (fig. 6) of the fan, 

upstream of the pasture lands. This steeper sloping 

medial segment of the fan is underlain by dominantly 

coarse-grained sediments, including numerous boulders, deposited both by Ophir Creek floods and by prehistoric landslides from the southeastern face of Slide 

Mountain (fig. 4). The upstream, proximal segment of 

the fan (fig. 6) was increasingly developed for houses a 

few years after the flood. The proximal and medial segments of the Ophir Creek fan (fig. 6) currently contain 

an increasing number of dwellings and, if the potential 

for future natural hazards is ignored, most of these 

areas, as well as the distal segment, will probably 

become prime candidates for future, full-scale, realestate development. The areally larger upstream part 

of the Ophir Creek Basin (fig. 1) is increasingly being 

used by hikers, skiers, and others for year-round recreational purposes.

Although the downstream, gently sloping areas 

(medial and distal segments) of the alluvial fan are 

mostly treeless, a Sierran coniferous forest, with an 

under story dominated by manzanita and bitterbrush, 

dominates the landscape upslope from Old U.S. Highway 395 to the crest of the Carson Range. Uplands of 

the Ophir Creek Basin near Price Lakes, at the base of 

the southeastward-facing slope of Slide Mountain, are 

composed of hummocky-configured slopes that were 

formed by deposition of prehistoric landslides from the 

face of the mountain. Most of these hummocky uplands 

are steeply sloping and deeply entrenched by the channel of Ophir Creek.

Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Figure 3. Vertical aerial photographs of Ophir Creek alluvial fan, western Nevada: A, preflood view (U.S. Forest 

Service photograph, July 15,1977). B, Postflood view (Nevada Department of Transportation photograph, June 6, 

1983).

THE SETTING
39°17'30" 39°18'30"

119°52'30"

119°50'

Contour interval, 200 feet 

Datum is sea level.

Base from U.S. Geological Survey, 1:24,000 quadrangles: 

Mt. Rose, Nev., 1968 and Washoe City, Nev., 1974

Map of deposits modified from Tabor and Ellen, 1975

Figure 4. Areal extent of landslide and fluvial deposits prior to the May 30,1983, flood, lower Ophir 

Creek Basin, Nevada.

8 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada May 30,1983
EXPLANATION

| x^: | Deposits of rockfall avalanches and other

landslides—From Slide Mountain (Tabor and 

Ellen, 1975)

Coarse-grained fluvial deposits of Ophir 

Creek—Includes silt, sand, gravel, and boulders 

deposited by floods. Called flood deposits by 

Tabor and Ellen (1975)

I | Fine-grained fluvial deposits—Dominantly sand 

and finer grained material. Contains some gravel, 

the amount and size of which increases upgradient 

toward the mountains. May contain lake deposits 

near Washoe Lake

I I Bedrock—Hornblende-biotite granodiorite 

(Tabor and Ellen, 1975)

[ | Basin alluvium and slope deposits—Mostly 

water-lain sediment (Tabor and Ellen. 1975)

"T T Scarp of major rockfall avalanches from Slide 

Mountain (Tabor and Ellen, 1975, p. 19)

—— • • —— Boundary of Ophir Creek Basin

c• Homes referred to in text

A Ogilvy

B Reed

C Thompson

D Stafford (originally Price)

E Cline

F Turek

G Graves

Figure 4. Continued.

Local climate is transitional between the arid 

Basin-and-Range climate to the east and the wetter 

Sierran climate to the west. On an annual basis, the 

Sierran snowpack is the product of the dominant precipitation component, but individual storms during any 

season can yield large amounts of rain. Severe regional 

flooding can be caused by heavy regional rainstorms or 

by rain on a thin or water-saturated snowpack. Summer 

convective storms frequently are intense and often have 

caused severe localized flash flooding, both in 

the Sierras and the adjacent Basin and Range region.

Basin Geologic Characteristics

Ophir Creek drains the east-facing slopes of the 

Carson Range of the Sierra Nevada, thus its drainage 

basin is situated exclusively in an igneous rock terrane 

(Thompson and White, 1964; Bonham, 1969; and 

Tabor and Ellen, 1975). The bulk of the igneous

bedrock exposed in the basin is Cretaceous-age, hornblende-biotite granodiorite that was emplaced as part 

of the Sierra Nevada batholith. In the upstream part 

of the basin (fig. 1), some Tertiary-age volcanic bedrock of the Kate Peak Formation (Miocene or Pliocene 

age) is exposed on the southern flanks of Mount Rose 

(Thompson and White, 1964, pi. I; Bonham, 1969, 

pi. 1). However, in the downstream part of the basin 

(fig. 1), including mainly drainage from Slide Mountain and the unnamed highlands to the south of Ophir 

Creek (fig. 4), the bedrock terrane is exclusively granodiorite and related intrusive, igneous rocks. Because 

the 1983 flood, which is the main subject of this report, 

originated within and was confined to this lower part 

of the basin, this geologic discussion is limited to the 

lower part of the Ophir Creek drainage (figs. 1 and 4).

The Carson Range (fig. 1), including Slide Mountain, and the easterly adjacent Washoe Valley, are landscape products of the tectonic evolution of Basin and 

Range physiography that has been ongoing regionally 

since mid-Tertiary time. Major faults in the granodioritic mass of the lower part of Ophir Creek Basin trend 

generally north-south (Tabor and Ellen, 1975). Carson 

Range uplift, relative to Washoe Valley downdrop, has 

resulted in a topographic relief of between 3,000 and 

3,500 ft, along the Ophir Creek floodway, from the 

southeast face of Slide Mountain to the western shoreline of Washoe Lake. This steeply sloping relief manifests over a distance of about 3.5 mi, over 95 percent of 

it in slightly less than 3 mi.

Landslide (including rock avalanche) and fluvial 

deposits dominate the landscape of lower Ophir Creek 

Basin (fig. 4). The landslide deposits were designated 

as "Debris Flows of Slide Mountain" by Tabor and 

Ellen (1975). They are referred to as landslide deposits 

in this report to clearly distinguish their genesis from 

the frequently discussed debris flows of the 1983 flood 

which emplaced the flood deposits through a different 

rheological process. The bedrock fracture pattern 

within the granodiorite mass that makes up the southeast-facing slopes of Slide Mountain played a critical 

role in the origin of the landslide that initiated the 1983 

flood. Geometric orientation of this joint-and-fracture 

system promoted downslope movement of the lithic 

mass into Upper Price Lake. Indeed, the orientation of 

bedrock fractures has been largely responsible for a 

long succession of prehistoric slides from Slide Mountain (Tabor and Ellen, 1975; app. A). The origin of this 

joint and fracture pattern is probably related to both the 

cooling (shrinkage) history of the granitic (granodiorite) batholith and subsequent Basin and Range structural stresses.

THE SETTING
The Drainageway 

Price Lakes

Upper Price Lake occupies a small natural 

depression astride Ophir Creek at the base of the 

southeastward-facing slopes of Slide Mountain (fig. 2). 

Downstream about 0.1 mi, Lower Price Lake was a 

small pond impounded by a man-constructed dam on 

Ophir Creek. There are few bathymetric data for either 

of the lakes. The Mount Rose and Washoe City 

l:24,000-scale topographic maps (U.S. Geological 

Survey, 1968a and b) show the lake-surface areas to be 

about 4 acres (Upper Price Lake) and 1 acre (Lower 

Price Lake). Measurements made after the 1983 flood 

suggest an average depth for the southern half of Upper 

Price Lake of 3 to 4 ft, and about 2 ft for Lower Price 

Lake. The northern half of Upper Price Lake was filled 

by debris during the May 30, 1983, landslide and, preceding the landslide, no accurate measurements of 

depths (only estimates discussed below) for this part 

of the lake are known.

Bottom sediments in both lakes, exposed by 

drainage of the lakes following the 1983 landslide, 

appear to consist chiefly of materials deposited by 

the through-flowing Ophir Creek. The lake-bedsurface deposits consist predominantly of sand-size 

and finer grained materials. The bottom sediments of 

Upper Price Lake also include a substantial amount of 

decayed organic material. The exposed bottom of the 

southern half of Upper Price Lake revealed a surface 

of relatively low and gentle relief assumed to result 

from long-term, generally uniform deposition of 

inflowing sediment. This lack of pronounced bottom 

relief, and a uniform depth as exhibited by the southern 

half of the lake, is difficult to reconcile with rumors of 

a previously deeper zone to the north that is now covered by the 1983 landslide deposits.

Norman Cliff, long-term Washoe Valley resident, 

recalls a "deep hole" (area and depth unknown) at the 

northwest corner of Upper Price Lake (oral communication, 1983). Cliff's recollection of greater-thanaverage depth in the northwest part of the lake has 

been independently bolstered through conversations 

with several fishermen and swimmers in the Washoe 

County and Carson City areas who adamantly insist 

that a "deep hole" existed, but are unable to quantify 

its depth and diameter.

Mark Warren, Nevada Department of Wildlife, 

made a biological stream survey of Ophir Creek several 

years before the flood that confirmed a perennial trout 

population in Upper Price Lake (oral commun., 1985).

Warren believes these trout required some water habitat 

deeper than 3 to 4 ft for winter survival because a lake 

of consistently shallow depth would have frozen solid 

during most average winters. According to Warren, 

replenishing the oxygen supply necessary for fish survival would also have required a zone deeper than 3 to 

4 ft that remained hydraulically connected continuously with the freshwater inflow from Ophir Creek. 

A former Washoe Valley resident, Warren recalls 

swimming and fishing in Upper Price Lake during his 

boyhood summers. Like Norman Cliff and the other 

local fishermen and swimmers, he is confident that a 

"deep hole" existed at the north or northwest part of the 

lake prior to the 1983 landslide. He estimated the maximum depth of the hole at about 15 ft. Although uncertain of the surface area or bottom configuration of this 

deeper-than-average zone, he agreed with the authors 

of this report that a surface area of 4 acres and an estimated average lake depth of 5 ft should adequately 

account for the overall lake volume at the maximum 

lake stage. Thus, on the basis of available evidence, 

the combined volumes of water contained in Upper 

and Lower Price Lakes at the time of the 1983 landslide 

are estimated to be about 22 acre-ft (20 and 2 acre-ft, 

respectively). The amount of water volume that was 

contained as ice at the time of the flood is uncertain 

(see eyewitness account of Ronald P. Mentgen, app. B).

Ophir Creek

Immediately downstream from Lower Price 

Lake, Ophir Creek descends through a deeply 

entrenched, steep canyon (referred to as the upper 

canyon in this report) for a distance of about 0.6 mi 

(fig. 5). Channel gradients of Ophir Creek, including 

those of the upper canyon, are shown in figure 6. The 

steep gradient in the upper canyon (average, 26 percent, 

or 14.6°) promotes very energetic streamflow. The 

upstream part of the confining canyon floor and walls 

consists of an easily erodible and incompetent mass of 

a granodiorite rock slide that Tabor and Ellen (1975) 

mapped as a shattered slide block. Individual fragments 

in this mass range from huge, house-size boulders 

down to silt- and clay-size particles. The unstable 

slopes of this severely shattered mass, exceptionally 

prone to erosion by the high-energy streamflow, are 

shown in figure 7. The remainder of the upper-canyon 

channel boundary also consists of prehistoric landslide 

debris that is equally susceptible to erosion by streamflow.

10 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Figure 5. Upstream view of upper canyon of Ophir Creek 

downstream from Lower Price Lake, western Nevada. 

Oblique aerial photograph by R.L. Jameson, U.S. Forest 

Service, May 31, 1983.

Downstream from the terminus of the upper canyon, the channel is less confined laterally throughout a 

reach of about 0.63 mi (fig. 6). The average gradient of 

this reach is about 12 percent (6.8°), about half that of 

the upstream canyon. This marked decrease in gradient 

may be partly the result of recurrent sediment deposition by intense floodflows that spread laterally after 

exiting the upper canyon mouth. The lateral spreading 

of flows decreases flow depths. The velocities of the 

flows diminish because of the increased frictional resistance to flow associated with decreasing depth 

and increasing width and also because of the decrease 

in channel gradient. The combined effects of spreading 

and slowing cause the variable floodflows to drop substantial fractions of their entrained sediment bedloads. 

The resultant deposits are the bouldery and dominantly 

coarse-grained flood deposits, as mapped throughout

this reach by Tabor and Ellen (1975). Downstream 

from this relatively open, and dominantly depositional 

reach, the channel enters a lower canyon that has a similar average gradient (about 12 percent, 6.8°; or 630 

ft/mi). This lower canyon was incised, mainly during 

late Quaternary time, by the creek for about 1.06 mi, 

mostly into unconsolidated deposits of prehistoric 

debris flows (landslides) that came from Slide Mountain (Tabor and Ellen, 1975).

The channel-bounding deposits of both the upper 

and lower canyons are susceptible to erosion by streamflow, particularly by severe floodflows that apparently 

recur frequently (Flood History, app. A). This erosive 

susceptibility is caused by several factors, including the 

generally unconsolidated character of the deposits, an 

abundance of fine-grained material (gravel size and 

smaller), and steep channel gradients that promote 

swift and turbulent streamflows capable of mobilizing 

and transporting eroded sediments. These factors are 

depicted by the photograph in figure 8. The incorporation of the eroded material within the floodflows 

increases their abrasive character and viscosity, and 

adds to the dynamic fluid momentum by increasing 

flow mass. This debris bulking can thereby increase the 

erosive character and sediment-transport capability of 

the fluid, and often promotes a progressively increasing 

destructive potential to the moving mixture of liquid 

and solid materials.

The deep channel incisions through the upper and 

lower canyons, particularly with regard to the relatively 

young geologic age of the channel-bounding deposits, 

attest to the severe geohydrologic instability of the 

terrain during flooding (figs. 5, 7, and 8). Stream 

downcutting is enhanced along the deeply entrenched 

channel because the narrow canyons restrain the normal tendency for the flows to migrate and meander 

laterally. In spite of this severe lateral confinement, 

floodflows persistently undercut the steep canyon 

walls. The undercutting resteepens the slopes periodically during the recurring large floods. The net effect 

of these short-duration, intense, and erosive flows is to 

promote and perpetuate the instability of the channel of 

Ophir Creek.

Downstream from the lower canyon mouth, 

channel gradients flatten throughout the roughly 0.4- 

mile channel reach to Old Highway 395 (fig. 6). 

The upstream extent of home development is about 

0.1 mi downstream from the Lower canyon mouth 

(fig. 2). These upstream home sites (Ogilvy's and 

Reed's) were situated on a stream terrace mantled by

THE SETTING 11
LU

CO 

LJJ

8CO

7,800

7,400 -

7,000 -

6,600 -

6,200 -|

LJJ 5,800 - 

Q

5,400 -

5,000 -

4,600 -

Outlet of

Upper Price Lake

Outlet of

Lower Price Lake

Channel reach

Approx- Approximate imate 

altitude channel 

difference distance

Approximate 

gradient

From To Feet Mile Percent

Outlet, Upper Price Lake 

Outlet, Lower Price Lake 

Mouth, upper canyon 

Head, lower canyon 

Mouth, lower canyon 

Old Highway 395 

Highway 395 Freeway

Outlet, Lower Price Lake 

Terminus upper canyon 

Head, lower canyon 

Terminus lower canyon 

Old Highway 395 

U.S. Highway 395 freeway 

Washoe Lake shoreline 

Total

25

830

400

680

165

60

23

0.19

.60

.63

1.06

.40

.38

.28

2.5

26

12

12

8.0

3.0

1.6

3.54

Feet 

per 

mile

Degrees

130

1,370

630

630

420

160

80

1.4

14.6

6.8

6.8

4.6

1.7

.9

Old Highway 395

U.S. Highway 395 freeway 

Washoe Lake

ALLUVIAL FAN

3.54

DISTANCE, IN MILES

Figure 6. Topographic gradients for Ophir Creek, western Nevada. Gradients extracted from topographic 

information shown on Mt. Rose and Washoe City, Nevada, 7-1/2-minute topographic maps.

coarse-grained fluvial deposits, most of which were 

probably emplaced in prehistoric time. The terrace is 

markedly lower than the hummocky ridge of older 

debris-flow (landslide) deposits dissected by the canyon immediately upstream. The two home sites are 

only a few tens of feet north of, and 10-15 ft above, 

the normal creek bed. The vulnerability of this terrace 

to inundation by exceptionally severe floods was dramatically displayed during the 1983 flood (fig. 9).

The older debris deposits underlying and laterally 

bounding the creek between the lower canyon mouth 

and Old Highway 395 confine minor floods and normal 

flows of the creek to a generally predictable path. 

A manmade southeastward diversion of the creek channel (figs. 9 and 10), capable of containing low-to-normal flows of the creek, is located about 0.1 mi upstream 

from Old Highway 395. During periods of major flooding, Ophir Creek largely bypasses this southeastward 

diversion and reverts to its preferred natural course 

which is generally along the axis of the alluvial fan. In 

general, this axial-fan route is weakly confined downstream from Old Highway 395. The fan gradient 

between Old Highway 395 and the U.S. Highway 395 

freeway averages only about 3 percent (about 160 ft/mi, 

or 1.7°, fig. 6). The weak channel confinement and the 

rapidly decreasing fan gradient promote marked 

spreading and rapid deceleration of floodflows. Thus, 

the area in the vicinity of and downstream from Old 

Highway 395 is the major area of deposition for debris 

carried by floodflows of Ophir Creek. Because of its 

decreasing slope (8 to 3 percent, or 4.6 to 1.7°) and low 

relief, this fan surface has also become a popular area 

for human habitation; as a result, inhabitants have been 

periodically subjected to the traumatic effects of severe 

flooding.

12 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
A

Figure 7. Upper canyon of Ophir Creek, Nevada, severely gouged and scoured by the highenergy flow of 1983 flood. A, Upstream (westward) aerial view toward Lower Price Lake, 

photographed June 3, 1983, by Patrick A. Glancy, U.S. Geological Survey. 6, Close-up view of 

south canyon wall just downstream from Lower Price Lake, July 27, 1983, photographed by 

Patrick A. Glancy. Note the widely ranging mix of fragment sizes and the easily erodible 

character of the debris comprising the canyon walls.

THE SETTING 13
Figure 8. Heavily eroded Ophir Creek channel, western 

Nevada, the day after the flood. Photograph by Kenneth 

Ganz, U.S. Forest Service, on the morning of May 31, 

1983.

Most of the surficially exposed, prehistoric landslides mapped by Tabor and Ellen (1975) do not extend 

downstream beyond Old Highway 395 (fig. 4). The surfaces of these older landslides are cluttered with huge 

boulders and have steep slopes and relatively rugged 

relief, which contrast sharply with the smoother, gently 

sloping fan surface constructed by the fluvial processes 

of Ophir Creek. The fluvial fan deposits bury older 

landslide deposits downgradient from Old Highway 

395. A few remnants that have not yet been buried protrude above the fluvial deposits; they are visible as isolated patches and as the island south of the fan axis as 

shown in figure 4.

Coarse-grained, bouldery flood deposits (map 

unit "Qf' of Tabor and Ellen, 1975) begin as a narrow, 

laterally confined strip of riparian deposits within the 

lower canyon (fig. 4). Downstream from the canyon

mouth, these "coarse-grained fluvial deposits of Ophir 

Creek" broaden into a conical shape and terminate 

about 0.15 mile downgradient from Old Highway 395. 

Interestingly, the downstream terminus of Tabor and 

Ellen's map unit (reproduced in fig. 4) is roughly coincident with the downstream extent of bouldery deposits 

from the May 30, 1983, flood (figs. 10 and 31), suggesting general hydraulic similarities between this 

recent flood and an unknown number of prehistoric 

floods that deposited coarse-grained materials within 

the boundaries of Tabor and Ellen's "flood deposits." 

Tabor and Ellen designated the remaining unconsolidated, relatively fine-grained sediments exposed at 

land surface downstream from the coarser-grained 

"flood deposits" as "alluvial fan" deposits. That unit is 

designated as "fine-grained fluvial deposits" in figure 

4. The sediments of this unit are dominantly sand and 

finer grained material. The channel gradient of Ophir 

Creek flattens to about 1.6 percent, or 0.9° (about 80 

ft/mi) downstream from the U.S. Highway 395 freeway 

to the creek's junction with Washoe Lake (fig. 6).

U.S. Forest Service aerial photographs of July 

1977 show the channel and riparian zones of Ophir 

Creek to have been generally well vegetated (figs. 3A 

and 11A). Deciduous plants were the dominant vegetal 

type but a scattering of conifers also was present. The 

dominant plants probably were quaking aspen, cottonwood, and willows. The perspective portrayed by the 

aerial photos suggests that vegetation was most dense 

within and along the channel throughout the upper and 

lower canyons. In the photos, the vegetated canopy 

appeared less dense within the laterally unconfined 

reach between the upper and lower canyons (fig. 11A). 

A moderately dense stand of riparian deciduous vegetation grew along the active-channel and irrigationdiversion routes downstream from the lower canyon 

mouth as far as Old Highway 395 (fig. 3A). Away 

from the active channel, the characteristically coarsegrained "flood deposits" (Tabor and Ellen, 1975) were 

dominated by shrubs and some conifers (figs. 3A and 

4). Downstream from Old Highway 395, a few scattered cottonwoods and willows also grew. The shrub 

cover was of similar density to that covering the 

adjacent prehistoric debris-flow (landslide) deposits. 

Downgradient from the "flood deposits," the 

dominantly fine-grained fan surface was vegetated 

mainly by meadow grass downstream to the normal 

shoreline of Washoe Lake.

14 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
SUMMARY OF LANDSLIDE AND FLOOD 

HISTORY

Landslides

The southeastern face of Slide Mountain, including Ophir Creek drainage, exhibits abundant evidence 

of multiple land-slope failures (landslides) during 

Quaternary time. The mountain is named for the large, 

unvegetated bedrock scars on its southeast face (frontispiece) that resulted from several land-slope failures. 

The deposits of these landslides were first mapped and 

discussed by Thompson and White (1964) and most 

recently by Tabor and Ellen (1975). Tabor and Ellen

differentiated nine separate slides in the deposits surrounding Ophir Creek. The small slide that precipitated 

the 1983 flood is but the latest (10th) recognized landslope failure in this series. A more detailed discussion 

of landslide history is in appendix A of this report.

Ophir Creek flows exclusively over and through 

the deposits of these slides from the area of Price Lakes 

to near Old Highway 395 (fig. 4). Thus, the physical 

character of the credible deposits plays an important 

role in the erosion and sediment-transport history of 

Ophir Creek. The physical makeup of the deposits 

and the incised nature of Ophir Creek resulting from 

its drainage evolution were major factors influencing 

the flow characteristics of the 1983 flood.

Figure 9. Downstream view of Ophir Creek, western Nevada, just below mouth of lower canyon. Ogilvy home behind 

tree at left; boulder-strewn terrace to left of creek contains displaced wreckage of Reed home. Manmade diversion 

angles through trees at upper right, across creek from where Reed's damaged recreation vehicle rests. Oblique aerial 

photograph taken during afternoon of May 30, 1983, by Washoe County Sheriff's Department.

SUMMARY OF LANDSLIDE AND FLOOD HISTORY 15
Figure 10. Oblique, aerial westward view of Ophir Creek alluvial fan, western Nevada, the major site of sediment 

deposition by the 1983 flood. Natural alignment of creek channel (lower right) was reestablished to the man-diverted 

route along left (southeast) part of fan by July 26, 1983, the date of this Patrick A. Glancy photograph.

Floods

Ophir Creek has had a substantial number of 

floods in the recent past that are not known to have been 

associated with, or accompanied by, landslides from 

Slide Mountain. Part of a chronology of flooding in the 

Truckee River Basin for the period 1861-1976 

describes floods in the Ophir Creek watershed (Goodwin, 1977). Goodwin's accounts of these floods were 

gleaned mainly from newspaper accounts and are 

descriptive rather than scientific and (or) quantitative 

(Victor Goodwin, U.S. Forest Service, retired, oral 

commun., 1984). Additional information was obtained 

from current and former residents of the Ophir Creek 

Basin, other eyewitnesses to past floods, and miscellaneous published accounts.

Winter floods, which are caused by regional 

storm systems, generally are less frequent than summer 

convective storms throughout the arid southwest;

however, they can be severe and because they are usually regional, they sometimes devastate large areas. 

A summary of Ophir Creek winter floods is listed in 

table 1; a more detailed discussion of some of these 

floods is in appendix A of this report.

Severe floods in the arid Great Basin are caused 

more frequently by summer convective storms than 

by winter, regional storm systems. In contrast to the 

wide-reaching storms of the winter season, the summer 

convective storms are geographically localized and 

flooding is often restricted to small areas, often to 

sub-basin areas, during a given storm. The Carson 

Range of the northern Sierra Nevada is no exception; 

severe summer convective storms are a common occurrence. A summary of some summer floods known to 

have occurred in the general proximity of the Ophir 

Creek Basin is listed in table 2. Documentary evidence

16 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
of these floods is from newspaper accounts, a flood 

documentary (Glancy, 1969), and streamflow data of 

the U.S. Geological Survey.

Currently, no known records exist of flooding at 

Ophir Creek caused by convective summer storms. 

However, the potential for this type of flood is indicated

by the number of documented floods that have occurred 

in nearby drainages, as listed in table 2. Therefore, 

there is a reasonable probability that flooding from 

summer convective storms has occurred historically, 

and an almost certain probability that, prehistorically, it 

occurred numerous times.

Figure 11. Vertical aerial views of Price Lakes and upper canyon of Ophir Creek, 

western Nevada, before and after the flood: A, U.S. Forest Service photograph of July 

15,1977, before the 1983 flood. B, Nevada Department of Transportation photograph 

of June 6, 1983, after the flood.

SUMMARY OF LANDSLIDE AND FLOOD HISTORY 17
Table 1. Summary of winter, or winter-related, floods of Ophir Creek, Washoe County, Nevada

[This summary does not include all historical winter-related floods of Ophir Creek, but only those for which specific data are available, or where regional 

flooding was so severe that Ophir Creek was very likely involved. Several other noteworthy floods may have occurred for which documentation is unavailable 

or, as yet, undiscovered. Most of the floods listed are discussed in greater detail in appendix A of this report]

Date Remarks Information source

January 1 874 Possible failure of natural impoundment of Upper Price Lake

November 1875 Reported failure of manmade dam on Upper Price Lake

July 1890 Major flood caused by failures of dams on Price Lakes

March 1907 Large-scale regional flooding; Ophir Creek flooding likely

December 1937 Major flood damage to highway crossing Ophir Creek

January 1943 Large-scale regional flooding; Ophir Creek flooding likely

November 1950 Serious flood damage to highway crossing Ophir Creek

December 1955 Large-scale regional flooding; Ophir Creek flooding likely

Jan./Feb. 1963 Large-scale regional flooding; Ophir Creek flooding likely

May 1983 Largest known flood; landslide flushed Price Lakes

Goodwin, 1977 

Goodwin, 1977

Reno daily newspapers, Carson City Appeal, and 

Goodwin, 1977

Goodwin, 1977

Reno daily newspapers and eyewitness accounts

Goodwin, 1977

Reno daily newspapers and eyewitness accounts

Reno daily newspapers

Reno daily newspapers

Eyewitness accounts and documentary field investigations

ANTECEDENT WEATHER CONDITIONS

The May 30,1983, flooding was primarily caused 

by the sudden emptying of Price Lakes by a landslide 

from the southeast slopes of Slide Mountain. Weather 

probably was closely related to and thus was a critical 

factor in the cause and flow characteristics of the flood.

Locally and regionally, the 1982 and 1983 water 

years were both very wet, at least partly as a result of 

a very strong El Nino climatic influence. Heavy flooding, debris flows, and landslides in northern California 

caused by winter storms during that time are a matter 

of public and scientific record (Ellen and Wieczorek, 

1988). These winter storms generally moved eastward 

and dropped substantial amounts of rain and snow 

across Nevada. As they continued farther eastward, 

these same weather systems and others also similarly 

blanketed Utah, hundreds of miles eastward. Utah 

flooding, landslides, and debris flows during the 1982- 

83 water years are a matter of scientific and historical 

record (Anderson and others, 1984).

During modern times, the winters of 1951-52, 

1968-69, 1981-82, and 1982-83 were seasons of especially great precipitation; however, severe Ophir Creek 

flooding occurred only in 1983. Winter precipitation 

data for those 4 years at Reno, the local measurement 

station of longest record, are listed in table 3. Also, 

degrees of winter wetness generally can be interpreted 

through comparisons of the water content in April 1 

snowpacks. Water stored in snowpacks near the Ophir 

Creek drainage for the wettest recent years listed above

are listed in table 4. These data indicate that cumulative 

snowpacks for the winters of 1981-82 and 1982-83 

were far greater than average, but substantially less 

than those of the winters of 1951-52 and 1968-69. 

Thus, some disparity exists between the inferences 

projected by Reno precipitation data of table 3 and the 

snowpack data of table 4.

Table 2. Summary of known summer floods during recent 

history in the Carson Range near Ophir Creek, Nevada

[This summary probably does not include all recent floods in these drainage 

basins; nor is it likely complete for all basins within 10-mile radius in the 

Carson Range. It is intended to portray the serious potential for summer 

floods in the general vicinity of Ophir Creek. Locations of these basins 

are outside the study area]

Date

August 15, 1941

July 29, 1952

July 20, 1956

July 29, 1960

August 15, 1965

August 15, 1965

August 15, 1965

August 2, 1966

August 25, 1967

August 25, 1967

Drainage basin

Galena Creek

do.

do.

North Fork Kings

Canyon Creek

Whites Creek

Third Creek

Galena Creek

do.

do.

Second Creek

Approximate 

distance from 

Ophir Creek

4.5 miles NNW

Do.

Do.

10 miles SSE

6 miles N

5 miles SW

4.5 miles NNW

Do.

Do.

6 miles WSW

18 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Table 3. Precipitation at Reno, about 15 miles northeast of the Ophir Creek Basin, Washoe County, Nevada, during 

October-May of years with historically wet winters

Precipitation1 (inches)

Period 

(A)-(B)

1889-90

1951-52

1968-69

1981-82

1982-83

Oct. 

(A)

0.36

.96

.01

.64

1.65

Nov. 

(A)

1.74

.61

.73

2.13

1.71

Dec. 

(A)

2.30

1.95

1.03

1.05

1.04

Jan. 

(B)

6.71

1.89

4.13

1.20

1.72

Feb. 

(B)

2.11

.62

1.74

.41

1.58

Mar. 

(B)

0.39

2.02

.07

1.14

1.31

Apr. 

(B)

0.30

1.63

.10

.34

1.35

May 

(B)

1.44

.02

.20

.10

.21

June2 

(B)

0.01

-

-

—

-

Oct.-May 

total

15.35

9.70

8.01

7.01

10.57

1 Data from official U.S. National Weather Service records (U.S. Weather Bureau, 1932, and National Climatic Center, 1921-84).

2 June data were included for 1890 because the severe flood of Ophir Creek was on July 6. See appendix A.

Table 4. April 1 water content of snowpack near Ophir Creek, Washoe County, Nevada, 

for highest years of record1

[Symbol: —, no information available]

Water content of April 1 snowpack (inches)

Site

Mount Rose

Mount Rose Ski Area3

Little Valley4

Altitude 

(feet above 

sea level)

9,000

8,850

6,300

1963-77 

average

35.9

38.5

6.9

Historically wet winters

1952 1969 1982

68.1 81.7 56.7

77.9

29.8 24.2 2.9

1983

57.0

75.6

16.1

1 Data from official records on file at the U.S. Soil Conservation Service. No data available for 1890. 

Located about 3.5 miles north-northwest of slide area.

3 Located about 1 mile north of slide area.

4 Located about 3 miles south of slide area.

In addition to the plentiful precipitation during 

the winter of 1982-83, and the abundant residual snowpack in and around the Ophir Creek drainage, as of 

April 1, 1983, cool and wet weather continued for at 

least an additional 6 weeks. At 14 sites monitored in the 

northern Sierra Nevada, the water content of the snowpack was greater than 200 percent of average on May 1 

(John Capurro, U.S. Soil Conservation Service, oral 

commun., 1985). By May 1, water content in two of the 

three snow courses (table 4) had increased: Mt. Rose, 

64.6 in., and Mt. Rose Ski Area, 83.6 in. Some lowaltitude melting had decreased the water content from

16.1 in. to 9.7 in. at the Little Valley course (U.S. Soil 

Conservation Service, 1983b, p. 10). During the month 

of April, the Mt. Rose snow course received 6.9 in. 

of precipitation and the Mt. Rose Ski Area course 

received 9.8 in. (U.S. Soil Conservation Service, 

1983b, p. 13). The first part of May continued unseasonably wet and cool; many of the snow courses in the 

Tahoe-Truckee area received more precipitation, some 

over an inch. The Mt. Rose Ski area, closest snow 

course to the 1983 landslide, received 0.9 in. during the 

month; no May data are available for the Mt. Rose and 

Little Valley courses (U.S. Soil Conservation Service,

ANTECEDENT WEATHER CONDITIONS 19
1983c, p. 4). As of April 1, the Soil Conservation Service was predicting snowmelt runoff in the TruckeeTahoe area to be about 200 percent of the average runoff during the 1963-77 period (U.S. Soil Conservation 

Service, 1983a, p. 9). Ultimately, local streamflows in 

the Sierra Nevada were about 250 percent of average 

(U.S. Soil Conservation Service, 1983c, p. 1).

Although the 1982-83 winter snowpack was 

exceptional in and around Ophir Creek and Slide 

Mountain, it had been equalled or exceeded several 

times. Therefore, if the May 30, 1983, landslide was 

triggered largely by snowmelt hydraulics, some factor, 

or factors, other than quantities of precipitation and 

snowpack may have played a critical role. The most 

likely additional influences were the residual moisture 

in the rock-fracture system from the winter of 1981-82 

and the melting rate of the 1982-83 snowpack, particularly the rapid infiltration of snowmelt into the bedrock 

fractures just prior to the landslide.

Maximum and minimum temperatures for May 

1983 at the Carson City, Glenbrook, and Reno weather 

stations are listed in table 5; Reno is about 15 mi northeast and Carson City is about 11 mi southeast of the 

slide area. Glenbrook is on the east shore of Lake 

Tahoe, about 15.5 mi south-southwest of the slide area.

The data in table 5 show that at meteorologicaldata sites reasonably close to the slide area, daily temperatures abruptly rose about May 20; the nights 

became noticeably warmer, and the days warmed dramatically. A similar temperature trend at all three stations emphasizes that the sudden warming was areally 

widespread and therefore, probably also affected the 

Ophir Creek drainage. A graph of daily mean temperatures at the Carson City weather station for the months 

of April-June of 1983 is shown in figure 12 (the 1983 

mean daily temperatures are the 5-day running average 

of daily mean temperatures). Departures of daily temperatures from the long-term, average-temperature 

increase, portray the extent to which daily temperatures 

conformed or deviated from long-term average conditions. As stated earlier, the superposed curves clearly 

show that unseasonably cool temperatures prevailed 

during most of April and particularly during the first 

two-thirds of May. A warming trend that abruptly 

shifted temperatures from below to above normal 

began about May 20 or 21. The heating continued and 

reached a peak on the 29th, at which time average daily 

temperature was over 10°F above normal.

The effect of this late-May heat wave on the 

snowpack in the vicinity of Ophir Creek and the 

landslide area was depicted by data collected at a snowAPRIL MAY 

1983

Figure 12. Daily mean air temperature at Carson City, 

Nevada, April 1-June 28, 1983 (Otto Moosburner, U.S. 

Geological Survey, written commun., 1985).

survey station located on the west flank of Slide Mountain, 1.2 mi northwest of the 1983 landslide. Daily 

fluctuations in snow-water depth, total precipitation, 

and minimum, maximum, and average air temperatures 

were recorded at this site (Mount Rose Ski Area). An 

analysis of temperature data for the days preceding and 

following the landslide (fig. 13) shows that a series of 

abnormally high, daily-average temperatures caused a 

sudden decrease in the snow-water (snowpack) depth. 

Beginning on May 23, the average daily temperature 

increased from 49.6°F to a high of 56.5°F on May 29. 

During the 5-day period, May 23-27, snowpack was 

depleted at a rate of about 0.325 in. of water per day 

(fig. 13). On May 27, the snowpack melted more rapidly; during the following 3 days (28-30), snowpack 

depletion intensified and averaged about 1.6 in. of 

water per day. The decrease of snow-water depth during this 3-day period accounts for about 35 percent 

of the total snowmelt that occurred prior to May 30. 

Although direct evidence that the landslide was 

triggered by hydraulic forces related to rapid infiltration of the quickly melting snowpack is impossible to 

obtain, circumstantial evidence for this type of triggering mechanism is strongly supported by these weather 

characteristics preceding the time of the slide. Regionally, rapid melting of other unusually heavy snowpacks 

by this same early-season heatwave also triggered 

numerous landsurface failures and severe floods in 

Utah (Anderson and others, 1984).

20 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
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23 24 25 26 27 28 29 30 31 1 2 3 

MAY JUNE 

1983

Figure 13. Snowpack moisture and average daily 

temperature in late May and early June of 1983, Mount 

Rose Ski Area snow-survey station, western Nevada. Data 

from U.S. Soil Conservation Service, Reno, Nevada.

THE LANDSLIDE

Lithologic Character and Structure of Slide 

Mountain

Slide Mountain is one of the highest peaks (9,698 

ft above sea level) on the eastern flank of the northern 

Sierra Nevada. It is composed largely of Late Cretaceous, hornblende-biotite granodiorite, which generally is uniform except for a shattered, chalky zone on 

the east side of the mountain (Tabor and others, 1983, 

p. 7, 18). The mountain is bounded on the east by a 

principal Quaternary trace of the Sierra Nevada frontal 

fault zone (Tabor and Ellen, 1975).

Structure in the granodiorite at Slide Mountain is 

variable, but many faults and prominent joints are 

northerly striking and generally steeply dipping 

(Thompson and White, 1964, and Tabor and Ellen, 

1975). Watters (1983) showed that orientation of the 

jointing changes from north-northwest to north-northeast on the southeast side of the mountain in the area of 

principal landsliding. The location of landsliding on the 

southeast face of the mountain may be spatially related 

to this change in structural orientation; other contributing factors include steep slopes above Ophir Creek and 

geographic slope orientation. The highly fractured,

sheared, and chalky bedrock mapped by Tabor and 

Ellen (1975) in this part of Slide Mountain also likely 

contributes to landsliding.

The Landslide of May 30,1983

The May 30, 1983, landslide was a composite of 

three nearly simultaneous, inter-related mass movements: rock slump, rockfall avalanche, and debris avalanche (terminology from Varnes, 1978). The location 

of the landslide is shown in figure 4 and a detailed map 

of landslide features compiled from aerial photography 

is shown in figure 14. The landslide components also 

are delineated on the photograph of figure 15. As indicated by overlapping relationships, movement of materials originated with multiple rock slumps that were 

followed by the rockfall and debris avalanches in the 

northern part of the landslide; the avalanche deposits 

overlie the slump blocks, indicating that they were a 

later phase of the sequence.

The rock slump zone consists of numerous parallel and sub-parallel, rotated, slump blocks that are 

300 ft or more wide and several hundred yards long. 

Each block is bounded by a headscarp, as much as 9 ft 

in height, which appears to be joint controlled. The 

scarps trend north-northwestward and extend southward nearly to Ophir Creek; they transect the ridgeline 

and lie oblique to the hillslope. Maximum downslope 

movement, as determined from displaced treelines, was 

about 100 yd. All slumping was confined to unweathered, jointed granodiorite. The failure-surf ace geometry is not clearly known (Watters, 1983, p. 179-180).

The rockfall avalanche is composed almost 

entirely of large blocks of granodiorite (as much as 10 

ft or more in diameter) that slid downward along the 

margin of the rock- slump zone to the base of the steep 

slope (fig. 16). Within the rockfall-avalanche zone, 

a fairly coherent slide block remains that apparently 

detached along its base and rafted downslope (figs. 14 

and 15). This slide block is characterized by deformed 

and crevassed (but intact) soil and by large trees that, 

through motion, were tilted back toward the hillside. 

An analysis of pre- and post-landslide aerial photography indicates that this block moved downslope about 

100 yd.

At about the time of the rockfall avalanche, a 

debris avalanche occurred along the northern edge of 

the rockfall avalanche. This finer grained component 

of the landslide consisted of a gravelly sand (mean 

particle diameter, 1 mm) derived from unconsolidated

22 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
119°52'55" 119052'30"

39°17'50" —

39°17'35" —

S5VAREA OF 1983 LANDSLIDE

1 \ - " - SHORELINE 

. \ -

1,000 FEET

r

0 300 METERS

Contour interval, 40 feet 

Datum is sea level.

Figure 14. Ophir Creek landslide features compiled from pre- and post-1983 aerial photographs. Shows approximate 

location of cross-section D-D' of figure 21.

surficial colluvium that overlaid the unweathered bedrock. The debris avalanche overrode a fairly thick 

snowpack, which may have accelerated and extended 

the movement and given it more flow-like characteristics.

Debris from the rockfall avalanche and the debris 

avalanche entered the northern half of Upper Price 

Lake, displaced the liquid contents, and filled the cavity. The force and mass of the avalanches also deformed 

and compressed peaty lake sediments (fig. 17) as they 

overrode most of the lake-bottom area. As shown by a 

muddy splashline on the surrounding snow (figs. 14 

and 22), the water in Upper Price Lake was rapidly displaced. Walters (1983, fig. 11; reproduced as fig. 21 of 

this report) showed this splash line to be about 6 ft

above the lake level of May 30,1983, on the southwest 

side of the lake and about 12-14 ft above lake level on 

the northeast side, indicating that the force of the splash 

was directed mostly eastward.

Thickness of the landslide was variable. Walters 

(1983, p. 179) shows that the thickness of the rockslump zone may have ranged from 30 to 100 ft. Deposits of the rockfall avalanche and debris avalanche are 

less than 3 to 7 ft thick in the upper portions of the landslide, but are 20 to 35 ft thick at the toe of the landslide. 

If an average thickness of 15 ft is assumed for the entire 

landslide, about 1,400,000 yd3 (about 870 acre-ft) of 

material was displaced. The terrane of the toe of the 

avalanche deposits is hummocky and chaotic and 

includes many large trees from upslope.

THE LANDSLIDE 23
Figure 15. North-westward view of 1983 landslide, Ophir Creek, western Nevada; scarps in rock-slump 

zone are visible in snow at left side of photograph. Oblique aerial photograph by Otto Moosburner, U.S. 

Geological Survey, on May 31, 1983.

Possible Causes of the Landslide

Possible causes for the 1983 landslide include 

loss of lateral support, seismic shaking, increase in surcharge, and increases in water content and pore pressure. These causes are evaluated for validity and 

importance, as follows.

Downcutting by Ophir Creek near the base of 

Slide Mountain has occurred throughout late-Quaternary time, as indicated by successive stream incisions 

into earlier landslide deposits. Undercutting of steep 

slopes by Ophir Creek, however, does not appear to 

have contributed directly to the 1983 landslide because 

there is little recent incision adjacent to the landslide 

and the slide movement appears to have been parallel to 

Ophir Creek rather than toward the creek.

Although seismic shaking (earthquake) is a common cause for landslides, there is no evidence that 

shaking initiated the 1983 landslide. A seismograph 

located 6.5 mi east of the landslide (fig. 1), and monitored by the University of Nevada, Reno, Seismological Laboratory, did not record any abnormal seismicity 

at the time of the landslide.

An increase in surcharge—the uncommonly thick 

snowpack—may have been a significant cause because 

the added weight of snow may have contributed to 

movement of the landslide. However, snowpack had 

been depleting rapidly for about a week (fig. 13) and, 

therefore, exerted less overall downhill force at the time 

of failure than it would have earlier.

24 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
The most likely cause for the landslide appears to 

have been an increase in subsurface water content, 

accompanied by probable increases in hydraulic pore 

pressures, that were the results of the rapid melting and 

likely infiltration of the exceptional 1982-83 snowpack 

described above. On the basis of this sudden melting of 

a substantial part of the record snowpack, we postulate 

that abnormally large quantities of meltwater permeated the surface of Slide Mountain during the few days 

preceding the landslide. Because permeability of the 

granodiorite is primarily through joint and fracture 

openings, the infiltrating water would primarily follow 

these discontinuities within the bedrock mass. An 

abnormal increase in subsurface moisture content 

would tend to decrease the shear strength of the discontinuities by increasing local pore pressures and reducing the effective stresses exerted on those discontinuities. The rapid increase in moisture content also 

would decrease shear strength in the unconsolidated 

surficial deposits mantling the bedrock slope.

The existence of high subsurface moisture content in materials at the landslide is supported by 

observations during the first few days following the 

landslide. Sandy surficial deposits on the undisturbed 

upper slopes near the landslide were observed to be saturated and susceptible to liquefaction and flowage 

downslope under foot impact. An uncertain volume of 

ground water probably flowed out from the landslide 

debris immediately following the slide (see report section entitled "Flood Volume and Water Sources").

Effects of the Orientation of Bedrock Joints

Studies of bedrock structure have shown that joint 

orientations in the area of the landslide are locally 

favorable for downslope movement (Robert D. Brown, 

U.S. Geological Survey, written commun., 1983; Tabor 

and Ellen, 1975; Tabor and others, 1983; Thompson 

and White, 1964; Walters, 1983). Strikes of prominent 

joints vary from north-northwest to north-northeast,

Figure 16. One of the largest granitic blocks involved in rockfall-avalanche phase of the 1983 landslide, Ophir Creek, 

western Nevada; block measures 25x12x8 feet. Backpack is 1-1/2 feet long. September?, 1983, photograph by Patrick 

A. Glancy.

THE LANDSLIDE 25
Figure 17. Bottom sediments of Upper Price Lake, 

western Nevada, deformed and uplifted by 1983 landslide. 

Six-inch knife (arrow) shows scale. Photograph by Patrick 

A. Glancy, July 27, 1983.

and variations of these trends occur at most sites. Some 

joints dip steeply (greater than 80°, fig. 18), but many 

dip gently (less than 45°). An analysis by Walters 

(1983, figs. 6 and 7) showed multiple joint sets surrounding the 1983 landslide, two of which are oriented 

in directions favorable to landsliding. These two joint 

sets trend northeastward, approximately parallel to the 

pre-landslide topography, and dip 30° to 38° downslope (joint-set poles Jjj and JL and their corresponding 

planes in fig. 19). Because the estimated pre-landslide 

slope was about 35°, these joint sets probably served as 

the primary failure surfaces.

Northwest-trending joints, marked by scarps 

within the rock-slump zone (fig. 14), are oriented 

obliquely to the slope and this oblique orientation may 

have contributed to the partial downslope movement of 

the rock slide. This partial movement has resulted in a 

potential for reactivation of the landslide and a continuing hazard. Robert D. Brown (U.S. Geological Survey, 

written commun., 1983) estimated that as much as

o

900,000 yd of rock remains perched on the slope north 

of Ophir Creek and may move again under conducive 

conditions.

THE FLOOD

The Ophir Creek flood of May 30, 1983, was the 

result of a rapid sequence of events that can be separated into four phases: (1) a sudden composite landslide 

down the steep, southeastward-sloping face of Slide 

Mountain that plunged into and buried the northern part 

of Upper Price Lake; (2) the quick downstream expulsion of the contents of Upper Price Lake by the landslide into Lower Price Lake, and the subsequent 

incorporation and downstream expulsion of the contents of that smaller lake into a highly energetic fluid 

surge; (3) swift downstream movement of the combined contents of both lakes that progressively scoured 

and bulked a massive quantity of sediment and debris 

into the flow; and (4) deposition of the sediment and 

debris load of the floodflow on the Ophir Creek alluvial 

fan.

Figure 18. Southwestward view of landslide area showing 

downslope dip of joint surfaces (foreground); northern margin 

of rockfall-avalanche zone in background. Photograph by 

John W. Bell, June 7, 1983.

26 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
North

West —

Strike of joint set JL

Strike of joint set Ju

— East

South

EXPLANATION

\, . | Joint-set poles—Jy and J L are shallow (30°-40°) principal 

joint sets from upper and lower hillslope surfaces, 

respectively. J2 , ^3, and J4 are other steeper, principal 

joint sets in bedrock surrounding landslide area

| | Average slope of pre-slide land surface 

> Approximate direction of landslide

Figure 19. Principal bedrock joint-set orientations in the area of the 1983 Ophir 

Creek landslide, western Nevada; orientations are plotted on a three-dimensional, 

lower-hemisphere stereographic projection. In this diagram, joint orientations are 

represented by drawing lines perpendicular to the joint planes and plotting the 

locations (poles) where the perpendicular lines pierce the lower hemisphere. The 

two-unshaded semi-circular planes are the joint planes for sets Jy and JL; the shaded 

plane is the average land-surface slope before the landslide (modified from Waiters, 

1983, figs. 6 and 7). For a discussion of stereographic projection, see Davis and 

Reynolds, 1996, p. 691-730.

The Expulsion of Price Lakes

The contents of Upper Price Lake were expelled 

by the combined dumping and piston-like actions of the 

landslide. Landslide movement was at least partially 

witnessed by Doug Cook, the hang-glider pilot whose 

observations are recorded in appendix B. He recalled, 

"I heard a roaring sound, kind of like the sound of a jet 

engine .... Out of the corner of my eye I could see a 

bunch of rising dust." Ronald Mentgen, another eyewitness, related the sound of the landslide movement to 

the rushing sound of air moving as wind. Mentgen also 

observed trees moving downslope in an upright position (probably part of the intact debris slide block 

described in the preceding landslide section of this 

report).

The force and movement of the landslide quickly 

expelled the lake contents that included ice, water, 

and unconsolidated sediments, and deformed the 

lake-bottom sediments. Postflood deformation of

THE FLOOD 27
lake-bottom sediments (fig. 17) indicates that the 

movements of the lake floor probably also caused a 

dumping action, somewhat analogous to the quick tilting of a pan of water to empty its contents. Cook (app. 

B) vividly described the visual effect of the emptying 

of Upper Price Lake: "When it hit the lake," he said, "it 

was like a huge explosion. It just blew the whole lake 

apart. It looked like a tidal wave at first and then the 

canyon gathered it up." This testimony verifies the sudden release of stored water from both lakes.

Cook's comparison of the surge of water exiting 

the lake to a tidal wave is corroborated by evidence left 

on the landscape by the departing fluid. Irregular discoloration of the snowpack near Price Lakes and along 

the interconnecting channel reach (figs. 20 and 22) 

defines the limits of the flow as it left the lakes. 

The fluid mixture imparted a dark color to the 

snow-covered landscape that is probably the result of

fine-grained, organic-rich, lake-bottom sediments 

expelled with the water. The residual color of these sediments is markedly darker than the fine-grained component of the debris avalanche, which consisted chiefly of 

light-colored, decomposed granodiorite.

Walters (1983, p. 181) described the displacement 

of Upper Price Lake as a wave of up to 16.5 ft in height 

above the lake level. He showed that the upper level of 

the surge line was not horizontal (fig. 21). A gradual 

and less dynamic expulsion of the contents of Upper 

Price Lake would have caused a more horizontal waveline perpendicular to the flowpath. In contrast, the tilted 

crest confirms the dynamic response of the fluid to the 

sudden combined dumping and pushing impacts of the 

landslide. The oblique aerial photograph of figure 22A 

shows the dominance of the wave-like surge compared 

to a milder appearing erosive scour caused by flow 

through the narrow break in the dam. The dam

Figure 20. View of terminus of 1983 landslide and point of origin of Ophir Creek flood at Upper Price Lake. View also 

shows Ophir Creek channel connecting Upper Price Lake and Lower Price Lake, and the steep canyon of Ophir Creek 

just downstream from Lower Price Lake, Nevada. Oblique aerial photograph by Patrick A. Glancy, June 3,1983.

28 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
D

7,240-

7,230-

7,220-

7,210-

Postflood drained surface, 

___June 30, 1983___

0 100 200 300 400

DISTANCE, IN FEET 

Vertical distance greatly exaggerated

Figure 21. Profile, looking upstream, of high-water surface 

of Upper Price Lake, western Nevada, when expelled by 

the landslide May 30, 1983. See figure 14 for approximate 

location of cross section. Adapted from figure 11 of Watters 

(1983).

probably failed concurrently with the wave-like surge, 

and as shown in figure 22A indicates that most of the 

lake contents escaped over the failed dam during the 

surge. Much of the entrenchment through the breach 

may have been caused by postflood recessional flow. 

Figure TIB shows the extended path of the displaced 

fluid downstream from Upper Price Lake into, and 

through, Lower Price Lake.

The tabular mass on the downstream face of 

Lower Price Lake dam (lower right in fig. 22B} appears 

to be a large piece of ice displaced from one of the 

lakes. This mass was gone by June 17, 1983, when the 

site was visited, indicating that it had melted during the 

intervening period. This information supports Ronald 

Mentgen's observation (app. B) that ice covered at least 

part of the surface of Upper Price Lake just prior to the 

landslide on May 30, 1983.

The rate at which Price Lakes were expelled probably is important to the subsequent hydraulic evolution 

of the flood. This rapid rate compounded the kinetic 

energy of the flow and increased its capacity to erode 

and mobilize debris along the channel of the steep canyon immediately downstream.

The Torrent in the Canyons of Ophir Creek

The upper canyon of Ophir Creek, which extends 

downstream from Lower Price Lake, is steep (average 

gradient about 26 percent, slope of 14.6°, fig. 6). 

narrow, and relatively straight throughout its roughly

Figure 22. Oblique aerial views of Price Lakes, western 

Nevada, showing muddy surge line on snow, June 3, 1983. 

A, Upstream view of the outlet of Upper Price Lake. B, 

Upstream view of Lower Price Lake and upstream reach of 

Ophir Creek channel. Photographs by Patrick A. Glancy.

THE FLOOD 29
0.6-mi reach. The steep descent of this reach is 

similar to a hydraulic chute, but—unlike a rock 

chute—the canyon walls and streambed are highly 

erodible (fig. 7a). The water-dominated floodflow exiting Lower Price Lake, containing a minor amount of 

fine-grained sediment in suspension, changed quickly 

after the flow entered the steep canyon below Lower 

Price Lake. A photograph taken during the flood (fig. 

23) by James Schumacher (eyewitness account, app. B) 

probably portrays the flow near peak stage in the upper 

canyon. The extreme turbulence of streamflow shown 

in the photograph is a visual indication of the magnitude of kinetic energy and power of the flow that 

eroded the steep channel-bounding hillslopes, thereby 

further steepening and destabilizing the slopes. In this 

manner, the flow rapidly incorporated large quantities 

of stream-bank materials immediately downstream 

from Lower Price Lake. The amount of debris thus

derived from canyon walls is reflected by the sizes and 

abundance of fresh erosion scars shown in figure 7. 

Debris incorporated in this manner included boulders 

from the streambed, colluvium, and landslide debris 

that bounded the channel, and trees and other vegetal 

debris that were readily stripped from the channel and 

its side slopes. The amount of vegetation swept away 

by the flow is shown through comparison of the photographs of figure 11. During transit of the upper canyon, 

the rapidly accumulating debris load progressively 

compounded the erosive action of the flood surge as it 

increased in inertial power and destructive force.

After a rapid journey of about 0.6 mi through 

the upper canyon, the now debris-choked flood surge 

exited the canyon mouth and spread over a flood 

plain that has a channel gradient about half that of the 

upstream canyon (fig. 6). This wider and flatter intercanyon reach of Ophir Creek is about the same length

Figure 23. Floodflow of Ophir Creek in upper canyon, downstream from Lower Price Lake, at about 11:55 

a.m. on May 30, 1983. Note the dark-colored, sediment-entrained, turbulent flow between the trees in right 

foreground. Photograph taken by hiker James Schumacher.

30 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
as the upper canyon (fig. 6), and was vegetated mainly 

by shrubs and quaking-aspen trees. The decreasing 

channel gradient and laterally expanding flood plain of 

the intercanyon reach caused decreases in the depth and 

velocity of the flow, the combined effects of which promoted deposition of some of the coarse-grained fraction of the sediment load.

Within this intercanyon reach, the leading edge 

of the flow encountered William and Elizabeth Willets 

(fig. 2 and app. B). Elizabeth's first warning of the 

approaching flood was the noise of its movement. 

Alerted by the sound, she watched trees being plowed 

asunder by the bulldozing effect of the boulder-laden, 

leading edge of flow. Although the Willets reacted 

instinctively and fled with haste, they barely escaped. 

They noted that the leading edge of flow was turbulent, 

boulder-laden, and laced with downed timber that was

being vigorously churned about. They also observed 

the preflood, bouldery streambed being uprooted by, 

and incorporated within, the flow, even though the 

stream gradient had decreased markedly downstream 

of the upper canyon mouth. The Willets noted that 

heavily debris-laden floodflow continued during their 

20 to 25 minute stay in this intercanyon reach of Ophir 

Creek.

About 10 to 15 minutes after taking the photograph shown in figure 23, James Schumacher arrived at 

the south edge of the flood plain, within the intercanyon reach (fig. 2), where he photographed the scene 

shown in figure 24. Although the flow surface pictured 

in the photograph shows turbulent zones, particularly 

along the edges of the channel, the fluid appears viscous. Large particles, some probably as much as a foot 

or more in diameter, appear to be floating at the surface

cr*,'TM- , **- ; . >••<* t

"v % *S^j^£

_.tr%^fcS

; r~*^ . - f ~ vpnw-,' i- ., * -5**1 *5fi,L'* **v •-. v*ff*^r" H^i^^^^^^ife-, ;l1|^-«^ iv^3^^.v ; ^^te^-ti^^^t^^^ -^

^^%.W. ^%fe'^J*fe-l^^ ^ •'*&&?.$*? ' _. <r>l

^_K ___{ ~' ^^r'^vvas i. - .—•*^ !** „,-«*•** ^,r" .... ^^^^^^:^tt.^9i&

Figure 24. Northward view of flood downstream from mouth of upper canyon of Ophir Creek, western Nevada. 

Photographed by James Schumacher about 10-15 minutes after the photograph in figure 23.

THE FLOOD 31
of the fluid. This apparent rafting of coarse particles 

indicates that the flow was probably moving as a debris 

flow at that time. Figure 24 also shows that the flow had 

receded below peak stage.

A substantial fraction of the sediment load that 

was eroded in the upper canyon was deposited on about 

15 acres between the upper and lower canyons. Much 

of the deposit consists of boulders and cobbles, but

trees and fragments of trees also were chaotically 

deposited throughout this intercanyon reach. These 

deposits and the sense of disarray that their deposition 

imparted to the landscape are shown in figure 25.

The erosive character of the leading flow surge 

continued as the flood entered the lower canyon; large 

volumes of older, unconsolidated, rockfall-avalanche 

debris that comprise the lower canyon walls were

Figure 25. Coarse-grained deposits on broad flood plain between upper and 

lower canyons of Ophir Creek, western Nevada: A, trees and bouldery rubble 

partially bury a standing tree; and B, coarse debris mantling the flood-plain 

surface. The battered crotch of a dismembered tree snared by two living trees 

suggests the degree of abrasive energy that characterized the flood. 

Photographs by Patrick A. Glancy, July 27, 1983.

32 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
removed by lateral erosion and incorporated in the 

flow. The lower canyon walls show abundant severe 

erosion by the flood, similar to those of the upper canyon pictured and described earlier. With the exception 

of some loss of debris in the intercanyon reach, the continued downstream channel erosion indicates that the 

flow progressively increased its sediment load during 

transit. The average gradient of the lower canyon (12 

percent, or 6.8°) is about the same as that of the intercanyon reach (fig. 6). Thus, the erosive character of the 

floodflow probably was revitalized mainly by the lateral confinement of flow exerted throughout this narrow and steep-walled canyon.

Eyewitness Mark Bridgewater (fig. 2 and app. B) 

was impressed by the viscous character of the leading 

edge of the flood, which appeared to him as a deep, 

soupy mud or sludge that was moving very fast. He also 

noted that the flow was choked with debris, and he 

observed super-elevated flow around curves in the 

channel. The momentum of the flowing mass was vividly impressed on Bridgewater's memory by the manner in which the flow ravaged large trees along its path.

Flow on the Alluvial Fan

The leading edge of the flood inspired both awe 

and fear among numerous eyewitnesses as it exited the 

lower canyon mouth. The witnesses seemed impressed 

by both its audible and visual characteristics. The combined accounts of Anne Ogilvy, the Reed party, Kathleen Thompson, the Staffords, Kathleen Cline, Patricia 

Sommers, Susan Graves, and Reed Dopf provide varying perspectives on the flood as they experienced it 

from a variety of vantage points and degrees of personal involvement (fig. 2 and app. B).

As the leading peak-flow surge emerged from the 

lower canyon mouth, it began to transform from a dominantly erosive flow to one of net-depositional character. Lateral cutting diminished greatly and differential 

deposition on the riparian landscape began. Some continued vertical downcutting of the channel was evident 

after the flood ended but the depth of this erosion is 

indeterminate because of subsequent backfilling by 

recessional flows. Two views of a boulder berm 

emplaced by the flow at the canyon mouth are shown in 

figure 26 (B, fig. 27). Boulder berms are characteristically formed by streamflow and hyperconcentrated 

flow (Costa, 1984, p. 292).

Downstream from the canyon mouth, the flood 

plain progressively widens and flattens from the average 12-percent gradient within the canyon to an average of about 8 percent, or 4.6° (fig. 6). These changes 

induced deposition of some of the coarse-grained fraction of the debris load (fig. 28) about 0.1 mi downstream from the mouth of the lower canyon. The 

leading flow surge swept across a terrace bordering the 

north bank of the stream channel; this terrace is about 

10 to 15 ft above the normal streambed. As the surge 

swept downstream over the terrace, it damaged the 

Ogilvy home (O, fig. 27) and destroyed the Reed home 

(R, fig. 27). Eyewitness testimony of Tom Reed (app. 

B) establishes clearly that the leading edge of the flow 

was virtually contemporaneous with peak flow; after 

barely outrunning the leading edge of the flow, Reed 

turned and observed that the flow had already receded 

from the terrace to the normal flood plain where it subsequently remained. Burruel, Miller, and Valenzuela 

were downed by the boulder-laden flow. Fine-grained 

matrix fluid continued moving downstream on the terrace, overtook Linda Reed, and subsequently swept her 

into Thompson's back yard (figs. 27 and 29).

The height of the leading peak-flow surge, from 

the mouth of the lower canyon downstream to Old 

Highway 395 is indicated by several lines of evidence. 

A channel cross-section measurement within the canyon mouth (fig. 27) indicates the surge height was 

about 25 ft above the normal streambed level; it may 

have been several feet higher a short distance upstream 

because the canyon mouth is beginning to expand laterally at the site of the cross section. The surge probably 

lost some height as it continued to spread laterally 

downstream from the canyon mouth. Ann Ogilvy (app. 

B) estimated the surge height at 23 ft when it struck her 

home about 0.1 mi downstream from the canyon mouth 

(O, fig. 27). The Reed home, just downstream from 

Ogilvy's, sat atop a terrace that measures at least 15 ft 

above the normal streambed. Destruction of the Reed 

home (R, fig. 27) by the flood required a surge height 

of several feet above the terrace to effect destruction in 

the manner described by the witnesses (Reed and others, app. B), and as documented by postflood field evidence. Therefore, we conclude that the surge height at 

Reed's homesite was on the order of 20 to 25 ft above 

the normal streambed. A tree along the north bank of 

the creek a short distance downstream from the Reed 

homesite (J, fig. 27) is shown in figure 30. Bark was 

abraded from the tree trunk by the bouldery mass of the 

flood surge to a height of about 15 ft above its base;

THE FLOOD 33
Figure 26. Boulder berm on northern edge of flood plain of Ophir Creek, western Nevada, at mouth of lower 

canyon. A, Narrow, elongate berm aligned parallel to the direction of flow; berm composed of chaotically 

stacked boulders with minimum interstitial fill. B, Wide variation in boulder size; clast sizes range from cobble 

size to more than 6 feet in diameter. Photographed July 14,1983, by Patrick A. Glancy.

34 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
119°50'30" 119°50' 119049'30"

39°18' -

Bowers Mansion 

County Park

39°17'30"

Base from U.S. Geological Survey, 1:24,000 quadrangles: 

Mt. Rose, Nev., 1968, and Washoe City, Nev., 1974

1/2 MILE

1/2 KILOMETER 

Contour interval, 200 feet 

Datum is sea level.

B

KJ

M

EXPLANATION

General location of flow-rate measurement reach

Approximate site of preflood and postflood crosssectional channel measurement depicted in 

figure 37

Location of boulder-berm deposits of figure 26 

Approximate vantage site of Kenneth Julian 

Approximate location of Charles McQuerry 

Flood-scarred Jeffrey Pine tree of figure 30

•

c

G

0

R

S

Th

Tu

Homesites of residents 

affected by flood

Cline

Graves

Ogilvy

Reed

Stafford

Thompson

Turek

Figure 27. Flood-related reference sites on Ophir Creek alluvial fan.

THE FLOOD 35
a

§aTl O Oa

<Q

21O

TJ

O3(D*•Bi WO (0

Figure 28. Effects of peak-flow surge on north terrace of Ophir Creek, 

western Nevada, downstream from lower canyon mouth, showing (A) 

relation of terrace to the creek thalweg, (B) devastation of Reed's home, and (C) characteristics of boulder deposition on terrace. 

Photographs by Patrick A. Glancy, June 1 and 2, 1983.
.feed 

recreatiemal •^fcw-'

vehicle

Figure 29. Northeastward route of mud-laden matrix fluid that swept away Linda Reed after it overflowed the northbank terrace of the Ophir Creek alluvial fan, western Nevada. Part of the severely damaged Ogiivy home shown at the 

lower right corner; Reed's demolished home and damaged motorhome are on terrace at right center. Oblique aerial 

photograph by Jon O. Nowlin, June 3, 1983.

the base of the tree is about 5 ft above the normal 

streambed. Thus, the boulder-laden flow front was 

probably on the order of 20 ft high at this site (J, fig. 

27). Eyewitness Kathleen Thompson (app. B) compared the flood-surge height to that of a three-story 

home (about 20-30 ft tall) from her site of observation 

just north of the tree shown in figure 30 (Th, fig. 27).

Reed Dopf (app. B) viewed the approaching surge 

while driving southward on the U.S. Highway 395 freeway (fig. 2). His distant perspective was broad and 

detached, similar to that of hang-glider pilot Doug 

Cook during the landslide and initial flood stages. Dopf 

described the scene from his fireman's frame of reference: "As it came out of the canyon, it was just volatile.

It looked exactly like opening a fire hydrant. It was that 

much turbulence. It was that much motion." He further 

described the flow as "a tabular mass of water and rock 

that was coming out of there." He described it as making "a dull roar like you'd hear at the ocean. The thing 

that was most impressive was this deep, percussive 

sound."

The natural channel of Ophir Creek near the battered tree shown in figure 30 was altered by man many 

decades ago (J, fig. 27). Normal streamflow was 

diverted sharply southeastward to irrigate fields downstream from Old Highway 395, and this constructed 

channel diverts low and moderate flows away from 

their natural path, the axis of the alluvial fan of Ophir

THE FLOOD 37
Figure 30. Jeffrey pine along the north bank of Ophir 

Creek (fig. 29), western Nevada, abraded by the flood. Tree 

records a peak flood-surge height of about 20 feet and is 

about 100 yards upstream from Old Highway 395. 

Backpack height is about 1-1/2 feet. Photographed by 

Patrick A. Glancy June 1, 1983.

Creek. The location and alignment of this diversionary 

channel can be discerned in figure 3B and is labeled in 

figures 27 and 29. The debris-laden surge easily 

bypassed the artificial channel bend, however, and 

flowed along the axis of the alluvial fan. Unrestrained 

by channel banks along the fan, the flow spread laterally and engulfed the developed area that included the 

Stafford, Cline, and Turek homes (S, C, and Tu, 

fig. 27). The progressively widening flood path downstream from the lower canyon mouth is best shown by 

the vertical aerial photograph of figure 3B. This June 6, 

1983, photograph shows the recessional realignment of 

the channel to the northern part of the fan and also the 

partial entrenchment by the receding floodflows. The 

photograph of figure 10 shows the postflood flow rediverted to its man-aligned course by July 26, 1983.

The stream-channel and alluvial-fan gradients 

(fig. 6) abruptly flatten downslope from Old Highway 

395 (fig. 2). During the flood, this flattening and rapidly expanding flowpath caused a correspondingly 

sharp decrease in flow depths and a rapid deceleration 

of the peak-flow surge. As the mass decelerated, the 

boulders and much of the associated finer grained sediment was deposited along about a 0.25-mi route. The 

area and limits of boulder deposition are shown in figures 10 and 31.

Testimony of eyewitness Susan Graves (app. B 

and G, fig. 27) indicates that boulder movement at Old 

Highway 395 continued for at least 10 minutes after the 

leading edge of the floodflow arrived. Vie Stafford 

(app. B) recalled that intense flow past his home (S, 

fig. 27) lasted about 45 minutes. Greg Stafford 

observed that most of the massive boulder deposition in 

the vicinity of the Stafford property occurred in a very 

short time during the early stages of the flood. Despite 

the intensity of the leading edge of the flow, as reported 

by eyewitnesses, progressive downstream flattening of 

the channel gradients implies that the overall velocity 

of fluid flow diminished enroute from the mouth of the 

lower canyon to the downstream limit of boulder deposition. Eyewitness accounts by Susan Graves and 

Tom Reed (app. B) indicate a high velocity near and 

upstream from Old Highway 395. The areal pattern of 

boulder deposits (fig. 31) suggests that the flow decelerated noticeably downstream from the tree shown in 

figure 30 (J, fig. 27) where flow began to rapidly spread 

laterally.

The extent of home damage downstream from 

Old Highway 395 is depicted in figures 32, 33, 34, and 

35, which picture three homes and the extent of their 

exterior damage. The Stafford home (S, fig. 27) 

appears to be structurally intact, but was partially filled 

with fine-grained deposits to over half the height of the 

ground floor (fig. 32). The Cline home (C, fig. 27) was 

destroyed (figs. 33 and 34); Mrs. Katy Cline's escape 

from that house (app. B) is rendered even more incredible by evidence shown in figures 33 and 34, which portray some sense of the chaos that must have prevailed 

in and around the Cline residence at, or near, the time 

she was forcibly ejected by the flood. The Turek house 

(Tu, fig. 27), like Stafford's, was not heavily damaged 

structurally, but was substantially damaged internally 

by water and the deposition of fine-grained sediment 

(fig. 35).

38 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Figure 31 . Downstream extent of boulder deposition on Ophir Creek fan resulting from the 1983 flood. Turek and Cline 

homes are separated by new alignment of creek. Stafford home and buildings among trees to south. Vertical aerial 

photograph by Nevada Department of Transportation, June 1, 1983.

Fine-grained, sediment-laden fluid flowed 

beyond the boulder field toward the freeway (fig. 10). 

Some of this fluid mixture appears to have come from 

the upper part of the interstices between surficial boulders. The partial draining of these interstices contributed to the rough appearance of the bouldery armored 

surface portrayed in figures 31, 40, and 48.

Eyewitnesses Shirley Stafford, Cline, Sommers, 

Julian, Dopf, and McQuerry, individually located at a 

variety of vantage points (fig. 2), all described movement of the fluid mixture of water and fine-grained sediment that flowed beyond the boulder deposits toward 

the freeway (app. B). The consensus of their accounts 

is that the mixture was heavily laden with entrained 

sediment. The flow appeared to be more viscous than 

water, and although its velocity had decreased greatly 

from that of the peak flow through the canyons, it still

retained a level of power that impressed Shirley 

Stafford (app. B). As the flow moved southward, parallel to the upstream side of the freeway, she watched it 

roll a helpless horse over and over. Similarly, Katy 

Cline tried to stand up in the flow but was repeatedly 

knocked down. Sommers observed Cline being rafted 

along by the viscous flow.

Flow Rates and Velocities

Flow rates and velocities are quantitative hydrologic variables important to the scientific characterization of flooding and the understanding of flood 

characteristics. These variables usually are measurable 

to acceptable degrees of accuracy during floods that are 

anticipated, rise gradually, peak smoothly, and recede 

over a prolonged time, are dominantly water rather than

THE FLOOD 39
debris laden, and are confined within a stable channel. 

Corresponding data usually cannot be measured 

directly during flash floods, which are of opposite and 

contrasting character: they usually are unexpected and 

they rise, peak, and recede before such direct measurements can be made. Also, flash floods can erode stream 

channels to a degree that hydraulic characteristics of

the resultant fluid are altered by high concentrations of 

entrained debris. Flow rates and velocities must be estimated indirectly, after flooding has ceased. Measurements made after a flood are potentially less accurate; 

consequently, confidence in the measurement results is 

inherently less than for data measured directly during 

flooding.

9*

**. r* > -1 SjaK.I-** ^-*:--•*". i:ss^i

^•"-^ "~-: _-- f-___ -rt~ w *f"'^3^.--: *w~ws> °^ ^^^-"--*

Figure 32. Stafford home, June 1, 1983. Photographs show damage caused 

by Ophir Creek flood, western Nevada: A, View downstream from just below 

Old Highway 395. B, Southeastward view of north end of house. Photographs 

by Patrick A. Glancy.

40 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
The Ophir Creek flood of 1983 was a particularly 

intense flash flood that, because of its unusual and 

unpredictable genesis, chaotic nature, and hazardous 

behavior, was largely unmeasurable by standard, direct, 

hydraulic techniques. The energetic severity of the 

flood produced streamflow heavily laden with

entrained sediment. This heavy sediment loading 

undoubtedly altered hydraulic characteristics of the 

fluid mixture. The distorted hydraulic character 

impaired indirect-measurement methods originally 

devised for streamflow where water, rather than sediment, is the dominant fluid component.

Figure 33. Cline home, June 1, 1983. Photographs show damage caused by 

Ophir Creek flood, western Nevada: A, View southwestward showing 

downstream side of house. B, View northwestward showing downstream side 

of house. Kathleen Cline was ejected from this side of the house by floodflow. 

Photograph by Patrick A. Glancy.

THE FLOOD 41
Figure 34. Downstream (eastward) view of Cline house. Distal margin of boulder deposits at top of 

photograph. Oblique aerial photograph taken by Washoe County Sheriff's Department during afternoon of 

May 30, 1983, after the leading flow surge of the Ophir Creek flood, western Nevada.

No hydraulic formulae handily quantify flow 

rates and velocities of streamflows that are dominated 

by entrained debris (debris flows), that vary rapidly in 

magnitude and intensity, and that flow through erosively unstable channels. Consequently, formulae 

devised for water-dominated (Newtonian) flows are, of 

necessity, often used as imperfect surrogate tools during debris-flow analyses. Resultant flow-measurement 

data are inherently imprecise. During the Ophir Creek 

study, estimates were therefore numerically rounded to 

reflect an appropriate level of confidence.

Keen observations by ideally located eyewitnesses were unusually abundant for the Ophir Creek 

flood, compared to most flash floods. Data derived 

from these accounts were used in numerical checks and 

balances on the frail results obtained by liberal applications of surrogate Newtonian-flow, indirect-measurement formulae.

In summary, several measurement methods, some 

less appropriate than others, were used, as available 

opportunities allowed, to compute flow rates and velocities. Results of the various methods, tempered by theoretical and practical considerations as well as by 

eyewitness accounts, were compared and weighed 

against each other, in check-and-balance fashion, to 

finalize rounded estimates of flow rates and velocities.

Average Rates and Velocities

Eyewitness observations allow an estimate of the 

average time of travel of the leading edge of the flood 

from Price Lakes to Old Highway 395. James Schumacher (app. B, fig. 2) noted the time of the landslide as 

11:53 or 11:54 a.m., according to his wristwatch. Eyewitness Kathleen Thompson (Th, fig. 27) noted that her 

electric power supply failed at 12:02 p.m., which 

agrees with Sierra Pacific Power Company's timing of

42 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Figure 35. Turek home on June 1,1983. A, View downstream to the northeast; B, view cross channel to the 

north. Photographs by Patrick A. Glancy taken after the Ophir Creek flood, western Nevada.

THE FLOOD 43
the power outage in the area. Electric power failed on 

the Ophir Creek fan because supply lines were cut by 

the leading edge of the flood where it crossed Old 

Highway 395. Thus, the overall travel time from the 

beginning of the spilling of Upper Price Lake to the 

time of arrival of the leading edge of flow at Old Highway 395 was about 8 or 9 minutes. Eyewitness Doug 

Cook, who observed the landslide and the travel of the 

flood surge from Price Lakes to Old Highway 395 

(hang-glider flight path, fig. 2), but did not document 

the rate of travel with a timepiece, independently estimated the travel time as ranging from 5 to 10 minutes 

(app. B). We believe the clock-time range of 8 or 9 minutes to be an acceptable estimate of the overall travel 

time. The map distance of the flowpath to Old Highway 

395, 2.88 mi (summation of several distances; see fig. 

6) is slightly less than the slope distance. The slope distance was computed as 2.91 mi and more correctly represents the true length of the stream-channel reach. The 

average flow velocity that is based on a travel time of 8 

or 9 minutes and either of those distances (2.88 or 2.91 

mi) would range between 19 and 22 mi/hr (about 28 to 

32 ft/s).

Fluid velocities in the range of 28 to 32 ft/s are not 

unreasonably high considering the steep channel gradient. This average velocity range is well within the range 

of peak velocities (10 to 40 ft/s) characterized by Van 

Dine (1985, p. 51) for debris torrents in Canada. 

Streamflow velocities as fast as 30 ft/s have been measured with a current meter in natural river channels by 

the U.S. Geological Survey (Leopold, 1974, p. 58).

The average velocity of the Ophir Creek flood is 

greater than the 5.6 ft/s (3.8 mi/hr) that was caused by 

the Lawn Lake and Cascade Lake dam failures in Colorado (Jarrett and Costa, 1984, p. 31). However, the 

average gradient of Ophir Creek (about 14 percent, fig. 

6) is about 2.8 times that of the channel in Colorado 

(about 5 percent; Jarrett and Costa, 1984). Overall, 

comparisons of release rates of ponded water, channel 

slopes along variable-length reaches, and characteristics of channel confinements and geometry between the 

two floods indicate that different average velocities 

would be expected.

Rates Associated With Expulsion of Price Lakes

A precise rate of expulsion of Upper Price Lake 

by the landslide is indeterminable because data necessary to establish the emptying rate, with a desirable 

degree of precision, are unavailable. Walters (1983,

p. 181) described displacement of Upper Price Lake as 

a large wave up to 16.5 ft high. This determination of 

wave height importantly verifies a rapid and dynamic 

emptying of the contents of the lake. The eyewitness 

account of Doug Cook (app. B) supports the observation of Walters regarding rapid expulsion.

Hydraulic evidence at the outlet of Lower Price 

Lake was used to speculate on varying rates of fluid 

movement from Lower Price Lake and into the head of 

the upper canyon. Figures 22B and 36A show the geometry of the creek channel at the outlet of Lower Price 

Lake as it existed shortly after the flood. By the time the 

geometry was surveyed in October 1983, snowmelt 

runoff had deepened and enlarged the outlet (fig. 36B). 

A vertical cross section of the area of flow as it left the 

lake was determined from measurements of the channel-bottom shape and the elevation of the high-water 

lines left by the flow at its peak stage (fig. 36B). The 

October 25 measurements were modified for the channel bottom, as shown in figure 365. This cross section 

is located approximately along the axis of the earthen 

dam that formerly impounded Lower Price Lake.

Immediately downstream from the dam, the channel bottom drops vertically at least 10 ft (fig. 36A); then 

the upper canyon of Ophir Creek falls steeply (figs. 5 

and 6). As a result, a minimum peak-flow rate can be 

estimated by assuming that the flood moved at critical 

velocity over a spillway. The only known hydraulic 

parameters are the approximate size and shape of the 

flow cross section, which is depicted in figure 36B. A 

flow analysis that assumes hydraulically critical flow at 

the site of the measured cross section implies the following hydraulic conditions: (1) The flow cross section 

is assumed to be analogous to one that might have 

resulted had an imaginary impoundment of that size 

existed at the site, and (2) flow through the cross section is analogous to that which would achieve a maximum rate following instantaneous removal of the 

imaginary impoundment. This analogy inherently 

assumes that the approach velocity to the flow cross 

section is zero. However, field evidence, eyewitness 

accounts, and common sense demonstrate that the 

actual approach velocity during the peak surge of the 

flood was much greater than zero; thus, this criticalflow analysis results in a minimum estimate of the rate 

of flow through the section.

44 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
NW 

SO-,

LJJ 

LLI 

U_

? 2Q

I

CL 

Ill 

Q

SE

High-water surface during 1983 flood

_ 

LU

I

o

10-

Likely bottom during peak flow,

as indicated in photo above

and in figure 22B

10 20 30 40 50 

CHANNEL WIDTH, IN FEET

60 70

Figure 36. Outlet of Lower Price Lake, western Nevada: A, Upstream view of breached dam, photographed by R.L. 

Jameson, U.S. Forest Service, on morning of May 31, 1983. B, Downstream view of cross section, as surveyed about 

5 months later by Robert R. Squires and Rodney L. Carson, U.S. Geological Survey, October 25, 1983.

THE FLOOD 45
For a rectangular channel, the critical-flow 

hydraulic state is given by:

(1)

where F is the dimensionless Froude number;

v is the average flow velocity at the lake exit, in

feet per second,

g is the gravitational constant of acceleration, 

equal to 32.2 feet per second per second, 

and

dm is the mean depth of flow through the vertical 

cross section, in feet, assumed to equal the 

critical-flow depth. ____ 

At critical flow, F = 1, and v = V32.2dra. Velocity can be readily calculated if the flow is assumed critical and if the mean flow depth representing the critical 

depth can be determined (Rouse, 1950, p. 71). Figure 

36B shows that an acceptably reasonable and accurate 

estimate of dm cannot be made for the entire cross 

section in a single step. Therefore, the vertical cross 

section of flow was subdivided into a series of nearly 

rectangular vertical elements, to allow application of 

the above equation, and velocities of the individual 

elements were calculated. Areas of the individual 

elements were also calculated.

Flow rates for the individual elements were subsequently calculated using the basic flow equation:

Q = VA, (2) 

where Q is flow rate, in cubic feet per second; 

V is velocity, in feet per second; and 

A is area perpendicular to direction of flow, in

square feet.

A summation of the individual flow rates and 

areas calculated for the individual elements at critical 

state results in a cumulative flow rate (Q) of about

o

6,000 ft/s and a corresponding cross-sectional flow 

area of about 400 ft2 . Average velocity (assuming a 

zero approach velocity) during the critical-flow state 

through the cross section shown in figure 36B, can then 

be simply calculated (V = QIA, or 6,000 -s- 400) as about 

15 ft/s. Dual links of evidence for the rapid expulsion 

of Upper Price Lake, described above, and the welldefined channel between Upper and Lower Price Lakes 

(fig. 20) assures that the flow surge into Lower Price 

Lake was large and swift. Thus, outflow from Lower 

Price Lake, through the cross section shown in figure 

36, was probably hydraulically supercritical and, if so, 

the flow rate would probably exceed 6,000 ft3/s.

Supercritical flows can and do occur naturally in 

erodible channels, but probably are uncommon 

throughout long channel reaches or within any given 

reach for prolonged periods of time. Hydraulic forces 

on the channel boundaries caused by supercritical flow, 

which is rapid, turbulent, and abrasive, remold erodible 

channels in a manner that transforms the depth-velocity 

relation and causes flow to progressively revert to and 

remain in a subcritical state. The landslide that emptied 

Price Lakes may have generated supercritical flow at 

the outlet of Lower Price Lake for the short duration 

that was required to empty the lakes. If so, the average 

velocity probably would have exceeded the critical 

average velocity of 15 ft/s calculated above.

Average flow velocities in the range of 28 to 

32 ft/s, which was determined by using travel time and 

distance, as described above, probably generally characterize the overall movement of the flow downstream 

from Upper Price Lake to Old Highway 395. At velocities of 28 and 32 ft/s, the application of the basic flow 

equation (Q = VA) indicates that corresponding peakflow rates through this cross section (fig. 36B, area = 

400 ft2) would range from about 11,000 to 13,000 ft3/s, 

or about twice the assumed minimum rate of 6,000 ft/s 

determined and described above.

The range of flow rates (6,000-13,000 ft3/s) estimated above for the outlet of Lower Price Lake can be 

hypothesized on the basis of time required to empty the 

contents of Upper and Lower Price Lakes. The combined contents of the lakes probably were about 22 

acre-ft, or about 960,000 ft3 . At a constant flow rate of

o

6,000 ft/s, 160 seconds would be required to move that 

amount of water; similarly, at 11,000 and 13,000 ft3/s, 

87 and 74 seconds, respectively, would be required. 

Because these hypothesized flow rates are assumed to 

be peak-flow rates, they would not prevail during the 

entire emptying of the lakes; thus, times somewhat 

greater than those estimated would have been necessary to empty the lakes at flows characterized by those 

peak-flow rates. Cook's observation (app. B) of the 

rapidity of lake spilling infers that the largest of the 

above postulated flow rates might be closest to the 

actual event. Even at that large rate (13,000 ft3/s), it 

may have taken about 1.5-2 minutes to evacuate 22 

acre-ft of water. Cook's observations thus imply that a 

peak rate greater than 13,000 ft3/s may have occurred. 

At a flow rate of 13,000 ft3/s, flow would have been 

supercritical at the outlet of Lower Price Lake, and 

average velocity would have been 32.5 ft/s.

46 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Eyewitness accounts, Walters' data (1983), and 

surge characteristics of high-water lines noted at the 

site all argue strongly for rapid expulsion of Upper 

Price Lake. A 1-minute duration for expulsion would 

require a constant flow rate from Lower Price Lake of 

about 16,000 ft3/s; the peak-flow rate to accomplish 

that magnitude of lake expulsion might have exceeded

fj

20,000 ft/s (an average cross-sectional peak velocity 

at the lake outlet of 50 ft/s). A 2-minute duration for 

lake expulsion would require a constant flow rate of

fj

8,000 ft/s and a peak-flow rate of perhaps on the order

fj

of 10,000 ft/s (which yields an average, cross-sectional, peak velocity of 25 ft/s).

The aerial photographs of figure 22 portray a 

flood surge that abraded the outlet of Upper Price Lake 

and much of the downstream channel between the two 

lakes. However, at the edges of the channel, the force 

and duration of the flow were not sufficient to fully 

remove the blanket of snow mantling the channel 

boundaries. This residual snowpack indicates low abrasive action or a short duration of submergence, or both, 

at the outer channel margins. Intense erosive abrasion 

along the inner parts of the channel argues for high 

velocity but probably over a longer flow duration. The 

combined evidence indicates a sudden peak surge of 

such a short duration that much of the snowpack survived; it also indicates that highest velocities and associated shear stresses were concentrated in the center 

two-thirds of the channel width. The interpretation of 

these features is that the complete emptying of Upper 

Price Lake may have required more than 1 minute, and 

that the momentary peak surge of flow was followed by 

moderate to heavy flow that may have lasted over a 

minute. Although data are inadequate to further resolve 

the rate and time of emptying, they probably are 

adequate to conclude that most of the contents of Upper 

Price Lake were probably disgorged in less than 2.5 

minutes after the landslide occurred.

The above discussion does not favor or verify any 

specific peak-flow rate for the expulsion of water from 

Price Lakes. However, it does imply that the peak-flow 'j

rate of expulsion was at least 6,000 ft/s. Although eyewitness accounts implicitly suggest that the rate was 

greater, there is no incontrovertible hydraulic evidence 

to demonstrate a greater rate. On the basis of eyewitness reports that describe the rapidity and characteristics of expulsion, and in spite of limited field evidence, 

a peak-flow rate of about 15,000-20,000 ft3/s is indicated. Even at a minimum peak-flow rate of 6,000 ft3/s,

the flow would have been an intense surge of fluid and, 

as such, would have possessed an alarming amount of 

both kinetic and potential energy at the beginning of its 

downward plunge into the highly erodible, steep, and 

narrow canyon below Lower Price Lake.

Rates in the Canyons

William and Elizabeth Willets witnessed the 

approaching flood surge from their vantage point along 

the flood plain between the upper and lower canyons of 

Ophir Creek (fig. 2 and app. B). William estimated the 

velocity of the leading edge at 20-30 mi/h (29 to 44 ft/s) 

just before it exited the upper canyon. Although wide 

ranging, that estimate seems reasonable, considering 

that the velocity of the leading edge of flow may have 

been near its maximum as it approached the terminus 

of the steep upper canyon. Willets' estimate also is reasonably compatible with the estimates of average 

velocities (28 to 32 ft/s) derived on the basis of overall 

travel time, as described above. The Willets sensed a 

general decrease in flow velocity as the flow spread laterally in the reach between the upper and lower canyons. Their intuitive sense is compatible with the 

evidence of debris deposition throughout the reach that 

implies both decreasing velocities and flow depths.

Direct estimates of flow rates, like that made by 

William Willets for the mouth of the upper canyon, are 

not available for the lower canyon. However, the peakflow rate was quantified after the fact by indirect-measurement means.

Indirect determination of the peak-flow rate is 

quantitatively founded on the basic equation of openchannel flow:

= VA, (3)

where Q is discharge rate of the streamflow, in cubic 

feet per second;

V is average flow velocity through a crosssectional area of the channel, perpendicular 

to the direction of flow, in feet per second; 

and

A is the cross-sectional area of flow in the 

channel, in square feet.

THE FLOOD 47
Slope-Area Measurement

Peak-flow rates in natural channels are commonly 

measured indirectly using the slope-area method (Dalrymple and Benson, 1967). The slope-area measurement method yields reliable results when prevailing 

streamflow conditions are within the hydraulic limitations for which the technique is applicable, and when 

field-measurement uncertainties are resolved or minimized.

The slope-area measurement is based on the Manning equation, an empirical expansion of the basic flow 

equation (Q = VA), which defines flow rate in an open 

stream channel as:

Q = (4)

where Q is discharge rate of the streamflow, in cubic

feet per second; 

A is cross-sectional area of flow in the channel

in square feet;

R is hydraulic radius of channel, in feet; 

S is friction slope of the channel reach, which 

is assumed equivalent to the slope of the 

high-water profile through the measurement 

reach, in feet per foot; and 

n is an empirical roughness coefficient,

expressed as a numerical constant. 

A comparison of the Manning equation with the 

basic flow equation shows that the basic components of 

stream discharge are still area (A) and velocity (V), but 

that velocity takes a new form:

V = (5)

Application of the Manning equation requires 

hydraulically steady and uniform-to-gradually varied 

flow of a Newtonian fluid (water-dominated rather than 

debris-dominated). Minimum scour or fill, or both, 

along the channel boundaries, during all phases of the 

flow, bolster confidence that the cross-sectional area of 

the channel at peak flow can be accurately portrayed by 

postflood measurements. Also, low concentrations of 

debris entrained in the peak-flow results in an empirical 

roughness coefficient (n) that is dominantly the product 

of channel-boundary roughness. For flows where channel scour and fill were minimal, a value for n can be 

estimated by visual inspection of channel-boundary 

conditions after the peak flow has subsided (Barnes, 

1967).

Eyewitness accounts and postflood field investigations indicates that the Ophir Creek flood failed to 

meet any of the ideal hydraulic scenarios and conditions described above, which decreased confidence in 

results of the slope-area method of indirect measurement. The peak flow was heavily charged with debris, 

the entrained debris load was almost exclusively the 

product of channel erosion, flow was likely unsteady 

and probably varied rapidly, and internal frictional 

resistance to flow caused by turbulent motion and characteristics of entrained debris of the fluid may have 

been at least as important as flow resistance caused by 

channel-boundary roughness.

Results of recent flume studies of debris flows 

(Major and Iverson, 1993, p. 315) indicate that mudline 

elevations along channel banks record the passage of a 

peak roll wave, but reveal little about mean flow depth, 

velocity, or discharge. However, characteristics of the 

flume-generated flows differ from those of the Ophir 

Creek flood. The magnitude of the peak flow and the 

range of particle sizes transported by the flood greatly 

exceed those in the flume studies, and the characteristics of the channel boundaries of Ophir Creek seem to 

bear little resemblance to those of a flume. Characteristics of the mechanism and rate of fluid release and 

subsequent flow response also may differ greatly. Eyewitness observations of the Ophir Creek flood by Anne 

Ogilvy and Tom Reed (app. B), from vantage points no 

greater than 0.2 mi downstream from the indirect measurement reach (O and R, fig. 27), describe the leading 

surge of the flood as the peak flow. This surge seemed 

to peak almost instantaneously and receded almost as 

quickly. It was choked with mud, boulders, and trees. 

Debris deposition by this peak-flow surge is shown in 

figures 28, 29, and 52. Because of its brief duration, 

there is little likelihood that any roll waves accompanied the rise, peak, or early recession of the surge. The 

initial surge at peak-flow rate, downstream at Old 

Highway 395 was similarly characterized by Patricia 

Sommers (app. B). Thus, the high-water profiles along 

channel banks at the indirect measurement site are 

probably those emplaced by the nearly instantaneous 

initial surge. Testimony of several other eyewitnesses 

(for example, Vie Stafford and Susan Graves, app. B 

and fig. 2) recall persistent bouldery flow for up to 45 

minutes after the initial peak surge. This recessional 

flow may have included roll waves, but at peak levels 

well below those of the initial surge.

Failure to meet the hydraulic requirements for 

a slope-area measurement reduces certainty in the 

results of the peak-flow measurement for this flood.

48 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
However, results of the slope-area measurement can 

nevertheless be usefully compared to results obtained 

through other measurement options. Therefore, a 

slope-area measurement of peak flow was made and 

the credibility of the results was tested through comparison with other methods. Results of several methods 

were evaluated and adjusted on the basis of complementary lines of evidence, and the selected result was 

then reported to a level of significance commensurate 

with the recognized level of uncertainty.

The slope-area measurement site encompassed a 

250-ft channel reach within the mouth of the lower canyon (fig. 27). This site was chosen for measurement for 

several reasons. Its location, just upstream from the 

area of human occupation and associated development, 

was conducive to provide needed quantification of the 

hazard potential this flood posed to the downstream 

residents. Also, the general hydraulic characteristics 

and geometric configuration of the channel through the 

selected reach generally were favorable for analysis 

after the flood.

A quantitative analysis of the peak-flow rate and 

hydraulic characteristics of the debris-charged flow for 

a flood of this size and intensity were subject to a variety of uncertainties. The area (A) term of the basic 

equation of flow (eq. 3) probably involved less, or at 

least more easily resolvable, uncertainties than the 

(V) velocity term.

Quantification of the cross-sectional flow area 

was necessarily based on postflood measurements of 

the high-water profiles along the channel banks 

through the measurement reach and on the postflood 

geometry of the channel bed and banks. The likelihood 

of severe channel scour and (or) filling during this 

flood raised uncertainty regarding the accuracy of postflood measurements in portraying the true cross-sectional shape and size during peak flow. Another 

uncertainty arose because significant scour and (or) fill 

during peak flow might have influenced the elevation 

and slope of high-water lines.

An unusual and beneficial aspect of this specific 

channel reach was the existence of a preflood, crosssectional channel measurement. A comparison of preflood and postflood channel topography is shown by 

the cross sections in figure 37. This comparison confirms that the flood did alter the channel geometry in 

the measurement reach to some degree. Planimetry of 

the two cross sections indicates that the postflood 

cross-sectional area is roughly 70 to 80 percent that of 

the preflood area; thus, effects of the flood appear to

NE

90 -i

80 -

SW

UJ 70 

LU

60 -

LU 

O

99 50 •<

40 -

30 -

20 -

10 -

Downstream view

Boulder berm shown 

in figure 26

xT"^ '

0 50 100 150 200 250 300 

DISTANCE, IN FEET 

Vertical exaggeration x5

Figure 37. Diagrammatic cross sections of Ophir Creek 

channel, western Nevada, measured near lower canyon 

mouth before and after the 1983 flood.

have reduced the area by about one-fourth through the 

process of net channel filling. Channel erosion was the 

dominant fluvial process during the rising and peakflow phases and channel refilling (deposition) dominated the recessional phase of flooding. Although the 

exact channel configuration at the time of peak flow is 

unknown, the data of figure 37 imply that the postflood 

area may be a conservative estimate of the area at the 

time of peak flow.

Postflood measurements through the 250-ft 

channel reach included four vertical cross sections having areas that ranged from about 1,500 ft2 to about 

2,400 ft2. The average of these areas is about 2,000 ft2, 

appropriately rounded to reflect the degree of confidence in portraying the average area of the measurement reach at the time of peak flow.

The slope-area measurement of the 250-ft 

channel reach yielded a peak-flow rate of about 

70,000 ft3/s on the basis of a visually estimated 

postflood, channel-boundary roughness of 0.05

THE FLOOD 49
(Barnes, 1967, p. 152, 153). This rate probably is 

excessive because (1) the frictional resistance factor (n 

of 0.05) accounts only for boundary friction and 

ignores internal friction caused by the turbulent debrischarged flow, and (2) the average flow velocity through 

the measurement reach at a discharge of about 70,000 

ft/s would be about 35 ft/s. This velocity seems inordinately high for the following reasons: The average 

flow velocity from Upper Price Lake to Old Highway 

395, as described earlier, and based on distance and 

travel time, was in the range of 28 to 32 ft/s. Channel 

slope in the indirect measurement reach is about 8 percent, or 4.6°, much less than the upper canyon (slope, 

26 percent, or 14.6°; fig. 6), and slightly less than the 

gradient downstream through the intercanyon reach 

and the lower canyon (slope, 12 percent, or 6.8°; fig. 6). 

Average channel gradient from Upper Price Lake to the 

mouth of the lower canyon is about 15 percent, or 8.5°. 

Thus, velocity through the measurement reach should 

likely be no more, or less than, the average velocity of 

28 to 32 ft/s. A velocity of about 30 ft/s, the mid-value 

of the range of averages, through the indirect measurement reach would result in a peak-flow rate of about 

60,000 ft3/s (VA = 2,000 x 30). However, a velocity of 

30 ft/s also is probably excessive for the reasons stated 

above.

Flow-Around-A-Bend Measurement

The indirect measurement reach is slightly 

curved, convex to the south. This curvature caused a 

super-elevation of the flow surface that probably was 

proportional to the velocity of the moving fluid and, 

thus, allowed an estimate of average velocity that is 

independent of those described above. The relation 

among fluid velocity and channel curvature, channel 

slope, and super-elevation of the fluid surface is specified by the following equation (Johnson and Rodine, 

1984, p. 307 and 308):

u = (RgcosStanB) , (6)

where u is the average fluid velocity;

R is the radius of curvature of the channel bed;

^

g is the acceleration of gravity (32.2 ft/s ); 

S is the angle of the channel slope; and 

B is the angle of tilt (super-elevation) of the

flow surface measured perpendicular to flow

direction.

The following data obtained through the slopearea measurement were used in the above equation:

R is about 320 ft,

cos S is 0.996; slope (S) used was 0.09 (average of 

channel slope of 0.083 and water-surface slope 

of 0.10); arc tan S = 5.14 degrees, and 

tan B is 0.053 ft/ft (average super-elevation of 8.9 ft at 

average channel width of 168 ft):

u = (320 x 32.2 x 0.996 x 0.053 ) 1/2 = 23.5ft/s. (7)

The peak-flow rate using this average velocity 

(23.5 ft/s) and the area (2,000 ft2) obtained from the 

slope-area measurement is 47,000 ft3/s (23.5 x 2,000) 

through application of the basic flow equation. However, because of the previously stated measurement 

uncertainties, the peak-flow rate was rounded to one

o

significant figure, 50,000 ft/s. The resultant average 

velocity of 25 ft/s (50,000 - 2,000) probably is a reasonable estimate that is based on the various eyewitness 

accounts and available postflood data.

Field measurements made as part of the slopearea measurement were further utilized to check validity of the selected peak-flow rate (50,000 ft3/s) through 

step-backwater analysis (Shearman and others, 1986). 

The step-backwater analysis, an application of the 

Manning equation (eq. 4) utilizing field-measured data, 

compares computer-generated high-water lines for 

varying selected flow rates to high-water lines measured in the field. It thereby tests the degree to which 

computed results replicate field data. Results of stepbackwater analyses best replicated field-measured 

high-water lines at a discharge of 52,000 ft3/s with the 

Manning n roughness coefficient ranging from 0.05 to 

0.10 through the measurement reach; at that discharge, 

computed and measured high-water profiles were reasonably similar. The acceptable degree of replication of 

these profiles reinforced confidence that a discharge of 

about 50,000 ft3/s is a reasonable estimate of peak flow 

for the Ophir Creek flood of May 30, 1983, near the 

mouth of the lower canyon.

Substitution of the peak-flow rate of 50,000 ft3/s 

in a rearrangement of the Manning equation allowed 

the calculation of the Manning n (empirical roughness 

coefficient) as a total flow-resistance factor (combined 

boundary and internal resistance); the calculated value 

of n was 0.10. This value implies that the field-estimated boundary friction of 0.05 was roughly equivalent 

to the internal flow resistance. The most probable cause 

of internal flow resistance, based on eyewitness

50 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
descriptions of the nature of the peak-flow surge, 

would have been intragranular friction caused by particle collisions. However, more subtle causes, including 

liquid viscosity and grain friction, probably also played 

important, and possibly dominant, roles (Iverson and 

LaHusen. 1993. p. 1606).

The estimated magnitude of the 1983 Ophir

Q

Creek flood (50,000 ft/s) also can be compared to 

maximum floodflows that historically have been documented for this geographic region. Ophir Creek is situated generally on the boundary between the Pacific 

Coast and Great Basin geographic regions (Fenneman, 

1931). Envelope curves for these geographic regions 

depicting relations of peak floods to drainage-basin 

areas are based on historical data collected within these 

regions (Crippen and Bue, 1977). Figure 38 shows the 

magnitude of the 1983 Ophir Creek flood (drainage 

area 4.5 mi2) relative to Crippen and Bue's peak-flood 

envelope curves for the Pacific Coast and Great Basin 

regions. Although the curves of Crippen and Bue are 

not based on floods resulting from the sudden release 

of ponded water (Crippen and Bue, 1977, p. 2), the 

relation shown in figure 38 nonetheless provides an 

added perspective on the severity of the 1983 Ophir 

Creek flood.

Rates on the Alluvial Fan

Notable deceleration of the floodflow downstream from the mouth of the lower canyon of Ophir 

Creek is indicated by abundant and areally extensive

1,000,000

o

ujO 100,000 

O CO iso^

< o

o

10,000

1,000

100

0.1 1 10 100 1,000 10,000 

DRAINAGE AREA, IN SQUARE MILES

Figure 38. Envelope curves for maximum measured 

floods in relation to the 1983 Ophir Creek flood, western 

Nevada, (modified from Crippen and Bue, 1977, figs. 18 

and 19).

sediment deposits. Estimates of flow velocities downstream from the lower canyon of Ophir Creek are based 

on eyewitness accounts (app. B). Kenneth Julian 

observed the flow front as it approached the U.S. Highway 395 freeway from his vantage point in the southbound lane (KJ, fig. 27). Average velocity of the 

approaching mud, which continued to flow after boulder movement ceased upstream on the alluvial fan near 

the Cline and Stafford homes (fig. 31), was estimated to 

be in the range of 4 to 11 ft/s on the basis of Julian's 

observations. He also noted that the fluid (mud) front 

was 4 to 5 ft thick and in appearance had a consistency 

that resembled freshly mixed concrete.

Charles McQuerry, also on the freeway (fig. 27), 

recorded the flow of the viscous fluid with a video camera from his vantage point (app. B). A surface velocity 

of about 5 ft/s was estimated for the fluid flow near the 

freeway, based on the rate at which vehicles and other 

debris were moved by the flow as they approached the 

freeway, as shown by McQuerry's video recording. 

McQuerry's precise location on the freeway during 

video filming is uncertain but generally was east-southeast of the Cline and Stafford homes and north of the 

Ophir Creek diversion beneath the freeway, as shown in 

figure 27.

On the basis of Reed Dopf's observations as he 

drove southward along the freeway (app. B and fig. 2), 

average velocity of the fluid (mud) front downstream 

from the terminus of boulder deposits near the Cline 

and Stafford homes to the freeway was estimated at 2- 

5 ft/s. Dopf also watched the muddy fluid move southward parallel to the freeway (fig. 3B) during his continued southward travel. Figure 39 shows the nearly 

vertical flow front of the viscous mass, laden with tree 

parts, as it flowed slowly near its journey's end. Dopf's 

ability to walk backward easily at a speed equal to that 

of the leading edge of the flow indicates a fluid velocity 

there of only a couple of feet per second.

In spite of the lack of agreement between some of 

the eyewitness accounts regarding specific velocities 

on the Ophir Creek fan, the flow clearly was moving 

only a fraction of the velocity ascribed to the leading 

flow surge throughout its journey from Price Lakes to 

Old Highway 395. The velocity decrease throughout 

the distal reach of the fan is largely caused by the flattening of the surface gradient (about 2 percent or less; 

fig. 6), and the spreading and directional change of the 

flow.

The flow rates and velocities described and discussed above are summarized in table 6.

THE FLOOD 51
..!««*.*. 

^ J, ;- ««j. jfeT- .•PWSMBG

- ^-^••.;S 4^-;^ 

^

Figure 39. Viscous, organic-laden leading edge of floodflow from Ophir Creek, western Nevada, advances 

southward at about 2 feet per second, parallel to the southbound lanes of U.S. Highway 395 freeway, as 

photographed by Reed Dopf on May 30, 1983.

Table 6. Summary of estimated flow rates and velocities of the May 30, 1983, peak-flow surge in Ophir Creek, western Nevada

[Symbol: —, no data available]

Channel site or reach 

(fig-2)

Estimated discharge .... . . ...

, . . . , M Estimated velocity (cubic feet ,. . ..

v JV (feet per second) 

per second)

Information source

Upper Price Lake to Old 

Highway 395

Outlet of Lower Price Lake

Mouth of upper canyon 

Mouth of lower canyon

0.2 mile below Old Highway 395 to U.S. 395 

freeway

Parallel to U.S. 395 freeway near junction of 

flow and freeway

Parallel to U.S. 395 freeway about 0.5 mile 

south of junction of flow and freeway

6,000-20,000, or 

greater

50,000

28-32 (average) Eyewitness accounts, map distances, and 

time of power outage

15-50, or greater Indirect flow measurements from field 

evidence

29-44 Eyewitness account

average about 25 Indirect flow measurements from field

evidence and verification by analytical 

comparisons and eyewitness accounts

4-11 Eyewitness accounts

2 or less

Evidence in videotape recording

Eyewitness account

52 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Discussion

The summarized discharge estimates of table 6 

indicate the likelihood of a large increase in the peakflow rate between the outlet of Lower Price Lake and 

the mouth of the lower canyon of Ophir Creek. This 

apparent amplification of the flood peak is contrary to 

most floods that originate from a point source; in fact, 

attenuation of the peak flow in a downstream direction 

is commonplace. The flood surge was virtually devoid 

of coarse-grained sediment when it passed the outlet of 

Lower Price Lake. It quickly amassed a significant 

coarse-grained component, including numerous boulders and trees, as it swept through the steep upper canyon. Rapid growth of the sediment load during transit 

compounded the size and intensity of the leading edge 

of the flow, which also was the peak of the flood. 

Entrainment of sediment and debris at the flow front 

continued downstream except for limited deposition 

between the upper and lower canyons. Frictional resistance of the boulder-laden front probably had a retarding effect on the flow so that the trailing fluid phase 

could overrun the bouldery front. The net effect of 

interactions between the bouldery front and the more 

mobile fluid phase was probably a compounding of the 

magnitude of the peak-flow front. The mass of debris 

and water probably assumed the flow characteristics of 

a growing, moving dam as it travelled down the channel. The erosive gouging by the bouldery front progressively increased the debris load, and the overriding 

tendency of the impounded fluid behind the front probably functional in concert to progressively increase the 

magnitude of the leading peak-flow surge. By the time 

it reached the mouth of the lower canyon, the peak flow 

probably attained its peak destructive potential—a discharge of about 50,000 ft3/s, a mean velocity of about 

25 ft/s, and was dominated by a large mass of entrained 

boulders and trees. As the flow then swept downstream 

over the alluvial fan, it transformed from the erosional 

character that dominated flow in the canyons to a 

dominantly depositional mode and progressively 

spread laterally and decreased in velocity, volume, 

and destructive potential throughout its roughly 1 to 

1.5-mi terminal reach.

DEBRIS MOVEMENT

Debris mobilization, transport, and deposition 

were key elements of the 1983 Ophir Creek flood. 

Debris is the rock-derived sediment, of widely varying 

particle sizes, and vegetal material incorporated and 

transported by the flood. Visual characteristics of the

flood, as well as resulting landscape changes and 

impacts on man, were largely the result of debris movement. The processes and characteristics of debris 

movement, and the significance of large quantities of 

debris transport by the May 30, 1983, flood are variously discussed throughout this report. These discussions are necessary because debris movement played a 

key role in different aspects of the evolution of flood 

events. The following discussion focuses mainly on 

aspects of debris transport not previously discussed, 

and summarizes information about debris movement 

that appear elsewhere within the report.

Landslide Debris

The landslide that initiated the flood furnished little debris to the water expelled from the Price Lakes 

Basin. Most of the landslide mass was deposited along 

the path of the slide upslope from the lake, on the bed 

of the northern half of Upper Price Lake, or around the 

immediate margins of the northeast lakeshore (figs. 14 

and 20). Some fine-grained sediment from the slide 

mass may have been incorporated within the floodflow, 

but the amount was small compared to the total mass of 

the slide or to the amount of channel debris eroded 

downstream by the flood. Figure 22 shows that the 

flow exiting the lakes carried enough dark-colored, 

fine-grained sediment to discolor the snowpack, but the 

flow did not completely dissolve or erode the snowpack.

Canyon Debris

Floodflow leaving Lower Price Lake was dilute 

and was transporting a relatively light sediment load; 

however, the flow was capable of mobilizing large 

amounts of debris based on water volume, flow rate, 

and channel characteristics of the upper canyon of 

Ophir Creek (figs. 5,6, and 7). The absence of evidence 

of heavy sediment entrainment in the flow leaving 

Lower Price Lake contrasts sharply with the appearance of entrained debris as the dominant flow component as witnessed by the Willets only 0.6 mi downstream at the upper canyon mouth (app. B and fig. 2).

The rapid increase in debris transport throughout 

the relatively short (0.6 mi, fig. 6) reach of the upper 

canyon, described earlier, was the combined result of a 

dynamically erosive flow process through a channel 

highly susceptible to erosion. The leading flow surge 

of the flood in the upper canyon of Ophir Creek 

was witnessed by hang glider Doug Cook (app. B and

DEBRIS MOVEMENT 53
fig. 2). He noted that the confinement of flow caused 

the flow to accumulate debris. He saw trees getting 

plowed down, and estimated a 40 to 50 ft height for the 

surge. James Schumacher photographed the flow in the 

upper canyon (fig. 23).

The process of debris mobilization in the upper 

canyon is probably best portrayed as a variation of the 

"firehose effect" described by Johnson and Rodine 

(1984, p. 329). They describe this process generally as 

the energetic force of a high-speed stream of water that 

impacts, disperses, and thereby mobilizes large masses 

of debris, ideally in steep channels or in bedrock 

chutes. This description characterizes the incorporation 

of debris within the upper canyon of Ophir Creek 

immediately downstream from Lower Price Lake. 

However, Johnson and Rodine restrict this mechanism 

to the special site condition of very steep talus slopes, 

and they imply that this erosive process is usually the 

result of intense rainstorms; these restrictions do not fit 

the Ophir Creek flood. Thus, the Ophir Creek process 

might be called a "channel firehose effect" wherein an 

abrupt surge of high-velocity streamflow incorporates 

and sweeps movable debris along its path. The flow 

leaving Lower Price Lake, deficient in entrained sediment and possessing high kinetic energy, impacted the 

poorly consolidated landslide debris bounding the 

steep channel of the upper canyon. An action view of 

this process is shown in figure 23. The "firehose effect" 

nomenclature, as specified by the Johnson and Rodine 

definition, also is inadequate because the erosive 

streamflow never encountered and was not confined by 

a steep bedrock chute, as specified in their criteria; 

instead it was confined by a steep and relatively narrow 

canyon consisting of highly erodible, unconsolidated 

debris. The canyon walls are steep and easily destabilized by energetic streamflow, and the debris thus 

mobilized was progressively and cumulatively incorporated within the fluid flow by bulking. The downstream 

increase in mass, and also possibly in velocity, caused 

momentum to increase, as noted by hang-glider pilot 

Doug Cook. Thus, flow transformation was an ongoing 

process as sediment content changed rapidly during 

evolution of the flood.

The Willets (app. B and fig. 2) describe characteristics of the flow as it exited the upper canyon and 

moved through the intercanyon reach upstream from 

the lower canyon. Their descriptions characterize the 

leading flood surge as strongly erosive. Postflood evidence shows the intercanyon reach also to be an area of 

net sediment deposition. The photograph taken by 

James Schumacher in the intercanyon reach (fig. 24),

about 10-15 minutes after his upstream photograph 

(fig. 23), depicts sediment transport in a somewhat different mode than that portrayed in the preceding photograph. The bulk of sediment deposited in the 

intercanyon reach may have come to rest during recessional flow; the precise sequence of events is uncertain.

The leading flow surge entered the lower canyon 

of Ophir Creek after passing through the intercanyon 

reach. Postflood evidence indicates that severe erosion 

continued throughout the transit of the lower canyon, 

thereby compounding the bulking of sediment by the 

floodflow. Mark Bridgewater (fig. 2) viewed progress 

of the leading flood surge through the lower canyon 

and was impressed by its speed and described its 

appearance as a deep, soupy mud or sludge (app. B). He 

also was impressed by the degree of super-elevated 

flow around bends and the destructive impact of the 

flow on trees in its path.

The 1983 flood severely altered the channel morphology of Ophir Creek, as shown in aerial photographs taken before and after the flood (figs. 3 and 11). 

A preflood, cross-sectional channel profile was surveyed near the mouth of the lower canyon in 1973 as 

part of a U.S. Geological Survey investigation of potential flood-and-debris hazards (Glancy and Katzer, 

1977). The measurement was made to define the width 

of the channel that would be inundated and the accompanying depths of inundation that should be expected 

during a 100-year flood. The site selected for measurement was about 0.15 mi upstream from the proximal 

limit of development on the Ophir Creek alluvial fan 

(fig. 27). This documented channel morphology subsequently served as a baseline for comparison of channel 

changes wrought by the 1983 flood. The site of the 

1973 topographic profile was remeasured in October 

1983 to determine changes in channel morphology 

caused by the flood (fig. 37). Preflood sloughing of the 

steeply sloping south canyon wall occurred between 

1973 and 1983. Although the magnitude of this sloughing was minor in comparison to channel erosion by the 

flood, it removed the monument marking the end-point 

of the 1973 profile and some channel-wall sediment. 

However, the alignment of the 1973 profile was substantiated using a 1973 photograph of the profile scene.

The cross-sectional profiles (fig. 37) measured at 

the mouth of the lower canyon before (1973) and after 

(1983) the flood show that a substantial quantity of 

debris was eroded from the south canyon wall by the 

flood. The south wall forms the outer bank of a gentle 

curve in the channel which, combined with the steep 

slope and poorly consolidated debris comprising the

54 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
hillslope, promoted erosion. In contrast, the north bank, 

located on the inside of the curve, was the site of sediment deposition by the 1983 flood (figs. 26 and 37). 

Recessional floodflow and the abundant spring and 

summer snowmelt runoff reworked the channel flood 

deposits south of the boulder berm, shown in figures 26 

and 37, and entrenched the active channel. Interestingly, the 1973 profile shows what may have been the 

relict of a berm on the flood plain. If so, it may have 

been deposited by the major flood of July 6,1890 (app. 

A). The 1983 profile does not show the maximum 

depth of scour that may have resulted during the 1983 

flood.

The leading flow surge began to transform from 

an agent of mainly erosion to one of deposition downstream from the mouth of the lower canyon. At this 

stage of its evolution and because of the entrained 

debris load, it posed a dual threat as it encountered 

human development—the potential to destroy by 

impact and (or) burial.

The 1983 flood incorporated and transported 

large quantities of sediment in the canyon reaches that 

ranged widely in its particle-size composition. Boulder 

movement was common, and many large boulders were 

moved into the human-occupied zone downstream 

from the lower canyon mouth. Evidence and characteristics of boulder movement are shown in many of the 

figures in this report. The largest boulder known to 

have been moved by the flood measures 6x8x12 ft (fig. 

40); its point of origin is unknown, but its postflood 

location at the surface of deposits up to 9 ft thick atop 

Old Highway 395 is proof of movement. The boulder 

weighed several tens of tons, which attests to the phenomenal energy and power of the flood.

Erosion

The rapid entrainment of sediment within the 

upper canyon resulted from the high turbulence and 

velocity (probably greater than 20 ft/s) of the streamflow, and the susceptibility of the channel boundaries to 

erosion. Both lateral and vertical channel scour were 

pervasive throughout the upper and lower canyons of 

Ophir Creek (figs. 7 and 8). The scour essentially 

removed the dense channel vegetation totally, as documented by photographs taken before and after flooding 

(figs. 3 and 11).

The volume of sediment eroded from canyon 

reaches was difficult to determine using preflood and 

postflood aerial photography. The preflood vegetal

Figure 40. Largest boulder known to have been moved by 

1983 flood, Ophir Creek, western Nevada. Boulder, 

measuring about 6x8x12 feet, came to rest on downstream 

side of Old Highway 395. June 3, 1 983. Photograph by 

Patrick A. Glancy

cover within the channel masked the underlying topography and prevented an after-the-fact quantitative 

assessment of volume changes by comparisons with 

postflood evidence of erosive scarring. Also, the crosschannel profiles of figure 37 indicate that the net morphology of the streambed resulting from the flood was 

probably a complex product of both erosion and deposition. The total depth of channel scour by the flood 

was not discernible because of sediment backfilling 

during the recessional stage of the flood. Thus, the 

morphological evolution of the active channel resulting 

from flooding was difficult to ascertain after the event. 

However, an estimate of the net volume of sediment 

eroded was obtained from an estimate of the volume of 

sediment deposited by the flood.

Sediment Deposition

Major areas of sediment deposition include 

(1) the relatively wide channel reach between the upper 

and lower canyons (intercanyon reach) and (2) the 

Ophir Creek alluvial fan below the mouth of the lower 

canyon. Sediment deposited by the flood recession is 

spread along the bed of the upper and lower canyons 

of Ophir Creek. The area of these deposits can be

DEBRIS MOVEMENT 55
measured, but their thickness is uncertain. However, 

these recessional deposits are believed to be volumetrically small compared to those within the major depositional zones listed above.

Volume

Intercanyon Reach

The intercanyon depositional reach is partially 

shown in figure 11. This reach was reconnoitered on 

August 27,1983, to assess the volume of sediment deposition. The deposits had an irregular surface and thickness. Postflood erosion of the deposits by snowmelt 

runoff exposed the variability in thickness along the 

main channel thalweg. Figure 41 shows the typical 

character and thickness of these key deposits. The depositional character of the sediments includes a lack of 

stratification and a presence of matrix support of the 

coarser clasts. The average deposit thickness throughout this reach was estimated to be about 3 ft; average 

width of the reach was estimated to be about 200 ft; and 

the length of the reach, scaled from aerial photographs 

of June 6, 1983, is 3,000-3,200 ft. The total volume of 

the deposits is estimated to be 42 to 45 acre-ft (table 7).

Alluvial Fan

Deposits on the Ophir Creek alluvial fan (fig. 10) 

begin at the mouth of the lower canyon and extend 

downstream to Washoe Lake (frontispiece). Figure 42 

shows the significant areas of deposition on the Ophir 

Creek fan as determined by field observations. On the 

basis of varying thicknesses of deposits, the depositional zone on the fan was divided into three categories. 

Areas were mapped and planimetered, and average 

thicknesses were multiplied by the planimetered map 

areas to determine sediment volumes (table 7).

« rr-ffi^.*^' x ^

H< 

r- -S*3V^ '•^^f^^^iS^^-^^m^^ ¥"r • V •J"^^»^*'v-.«tc*.J*fc •:;:•,:-1* ' -'-.-^?

' '•'- * v

Figure 41. Unstratified and unsorted debris deposited by 

the 1983 flood on broad flood plain between the upper and 

lower canyons of Ophir Creek, western Nevada. Deposit 

was exhumed by recessional floodflow and later springsnowmelt runoff. Hammerhead rests on preflood surface. 

Hammer length, about 1 foot. Photograph by Patrick A. 

Glancy on August 27, 1983.

The total area of deposition on the Ophir Creek fan is 

about 140 acres, and the cumulative volume of sediment deposits is estimated to be about 400 acre-ft.

Total

The approximate volume of sediment deposited 

by the flood is therefore estimated as the cumulation 

of intercanyon and alluvial fan deposits, or about 

450 acre-ft. This estimate is inherently conservative 

because the volume of debris deposited in the canyons 

by flood-recessional flows was not determined.

Table 7. Estimated areas and volumes of sediment deposited by the May 30, 1983, Ophir Creek flood, 

western Nevada

Area 

(fig. 42)

Area A of Ophir Creek fan

Area B of Ophir Creek fan

Area C of Ophir Creek fan 

Subtotal

Intercanyon reach between upper and lower canyons

Land-surface 

area (acres)

43

48

49

140

14-15

Average depth 

of deposits (feet)

5

3

1

3

Total

Sediment volume 

(acre-feet)

215

144

49

400 (rounded)

42-45 (aboutSO)

450 (rounded)

56 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
119°50' 119°49'

390 18'30"

39°17'30"

Bowers Mansion 

County Park

Washoe Lake

Base from U.S. Geological Survey, 1:24,000 quadrangles: 

Mt. Rose, Nev., 1968 and Washoe City, Nev., 1974

EXPLANATION

1/2 MILE 

_I I I

1/2 KILOMETER

Contour interval 200 feet 

Datum is sea level.

Approximate average thickness of sediment deposits 

in designated areas, in feet

|A| 5

E3U 3

Pel i

Figure 42. Major areas of sediment deposition by the 1983 flood on Ophir Creek alluvial fan, western 

Nevada. Sampling sites shown in figure 43 and results of analyses listed in table 8.

DEBRIS MOVEMENT 57
Additional perspective on the flooding process is 

gained when the volume of sediment deposited by the 

flood (450 acre-ft) is compared to the estimate of the 

volume of water released from Price Lakes (22 acre-ft). 

The bulk volume of sediment deposited by the flood, 

uncorrected for intergranular porosity, is greater than 

20 times the volume of water that initiated the flood. 

Additional sources of water incorporated in the flood 

are discussed in the section "Flood Volume and Water 

Sources."

Sediment Particle-Size Characteristics

Information regarding the distributions of sediment particle sizes in flood deposits improves the 

understanding of hydraulic-behavioral characteristics 

of floodflows. Sediment deposits were sampled after 

the flood at four sites (fig. 43) to characterize particlesize distributions within the deposits. Detailed particlesize data are listed in appendix C, and these data are 

summarized in table 8. Samples 1 and 2 are duplicates 

collected from a single site, as are 3 and 4. Photographs 

of the deposits yielding samples 1-4 (figs. 41 and 44) 

show the sediment to be unstratified and largely composed of matrix-supported cobbles and boulders.

Abundant large clasts (cobbles and boulders up to 

10 ft in diameter, some weighing tons, fig. 40) within 

the two upstream deposits (figs. 41,43, and 44) complicated sampling procedures and effectively prevented a 

true characterization of particle-size distribution within 

those deposits; therefore, only matrix materials (pebbles and finer grained sediment) of those deposits were 

sampled (samples 1-4). Samples 5 and 6 were collected 

from deposits that contained particles no larger than 

pebbles (particles less than 64 mm diameter); those

samples from the two downstream sites (figs. 45 and 

46), thus, characterize the complete deposits rather 

than just the finer-grained matrix components.

Particle-size distributions of the samples are 

graphically portrayed by cumulative curves (fig. 47) 

and histograms (fig. 43). The histograms show samples 

3 and 4 to be bimodally distributed, and sample 5 

appears to be weakly trimodal. If the coarser grained 

(cobble and boulder) components of the deposits represented by samples I to 4 could have been included in 

sampling, they might have contributed to a higher level 

of multimodality. The multimodal character of samples 

3 to 5 also is reflected by the multiple inflections shown 

by their respective cumulative curves (fig. 47).

A minimal quantity of clay-size sediment (particle diameters, less than 0.004 mm) is a common characteristic of all particle-size samples (table 8 and fig. 

43). The absence of clay reflects the dominance of 

physical weathering over chemical weathering in the 

source materials (granodioritic landslide deposits) and 

may therefore indicate a relatively young geologic age 

for the landslide deposits. The overall paucity of claysize material (much less than the 3 to 5 percent lower 

limit) characterizes the debris transported by this flood 

as generally non-cohesive (Scott and others, 1995, p. 

8). The total percentage of clay-size material in the 

proximal deposits is even less than that shown by the 

data (samples 1-4) because the matrix materials sampled for those deposits comprises only fractions of the 

total volumes of the deposits. The bulk of the finegrained sediment of the sampled flood deposits generally can be characterized qualitatively as pebbly sand 

(table 8).

Table 8. Summary of particle-size data from sediment deposits, Ophir Creek Basin, Nevada

Sample

Percentage of weight in size, in millimeters (mm) and phi (<|>) units

1 no. ' Pebbles Granules Sand Silt Clay Mud: silt and clay

(fig. 43) (64-4 mm, (4-2 mm, (2-0.0625 mm, (0.0625-0.004 mm, (finer than 0.004 mm, (finer than 0.0625 mm,

-6 to -2 (j) units) -2 to -1 $ units) -1 to 4 § units) 4 to 8 § units) finer than 8 $ units) finer than 4 § units)

1

2

3

4

5

6

28.6

20.3

34.3

39.7

39.5

0

15.1

26.9

7.6

6.5

14.3

1.0

54.8

47.6

55.0

49.2

43.3

93.9

1.1

3.9

2.7

4.3

2.6

4.3

0.4

1.3

.4

.3

.3

.8

1.5

5.2

3.1

4.6

2.9

5.1

1 Detailed particle-size-distribution data for these samples are in appendix C.

58 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
CO 

CO

o

LJJ 

O 

DC 

LJJ

a.

25-

20-

15-

10-

5-

o30

25-

20-

15-

10-

5- 

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PARTICLE-SIZE CLASS, IN PHI (([>) UNITS

-6-5-4-3-2-1-01234567 

PARTICLE-SIZE CLASS, IN PHI (([>) UNITS

39 161 -.

I '. \ _

\ \ Bouhdary.of lower part 

1 * v bf.Ophir'CreekxBasin • \nirc"

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County Park.

Base from U.S. Geological Survey, 1:24,000 quadrangles 

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PARTICLE-SIZE CLASS, IN PHI (([)) UNITS

-6-5-4-3-2-1-01 23456789 

PARTICLE-SIZE CLASS, IN PHI (([)) UNITS

Figure 43. Locations of sediment sampling sites and histograms of particle-size distributions of sediment sampled, 

Ophir Creek Basin, western Nevada.

DEBRIS MOVEMENT 59
torv ^^tfffl ?%£&$&*:&*'*• **** j^ ,^^'^,'w- 'nA?C^f '^^

-^^''feitlfe^t,-

-"*;<!" *SMfe®T i1

./•**, * *..iK.'Wf • • ^-•Lk«ii«r"wr-'> T*- :-

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.,»- *i*.^ * *.^. **?v/ ^ "5," •

"^.^^- •fe'.^.. . '•'%- ^ ^•*j5»\^t'~O' ''J^?

Figure 44. Freshly exhumed debris deposits of May 30,1983, flood on Stafford property just downstream 

from Old Highway 395, western Nevada. A, Northward view of 7-foot-thick deposit. B, Northwestward 

view showing black organic-rich zone (white arrow) on preflood land surface, and freshly dug scars (black 

arrows) marking sites of sediment samples 3 and 4. Shovel length, 4-1/2 feet. Photographed by Patrick 

A. Glancy, November 16, 1990.

60 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
.^^W*?"''''.:*^'

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ifc.*-V^" ^^^^^l^^^^fef*

Figure 45. Collection site of sediment sample 5 (fig. 43). 

A, Westward view of Ophir Creek fan, western Nevada; 

Stafford home in background; sample pit in foreground. 

B, Sample 5 collected from back and bottom of pit. Pick 

length, 1-1/4 feet. Flood deposit is several feet thick.

P^r,

Mfc£f»«V "" ~-'r *2.i'*££ •;S*^-i«<!lfci

^iSfeS^v" • ^SM?S^i

gs-^,,--?,

Figure 46. Collection site of sediment sample 6 (fig. 43). A, 

Southwestward view of Ophir Creek fan, western Nevada; 

shovel in sample pit, 4-1/2 feet long. B, Westward view of 

sample pit; sample 6 collected from backside of pit about 

half a foot below land surface; pick length, 1-1/4 feet. Base 

of deposit is less than 1 foot below pit bottom. 

Photographed by Patrick A. Glancy on May 22, 1991.

DEBRIS MOVEMENT 61
HI 

O 

DC 

HI 

0_

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HI 

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99.8

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0.5

2

0.25

3

0.125

4

0.0625

5

0.031

6

0.016

7

0.008 0.004

PARTICLE SIZE, IN PHI (())) CLASS (UPPER NUMBERS), AND MILLIMETERS (LOWER NUMBERS)

Figure 47. Cumulative distribution of particle sizes for samples of sediment deposits, Ophir Creek Basin, western 

Nevada. Numbers 1-6 are sample numbers (collection sites shown in fig. 43). Particle-size information in tables 8, 9, 

and appendix C.

Graphic statistics (Folk, 1980) derived for the 

particle-size data (table 9) indicate that sampled sediment components of the floodflows were all poorly 

sorted. Implications of this generally poor sorting are 

discussed later with regard to flow dynamics of the 

depositing fluids.

FLOOD VOLUME AND WATER SOURCES

The importance of the sudden release of about 22 

acre-ft of water from Price Lakes in the initiation of the 

flood May 30,1983, in Ophir Creek and the subsequent 

downstream flow rates and velocities of the peak flow 

surge were discussed earlier. However, the approximate 

22 acre-ft of water released from the lakes represents 

only a fraction of the total volume of the flood. For 

example, the "Sediment Deposits" section of this report 

documents the cumulative volume of flood sediment 

deposits to be about 450 acre-ft (table 7). Few data are 

available to allow assessment of floodflow volumes

because of the absence of streamflow gages on Ophir 

Creek. However, several streamflow measurements and 

estimates made before, during, and after the flood (discussed below) provide a quantitative perspective on the 

timing and cumulative volume of floodflow.

Volume

The flood surge at the lower canyon mouth 

reached an estimated peak-flow rate of about 50,000 

ft3/s almost instantaneously and receded greatly within 

seconds, as described earlier. The exact magnitude of 

Ophir Creek flow just prior to the flood is unknown, but 

eyewitness Tom Reed (app. B and fig. 2) recalls the 

flow as about twice that of "normal flow." Tim Miller, 

a companion of Reed, noticed that the creek was flowing faster than normal, but the flow was not great 

enough to be frightening. Washoe County hydrologists 

measured the flow of Ophir Creek at about 60 ft3/s just 

downstream from Old Highway 395 at about 2:00 p.m.

62 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Table 9. Statistics for particle-size data from sediment deposits, Ophir Creek Basin, Nevada1

Sorting coefficients

Mean size

Sample 

no.3 

(fig. 43)

1

2

3

4

5

6

Median size

(Mz) (Md)

Phi 

unit

-0.87

-.50

-.80

-1.45

-1.32

1.27

Millimeters

1.87

1.50

1.80

2.45

2.32

.47

Phi 

unit

-0.70

-.85

-.20

-.80

-1.30

1.20

Millimeters

1.70

1.80

1.20

1.80

2.30

.45

So, 

Trask2

2.6

Well sorted

2.3

Well sorted

5.36

Poorly sorted

7.54

Poorly sorted

3.07

Normal

1.92

Well sorted

Standard

deviation

phi unit

2.00

1.92

3.40

3.85

2.28

1.40

Inclusive standard

deviation

ol 

phi unit

1.93

Poorly sorted

2.05

Very poorly sorted

3.06

Very poorly sorted

3.49

Very poorly sorted

2.30

Very poorly sorted

1.42

Poorly sorted

Inclusive

skewness

Sk, 

phi unit

-0.09

Near symmetrical

.31

Strongly fine-skewed

-.21

Coarse skewed

-.20

Coarse skewed

.03

Near symmetrical

.22

Fine skewed

Equations used to calculate grain-size statistics and rating criteria are in appendix C.

Trask (1932) sorting coefficient considered obsolete, but included here for comparison with results of other investigations.

Samples 1 and 2 collected at same site; samples 3 and 4 collected at same site.

on May 26, 1983 (Michael Widmer, Washoe County 

Public Works Department, written commun., 1983), 

well into the warming trend that began about May 20 

(table 5). For comparison, the previous measurement 

recorded by Washoe County personnel, about noon on 

May 19, was only about 22 ft /s. This earlier and lower 

flow rate coincided with considerably cooler weather 

that preceded the sudden heat wave of late May (table 

5). They next measured it about 2:30 p.m. on June 3, 

1983, at the same site, and it was flowing about 65 ft3/s. 

Robert Squires and Otto Moosburner (U.S. Geological 

Survey, written commun., 1983) also measured the 

flow on June 3, time unknown, at 77 ft3/s. The continuing heat wave during May 27-29 probably amplified 

rates of the diurnally fluctuating streamflow. However, 

the recollections of Reed and Miller and the measurement data of May 26 and June 3 indicate that flow during the late morning of May 30 was probably less than 

100 ft /s; we speculate that it was possibly around 80

o

ft /s shortly before flooding.

The flood reportedly continued intensively for 

several hours (app. B), probably longer, even though 

the initial and most damaging surge was over in a few 

minutes, or less. James Schumacher's photographs of 

the flood (figs. 23 and 24) were taken about 10 to 15 

minutes apart. William and Elizabeth Willets recall 

watching the flood for about 20-25 minutes between

the upper and lower canyons. Vie Stafford remembered 

heavy flow across his land for about 3 hours, with the 

most intense flooding lasting about 45 minutes. Susan 

Graves recalled the intense audible roar of the flood 

lasting at least 10 minutes. The preponderance of eyewitness testimony suggests that elevated stream discharge continued for a considerable time after the 

damaging leading edge of the flow had passed.

The prolonged recession of the flood was quantitatively verified by onsite hydrologic observations. 

Otto Moosburner (U.S. Geological Survey, oral commun., 1983) estimated the flow of Ophir Creek at about 

400 ft3/s, just upstream from Old Highway 395, at 3 

p.m. on May 30, 1983, about 3 hours after the peak 

surge. Views of the flow at about that time are shown in 

figure 48; however, these photographs do not show the 

proportion of flow through the manmade diversionary 

channel (fig. 27) to the south (right) of the area shown 

in figure 485. The relatively heavy recessional flow 

shown in these figures, a few hours after the peak, was 

poorly confined by a braided, distributary-channel system that developed on the Ophir Creek alluvial fan. 

Moosburner and Squires (U.S. Geological Survey, 

written commun., 1983) again estimated the flow at the 

same site at about 250 ft3/s on May 31, at 8:30 a.m.

FLOOD VOLUME AND WATER SOURCES 63
Figure 48. Northeastward panorama of boulder- and tree-laden sediment deposits interlaced by recessional Ophir 

Creek floodflow, at and downstream from Old Highway 395, western Nevada. A, Turek home at top left and Cline 

home near top center. B, Part of Cline property at extreme left and Stafford home behind trees at right. Oblique 

aerial photographs taken by Washoe County Sheriff's Department during afternoon of May 30, 1983.

64 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Flow conditions too hazardous for wading prevented 

actual streamflow measurements during these times. 

Figure 49 shows the bulk of the creek flow on the alluvial fan about 27 hours after peak flow. The flow rate 

at that time is estimated to have been 100 to 200 ft3/s; 

it does not include flow through the manmade diversion to the south (fig. 27). This estimate and the measurement (about 65 ft3/s) on June 3 by Washoe County 

personnel indicate that "normal snowmelt flow" probably resumed sometime around June 3. This return to 

"normal" flow was enhanced by a cooling trend that 

began on May 31, as shown by the sudden drop in 

maximum daily temperatures (table 5). Cooler weather 

continued for several days and further decreased the 

snowmelt rate that had accelerated sharply in late May.

The information and data described above, 

although imprecise and sparse, were used to synthesize 

a flood hydrograph (fig. 50). The hydrograph was analyzed quantitatively to estimate the duration and volume of the flow (table 10). Results of this approximation indicate that overall, floodflow volume was on 

the order of 800 acre-ft, and lasted about 5 days. 

A comparison of floodflow volume to the volume of 

sediment deposits, adjusted for an estimated porosity of 

one-third (Morris and Johnson, 1967, table 5, p. D20), 

indicates that overall the flood was composed of about 

two-thirds water (530 acre-ft) and one-third solids (270 

acre-ft).

A comparison of the estimate of floodflow volume (800 acre-ft) with the sudden release of roughly 22 

acre-ft of water from Price Lakes that initiated the flood 

raises a pertinent question—What was the source of 

additional water that caused a flood volume of about 36 

times that of the initial Price Lakes release?

Sources

Sources of water that probably supplemented the 

hastily released contents of Upper and Lower Price 

Lakes include:

1. Increases in streamflow draining from the 

headwaters of the Ophir Creek Basin during 

the 5-day period, upstream from Price Lakes 

and the landslide area;

2. Ground water that drained from interstices of 

the regolith mantle and bedrock fractures of 

the slide material during and following the 

slide;

3. Streamflow downstream from Lower Price 

Lake incorporated within the faster moving 

floodflow;

4. Increased tributary inflow downstream from 

Lower Price Lake;

5. Ground water contained within interstices of 

debris scoured from the bed and banks of 

Ophir Creek;

6. Release of ground water stored within the streambed and banks of Ophir Creek to the channel after debris was scoured away by the flood; 

and

7. Snow stored atop the slide mass, on and around 

the lakes, and along the downstream channel of 

Ophir Creek that was subsequently swept up 

by the floodflow.

Source 1

The flow of Ophir Creek upstream from Price 

Lakes was measured on the morning of May 31 to 

assess the magnitude of flow coming from the 

upstream part of the drainage. About 14 ft3/s was measured by Kerry Garcia (U.S. Geological Survey), 

approximately 150 ft downstream from the Mount 

Rose Highway (State Route 431, fig. 1) at 11:30 a.m. 

Garcia also noted that the heavy snowpack throughout 

this upper part of the Ophir Creek drainage did not 

appear to have been melting as vigorously during 

recent days as it had been downstream along the eastfacing slopes of Slide Mountain (oral commun., 1983). 

This low-flow rate and the concurrent lack of evidence 

of accelerated snowmelt upbasin from Slide Mountain 

further confirms that the major components of floodflow originated near and downstream from Price Lakes.

The minor amount of flow coming from the drainage upstream from Price Lakes also is verified by the 

oblique aerial photographs that show the freshly 

exposed bed of Upper Price Lake on the afternoon of 

May 30 and the morning of May 31 (fig. 51). All drainage from the upper part of the Ophir Creek Basin is 

flowing across the exposed lake-bed surface. At about 

the same time of the photographs (fig. 51A and B), 

Moosburner and Squires estimated flows downstream 

near Old Highway 395, at 400 and 250 ft3/s, respectively. Flow from Upper Price Lake appears to have 

been minimal compared to that exiting the lower canyon near Old Highway 395.

FLOOD VOLUME AND WATER SOURCES 65
^-^^5*?*^*^gS£?t^' - "- " •'^^y^w-gv^^^-r:J» i^i• • •'-- >,v-

, - - ^^-^^^^^^ ...,

Figure 49. The continuation of recessional Ophir Creek floodflow on the afternoon of May 31, 1983, about 27 

hours after the peak-flood surge. A, Upstream view. B, Downstream view, about 100 yards upstream from Old 

Highway 395, western Nevada. Photographs by Patrick A. Glancy.

66 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
60,000

50,000 -

O 

O

LU 

CO

DC 

LU 

D_

LLJ 

LU 

LL

O 

CD

=> 

O

LU 

O 

DC 

<

X 

O 

CO

Q

800 -

600 -

May 26 2:00 p.m.

May 30 11:30 a.m

May 30 Noon

May 30 3:00 p.m.

May 31 8:30 a.m.

June 3 2:30 p.m.

400 -

200 -

JUNE

1983

Figure 50. Synthetic hydrograph of 1983 Ophir Creek flood, western Nevada. Abbreviation: ft3/s, cubic feet per second. 

Estimate sources: A, Michael Widmer, Washoe County Public Works Department; B, authors; C, indirect measurements 

by U.S. Geological Survey staff; D, Otto Moosburner, U.S. Geological Survey; E, Otto Moosburner and Robert R. 

Squires, U.S. Geological Survey; F, Washoe County Public Works Department and Robert R. Squires and Otto 

Moosburner, U.S. Geological Survey.

Table 10. Estimated floodflow volume on alluvial fan, 1983 Ophir Creek flood, western Nevada

[Flow volumes derived from synthesized hydrograph of figure 50 and rounded to reflect confidence in estimation]

Time and date Streamflow 

(acre-feet)

Base flow 

(acre-feet)

Floodflow1 

(acre-feet, rounded)

0000-Noon

5-30-83 (pre-flood)

Noon

5-30-83 (30-second peak surge)

Noon-2400

80

20

80

.06 20

5-30-83 (recession)

5-31-83

6-1-83

6-2-83

6-3-83

Total (rounded)

400

500

300

200

100

1,600

90

200

200

100

100

800

300

300

100

100

0

2800

Floodflow is difference between Streamflow and base flow.

Sediment deposits of 400 acre-ft (table 7) adjusted for porosity (about 33 percent) result in volumetric proportions of about 

530 acre-ft of water (66 percent) and 270 acre-ft of sediment (34 percent); proportions by weight are about 40 percent water and 

60 percent sediment.

FLOOD VOLUME AND WATER SOURCES 67
Figure 51 . Oblique aerial views of the freshly drained bed of Upper Price Lake, Nevada. A, Upstream view 

photographed by Washoe County Sheriff's Department during mid-afternoon, May 30, 1983. B, Downstream 

view photographed by R.L Jameson, U.S. Forest Service during mid-morning, May 31, 1983.

68 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
The combination of measured flow data in the 

upper basin, flow estimates on the alluvial fan, and photographic evidence of flow into and out of Price Lakes on 

May 30 and 31 indicates that the Ophir Creek drainage 

above Upper Price Lake contributed only a minor 

amount of water to the flood.

Source 2

Some water contained within the slide mass 

drained into Upper Price Lake and added to the floodflow. The volume of ground water that potentially 

drained from interstices of the regolith mantle and bedrock fractures of the landslide mass was estimated as follows:

Landslide volume was approximately 1,400,000 

yd , as described earlier. Fracture porosity of the bedrock 

prior to sliding was probably on the order of 2 to 5 percent (D.E. Prudic, U.S. Geological Survey, oral commun., 1998). Porosity of the regolith mantle was 

probably about 33 percent (Morris and Johnson, 1967, 

table 5, p. D20). Intensive snowmelt during several days 

prior to the landslide assures that the lithic mass was at, 

or near, saturation prior to the landslide. If the entire 

mass is assumed to be bedrock, pore volume would 

range from 17 to 44 acre-ft, on the basis of a 2 to 5 percent porosity range. If the mass is assumed to be all 

regolith, computed pore volume would be 286 acre-ft. 

We assumed that two-thirds of the mass was bedrock and 

one-third was regolith mantle; this assumption yields a 

computed pore-volume range of 106 to 124 acre-ft. Not 

all of the entrained water would readily drain from the 

mass; however, additional water, under artesian pressure 

prior to the slide, would drain from freshly exposed slide 

scars. Thus, an estimated 100 acre-ft (rounded) of pore 

water probably drained from the slide mass during the 

first few hours following the slide. This drainage helped 

sustain the debris-flow recession pictured in figure 24.

The photographs of figure 51, however, show no 

evidence of large-scale drainage from the slide material 

or the slide scar between 3 and 4 hours after the slide to 

nearly a day later. If substantial drainage had been taking 

place for a period of days after the landslide, this flow 

should be apparent in the photographs showing the 

exposed bed and outlet of Upper Price Lake. This indicates that ground water draining from the slide contributed to the early period of flood recession but did not 

contribute significantly after the first few hours.

Source 3

Downstream movement of the initial flood surge 

was rapid enough to overrun streamflow in the channel 

of Ophir Creek and incorporate it into the leading edge 

of the floodflow. Travel time of the leading edge of the 

flood between Upper Price Lake and Old Highway 395 

was about 8-9 minutes, during which the flood overran 

streamflow estimated at 80 ft/s. The maximum amount 

of streamflow incorporated by the flood under those 

conditions, assuming an average velocity of preflood 

streamflow of 5 ft/s, was estimated, as follows:

o ••}

80 ft/s •*- 5 ft/s = 16 ft , average streamflow crosssectional area;

,-\

16 fr x 2.3 mi (distance from outlet of Lower Price 

Lake to lower canyon mouth; fig. 6) x 5,280 

ft/mi =194,304 ft3 .

194,304 ft3 -H 43,560 ft3/acre-ft = 5 acre-ft.

Thus, the flood may have gained up to 5 acre-ft of 

floodflow by overrunning and incorporating preflood 

streamflow. This volume is less than one-fourth of the 

estimated contents of Price Lakes. This additional flow 

contributed mainly to the leading flood surge and added 

little to the recessional flow.

Source 4

The atmospheric heat wave undoubtedly caused 

snowmelt inflow to Ophir Creek from a number of tributary drainages downstream from Lower Price Lake. 

Because the flow rate of Ophir Creek just downstream 

from the lower canyon was about 80 ft/s just prior to the 

flood, and because measured flow of Ophir Creek near 

the Mount Rose Highway on the morning of May 31 was 

14 ft3/s, we infer that about three-fourths of the estimated 

preflood downstream flow entered the creek downstream 

from Price Lakes. Most of that tributary inflow came 

from the rapidly melting snowpack along the east-facing 

slopes of the Carson Range, particularly from the southeast-facing slopes of Slide Mountain. Most of the estimated 5 acre-ft of water that was entrained when the 

leading surge overran preflood streamflow was probably 

tributary inflow derived downstream from Price Lakes 

(source 3). An increase in snowmelt, and a resultant 

increase of tributary runoff, probably occurred during 

the hot afternoon on May 30. This increase is depicted as 

a gentle increase in estimated base flow of the synthetic 

hydrograph of figure 50. As such, it contributed little to 

the flow rate of 400 ft3/s (Moosburner's 3:00 p.m. estimate) downstream from the lower canyon mouth.

FLOOD VOLUME AND WATER SOURCES 69
Source 5

The intense scouring of the upper and lower canyons by the flood eroded sediment from the bed and 

banks of the stream channel that subsequently was 

deposited on the flood plain between canyons and on 

the alluvial fan below the lower canyon. Owing to the 

enhanced snowmelt caused by continued high temperatures (table 5) during about 10 days preceding the 

flood, most of the unconsolidated debris in the canyons 

probably was saturated. When that sediment was 

eroded, largely by the leading flood surge, the debris 

and its entrained water became part of the flood.

It is assumed that at least 450 acre-ft of material 

was scoured by the flood, equal to the accountable volume of sediment that was deposited. An unaccountable 

quantity of fine-grained sediment was flushed to 

Washoe Lake. An additional unaccountable quantity of 

debris moved through parts of the channel system and 

progressively backfilled the channel during the flood 

recession. The estimated porosity of the prescoured 

debris was roughly one-third of its volume, on the basis 

of data compiled by Morris and Johnson (1967, table 5, 

p. D20), and it is assumed that virtually all of the undisturbed material was saturated with water. On this basis, 

the entrained volume of water, at one-third the volume 

of accountable saturated debris was at least 150 acre-ft.

According to these assumptions, the water 

released by the scour of channel debris and incorporated into the flood was a major component of the 

floodflow, almost seven times the amount of water 

expelled from Price Lakes. Much of the debris and 

associated pore water scoured from the channel is 

believed to have been incorporated by the leading flood 

surge. Thus, much of this water became a major component of the early phase of the flood, but probably 

contributed little to the flood recession. The amount of 

water incorporated by this process that contributed to 

recessional flow is indeterminable.

Source 6

Heavy snowmelt during several days preceding 

the flood undoubtedly recharged the shallow groundwater system beneath and adjacent to the Ophir Creek 

channel. Intense scour of the creek channel by the leading flood surge not only incorporated a substantial 

amount of interstitial pore water within the floodflow 

(at least 150 acre-ft, source 5), but the abrupt incision 

of the channel also probably accelerated drainage of 

ground water into the channel. The rate of this groundwater release to the channel probably was greatest

immediately following the incision, then decreased 

exponentially with time, as ground-water levels 

declined and as the abruptly incised channel was 

progressively backfilled by debris emplaced by the 

receding flood. Alluvium beneath drainages tributary 

to Ophir Creek were similarly saturated, and mainchannel incision likely increased discharge from these 

deposits at the junctions of the main and tributary channels. Such an abrupt discharge of ground water may 

account for Elizabeth and William Willets observation 

(app. B) of "water gushing out of the side of the mountain."

David E. Prudic, U.S. Geological Survey (written 

commun., 1999), tested the hypothesis that substantial 

amounts of ground water may have been released and 

subsequently transformed to floodflow as the result of 

severe channel scour by the leading peak-flow surge of 

the flood. He tested the hypothesis through the application of a simple numerical ground-water model. Principal modelling assumptions were as follows:

1. Unconsolidated sediments beneath and adjacent to the stream channel were saturated, and 

the water table sloped toward the stream axis 

throughout the reach from approximately the 

head of the upper canyon to beyond the mouth 

of the lower canyon of Ophir Creek;

2. An approximate 2-rni reach was abruptly 

scoured to an average depth of 10 ft, and the 

ground-water head in the stream channel after 

the surge, was 10 ft lower than prior to the 

surge, and remained at this level for 3.5 days;

3. Incised channel walls were nearly vertical and 

did not immediately collapse into the scoured 

channel;

4. Ground-water flow to the stream was parallel 

to the water-table surface a short distance from 

the creek;

5. Hydraulic conductivity and specific yield of 

the incised sediment deposits were constant 

along the reach for at least 500 ft laterally perpendicular to the incised channel walls;

6. Water drained freely, coincident with a declining water table;

7. Ground-water drainage to the channel through 

the incised walls was not restricted by a confining layer;

8. The full 2-mi extent of incision essentially was 

instantaneous; that is, the time required for the 

complete channel scour was minimal compared to the overall 3.5-day flood duration.

70 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
In reality, many of these simplifying assumptions 

deviate from actual conditions, as follows. Although 

the channel likely scoured to an approximate average 

depth of 10 ft, it regraded towards the preflood level 

throughout the prolonged recessional period that began 

shortly after the initial flow surge. Some of the sediment backfilling the channel probably came from 

slumping of the vertically incised deposits because the 

saturated wall deposits could not retain vertical slopes 

during heavy ground-water discharge. Therefore, 

assumptions 2 and 3 are not wholly valid throughout 

the entire 3.5-day flood period. The assumption that 

ground-water flow paralleled the water-table surface is 

believed to have been reasonable because of the coarsegrained, permeable nature of the sediment deposits; 

however, some upward flow probably occurred near the 

stream. The depth at which upward flow contributed to 

the stream is unknown. Hydraulic conductivity and 

specific yield of the alluvium probably vary along the 

channel, although presumably less than they do laterally perpendicular to the channel. Furthermore, free 

drainage of pores accompanying decline of the watertable surface (assumption 6) is not instantaneous; however, the coarse-grained character of the deposits probably resulted in drainage over a period of only several 

minutes, and thus the assumption is probably not 

unreasonable. The brief time required to drain the pore 

spaces would have decreased the peak ground-water 

discharge immediately following the flood surge and 

would have prolonged ground-water discharge during 

flood recession.

Lateral extent of hydraulic uniformity of the 

deposits, perpendicular to the channel axis, is 

unknown. However, the lengthy canyon segments 

traverse mainly unconsolidated debris and landslide 

deposits having hydraulic properties that probably are 

similar to the channel bounding deposits. Assumption 

8, that the entire canyon segment was instantly scoured, 

mainly affected the peak flow rate of ground-water discharge and the duration of the peak flow rate (peak flow 

of ground-water drainage probably lasted only a duration of minutes). The total volume of ground-water discharge would have been less affected by this 

assumption than by assumptions 2 and 4. Although the 

uncertainties associated with this assumption place 

limitations on the actual quantity, and specifically, the 

timing of ground-water discharge, the resultant quantitative estimates nevertheless provide valuable insight 

regarding the probability that ground-water discharge

supplied a substantial component of the total floodflow 

estimated a short distance downstream from the lower 

canyon mouth.

Prudic utilized a finite-difference ground-water 

flow model (MODFLOW-96; Harbaugh and 

McDonald, 1996) to estimate ground-water discharge 

along the scoured channel. A single layer, cross-sectional model with a 1 ft width corresponding to a 1 ft 

length of stream channel was constructed. The modelled boundaries were: (1) constant ground-water flow 

into the model area, at a perpendicular distance of 500 

ft from the stream; (2) no flow across the water-table 

surface; (3) no flow across the base of the model layer; 

and (4) head-dependent flow into Ophir Creek. The 

river package option (Harbaugh and McDonald, 1996, 

p. 98-109) was used in simulating real-dependent flow 

into Ophir Creek. The streamflow head in Ophir Creek 

was assumed to be 10 ft prior to channel scour, whereas 

after scour, the head was assumed to be 0 ft.

The base of the model layer was assumed to be 10 

ft below the pre-flood water table at a lateral distance 

of 50 ft beyond the stream and continued to the constant flow boundary at a lateral distance of 500 ft. 

Between Ophir Creek and a distance of 50 ft beyond its 

channel, the thickness of the model layer increased 1 ft 

for every 5 ft laterally, and thereby the model layer 

reached a thickness of 20 ft at the stream channel. The 

layer thickness was increased near the stream to allow 

drainage from sediments to the abruptly lowered head 

level in Ophir Creek without causing the model cell at 

the channel boundary to desaturate. Although the true 

thickness of sediment deposits contributing groundwater flow to Ophir Creek is unknown, only the upper 

part of the saturated deposits likely contributed flow 

while deeper ground water continued flowing parallel 

to the stream channel similar to streams west of Carson 

City, about 8-9 mi south of Ophir Creek (Maurer and 

others, 1996, p. 7). Doubling the thickness of deposits 

contributing to Ophir Creek is effectively equivalent to 

doubling the hydraulic conductivity. Thus, only 

hydraulic conductivity was varied within a reasonable 

range and according to constraints governing likely 

ground-water discharge to Ophir Creek before channel 

incision.

The 500-ft lateral distance, perpendicular to the 

channel, was divided uniformly into 100 cells, each of 

which was 5-ft long and 1-ft wide. The lateral distance 

of 500 ft was purposely selected to be greater than 

needed; thus, the outer boundary was sufficiently 

distant from the channel incision to eliminate any

FLOOD VOLUME AND WATER SOURCES 71
model-boundary effects. Changes in water levels and 

flow for each model cell were solved using the Strongly 

Implicit Procedure within MODFLOW (Harbaugh and 

McDonald, 1996, p. 37). A closure criteria of 2 x 10'6 

ft and an acceleration parameter of 0.70 were specified 

in the solution. The 3.5-day period was divided into 

100 time steps. A time-step multiplier of 1.05 was used 

that resulted in an initial time step of 116 seconds.

Because the model simulated ground-water discharge for only a 1-ft length of channel, results were 

multiplied by the 2-mi (10,560 ft) length of the reach 

and then doubled to account for discharge from both 

sides of the channel. A separate steady-state model initially was done for each variation in hydraulic-conductivity to obtain water levels for each model cell prior to 

simulating channel scour.

Constant flow at the lateral distant boundary (500 

ft) was assigned a rate that maintained a water-table 

gradient of 0.10 ft/ft to simulate conditions prior to 

channel scour. Consequently, the assigned constant 

flow rate varied, depending on the value of hydraulic 

conductivity assigned to the sediment deposits. 

Hydraulic conductivity was assumed to range from 20 

to 100 ft/d, within the range of estimates of hydraulic 

conductivity for similar sediment deposits near streams 

west of Carson City (Maurer and others, 1996, p. 21), 

and for lithologically similar sediment deposits in Carson Valley (Maurer, 1986); this conductivity also is 

within the range of hydraulic conductivity for a clean 

sand (Freeze and Cherry, 1979, p. 29). The ranging 

hydraulic conductivity and assumed gradient resulted 

in a calculated range of ground-water discharge to 

Ophir Creek throughout the 2-mi reach of from 5 to 24

ft /s. The lesser part of the range is similar to estimates 

of ground-water discharge along the Upper Truckee 

River (near South Lake Tahoe, Calif.) documented in 

late September 1996 (T.G. Rowe and K.L. Allander, 

U.S. Geological Survey, written commun., 1998). The 

greater part of the range is believed to be reasonable for 

spring runoff conditions, but precise measurements of 

ground-water contributions during these times are 

unavailable.

A specific yield of 20 to 35 percent, by volume, 

was assumed for model simulations; this range is 

within that for coarse to gravelly sand and fine gravel 

(Johnson, 1967, p. Dl). Model results are summarized 

in table 11. The calculated volumes of water released 

from storage during the 3.5-day period depend on specific combinations of hydraulic conductivity and specific storage for the water-bearing deposits. Thus, the 

cumulative volume of water that likely drained from 

the sediment deposits throughout the composite 2-mi 

reach ranges from about 50 to 100 acre-ft; this volume 

is solely the quantity of water removed from storage 

and does not include the natural ground-water discharge of preflood conditions. Table 11 lists the lateral 

distance beyond the channel that a water-table decline 

of at least 1 ft reached during each simulation. Lateral 

distances where the water table declined 8 ft or more 

during the various simulations also are listed in the 

table. The maximum rate of simulated ground-water 

discharge occurred during the first 2 minutes following 

channel scour and ranged from 0.04 to 0.14 ft /s per 

longitudinal foot of channel (both sides). Peak groundwater discharge immediately followed the initial floodsurge incision. If all the ground water that discharged to

Table 11. Summary of model results for ground-water discharge to Ophir Creek caused by flood-induced channel incision 1

Lateral distance from

Estimated Estimated 

hydraulic conductivity specific yield 

(feet/day) (percent)

20

30

30

30

50

50

100

100

20

20

25

30

25

30

30

35

Volume of groundwater discharge 2 

(acre-feet)

50

54

64

74

71

84

93

106

Initial ground-water 

discharge to Ophir Creek 

following incision 

(cubic feet per second)

400

570

580

640

850

890

1,400

1,520

channel (feet) attained 

by drawdown of:

8 feet or

more

20

25

25

25

25

25

30

30

1 foot or

more

100

110

105

100

120

115

130

130

1 Incision depth estimated at 10 feet; discharge is cumulative from both sides of the channel throughout a 2-mile reach. 

" Cumulative volume during 3.5 days following incision.

72 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
the channel during the first 2 minutes reached the bottom of the canyon at the same time, the maximum rate 

for the 2-mi reach would have been about 1,500 ft3/s 

(table 11). However, because of the time required for 

the initial surge to travel from the top of the canyon to 

the bottom (about 8 or 9 min.), the peak flow from 

ground-water discharge along the channel probably 

was less, but the flow probably continued somewhat 

longer than that estimated by the calculations. On the 

basis of the model simulations, ground-water discharge 

probably continued at rates greater than those just prior 

to the flood surge throughout the 3.5-day flood period. 

Model simulations, however, include the assumption 

that the channel did not refill with sediments during the 

3.5-days following the surge. If it did, ground-water 

discharge probably was less than that simulated by the 

model. Data on channel backfilling rates are unavailable.

Model results indicate that an appreciable component of the overall floodflow was ground-water discharge resulting from channel incision caused by the 

initial flood surge. Although, the quantity of groundwater discharge is not precisely known, model simulations suggest that the total volume may have been 

between 50 and 100 acre-ft, with much of the discharge 

occurring during the first 12 hours following the abrupt 

channel incision as listed in table 12.

Source 7

Snowpack atop the landslide mass, on and around 

the lakes, and within and adjacent to the flood plain of 

Ophir Creek downstream from the lakes, contributed 

some water to the flood. Figure 20 shows that not all of 

the snowpack overlying the landslide mass was incorporated into the water expelled from Upper Price Lake. 

Also, figures 20 and 22 show that a substantial snowpack remained peripheral to Price Lakes and the intervening channel reach after the flooding had ceased. 

Some of that snowpack was etched by the expelled lake

water, but most was not incorporated within the flow. 

Much of the snowpack along the channel of Ophir 

Creek canyons downstream from Lower Price Lake 

undoubtedly was incorporated suddenly by the erosive, 

leading peak-flow surge. The amount of water derived 

from these snowpack sources is unknown. Much of the 

water from the entrained snow became part of the initial flood surge. Much smaller amounts of snow, however, are believed to have been incorporated in the 

recessional stage of the flood because the initial flood 

surge effectively eroded the snowpack that had accumulated along the channel. Recessional flow would 

have been enhanced mainly by minor sloughing and 

sliding of snowpack from areas above the highwater 

limits of the peak-flow stage.

Although impossible to account for with precision, snowpack thus incorporated within the floodflow 

can be estimated indirectly, as follows:

Estimated components of flood water from Price 

Lakes and sources 1-6 described above, are cumulated:

Source

Price Lakes

1

2

3

4

5

6

Total (rounded)

Quantity 

(acre-feet)

22

minor

100

5

minor

150

50-100

350-400

Floodflow portrayed by the hydrograph of figure 

50 and data of table 10 included about 270 acre-ft 

of sediment. Thus, sediment (270 acre-ft) plus cumulative water from seven sources tabulated above (350 to 

400 acre-ft) is about 620 to 670 acre-ft. Unaccounted 

water, as portrayed by the hydrograph, is therefore 

about 130 to 180 acre-ft (800 minus 670 or 620). 

This unaccounted component represents a reasonable

Table 12. Simulated ground-water discharge during duration of the flood as the result of channel incision

Duration 

following 

incision 

(hours)

0-12 

12-36 

36-60 

60-84

Total

Discharge volume (acre-feet) at varying combinations of hydraulic conductivity, 

K (feet per day); and specific yield, S (percent)

K=20; S=20

26

13 

6

5

50

K=30; S=20

30 

14 

6 

4

54

K=30; S=25

35 

17 

7 

5

64

K=30; S=30

39 

20 

9 

6

74

K=50; S=25

42 

17 

7 

5

71

K=50; S=30

48 

21 

9 

6

84

K=100; S=30

60 

20 

8

5

93

K=100; S=35

67 

24 

9 

6

106

FLOOD VOLUME AND WATER SOURCES 73
order of magnitude for floodwater derived from snowpack (1) atop the landslide mass, (2) on or around the 

lakes, and (3) adjacent to the floodpath of Ophir Creek 

downstream from Price Lakes. Because of the frail 

nature of all involved estimates, however, the actual 

snowpack component of contributing floodflow probably is in the numerically rounded range of 100 to 200 

acre-ft.

Timing of the arrivals of individual floodflow 

components at the apex of the Ophir Creek alluvial fan, 

the site represented by the synthesized hydrograph, is 

less certain. Whether a substantial quantity of the 

cumulative floodflow lags behind the leading peakflow 

surge, as portrayed by the hydrograph, is indeterminable on the basis of the paucity and uncertainty of data 

that define the hydrograph.

DESCRIPTIONS, DISCUSSIONS, AND 

INTERPRETATIONS OF FLOODFLOW 

DYNAMICS

The term floodflow dynamics, as described and 

discussed in this report, refers to the hydraulic, rheologic, and geomorphic characteristics and behaviors of 

the flowing fluid. Flow characteristics and behaviors of 

the 1983 Ophir Creek flood were related to flow rates 

and velocities, channel-boundary effects (geometry 

and roughness) and, importantly, were influenced by 

varying characteristics of the entrained sediment load 

(concentrations, lithologic composition, particle-size 

distribution, and possibly vegetal matter). Sediment 

concentration varied widely over time and from place 

to place during the duration and evolution of the flood, 

and these variations in concentration strongly influenced floodflow behavior. The lithologic composition 

of the debris component of the floodflow was dominantly that of granodiorite, the parent material that 

comprises the easily erodible landslide-related deposits 

forming the channel boundaries. Because these debris 

clasts were not exposed to chemical weathering for 

long periods of time and local rates of chemical weathering are low, the variably-sized granodiorite clasts are 

dominantly the product of physical decomposition and 

were only mildly altered by chemical decomposition. 

As a result, clay particles (as defined by both size and 

chemical composition) are in short supply in sediment 

deposits of the 1983 flood (table 8).

Classifications of flowing, water-sediment mixtures adopted to characterize the 1983 Ophir Creek 

flood are based on those described by Costa and Jarrett 

(1981), Pierson and Costa (1987), and Costa (1988).

The major classifications utilized in this report are 

(1) normal streamflow (herein called streamflow, 

or Newtonian flow), (2) hyperconcentrated flow 

(Beverage and Culbertson, 1964), and (3) debris flow 

(non-Newtonian, slurry flow). In essence, streamflow 

(dominantly water) has little or no yield strength and 

quickly flows downhill under the stress of gravity; 

hyperconcentrated flow has measurable, but low, yield 

strength (Costa, 1988, p. 114); and debris flow has 

measurable yield strength that can vary widely, therefore it will resist gravitational stress, and can efficiently 

transport large-size clasts. Hyperconcentrated flow is a 

transitional state between streamflow and debris flow 

(Pierson and Costa, 1987, p. 2).

No samples of the Ophir Creek floodflow were 

collected during the flood; therefore, classifications are 

indirectly based on photographs of flow, qualitative testimony by eyewitnesses, and physical characteristics of 

resultant sediment deposits. Thus, classification is 

inherently imprecise and depends on the authors' interpretations of the available evidence.

Flow dynamics of the 1983 Ophir Creek flood 

were complex and are not completely understood. In 

simplest terms, flow began as relatively dilute streamflow that quickly transformed to sediment-laden flow 

through erosive bulking of channel debris. Over time 

and travel distance, rheologic transformation probably 

progressed from Newtonian flow to hyperconcentrated 

flow and then to debris flow; it then regressed, probably 

from debris flow to hyperconcentrated flow, and ultimately back to Newtonian streamflow. Rheologic flow 

evolution probably was more complex than this simplified scenario, but data are inadequate to document and 

verify greater levels and degrees of complexity.

The Canyon Reach

Streamflow initiated the flood as the contents of 

Price Lakes were expelled into the upper canyon of 

Ophir Creek. During this initial phase, flow was composed mainly of water, and an unknown amount of 

snow and ice, that mobilized a mixture of fine-grained 

sediment and organic sludge that was scoured from 

the beds of Price Lakes. The initial fine-grained, 

suspended-sediment, fluid mixture may have scoured a 

small amount of bedload (fig. 22) from the relatively 

short (about 0.1 mi) channel reach between the two 

lakes (fig. 6). No evidence was discovered that any significant quantity of debris from the flood-triggering 

landslide was incorporated within the streamflow that 

entered the upper canyon of Ophir Creek located

74 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
immediately downstream from Lower Price Lake. The 

rapid expulsion of Price Lakes was likened to a "tidal 

wave" by hang-gliding eyewitness Doug Cook (app. B 

and fig. 2).

Evidence of heavy channel scour in the upper 

canyon of Ophir Creek, immediately downstream from 

Lower Price Lake (figs. 5 and 7), indicates that the initially sediment-lean streamflow quickly began to transform by sediment bulking, thereby rapidly altering the 

relative proportions of water and sediment making up 

the fluid mixture. Hereafter in this text, this abrupt 

leading edge of the floodflow is referred to as the leading flow surge. Hang-gliding eyewitness Doug Cook 

observed the streamflow plowing down vegetation and 

eroding debris in the upper canyon, thereby gaining 

momentum enroute downstream. Floodflow, incompletely pictured by figure 23, is believed to be following near the leading flow surge and appears very 

turbulent. The visual impression imparted by the photograph is that of a fluid charged with sediment that 

may be low in yield strength; however, channelized 

debris flows can be quite turbulent (Pierson and others, 

1990, p. 49).

The leading edge of the approaching floodflow 

was witnessed head on by the Willets (app. B and fig. 

2) at the mouth of the upper canyon. The flow appeared 

to them as a vertically standing wall of brown-colored 

fluid, loaded with debris, which was actively eroding 

the channel bed. The leading flow surge appeared 

intensely turbulent and the fine-grained matrix fluid 

exhibited low yield strength as it splattered the Willets 

with mud from a distance of about 50 ft as they ran 

from it within the intercanyon reach.

The general appearance of the flow in the intercanyon area, as described by the Willets, verifies that 

the fluid had undergone extensive transformation during transit through the upper canyon. The fine-grained 

matrix fluid that splattered the Willets may have been 

hyperconcentrated flow but verification data are 

unavailable. The flow transformed from a sedimentlean fluid as it left Lower Price Lake to a muddy, bouldery, debris-charged flow throughout the steep journey 

of about 0.6 mi (fig. 6). At an average velocity of 28-32 

ft/s, calculated for the 2.88 mi reach from Upper Price 

Lake to Old Highway 395, this fluid transformation 

would have occurred in less than 1.65-1.68 minutes; 

considering the steepness of the upper canyon (slope, 

26 percent, or 14.6°) compared to the average gradient 

(13.8 percent, or 7.9°) between Upper Price Lake and

Old Highway 395, transformation from Newtonian 

flow to debris flow may have occurred in less than 1.5 

minutes.

The leading flow surge, laden with debris, 

actively eroding the channel bed, and incorporating 

large boulders in the flow, are characteristics of debris 

flow. The high fluid density associated with debrisladen flow, as described, can compound the shear stress 

exerted on the streambed and thereby greatly amplify 

its erosive character (Costa, 1984, p. 274). However, 

the tendency to splatter mud indicates that the matrix 

fluid lacked cohesion or yield strength, or both. The 

lack of clay-size particles in all sampled debris deposits 

(table 8) implies that debris cohesion was low during 

most or all phases of the flood. The rheological behavior of the leading surge of floodflow is therefore uncertain at the mouth of the upper canyon but much 

evidence favors a debris-flow classification.

Eyewitness Bridgewater's description (app. B and 

fig. 2) of the leading flow surge, probably sighted in the 

lower canyon, infers a debris-flow nature. He characterizes it as a quickly moving, deep, soupy mud or 

sludge, choked with debris, that severely damaged 

large trees.

The rheological character and fluid-flow dynamics of the flood in the intercanyon reach, as depicted by 

the photograph of figure 24, appear different than those 

shown in figure 23. The flow shown in figure 23 was 

photographed about 10-15 minutes before that of figure 

24. Although still visibly turbulent, mainly at the edges 

of the flow, the fluid shown in figure 24 appears viscous 

and seems to have yield strength because it appears to 

support coarse-size clasts at the flow surface. As pictured, the flow mode is probably that of debris flow. 

The less-turbulent central mass of the flow implies the 

possible formation of a somewhat rigid plug. Photographic evidence shows that the flow stage has fallen 

(high-water marks are above the flow surface) and the 

flood appears to be in the early recessional stage. This 

indirect evidence of possible flow transformation 

(apparent differences in floodflow rheology between 

figures 23 and 24) over time adds further complexity to 

the earlier described scenario of downstream flow 

transformation of the leading peak-flow surge.

Postflood, particle-size data collected from a sediment deposit near the downstream end of the intercanyon reach (samples 1 and 2; tables 8 and 9; figs. 41,43, 

and 47) indicate a probable debris-flow genesis for the 

sediment deposit (Scott, 1988, and Scott and others, 

1995). The deposit is unstratified, coarse clasts are 

randomly distributed and are supported by a fineDESCRIPTIONS, DISCUSSIONS, AND INTERPRETATIONS OF FLOODFLOW DYNAMICS 75
grained matrix (fig. 41), and the sediment matrix is 

poorly sorted (1.92-2.05 (|), table 9). However, the time 

of sediment deposition, with regard to flood stage and 

flow duration, is unknown. The intercanyon reach was 

one of net deposition, possibly during the leading peakflow surge and also probably later during flow recession.

Proximal Segment of the Ophir Creek Fan

At the mouth of the lower canyon, on the proximal segment of the alluvial fan of Ophir Creek (fig. 6), 

the leading flow surge appeared similarly to Tom Reed 

and his companions as it did to the Willets upstream 

(app. B and fig. 2): a vertical-walled mass of boulders, 

timbers, brush, and muddy water churning over itself, 

and through this process generating a loud percussive 

rumble, all debris-flow characteristics. Eyewitness 

descriptions of the abrupt, wave-like character of the 

flood front create the impression that frictional resistance, both internal and external, to the flowing, bouldery mass controlled its motion and created a moving 

dam that maintained forward movement by overtopping and rolling over itself. The fine-grained, matrixfluid component provided both fluidity and lubrication 

to the overall mass that aided downslope movement 

and helped prevent the coarse-grained component from 

locking up and stopping. The pronounced percursive 

rumble indicated strong inertial forces transferring 

downslope momentum through boulder collisions.

Downstream from the canyon mouth, the leading 

flow surge badly damaged the Ogilvy residence and 

destroyed the Reed home, destructive characteristics of 

both streamflow and debris flow (figs. 27, 28, and 52). 

Overbank debris deposits of the leading flow surge, at 

and immediately downstream from the lower canyon 

mouth, were mainly composed of mud-coated boulders 

and trees, some cobbles and gravel, and a relatively thin 

(generally less than an average 1-ft thickness) veneer of 

mud plaster on the landscape (figs. 28 and 52). This 

mud plaster indicates some cohesion within the fluid 

matrix (Pierson, 1985, p. 1066; and Pierson and others, 

1990, p. 43); however, the minimal thickness of the 

plaster attests to the weakness of cohesive forces. 

The presence of overbank deposits of boulders on the 

north-bank terrace, at the Ogilvy and Reed homesites, 

indicates that boulders were present near the top of the 

leading flow surge and not just moving as bedload. 

A lack of fine-grained debris (particle diameters less 

than 64 mm) in the interstices of the boulder berm of 

figure 26 indicates that the fine-grained, matrix-fluid

component of the leading flood surge possessed low 

yield strength and, as a result, continued to flow after 

deposition of the cobbles and boulders. It was this gravity-separated, muddy fluid that engulfed and swept 

Linda Reed across and down the north-bank terrace 

(fig. 29) beyond the limits of boulder deposition (eyewitness accounts of Tom Reed and companions and 

Kathleen Thompson, app. B and fig. 2). Rheology 

(hyperconcentrated or debris flow) of the matrix fluid 

is uncertain.

The leading flow surge continued downstream 

beyond the north-bank terrace area and apparently lost 

height and velocity as it gained width. Boulder impacts 

demolished vegetation in the flowpath and scarred trees 

along the flow margins (fig. 30).

In summary, the leading flow surge, which moved 

at the peak-flow rate, displayed the following flow 

characteristics on the proximal part of the Ophir Creek 

fan, downstream from the lower canyon mouth to just 

upstream of Old Highway 395: (1) Flow was laden with 

boulders and vegetation that seemingly controlled the 

geometric configuration and speed of the flow front; (2) 

the abrupt flow front was as high as 25 to 30 ft, depending on the degree of lateral confinement by channel 

banks; (3) at the canyon mouth, the flow front moved at 

a velocity of about 25 ft/s, and its speed progressively 

decreased downstream as the flowpath widened and 

streambed gradient decreased; (4) the leading peakflow surge was of short duration, probably only a few 

seconds; (5) the bouldery flow front was very destructive to vegetation, most homes, and people in and along 

the channel; (6) overbank flow produced boulder 

berms, boulder splays, and a thin veneer of mud plaster 

on the boulders and land surface; (7) the flow-front 

fluid was of a dual-phase character wherein the coarsegrained fraction tended to separate and deposit as the 

flowpath widened; (8) the fine-grained, muddy, matrixfluid fraction had some cohesion, but low yield 

strength, and continued to flow after movement of the 

coarse-grained fraction ceased; and (9) no discernible 

debris-flow levees or lobes were formed when sediment was deposited by the leading peak-flow surge.

The above listed flow characteristics vary with 

regard to furnishing definitive evidence of Newtonian 

or non-Newtonian flow. The formation of boulder 

berms, selective boulder deposition, and a tendency 

for flow to separate into dual fractions (coarse-grained 

compared to fine-grained matrix fluid) favors a 

Newtonian streamflow classification. However, this is 

inconsistent with normal debris-flow (non-Newtonian) 

characteristics and is less important than the general

76 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
eed home 

foundatidri

:f 3 .- , , ., _1?

Figure 52. Mud-coated north-bank terrace of Ophir Creek just downstream from lower canyon mcuth. Badly damaged 

Ogilvy home in background and foundation of destroyed Reed home at extreme lower right. Boulders covering terrace 

were deposited by May 30 flood. Oblique aerial photograph by Jon O. Nowlin, U.S. Geological Survey, June 3, 1983.

character of the flowing mass of heterogeneous components exiting the canyon mouth. John Burruel's observation of the leading flow surge (app. B)". . . we saw 

a mountain of dust and trees coming out of the ground 

like someone was tearing things up with a big bulldozer" strongly favors a non-Newtonian mode of flow. 

The mixture of mud, boulders, and vegetation moving 

as a vertically appearing fluid front is difficult to relate 

to a surge of streamflow. The movement of large 

boulders (fig. 28) in suspension by streamflow or 

hyperconcentrated streamflow seems impossible, and 

eyewitness descriptions verify that not all boulders 

moved as bedload. However, the above listed characteristics that are inconsistent with debris flow testify to the 

rheologic complexity of the leading flow surge. On the 

basis of available evidence, the leading flow surge is 

classified as a heavily water-saturated debris flow having a fine-grained fluid matrix of low cohesion and low

yield strength. The low cohesion is a function of low 

silt and clay content (less than 6 percent, table 8), but 

principally a function of the minimal clay content.

Medial Segment of the Ophir Creek Fan

Hydraulic transformation of the leading flow 

surge became more pronounced just upstream from 

Old Highway 395 near the battered pine tree of figure 

30 (J, fig. 27). Lateral confinement of the floodflow 

decreased abruptly allowing the flow to spread quickly 

over the progressively widening surface of the Ophir 

Creek alluvial fan. The rapidly expanding flow width 

was accompanied by thinning of the leading edge of the 

leading flow surge. Also, the flowpath progressively 

flattened downstream (fig. 6). These synchronous 

changes along the flowpath triggered responsive 

changes in floodflow dynamics that are described 

and interpreted as follows.

DESCRIPTIONS, DISCUSSIONS, AND INTERPRETATIONS OF FLOODFLOW DYNAMICS 77
Downstream from Old Highway 395, the destructive effects of the flood varied. The Cline home (C, fig. 

27) was structurally destroyed (figs. 33 and 34), but the 

Stafford home (S, fig. 27) remained structurally intact 

(fig. 32). The Turek home was not invaded by debris 

and suffered only minor damage (fig. 35). The partially 

collapsed Cline home was filled with bouldery deposits, whereas the Stafford home was partly filled with 

fine-grained sediment and engulfed by debris deposits 

containing boulders. The remains of the Cline home 

were liberally surrounded by bouldery deposits (figs. 

31, 33, and 34). Boulders also were deposited at the 

surface in the vicinity of the Stafford home but were 

most densely concentrated on the land upstream from 

(west of) the house (figs. 31 and 32).

The structural collapse of the Cline house, caused 

by the leading flow surge (Katy Cline, app. B), could 

have resulted from either streamflow or debris flow; 

another striking example of the destructive capability 

of the leading flow surge was the fate of Tom Reed's 

home upstream. However, the contrasting debris 

engulfment of the Stafford home, without accompanying structural collapse, is symptomatic of debris flow 

(Johnson and Rodine, 1984, p. 257). The contrast 

in damages and dissimilarities in debris deposition 

between the Cline and Stafford homes are in themselves puzzling, but these differences become understandable with the perspective provided by Katy 

Cline's experience.

Katy Cline's survival seems enigmatic as 

described through her recollections (app. B) and by the 

general postflood evidence shown in photographs (figs. 

31, 33, and 34). She was apparently ejected from her 

home in an unconscious state during the leading peakflow surge (Katy Cline, app. B). Her departure route 

was likely downward and outward through floodinduced holes in the east side of the house (fig. 33). Her 

recollection of the rapid filling of the house by water 

(no mention of boulders impacting or entering the 

home), combined with postflood evidence of the nature 

of wall failure (fig. 33), indicates that the walls were 

probably forced outward at the base of the house by 

mounting hydraulic pressure as the house filled with 

fluid. The east-wall failure inadvertently provided the 

exit pathway. Her survival immediately after her ejection is especially puzzling because evidence in postflood photographs (figs. 31, 33, and 34) implies that 

she travelled through a moving bouldery field of debris 

that should have crushed her. Equally puzzling is her 

earlier survival of assumed boulder movement within 

the home; the home wreckage was filled with bouldery

sediment (Howard C. Cline, husband of Katy, oral 

commun., 1996). Key evidence regarding her survival 

was first noted by study of the photograph of figure 34.

The heavily damaged Cline home, largely surrounded by boulders, is clearly depicted in the photograph of figure 34; the photograph also shows a 

partially overturned bus about 75 to 100 yds downstream from the house (fig. 31). The bus was parked 

beside the house prior to the flood (Howard C. Cline, 

oral commun., 1996), and was moved by floodflow to 

its postflood position beyond the downstream edge of 

the boulder field as shown in figures 31 and 34. The bus 

was muddied, but otherwise undamaged, during transit 

(Howard C. Cline, oral commun., 1996). The lack of 

damage to the bus body, and at least one other similarly 

transported Cline vehicle, indicates convincingly that 

vehicle transport occurred before the boulders arrived. 

Several vehicles were similarly transported from the 

Stafford yard, some moved all the way to the U.S. 

Highway 395 freeway; these vehicles also did not 

exhibit obvious body damage, according to our recollection and study of postflood photographs.

Katy Cline's ejection and departure from the 

proximity of her home is believed to have been generally coincident with vehicular movement—shortly 

before the arrival of boulders. The vehicular evidence 

and Katy Cline's survival indicate that the forward edge 

of the leading flow surge was dominantly a muddy 

fluid virtually devoid of boulders.

The above cited evidence verifies that a leading 

surge of mud and water struck both the Cline and 

Stafford homes. This leading flow surge was quickly 

followed by boulder- and tree-laden debris. The leading 

flow surge, which moved at the peak-flow rate, incorporated a mixture of boulders, trees, and mud, where it 

exited the lower canyon mouth; it transformed hydraulically as it moved down the Ophir Creek fan from the 

site of the damaged Jeffrey Pine tree (fig. 30) to the 

Cline and Stafford homes (fig. 31). The vertical-walled 

mixture of boulders, timber, and mud, viewed by many 

witnesses just downstream from the mouth of the lower 

canyon, separated into two distinct fluid phases on the 

medial reach of the Ophir Creek fan—(1) a leading 

flow surge that was either muddy streamflow, hyperconcentrated flow, or fine-grained debris flow, followed rapidly by (2) a less watery surge of boulder- and 

tree-laden debris.

A hypothesis of the hydraulic processes that 

are responsible for the transformation of the leading 

flow surge into a dual-phase surge is that as the supersaturated mixture of boulders, trees, and mud began

78 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
spreading laterally and decreasing in flow thickness 

just upstream from Old Highway 395, the rapidly widening flowpath quickly increased the area of surface 

resistance between the base of the flow and the land 

surface. This increasing streambed area caused a rapid 

increase in frictional drag along the base of the bouldery flow that, coupled with the downstream decrease 

in flowpath gradient, resulted in a general deceleration 

of the boulder-laden mass. The flow-front thinning is 

hypothesized to have promoted expulsion of the highly 

fluid matrix flow. The lack of cohesion within the finegrained component of the debris flow aided the expulsion of the matrix fluid as a product of dissipation of 

internal pore pressure. The abundant water content of 

the leading flow surge that caused it to flow as a heavily 

saturated debris flow just upstream, allowed part of the 

mud-laden, matrix fluid to progressively separate and 

outrun the more rapidly decelerating bouldery debris, 

as seemingly also happened, as evidenced by Linda 

Reed's experience, on the upstream north terrace at 

Tom Reed's place (figs. 27 and 29).

The main thrust of the leading, mud-laden, flow 

surge (muddy streamflow, hyperconcentrated flow, or 

fine-grained slurry flow) was directed down the axis of 

the Ophir Creek fan and directly impacted the Cline 

home along this route with a force sufficient to initiate 

structural collapse of the house and eject Katy Cline. 

The Stafford home, located southeastward from the 

axial-fan route (figs. 27 and 31), probably did not 

receive as forceful a surge of the turbid fluid as the 

Cline home, and thereby escaped fatal structural damage. The mud-laden flow front had sufficient energy to 

raft numerous vehicles away from the approaching 

boulders.

The separation, or bleeding away, of the muddy 

matrix fluid within the leading flow surge undoubtedly 

decreased fluidity (increased viscosity) of the trailing 

bouldery debris. Separation of the watery matrix fluid 

increased the overall sediment concentration of the 

trailing mass and probably caused the bouldery debris 

to transform to a more coherent debris flow. Such a 

fluid transformation might explain inundation of the 

Stafford home by bouldery debris rather than a more 

destructive impact. The Cline house was already structurally incompetent by the time the bouldery debris 

flow arrived and was thus infused easily by the following boulder-laden debris. Hydraulic transformation of 

the bouldery mass to more coherent debris flow also 

explains the stratigraphic and particle-size characteristics of sediment deposits just downstream from Old 

Highway 395 (fig. 44 and samples 3 and 4 of fig. 47 and 

tables 8 and 9).

Flood deposits sampled for particle-size distribution in both the upstream intercanyon reach (figs. 41 

and 43) and in the medial fan area (figs. 43 and 44) display the following characteristics of debris-flow deposition: (1) lack of stratification, (2) matrix-supported 

coarse clasts, (3) concentration of coarse clasts at surfaces of deposits, implying inverse grading, and (4) 

large sorting coefficients (evidence of poor sorting) of 

table 9 (Scott, 1988, p. A57-A64, and Scott and others, 

1995). The minimal amount of clay in the sampled 

debris-flow deposits (table 8) characterizes the depositing fluids generally as noncohesive debris flows 

(Scott and others, 1995, table 5). Times of deposition of 

these sediments relative to the leading peak-flow surge 

are uncertain.

Deposition of the sediments in the intercanyon 

reach (particle samples 1 and 2) probably followed the 

leading flow surge during an early phase of flood recession. This is based on features shown in figure 24 that 

indicate a debris-flow phase of the flood that followed 

the leading peak-flow surge for a period of at least 15 

minutes, and probably longer. In contrast, much debrisflow deposition on the medial fan area (particle-size 

samples 3 and 4) was a product of the hydraulically 

transformed, peak-flow surge where debris-flow deposition closely (probably within seconds) trailed the 

freshly separated, fine-grained, matrix flow.

Major (1996), during study of a number of flumegenerated, experimental debris flows, noted that the 

processes of deposition were strongly influenced by the 

water content of the flows. Water content of the leading 

flow surge of the Ophir Creek flood was great enough 

to maintain some characteristics of streamflow until the 

spreading flow transformed the bouldery fraction to a 

more typical debris flow. However, the subsequent 

bouldery debris-flow phase was probably highly saturated. The high degree of saturation explains the very 

weakly lobate margins, low-relief surface morphology, 

and the generally variable margin of the downstream 

limit of boulder deposition (fig. 31) on the medial segment of the fan, according to comparisons with the 

results of Major's (1996) experiments.

The prolonged flow of debris over the medial segment of the alluvial fan, following the leading flow 

surge as described by eyewitnesses (Vie Stafford and 

Susan Graves, app. B and fig. 2), may have occurred as 

saturated debris flow (similar to that shown in fig. 24 in 

the upstream intercanyon reach). If so, debris deposition probably occurred on the medial fan segment as a 

series of overlapping layers of debris that would probably be stratigraphically indistinguishable when 

exposed (fig. 44 and Major, 1996). Continued surges of

DESCRIPTIONS, DISCUSSIONS, AND INTERPRETATIONS OF FLOODFLOW DYNAMICS 79
saturated debris flow, accumulating irregularly atop 

earlier deposits on the medial fan area, may account for 

the clusters and streaks of coarse clasts at the surface, 

as shown in figure 31.

About 0.2 mi downstream from Old Highway 

395, boulder movement stopped. This downstream 

limit of boulder movement generally defines the downstream limit of the medial segment of the Ophir Creek 

fan (figs. 6 and 31).

Distal Segment of the Ophir Creek Fan

The fine-grained, matrix fluid of the leading flow 

surge exhibited characteristics of both hyperconcentrated flow and debris flow after it flowed beyond the 

limits of boulder deposition. Hyperconcentrated-flow 

characteristics include: (1) separation of the matrix 

fluid from the coarse-grained bouldery fraction, (2) the 

absence of detectable yield strength in the matrix fluid,

(3) Katy Cline's description (app. B) of the fluid that 

transported her toward the freeway more closely 

approximates water than a mud-dominated fluid, and

(4) statistical characteristics of particle size samples 5 

and 6 (fig. 43 and tables 8 and 9); sorting coefficients 

(sample 5, 2.3 (()) decrease downstream (sample 6, 1.4 

(()). Mean and median particle sizes of sample 5 (both 

2.3 mm) are greater than those of downstream sample 

6 (0.47 mm and 0.45 mm, respectively). These downstream trends in particle-size statistics indicate sorting 

and selective deposition in a downstream direction, 

characteristics of streamflow rather than debris flow. 

Characteristics of the fine-grained matrix fluid 

that favor classification as debris flow are: (1) eyewitness Kenneth Julian (location, fig. 27) saw "a wall of 

very muddy water flowing quickly . . . toward the 

freeway;" he observed a flow front 4 to 5 ft high

... of a consistency resembling freshly mixed concrete (implying viscosity and yield strength greater 

than muddy water); (2) eyewitness Reed Dopf photographed the leading edge of the flow front near its 

terminus (fig. 39); as pictured, the fluid exhibits the 

characteristics of high yield strength and high viscosity 

(vertical flow front at low-flow velocity); and (3) sorting coefficients for samples 5 (2.3 (()) and 6 (1.4 (()) are 

in ranges (2.2 to 2.4 for debris flow, and 1.2 to 1.5 for 

hyperconcentrated flow) greater than those (0.7 to 0.9) 

characteristic of streamflow (Scott, 1988, p. A63).

The seeming contradiction in rheologic classification of flow downstream from the limit of boulder 

deposition may be the result of several factors. As 

described above, fluid dynamics varied both geographically and over time during the duration of flooding.

Particle-size data were collected long after flooding 

(app. C). The apparent conflict between statistics of 

particle-size samples and eyewitness accounts and photographs of flow on the distal part of the Ophir Creek 

fan may be the result of too few samples and sampling 

too near the surface of the deposits. Samples 5 and 6 

were collected near the land surface (figs. 45 and 46) 

and, therefore, may represent flow during the flood 

recession, when flow dynamics may have differed from 

those of the initial flow surge. Also, proportions of 

water and sediment may have varied enroute as the 

fluid transporting fine-grained sediment flowed across 

the dry surface of the distal part of the alluvial fan. 

Regardless, the paucity of particle-size data, both 

areally and vertically within the fine-grained deposits, 

precludes a resolution of the apparent uncertainties of 

flow dynamics on the distal reaches of the Ophir Creek 

fan.

Variation in the Water-Sediment Mixture Over 

Time

The duration of intense sediment transport is 

uncertain even though the onset is clearly documented 

by the timing of the arrival of the sediment-laden, leading, peak-flow surge. Oblique aerial photographs 

(fig. 53) taken by Mrs. E.H. Thorn (app. B) show moderately turbulent, viscous, sediment-laden fluid with an 

overall appearance similar to pancake batter moving 

through the lower canyon and over the alluvial fan 

sometime between 12:15 and 1:00 p.m. (the leading 

flow surge arrived at Old Highway 395 at 12:02). By 

general appearances, described above, the fluid could 

be debris flow; if not, it was probably hyperconcentrated flow. Photographic resolution is inadequate to 

precisely verify the flow mode with confidence. The 

areally extensive sediment deposits on the Ophir Creek 

alluvial fan were largely emplaced before the times of 

these-photographs. Therefore, sediment deposition at 

the time of Mrs. Thorn's photographs presumably was 

mainly thickening the deposits. Sediment deposits in 

the photographs do not appear to have risen to a level 

of encroachment on the southbound (westward) lanes 

of the freeway, as ultimately occurred; southbound 

highway traffic appears to be moving freely, and at 

least half a dozen vehicles are parked on the west road 

shoulder. The leading flow front had likely reached and 

passed the site where the vertically standing flow front 

was photographed by Reed Dopf (fig. 39).

Mrs. Thorn's photographs of the lower canyon 

and the proximal and medial parts of the alluvial fan 

clearly show that the flood is in recession and that flow

80 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
DESCRIPTIONS, DISCUSSIONS, AND INTERPRETATIONS OF FLOODFLOW DYNAMICS 81
stage may have fallen 10 ft, or more, from the peak; 

eyewitness Tom Reed noted a fall of that magnitude 

within seconds after peak flow. Thorn's photographs 

show flow confined to the main channel upstream from 

Old Highway 395, but broadly spread across the medial 

fan reach extending from just upstream of Old Highway 395 to the limits of boulder deposition, downstream from the Turek, Cline, and Stafford homesites 

(fig. 27). Near the limit of boulder deposition, heaviest 

flow appears to be moving predominantly southeastward. Even though sediment deposits were broadly 

emplaced before Thorn's photographs were taken, 

heavy sediment transport by the flood is still evident in 

the photos. Evidence disclosed by these photographs 

confirms Vie Stafford's observations of flood severity 

for at least 45 minutes after the onset of flooding. 

Mrs. Thorn's photographs verify that most sediment 

deposition occurred during the first hour of flooding 

and that heavy sediment transport continued for at least 

that length of time.

Numerous additional photographs (not shown in 

this report), both from the land and the air, were taken 

by observers several hours after the onset of flooding. 

Photographs taken sometime between 2:30 and 4:00 

p.m. depict floodflows of differing character than that 

photographed earlier (12:15-1:00 p.m.) by Mrs. Thorn. 

Differences from Thorn's photos, most evident in the 

vicinity of Old Highway 395, were as follows. Flow 

rate had receded markedly and no longer inundated 

most of the flood deposits that buried Old Highway 

395. Instead, numerous braided distributary channels 

laced the sediment deposits, and erosion of the depositional surface appeared to be the dominantly active 

hydraulic process (fig. 48). Many of the numerous 

boulders armoring the depositional surface protruded 

up to several feet above the flow that was occurring in 

the distributary channels, and many boulders had dried 

after their mudcaked surfaces were exposed to the 

atmosphere. This drying process must have taken at 

least an hour, implying that the widespread and heavy 

debris-laden flow photographed by Mrs. Thorn was relatively short lived.

The 2:30-4:00 p.m. photographs show a highly 

turbid fluid that may have been moving as hyperconcentrated flow but was probably streamflow. These 

photos confirm Vie Stafford's observations (app. B) 

that after about 3 hours, floodflow had noticeably 

receded, the sediment load had decreased, and recessional flow began to entrench the debris deposits to 

form a dominant, eastward-flowing channel between 

the Cline and Turek homes. Otto Moosburner, (U.S. 

Geological Survey, oral commun., 1996), observed

flooding near and upstream of Old Highway 395 about 

3:00 p.m. The flow was turbid and gray colored, 

because of entrained sand, but was definitely streamflow (Newtonian flow).

Oblique aerial photographs taken by the U.S. Forest Service during the morning of May 31,1983, show 

Ophir Creek flow on the alluvial fan to be largely integrated into a single channel, as described by Stafford, 

and flowing east-northeastward just south of the Turek 

home (see figs. 3B and 31 for channel position and 

alignment). The flow shown in the Forest Service photos is obviously streamflow but appears turbid.

Summary

Floodflow began as a rapid surge of relatively 

dilute streamflow as a result of the rapid expulsion of 

Price Lakes. The dilute flow quickly transformed to 

sediment-laden streamflow through the process of erosive bulking of channel debris in the upper canyon of 

Ophir Creek. The initial, leading flow surge appeared 

as a vertically standing, churning wall of muddy fluid 

laden with boulders and uprooted vegetation as it exited 

the upper canyon mouth. The leading flow surge was 

moving at the peak-flow rate. The mixture of mud, 

boulders, and vegetation and the erosive nature of the 

flow front, as witnessed, favor classification of the 

leading flow surge as debris flow. However, the apparent lack of yield strength of the muddy, matrix-fluid 

component indicates that the overall fluid mass was 

supersaturated and may have been close to hyperconcentrated flow.

The leading flow surge probably retained its 

ambivalent rheologic character during transit of the 

intercanyon reach as it deposited some of its sediment 

load. However, it was followed by a prolonged and 

more certain debris-flow episode that also deposited 

sediment in the intercanyon reach.

The leading flow surge aggressively eroded the 

lower canyon and exited that reach as a debris-flow 

surge loaded with boulders and vegetal debris. It was 

very destructive to homes and people as it spread over 

the north-bank terrace of the proximal segment of the 

Ophir Creek fan. Flow deposits in this reach were 

largely mud-coated boulders and trees; flow spreading 

was distinguished by a propensity for the flow surge to 

separate into a mud-laden matrix fluid that continued to 

flow after the coarse-grained bouldery debris stopped. 

The lack of yield strength by the muddy, matrix-fluid 

component indicates that, overall, the leading flow 

surge Theologically resembled hyperconcentrated flow.

82 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
However, the eyewtiness descriptions that the surge 

was laden with boulders throughout its depth confirms 

a debris-flow classification.

The leading flow surge transformed quickly 

downstream from the north-bank terrace as it moved 

down the medial segment of the Ophir Creek fan. It 

quickly spread laterally, thinned, and began to separate 

into a watery, but muddy, leading edge. The leading 

flow front, of uncertain rheological character, was 

quickly followed by a bouldery debris flow that further 

evolved as the decelerating coarse-grained component 

was progressively dewatered by the faster moving, 

escaping, fine-grained component of flow. The finegrained matrix fluid destroyed a home, swept away its 

occupant, and mobilized vehicles near several homes 

enroute downstream toward the U.S. Highway 395 

freeway. The closely following, bouldery, debris-flow 

phase deposited on the medial fan segment and inundated homes in its path. Debris flow seemingly continued for a half to three-quarters of an hour, possibly as 

multiple flow surges, and added to the debris deposits 

on the medial fan segment. The highly saturated, 

poorly cohesive debris flow, or flows, left a depositional surface of generally low relief, no debris-flow 

levees, and weakly lobate margins.

The leading fine-grained-fluid matrix flowed in a 

progressively decelerating manner over the distal segment of the Ophir Creek fan. Its precise hydraulic mode 

is uncertain but it seems to have transformed, possibly 

through selective deposition of coarser-grained sediment, from a muddy, watery, hyperconcentrated flow to 

a vegetally clogged, fine-grained debris flow during 

transit across the distal fan segment.

Sometime during the first hour after the initial 

flood surge, floodflow on the Ophir Creek alluvial fan 

progressively transformed from debris flow into hyperconcentrated flow, then into turbid streamflow, as flow 

rates progressively decreased. Within 4 hours following the peak-flow surge, the continually receding 

streamflow was actively eroding the bouldery surface 

of the medial fan segment, as a new channel system for 

the creek developed. Floodflow continued for several 

days, and sediment loads and associated turbidity progressively decreased as channel-cleaning processes 

diminished and the new creek channel evolved.

FLOOD DAMAGE

Damage caused by the May 30, 1983, flood was 

extensive, varied, and complex. Results of a limited and 

conservative assessment indicates that damage was

about $2 million (table 13). However, the limited nature 

of the assessment indicates that comprehensive damage 

probably exceeded $2 million. The assessment 

addresses damage to homes and associated real-estate 

improvements, public utilities, highways, and irrigation works.

The assessment did not include several intangible 

components: human life and suffering are inadequately 

measured in terms of monetary value. Likewise, the 

costs of stream-channel and riparian damage, aesthetic 

and environmental degradation, and landscape alterations are difficult to evaluate monetarily. Public services that include police, search and rescue, onsite 

medical assistance and associated volunteer help, also 

are difficult to evaluate. Livestock losses (pets, chickens, and horses) were not assessed economically, nor 

were the costs of legal and other miscellaneous services.

Although incomplete, in terms of total damage 

assessment, this limited and conservative accounting 

(table 13) provides some economic perspective on this 

flood for comparison with other floods.

THE 1983 FLOOD—A TEST OF FLOODHAZARDS PREDICTION

Flooding and related fluvial-debris hazards were 

predicted for Ophir Creek as part of a hydrologic-hazards investigation made during 1973 and 1974 (Glancy 

and Katzer, 1977; Tabor and others, 1983, p. 37-40). 

The estimated magnitude of the " 100-year flood" for 

Ophir Creek at the head of its alluvial fan was 2,000 

ft /s, on the basis of the 1973-74 study. Hazards predictions for Ophir Creek were based on the expectation 

that flooding would occur as direct runoff of rainfall or 

snowmelt, or both; they did not take into account the 

unusual circumstance of landsliding and resultant 

expulsion of the contents of Price Lakes. The flood 

of July 6, 1890, which could be used to analyze the 

effects of flooding, was caused partly by the rapid emptying of Upper Price Lake. But that was not included in 

the analysis by Glancy and Katzer because streamflow 

data for that flood and the storage capacity and the rate 

of emptying of Upper Price Lake in 1890 are unknown. 

The 1983 flood provides an opportunity to compare 

actual impacts from a large-magnitude flood with 

predicted results. This opportunity is unusual because 

predictions of the hazards posed by debris transport are 

uncommon. Both the flood-hazard predictions and 

actual results of the 1983 flood are portrayed in 

figure 54.

FLOOD DAMAGE 83
Table 13. Damage caused by the May 30,1983, Ophir Creek flood, Washoe County, Nevada

Property damage

Damage assessment

(in 1983-84 dollars,

rounded)

Source of information

Upper Price Lake dam and irrigation works $ 100,000

Old Highway 395 480,000

Telephone lines and equipment 50,000

Power lines and equipment 50,000

Private real property and attached structures 1 1,105,000

M.B. Twyeffbrt, U.S. Soil and Conservation Service, and James 

Lathrop, Franktown Irrigation Company

RE. "Joe" Crowdis, Nevada Department of Transportation

Dennis Woll, Nevada Bell Corporation

F.R. Masayko, Sierra Pacific Power Company

D.A. DeCrona, Washoe County Division of Emergency 

Management

TOTAL (rounded) $1,800,000

Estimated. All other values listed represent actual costs incurred in replacing or repairing the property.

Comparisons of the predicted flood hazards and 

the actual flood impacts disclose the following: (1) The 

1983 flood was exceptionally large; its estimated magnitude was about 25 times greater than that predicted 

for a 100-year flood; (2) the north-bank stream terrace, 

where the Ogilvy and Reed homes were located, was 

considered safe for the predicted flow rate of the 100- 

year flood, but was extremely vulnerable during the 

1983 flood; (3) predicted fluvial-debris hazards are 

similar to those that occurred during the 1983 flood, but 

the areas subject to the more intensive 1983 hazards are 

expanded northward. A flood equal to the 100-year 

flood (2,000 ft3/s) was expected to follow the general 

route of the man-diverted channel; however, the bigger 

1983 flood (about 50,000 ft3/s) largely bypassed the 

manmade channel and followed a more natural route 

down the axis of the alluvial fan; (4) the route taken by 

the 1983 flood subjected the Stafford, Cline, and Turek 

homes to hazards not predicted for a 100-year flood; 

(5) the severity of the 1983 flood caused streamflow 

and associated debris to impact a much greater area 

than that predicted for a 100-year flood, including 

debris deposition down to, on top of, along, and past the 

U.S. 395 freeway; and (6) the unusual size and force of 

the 1983 flood redefined the flood-plain boundaries of 

Ophir Creek for practical planning purposes. Although 

boulders were not incorporated within the zone classified as one of moderate hazard (fig. 54B) by the 1983 

flood, the transport of fine-grained sediment (pebbles 

and finer grained material) was so intensive that most 

of it was classified as a moderate, rather than a low hazard. This classification is somewhat in disagreement 

with preflood predictions by Glancy and Katzer (1977), 

but no more so than the difference between the magnitudes of predicted and actual flooding.

Although the 1983 flood exceeded the magnitude 

of floods historically throughout the region for precipitation-generated floods (fig. 38), the unusual character 

of the canyons of Ophir Creek could promote severe 

floods without triggering by bedrock landslides. Massive land-slope failures resulting from severe precipitation, or effects of the precipitation, could dam the creek 

in the future. Such an impoundment could result in 

flow overtopping the naturally formed dam, thereby 

causing rapid release of the impounded water and 

flooding that could equal, or exceed, that of the 1983 

flood.

Flood- and associated debris-hazard predictions 

within most small drainages of the arid southwest are 

inherently uncertain because the streamflow data base 

generally is inadequate for accurate flood predictions. 

Also, geohydrologic processes of flooding in the arid 

environment are incompletely understood.

AFTER THE FLOOD

The 1983 flood caused major landscape changes 

along Ophir Creek. These changes are particularly 

noticeable on the alluvial fan because this area is most 

visible from the old and new highways. The most obvious change was the extensive barren area caused by 

sediment deposits on the Ophir Creek fan. An early 

aerial view of the extent of these deposits is shown in 

the frontispiece. The surficial character of these deposits since has been gradually healing through natural 

revegetation. Healing rates were documented to provide calibration data for future paleoflood, debris-flow 

studies in the region. Flood and postflood changes are 

documented by a time-lapse sequence of upstream 

views of the Ophir Creek alluvial fan photographed 

from the freeway before and after the flood (fig. 55).

84 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
, r

Bowers Mansion 

County Park

- f

I

n : 

} I 7- Washoe 

Lake

EXPLANATION

Degree of debris hazard—

Boundaries are approximate

• High—Abundant debris 

movement, including 

numerous boulders

I Moderate—Abundant debris 

movement, including few 

boulders

Low—Light to moderate 

debris movement of 

fine-grained sediment

Location of flood-peak 

discharge (A) prediction 

and (B) estimated actual

1/2 MILE

0 1/2 KILOMETER

Contour interval, 200 feet 

Datum is sea level.

Bowers Mansion 

County Park

Base from U.S. Geological Survey, 1:24,000 quadrangles: 

Mt. Rose, Nev., 1968 and Washoe City, Nev., 1974

Figure 54. Fluvial-debris hazards on the Ophir Creek alluvial fan, western Nevada: A, As predicted by Glancy and 

Katzer (1977); flood peak, 2,000 ft3/s. B, As realized during the May 30, 1983, flood; estimated flood peak, 50,000 

ft3/s. Abbreviation: ft3/s, cubic feet per second.

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86 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
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AFTER THE FLOOD 87
Pasture land dominated the preflood view in 1973 as 

shown in figure 55A. The unvegetated sterile deposits 

left by the 1983 flood are shown in figure 55B. Later 

postflood photographs show that natural revegetation 

started slowly but accelerated after 1986. The first 

notable signs of revegetation were mainly annual 

weeds with sparse sprouts of native grass in late summer of 1986 (fig. 55C). Perennial rabbitbrush and 

native grasses mixed with weeds were visible by late 

summer of 1988 (fig. 55D), and these species had 

thickened noticeably by 1990 (fig. 55E). A dense cover 

of rabbitbrush was well established by the spring of 

1992 (fig. 55F). Ten years after the flood, nonirrigated 

rabbitbrush dominates the area that was irrigated pasture land before the flood (fig. 55G).

As of 1996, the Reed home was not rebuilt, but 

the Ogilvy home has been restored and renovated. 

Minor debris damage to the Thompson's property was 

corrected, and irrigation diversions at the mouth of the 

lower canyon were repaired and re-established. Several 

new homes have been built downstream from the lower 

canyon mouth onpre-1983 landslide deposits, adjacent 

to both sides of the creek but outside of the 1983 flood 

zone, in the general vicinity of the Ogilvy and Reed 

properties. The Stafford home was torn down. A new 

home was built south of Staffords. Some of the boulder-laden deposits upstream and downstream from Old 

Highway 395 have been commercially marketed (fig. 

56). Another home has replaced the one destroyed by 

the flood on the Cline property, and residents of the 

Stafford, Cline, and Turek properties have regraded 

their buried access roads. Old Highway 395 was 

exhumed and rebuilt where it was buried by debris. The 

channel of Ophir Creek was rediverted to the preflood 

route preferred by irrigators.

The destabilized canyons of Ophir Creek are geomorphically readjusting as natural processes move 

debris down and along the slopes. The channel reach 

between the canyons is slowly revegetating. A new 

dam was built at the outlet of Upper Price Lake to allow 

continued diversions of irrigation water southward to 

nearby Little Valley (south of Ophir Creek Basin; fig. 

1), to accommodate long-vested Nevada water rights. 

The new impoundment behind the dam of Upper Price 

Lake holds only a few acre-feet of water, thereby reducing—but not eliminating—the potential flooding risks 

caused by any future rapid release of the contents of the 

lake.

Ophir Creek did not have the serious flooding that 

many other small drainages did during the heavy winter 

rain of mid-February 1986. Much of its drainage area is 

at a high altitude and received snow rather than rain 

during that storm. The creek subsequently flooded during heavy snowmelt runoff in late May to early June of 

1986. The snowmelt runoff was accelerated, at least 

once, by a thunderstorm during late spring of 1986. The 

resultant flood was energetic enough to plug the Old 

Highway 395 drainage culvert with sediment, which 

caused the sediment-laden flow to overtop and blanket 

the road. Indirect measurements of the peak discharge 

of that runoff were made on July 20, 1986, about 0.1 to 

0.25 mi upstream from Old Highway 395. The measurements indicated a peak flow during the night of 

May 31-June 1, 1986, of about 600 ft3/s.

SUMMARY AND CONCLUSIONS

The May 30,1983, flood of Ophir Creek was sudden, large, and severe. It was unusual because it 

occurred near noon on a clear, hot day that was both 

locally and regionally devoid of storm activity. The 

winter just concluded had been the second consecutive 

wet winter and had produced a near-record snowpack, 

but recent weather was unseasonably hot. The inviting 

weather during a holiday weekend attracted many outdoor recreationists to the eastern slopes of the Sierra 

Nevada. Some of these people became unwitting participants in the flood and others were astonished, and 

valuable, eyewitnesses.

Flooding was triggered by an unexpected landslide high on the southeast-facing slopes of appropriately named Slide Mountain, located between Reno 

and Carson City, Nevada. This landslide was the most 

recent and probably one of the smallest, of about a 

dozen or more, landslides from the same mountain face 

during late-Quaternary time (the last 100,000 years, or 

so). The slide probably resulted from the combined 

influences of gravitational force, favorable geostructural orientations of joint-and-fracture surfaces within 

the granodioritic mountain bedrock, and sudden and 

transient hydraulic imbalances caused by ground-water 

movement through the bedrock mass. The triggering 

mechanism was probably the aberrant hydraulic pressures generated during the brief antecedent period of 

intensive melting and subsequent infiltration of the 

heavy snowpack.

88 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Figure 56. Debris deposited on Stafford property by 1983 Ophir Creek flood, western Nevada. Deposits are 

being excavated and size sorted for commercial use, June 23, 1992. Photograph by Patrick A. Glancy.

The landslide was rapid and consisted of a composite of three nearly simultaneous interrelated mass 

movements: rock slumping, a rockfall avalanche, and a 

debris avalanche. The cumulative slide mass encompassed about 1,400,000 yd3 of bedrock and associated 

products of bedrock weathering. The toe of the slide 

plummeted into the northwestern part of Upper Price 

Lake, a small pond that sat within and adjacent to the 

channel of Ophir Creek, high on the southeastern flank 

of Slide Mountain. Momentum of the sudden incursion 

of rock debris into the lake caused the rapid expulsion 

of the lake contents down the Ophir Creek channel. The 

contents were mostly water, with some entrained snow 

and ice and fine-grained, organic lake-bottom sediments that discolored the water but were present in 

small enough concentrations that they did not greatly 

modify the Newtonian hydraulic character of the fluid. 

The expelled contents of Upper Price Lake was about 

20 acre-ft; an additional couple of acre-feet of mostly 

water were swept up by the flow surge a few hundred 

yards downstream as the smaller Lower Price Lake 

was, in turn, forcibly emptied.

The combined contents of Upper and Lower Price 

Lakes abruptly cascaded into the steep (average gradient, 26 percent, or 14.6°) upper canyon of Ophir Creek. 

The peak-flow rate entering the canyon was at least 

6,000 ft3/s, but more likely in the range of 13,000 to 

20,000 ft3/s, based on eyewitness observations of the 

chaotic expulsion of Upper Price Lake.

The fluid surge of low sediment content was erosively energetic as it cascaded into the upper canyon of 

Ophir Creek. It raced 0.6 mi through the deeply 

entrenched, steep canyon. Enroute, it gouged, bulked, 

and incorporated the easily erodible channel materials, 

and thereby progressively compounded in volume, 

mass, and momentum during downstream transit. 

Debris abraded from the channel boundaries included 

almost all of the riparian vegetation and large quantities 

of unconsolidated landslide debris of widely ranging 

particle sizes of late Quaternary age; it also incorporated snow and additional water as it overran normal 

streamflow and gouged saturated underlying channel 

deposits. The hydraulic character of the leading flow 

surge transformed dramatically during the 0.6-mi

SUMMARY AND CONCLUSIONS 89
transit of the upper canyon from that of a dilutely concentrated Newtonian fluid to a possible debris flow. 

Flow velocities in the upper canyon are unknown; however, because of the pronounced channel steepness, 

they probably equalled or exceeded the estimated average velocity of the leading flow surge throughout the 

2.9-mi reach between Price Lakes and Old Highway 

395 described below.

Floodflow transformed from a dominantly erosive mode within the upper canyon to one of mixed erosive and depositional mode through the wider (200 ft 

wide) and flatter (gradient, 12 percent, or 6.8°) intercanyon reach, also of 0.6 mi-length, just downstream 

from the upper canyon. Net debris deposition within 

this reach was about 50 acre-ft. A photograph of flow 

in this reach depicts the early recessional flow as probably that of a debris flow.

Downstream from the 0.6-mi long, net depositional reach, the leading flood surge entered the lower 

canyon of Ophir Creek and again became dominantly 

erosive. The erosive surge incorporated much lithic 

debris of mixed sizes and most of the trees and brush 

that mantled the flood plain throughout the 1.06-mi 

long lower canyon. Channel characteristics of the lower 

canyon are similar in lithic composition and erosive 

susceptibility to those of the upper canyon, but the 

average channel gradient of the lower canyon is much 

less steep (average gradient, about 12 percent, or 6.8°). 

Average flow velocity through this canyon reach is 

undocumented, but probably is somewhat less than that 

in the much steeper upper canyon.

The peak discharge of the leading flow surge had 

grown to about 50,000 ft3/s, and average flow velocity 

was about 25 ft/s about 0.1 mi upstream from the lower 

canyon mouth. There, average channel slope was measured at about 8 percent, or 4.6° (eq. 6), and the flood 

surge was probably at its peak magnitude and was composed of an incongruous mixture of vegetal matter, 

boulders (some over 6 ft in diameter), cobbles, sand, 

and fine-grained sediment that maintained fluidity 

because of an abundant water content.

The leading flow surge spilled out of the lower 

canyon mouth overtopping a north-bank channel terrace about 10 to 15 ft higher than the normal streambed. 

The hydraulic character of the leading flow surge at this 

stage of its journey was that of a highly mobile, abundantly wet debris flow of low cohesion. As a result of 

the lack of cohesion (minimal clay content) and abundance of entrained water, decreasing flow velocities 

caused by a widening flowpath and a decreasing channel gradient enabled a fine-grained matrix fluid to 

begin to separate and flow beyond the coarse-grained 

debris flow and its subsequent bouldery deposits.

The leading flow surge struck two houses occupying the north-bank terrace about 0.2 mi downstream 

from the lower canyon mouth. One home was badly 

damaged, but the occupants escaped unhurt; the other 

home was totally destroyed and one of its five occupants was killed as he raced for safety. Three other 

occupants were injured, two seriously, and only one 

escaped unscathed. The leading flow surge, at the 

homesites, reached 20 to 30 ft above the normal channel bottom and was about 200 ft wide; normal channel 

gradient is about 8 percent, or 4.6°. The flow surge, 

coincidentally moving at peak discharge rate, receded 

from the terrace almost instantaneously and left a carnage of battered dwellings among a dense field of large 

boulders, some as large as 6 ft in diameter, that it deposited on the narrow streamside terrace.

The leading flow surge transformed quickly 

downstream from the north-bank terrace as it moved 

down the medial segment of the Ophir Creek fan. It 

quickly spread laterally, thinned, and began to separate 

into a watery, but muddy, leading edge. This leading 

edge, of uncertain rheological character, was quickly 

followed by a bouldery debris flow that further evolved 

as the decelerating coarse-grained component was progressively dewatered by the faster moving, escaping, 

fine-grained component of flow.

The Theologically compound, leading flood surge 

largely bypassed a manmade channel diversion just 

downstream from the house-bearing terrace; it instead 

flowed straightforwardly along the axis of the Ophir 

Creek alluvial fan toward Old Highway 395 and other 

downgradient homes. Lateral channel confinement 

ends near the site of the manmade diversion; the diminished confinement allowed the debris-laden flow to 

spread laterally, and the height of the peak surge rapidly decreased. The spreading and thinning of the leading flow surge increased frictional drag on the boulderladen fluid, thereby decelerating flow velocity, and the 

decreasing velocity promoted debris deposition on the 

land surface.

The flood left bouldery debris deposits up to 9-ft 

thick on and near the roadway. The propensity for the 

fine-grained matrix fluid to separate from the coarsegrained fraction at the leading edge of the debris flow 

caused the matrix fluid to begin to outrun the coarser 

grained fluid as it moved down the medial segment of 

the Ophir Creek fan. About 0.1 mi downstream from 

the north-bank terrace, the spreading and flattening

90 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
flow surge crossed Old Highway 395. Travel time of 

the surge from the moment of the landslide to the interruption of electrical power service by destruction of a 

powerline at Old Highway 395, was about 8 to 9 minutes; travel distance from Upper Price Lake to Old 

Highway 395 is about 2.9 mi; the resultant average 

velocity of the leading flood surge was later computed 

as between 19 and 22 mi/h (28 to 32 ft/s).

The continued widening and flattening flood 

plain (channel slope, 3 percent, or 1.7°) downstream 

from Old Highway 395, caused further deceleration of 

the floodflow. As a result, the bouldery debris was 

deposited, but the fine-grained matrix fluid continued 

to flow. The matrix fluid engulfed and penetrated one 

home about 0.1 mi downstream from Old Highway 

395. It swept away its occupant, vehicles parked by the 

home, and vehicles near a neighboring home to the 

south. The closely following, bouldery, debris-flow 

phase deposited a heterogeneous debris mass on the 

medial fan segment and damaged and inundated the 

three houses in its path. Occupants of two of the homes 

narrowly escaped with their lives. The occupant 

expelled from her home, described above, was injured 

during expulsion and as she was swept downstream 

toward the U.S. Highway 395 freeway by the viscous, 

fine-grained matrix fluid. She survived, but some 

domestic animals were killed. Debris flow seemingly 

continued for one-half to three-quarters of an hour, possibly as multiple flow surges, and added to the debris 

deposits on the medial and distal fan segments. The 

highly saturated, poorly cohesive debris flow, or flows, 

left a depositional surface of generally low relief, 

no debris-flow levees, and weekly lobate margins. 

Cobble and boulder movement ceased just downstream 

from the three homes, about 0.2 mi upstream from the 

U.S. Highway 395 freeway.

Although boulder movement ceased at the downstream limit of the homes, the finer grained matrix fluid 

travelled to and onto the southbound (westward) lanes 

of the freeway. Some matrix-fluid flow, transporting 

abundant vegetal debris, continued southward along 

the west side of the freeway. The matrix fluid was possibly hyperconcentrated flow along some of its route, 

but was clearly a fine-grained debris flow near its terminus; it was composed of water and fine-grained sediment, and it transported large amounts of vegetal 

debris. Cumulative sediment deposits of the flood 

downstream from the lower canyon mouth on the Ophir 

Creek fan, were estimated to be about 400 acre-ft.

A unique aspect of the flood was the rapidity with 

which water was expelled from Upper Price Lake by 

the landslide. Eyewitnesses and field evidence indicate 

that it probably took less than a couple of minutes. This 

rapid release rate and the following plunge down a 

steep, credible channel caused the initial 20 to 22 acreft of water to compound its volume severalfold. Resultant sediment deposits amounted to about 450 acre-ft, 

more than 20 times the initial volume of Price Lakes. 

When the slide was confined by canyons, it cleanly 

scoured all vegetation in its path and badly eroded the 

confining channel.

The cumulative volume of floodflow, water plus 

debris (vegetation and sediment), was estimated at 

about 800 acre-ft, which greatly exceeded (over 36 

times) the combined contents of Price Lakes (22 acreft). Additional water probably came from the following 

sources: snowmelt upstream from the landslide, 

ground-water outflow from the slide mass and scar, 

streamflow in the channel overrun and incorporated by 

the flood surge, tributary inflow downstream from 

Price Lakes, from ground water in pores of debris 

eroded from the channel bed and the release of pressurized ground water from the scoured channel boundaries, and snowpack in the canyons that was 

incorporated in the floodflow.

The 1983 flood in Ophir Creek was probably the 

largest during historical times. Although the flood of 

July 6,1890, was frighteningly similar, as described in 

newspaper accounts, no quantitative data on the 1890 

flood are known for comparison with the 1983 flood. 

However, the description of the 1890 flood indicates 

that the 1983 flood was not unique. The peak-flow rate 

near the mouth of the lower canyon during the 1983 

flood was about 25 times greater than that predicted for 

a 100-year flood. Predicted areas of potential debris 

hazards were predicated on much less severe flooding; 

as a result, the alignment of actual hazardous areas 

were skewed from those predicted, and the predicted 

degrees of hazards generally were exceeded. The large 

number of eyewitnesses and participants in the 1983 

flood temporarily focused local attention on the severity of both real and potential hydrogeological hazards 

on the slopes and around the eastern base of Slide 

Mountain. However, over time, concerns about potential hazards apparently decreased and the development 

and occupation of the area quickly resumed and currently (1996) continues. Natural revegetation of the

SUMMARY AND CONCLUSIONS 91
originally barren land surface created by debris deposition of the flood have been documented by photographs 

for more than a decade.

Ophir Creek and the southeastern slopes of Slide 

Mountain have been subjected to catastrophic landsliding and associated flooding for thousands of years. The 

most recent landslide and flood of 1983 was small in 

comparison to at least nine prehistoric events. Natural 

hydrogeological processes and specific peculiarities of 

the local geologic setting of the landscape all favor repetition of these types of catastrophes in the future.

Future hazardous landslides at Slide Mountain, 

with or without flooding, are almost certain. Flooding 

of a magnitude and severity greater than the 1983 flood 

is still possible, even if upstream manmade reservoirs 

are kept smaller than those in 1983, because damming 

of the deep canyons also can take place through natural 

landslide processes. Subsequent overflows of the natural impoundments caused by these unpredictable, 

localized landslides could result in the rapid releases of 

volumes of water equal to or greater than those chaotically released in 1983. The probable magnitudes, characteristics, and timing of these potential floods and 

landslides are unpredictable because of a lack of both 

general and detailed knowledge of the necessary antecedent conditions and subsequent actions and interactions of the triggering hydrogeological processes.

The prolific record of past landslides and floods at 

Slide Mountain emphasizes the likelihood of recurrences. This substantial history, combined with the 

uncertain nature and current unpredictability of these 

landslide-flooding events, serves notice of a continued 

threat to safety.

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Journal, v. 22, p. 44-68.

Varnes, D.J., 1978, Slope movement and processes, in

Schuster, R.L., and Krizek, R.J., eds., Landslides, analysis, and control: National Research Council, Transportation Research Board Special Report 176, p. 11-33.

Walters, R.J., 1983, A landslide induced waterflood-debris 

flow: International Association of Engineering Geology Bulletin, no. 28, p. 177-182.

94 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
APPENDIX A

LANDSLIDE, FLOOD, AND WEATHER HISTORY

APPENDIX A A-1
Previous Landslides

The Slide Mountain landscape shows abundant 

evidence of a long and continuous record of landsliding, especially large-scale rockfall avalanching. The 

barren, precipitous southeastern face of the mountain 

(frontispiece) is a large, composite, landslide scar from 

which the mountain derives its name. The deposits of 

these slides were first mapped by Thompson and White 

(1964, pi. 1). They differentiated the deposits by age 

into the general categories of "older" and "younger" 

slides from Slide Mountain, although they acknowledged "intermittent sliding over a long range of time is 

clearly demonstrated by differences in weathering and 

erosion of the debris and by alluvial burial of the lower 

parts of the oldest slides" (Thompson and White, 1964, 

p. A23). They calculated a conservative estimate of the 

total volume of granodiorite that slid away from the 

southeastern face of the mountain to be on the order of 

125 million yd3 . About a decade later, Tabor and Ellen 

(1975) prepared a more detailed map of the Slide 

Mountain landslide deposits. Their investigation 

revealed evidence of at least nine rockfall-avalanche 

and debris-flow (landslide) deposits extending from the 

large main scar downgradient along the axis of Ophir 

Creek. The characteristics of these deposits are 

described in detail by Tabor and others (1983, p. 18- 

21). The landslide deposits mapped by Tabor and Ellen, 

which they called the "Debris Flows of Slide Mountain," include most of those mapped earlier as the 

"older and younger slides from Slide Mountain" by 

Thompson and White (1964). (Area mapped by 

Thompson and White is greater than that of Tabor and 

Ellen.) Figure 4 depicts the areal extent of Tabor and 

Ellen's "debris flows" (dominantly rockfall-avalanche 

deposits; S. Ellen, U.S. Geological Survey, written 

commun., 1994). The figure does not differentiate the 

separate episodes of movement as interpreted by them; 

however, it separates areally the rockfall-avalanche 

deposits from the dominantly fluvial deposits of Ophir 

Creek that they also mapped as part of their investigation.

Some of the larger avalanche deposits extend 

along the entire length of the combined upper and 

lower canyons of Ophir Creek and onto the floor of 

Washoe Valley (about 3.4 mi; fig. 6); they are the products of massive and catastrophic movements of rock 

and debris. Other smaller landslides also are recognizable, some of which are located just west of the area 

mapped by Tabor and Ellen in the main slide-scar area; 

they include a series of relatively young lobate deposits

located north and east of Upper Price Lake (fig. 14). 

Some of these young avalanche deposits appear to have 

created, or contributed to the creation of, the depressions which contain Upper and Lower Price Lakes.

A partially exhumed log, 3 ft in diameter, was discovered at the base of the steep slope beneath the outlet 

of Lower Price Lake during investigation of the 1983 

flood (fig. 14). It appeared to have been exhumed by 

heavy cascading streamflow during the expulsion of 

the lake. A carbon-14 sample of the log yielded an age 

of 999 + 55 years. The log was probably buried by earlier rockfall avalanche deposits (fig. 14) and may date 

the age of some of those deposits. It is uncertain which 

of the relatively young rockfall-avalanche deposits 

contain the tree because the undifferentiated deposits 

shown in the map of figure 14 appear to have been 

emplaced by multiple events. The apparent age of the 

tree does agree, within the range of uncertainty, with 

the 1,100-year-old age obtained by Tabor and others 

(1983, p. 20) from debris buried by their rockfall-avalanche "unit 5."

Tabor and others (1983, p. 18-21) describe the 

physical characteristics of the deposits that mantle the 

land surface of most of the Ophir Creek Basin downstream from Slide Mountain and the flow processes 

responsible for those deposits. Of the nine deposits they 

differentiated, the oldest eight were emplaced primarily 

as rockfall avalanches (p. 18), whereas the youngest 

appears to be the product of a debris flow (Tabor and 

others, 1983, p. 20). The rockfall-avalanche deposits 

typically consist of a poorly sorted mixture of granitic 

blocks in a silty sand matrix. Locally, they consist 

almost entirely of granitic blocks up to, or greater than, 

9 ft in diameter (Tabor and others, 1983, p. 18). Discrete units are characterized by hummocky, chaotic terrane with bulbous frontal lobes locally in excess of 90- 

ft high. The deposits have partly filled the canyons 

occupied by Ophir Creek, a normally small stream, 

which has incised into the successive deposits. Debrisflow deposits (of fluvial genesis) of lesser volume and 

extent are recognizable along, and confined to, the canyon beds.

The general age of landsliding is late Quaternary. 

The oldest mapped, and most areally extensive, rockfall-avalanche deposits are considerably older than the 

deposits of succeeding flows; those earliest deposits are 

estimated to be several hundreds of thousands of years 

old (Tabor and others, 1983, p. 20). Several of the succeeding avalanches and flows appear to postdate 

Tahoe-age (60,000 -120,000 years ago) glacial till that 

surficially is exposed on the south side of Upper Price

A-2 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Lake. At least four rockfall-avalanche deposits and one 

debris-flow deposit generally are younger than 1,100 ± 

200 years, based on the age of a sample of carbonized 

wood discovered by Tabor and others (1983, p. 20) in 

deposits beneath their "unit 5." Younger deposits, 

including those confined within the creek canyon and 

downstream on the alluvial fan, include deposits of 

debris flows or water-dominated, debris-laden floods, 

or both.

Slemmons and others (1965, p. 533) mention an 

alleged historical (1852) landslide from Slide Mountain. Newspapers and other documents on file at the 

Nevada Historical Society, Reno, Nev., also indicate 

that a rockf all-avalanche occurred in 1852, and that a 

probable debris flow happened in the early 1860's. The 

rockfall-avalanche report seems to be substantiated, but 

the volume of displaced rock as reported in newspaper 

accounts seems to have been over estimated. The 

Washoe Weekly Times newspaper of June 10, 1865, 

describes the avalanche as happening in late November 

or early December of 1852; the November 27, 1894, 

issue of the Virginia City Territorial Enterprise cites 

Paiute Indian accounts of a large earthquake and related 

landslide at Slide Mountain "a great many years ago." 

On the basis of these historical accounts, and possibly 

others, Slemmons and others (1965, p. 533) concluded 

that an earthquake of unknown intensity near Pyramid 

Lake (about 45 mi northeast of Ophir Creek) was 

responsible for the slide. However, the mapping of 

Tabor and Ellen (1975) and the accompanying text 

(Tabor and others, 1983) indicate that the bulk of the 

landslide debris in the Ophir Creek drainage to be significantly older than the earliest historical records. Scientific evidence for any landslides during 1852 is 

lacking. The newspaper accounts seem to be largely 

based on unsubstantiated non-scientific information; 

the size and severity of a landslide, as they describe it, 

seems grossly overestimated. If a slide occurred in 

1852, its deposits probably are contained within the 

sequence of smaller, multiple-landslide deposits identified as having occurred during the last 1,100 years.

Several other accounts of relatively recent landslides at Slide Mountain have been printed and 

reprinted from time to time, including a humorous fictional account titled the "Great Landslide Case" in 

Mark Twain's book, "Roughing It." Ratay (1973, p. 

335-336), describes several accounts of Slide Mountain 

landslides. Although interesting, the accounts are not 

known to have been verified by any documented factual 

data nor by any known scientific evidence.

The numerous episodes of mass debris movement 

chronicled above portray a complex and persistent 

Quaternary-age history of catastrophic events along 

Ophir Creek. Debris deposits from these numerous 

events range up to hundreds of feet thick in many 

places, and they may overlie and conceal evidence of 

additional earlier events. Tabor and others (1983, p. 18) 

indicated that some of the slide deposits may have been 

cut by post-depositional faulting, which implies that 

tectonic activity may have played some part in landscape instability. All in all, the overwhelming evidence 

of prolonged landscape instability clearly characterizes 

the lower Ophir Creek drainage as an exceedingly hazardous area.

Previous Floods

Floods Caused by Winter Storms

Severe winter floods, caused by regional storm 

systems, generally are less frequent than summer convective storms in the arid southwest; however, they can 

be severe and, because they are regional, sometimes 

devastate large areas. The following floods and some 

others are summarized in table 1 of this report.

January 1874

Goodwin (1977) attributes the January 1874 flood 

to rain on snowpack. Reportedly, this flood triggered 

some sort of failure of a natural earthen dam that 

impounded "Price Lake" (he did not specify Upper or 

Lower), and the downstream rainfall-runoff flooding of 

Ophir Creek was thus intensified by the untimely 

release of some unknown amount of impounded water. 

Damage caused by this Ophir Creek flood was apparently minimal, or unknown.

November 1875

A flood in November 1875 was the result of 

heavy rainfall runoff caused by a regional, early winter 

storm (Goodwin, 1977). Goodwin states that this Ophir 

Creek flood also was intensified by partial failure of 

William Price's impoundment of "Price Lake." Resultant damage was reportedly inflicted on Price's logging 

flume, located adjacent to the downstream creek 

channel, and to the Virginia and Truckee Railroad 

trestle where the railroad crossed Ophir Creek on the 

valley floor.

APPENDIX A A-3
July 1890

The greatest historical flood of Ophir Creek, 

before that in 1983, was on July 6, 1890. The flood 

probably resulted from the failure of a dam at Price 

Lakes (Goodwin, 1977). Apparently, the 1890 flood 

was at least partially the product of heavy runoff of 

snowmelt following a winter of abnormally heavy 

snowfall in the Sierra Nevada. Because there are no 

known records of mountain snowpack during the winter of 1889-90, the only meaningful quantitative comparison of the 1889-90 and 1982-83 winters is the 

precipitation recorded in nearby Reno (table 3). Cumulative precipitation there for the 1889-90 period (October 1889-June 1890), before the July 6, 1890, flood, 

was 15.35 in. Cumulative precipitation for the 1982-83 

winter (October 1982-May 1983), before the May 30, 

1983, flood was 10.57 in. In comparison, mean annual

precipitation recorded at Reno for the 113-year period 

of 1871-1983 is 7.27 in. The heaviest calendar-year 

precipitation recorded in Reno during the period was 

13.73 in. during 1890; the second heaviest was 13.23 

in. in 1983. In contrast, the minimum calendar-year 

accumulation during that period in Reno was only 1.55 

in. during 1947.

The July 6, 1890, flood was described within a 

few days, in varying degrees of detail, by several daily 

newspapers of northwestern Nevada. The most detailed 

and vivid description was that published by the Carson 

City Morning Appeal on Tuesday, July 8, 1890. The 

article is reproduced verbatim here to retain the journalistic flavor of its time and to allow reader comparisons of the unedited text with eyewitness accounts of 

the 1983 flood of appendix B in this report. The Appeal 

report of the 1890 flood is as follows:

"'A BROKEN DAM' 

Wm. PRICE RUINED BY A BURSTED RESERVOIR

How the Flood Came Down the Ravine

On Sunday afternoon at about quarter of 5 o'clock, Price's reservoir at the foot of Slide 

Mountain burst, and the water rushing down the Canyon submerged the V. & T. track at Franktown, causing a delay of the passenger train, which returned to Carson for the night.

SCENE OF THE BREAK

Slide Mountain takes its name from the fact that some years ago about half the mountain 

caved away and fell into the valley.

The land slide occurred in the night, and it was believed that a band of Mormon emigrants 

camping at the foot of the mountain were buried in the debris, but the story has never been 

authenticated.

The convulsion of nature left a hollow place that was utilized by W. E. Price as a site for 

water storage. He turned a mountain stream into the depression and dammed the lower end.

This gave him a lake three miles long, half a mile wide and seventy-five feet deep. Below 

this he made another reservoir covering about five acres of land, with the water fifteen feet deep.

These two reservoirs are situated about three miles from the V. & T. R. R. track at an elevation of about two thousand feet.

Leading from the reservoirs is a ravine through which a flume runs. The flume was used for 

fluming ice and water from the reservoirs. Mr. Price's is at the foot of the flume and here are his 

barnes[sic], residence and ice houses. The improvements and reservoirs are valued at $25,000.

A-4 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
A FEARFUL SIGHT

Some of Price's men were in the ravine at work on the flume, when they heard a roar like a 

train of cars coming. As they looked up the ravine they saw a wall of water thirty feet high and 

one hundred feet across coming down the ravine. From base to crest it was white as marble, and 

at the summit it carried a load of logs and boulders.

As the ends lashed and writhed against the sides of the narrow ravine it licked up everything 

in its path. Fallen trees, underbrush and rocks were sucked into the swirl, and above all was a 

roar that shook the earth.

A RACE FOR LIFE

There were three men in the ravine at a point where the sides were too steep to climb, and 

the only means of escape were down the path about three hundred yards.

The instant the wall of water flashed in sight at the turn of the ravine they dropped everything and fled down the rocky path.

The water was several hundred yards away but gaining at a fearful pace. There was a narrow 

point in its path where the rocks jutted out from the sides. Here it paused for a few seconds as 

the accumulation of logs and boulders were caught in the jam, but weight of the water piled up 

behind soon amounted to thousands of tons, and with a crash the temporary obstruction fell away 

and the water cleared a hundred feet at one leap.

The three men who were just ahead were nephews of Price, and they think that this temporary checking of the downward sweep of the flood saved their lives.

They reached a spot where they could climb to higher ground, and they barely did so when 

the water shot past them with a rush and only a few feet below them.

Reaching the hill they tried to sound the alarm to those below, but they were too far away.

A COURIER SENT DOWN

At this point, however, they found a band of gypsies and one who had a fast horse was sent 

down to warn Price of his danger. He had to go a round-about way about two miles and reached 

the ranch too late to be of any service.

Price, however, had seen the water coming and got his family out of the house in time. The 

foot of the ravine is about half a mile from the house and the water spread out as soon as it ceased 

to be confined, spreading over about twenty-five acres of land.

It swept away the barn, rose above the lower floors of the house, went through the ice house 

and then covered the railroad track with debris for about five hundred yards.

The down passenger train which contained an extra quota of ladies and children en route to 

Reno to attend some school excercises[sic], was delayed until nearly midnight when all efforts 

to clear the track failed and the train returned to Carson.

APPENDIX A A-5
CLEARING THE TRACK

When the news of the break reached Carson, men were sent down on a construction train 

to clear the track. It was covered with logs and boulders and the water was flowing over it. In 

about an hour the water stopped and the men were able to work, but suddenly there came 

another rush of driftwood, water and boulders and covered the track again. When the second 

rush came, it was supposed that the upper lake dam had broken.

The water subsided and came down again at intervals all night and the men who were at 

work, about thirty, gave up exhausted about three in the morning. There was also a gang of 

twenty Chinamen higher up the creek cutting a new channel to divert the torrent by removing 

boulders, but did not succeed, and in the morning the boulders were blown out with giant powder. This accomplished the desired result and by noon the track was clear.

At the present time it is not known for certain whether the big reservoir is broken or only 

partially so.

Big waves came down at intervals but smaller than at first. The place is inaccessible 

except by the ravine and no one dared go up.

The dam was never regarded as strongly constructed and Price has always feared high 

water. The water which escaped had flowed into Washoe Lake and now men are guarding the 

Washoe dam for fear of a break.

Several years ago a dam broke near the present one and nearly wiped out Franktown."

The foregoing account is remarkable for the similarities it depicts between the 1890 and 1983 floods. 

Although the cause of the sudden releases of water 

from the Price Lakes appear to be different, the downstream effects of these releases seem very similar.

The newspaper account contains some obvious 

factual errors and other points worth noting. The article 

implies that the numerous landslides of Slide Mountain 

were a single event during relatively recent (possibly 

historical) times; in fact, separate landslides during 

possibly hundreds of thousands of years have influenced the form of the landscape surrounding the southeastern base of the mountain. The original land-surface 

depression, currently known as Upper Price Lake, 

appears to have been a natural sagpond formed along 

the backside of a slide mass as it moved into the Ophir 

Creek drainage. Therefore, it was probably a perennial 

pond before W.E. "Billy" Price increased its storage 

capacity by increasing the height of the earthfill 

impoundment at its outlet. The 3-mi length, 0.5-mi 

width (960 acres), and 75-ft depth attributed to the lake 

are physically impossible; more realistic dimensions, 

as described earlier in the "Price Lakes" section of this 

report, are 4 acres in area with an average depth of 5 ft.

Eyewitness descriptions of the 1890 flood were 

attributed to workmen who were apparently caught in 

the lower part of the upper canyon below Lower Price 

Lake. Their point of escape probably was near the 

mouth of the upper canyon at the broader channel 

reach, about 0.6 mi below the outlet of Lower Price 

Lake (fig. 6). At their speediest, few men can sprint 

faster than 100 yards in 10 seconds, or 30 ft/s. Because 

of the rough terrain along the canyon floor, the likelihood that all three were not excellent sprinters, and 

their required run was about 300 yards, they probably 

did not average much more than 20 ft/s, or 14 mi/h. 

They described the flood front as "several hundred 

yards away but gaining at a fearful pace." This indicates that the flood velocity in the upper canyon may 

have been on the order of 25-30 ft/s.

The eyewitness description of how the 1890 flood 

front paused for a few seconds at a narrow spot in the 

canyon differs from accounts of the 1983 flood, 

wherein no witnesses noted any stopping or slowing 

of the debris-laden flood front during its downstream 

transit. Momentum of the 1983 flood was likely greater 

than that of the 1890 flood because, although the 

release of water by the dam failure of 1890 was rapid 

enough to cause an abrupt vertical front to form at the

A-6 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
leading edge of flow, the rate of release of the lake contents during 1983 probably could not have been 

equalled or exceeded by a simple collapse of the 

earthen impoundment. The probable release rate of 

lake waters during the 1983 flood is discussed elsewhere in this report.

The Nevada Appeal article did not allude to the 

cause or mechanism of failure of the earthen impoundment other than to concede it was poorly engineered 

and constructed. However, Goodwin (1977) attributes 

the dam failure to a strong, down-canyon wind that 

induced heavy wave action apparently against and over 

the poorly constructed impoundment. The impounded 

lake allegedly was filled to capacity by the abnormally 

heavy snowmelt runoff. According to Goodwin (1977), 

Lower Price Lake, a reservoir created by another of 

Price's dams just above the upper canyon, existed 

before the 1890 flood; its dam too may have failed. The 

newspaper account includes confusing speculations 

about which surface-water impoundment actually 

failed and caused the 1890 flood.

The alleged dispatch of the horse-mounted gypsy 

to sound a warning downstream also has a parallel in 

the 1983 flood, wherein Douglas Cook attempted to 

outrace the leading flood surge by hang glider to warn 

downstream residents; ironically, airborne technology 

of nearly a century later was equally as ineffective as 

the mounted rider at outdistancing the onrushing flood 

waters.

Descriptions of damage caused by the 1890 flood 

generally replicate that of 1983, although dollar costs 

were much greater for the recent flood. There were no 

fatalities in 1890, but there were fewer human targets 

along the floodpath. Price's home, owned by the Victor 

H. Stafford family in 1983, seemed to suffer a nearly 

identical fate in both floods. In 1890, traffic was halted 

on the railroad, whereas freeway traffic was halted or 

delayed in 1983.

The 1890 report of flood waters periodically subsiding and regenerating is difficult to interpret. Canyon 

walls that were destabilized by the initial onrush of the 

flood could have periodically caved, temporarily 

dammed, and subsequently released varying volumes 

of heavy snowmelt runoff. Or periodic debris-flow 

surges during the flood recession may have contributed 

to oscillating flow rates.

The 1983 flood and subsequent snowmelt runoff 

exhumed older fluvial deposits of Ophir Creek near the 

mouth of the lower canyon. Figure 57 shows some of 

these older deposits, including two interstratified zones

of organic-rich sediments. These older sediments are 

located along the south side of the canyon in the general vicinity of the channel profiles of figure 37. The 

thickness of this exposed stratigraphic section 

increases moderately a short distance (50 to 100 ft) 

upstream from the exposure shown in figure 57; the 

thicker exposure contains three organic-rich strata. 

Wood fragments were collected August 26,1983, from 

the bottom and middle strata to assess their age by carbon-14 analysis. The approximate ages of the wood 

fragments are as follows: bottom strata, 130 years; middle strata, 100 years. Because the ages of wood fragments are at least as old as the debris deposits, and 

probably somewhat older, the overall deposit is interpreted to be a likely product of the July 6, 1890, flood.

March 1907

A major rain-on-snow flood affected both the 

Carson and Truckee River Basins on March 16-21, 

1907 (Goodwin, 1977). The severe regional nature of 

this flood virtually ensures that Ophir Creek also was 

affected, but no specific information on Ophir Creek 

flooding has yet been discovered.

December 1937

A heavy rainstorm that caused serious flooding 

throughout western Nevada, including major flooding 

of the Carson and Truckee Rivers, also caused intense 

flooding of Ophir Creek on December 11, 1937 

(Nevada State Journal, December 12, 1937, p. 1). 

Although no quantitative data are available regarding 

the magnitude, quantity, or duration of streamflow, 

some perspective on the severity of the flood is contained in a front page photograph of the December 14, 

1937, Nevada State Journal. It shows Old Highway 395 

where it crosses Ophir Creek littered with debris, 

including boulders up to several feet in diameter. The 

photo caption states, "The lost was found last night by 

Nevada highway department crews when they uncovered the Reno-Carson City highway near Bowers Mansion and opened the road to travel for the first time 

since Saturday [December 11]. All these boulders were 

washed onto the road when the normally-diminutive 

Ophir Creek went on a flood-drunk binge. A four by 

seven foot culvert was filled rapidly with dirt and rocks 

and the near-river took out across the highway, leaving 

a trail of debris that required men and equipment three 

days to remove." The damage to the highway was characterized as "A 100-yard washout" in an earlier edition

APPENDIX A A-7
•Srjfe -; *• w~-i$£4'#£;; <:&

•^ >®^.'*t>iS3: C-r « ."_£*•+ -^*ie-ij(i?* ^.-ZsTK'k,x..4»a»

.,*.^Wx^w*5 :\J^*

Figure 57. Old fluvial deposits near the lower canyon mouth of Ophir Creek, western Nevada, which were exhumed 

by the 1983 flood. Note dark organic-rich zones exposed within the vertical stream bank—one about a foot above the 

present streambed, the other about a foot below land surface. Photographed by Patrick A. Glancy on September 8, 

1983.

of the newspaper (Nevada State Journal, December 12, 

1937, p.l). Edward Parmenter, Nevada Division of 

Water Resources, retired, was a Civil Engineer with the 

Nevada Highway Department at the time. He recalls 

that the flood closed the highway by damaging an 

approximately 150-ft length of the roadway; he also 

noted that flow rates were adequate to erode the blacktopped surface of the highway (Edward Parmenter, oral 

commun., 1983). There are no known reports of dam 

failures at Upper or Lower Price Lakes during this 

flood.

January 1943

Rain fell below 8,000-ft altitude throughout the 

Sierra Nevada and the Sierra-front foothills during January 20-22,1943. The rainfall was very intense at some 

times, and caused regional flooding along the eastern 

Sierra front. Although no specific information on

flooding at Ophir Creek has been discovered, the severe 

regional character of the storm and resultant flooding 

implies that Ophir Creek was similarly affected (Goodwin, 1977).

November 1950

Gustav "Gus" Bundy, a former resident of the 

property just north of Ophir Creek and just upstream of 

Old Highway 395, remembered an intense flood during 

the Thanksgiving period of 1950 (oral commun., 

1983). He recalled that, as a result of heavy rainfall, 

Ophir Creek rumbled boulders along its bed so loudly 

during the night of heaviest flooding that the sound 

awoke him from sleep. He also remembered that the 

highway was closed for some time and that the former 

"Billy" Price residence downstream from Old Highway 

395 received considerable deposition of flood debris 

from the creek.

A-8 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
Bundy's recollections are supported by an article 

in the Reno Evening Gazette of November 20, 1950 

(p. 13). The news report was summarizing impacts of 

regional flooding resulting from a series of late November storms that climaxed on November 19 and 20; it 

characterized Ophir Creek flooding, as follows: "In 

Washoe County, Ophir Creek overflowed and caused 

considerable damage north of Bower's Mansion. The 

creek received the full force of the rain runoff early 

Sunday morning (Nov. 19), with boulders and sand filling the ditches and plugging the culvert."

"The stream cut deeply into the roadbed and 

washed 12 to 24 inches deep across the highway, stopping traffic. Highway maintenance crews manning road 

graders and a scoopmobile were in operation."

"The road was closed shortly before noon Sunday 

and was reopened at 5 p.m...."

No known quantitative streamflow data are available for either the 1937 or 1950 floods. However, as 

described by eyewitnesses and the newspaper reports, 

the 1937 flood probably was more severe.

January-February 1963

Historically, western Nevada has had widespread 

flooding from regional storms on occasions other than 

those specified above for Ophir Creek. A particularly 

notorious regional flood occurred in both the Carson 

and Truckee River Basins during late January and early 

February of 1963. Cumulative rainfall on snowpack in 

the lower elevations of the Lake Tahoe Basin was 11.42 

in. in a few days; similarly, 2.34 and 7.30 in. accumulated in Reno and Carson City, respectively (Reno 

Evening Gazette, February 1, 1963, p. 1). As a result, 

intensive flooding caused by the rainfall and melted 

snowpack was universal in all northern Sierra Nevada 

drainages. Flooding was so widespread that Ophir 

Creek did not get specific recognition in newspaper 

accounts, but some flooding of that drainage very likely 

took place.

Weather Data and History

A systematic network of snowpack measurements was initiated in the Sierra Nevada, and locally in 

the Lake Tahoe area, in 1910 (Nevada Division of 

Water Planning and U.S. Soil Conservation Service, 

1981, p. 1). Shortly thereafter, this network expanded 

statewide. As part of the operation and management of 

this network, summaries of snowpack measurements

are periodically published by the Natural Resources 

Conservation Service. Monthly water-supply forecasts 

are published during January-May each year. An edition also is published in October of each year that summarizes the past year and predicts the water-supply 

outlook for the corning water year. The autumn predictions are largely based on summaries of precipitation, 

runoff, and reservoir storage for the preceding year. 

These snowpack records, combined with precipitation 

records collected by the U.S. National Weather Service, provide a valuable data base to compare weather 

conditions between different places and over varying 

time periods. Specifically, they allow comparisons of 

the varying degrees of wetness between winters, both 

locally and regionally.

Before 1910, systematically collected weather 

data consisted mainly of precipitation and temperature 

information collected at towns and settlements 

throughout the local area. Most of the measurement 

sites were at low altitudes and no systematically collected, quantitative data were available regarding 

snowpack accumulations in the higher altitude parts of 

the Sierra Nevada where most precipitation falls and 

accumulates. Locally, the precipitation records for 

Reno, about 15 mi to the northeast, provide the best 

information on the degree of winter wetness that likely 

prevailed in the Ophir Creek area prior to 1910. These 

Reno data indicate that the wettest winter of historical 

record in the region was probably the winter of 1889- 

90. Cumulative precipitation during the period 

October 1, 1889-June 30, 1890 (about 1 week before 

the July 6, 1890, Ophir Creek flood discussed above in 

this appendix), was 15.36 in. (table 3). The notorious 

character of this severe winter is further borne out by its 

name "The Winter of White Death," which was 

bestowed by ranchers and others of the time. That name 

singularly characterizes it as a winter of unusually 

heavy snowfall and cold temperatures that killed large 

numbers of livestock across northern Nevada. Therefore, the precipitation data of table 3 and general historical notoriety strongly indicate that the 1889-90 winter 

was the wettest, or certainly one of the wettest, in the 

recorded history of the northern Sierra region. Further 

comparisons of precipitation at Reno between the 

1889-90 and 1982-83 winters are given in the part of 

this appendix describing the flood of 1890.

APPENDIX A A-9
A-10 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
APPENDIX B

EYEWITNESS ACCOUNTS OF THE LANDSLIDE AND FLOOD

APPENDIX B B-1
The May 30, 1983, landslide-induced flood was 

witnessed and experienced by an unusually large and 

diverse group of people, compared to most other 

Nevada floods that have occurred in small drainages. 

Some of the eyewitness accounts described herein were 

printed in local newspapers and others were obtained 

through personal interviews. The accounts are summarized in this report because most provide some valuable 

scientific information regarding the physical character 

of, and processes involved in, the landslide and flood. 

Also, they provide an important humanistic dimension 

and perspective to this natural disaster. Figure 2 shows 

locations of the eyewitnesses during the time they 

observed the event. Locations of a few of the observers, 

as noted in figure 2, are only approximate. However, 

the few tenuous locations represent the authors' best 

judgment of the vantage points of the observers based 

on their recollections and testimony. One observer, 

Mrs. E. H. Thorn, witnessed the flood from a circling 

aircraft; thus, her locations are not shown in the figure. 

A possible flight path for Doug Cook, who observed 

the slide and flood during a hang-glider journey is estimated on the basis of his testimony; this assumed path 

probably is a reasonable approximation of his actual 

route over the terrain.

Ronald P. Mentgen (interviewed by P.A. Glancy on 

July 21, 1983)

Mentgen was cross-country skiing in the upper 

part of the Ophir Creek Basin during the morning of 

May 30, 1983. His route was generally southeastward 

from the Mount Rose Highway (Nevada State Route 

431) and generally was downslope across the Tahoe 

Meadows area (a broad, gently sloping, grassy area 

adjacent and downstream from Nevada State Route 

431 and upstream from Price Lakes; fig. 1). He arrived 

at the crest of a ridge several hundred feet vertically 

above Upper Price Lake, which overlooks the lake and 

the southeast face of Slide Mountain, about 11:30 a.m. 

(fig. 2). He observed that the northern half of the lake 

was ice-covered, and he then retreated a short distance 

behind the ridgecrest and sat down to eat lunch. From 

that position he was unable to see the lake, but he could 

still see part of the southeastern slopes of Slide Mountain. While eating lunch, he heard a rushing sound suggestive of wind, and, glancing toward Slide Mountain, 

he observed trees moving downslope in an upright 

position. He noted that the trees moved in one smooth 

pulse. His vantage point did not permit him to observe

the slide mass entering the lake. After not less than 2, 

nor more than 5 minutes, he returned to the ridgecrest 

and noted that Upper Price Lake was essentially 

drained, but that some very turbid "coffee-colored" 

water continued to drain down the creek from the lake 

outlet.

Douglas R. Cook

The following account by Doug Cook was summarized from a newspaper article and an interview of 

Cook by P.A. Glancy on June 23, 1983. All direct 

quotations are from the North Lake Tahoe Bonanza of 

June 1, 1983 (p. 1 and 2). Cook is the only known witness to the emptying of Upper Price Lake by the landslide.

Doug Cook recalled launching his hang glider 

from the Slide Mountain ski resort parking lot (northeast of Price Lakes; not shown in fig. 1) on the east-facing slope of Slide Mountain between 11:00 and 11:30 

on the morning of May 30, 1983. Cook is a seasoned 

glider pilot of over a thousand successful launches, 

many from this same ski-area site. He became airborne 

at an altitude of about 8,200 ft and, taking advantage of 

thermal air currents associated with the unseasonably 

warm day, managed to quickly gain about 500 ft of altitude. He then soared a distance of about 1.5 mi southwestward around the southeast-facing slopes of the 

mountain toward the barren slide-scarred slopes above 

and north-northeastward of Upper Price Lake. More 

rising thermal air currents over this terrain allowed him 

to gain nearly another 1,000 ft of altitude, and he thus 

became positioned about 2,000 to 2,500 ft above and 

over the lake at an altitude approximately equal to that 

of the mountain summit, or about 9,700 ft. At that stage 

of the flight he recalls, "I heard a roaring sound, kind of 

like the sound of a jet engine really close ... I 

thought I was going to get hit. Out of the corner of my 

eye I could see a bunch of rising dust."

Looking down toward the source of the rising 

dust, Cook witnessed the landslide moving down the 

mountain face and finally halting in Upper Price Lake 

at the base of the slope.

"When it hit the lake," he said, "it was like a huge 

explosion. It just blew the whole lake apart. It looked 

like a tidal wave at first and then the canyon gathered it 

up."

Cook was unaware that the flood also dislodged 

the contents of Lower Price Lake about 0.1 mi downstream from Upper Price Lake. "As far as I could see it

B-2 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
was Upper Price Lake spilling into the canyon. I don't 

remember it hitting Lower Price Lake." It is likely that 

most of the lower lake was covered with ice and snow 

and not discernible by Cook as a body of standing 

water prior to its expulsion by the onrushing "tidal 

wave." He noted that the confinement of the flow in the 

upper canyon of Ophir Creek caused the deluge to 

accumulate debris as it flowed downgradient. He did 

not note any pauses or subsequent surges of the mass 

during its transit. "It didn't have a chance to dissipate 

before it got down there. I saw trees just getting plowed 

down and it was gaining momentum. At this time it was 

between 40 and 50 ft high, weaving down the canyon."

"I was really concerned because of the fact that I 

know a lot of people go to that area and a lot of people 

fish there and if they were down there it would be all 

over." Cook also recognized the impending crisis to 

unsuspecting residents downstream. He began to race 

with the flood surge to try to warn downstream victims, 

but soon realized the futility of outrunning the flood 

with a great enough time margin to allow him to sound 

adequate warnings.

During his chase he witnessed the "snake's head" 

(leading flood surge) enter a gorge (probably the lower 

canyon) and he turned his craft and glided back to the 

ski area. "I left my glider there and ran down to the 

launch area and started telling all my friends to look 

down there and watch. Then all of a sudden we saw that 

big, brown wave cross Bower's Mansion road (Old 

Highway 395) and we saw a school bus and cars being 

washed out."

On questioning by Glancy, Cook first estimated 

the time span between the entry of the slide into the 

lake and the floodflow crossing Old Highway 395 (NV 

State Route 429) as about 5 minutes. On suggestion, he 

conceded it could have taken 8 or 9 minutes, but was 

adamantly unwilling to extend the travel time beyond 

10 minutes. The approximate route of Cook's hang 

glider traverse is shown in figure 2.

James Schumacher (interviewed by P.A. Glancy 

during early June 1983)

Schumacher and a friend were hiking uphill 

toward the Price Lake area along the forest trail south 

of Ophir Creek during the morning of May 30. They 

had ascended beyond the mouth of the upper canyon 

and were climbing up the nose of the steep ridge that 

forms the south canyon wall (fig. 2). They were 

approaching Lower Price Lake, and although their

actual proximity to that site is not certain, they were 

probably within a 0.25-mi map distance from the lake. 

Suddenly, they heard a roaring sound that they later 

realized was that of the moving landslide. Their location was out of sight of the slide or of Price Lakes. At 

the request of Schumacher's friend, he noted the time of 

the roaring sound by his wristwatch as about 11:53 or 

11:54 a.m., depending on the accuracy of the timepiece.

Schumacher quickly walked a few tens of feet 

northward to the canyon rim to view the possible 

source of the roaring sound and, instead, caught a 

glimpse of the flood roaring down the canyon below. 

The sight he witnessed is shown in the photograph of 

figure 23. It shows a glimpse of highly turbulent and 

turbid streamflow thrashing about in the canyon. The 

photograph is believed to depict the earlier stages of the 

flood, possibly the leading edge of the flood surge or 

possibly the early recession of the leading edge. Based 

on the extreme turbulence shown in the photo, the flow 

may have been water dominated during this early stage.

The couple then decided against continuing uphill 

toward the slide area and retraced their route downhill. 

The trail swings northward sharply at the mouth of the 

upper canyon and descends onto the relatively open 

flood plain of the creek. The flood plain broadens 

through this short reach that is unconfined by the canyon walls. Schumacher again photographed the flood 

in progress from a site where the trail formerly 

descended to the flood plain at the upper canyon mouth 

(fig. 24). He recalls the period between the times of the 

two photographs as about 10-15 minutes (oral commun., 1983). His approximate positions when he took 

the photographs are shown in figure 2.

Figure 24 shows a different hydraulic character 

than that shown in figure 23. The fluid appears to be a 

sediment-dominated mixture in the later photo, and the 

debris-choked mass seems to be moving as an integral 

block, or plug, bounded by frothing fluid turbulence 

along the edges of the flow. Boulders moving at the surface of the flow appear to range in size up to 1 or 2 ft in 

diameter. The flow character depicted by this photograph is probably that of a debris flow.

Mark Bridgewater (interviewed by P.A. Glancy on 

the afternoon of June 1, 1983)

Mark Bridgewater and his wife were hiking along 

the forest trail south of Ophir Creek, from Old Highway 395 to Price Lakes, on the morning of May 30,

APPENDIX B B-3
1983. His first recollection of the slide was an audible 

rumble, reminiscent of the sound of a jet aircraft. He 

was in a position to see the movement of the slide 

almost immediately after he heard the initial rumbling 

sound. He watched the triangular-shaped rock mass 

slide downward almost as an integral unit. Its velocity 

appeared to accelerate with time and travel distance. 

The edges of the moving mass were the zones of visual 

turbulence. There was a small amount of airborne dust 

kicked up by the slide movement. His vantage point did 

not allow a view of the slide entering Upper Price Lake.

Bridgewater first sighted the flood after it had 

flowed about a mile, according to his estimate. He is 

certain he first saw the flood less than 10 minutes after 

he first noticed the slide movement. Bridgewater estimates his vantage point was about a mile above and 

away from the channel site when he first spotted the 

flood (fig. 2). It is unclear whether he was observing it 

in the upper or lower canyon segment, but most likely 

in the lower canyon. The leading edge of the flood did 

not appear as a vertically standing wall from his angle 

of view, but instead appeared as a deep soupy mud or 

sludge that was moving very fast. He was particularly 

impressed by the superelevated surface of the mass as 

it negotiated curves in the channel, and by the debrischoked nature of the fluid. Effects of the debris colliding with large conifer trees in its path were most 

impressive to Bridgewater; the flow would flex the 

large trees so violently during impact that their top 6 to 

8 ft would abruptly break from the main trunk.

William and Elizabeth Willets (interviewed by 

P.A. Glancy on February 24, 1985)

The Willets had been hiking up the north side of 

Ophir Creek from the Davis Creek Park campground 

about a mile north of Ophir Creek (fig. 2) during the 

late morning of May 30. After hiking about 1.5 mi 

southwest from the campground, they reached a meadowlike area where some smaller tributaries join Ophir 

Creek from the north; this site is part of the wide floodplain area between the upper and lower canyon segments of Ophir Creek (fig. 2). They were hoping to ford 

the creek and continue hiking up the south side, but the 

flow of the creek was greater than they had seen it on 

previous visits. Bill approached the swiftly flowing 

stream and made his way across a small overflow channel to an island adjacent to the main channel.

Elizabeth was watching his attempts to cross the 

creek when she heard a loud roaring noise upstream. 

She looked toward the source of the noise and saw 

large trees falling down the upper canyon walls into the 

channel. She then sighted a huge wave of water and 

debris approaching. The leading edge of the flow front 

appeared vertical. She screamed to Bill to warn him of 

the approaching hazard, and he quickly leaped back 

across the small channel that separated them. He then 

glanced upstream and saw the approaching flood front, 

which appeared so close and seemed to be moving so 

rapidly that he instinctively crouched to the ground and 

covered his head with his hands for self protection. 

After a brief moment, he realized the flood had not yet 

struck so he looked upstream again, reassessed the situation, and then they both scrambled away from the 

creek channel. They both noted that the approaching 

flood mass was brown colored and that the front of it 

was carrying numerous large trees that were being 

tossed about like toothpicks. They also noted that the 

moving mass was plowing large boulders from the 

creekbed and incorporating them as it flowed.

As they raced northward, the flood front exited 

the upper canyon mouth and began to spread out over 

the wider flood plain where they were fleeing. As the 

flow spread laterally, it reached to within 50 ft of them 

and splattered them with mud. The velocity of the 

approaching fluid appeared to decrease during the lateral spreading of the flow, and they managed to outrun 

it.

They continued toward higher ground and ultimately climbed a small hill, still within sight of the 

flood. Bill estimates that the velocity of the approaching flood front when first sighted in the canyon was on 

the order of 20 to 30 mi/h. As they looked back 

upstream from their hilltop vantage, Elizabeth noted 

"water gushing out of the side of the mountain." Bill 

observed, "It looked like a good waterfall." During the 

20 to 25 minutes they remained in the area after the 

arrival of the initial flood front, heavy debris-laden 

floodflow continued to come down the channel within 

their field of view. They could still hear the flow roaring after they hiked across the ridge to the north.

Tom Reed and Others

The following experiences of occupants of the 

Tom Reed residence on the proximal (upstream part) of 

the Ophir Creek fan are summarized from (1) newspaper stories in the Reno Gazette-Journal (June 1, 1983,

B-4 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
p. 3A; and May 28, 1984, p. 1C) and the Nevada 

Appeal (June 1, 1983, p. 8A); (2) an interview of Tom 

Reed by P.A. Glancy on June 1, 1983; (3) a discussion 

between Raymond Isernhagen and Glancy in 1985; and 

(4) an interview of Kathleen Thompson by Glancy on 

June 15,1983. All direct quotations are extracted from 

the newspaper stories.

Tom and Linda Reed were completing construction of their new home situated on the north-bank terrace of Ophir Creek, about 0.2 mi upstream from Old 

Highway 395 (Nevada State Route 429). During the 

late morning of May 30, 1983, Tom was performing 

interior work on the home with the assistance of three 

friends, Joseph Valenzuela, Tim Miller, and John Burruel. Reed recalls that the flow of the creek appeared to 

be about twice that of normal flow. Miller also noticed 

the creek was flowing faster than normal, but the flow 

was not great enough to be frightening. Burrael 

recalled, "I was in the back part of the house watching 

the river and suddenly it started making a real roaring 

noise."

"I heard the creek make a rumbling sound and I 

asked Tom if it always did that. Then Tom and I both 

looked out the back window and we saw a mountain of 

dirt and trees coming out of the ground like someone 

was tearing things up with a big bulldozer."

Valenzuela also noticed the oncoming debrisladen flood front and exclaimed, "Oh my God!" Reed 

immediately and urgently yelled to the rest of the group 

to run for safety. He recalled that, at first sighting, the 

onrushing surge appeared to be about a hundred yards 

upstream. Tom was reportedly the first out of the house, 

followed by Burrael and Valenzuela; Miller was last. 

Linda was preparing lunch in a motorhome parked next 

to the house (Raymond Isernhagen, neighbor, oral 

commun., 1985). She apparently ran about the same 

time the men were abandoning the house.

They ran eastward, roughly parallel to the direction of the onrushing flow front, along a well-used path 

that Reed recalled led toward a high mound about a 

hundred yards ahead (eastward), which he hoped 

would provide refuge. Miller only managed to ran 

about 20 ft before he was overtaken and swept up by 

the flood. He estimates he was transported 350 to 375 

ft within about 4 seconds. [NOTE—The time of travel 

may be about correct, but the distance was probably 

closer to 100-200 ft.]

Burrael remembers tripping on the brush and falling along the path shortly after exiting the house. "I got 

up and looked. There was the house. It was moving

toward me." He then ran between two parked tracks. 

The flood surge slammed the two trucks together and 

Burrael was almost pinned and crushed between them. 

He was somehow overran by one of the moving tracks. 

"The right front tire rolled on my back and I couldn't 

breathe. Then another wave of mud washed it off me, 

but when it did, the truck swirled to my left and I went 

further under it and it pinned my leg."

Burruel also recalled, "I couldn't breathe. The 

mud was coming up to my nose. Then it (the mud) 

peaked out and started going down."

Reed recalls looking backward only once during 

his race and noted that his house was racing with him, 

and gaining; this realization spurred him on to greater 

speed and he managed to make it safely to the high 

ground. On arrival, he turned and noted that the floodfront surge had passed and the flow following the peak 

surge had already receded from the higher terrace, 

along which they had raced, back into the normal flood 

plain of the creek. Numerous flood-deposited boulders, 

wreckage of his home, and vehicles were scattered 

about over the terrace. He was unable to see the other 

members of his group.

Reed was near Miller, whose urgent screams 

quickly attracted him, and he pulled Miller's broken, 

but live, body from the mud. He next discovered Burrael trapped in the mud beneath the pickup track, 

extracted the jack from the track, jacked the truck up, 

and pulled Burrael to safety. After searching, he was 

unable to locate his wife, and after a long period of further searching, he discovered Valenzuela1 s body.

Linda Reed also was overtaken by the flood 

surge, apparently by the fine-grained, muddy, matrix 

fluid that continued flowing after the accompanying 

boulders came to rest on the terrace. She was swept 

along by the muddy matrix fluid that drained from the 

terrace toward the northeast and away from the main 

creek channel (fig. 29). The mud-choked flow flushed 

Linda around the north side of the mound to which 

Tom had escaped, and swept her into Gordon Thompson's backyard, about 0.1 mi east-northeast of the Reed 

residence. Thompson, and his wife Kathleen, witnessed Linda being tumbled into their yard on the crest 

of the muddy surge, through a hole in their chain-link 

fence. Despite being so rudely dumped in the yard and 

obviously dazed, caked with mud, and badly braised, 

she managed to crawl to the Thompson's wooden deck. 

She rested for a few minutes on the Thompson's back 

porch before walking down to Old Highway 395, 

where she obtained medical assistance.

APPENDIX B B-5
The men helping Tom Reed had originally 

planned to bring their wives and children along to picnic and socialize while they worked. If things had 

occurred as planned, the tragedy could have been much 

greater.

Anne Ogilvy (interviewed by P.A. Glancy on 

June 15, 1983)

Ms. Ogilvy lived in a house on a high flood-plain 

terrace along the north bank of Ophir Creek, about 0.1 

mi downstream from the mouth of the lower canyon 

(fig. 2). Her house was the farthest upstream on the 

flood plain and less than 100 yd upstream from but 

slightly north of Tom Reed's home and, thus, farther 

from the main creek channel (fig. 27).

A grove of large conifer trees were fortuitously 

located a few tens of yards upstream from her home. 

They trapped a large amount of organic debris from the 

leading edge of the flood and thus developed a formidable buttress that partially deflected the momentum of 

the peak flow just enough to prevent total destruction 

and (or) burial of her home.

Ms. Ogilvy's first warning of the approaching 

flood mass was the sound of a "great rumbling, like 10 

or 12 army jets" which she dismissed as overhead flying aircraft. Momentarily, from her southward view 

toward the creek, she witnessed "great boulders accompanied by lots of mud" coming toward her. The 

approaching mass was higher than her doors and windows, and was at least 8 ft above the stream-terrace surface on which the house was located, which in turn was 

at least 15 ft above the bottom of the normal stream 

channel. She immediately dashed out a door to the 

north away from the channel. By the time she was out 

the door, the upstream part of the home, separated from 

the main building by a breezeway, was partially 

destroyed by the impact of the debris. She luckily 

found a safe site just a few feet beyond the north side of 

the house that remained out of the flood path.

Ms. Ogilvy was aware of only a single surge of 

debris that collided with her house. This suggests rapid 

recession of the peak-flow surge that prompted her to 

abandon the building. Her experience also suggests that 

the peak flow was almost coincident with the leading 

edge of the flood. However, a substantial and sudden 

increase in the flow of the creek just prior to the peak 

surge of debris could have occurred within the normal 

channel out of Ms. Ogilvy's sight.

Kathleen Thompson (interviewed by P.A. Glancy 

on June 15, 1983)

Kathleen and Gordon Thompson live about 0.2 

mi east-northeast of the Ogilvy and Reed homes (fig. 

2). Their home is about 0.1 mi north of the main channel of Ophir Creek and is at a sufficient altitude above 

the creek that it was well out of the path of the main 

floodflow. However, they did receive some of the mudladen fluid runout from the peak-flow surge that 

engulfed the upstream north-bank terrace where the 

Ogilvy and Reed houses were situated. As described in 

the Tom Reed section, the Thompsons observed Linda 

Reed being swept into their back yard on the crest of 

the mud-laden runout from the peak-flow surge that 

destroyed the Reeds' home.

Mrs. Thompson noted that their electric power 

supply failed at 12:02 p.m., the same time that Sierra 

Pacific Power Company recorded a power outage 

caused by the destruction of their main powerline by 

the peak-flow surge as it crossed Old Highway 395. 

She also observed the peak surge of mud and debris as 

it raced down the main channel to the south of their 

home. She recalls its height as equivalent to that of a 

three-story house, that is, about 30 ft above the channel 

bottom.

Greg Stafford (interviewed on July 21,1983, by P.A. 

Glancy)

Near noon on May 30,1983, Greg and his brother 

Mark Stafford were traveling in a pickup truck up the 

driveway from their father's (Vie Stafford) home 

toward Old Highway 395 (Nevada State Route 429). 

The Stafford home originally was built in the 1870's by 

William "Billy" Price, after whom Price Lakes were 

named. The driveway heads up the alluvial fan of Ophir 

Creek (fig. 2). When they had nearly reached the junction with the public roadway, they observed a rising 

dust cloud near the canyon mouth about 0.3-0.4 mi 

upstream. The dust was immediately followed by a 

churning mass of mud laden with boulders, trees, and 

rootballs. Although Greg and Mark at first believed this 

disturbance might be from heavy construction, they 

quickly realized the true nature of the hazardous situation. In an instant, Greg shifted the truck into reverse 

and quickly retreated back down the driveway.

Upon rearrival at the house, they shouted to all 

family members in the yard to quickly get into the 

house and go upstairs. Everyone, including several

B-6 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
small children, reached safety by the time the debrisladen flood mass arrived. Shirley Stafford (Mark's 

wife) and two adult friends ran south to high ground 

and later climbed a tree for safety.

Before the flood ended, it had buried the home 

with debris nearly to the top of the ground floor (fig. 

32). The yard surface was transformed into a tightly 

packed mass of boulders, some of which measured as 

much as 6 ft in diameter. Much of this heavy coarsegrained debris may have arrived within seconds after 

the family members reached the upstairs part of the 

house.

Although the people escaped serious injuries, 

several horses ultimately became snared in the mud; 

some were rescued, but others were lost. Chickens and 

some other small animals were not very lucky—most 

died. Several vehicles were swept toward the U.S. 

Highway 395 freeway.

Shirley Stafford (interviewed by P.A. Glancy on 

February 20, 1985)

Shirley and Mark Stafford and their young children were visiting Mark's parents at the Vie Stafford 

home just before noon on May 30, 1983 (fig. 2). The 

Stafford pasture land, on the lower Ophir Creek fan 

east of the house, was being used for livestock grazing 

as part of a horse-boarding enterprise. Mark and his 

brother, Greg, had just driven up the driveway in a 

pickup toward Old Highway 395. Shirley and two 

young adult friends were tending to horses at the barn 

and corrals just south of the house. Mark and Shirley's 

children were playing in the yard next to the house.

Suddenly, the pickup roared wildly backwards 

into the yard at high speed. Shirley was instantly irritated at what she thought to be a display of reckless 

driving. Greg and Mark leaped from the truck shouting 

for everyone to take cover. Mark ran toward several 

horses grazing in the pasture to the east. In less than a 

minute after the arrival of Mark and Greg, the leading 

flood surge struck the property.

Heeding the warning, Shirley and her friends 

dashed to slightly higher ground a short distance to the 

south of the barn. They were safe from the initial flood 

surge, but the runout of mud from the mass of freshly 

dumped boulders quickly began to ooze around their 

feet, and they climbed trees for added safety, fearing 

that another and larger debris surge might be coming. 

After just a couple of minutes, when things did not 

seem to worsen, the three decided to walk eastward and

try to assist Mark in his attempt to rescue the horses. 

Shortly thereafter, they joined Patricia Sommers who 

was fleeing barefoot toward the U.S. 395 freeway after 

abandoning her car on Old Highway 395.

After a few minutes, the four joined Mark 

Stafford near the freeway. Several of the horses were 

becoming bogged down in the laterally expanding and 

deepening mud that was draining from the boulder field 

deposited around the Stafford home and neighboring 

homes to the north.

During their attempts to rescue the livestock, they 

also rescued Mrs. Cline (Stafford's neighbor to the 

north) who was being swept toward the freeway by the 

viscous, muddy flow. Mrs. Cline was soon evacuated 

by helicopter to a Reno hospital. Helicopters also were 

used to rescue livestock after several became mired in 

the layer of fine-grained debris that continued to 

deepen in the pasture land. Ultimately, two horses were 

lost but several others were rescued.

Shirley was particularly impressed by the 

momentum of the flood as it continued southward parallel to the freeway; she witnessed a large mare being 

rolled helplessly over and over by the moving fluid.

Vie Stafford (interviewed by P.A. Glancy on June 1, 

1983)

Stafford recalls seeing and hearing the approaching flood front during the time his sons were hurriedly 

driving their truck back to the Stafford home to warn 

their families of the danger (fig. 2).

He remembers that, after the initial debris surge, 

there was continuous heavy movement of water and 

debris across his land for about 3 hours. He recalls the 

flood being quite severe for about 45 minutes. After 

about 3 hours, the flow had noticeably receded and the 

sediment load had diminished enough so that the receding flow began to incise a channel into the newly 

emplaced debris deposits between the Cline and Turek 

homes, about 0.1 mi north of the Stafford home.

Kathleen "Katy" Cline (interviewed by P.A. Glancy 

on February 22, 1985)

The Cline home was located on the alluvial fan of 

Ophir Creek about 0.1 mi north of the Stafford home 

and about 0.1 mi east of Old Highway 395 (fig. 2). 

About noon on May 30, 1983, Mrs. Cline, a senior citizen, and her daughter had just stepped from their 

house to the yard. Suddenly they heard a loud roaring

APPENDIX B B-7
sound from the direction of Ophir Creek, upstream 

from Old Highway 395. Katy glanced in the direction 

of the sound and saw trees flying through the air as the 

leading edge of the flood surge thundered across the 

upper part of the Ophir Creek fan. She promptly urged 

her daughter to escape northward to safety with the 

family pets; she planned to get her purse from the house 

and follow her daughter. Inside the house, she grabbed 

her purse and decided to telephone her sister to request 

help. During the conversation, the telephone suddenly 

went dead and immediately the flood gushed into the 

house. Katy was swept off her feet and into the bathroom by the onrashing torrent. As she rose to the surface of the rapidly rising fluid, she managed to grab the 

top of the bathroom door and hung tightly to it with all 

her strength. Within seconds, the muddy fluid had risen 

nearly to the ceiling, and Katy lost consciousness 

regarding events that immediately followed.

Mrs. Cline's next recollection was that of being 

submerged and swept along by the floodflow. She 

reported sensing an inner voice that urged her to lift her 

head above the surface to breathe. She repeatedly 

obeyed this suggestion and filled her lungs with air. At 

this time, she was apparently outside the house but 

without knowledge or comprehension of how she 

exited the bathroom or the house.

Figure 33 shows the downstream side of the Cline 

house after the flood. The character of the damage indicates structural failure near the base of the wall, probably resulting from hydrostatic-pressure buildup as the 

house filled with fluid. It is likely that Mrs. Cline was 

flushed down and out through the lower wall openings 

as the house quickly drained after the wall had yielded 

to the hydrostatic pressure.

Without knowing her whereabouts, Katy was 

swept generally eastward (downstream) by the debrischoked floodflow. She continued to gasp for breath 

during the brief periods that her head emerged. The 

flow was turbulent and overpowering. During her journey, she recalls seeing a track nearby. She struggled to 

reach the truck, but surging waves kept resubmerging 

her and impeding her efforts. She recalls trying to stand 

up but being knocked down repeatedly by the flow.

After floating and thrashing along for some time, 

she caught a glimpse of some horses trapped by wire 

(probably fencing) and recalls sorrow at being unable 

to assist the animals. About this time, she became 

aware of her ebbing strength and increasing discomfort 

from the cold of the icy fluid that she had been 

immersed in for several minutes.

Suddenly, Mrs. Cline heard a female voice (Shirley Stafford) shout, "There's Katy, there's Katy over 

there!" Mark Stafford and his group pulled Katy to 

safety after much difficulty. She had been swept along 

for 0.3 to 0.5 mi, she was caked with mud and badly 

bruised, and her left leg was seriously injured. She was 

subsequently flown to a Reno hospital.

Patricia Sommers (interviewed by P.A. Glancy on 

August 1, 1983)

Sommers had been visiting Bowers Mansion 

County Park on the morning of May 30,1983. She was 

driving back to Reno along Old Highway 395 (Nevada 

State Route 429) about noon. She had just driven across 

the diverted channel of Ophir Creek where it passed 

beneath the highway through a concrete box culvert at 

the south margin of the Ophir Creek fan (fig. 27), and 

she did not notice any unusual flow in the channel. 

About 0.05 mi beyond and a couple of seconds later, as 

her car came to the crest of a small rise, she noted the 

power lines shaking and waving ahead of her where the 

line paralleled the upslope side of the roadway. She 

quickly stopped the car and, in the next instant, a thundering surge of debris cascaded across the roadway just 

ahead of her car, tearing down the power lines in the 

process.

She attempted a U-turn but midway into the turn, 

her car's engine stalled and died. She looked quickly 

back along the highway toward Bower's Mansion 

County Park and saw a deluge of muddy water and 

debris cascade across the road where she had just 

crossed. She was consumed by a sense of panic when 

she realized her entrapment, particularly when she considered the possibility that another surge of debris 

might engulf her.

In a state of anxiety intensified by the roar of the 

deluge, she abandoned her car and dashed downstream 

toward the freeway for safety. As she ran, she lost her 

shoes but continued without them. After scrambling 

about 0.1 mi downstream across rocky, brushy, and 

tree-covered high ground untouched by the flood, she 

met up with Shirley Stafford and her two friends who 

also were heading toward the freeway.

The group moved southeastward, skirting the 

southern edge of the floodplain. After a distance of a 

few hundred yards or less, they came to the mandiverted channel of Ophir Creek that was now clogged 

with some of the debris that Sommers had earlier 

observed flowing both eastward across the highway

B-8 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
behind her and southward down the sloping roadway 

toward Bowers Mansion. Sommers tried to cross the 

debris-clogged channel but quickly sank to her waist in 

the quicksand-like mixture. She had to be extricated by 

one of Shirley's friends.

The group was finally able to cross the mandiverted channel after the bulk of the flood bypassed 

the diversion and flowed on through the Turek, Cline, 

and Stafford properties to the north. As they hiked eastward toward the freeway, flow of the fine-grained 

debris component of the flood continued and the zone 

of inundation was gradually expanding eastward and 

southward. Piles of organic debris accumulated along 

the southern border of the highly viscous fluid. After 

walking several hundred yards eastward and nearing 

the freeway, they joined Mark Stafford, who had been 

trying to rescue livestock. Suddenly they heard someone moaning in distress. Stafford climbed atop one of 

the piles of debris and spotted a human form being 

rafted along by the flowing mud. With great difficulty, 

he pulled Katy Cline out of the mud.

Susan S. Graves (interviewed by P.A. Glancy on 

Julyl, 1983)

Ms. Graves was inside her residence, just east of 

Old Highway 395, along the north part of the alluvial 

fan of Ophir Creek at the time the flood was approaching (fig. 2). Her first indication of the impending deluge was feeling the house begin to vibrate because of 

ground shaking. In a few seconds, the vibrations 

became so intense that doors began to swing wildy on 

their hinges. During a period of at least 30 seconds of 

continuing and intensifying vibrations, Ms. Graves 

moved to a position that allowed her to view the leading edge of the debris flow across Old Highway 395. 

She estimates that it moved at a speed of about 20 mi/h. 

She was most impressed by the sound, particularly the 

fierce sharp cracks of breaking tree trunks and power 

poles, and recalls that the intense roaring of the flood 

lasted for at least 10 minutes after it first crossed Old 

Highway 395.

The Graves property was mostly outside the flood 

plain and sustained minor damage. The family raises 

Arabian horses and, during the period of the flooding, 

they worked to control and calm the panicked animals.

Kenneth Julian (interviewed by P.A. Glancy on 

February 27, 1985)

Mr. Julian was driving southward along the U.S. 

Highway 395 freeway during the late morning of 

May 30, 1983 (fig. 2). About the time he passed the 

turnoff to Old Highway 395, just north of Ophir Creek, 

he noted a number of cars parked some distance ahead 

along both the northbound and southbound lanes. As he 

approached the parked cars, he saw that many of the 

passengers were outside the cars looking westward; 

some were taking photographs. He then looked westward and saw a wall of very muddy water flowing 

quickly eastward toward the freeway. The muddy fluid 

was transporting numerous trees, many as large as 2 ft 

in diameter, with their bark stripped away. When he 

first sighted the flow, it was near the Cline and Turek 

houses, about 0.25 mile upstream (west) of the freeway. He stopped his car a short distance south of the 

other cars that were parked on the shoulder of the 

southbound lanes. He estimates the muddy flow 

reached the freeway about 2 minutes after he first 

sighted it; he is adamant that it could not have been 

more than 5 minutes. Based on Julian's observations of 

time and travel distance, the velocity of the leading 

edge of the flow averaged between 4 and 11 ft/s. Julian 

noted that the front was 4 to 5 ft high and of a consistency resembling freshly mixed concrete.

When the flow front reached the freeway, it was 

abruptly diverted southward, parallel to the roadway. 

Its velocity diminished noticeably as it flowed southward. Julian watched the front move southward past 

him. To the best of his recollection, his position was 

near the culvert where Ophir Creek normally flowed 

beneath the freeway. About 50 to 100 yards behind the 

leading flow edge, he noticed an approaching round 

object that was bobbing above and below the fluid surface. At first it resembled a ball, but when it came 

opposite him, about 10 to 20 yards away, he identified 

it as a human head. He could clearly see the victim's 

eyes. One or both hands of the person weakly and 

slowly raised above the fluid surface. The victim gazed 

into his eyes and spoke, "Help me!" Julian was shaken 

by the request because the person was far out of reach 

and the moving fluid of unknown depth appeared too 

treacherous to attempt to enter.

By this time, most of the parked southbound 

traffic had departed, probably in fear of being permanently delayed if the flow overtopped the roadway. 

Julian looked for assistance but no one was nearby.

APPENDIX B B-9
He remembered a rope on the backseat of his car, and 

reluctantly raced from the victim to the car and back 

again with the rope, but during the interim, the person 

disappeared. Julian frustratedly walked back and forth 

for about 20 minutes searching for the victim, but never 

sighted the person again.

Shortly after losing sight of the victim, Julian 

observed a woman being pulled from the flow by several people upstream from the freeway. This was Mrs. 

Cline being rescued by the Stafford party. He is certain 

the victim he sighted could not have been Katy Cline 

because the victim was clearly moving downstream 

ahead of Mrs. Cline. Amid the floating debris that 

included vehicles and household goods, Julian identified at least two sleeping bags and a canteen. Because 

of the heavy mud coating the person, Julian could not 

determine whether the victim was male or female.

Julian remained at the site for a prolonged time 

and reported his sighting to several members of the rescue parties that arrived later. He also later reported the 

sighting to Washoe County Sheriffs personnel.

The mystery of Julian's sighting remains 

unsolved. His recollection of the events and the details 

are impressive and compelling. According to Julian's 

information, it seems possible that some unknown victim remains buried within the debris along the freeway 

somewhere south of the Ophir Creek crossing.

Reed W. Dopf (interviewed by P.A. Glancy during 

early July 1983)

Dopf, a professional fireman, was driving southbound in his motorhome on the U.S. Highway 395 freeway through Washoe Valley shortly before noon on 

May 30, 1983, accompanied by a male friend and their 

families. His friend, looking westward from the front 

passenger seat, suddenly exclaimed, "I think I just saw 

an avalanche!" Dopf allowed the vehicle to decelerate 

while both men looked over the landscape; they both 

soon witnessed a rising cloud of dust winding its way 

down Ophir Creek. They parked, got out of the vehicle, 

and speculated further about the cause of the rising trail 

of dust that was persistently working its way downslope. After some undetermined lapse of time, they saw 

the leading edge of the flood burst from the lower canyon mouth, rumble about 0.3 mi farther down its channel, and then spill across Old Highway 395, about 0.7 

mi to the west of their vantage point on the freeway 

(fig. 2).

Dopf recalls, "As it came out of the canyon, it was 

just volatile. It looked exactly like opening a fire 

hydrant. It was that much turbulence. It was that much 

motion." He also described the emergence of the flood 

front as appearing,"... just like it was coming out of 

a sluiceway. It would have been white water had it not 

been so dark (colored)." He also describes the overall 

mass of fluid as "a tabular mass of water and rock that 

was coming out of there."

Dopf was likewise impressed by the character and 

intensity of sound that accompanied the flood, and he 

described it as making "a dull roar like you'd hear at the 

ocean. The thing that was most impressive was this 

deep, percussive sound." The percussive sounds were 

undoubtedly the huge boulders pounding together 

within the mass of water and debris. He did not recall 

sensing any ground vibrations, such as those described 

by several observers in the vicinity of Old Highway 

395, although he concedes he may have been "unaware 

of ground shaking because of other audible and visual 

distractions." Dopf noted that the percussive sounds 

continued only until the leading turbulent flood peak 

had dissipated.

As the turbulent, boulder-laden, leading wave of 

the flood came to a standstill, a mud-laden fluid flowed 

out of the massive boulder deposits and moved downgradient toward the freeway. Dopf believes it took 5 to 

10 minutes for the leading edge of this fine-grained 

fluid mixture to travel the approximately 0.25-mi distance from the downstream edge of the boulder field to 

the freeway. His estimate of the traveltime suggests 

that the fluid moved at an average velocity of between 

2 and 5 ft/s, much slower than the estimated 25 to 30 

ft/s velocity of the boulder-laden flood front as it exited 

the canyon and crossed Old Highway 395. This greatly 

attenuated velocity of the muddy, runout fluid partly 

explains how it was possible for Patricia Sommers and 

the Stafford group to have time to hike downstream and 

pluck Mrs. Cline from the slow-moving flow.

After the muddy flow reached the freeway, Dopf 

and friends slowly drove southward watching the leading edge of the mud-choked mass slowly flow parallel 

to the roadway. He describes the moving fluid front as 

a vertical wall of mud about 2 to 3 ft high with a leading 

edge comprised largely of tree limbs, branches, and 

twigs. The visual character of this moving debris is 

shown in figure 39. He observed that he could easily 

walk backwards at a speed equal to that of the leading 

edge of the flow, which indicates a fluid velocity of 

only a couple of feet per second. Dopf is confident that

B-10 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
the slow-moving, organic-choked, fine-grained, viscous mixture took a full 20 minutes to move southward 

and into some ponds along the roadway, a distance of 

about half a mile. That estimate also indicates an average velocity of 2 ft/s, or less.

Charles McQuerry (interviewed by P.A. Glancy on 

August 1, 1983)

Mr. McQuerry was driving along the U.S. Highway 395 freeway shortly after noon on May 30, 1983. 

He arrived at the site of flooding along the freeway (fig. 

2) sometime after the large boulder deposit had been 

emplaced upstream by the initial flood surge (fig. 10). 

With his video camera, he filmed the viscous, muddy 

fluid flowing along the edge of the roadway. His videotape record includes a brief glimpse of a vehicle and a 

floating propane tank moving southward, parallel to the 

roadway, very near the site where the flow first arrived 

at the freeway. We estimated a surface velocity of about 

5 ft/s for the flow, on the basis of the movement rates 

of the vehicles and propane tank as shown by the videotape recording.

McQuerry described his recollection of the flow 

rate as fast enough to require a fast walk or slow trot to 

keep pace with the floating objects. That rate generally 

confirms a surface velocity of about 5 ft/s. He also 

sensed a vibration of the roadway, but was not positive 

whether the source of shaking was coarse debris moving in the vicinity of the boulder deposits upstream or 

flow along the freeway.

Mrs. E.H. Thorn (interviewed by P.A. Glancy on 

June 13, 1983)

Mrs. Thorn, along with her husband, son, and 

daughter-in-law took off in a light airplane from Reno 

Cannon International Airport between 11:30 and noon 

on May 30, 1983. They were on a sight-seeing trip 

toward Lake Tahoe. Their first view of the flood scene 

was about 12:10 p.m., according to Mrs. Thorn's recollection. The mud-laden floodflow was just reaching the 

upstream edge of the U.S. Highway 395 freeway when 

they arrived overhead. After circling and reconnoitering the flood scene, Mrs. Thorn photographed the 

recession of the floodflow during repeated circular 

flights (fig. 53). Most of her photographs were probably taken between 12:15 and 1:00 p.m.

APPENDIX B B-11
B-12 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
APPENDIX C

PARTICLE-SIZE DISTRIBUTION OF SAMPLES AND 

EQUATIONS USED IN CALCULATIONS

APPENDIX C C-1
Appendix C. Particle-size distribution of samples from sediment deposits 1

Percent of weight finer than sizes shown, in millimeters (mm) and phi units (<)>)

Sample —————————————————————————————————————————————————————————————— 

no. 2 „ al? . mm 64 32 16 8 4 2 1 0.5 0.25 0.125 0.0625 0.031 0.016 0.008 0.004 0.002 (fig.43) C°"eCted

<)> -6 -5 -4 -3 -2 -1 0 1 23 4 56789

1 08-27-83 100 96 84.4 71.4 56.3 35.8 17.3 6.1 2.5 1.5 1.0 0.7 0.5 0.4 0.3

2 08-27-83 100 94.6 79.7 52.8 33.0 21.5 12.8 8.1 5.2 3.4 2.3 1.5 1.3 1.1

3 11-16-90 100 88.8 79.3 72.8 65.7 58.1 46 31.2 18.5 8.6 3.1 1.5 .7 .5 .4 .3

4 11-16-90 100 78.8 71.2 66.3 60.3 53.8 41.9 29.9 17.1 8.2 4.6 1.1 .5 .4 .3 .2

5 05-22-91 100 88.7 75.7 60.5 46.2 29.2 14.4 7.5 4.4 2.9 1.0 .5 .3 .3 .2

6 05-22-91 100 99 83.4 54.6 30 13.4 5.1 2.7 1.4 .9 .8 .5

1 Sediment analyses done at U.S. Geological Survey, Cascade Volcano Observatory Sediment Laboratory, Vancouver, Wash. Samples 1-4 were 

collected from the matrix material of the debris deposits because of the inability to obtain a representative volume of the debris that included boulders 

more than 10 ft in diameter. Samples 5 and 6 were collected from the whole debris deposits. Sand and coarser grained fraction analyzed by wet sieving; 

distribution of fines (silt and clay) analyzed by pipette using chemical dispersant and distilled water.

*• Samples 1 and 2 collected at same site; samples 3 and 4 collected at same site.

EQUATIONS USED IN CALCULATING STATISTICS OF PARTICLE-SIZE DISTRIBUTIONS

The statistics of the grain-size distribution are described by the graphically derived measures of Folk (1980) 

with cumulative frequency plotted on probability paper as weight percentage of grains finer than the limit of each 

phi <j) class.

Mean grain size (Mz) is defined as the graphic mean.

M,,=((j)i6H-(j)50H-(j)84)/3 and can be expressed in (j) units or millimeter size.

Median grain size (Md) is defined as that size on the cumulative curve for which 50 percent of the sample is 

finer.

M^=D5o and can be expressed in <|) units or millimeter size. 

Sorting Coefficients (aG and a/): 

Standard deviation (aG) is defined as the graphic standard deviation. (It includes the central 2/3 of the sample.)

aG~((l) l6"(l)84V2 and is expressed in <|) units.

Standard deviation (a/) can also be defined as the inclusive graphic standard deviation. (It includes 90 percent 

of the sample.)

G/-((l) l6~(l)84V4+((|)5-(|)95)/6.6 and is expressed in § units.

Proposed criteria for verbally expressing a/ degrees of sorting are:

0.35(|), very well sorted,

0.35-0.50<|>, well sorted,

0.50-0.7It)), moderately well sorted,

0.71-1.0(|), moderately sorted,

1.0-2.0<]), poorly sorted,

2.0-4.0()), very poorly sorted, and

over 4.0<]), extremely poorly sorted.

C-2 Landslide-Induced Flooding at Ophir Creek, Washoe County, Western Nevada, May 30,1983
An older (obsolete) measure of sorting is the Trask Sorting Coefficient (Trask, 1932) and is derived graphically, with cumulative frequency plotted on probability paper as the weight percentage of grains finer than the limit 

of each metric class, as

1 /O 50=(Z)25 -5- D75) and is computed only using particle

diameters expressed in millimeters. 

Proposed criteria for verbally expressing S0 degrees of sorting are:

<2.5, well sorted, 

=3.0, normally sorted, and 

>4.5, poorly sorted.

Skewness is defined as the Inclusive Graphic Skewness (Skj).

=

Proposed criteria for verbally expressing Skj degrees of skewness are: 

from +1.00 to +0.30, strongly fine skewed, 

+0.30 to +0.10, fine skewed, 

+0.10 to -0.10, near symmetrical,

-0.10 to -0.30, coarse skewed, and

-0.30 to -1.00, strongly coarse skewed.

APPENDIX C C-3



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