42' 

METRIC CONVERSION FACTORS 

Multiply 

foot (ft) 

cubic yard (yd3 ) 

mile (mi) 

square mile (mi2 ) 

cubic foot per second (ft3 /sec) 

By 

0.3048 

0.7646 

1.609 

2.590 

.02832 

To obtain 

meter (m) 

cubic meter (m3 ) 

kilometer (km) 

square kilometer (km 2 ) 

Cubic meter per second (m3 /s) 

105° 

120' 110' I 490 _____ L 115° 1 ---------:----; 

~ ~~ - ------IT_j______________ I , _ _/ ' I \ 

I ! , Spokane o ' \ I / I , I '-, MONTANA \ 

I \ 0 \ 

\ • Mount St Helens / 'I[, Helena 'I 

I ..------------\ 

~--------- ' l \ Portland ) '~ __ .l 

I \ ---------------- / '\ , __ [\~ 1 ... _,-- I 

·Seattle 

0 

Salem 

I \ 

r ~~ \ 

i IDAHO I 

' \ 

OREGON 

! \ ---- ______________ _j ____________ ___ _______ ~ 

0 100 200 300 MILES 

0 100 200 300 KILOMETERS 

COVER: North Fork Toutle River, June 30, 1980. Volcanic mud flow breccia 

and debris from the May 18, 1980, eruption of Mount St. Helens (in upper 

right) are as much as several hundred feet thick in the reach shown. 

Photograph by Austin Post, U.S. Geological Survey. 
Characteristics of Columbia River Sediment 

Following the Eruption of Mount St. Helens 

on May 18, 1980 

By David W. Hubbell, Julija M. Laenen, and Stuart W. McKenzie 

Hydrologic Effects of the Eruptions 

of Mount St. Helens, Washington, 1980 

GEOLOGICAL SURVEY CIRCULAR 850-J 

1983 
United States Department of the Interior 

JAMES G. WATT, Secretary 

Geological Survey 

Dallas L. Peck, Director 

Free on application to Distribution Branch, Text Products Section, 

U. S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 
FOREWORD 

On May 18, 1980, after more than a month of earthquakes and eruptions, Mount St. 

Helens, in southwestern Washington, exploded in a volcanic eruption more violent than 

any in the conterminous United States during the 20th century. A lateral blast of hot gas 

and rock particles devastated an area of about 150 square miles on the northern side 

of the mountain knocking down trees to a distance of 15 miles. Several minutes later, a 

giant ash cloud rose to about 60,000 feet. Winds then carried the ash cloud across the 

United States, with heavy fallout and deposition in eastern Washington and parts of 

Idaho and Montana. Earlier, smaller eruptions deposited ash in western Washington 

and parts of Oregon and Canada. 

The hydrologic effects of the May 18 eruption have been both widespread and intense. 

During the eruption, a massive debris avalanche moved down the north flank of the 

volcano depositing about 3 billion cubic yards of rock, ice, and other materials in the 

upper 17 miles of the North Folk Toutle River valley. The debris deposits are about 

600 feet thick in the upper reaches of the valley. Following the avalanche, runoff from 

the melted glaciers and snow, and possible outflow from Spirit Lake, caused an extraordinary mudflow in the North Fork Toutle River. The mudflow shattered and uprooted 

thousands of trees, destroyed most of the local bridges, and deposited an estimated 

25,000 acre-feet of. sediment in the Cowlitz River channel. A considerable amount ot 

additional sediment was conveyed through the lower Cowlitz into the Columbia River 

where it was deposited and formed a shoal that blocked the shipping channel. Mudflows 

also occurred in the South Fork Toutle River and in tributaries on the east flank of 

Mount St. Helens which enter Swift Reservoir. 

As part of a concerted Geological Survey effort to study the volcanic event and to 

identify potential hazards, Survey hydrologists have mounted an intensive program to 

document the hydrologic effects of the eruptions. The major initial hydrologic findings 

are reported in this circular series. Quick, useful assessment was made possible only 

because the Survey has long conducted extensive water-resources investigations in the 

affected areas of Washington, Oregon, and Idaho. Hence, there was a well-defined basis 

for identification and documentation of the typeR and magnitudes of hydrologic changes. 

The Geological Survey Circular 850, "Hydrologic Effects of the Eruptions of Mount 

St. Helens, Washington, 1980," consists of individually published short chapters that 

emphasize data collection activities, field observations, and initial comparisons of preand post-eruption conditions. The series will cover hydrologic events occurring on 

May 18 in the Toutle and Cowlitz River; physical alteration of the Toutle River system; 

the chemical and physical quality of precipitation, streams, and lakes affected by volcanic ash fall; ash-leaching studies; and Mount St. Helens glaciers. 

Director 

III 

CONTENTS 

Abstract 

Introducti~~-================================================================== Acknowledgments ----------------------------------------------------------

Data collection ----------------------------------------------------------------

Suspended sediment -------------------------------------------------------- Bed material --------------------------------------------------------------- Data analysis ------------------------------------------------------------------

Longitudinal distribution of suspended-sediment transport rates ---------------------

Vertical distribution of suspended sediment --------------------------------------

Longitudinal distribution of bed material 

Specific gravity and shape factor of post-;~~ti~;b~1-;;t";ri;1====================== 

Specific gravity ---------------------------------------------------------

Particle-shape factors ----------------------------------------------------

Conclusions ------------------------------------------------------------------- References cited ---------------------------------------------------------------

ILLUSTRATIONS 

Page 

J1 

1 

4 

4 

4 

6 

10 

10 

11 

13 

14 

16 

18 

20 

21 

Page 

FIGURE 1. Map of Columbia, Cowlitz, and Toutle Rivers ------------------------------ J2 

2. Photograph of the confluence of the Cowlitz and Columbia Rivers______________ 3 

3. Photograph showing section of typical exposed sandbar in the lower Cowlitz River 8 

4. Graph showing variation of bed-material particle-size statistics between Columbia 

River miles 106.4 and 14.0 for pre- and post-eruption periods---------------- 17 

5. Graph showing relations between sieve and fall diameters of naturally worn quartz 

particles for different shape factors------------------------------------ 19 

TABLES 

Page 

TABLE 1. Suspended-sediment discharge measurement data for locations along the Columbia, Cowlitz, and Toutle Rivers ---------------------------------------- J5 

2. Particle-size distribution of depth-integrated suspended-sediment samples from 

the Columbia, Cowlitz, and Toutle Rivers -------------------------------- 6 

3. Particle-size distribution of point-integrated suspended-sediment samples from the 

Columbia River ---------------------------------------------------- 7 

4. Particle-size distribution of surficial bed material finer than 2 mm from the Columbia, Cowlitz, and Toutle Rivers ---------------------------------------- 9 

5. Longitudinal distribution of suspended-sediment discharges between Columbia 

River miles 73.5 and 54.0 during the period August 13-20, 1980 ------------- 13 

6. Vertical distributions of suspended sediment at Columbia River cross sections as 

characterized by measured Z values------------------------------------ 14 

7. Particle-size statistics of surficial bed material finer than 2 mm from the Columbia, 

Cowlitz, and Toutle Rivers ------------------------------------------- 15 

8. Specific gravity of Columbia, Cowlitz, and Toutle River sediments ------------- 18 

9. Summary statistics of bed-material shape factors at Columbia River cross sections 20 

III 

HYDROLOGIC EFFECTS OF THE ERUPTIONS OF MOUNT ST. HELENS, WASHINGTON, 1980 

CHARACTERISTICS OF COLUMBIA RIVER 

SEDIMENT FOLLOWING THE ERUPTION OF 

MOUNT ST. HELENS ON MAY 18, 1980 

By David W. Hubbell, Julija M. Laenen, and Stuart W. McKenzie 

ABSTRACT 

The cataclysmic eruption of Mount St. Helens, in 

southwestern Washington, on May 18, 1980, produced devastating mudflows that delivered large quantities of debris to 

the lower reaches of the Cowlitz River and the Columbia River 

near Longview, Wash. To obtain information on the character 

of the "new'' sediment and its disposition in the rivers, data 

were collected during a 9-day period in mid-August 1980. 

Measured suspended-sediment discharges indicate that material 

is being scoured from the reach of the Columbia River directly 

seaward from the Cowlitz River mouth at Columbia River mile 

(CRM) 68.0, and that some of the scoured material is redeposited between CRM 63.8 and CRM 54.0. Most material in 

transport is of silt and clay size. Pumice particles larger than 2.0 

millimeters in diameter are randomly distributed throughout 

the bed material (bottom sediment). Mean size of bed material 

finer than 2.0 millimeters in the reach directly seaward from the 

Cowlitz River mouth is less than half the size of similar material 

directly upstream from the mouth and is somewhat finer than 

pre-eruption material. Specific gravity of bed material finer 

than 2.0 millimeters in the reach below CRM 73.5 is about 2.65, 

and the majority of particle-shape factors (determined indirectly) are between 0.5 and 0.8. 

These values are similar to comparable values for bed 

materials at CRM 106.4. On the basis of this information, corrections for unusual sediment properties are not necessary in 

sediment-transport or dredging-earthwork computations for 

the Columbia River. 

INTRODUCTION 

On May 18, 1980, at 8:32 a.m., Mount St. Helens, 

in southwestern Washington, erupted in a cataclysmic explosion. Fragmented and pulverized 

rock, blasted from the mountain, devastated the 

landscape over a fan-shaped, 200 mi2 area to the 

north. On the mountain, debris accumulated in the 

J1 

channel of the North Fork Toutle River to a 

thickness of 600 ft, and nearby lakes filled with 

lesser thicknesses of sediment. Glassy volcanic ash 

rose 60,000 ft into the air and drifted to the northeast. Ash deposits 10 mm (millimeters) thick occurred as far away as 400 mi. Several cubic 

kilometers of debris discharged from the mountain, lowering the peak by about 1,300 ft (Findley, 

1981; Cummans, 1981). 

Melted glacial ice, released ground water, and 

natural surface flow combined with the enormous 

quantities of debris to produce mudflows down the 

valleys of the North and South Forks of the Toutle 

River that drain to the west and in the Smith and 

Pine Creeks that drain to the southeast. The most 

extensive mudflow traveled down the North Fork 

Toutle River, combined with the mudflow from the 

South Fork, continued down the Toutle River to 

the Cowlitz River, and then into the Columbia 

River at Longview, Wash. Throughout the approximately 70-mi-long course to the Columbia (fig. 1), 

the mudflow flooded the river valleys and deposited vast quantities of debris in many places 

across the entire valley floor. At the lower end of 

the Cowlitz River (fig. 2), the streambed aggraded 

approximately 15 ft, reducing the channel capacity 

to roughly 15 percent of normal (Bechly, 1980). 

Approximately 36 million yd8 of sediment, mostly ranging from clay-size particles to 1

/2-in gravel, 

were deposited in the Columbia River less than 24 

hours after the eruption. The 600-ft-wide by 40-ftdeep navigational channel in the Columbia River 

was reduced to a depth of 14 ft at the mouth of the 
0 1 2 

t 1 'r 1' 

3 5 MILES 

1 'r ' 0 1 2 3 4 5 KILOMETERS 

FIGURE I.-Columbia, Cowlitz, and Toutle Rivers. Leaders indicate location of sampling sites in river miles from mouth. 

J2 
FIGURE 2.- Northeast view of confluence of the Cowlitz and Columbia Rivers. The Cowlitz River enters from the upper left. 

Seaward flow in the Columbia River is from right to left. 

Cowlitz River, and new deposits were readily 

measured in a reach 7 mi landward and 2 mi 

seaward from the confluence (Bechly, 1980; Haeni, 

1981). 

In addition to the immediate devastation along 

the Cowlitz River and disruption of navigation in 

the Columbia River caused by flooding and sediment deposition, serious long-term problems now 

exist in the lower reaches of the Cowlitz River and 

in the Columbia river and its estuary from drastic 

alteration of the sedimentation regimen. Because 

of (1) increased erosion from extensive areas in the 

Toutle and Green River drainage basins covered by 

ash or by unconsolidated and (or) unvegetated surface material, (2) increased bank erosion along the 

channels, and (3) progressive streambed degradation, sediment loads may be substantially greater 

J3 

than they were in the past. The increased loads 

present the potential for increased deposition in 

the lower Cowlitz and Columbia Rivers. Hence, 

channel maintenance to reduce flood hazards and 

sustain navigation very likely will require increased dredging. Additional major mudflows 

would substantially compound this problem. 

Deleterjous consequences in the Columbia River 

estuary are less obvious, but potentially serious. 

Mass-balance computations based on radioactivity 

indicate that prior to the eruption, approximately 

30 percent of the sediment finer than 0.062 mm 

(clays and silts) delivered to the estuary became 

permanently deposited there (Hubbell and Glenn, 

1973). Also, current and bottom-sediment 

transport patterns suggest that little, if any, sand 

or coarser sediment leaves the estuary, except 
possibly during extreme upland-flow or storm 

events (Hubbell and others, 1971). Continual 

deposition of unusually large quantities of sediment in the estuary for some time in the future not 

only will increase the normal dredging burden, but 

also may have important physical, ecological, and 

esthetic consequences from significant changes in 

water clarity and in depositional patterns in nondredged areas. 

Because of the variety of potential problems 

associated with changes in the sedimentation 

regimen, the magnitude of anticipated changes 

must be forecast as accurately as possible. 

Engineering calculations of the competence of the 

rivers to entrain and transport sediment and of the 

effectiveness of control measures to perform their 

design functions, as well as other types of calculations, can be made accurately only if up-to-date information is available on the character of the sediment and its disposition in the rivers. To provide 

such information, the Oregon District of the Water 

Resources Division, U.S. Geological Survey, 

cooperated with the U.S. Army Corps of Engineers, Portland District, in a study of the 

physical characteristics of sediment deposited in 

the lower Cowlitz and Columbia Rivers as a result 

of the Mount St. Helens eruption. The primary intent of the investigation was to ascertain to what 

extent, if any, the "new" sediment differed from 

normal Columbia River sediments. In addition, the 

spatial distribution of suspended sediment in the 

Columbia River was observed at several locations 

to ascertain any trends that might exist. 

This report presents hydrologic data collected 

for the investigation and discusses the findings. 

The information pertains mainly to the particlesize distribution, shape factor, and specific gravity 

of bottom sediments, although some information is 

given on the disposition of suspended sediment; 

the results are based on limited data that were collected over a very short span of time. 

ACKNOWLEDGMENTS 

Field measurements and samplings for this investigation were made by Oregon District personnel, U.S. Geological Survey. Oregon District personnel also determined the concentration and particle-size distribution of suspended-sediment 

samples from all locations, except one on the 

Cowlitz River. Washington District personnel furnished sediment-discharge data for Cowlitz River 

mile 17.0 and water discharges for the Cowlitz and 

J4 

Toutle Rivers. Particle-size analyses of bed 

material by sieving were made by the Materials 

Laboratory, U.S. Army Corps of Engineers, North ' 

Pacific Division. Oregon District personnel analyzed the particle size of bed material by the visualaccumulation-tube method, and they determined 

specific gravities. The writers gratefully 

acknowledge the contributions of all involved 

groups and individuals, who worked under a 

demanding time schedule. 

DATA COLLECTION 

SUSPENDED SEDIMENT 

From August 11 to August 20, 1980, suspended 

sediment was sampled intermittently at locations 

in the Columbia River in the vicinity of Longview, 

Wash. The purpose of sampling was to determine 

the particle-size distribution, concentration, 

discharge, and spatial distribution of suspended 

sediment at locations upstream and downstream 

from the mouth of the Cowlitz River, after a 

moderate period of restabilization. In addition, 

some suspended-sediment samples were obtained 

in the Cowlitz River and in the two forks and main 

stem of the Toutle River, to define suspendedsediment discharges during the investigative 

period. 

Depth-integrated suspended-sediment samples 

were collected on several occasions from cross sections at Columbia River miles (CRM) 73.5, 63.8, 

and 54.0, and at Cowlitz River mile 0.2; one crosssection measurement also was made at Cowlitz 

River mile 4.2. Except for the measurements made 

on August 19 and 20, 1980, all sampling in the Columbia was done at five verticals in the cross section by the equal-discharge-increments (EDI) 

method (Office of Water Data Coordination, 1978) 

using a U.S. D-77 sampler modified to operate 

isokinetically as a collapsible-bag sampler (Stevens 

and others, 1980). Near-equal-volume samples of 

about 2 L (liters) of water-sediment mixture were 

obtained at each vertical and were composited for 

analysis. On August 19 and 20, samples also were 

collected at five verticals by the EDI method, but a 

U.S. P-61 suspended-sediment sampler, rather 

than a D-77 collapsible-bag sampler, was used. 

Sampling at each vertical was by one-way integration over the full depth. To provide representative 

samples, individual samples (bottles) were obtained 

from depth segments not exceeding 30 ft, until the 

entire depth was sampled. In this process, the 
TABLE 1.-Suspended-sediment discharge measurement datafor locations along the Columbia, Cowlitz, and Toutle Rivers 

[Due to rounding procedures, the sum of sediment discharges greater than and less than 62 llm may not equal the total measured suspended-sediment discharge] 

Daily 

Time mean Measured suspended sediment 

(P.d.t., discharge Concentration (mg/L) discharge (t/d) 

River mile Date (1980) 2400 hours) (ft3/s) <62/lm >62/lm Total <62/lm >62/lm Total 

Columbia River 

73.5 Aug. 12 ____ 0900 139,000 11 2 13 4,130 750 4,880 

73.5 ____ do ____ 1025 139,000 8 4 112 3,000 1,500 4,500 

73.5 Aug. 14 ____ 1400 140,000 20 3 23 7,560 1,130 8,690 

73.5 Aug. 18 ____ 1200 124,000 9 1 10 3,010 330 3,350 

73.5 ----- ____ do ____ 1205 124,000 12 3 115 4,000 1,000 5,000 

73.5 ----- Aug. 20 ____ 1330 149,000 12 2 14 4,830 800 5,630 

73.5 ----- ____ do ____ 1330 149,000 13 3 1 16 5,200 1,200 6,400 

63.8 ----- Aug. 13 ____ 1430 142,000 70 12 82 26,800 4,600 31,400 

63.8 ____ do ____ 1535 142,000 59 1 160 22,600 400 23,000 

63.8 Aug. 14 ____ 1000 143,000 48 7 55 18,500 2,700 21,200 

63.8 Aug. 18 ____ 1530 127,000 86 7 93 29,500 2,400 31,900 

63.8 Aug. 20 ____ 1030 152,000 29 13 142 11,900 5,300 17,200 

63.8 ____ do ____ 1030 152,000 34 2 36 14,000 820 14,800 

54.0 Aug. 13 ____ 1130 142,000 60 5 65 23,000 1,920 24,900 

54.0 ----- ____ do ____ 1150 142,000 55 15 170 21,100 5,700 26,800 

54.0 ----- Aug.18 ____ 1030 130,000 29 1 130 10,200 400 10,500 

54.0 ____ do ____ 1030 130,000 42 1 43 14,700 350 15,100 

54.0 ____ do ____ 1328 130,000 46 4 150 16,100 1,400 17,600 

54.0 ----- ____ do ____ 1330 130,000 55 2 57 19,300 700 20,000 

Cowlitz River 

.2 Aug. 12 ____ 1300 3,000 609 0 609 4,930 0 4,930 

.2 Aug. 18 ____ 1345 2,500 601 0 601 4,060 0 4,060 

.2 Aug. 20 ____ 1140 2,700 1,070 0 1,070 7,800 0 7,800 

4.2 Aug. 11 ____ 1000 3,000 400 600 1,000 3,240 4,860 8,100 

17.0 Aug.11 ____ 1230 2,960 1,140 9,110 

17.0 Aug. 12 ____ 0705 2,960 2 1,100 8,790 

17.0 Aug. 13 ____ 0705 2,970 21,600 12,800 

17.0 Aug. 14 ____ 0710 2,940 21,400 11,100 

17.0 Aug. 18 ____ 0705 2,540 21,400 9,600 

17.0 Aug. 19 ____ 0705 2,520 2 1,400 9,500 

17.0 Aug. 20 ____ 0705 2,680 21,500 10,900 

Toutle River 

6.5 ----- Aug. 11 ____ 264 3,650 2,650 6,300 2,600 1,890 4,490 

North Fork Toutle River 

1.2 ----- Aug.11 ____ 160 190 930 1,120 80 400 480 

South Fork Toutle River 

.0 ----- Aug. 11 ____ ---- 104 8,350 3,250 11,600 2,340 910 3,260 

.0 ----- Aug. 13 ____ ---- 103 12,700 3,530 

1 Estimated from point-integrated samples listed in table 3. 2 Estimated from single vertical concentration furnished by the Washington District, U.S. Geological Survey, Water Resources Division. 

sampler was traversed vertically at a selected constant rate that provided a volume of water-sediment mixture from the entire vertical, which was 

about equal to the volume from each of the other 

verticals; the near-equal volumes from each vertical were composited for analysis. 

Depth-integrated suspended-sediment samples 

from the Cowlitz River were collected at seven verticals spaced according to the equal-widthincrements (EWI) method (Office of Water Data 

Coordination, 1978) using a U.S. P-61 sampler; the 

quart-size samples were composited for analysis. 

Toutle River samples were obtained by wading and 

using a U.S. DH-48 depth-integrating hand 

sampler. Because of streambed instability, some 

measurement sections on the Cowlitz and Toutle 

Rivers could not be waded and sampled across 

their full widths. Despite this difficulty, the sampling was considered to be in accordance with the 

EWI method at all sections, and samples were 

J5 
TABLE 2. -Particle-size distribution ofdepth-integratedsuspended-sediment samplesfrom the Columbia, Cowlitz, and Toutle Rivers 

[Method of analysis: S, sieve; VA, visual-accumulation tube; P, pipette] 

Time Daily Sediment 

(P.d.t., mean concen- Date 2400 discharge tration Percent finer than indicated size, in micrometers Method of 

(1980) hours) (fta/s) (mg/L) 8 16 31 62 88 125 175 250 350 500 1,000 analysis 

Columbia River mile 73.5 

Aug. 12 __ 0900 139,000 13 86 s 

Aug. 14 __ 1400 140,000 23 86 s 

Aug. 18 __ 1200 124,000 10 88 s 

Aug. 20 __ 1330 149,000 14 87 s 

Columbia River mile 63.8 

Aug. 13 __ 1430 142,000 82 85 s 

Aug. 14 __ 1000 143,000 55 88 s 

Aug. 18 __ 1530 127,000 93 93 s 

Aug. 20 __ 1030 152,000 36 94 s 

Columbia River mile 54.0 

Aug. 13 __ 1130 142,000 65 92 s 

Aug. 18 __ 1030 130,000 43 98 s 

1330 130,000 57 96 s 

Cowlitz River mile 0.2 

Aug. 12 __ 1300 3,000 609 21 30 64 87 95 100 p 

Aug. 18 __ 1345 2,500 601 28 40 66 87 96 100 p 

Aug. 20 __ 1140 2,700 1,070 32 46 71 86 92 100 p 

Cowlitz River mile 4.2 

Aug. 11 __ 1000 3,000 1,000 9 15 20 24 27 40 41 44 50 70 86 94 100 VA,P 

Toutle River mile 6.5 

Aug. 11 ______ 264 6,300 5 11 16 27 40 58 67 75 80 83 87 92 100 VA,P 

North Fork Toutle River mile 1.2 

Aug. 11 ______ 160 1,120 2 2 4 7 11 17 21 31 41 55 69 79 97 VA,P 

South Fork Toutle River mile 0.0 

Aug. 11 ______ 10411,600 5 10 17 31 

composited for a single analysis at each section and 

time. 

Suspended-sediment discharge-measurement 

data for the various cross sections and times of 

sampling are listed in table 1. Sediment in lowconcentration samples was divided by sieving into 

portions finer than 62 J.Lm (micrometers) and equalto or coarser-than 62 J.Lm, to permit the discharge 

of silt plus clay to be determined separately from 

the discharge of sand. Complete size analyses were 

made of samples from the Cowlitz and Toutle 

Rivers that contained an adequate amount of sediment. Particle-size distributions defined by the 

analyses are given in table 2. 

Point-integrated suspended-sediment samples 

were obtained in the Columbia River at CRM 73.5 

and 54.0 at three different times, and at CRM 63.8 

on two occasions. For each measurement, duplicate quart samples were collected with a U.S. P-61 

sampler, generally from five points in the depth, at 

48 72 82 89 93 96 98 99 100 VA,P 

J6 

a single vertical in midstream. Because of relatively low concentrations, only percentages, by 

weight, of sediment finer than 62 J.Lm (by sieving) 

could be accurately defined. These values, with 

other pertinent information, are shown in table 3. 

BED MATERIAL 

Samples of bed material (bottom sediment) were 

collected at six cross sections in the Columbia 

River and at nine locations along the Cowlitz and 

Toutle Rivers. Except for samples collected from 

the Interstate Highway 5 bridge at Vancouver, 

Wash. (CRM 106.4), on September 17, 1980, all 

Columbia River sampling was done on August 12 

and 13, 1980. Sampling on the Cowlitz and Toutle 

Rivers was done on August 11, 1980. The primary 

purposes for examining bed material in the Columbia River were to determine the particle-size 

distribution of bottom sediments in the reach 
TABLE 3.-Particle-size distribution of point-integrated suspended-sediment samples from the Columbia River 

Sediment 

Time (P.d.t., Daily mean discharge Total depth Height above bed concentration Percent 

Date (1980) 2400 hours) (ft3/s) (ft) (ft) (mg/L) <62!-lm 

River mile 73.5 

Aug. 12 ----------------------- 1015 139,000 65 1 14 70 

1020 139,000 65 15 14 63 

1025 139,000 65 25 12 81 

1030 139,000 65 47 11 81 

1035 139,000 65 60 13 61 

Aug. 18 ----------------------- 1203 124,000 40 1 10 81 

1205 124,000 40 4 25 87 

1207 124,000 40 12 

1209 124,000 40 24 16 76 

1210 124,000 40 35 9 78 

Aug. 20 ----------------------- 1330 149,000 45 1 54 32 

1330 149,000 45 5 27 82 

1330 149,000 45 15 16 78 

1330 149,000 45 28 12 87 

1330 149,000 45 40 12 78 

River mile 63.8 

Aug. 13 ----------------------- 1525 142,000 36 1 70 92 

1535 142,000 36 4 66 88 

1545 142,000 36 11 75 88 

Aug. 20 ----------------------- 1025 152,000 45 1 57 71 

1027 152,000 45 5 58 61 

1029 152,000 45 10 42 67 

1030 152,000 45 29 41 72 

1032 152,000 45 40 40 76 

River mile 54.0 

Aug. 13 ----------------------- 1140 142,000 

1145 142,000 

1150 142,000 

1152 142,000 

1155 142,000 

Aug. 18 _______________________ 1023 130,000 

1026 130,000 

1028 130,000 

1030 130,000 

1032 130,000 

Aug. 18 ----------------------- 1328 130,000 

1328 130,000 

1328 130,000 

1328 130,000 

1328 130,000 

where sediment derived from the Mount St. Helens 

eruption was initially deposited and to learn if the 

shapes of particles that presently (August 12-20, 

1980) make up the bed material in this reach are 

substantially different from the shapes of normal 

Columbia River sediments as characterized by bed 

material at Vancouver. Cowlitz and Toutle River 

samples were obtained and analyzed to define the 

size distributions and shapes of bed-material particles that could be transported to the Columbia. 

Samples from the Columbia River were collected 

at CRM 106.4, 73.5, 70.0, 69.2, 67.0, and 63.8 with 

J7 

60 1 64 82 

60 5 91 76 

60 20 74 78 

60 42 59 75 

60 55 79 78 

57 1 53 96 

57 4 36 96 

57 19 39 94 

57 40 28 95 

57 52 20 93 

61 1 72 92 

61 6 57 92 

61 21 55 94 

61 43 44 96 

61 56 41 94 

a U.S. BM-54 sampler. Five or more samples, 

generally spaced an equidistance apart across the 

full width, were obtained from each cross section. 

A midstream sample from river mile 0. 9 on the 

Cowlitz River also was collected with the U.S. 

BM-54 sampler. At the other locations on the 

Cowlitz and Toutle Rivers, samples were collected 

with scoop-type samplers; because of physical conditions, sampling was limited to the parts of the 

cross sections that were accessible by wading. 

Although the sampling on the Cowlitz and Toutle 

Rivers probably was not completely representative 
of the entire cross section, samples generally were 

satisfactory for the purposes of the study. 

Many of the bed-material samples collected from 

the Columbia River near the mouth of the Cowlitz 

River (CRM 68.0) had unusual characteristics. On 

the basis of sieve separations, roughly 21 percent, 

by weight, of sample material collected from the 

north (Washington side) two-thirds of the channel 

at CRM 73.5, 70.0, and 69.2 consisted of particles 

coarser than 2.0 mm (2,000 J.lm), whereas only 

about 7 percent of the material from the south onethird of the channel was of that size. A typical 

sample having particles coarser than 2.0 mm consisted of well-sorted material between 0.125 and 

2.0 mm and various heterogeneously sized larger 

particles. Samples having a high percentage of particles coarser than 2.0 mm invariably had several 

very large pumice particles up to about 25 mm in 

diameter. At CRM 73.5, virtually all particles 

coarser than 2.0 mm were visually observed to be 

pumice. At CRM 70.0 and 69.2, roughly one-fourth 

of the coarser material was pumice; the remainder 

was fairly angular rock fragments. During sampling at several of the cross sections, pumice was 

observed to be floating on or near the surface. 

Material collected from the lower Cowlitz River 

contained fine, clay-size particles. Unlike clay, 

however, the fine material exhibited little or no 

cohesion. Typically, in the lower Cowlitz, exposed 

sandbars were capped with a 1

/2-in layer of this fine 

material (fig. 3). 

To facilitate determinations of the shape factor 

and specific gravity of bed-material particles and 

to permit more representative comparisons of the 

particle-size distributions of pre- and posteruption bed material, detailed size analyses were 

made only of the material finer, by sieving, than 

2.0 mm. Elimination of the coarse material effectively excluded most of the pumice and all the large 

particles (erratics) from the analyses. In addition 

to practical reasons, this procedure seemed warranted, because the distribution of visually discernible pumice and other large particles is random and local; and the present (August 1980) 

FIGURE 3.-Section of typical exposed sandbar in the lower Cowlitz River. Fine-grained surface layer is about 0.5 in thick. 

J8 
disposition of pumice is a temporary condition due 

to its extreme mobility and susceptibility to fracturing. 

Particle-size distributions of all bed-material 

samples are given in table 4. The size distributions 

are expressed in terms of 100 percent finer than 2. 0 

mm even though physically larger particles may 

have been present in the sample. The percentage, P, 

of the total sample represented by the tabulated 

size distribution is listed in the third column of 

table 4. To convert the listed percent finer values 

to represent the whole original sample, multiply 

each value by the fraction, P/100. 

The portion of each sample finer than 2.0 mm 

was analyzed by two different methods-the 

visual-accumulation tube (VA) method (Guy, 1969) 

and sieving (S). VA analysis expresses the size 

distribution in terms of fall diameters; the distribution indicates the percentage of particles, by 

weight, that have fall diameters less than the indicated diameter (size). The fall diameter of a particle is defined as the diameter of a sphere that has a 

specific gravity of 2.65 and the same standard fall 

velocity as the particle. The standard fall velocity 

of a particle is the average rate of fall that the particle would finally attain, if falling alone in quiescent distilled water of infinite extent, at a t~mperature of 24 oc (degrees Celsius) (Inter-Agency 

Committee on Water Resources, 1957). The fall 

diameter of a particle depends on the size, threedimensional shape, and density of the particle. 

Sieve analysis expresses the size distribution in 

terms of a linear dimension; the distribution indicates the percentage of particles, by weight, that 

can be oriented so they will pass through a square 

opening having a side dimension equal to the indicated diameter size. The sieve diameter of a particle depends only on the size and cross-sectional 

shape of the particle. Because sizing is based on 

different criteria, particle-size distributions defined by the two methods generally are different. 

The purpose for the dual analyses is discussed in 

the section on shape factor and specific gravity of 

post-eruption bed material. For a few samples, 

sizes finer than 62 #-'m were determined by the 

pipette method (Guy, 1969). This method also gives 

sizes in terms of fall diameters. 

TABLE 4.-Particle-size distribution of surficial bed material finer than 2 mmfrom the Columbia, Cowlitz, and Toutle Rivers 

[Method of analysis: VA, visual-accumulation tube; P, pipette; S, sieve] 

Percent Date Lateral of total Percent finer than indicated size, in micrometers Method of 

(1980) positionl sample 2 4 8 16 31 62 74 88 125 149 175 250 297 350 500 590 1000 1190 2000 analysis 

Sept. 17 __ 10 

30 

50 

70 

90 

99 

100 

100 

100 

100 

Aug. 12 __ 5 100 

20 85 

30-35 100 

40 100 

45 99 

50 100 

70 87 

85 59 

95 78 

4 

Columbia River mile 106.4 

1 1 1 8 27 64 87 98 __ 100 VA 

0 6 32 91 98 100 s 

0 1 20 64 81 99 __ 100 VA 

0 19 82 97 100 s 

0 3 28 56 98 100 VA 

0 9 62 94 100 s 

0 2 11 33 68 99 100 VA 

0 2 18 71 98 100 s 

0 2 12 34 54 98 100 VA 

0 3 30 60 85 100 s 

Columbia River mile 73.5 

26 

9 18 

0 

0 

6 14 29 53 56 

44 44 

1 

0 

0 

1 1 

1 

0 

0 

0 

35 54 

1 2 

56 57 

0 

0 

0 

1 1 

1 1 

J9 

1 

62 

4 

46 

1 

2 

1 

2 

5 

2 56 

71 86 

22 77 

61 82 

0 2 

5 53 

2 21 

1 22 

6 38 

52 

91 

56 

86 

26 

60 

42 

23 

60 

95 99 

97 100 

96 99 

97 99 

18 60 

94 97 

59 77 

68 94 

71 85 

100 

95 

99 

99 

63 

100 

83 

54 

86 

100 

100 

100 

100 

98 

99 

100 

97 

99 100 

100 

100 

98 100 

100 

100 

99 100 

80 100 

100 

98 100 

VA 

s 

VA 

s 

VA 

s 

VA,P 

s 

VA 

s 

VA 

s 

VA 

s 

VA 

s 

VA 

s 
TABLE 4. -Particle-size distribution of surficial bed material finer than 2 mm from the Columbia, Cowlitz, and Toutle RiversContinued 

Percent Lateral of total 

[Method of analysis: VA, visual-accumulation tube; P, pipette; S, sieve] 

Date Percent finer than indicated size, in micrometers Method of (1980) position1 sample 2 4 8 16 31 62 7 4 88 125 149 175 250 297 350 500 590 1000 1190 2000 analysis 

Aug. 12 __ 5 

10 

20 

35 

50 

75 

Aug. 12 __ 5 

15 

25 

45 

55 

65 

75 

95 

95 

Aug. 12 __ 5 

10 

20 

30-50 

60-80 

90 

Aug. 13 __ 

95 

95 

95 

10 

20 

30 

40 

50 

60 

80 

90 

92 

94 

95 

64 

83 

59 

98 

82 

90 

50 

96 

63 

77 

72 

91 

100 

97 

99 

100 

100 

95 

100 

93 

100 

96 

100 

100 

98 

58 

98 

100 

3 

4 

3 

1 

5 

3 

4 

Columbia River mile 70.0 

1 1 1 5 24 69 85 95 100 VA 

0 2 28 83 96 100 s 

0 1 8 30 56 94 100 VA 

0 1 9 62 95 100 s 

0 1 14 44 96 100 VA 

0 1 10 54 91 100 s 

0 2 16 31 45 92 100 VA 

0 1 4 34 58 84 100 s 

0 2 9 U ~ ~ lOOVA 

0 2 18 51 81 100 s 

0 4 20 33 84 100 VA 

1 1 1 8 37 70 100 s 

Columbia River mile 69.2 

0 7 37 69 97 100 VA 

0 1 14 76 97 100 s 

0 2 12 29 54 100 VA 

0 1 15 59 87 100 s 

1 1 1 2 5 21 41 92 100 VA 

1 1 3 17 65 92 100 s 

0 3 9 19 34 91 100 VA 

0 2 14 37 74 100 s 

0 1 2 8 25 93 100 VA 

0 1 4 29 87 100 s 

0 3 10 22 42 88 100 VA 

0 1 12 40 7 4 100 s 

0 1 13 45 63 94 100 VA 

0 1 17 63 86 100 s 

0 3 14 32 93 100 VA 

0 1 7 35 78 100 s 

0 4 16 93 100 VA 

0 3 30 80 100 s 

Columbia River mile 67.0 

6 11 19 50 72 88 97 98 98 98 99 

36 44 99 99 100 

0 1 8 22 52 77 98 

0 1 4 20 66 

0 1 9 47 74 91 97 

0 6 70 93 

0 1 13 52 90 98 100 

0 10 82 100 

0 1 8 52 94 98 100 

0 3 50 100 

1 1 3 13 58 91 98 99 

1 2 14 92 98 

77 92 96 96 98 100 

91 95 99 100 

10 16 24 46 87 97 99 100 

9 13 34 91 98 

8 20 43 79 88 95 98 99_ 100 

77 84 95 -- 100 

Columbia River mile 63.8 

4 100 

6 11 99 100 

100 VA, P 

s 

100 VA 

93 100 s 

100 VA 

99 100 s 

VA 

s 

VA 

s 

100 VA 

99 100 s 

VA 

s 

VA 

99 100 s 

VA,P 

s 

VA 

s 

20 70 

0 8 

0 4 

2 11 

94 100 VA 

7 7 

0 1 

1 

74 97 100 

99 100 

94 100 

99 100 

s 

VA 

s 

VA 

2 3 

5 8 11 14 16 19 37 

9 30 

0 4 

86 

21 

12 

19 

92 96 

24 37 

15 42 

20 25 

57 62 

48 54 

14 18 

44 

58 

31 

53 69 

80 92 

43 81 

74 91 

65 76 

33 56 

72 98 100 

100 

s 

VA,P 

VA,P 

VA 

1 2 3 4 5 

0 

6 16 52 77 97 99 100 

94 97 

JlO 

5 

99 

17 

100 

95 100 

82 100 

70 96 100 s 

VA,P 

s 
TABLE 4. -Particle-size distribution of surficial bed material finer than 2 mmfrom the Columbia, Cowlitz, and Toutle RiversContinued 

Percent Date Lateral of total 

(1980) position' sample 2 

Aug. 12 __ 5 

50 

90 

Aug. 11 __ 50 

Aug. 11 __ 

Aug. 11 __ 

Aug. 11 __ 

15 

20 

60 

30 

70 

99 

99 

Aug. 11 __ 1 

Aug. 11 __ 33 

67 

Aug. 11 __ 16 

50 

100 

100 

100 

99 

89 

92 

99 

99 

97 

98 

95 

83 

96 

95 

78 

[Method of analysis: VA, visual-accumulation tube; P, pipette; S, sieve] 

Percent finer than indicated size, in micrometers Method of 

8 16 31 62 74 88 125 149 175 250 297 350 500 590 1000 1190 2000 analysis 

Cowlitz River mile 0. 7 

6 8 8 18 89 100 p 

99 99 

6 9 23 63 97 100 

100 

99 

100 

s 

p 

99 99 

99 99 

Cowlitz River mile 0.9 

100 s 

s 

1 2 4 14 31 65 -- 87 97 -- 99 100 VA,P 

s 

0 1 

0 

2 

2 

0 

3 

3 

0 

1 

4 

39 53 -- -- 97 100 

Cowlitz River mile 4.2 

9 

8 11 

5 

15 16 

1 

1 1 

16 37 57 92 98 99 100 VA 

42 96 99 100 s 

5 6 9 27 49 62 95 100 VA, P 

23 46 78 94 100 s 

1 2 5 14 29 49 97 100 VA 

7 26 56 89 100 s 

Cowlitz River mile 9.6 

2 4 19 51 74 90 97 100 VA 

8 41 41 83 96 100 s 

6 16 18 35 70 89 96 98 100 VA, P 

1 

2 

4 5 24 88 98 99 100 s 

Cowlitz River mile 13.5 

4 6 14 48 78 82 87 96 100 VA, P 

3 -- 3 10 -- 46 88 95 97 99 100 VA, P 

1 1 -- -- 15 90 97 99 100 s 

Cowlitz River mile 29.9 

2 -- 2 8 -- 18 48 90 100 

2 3 -- -- 16 65 100 

Toutle River mile 6.5 

VA 

s 

0 6 21 57 72 94 100 VA 

0 1 4 27 62 88 100 s 

0 1 3 18 40 70 95 100 VA 

1 1 6 34 64 89 100 s 

North Fork Toutle River mile 1.2 

1 1 

1 1 

0 2 11 28 94 100 VA 

2 8 36 84 100 s 

0 1 11 32 88 100 VA 

2 12 51 81 100 s 

South Fork Toutle River mile 0.0 

Aug. 11 __ 1 

5 

5 

63 

80 

98 

3 6 12 16 22 30 

2 

35 41 48 56 66 75 98 100 VA, P 

0 1 2 8 

5 

2 

1 

7 23 45 69 89 100 s 

15 28 38 50 58 63 96 100 VA, P 

8 23 47 67 90 100 s 

7 13 20 45 75 90 95 100 VA 

3 15 58 92 98 100 s 1 Relative distance from left bank (looking downstream), expressed as percentage of full width. 

DATA ANALYSIS 

LONGITUDINAL DISTRIBUTION OF SUSPENDEDSEDIMENT TRANSPORT RATES 

material coarser and finer than 62 J.Lm at various 

locations in the reach between CRM 73.5 and 54.0. 

Although the data are sparse and partly estimated, 

several general conclusions can be made about the 

Suspended-sediment discharge data presented in disposition of suspended sediment in the Columbia 

table 1 have been arranged in table 5 to facilitate River. All suspended-sediment data suggest that, 

comparisons of suspended-sediment discharges of during the data-collection period, sediment was 

Jll 
scoured from the streambed immediately downstream from the mouth of the Cowlitz River (CRM 

68.0). It is not possible to determine from the data 

how far downstream the degradation occurred; 

however, a significant amount of sediment was 

scoured from the reach between CRM 68.0 and 

63.8, as evidenced by the consistently higher 

suspended-sediment discharges, on all days, at 

CRM 63.8 than at CRM 68.0 (table 5). Conversely, 

the general decrease in suspended-sediment discharges from CRM 63.8 downstream to CRM 54.0 

during the same period suggests that suspended 

matter was being deposited in that reach (table 5). 

Because the decrease in suspended-sediment 

discharge between CRM 63.8 and 54.0 is roughly 

half the increase between CRM 68.0 and 63.8, apparently the Columbia is capable of transporting 

the suspended sediment presently being discharged by the Cowlitz River, but it cannot sustain 

the seaward transport of the additional burden of 

the total amount of sediment scoured upstream 

from CRM 63.8. Although the Columbia River is 

capable of transporting all the suspended sediment 

now being supplied by the Cowlitz River, this 

might not be true if suspended-sediment inflow 

from the Cowlitz became significantly higher. 

The general absence of suspended sand at 

Cowlitz River mile 0.2 suggests that the quantity 

of bedload discharged into the Columbia River 

from the Cowlitz during the data-collection period 

was relatively small. Also, because hydraulic conditions are not greatly different, it seems unlikely 

that bedload discharges in the Columbia River 

upstream from CRM 68.0 would be substantially 

larger than those at CRM 54.0. For these reasons, 

the scour and fill sequence suggested by the 

suspended-sediment discharge data probably can 

be considered indicative of actual net degradation 

and aggradation. 

VERTICAL DISTRIBUTION OF SUSPENDED SEDIMENT 

Point-integrated suspended-sediment samples 

were collected at CRM 73.5, 63.8, and 54.0 (table 3) 

to provide information on whether the vertical 

distribution of suspended sediment downstream 

from the mouth of the Cowlitz River is unusual in 

any way because of the presence of deposited 

eruption-derived debris. The data were analyzed 

within the framework of conventional suspendedsediment theory. 

Under conditions of moderately steady flow, the 

vertical distribution of suspended sediment in a 

narrow size range can be approximately characterized by 

~: = ( d ~ y d ~a r (l) 

where 

Cy and Ca are the concentrations of suspended 

sediment in the size range at 

heights of y and a, respectively, 

above the streambed; 

d is the total depth of flow at the vertical; and 

Z is an exponent that theoretically 

equals VJk u. 

in which 

V s is the fall velocity of particles in the 

size range; 

k is the von Karman coefficient for turbulent exchange; and 

u. is the shear velocity. 

For any height, a, with a given distribution and 

total depth, Ca and (-a-)z are constants, 

d-a 

and equation 1 can be written as 

c,=K (d;yt (2) 

The exponent Z in equation 2 can be determined 

for measure distributions by plotting values of ey, 

defined from point-integrated samples collected at 

various heights, y, above the bed, against corresponding values of ( d- y)/y on logarithmiccoordinate graph paper; Z is the slope of the 

straight line defined by the points. Low values of Z 

result when the concentration of the size range is 

nearly uniform (constant) throughout the depth, 

and high values occur when the concentration is 

much higher near the bottom than it is near the 

surface. 

Data listed in table 3 for material finer than 62 

I-'m and coarser than 62 I-'m were used to compute 

values of Z (table 6). Because of generally low concentrations and tide effects, comparisons among 

data for different days and different locations are 

inconclusive. However, by comparing concentrations at CRM 73.5 at all levels throughout the 

depth with those at CRM 63.8 and 54.0 (table 3), it 

J12 
TABLE 5.-Longitudinal distribution of suspended-sediment discharges between Columbia River miles 73.5 and 54.0 during the 

period August 13-20, 1980 

[CRM, Columbia River mile] 

Discharges Discharge of sediment finer than 62 11m Discharge of sediment coarser than 62 11m Total discharge at specific Location or (tons per day) (tons per day) (tons per day) 

river miles reach 8-13 8-14 8-18 8-20 8-13 8-14 8-18 8-20 8-13 8-14 8-18 8-20 

CRM ________ 73.5 15,600 7,560 3,500 5,000 11,100 1,130 700 1,000 16,700 8,690 4,200 6,000 

Cowlitz RM ___ 0.2 2 11,500 310,000 4,100 7,800 2 1,300 31,100 0 0 2 12,800 311,100 4,060 7,800 4CRM _______ 68.0 4 17,100 4 17,600 47,600 412,800 42,400 42,200 4700 4 1,000 4 19,500 419,800 48,300 4 13,800 CRM ________ 63.8 24,700 18,500 29,500 13,000 2,500 2,700 2,400 3,100 27,200 21,200 31,900 16,000 

CRM 54.0 22,100 15,100 3,800 700 25,900 15,800 

Increase or (decrease) through the reach 

CRM 68.0-63.8 7,600 940 21,900 200 100 500 1,700 2,100 7,700 1,400 23,600 2,200 CRM 63.8-54.0 (2,600) (14,400) 1,300 (1,700) (1,300) (16,100) 

1 Estimated from measured discharges on 8-12 and 8-14. 2 Estimated from discharge at Cowlitz River mile 17.0 on 8-13 and available particle-size distributions at river mile 0.2. 3 Estimated from discharge at Cowlitz River mile 17.0 on 8-14 and available particle-size distributions at river mile 0.2. 4 Sum of discharges at CRM 73.5 and Cowlitz River mile 0.2. 

is evident that suspended-sediment concentrations 

downstream from the Cowlitz River are consistently higher than those upstream, even at times in the 

tidal cycle when flow conditions are much less 

dynamic downstream than they are upstream. The 

somewhat lower Z values, which occurred when 

shear velocities were low because of low velocities, 

suggest that the sizes of material in suspension at 

CRM 63.8 and 54.0 are not substantially different 

from those at CRM 73.5. 

LONGITUDINAL DISTRIBUTION OF BED MATERIAL 

Particle size statistics that characterize the size 

distribution of bed material finer than 2.0 mm (see 

table 4) are presented in table 7. In the table, particle sizes at specific percentiles and percentile 

ranges are expressed in millimeters; distribution 

statistics are given in phi notation. By definition, 

+= -log1 D 

(Krumbein, 1934) (3) 

or, more precisely, 

+= -log2 ( D ) 

1.0 mm 

(McManus, 1963) (4) 

where 

+ is particle diameter, in phi notation, and 

Dis particle diameter, in millimeters. 

Equation 4 relates phi and millimeter values, 

within the range from 0.062 to 4.00 mm, as 

follows: 

Phi 4 3 2 1 0 - 1 - 2 

Millimeters 0.062 0.125 0.250 0.500 1.00 2.00 4.00 

J13 

Use of phi notation facilitates comparison of 

particle-size distributions, because statistics are 

expressed in relative terms; that is, particles one 

phi unit apart are different in size by a factor of 2, 

regardless of whether the particles are large or 

small. Similarly, multiples of the deviation 

measure (comparable to standard deviation) express the number of times particles at a particular 

point in the size distribution are greater or smaller 

than the mean particle size. Distribution statistics, 

based on Inman's (1952) formulas, are as follows: 

Mean (M+) = 1

12( +16 + +s4) (5) 

Median (Md+)= +so (6) 

Sort or deviation measure (u.p = 1h(u16 - 4>84) (7) 

Skewness-Alpha 1 (a1

) = (M.p- Md.p) (8) O".p 

(9) 

where 

cpp is the phi value of the particle size for which 

p, percent of the analyzed material by weight, 

is finer. 

Values of these statistics for all bed-material 

samples are listed in the farthest right columns of 

table 7. 

Average M+ and o+ values for each measurement 

cross section along the Columbia River have been 

used to examine how the particle-size distribution 

of present (August 12-20, 1980) surficial bed 

material differs from that in the river, prior to the 

Mount St. Helens' eruption. Data collected in 

1962-63 (Haushild and others, 1966) and 1965 
TABLE 6.-Vertical distributions of suspended sediment at Columbia River cross sections as characterized by measured Z vcllues 

[CRM, Columbia River mile) 

Time Daily Cross Z value section Date (P.d.t., mean discharge 

(CRM) (1980) 2400 hours) (ftJ"/s) <62,..m >62,..m Flow condition 

73.5 ------- Aug. 12 _____ 1025 139,000 

73.5 ------- Aug. 18 _____ 1205 124,000 

73.5 ------- Aug. 20 _____ 1330 149,000 

63.8 ------- Aug. 13 _____ 1535 142,000 

63.8 ------- Aug. 20 _____ 1030 152,000 

54.0 ------- Aug. 13 _____ 1150 142,000 

54.0 ------- Aug. 18 _____ 1030 130,000 

54.0 ------- _____ do _____ 1328 130,000 

(Hubbell and Glenn, 1973) are plotted in figure 4 to 

represent pre-eruption conditions. None of the preeruption samples from CRM 64 and fewer than 15 

percent of the samples from CRM 59 or CRM 54 

contained particles coarser than 2.0 mm; hence, 

the data essentially are comparable with the data 

in table 7. Arbitrary lines, based on the preeruption data, are drawn to delimit the range in 

which M+ values would be expected to occur along 

the length of the Columbia between river miles 

106.4 and 14.0. Post-eruption data from table 7 

also are plotted in figure 4. 

Computed average M+ values of material 

presently in the river at measurement cross sections close to the Cowlitz River mouth generally lie 

outside the expected range (fig. 4) for pre-eruption 

conditions. Upstream, at CRM 70.0 and 69.2, the 

material appears to be significantly coarser (about 

0.8 phi unit) than the pre-eruption bed material. 

Immediately downstream from the confluence, 

there is an abrupt change in the mean particle size. 

M+ increases, roughly, from 1.0 to 2.3, which indicates that the mean size of present bed material 

downstream from the confluence is less than half 

the mean size of material upstream from the confluence (0.20 mm compared to 0.50 mm). Material 

downstream from the confluence is roughly 0.5 phi 

unit finer than pre-eruption material in that reach. 

Whereas material in the navigational channel 

generally is coarser than that on the marginal 

slopes and adjacent flats, the reduction in mean 

size at CRM 63.8 from pre-eruption material is 

fairly consistent over the entire width (see Hubbell 

and Glenn, 1973, p. L53). The increase in fine 

material downstream from the confluence probably is due to the continual influx of significant 

amounts of fines from the Cowlitz River, as well as 

the presence of remnant material from the mud0.03 0.13 Strength of flow during strong ebb. 

.10 .12 About 1 h before strength of flow on fairly 

weak ebb. 

.11 .24 Beginning of ebb flow on a weak ebb. 

.01 -.16 Beginning of floodflow. 

.04 .15 End of weak floodflow. 

.03 .07 About 11

/z h after strength of flow on strong 

ebb. 

.12 .04 About 1 h before strength of flow on fairly 

weak ebb. 

.07 .19 Do. 

flow. The slight downstream decrease in size between CRM 67.0 and 63.8 suggests that fine 

material being entrained immediately downstream 

from CRM 68.0 (see table 5) may be depositing in 

the vicinity of CRM 63.8 and downstream from 

that point. 

Average o+ values at all cross sections except 

CRM 63.8 show that the relative range of particle 

sizes finer than 2.0 mm included in the present bed 

material is virtually the same as it was in the past, 

even though M+ values are different. At CRM 63.8, 

the material in the north half of the channel is composed of an unusually wide range of particle sizes. 

SPECIFIC GRAVITY AND SHAPE FACTOR OF POSTERUPTION BED MATERIAL 

Because of the large quantities of debris that 

were created through violent explosion and pyroclastic activity, the potential existed for much of 

the sediment delivered by the Cowlitz River to the 

Columbia to be substantially more angular and of a 

different specific gravity than normal Columbia 

River sediments. To ascertain differences between 

the "old" and "new" bed material, specific gravities 

were measured in the laboratory, and particleshape factors were estimated from empirical relations between fall and sieve diameters. 

SPECIFIC GRAVITY 

Specific gravities of selected samples were determined by the standard pycnometer procedure 

(American Society for Testing and Materials, 

1969). In this procedure, specific gravity (sp gr), is 

computed from 

J14 
TABLE 7.-Particle-size statistics of surficial bed material finer than 2 mm from the Columbia, Cowlitz, and Toutle Rivers 

Geometric-mean size of particles in different 

percentile ranges, expressed in terms of sieve (S) Shape factor of Fall diameter at indicated 

Date Lateral and fall (F) diameters, in millimeters particles in indicated percentile, 

(1980) position1 10-20 45-55 80-90 percentile ranges in millimeters Inman values, in phi units 

s F s F s F 10-20 45-55 80-90 35 50 65 Mean Sort Alpha 1 Alpha 2 

Columbia River mile 106.4 

Sept. 17 ----'----- 10 0.202 0.205 0.342 0.311 0.513 0.497 0.64 0.52 0.76 0.271 0.311 0.358 1.66 0.58 -0.04 -0.26 

30 .268 .237 .403 .319 .657 .544 .35 .30 .61 .285 .319 .360 1.48 .57 -.29 -.50 

50 .322 .311 .505 .466 .903 .697 .62 .67 .63 .388 .466 .544 1.11 .55 .00 -.08 

70 .264 .269 .442 .418 .745 .624 .69 .67 .66 .361 .418 .484 1.28 .57 .04 .09 

90 .223 .264 .456 .465 1.160 .703 >1.00 .83 .46 .360 .467 .553 1.21 .67 .17 .20 

Columbia River mile 73.5 

Aug. 12 _________ 5 .214 .207 .284 .244 .373 .309 .52 .30 .35 .230 .244 .264 1.99 .27 -.17 -.30 

20 .069 .055 .127 .116 .245 .242 .61 .088 .116 .155 3.12 1.04 .01 -.06 

30-35 .194 .163 .274 .211 .379 .279 <.30 <.30 <.30 .193 .211 .231 2.23 .36 -.05 -.14 

40 .008 .133 .035 .286 .262 .47 .019 .029 .187 4.40 2.45 -.30 -.04 

45 .251 .338 .452 .464 .777 .619 >1.00 .84 .62 .414 .464 .518 1.13 .41 .04 .08 

50 .201 .199 .267 .246 .365 .315 .57 .46 .43 .228 .246 .269 2.00 .31 -.07 -.30 

70 .221 .233 .325 .328 .613 .576 .78 .72 .77 .288 .328 .393 1.46 .62 -.25 -.37 

85 .248 .234 .526 .310 1.286 .427 .49 <.30 <.30 .279 .310 .345 1.66 .41 -.06 -.20 

95 .187 .203 .264 .283 .569 .516 .90 .86 .68 .245 .283 .330 1.66 .62 -.27 -.66 

Columbia River mile 70.0 

Aug. 12 _________ 5 .237 .219 .373 .306 .652 .540 .43 .33 .61 .274 .307 .342 1.60 .56 -.20 -.82 

10 .321 .286 .503 .463 .892 .784 .45 .67 .78 .380 .463 .561 1.08 .69 -.05 -.12 

20 .317 .357 .544 .528 1.039 .778 >1.00 .79 .65 .458 .528 .608 .93 .53 .oo -.06 

35 .213 .252 .457 .529 1.192 .856 >1.00 > 1.00 .65 .392 .529 .630 1.13 .87 .24 .17 

50 .271 .291 .567 .547 1.260 .939 .87 .79 .69 .436 .547 .667 .93 .80 .07 .12 

75 .355 .325 .771 .618 1.376 1.016 .55 .62 .71 .513 .618 .745 .79 .79 .12 .13 

Columbia River mile 69.2 

Aug. 12 _________ 5 .286 .283 .438 .406 .738 664 .65 .64 .76 .348 .406 .477 1.21 .58 -.15 -.32 

15 .287 .380 .510 .890 1.110 1.271 >1.00 > 1.00 >1.00 .597 .899 1.073 .52 .84 .43 .53 

25 .263 .318 .472 .551 .968 .864 >1.00 >1.00 .82 .455 .551 .648 .93 .68 .10 .08 

45 .298 .308 .740 .589 1.347 .896 .76 .60 .61 .505 .589 .685 .91 .72 .20 .38 

55 .433 .416 .741 .621 1.186 .875 .69 .66 .67 .549 .622 .704 .72 .50 .07 .19 

65 .318 .290 .711 .553 1.347 .940 .49 .55 .66 .447 .554 .672 .93 .80 .09 .20 

75 .275 .257 .484 .389 1.127 .756 .50 .43 .56 .323 .389 .515 1.20 .74 -.23 -.39 

95 .370 .362 .739 .591 1.316 .863 .68 .61 .59 .515 .591 .678 .84 .59 .13 .17 

95 .437 .478 .775 .661 1.299 .890 1.00 .69 .63 .593 .661 .736 .60 .41 .00 .14 

Columbia River mile 67.0 

Aug. 12 _________ 5 0.021 0.075 0.062 0.106 0.116 1.00 0.046 0.063 0.079 4.25 1.10 0.22 0.88 10 .247 .213 .458 .347 .906 .593 .30 .30 .44 .294 .346 .418 1.49 .69 -.06 -.09 

20 .178 .191 .245 .261 .422 .435 .84 .83 .84 .230 .259 .312 1.80 .56 -.26 -.72 30-50 .165 .180 .222 .246 .304 .332 1.00 1.00 1.00 .220 .246 .275 2.03 .42 .02 -.08 60-80 .202 .192 .285 .247 .382 .316 .46 .33 .36 .225 .247 .270 2.02 .34 .01 .00 

90 .148 .177 .202 .237 .263 .325 >1.00 >1.00 >1.00 .215 .237 .264 2.05 .40 -.07 -.03 95 .074 4.14 .34 -.19 -.89 95 .080 .082 .179 .181 .262 .249 .62 .53 .150 .182 .203 2.78 .73 .44 .66 

95 .012 .035 .082 .079 .025 .035 .046 5.01 1.27 .14 .41 

Columbia River mile 63.8 

Aug. 13 --------- 10 .075 .081 .107 .109 .155 .154 .54 .54 .100 .109 .121 3.16 .43 -.08 -.34 20 .116 .148 .331 .331 .751 .724 >1.00 .70 .86 .238 .332 .456 1.62 1.09 .02 -.08 30 .161 .173 .262 .267 .446 .405 .85 .69 .61 .232 .267 .304 1.92 .56 .02 -.13 40 .138 .147 .396 .375 .736 .548 .80 .65 .50 .306 .375 .425 1.81 .89 .44 .49 50 .034 .157 .435 .121 .157 .271 2.65 1.41 -.02 1.22 

60 .099 .208 .650 .138 .198 .353 1.99 1.30 -.27 -.26 80 .250 .205 .449 .458 .801 1.032 <.30 .83 >1.00 .365 .458 .618 1.11 1.15 -.02 .12 90 .007 .015 .038 .012 .015 .022 5.89 1.12 -.15 .45 

Cowlitz River mile 0.7 

Aug. 12 --------- 5 .012 .021 .029 .190 .021 .024 5.64 .53 .12 2.40 50 .005 .012 .021 .010 .013 .016 6.50 .93 .20 .80 

Cowlitz River mile 0.9 

Aug. 11 --------- 50 .016 .070 .046 .108 .086 .034 .046 .063 4.72 1.14 .25 .49 

Cowlitz River mile 4.2 

Aug. 11 _________ 15 .082 .080 .165 .157 .233 .277 .41 .56 .122 .157 .188 2.84 .67 .24 .49 20 .202 .310 .371 .773 .739 >1.00 .85 .286 .363 .521 1.37 .89 -.10 .60 60 .211 .254 .506 .497 1.083 .742 >1.00 .79 .57 .395 .505 .580 1.19 .73 .28 .44 

J15 
TABLE 7. -Particle-size statistics of surficial bed material finer than 2 mm from the Columbia, Cowlitz, and Toutle RiversContinued 

Geometric-mean size of particles in different percentile ranges, expressed in terms of sieve (S) Shape factor of Fall diameter at indicated Date Lateral and fall (F) diameters, in millimeters particles in indicated percentile, 

(1980) position1 10-20 45-55 80-90 percentile ranges in millimeters Inman values, in phi units 

s F s F s F 10-20 45-55 80-90 35 50 65 Mean Sort Alpha 1 Alpha 2 

Cowlitz River mile 9.6 

Aug. 11 _________ 30 0.065 0.116 0.173 0.177 0.320 0.314 0.65 0.65 0.151 0.175 0.216 2.40 0.67 -0.18 -0.29 

70 .114 .064 .194 .145 .284 .232 <.30 .30 .125 .145 .168 3.09 .92 .32 .70 

Cowlitz River mile 13.5 

Aug. 11 --------- 99 .146 .121 .203 .181 .269 .419 <.30 .30 > 1.00 .158 .181 .212 2.13 .83 -.41 -.63 

Cowlitz River mile 29.9 

Aug. 11 _________ .141 .158 .242 .252 .356 .334 1.00 .75 .60 .219 .253 .280 2.10 .49 .23 .62 

Toude River mile 6.5 

Aug. 11 _________ 33 .224 .222 .460 .332 1.074 .704 .60 .30 .50 .290 .332 .422 1.35 .78 -.31 -.46 67 .203 .239 .415 .396 1.056 .697 > 1.00 .67 .51 .330 .396 .470 1.31 .73 -.04 -.21 

North Fork Toude River mile 1.2 

Aug. 11 _________ 16 & 84 .364 .388 .704 .604 1.220 .852 .88 .67 .63 .533 .604 .684 .79 .53 .12 .21 

50 .306 .383 .574 .609 1.272 .953 >1.00 1.00 .70 .518 .609 .716 .73 .62 .02 -.02 

South Fork Toude River mile 0.0 

Aug. 11 _________ .110 .013 .327 .191 1.018 .607 <.30 .37 .088 .193 .341 3.40 2.63 .38 .72 

.107 .138 .321 .264 .995 .441 >1.00 .30 < .30 .221 .264 .312 2.00 .77 .10 -.13 .145 .085 .261 .259 .479 .714 .63 > 1.00 .160 .250 .513 1.99 1.47 -.01 .15 

1 Relative distance from left bank (looking downstreams), expressed as percentage of full width. 

where 

Ws is dry weight of sediment introduced into 

the pycnometer, 

W w is weight of distilled water at temperature, T, required to fill the 

pycnomete:r:, 

w m is weight of the water-sediment mixture 

at temperature, T, in the filled pycnometer. 

Material coarser (by sieving) than 2.0 mm was excluded from the specific gravity determinations as 

it had been from the particle-size analyses. The 

purpose of rejecting this material was to eliminate 

large lightweight pumice particles and other erratics. Visual observation of the samples revealed 

that pumice particles coarser than 2. 0 mm occurred in random quantities, and that many 

samples contained no pumice particles of that size. 

Results of the specific-gravity determinations 

are given in table 8. With the exception of several 

samples that visibly contained fine pumice (see 

"Remarks" in table 8), measured specific gravities 

of bed material from the Columbia River at anstl 

below CRM 73.5 averaged 2.63 and had a standard 

deviation of 0.07. Similar specific gravities were 

measured for the bed material in the Cowlitz and 

Toutle Rivers. Interestingly, the two suspendedsediment samples that were analyzed had lower 

specific gravities of about 2.57 (table 8). On the 

basis of these determinations, it seems that the 

specific gravity of Columbia River bed material 

finer than 2.0 mm has not changed significantly, 

and a nominal value of 2.65 can be used to 

characterize the bottom sediments in the Columbia, lower Cowlitz, and lower Toutle Rivers. 

The validity of computing shape factors in this 

manner is contingent on the accuracy of figure 5 

and the extent to which the following conditions 

are satisfied: 

1. The specific gravity of individual particles 

equals 2.65. 

2. The "ordered" position of each particle relative 

to every other particle is exactly the same 

whether ordering is based on standard fall 

velocity, which establishes the fall diameter, 

or on controlling cross-sectional area, which 

establishes the sieve diameter. That is, the 

particle having the lowest standard fall velocity (smallest fall diameter) also has the 

smallest controlling cross-sectional area 

(smallest sieve diameter), the particle with 

the second smallest fall diameter has the second smallest sieve diameter, and so forth. 

When condition 2 is satisfied, the same particles 

are in the same relative weight ranges, regardless 

of the method of analysis. Because of this 

equivalency within any selected relative weight 

range, representative fall and sieve diameters for 

any range can be used with the relations in figure 5 

J16 
~ 

...... 

-.::] 

en 

E-o 

~ 

s 

p., 

~ 

"'-I 

Cl:: 

~ 

~ "'-I 

:.:E 

~ 0.4 

~ 

> 1:5 0.2 

~ E= 

< E-o 

0 

z 

~ 

~ 

1 

"'-I 

N 

v:; 

~ "'-I 

:::s 

4.0 

0 

0 

10 

0 0 

0 

0 0 

EXPLANATION 

Pre-eruption (Haushild and others, 1966) 

Pre-eruption (Hubbell and Glenn, 1973) 

Post-eruption (Table 7) 

0 

0 

0 

0 

______ --------oo----f------------

-* • -------------

i 

• 

0 0 

0 

0 0 0 ___3-.------------- 0 

50 

COLUMBIA RIVER MILE 

70 

EXPLANATION 

A Pre-eruption (Haushild and others, 1966) 

0 Pre-eruption (Hubbell and Glenn, 1973) 

e Post-eruption (Table 7) 

-- limits of expected range prior to eruption 

80 100 

FIGURE 4.-Variation of bed-material particle-size statistics between Columbia River miles 106.4 and 14.0 for pre- and post-eruption periods. 

1.0 

I ~-- gz 

"'-I 

E-o 

"'-I 

:::s 

::J 

...l 

:i 

~ 

~ N 

v:; 

z 

< "'-I 

:::s 
TABLE 8. -Specific gravity of Columbia, Cowlitz, and Toutle were not met in all samples, because some comRiver sediments puted shape factors were unrealistically low (less 

[Type of material: BM, bed material; SS, suspended sediment] than 0.3) or impossibly high (greater than 1.0). 

River Lateral Type of Specific River mile position1 material gravity Remarks PARTICLE-SHAPE FACTORS 

Columbia __ 106.4 10 BM 2.58 

106.4 30 BM 2.68 Shape factors were estimated for all samples of 

106.4 50 BM 2.64 bed material collected from both the unaltered part 

73.5 30 BM 2.61 (CRM 106.4) and the affected part (downstream 

73.5 40 BM 1.62 Fine pumice from CRM 73.5) of the Columbia River. Estimapresent. 

73.5 tions were made using the fall-diameter distribu- 50 BM 2.70 

tion for each sample, as defined by VA analysis; 70.0 40 BM 1.58 Fine pumice the sieve-diameter distribution for the same sampresent. 

ple, as defined by sieve analysis; and the empirical69.2 25 BM 2.64 ly defined relationships graphed in figure 5. In 69.2 55 BM 2.63 

69.2 65 BM 2.10 Fine pumice these relationships, the shape factor, S .F., of a parpresent. ticle is defined as: 

69.2 75 BM 2.55 

67.0 20 BM 2.65 S.F.=cl~ (11) 

67.0 50 BM 2.69 where 67.0 60 BM 2.67 

67.0 90 BM 2.66 a is length of the longest axis, 

63.8 40 BM 2.58 b is length of the intermediate axis, and 

63.8 50 BM 2.73 c is length of the shortest of the three mu63.8 60 BM 2.48 tually perpendicular axes of the particle. 

Cowlitz ____ .9 50 BM 2.69 For the analysis, geometric-mean fall diameters 

4.2 20 BM 2.66 and sieve diameters of particles in the 10-20, 

9.6 30 BM 2.68 45-55, and 80-90 percentile ranges (by weight) 

were determined from the size distributions de- 9.6 40 BM 2.63 

fined by VA analysis and sieving; computed geo- 13.5 99 BM 2.72 metric-mean sizes for each sample are listed in 13.5 99 BM 2.66 table 7. Fall and sieve diameters for each percent29.9 1 BM 2.63 ile range were used, in turn, to estimate corToutle _____ 6.5 220 BM 2.68 responding shape factors from figure 5. No shape 

6.5 33 BM 2.64 factor was determined for a percentile range, if 

6.5 67 BM 2.55 either the fall or sieve diameter (or both) was less 6.5 290 BM 2.58 

than 0.1 mm because of the insensitivity of the 

N. Fork relationships for small particles. Estimated shape Toutle ___ 1.2 16 BM 2.64 

1.2 50 BM 2.58 factors are listed in the center columns of table 7. 

1.2 ss 2.59 Approximately 60 percent of the shape factors are 

S. Fork between 0.5 and 0.8. 

Toutle ___ 0.0 1 BM 2.73 In addition to verifying that condition 1 was 

0.0 99 BM 2.76 generally satisfied (specific gravities were close to 0.0 ss 2.55 2.65), an effort was made, by an independent 1 Relative distance from left bank (looking downstream), expressed as percentage method, to confirm that condition 2 also was of full width. 

2 No particle-size analysis. reasonably well satisfied. Four different samples, 

two from the Columbia River and one each from 

to estimate a shape factor, provided condition 1 the Cowlitz and Toutle Rivers, that had been realso is satisfied. In reality, of course, neither of tained as size-range separates following routine 

these conditions is completely satisfied. However, sieve analysis of the sample, were reanalyzed by 

if the actual conditions are not too different from VA analysis. For each analyzed size range, a 

those that existed for the sediment used to define geometric-mean sieve diameter was determined 

figure 5, estimated shape factors should be fairly from the upper and lower sieve sizes of the range, 

reliable. It is obvious that the governing conditions and a geometric-mean fall diameter was deterJ18 
n~ ~ 7 ~ l ? ~ 4 ~ ~ ? 8 2 3 ~ ~ ~ 7 ~ 

e 

e 

c 

-

CD 

> CD 

u; 

0 

I 

.I 

I 

--

-· 

--

·: 

' 

.. 

...... 

l 

F: . . 0 

.05 

~ 

fi+iffff+f 

[,1~ 

(.1~ 

t- rA~ 

~ 

0.1 

Wit ~ 

~7 

~6 

5 

4 

3 

2 

If 

,, 17~ 

1/LI i 

.)[/ 

v I ~1 

~8 

~7 

~6 

~5, 

I 4 

~3 

~2 

fH-ffif.ll 

I i 1 

ls 

~7 

6 

5 

10 

Fall diameter, in m m 

FIGURE 5.-Relations between sieve and fall diameters of naturally worn quartz (sp gr = 2.65) particles for different shape factors 

mined from the largest and smallest fall diameters 

defined from the VA analysis. The two geometricmean diameters for each defined size range were 

used to obtain a shape factor from figure 5. These 

shape factors, in turn, were compared with shape 

factors given in table 7 for the same sample. 

Because particle sizes represented in the individual 

size separates did not necessarily coincide closely 

with sizes represented by the percentile ranges 

listed in table 7, only nine computed shape factors 

were truly comparable to values in the table. The 

purpose of the comparisons was to determine if 

shape factors computed from the entire sample 

(S.F. -1 values), under the assumption that condition 2 was satisfied, agreed with shape factors 

computed from size separate data (S.F. -2 values) 

for which condition 2 was known to exist. 

Statistical analysis of seven possible comparisons from the Columbia and Cowlitz River 

samples indicates a correlation coefficient of 0. 71 

J19 
between S.F. -1 and S.F. -2 values and a standard error of estimate of S.F. -1 values of 0.18. 

When two possible comparisons from the Toutle 

River sample are included, the correlation coefficient decreases to 0.53. On the basis of this test 

and the assumption that higher correlations would 

have been achieved with more observations and exactly comparable shape factors, it seems 

reasonable that most shape factors determined for 

the Columbia and lower Cowlitz Rivers that lie in 

the interval, 0.3-1.0, will be within about ±0.2 of 

the actual shape factor defined by figure 5. 

Shape factors listed in table 7 have been combined to summarize the shape-factor data at each 

cross section. In this process, shape factors less 

than 0.3 and greater than 1.0 were rejected on the 

basis that one or both conditions which were required to relate fall and sieve diameters to the 

shape factor probably had not been satisfied. 

Shape factors within the range 0.3 to 1.0 were 

assumed to be valid, although subject to error. The 

mean and standard deviation of individual shape 

factors for each cross section and percentile range 

are given in table 9 with the number of values, N, 

in each statistic. Because differences between fall 

and sieve diameters due to particle shape become 

more pronounced as size increases (fig. 5), shape 

factors for the 80-90 percentile range probably are 

the most reliable. 

Uniformity in mean values between sections and 

the fairly large standard deviation for each section 

suggest that there is substantially more variability 

in shape factors (or specific gravities) within each 

cross section than between cross sections, including the cross section at CRM 104.6. Hence, for 

such considerations as one-dimensional sedimenttransport computations and dredging or earthwork determinations involving bulk density, it appears that no corrections are needed to account for 

unusual particle shapes or substantially different 

specific gravities of the sediment in the reach from 

CRM 106.4 to CRM 63.8, except possibly for sediment in the vicinity of CRM 67.0, where variability 

of the data is too large to allow any reliable conclusion. 

CONCLUSIONS 

Lesser suspended-sediment discharges at CRM 

68.0 than at CRM 63.8 during the data-collection 

period (August 11-20, 1980) indicate that the bed 

of the Columbia River immediately downstream 

from the mouth of the Cowlitz River (CRM 68.0) 

J20 

TABLE 9. -Summary statistics of bed-material shape factors at 

Columbia River cross sections 

[SD, standard deviation; N, number] 

Percentile range 

Columbia 10-20 45-55 80-90 

River mile Mean SD N Mean SD N Mean SD N 

106.4 ------ 0.58 0.15 4 0.60 0.20 5 0.62 0.11 5 

73.5------ .65 .18 5 .64 .25 5 .56 .15 7 

70.3------ .58 .20 4 .64 .19 5 .68 .06 6 

69.2------ .68 .17 7 .60 .09 7 .66 .09 8 

67.0------ .65 .33 4 .62 .31 5 .70 .29 6 

63.8------ 2 .68 .10 5 .63 .16 4 

was degrading; greater discharges at CRM 63.8, 

than at CRM 54.0, suggest that some of the 

scoured material is redeposited downstream from 

CRM 63.8. 

Suspended-sediment concentrations are greater 

throughout the total depth at locations downstream from CRM 68.0 than they are upstream 

from that point, even during times in the tidal cycle 

when the flow is relatively quiescent, which suggests that most of the suspended sediment is very 

fine. 

Lightweight pumice particles larger than 2.00 

mm are distributed randomly throughout the bed 

material in the Columbia River near the mouth of 

the Cowlitz River. Most of the pumice has a 

physical size larger than 2.0 mm. Samples having a 

high percentage of particles coarser than 2.0 mm 

invariably had several very large pumice particles. 

The present (August 1980) areal distribution and 

size gradation of pumice probably is temporarily 

due to its extreme mobility and its susceptibility to 

fracturing. 

On the basis of particle-size analyses by the VA 

method of sieved material finer than 2.0 mm, the 

mean size of the bed material immediately 

upstream from the Cowlitz River mouth seems to 

be significantly coarser than it was before the 

eruption. Downstream from the mouth, the mean 

size decreases abruptly across the full width of the 

Columbia River. At CRM 67 .0, the mean size was 

less than half of what it was at CRM 70.0 and 69.2 

and somewhat less than the mean size of preeruption bed material. At CRM 63.8, the mean was 

even finer than at CRM 67 .0. Progressive 

downstream decrease in the size of the bed 

material further suggests that material entrained 

immediately below the mouth of the Cowlitz may 

begin redepositing several miles downstream. In 

the bed material of the Columbia River, the 

relative spread of particle sizes finer than 2.0 mm 

about the mean, as indicated by Sort values (phi 
notation), is essentially the same as it was prior to 

the eruption. 

Specific-gravity determinations of bed material 

finer than 2.0 mm that was sampled at and 

downstream from CRM 73.5 averaged 2.63 and 

had a standard deviation of 0. 07. From these determinations, it seems that the specific gravity has 

not changed significantly from pre-eruption conditions and that 2.65 can be taken as a nominal 

specific-gravity value. 

Shape factors determined by an indirect means 

indicate that variations in the shape of bedmaterial particles are much greater within a cross 

section than among different cross sections 

throughout the reach of the Columbia River from 

mile 106.4 to mile 63.8. Similarities in shape factors of material from CRM 106.4 and from cross 

sections downstream of CRM 73.5 imply that there 

are no large differences between the shape of preand post-eruption surficial bed material. The majority of shape factors are between 0.5 and 0.8. 

Reasonable uniformity in the specific gravity of 

bed material finer than 2.0 mm and in mean shape 

factors from one cross section to another suggests 

that, for one-dimensional sediment transport computations and gross dredging or earthwork 

estimates involving bulk density, no corrections 

need to be made for unusual bed-material properties. 

Sediment-transport and channel conditions 

observed during the 9-day, mid-August, 1980, 

data-collection period of this investigation can be 

expected to change as the Columbia, Cowlitz, and 

Toutle River systems, aided by man's dredging and 

river maintenance activities, tend toward a new 

quasi-equilibrium (sedimentation regime). Additional data, similar to the data in this report, collected periodically could be used to assess the rate 

of change. 

REFERENCES CITED 

American Society for Testing and Materials, 1969, Standard 

method of test for specific gravity of soils: American National Standards Institute, 19, designation D 854-58. 

Bechly, J. F., 1980, Mt. Saint Helens eruption, restoration of 

Columbia and Cowlitz River channels: Technical paper 

presented at Texas A&M University dredging seminar, U.S. 

Army Corps of Engineers, Portland, Oreg., 52 p. 

Cummans, John, 1981, Mudflows resulting from the May 18, 

1980, eruption of Mount St. Helens, Washington: U.S. 

Geological Survey Circular 850-B, 16 p. 

Findley, Rowe, 1981, St. Helens, mountain with a death wish: 

National Geographic, v. 159, no. 1, p. 3-33. 

Guy, H. P., 1969, Laboratory theory and methods for sediment 

analysis: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. C1, 58 p. 

Haeni, F. P., 1982, Sediment deposit in the Columbia and lower Cowlitz River, Washington-Oregon, due to the May 18, 

1980, eruption of Mount St. Helens: U.S. Geological Survey 

Circular 850-K [in -press]. 

Haushild, W. L., and others, 1966, Radionuclide transport in ~he 

Pasco to Vancouver, Washington, reach of the Columbia 

River, July 1962 to September 1963: U.S. Geological Survey 

open-file report, 188 p. 

Hubbell, D. W., and Glenn, J. L., 1973, Distribution of radionuclides in bottom sediments of the Columbia River estuary: 

U.S. Geological Survey Professional Paper 433-L, 63 p. 

Hubbell, D. W., Glenn, J. L., and Stevens, H. H., Jr., 1971, 

Studies of sediment transport in the Columbia River 

estuary: Technical Conference on Estuaries of the Pacific 

Northwest, Oregon State University, Corvallis, Oreg., 

1971, Proceedings Circular 42, p. 190-226. 

Inman, D. L., 1952, Measures for describing the size distribution of sediments: Journal of Sedimentary Petrology, v. 22, 

no. 3, p. 125-145. 

Inter-Agency Committee on Water Resources, 1957, Some fundamentals of particle-size analysis, rept. 12, in A study of 

methods used in measurement and analysis of sediment 

loads in streams: U.S. Government Printing Office, 1958, 

55 p. 

Krumbein, W. C., 1934, Size frequency distributions of sediments: Journal of Sedimentary Petrology, v. 4, no. 2, p. 

65-77. 

McManus, D. A., 1963, A criticism of certain usage of the phinotation: Journal of Sedimentary Petrology, v. 33, no. 3, p. 

670-674. 

Office of Water Data Coordination, 1978, National handbook of 

recommended methods for water-data acquisition, chapter 

3, Sediment: U.S. Geological Survey, Reston, Va, p. 3-1 to 

3-100. 

Stevens, H. H., Jr., Lutz, G. A., and Hubbell, D. W., 1980, Collapsible-bag suspended-sediment sampler: American Society of Civil Engineers Proceedings, Hydraulics Division 

Journal, v. 106, no. HY4, Technical Notes, p. 611-616. 

J21