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Bed load transport in a steep snowmelt-dominatedmountain stream as inferred from impact sensorsGeir Vatne; Øyvind Takøy Naas; Tommy Skårholen; Achim A. Beylich; IvarBerthling

Online Publication Date: 01 June 2008

To cite this Article: Vatne, Geir, Takøy Naas, Øyvind, Skårholen, Tommy,Beylich, Achim A. and Berthling, Ivar (2008) 'Bed load transport in a steepsnowmelt-dominated mountain stream as inferred from impact sensors', NorskGeografisk Tidsskrift - Norwegian Journal of Geography, 62:2, 66 — 74

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Bed load transport in a steep snowmelt-dominated mountain stream asinferred from impact sensors

GEIR VATNE, ØYVIND TAKØY NAAS, TOMMY SKARHOLEN, ACHIM A. BEYLICH & IVAR BERTHLING

Vatne, G., Naas, Ø.T., Skarholen, T., Beylich, A.A. & Berthling I. 2008. Bed load transport in a steep snowmelt-dominated

mountain stream as inferred from impact sensors. Norsk Geografisk Tidsskrift�Norwegian Journal of Geography Vol. 62, 66�74.

Oslo. ISSN 0029-1951.

The article reports results from bed load transport investigations using impact sensors in Vinstra, a steep snowmelt-dominated

mountain stream in Central Norway. The impact sensors proved able to detect thresholds for bed load entrainment. With increasing

discharges surpassing the threshold for entrainment, both the magnitude and variance in impact force increases, but also showing

differing rating relationships on rising and falling flows. Substantial bed load transport was only observed during the snowmelt-

dominated spring flood period and impact magnitude was observed on average to follow diurnal variations in discharge during the

spring flood event, but with a clockwise hysteresis relationship.

Keywords: bed load entrainment, impact sensors, mountain stream

Geir Vatne, Øyvind Takøy Naas, Tommy Skarholen, Achim A. Beylich, and Ivar Berthling, Department of Geography, Norwegian

University of Science and Technology (NTNU), NO-7491 Trondheim, Norway. E-mail: geir.vatne@svt.ntnu.no; achim.beylich@svt.

ntnu.no; ivar.berthling@svt.ntnu.no; Achim A. Beylich also at Quaternary Geology and Climate Group, Geological Survey of Norway

(NGU), NO-7491 Trondheim, Norway. E-mail: achim.beylich@ngu.no

Introduction

Bed load transport in mountain streams is of crucial

importance as such streams are the main sediment sources

of lowland channels and exhibit extremely variable sediment

transport depending on the magnitude of events. Measured

under comparable conditions of flow, rates of bed load

transport can differ by an order of magnitude, due to the

irregular nature of sediment movement (e.g. Emmet 1980;

Gomez & Church 1989). Bed load transport at a site

depends on factors such as local flow conditions, bed

material composition and amount of sediment supply from

upstream sources (Hassan & Woodsmith 2004). Further-

more, the magnitude of previous floods and external

sediment sources are important because they can greatly

modify sediment entrainment, transport processes, and the

storage of sediment (Lenzi et al. 2004). Large, irregular

deviations from mean rates of transport may be attributable

to sporadic inputs of sediment from hillslopes. Deeper

knowledge of the dominant dynamics of bed load transport

can improve river engineering management and hazard

mitigation projects.

A wide range of field methods has been developed to

measure bed load transport rates. These include sampling

using either hand-held traps or pit traps, measuring the

entire load on slot traps or settling ponds, tracking grain

movement with tracer gravel, and constructing a local

sediment budget from volumetric changes in stream beds

(e.g. Wilcock 2001). The accuracy of bed load transport

measurements is often doubtful (Duizendstra 2001) and

many methods require considerable labour input and are

difficult to carry out at high flows, thus the full range of flow

conditions cannot be sampled (Church et al. 1991). Hence, it

is argued that many of the methods developed to date do not

fulfil the criteria of obtaining a true empirical relationship

between water discharge and sediment transport, as a large

number of samples are needed over a complete range of

flows (Wilcock 2001). Consequently, there has been a

continuous search for improved methods for measuring

bed load transport rates.

In recent years promising studies have been conducted

using motion-sensing radio transmitters (Habersack 2001;

McNamara & Borden 2004) and impact sensors placed on

the stream bed (Richardson et al. 2003; Reid et al. 2007)

to obtain high resolution temporal data on bed load

transport without having to carry out work in the stream

during high flows. In this study we used impact sensors

that record the maximum acceleration produced by

impacting bed load particles during a predetermined

sampling interval. The main aim was to further elaborate

on the potential of impact sensors in bed load transport

studies to improve our understanding of the complex

relation between discharge and bed load transport in steep

mountain streams.

Study area

The study was conducted in Vinstradalen, a mountain valley

in the Dovre Mountains, Central Norway (Fig. 1). Vinstra

can be classified as a steep headwater stream with channel

slopes varying between 0.03 and 0.07 m m�1. According to

Montgomery & Buffington’s (1997) scheme, the channel

form assessed visually varies between plane bed, riffle-pools,

step-pools, and cascades. Discharge is strongly seasonal,

with snowmelt-dominated spring floods producing sustained

high discharge for several weeks. Summer discharge is

characterized by low flows interrupted by flash floods

following thunder storms.

In August 2003, the area received c.200 mm precipita-

tion within 48 hours, causing a flood with an estimated

recurrence interval of between 100 and 200 years (NVE

Norsk Geografisk Tidsskrift�Norwegian Journal of Geography Vol. 62, 66�74. Oslo. ISSN 0029-1951

DOI 10.1080/00291950802094817 # 2008 Taylor & Francis

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2003). The flood damaged the railway and the main road

connecting Central and Southern Norway. Massive slope

destabilization followed the precipitation event, and more

than 50 debris flows were triggered, delivering in the order

of 8900 m3 of sediment to the stream channel (Onsøyen

2005). The present study is part of a series of investiga-

tions to study the effect and consequences of this extreme

event on hillslope-channel coupling and fluvial sediment

transport.

The Vinstra valley follows a fault zone which divides the

valley into two geologically distinct zones. Ordovician-

Silurian greywacke, siltstone and clay schist’s dominate

the eastern side of the stream, whereas less resistant

phyllites, mica-schists, and some garbenschists and gneisses

dominate the western side (NGU1). The schists produce a

high proportion of disc-shaped pebbles and cobbles which

are found in both the colluviums and the stream channel.

Steep valley slopes (in many places exceeding 358) with a

thick cover of till and colluviums cause extensive mass

wasting, with debris flows being a dominant process

causing extensive hillslope-channel coupling (Fig. 1). The

dominant control of river behaviour is thus the down-

stream variation in slope, bedrock and sediment supply

from mass wasting, which causes variations in bed load

transport, temporal sediment storage and channel mor-

phology.

The 75 m reach studied is located at 900 m a.s.l. and has

a drainage area of 25 km2. The channel is steep (: 0.06)

and consists of 11 steps and pool segments (Fig. 2) with

channel width varying from 7 m to 11 m. The stream

running between the steps contains pebbles and cobbles

with occasional boulders (D16 26 mm, D50 55 mm and

D85 mm, n�550). The bed has a high proportion of disc-

shaped particles (60%, n�118) with a densely packed

imbricated armouring layer. Steps are formed around key

stones with b axis ranging from 300 mm to 1300 mm,

which have not been observed to be mobilized since spring

2004. A few key stones seem to be large immobile colluvial

blocks.

Methods

A few previous studies have reported on the use of

continuous logging impact sensors that detect the number

of impacts on a steel plate fixed flush with the channel bed

after the plate is struck by a particle in motion (Richardson

et al. 2003; Reid et al. 2007). Impact sensors have previously

been found to be useful for studying the timing of sediment

entrainment and transfer cessation, and the relative inten-

sities of transport over time (Reid et al. 2007).

We used Gemini Tinytag Plus data loggers2 (TGP-0610) of

cubic dimensions 34�68�73 mm and weighing 140 g, to

measure the maximum acceleration caused by impacting

particles in a given sampling interval. The instrument

measures impacts along one axis from the lid to its base

using a piezoelectric sensor, and has a reading range of

0�100 g (980 ms�2) and a sensitivity and accuracy of 0.4 g

(3.5 ms�2), thus it is capable of measuring impacts of gravel

down to 10 mm (intermediate axis). The sensors were

mounted on aluminium plates of dimensions 150�150�2

mm that were perforated by 3�6 holes of 15 mm diameter.

The aluminium plates were then mounted on the upstream

side of boulders in the range 32�55 kg which were deployed

on the stream bed (Fig. 3). As bed load is commonly routed

along well-defined and narrow pathways within upland

rivers (Richardson et al. 2003), five sensors were deployed

along what was observed to be the thalweg over the reach at

flows less than 1 m3s�1. During the spring melt it was

observed that what was the thalweg during low flows was

not necessary the main sediment transport route during high

flows. The impact sensors were installed on 9 May 2007 and

were programmed to store the maximum acceleration at

one-minute intervals. The loggers were downloaded at least

every 11 days until 24 June, when the sensors were

reprogrammed to five-minute sample intervals which re-

quired downloading only every 50 days. No attempt has

been made to calibrate the impact sensors thoroughly as

only brief testing of their sensitivity has been carried out. In

the following discussion we are aware that any impact of a

given magnitude can be generated by a range of flows,

Fig. 1. An example of the high degree of coupling of the hillslope system with

the fluvial system in Vinstradalen following the 2003 extreme rainfall event.

Insert shows the location of Vinstradalen in the central mountains of Norway.

Fig. 2. Step-pool sequences in the upper part of the studied reach in Vinstra,

in the Dovre Mountains, Central Norway.

NORSK GEOGRAFISK TIDSSKRIFT 62 (2008) Bed load transport inferred from impact sensors 67

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particle shapes and particle sizes, and that there is probably

no straightforward relationship between impact magnitude

and particle size. Nevertheless, we argue that an overall

increase in mean impact magnitude reflects an increase in

average particle sizes impacting on the sensor. Moreover, as

the sensor is limited to recording impacts up to 1000 ms�2,

impacts at the upper end of the scale will be truncated, hence

influencing average values calculated from samples contain-

ing maximum values. It should also be emphasized that the

results from the impact sensors do not contain information

on the number of particles in transport, as only maximum

acceleration is measured. Thus, any large impact probably

masks a number of smaller impacts.

Stream stage was measured using a Global Water WL400

pressure transducer vented to the atmosphere to correct for

atmospheric pressure variations, and logged at 10-minute

intervals using a Campbell CR200 data logger. Stage was

converted to discharge using rating curves based upon the

salt dilution method due to the turbulent nature of the

channel.

Results

Figure 4 shows the seasonal hydrograph for 2007. Peak

discharge of 12.3 m3s�1 was recorded on the evening of 31

May after a steep rise in flow followed by several days of

sustained high flows showing pronounced diurnal cycles.

The summer was dry and discharge was characterized by

general flow recession from spring snowmelt and low flows

interrupted by a few substantial flash floods. Good quality

data from the impact sensors were obtained from 9 May

until 21 May, 6 June until 24 June, and from 31 July until 25

September, as at least one impact logger was working

properly and had not been moved by the flow. The impact

sensors only recorded sporadic and small impacts

(B30 ms�2) from when they were installed 9 May until 21

May. During peak spring flooding on 31 May all ‘impact

boulders’ were entrained and moved out of position, hence

reliable data do not exist for this event. The site was revisited

on 2 June and the impact boulders were relocated. During

the periods 9 May until 24 June and 31 July until 25

September, bed load transport was observed to take place

approximately 15% of the time, being concentrated in the

main snowmelt period, during which flows were substan-

tially higher than in any other period. Impact data are

lacking for the two substantial flash floods that occurred in

July, but some data exist from the recession following the

flood on 31 July exist from one of the sensors, showing

sediment transport as discharge at c.2 m3s�1. In the

following, the focus will be on the period 2�13 June, when

flow was high and good quality data for two impact sensors.

Figure 5 shows the flow hydrograph and impact magnitudes

for the two sensors that were stable during this period, with

parallel scatter plots for discharge�impact magnitude

(Fig. 6). The data strongly indicate limited bed load

transport for flows less than 1�2 m3s�1, in accordance

with the data from 1 August until 25 September which

hardly contained registered impacts for any sensor. The

number and magnitude of impacts recorded when flows

surpassed this threshold show a rapid increase in both

average impact magnitude for defined flow intervals and

impact standard deviation (Table 1). At flows exceeding

5 m3s�1, the number of sampling intervals without regis-

tered impacts is very low, suggesting continuous bed load

transport. An enveloping curve can be drawn for maximum

impacts recorded at any given discharge (Fig. 6). The

number of impacts near the enveloping curve is low, with

mean impact magnitude being less than one-third of the

maximum impact recorded at a given flow. Exemplified by

the diurnal flow cycle with highest relative discharge

variations, starting on 5 June (Fig. 7) an overall good

correlation between discharge and average impact magni-

tude is revealed, although the average impact magnitude is

generally higher on the rising stage (280 ms�2 sensor 5, 123

ms�2 sensor 3) than during the falling stage (147 ms�2

sensor 3, 48 ms�2 sensor 5). The data do, however,

demonstrate bed load transport to have a large stochastic

element, as impact magnitude varies by two magnitudes

when flow exceeds 4 m3s�1. Flow plotted against smoothed

impact force using a 60 minutes moving average (Fig. 8)

Fig. 4. Seasonal flow hydrograph at the study site in Vinstra 2007.

Fig. 3. The impact sensors mounted on boulders deployed on the stream bed.

The impact sensors were mounted on the downstream side of aluminium

plates :150 *150 mm perforated with 3�5 holes of 15 mm diameter. The

aluminium plate protruded 50 mm from the boulder. The boulders were

deployed with the aluminium plates installed flush with the stream bed.

68 G. Vatne et al. NORSK GEOGRAFISK TIDSSKRIFT 62 (2008)

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show a clockwise hysteresis for both sensors. The hysteresis

is less pronounced for discharges exceeding 7 ms�1.

Relation between discharge and bed loadtransport

We have examined the discharge�bed load transport

relationship in a gravel bed stream using impact magnitude

sensors mounted on large boulders deployed on the stream

bed’s upstream steps in a step-pool reach in a Norwegian

mountain stream. In an attempt to obtain high resolution

temporal variation in bed load transport, maximum impact

was logged every minute during the spring melt period when

discharge was observed to be highest.

The scatter plots of discharge�impact magnitude and the

calculated mean impact values for steps of 0.5 m3s�1

increase in discharge indicate a clear phase change for bed

load transport occurring at flows of :2 m3s�1 at these

specific reaches. As the sensitivity of the impact sensor is

sufficient to detect particles in the order of 10 mm

(intermediate axis) this phase change can be interpreted as

the threshold for incipient motion of bed load transport

having been surpassed. The significant increase in impact

magnitude with increasing flows and the parallel reduction

in number of sampling periods with no impacts recorded

clearly indicate increased bed load transport rates with

increasing flows. It also follows that if one accepts that

average impact magnitude is correlated with average particle

size, the data indicate size-selective transport over the range

of discharges observed.

These observations are in accordance with previous field

measurements that have identified bed load to take place in

two or three phases (Jackson & Beschta 1982; Andrews

1983; Ashworth & Ferguson 1989; Warburton 1992; Wil-

cock 1997). Phase 1 is found at low flows and is proposed to

consist of overpassing sand. Moving sand cannot be

registered by the impact sensors used in this study, hence

Fig. 5. Flow hydrograph and impact magnitude for two impact sensors (sensor 3, middle graph; sensor 5, lower graph) from 2�13 June, when diurnal flow cycles

were particularly well developed.

NORSK GEOGRAFISK TIDSSKRIFT 62 (2008) Bed load transport inferred from impact sensors 69

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phase 1 will occur at flows below the threshold for impact

registration, which in the case of Vinstra seem to be

:2 m3s�1. That sand and fine gravel is transported at

low flows in Vinstra is evident from observations of deposits

of fines in the lee of large boulders and in pools during low

flows (Fig. 9). Phase 2 is advocated to take place during

higher flows when coarser bed material is entrained. This

may indicate size-selective transport, which is well docu-

mented within reaches, along with observations that mean

travel distance of tracer gravel decreases with increasing

grain size (Church & Hassan 1992; Ferguson & Wathen

1998). Ashworth & Ferguson (1989) proposed a three-phase

model where phase one consists of overpassing sand, phase

two occurs at moderate flows when size-selective entrain-

ment and transport of local bed material occurs, and phase 3

occurs at the highest flows under conditions of equal

mobility. As the impact sensors did not work during peak

spring flow we cannot test Ashworth & Ferguson’s model,

but the lack of increase in mean impact magnitude on flows

exceeding 5 m3s�1, may indicate a phase 3 to have been

present, but where key stones in steps were not mobilized.

This is indicated by parallel tracer studies in which tracer

stones in excess of 20 kg were entrained during the peak

spring flood in 2007. Tracer cobbles with b axes in the range

Fig. 6. Scatterplots of discharge�impact magnitude for sensor 3 (upper image) and sensor 5 (lower image) with subjectively fitted enveloping curves.

70 G. Vatne et al. NORSK GEOGRAFISK TIDSSKRIFT 62 (2008)

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Table 1. Summary of impact statistics for the period 2�13 june 2007 for impact sensors 3 and 5, comprising 16,120 sampling periods. Q is discharge, Mean and Sd

are mean and standard deviation of impact force, and % zi is the percentage of sampling periods with no measured impact for the respective discharge interval;

# denotes the number of sampling periods within each discharge interval.

Impact sensor 3 Impact sensor 5

Q Mean Sd % zi Mean Sd % zi #

�8.0 147 98 2 361 167 0 40

7.5-8.0 108 114 3 359 165 0 70

7.0�7.5 99 111 13 347 182 0 150

6.5�7.0 117 100 3 320 175 0 100

6.0�6.5 143 111 0 341 169 0 109

5.5�6.0 126 97 2 212 108 0 230

5.0�5.5 100 81 2 193 108 0 802

4.5�5.0 76 70 9 146 100 2 1488

4.0�4.5 49 62 30 97 79 13 2400

3.5�4.0 35 72 53 63 64 24 5850

3.0�3.5 28 46 47 53 54 27 1930

2.5�3.0 18 23 29 49 56 32 1880

2.0�2.5 7 14 22 43 45 35 590

1.7�2.0 5 24 22 31 60 51 481

Fig. 7. Diurnal variations in flow and impact magnitude 5�6 June 2007 (sensor 3, upper graph; sensor 5, lower graph).

NORSK GEOGRAFISK TIDSSKRIFT 62 (2008) Bed load transport inferred from impact sensors 71

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329�441 mm had a recovery rate of 60% with a mean travel

length of 10.5 m (T. Skarholen, unpublished data).

Hysteresis effects is clearly present in the relation between

flow and impact magnitude during pronounced diurnal flow

cycles, as they show pronounced clockwise hysteresis loops

(Fig. 8). This result is similar to observations made using pit-

type sediment traps (Hassan & Church 2001) and motion-

sensing radio transmitters (McNamara & Borden 2004).

Hassan & Church (2001) showed that for certain discharges

sediment transport rates during rising stage were generally

higher than during falling stage, and that coarse material

mobilized and ceased motion much more abruptly than fine

material. However, they did not find the same pattern for

high flows. McNamara & Borden (2004), on the other hand,

showed that rocks were two to seven times more likely to

move on rising hydrograph limbs than on falling hydrograph

limbs. In Vinstra it is also evident that the largest difference

in impact magnitude for rising and falling flows occurs on

Fig. 8. Clockwise hysteresis loops in discharge�impact magnitude relationship of two independent impact sensors (filled circles � sensor 3, open circles � sensor 5),

during the diurnal flow cycle on 5 and 6 June.

Fig. 9. Temporal storage of sand and fine gravel within the stream channel.

72 G. Vatne et al. NORSK GEOGRAFISK TIDSSKRIFT 62 (2008)

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the lower part of the diurnal flow peaks, which is in line with

observations made by Hassan & Church (2001).

Stochastic nature of bed load transport

The temporal variations in impact magnitude show a very

high variation within single flow cycles, and even on

individual rising and falling limbs of daily flow cycles,

generally producing poor rating relationships between flow

and impact magnitude. This can be attributed to several

factors. Firstly, the individual impact sensors monitor only

1�2% of the stream’s cross-sectional width. The large

temporal variation thus probably relates to the small

sampling area which is not representative of the entire

cross-section, a problem similar to that observed for bed

load samplers (Church et al. 1987). The poor covariance and

relatively large difference in average impact magnitude

between the two sensors over the period 2�13 June further

demonstrate the sensitivity of such devices to their location

on the stream bed. This clearly shows that a number of

sensors are needed over a cross-section in order to obtain

reliable estimates of bed load transport.

The highly variable impact magnitude recorded over short

time spans during flow cycles is explained by the laboratory

observations made by Einstein (1937), who proposed that

once entrained, the transport of bed load is a stochastic

process in which particles move along the bed in discrete

steps, separated by rest periods, until final deposition. The

stochastic nature of intervening rest and transport periods

stems from a number of factors, including particle shape,

embedding, relative size, boundary roughness, and the many

ways in which turbulent flow imparts lift and drag forces on

a particle. This behaviour has been confirmed in natural

streams by McNamara & Borden (2004) where motion

groups were identified. The relatively wide range of particles

sizes that characterize step-pool sections further complicates

the sediment transport process as the mobility difference

between large and small particles in the bed is reduced

(Gintz et al. 1996). In any given sample period when critical

boundary shear stress is exceeded for a given particle size

(Shields 1936), Einstein’s (1937) observations suggest that

parts of the population will be in motion and parts will be at

rest.

Conclusions

The use of impact magnitude sensors in studying bed load

transport is promising as they provide high temporal

resolution data without the necessity for wading in the

stream. The impact sensor clearly shows potential for

identifying flow thresholds for sediment entrainment and

for studying the presence of hysteresis effects in discharge�bed load relationships.

In future studies emphasis should be on research design,

calibration and testing different types of impact sensors so

that grain-size rating curves can be constructed. One

problem with the impact sensor used in this study is that

only the maximum acceleration during a sampling period

was recorded. During high intensity transport events with

many high energy impacts, many small impacts are masked

by the higher impacts during the same period, hence

transport rates cannot be estimated. The sensors therefore

have the greatest potential when used in combination with

other methods, such as impact counting sensors, pit and

hand-held samplers, tracer studies, etc. Although the intense

temporal sampling that is possible with the impact sensors

may reduce the number of sensors required in such studies, a

number of impact sensors should be used to obtain spatial

resolution of bed load transport.

Notes1 Geological Survey of Norway, Trondheim (www.ngu.no accessed 30 March

2007)2 Tinytag Plus Shock (0�100 g) (www.geminidataloggers.com accessed

October 2007)

Acknowledgements. � D. Gintz and M. Hassan are thanked for their reviews of

this paper which resulted in considerable improvement to it.

Manuscript submitted 23 April 2007; accepted 5 December 2007

References

Andrews, E.D. 1983. Entrainment of gravel from naturally sorted river bed

material. Geological Society of America Bulletin 94, 1225�1231.

Ashworth, P.J. & Ferguson, R.I. 1989. Size-selective entrainment of bed-load

in gravel bed streams. Water Resources Research 25:4, 627�634.

Church, M. & Hassan, M.A. 1992. Size and distance of travel of

unconstrained clasts on a streambed. Water Resources Research 28:1,

299�303.

Church, M., McLean, D.G. & Wolcott, J.F. 1987. River bed gravels: Sampling

and analysis. Thorne, C.R., Bathurst, J.C. & Hey, R.D. (eds.) Sediment

Transport in Gravel-bed Rivers, 43�48. John Wiley, New York.

Church, M., Wolcott, J.F. & Fletcher, W.K. 1991. A test of equal mobility in

fluvial sediment transport: Behaviour of the sand fraction. Water Resources

Research 27:11, 2941�2951.

Duizendstra, H.D. 2001. Determination of the sediment transport in an

armoured gravel-bed river. Earth Surface Processes and Landforms 26:13,

1381�1393.

Einstein, H.A. 1937. Der Geschiebetrieb als Wahrscheinlichkeitsproblem.

Mitteilungen der Versuchsanstalt fur Wasserbau an der ETH, 3�112. Verlag

Rascher, Zurich.

Emmet, W.W. 1980. A field calibration of the sediment trapping character-

istics of the Helley-Smith bedload sampler. U.S. Geological Survey

Professional Paper 1139.

Ferguson, R.I. & Wathen, S.J. 1998. Tracer-pebble movement along a concave

river profile: Virtual velocity in relation to grain size and shear stress. Water

Resources Research 34:8, 2031�2038.

Gintz, D., Hassan, M.A. & Schmidt, K.H. 1996. Frequency and magnitude of

bed load transport in a mountain river. Earth Surface Processes and

Landforms 21:5, 433�445.

Gomez, B. & Church, M. 1989. An assessment of bed-load sediment

transport formulas for gravel bed rivers. Water Resources Research 25:6,

1161�1186.

Habersack, H.M. 2001. Radio-tracking gravel particles in a large braided

river in New Zealand: A field test of the stochastic theory of bed load

transport proposed by Einstein. Hydrological Processes 15:3, 377�391.

Hassan, M.A. & Church, M. 2001. Sensitivity of bed load transport in Harris

Creek: Seasonal and spatial variation over a cobble-gravel bar. Water

Resources Research 37:3, 813�825.

NORSK GEOGRAFISK TIDSSKRIFT 62 (2008) Bed load transport inferred from impact sensors 73

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Hassan, M.A. & Woodsmith, R.D. 2004. Bed load transport in an

obstruction-formed pool in a forest, gravelbed stream. Geomorphology

58:1-4, 203�221.

Jackson, W.L. & Beschta, R.L. 1982. A model of two-phase bed load

transport in an Oregon Coast Range stream. Earth Surface Processes and

Landforms 7: 517�527.

Lenzi, M.A., Mao, L. & Comiti, F. 2004. Magnitude-frequency analysis of

bed load data in an Alpine boulder bed stream. Water Resources Research

40:7, 257�276.

McNamara, J.P. & Borden, C. 2004. Observations on the movement of coarse

gravel using implanted motion-sensing radio transmitters. Hydrological

Processes 18:10, 1871�1884.

Montgomery, D.R. & Buffington, J.M. 1997. Channel-reach morphology in

mountain drainage basins. Geological Society of America Bulletin 109:5,

596�611.

NVE [Norges vassdrags- og energidirektorat]. 2003. Hydrologisk maned-

soversikt, August 2003. Norwegian Water Resources and Energy Directo-

rate, Oslo.

Onsøyen, R. 2005. Flomskred i Vinstradalen. Master avhandling (Master’s

thesis), Norwegian University of Science and Technology, Trondheim.

Reid, S.C., Lane, S.N., Berney, J.M. & Holden, J., 2007. The timing and

magnitude of coarse sediment transport events within an upland, temperate

gravel-bed river. Geomorphology 83:1-2, 152�182.

Richardson, K., Benson, I. & Carling, P.A. 2003. An instrument to record

sediment movement in bedrock channels. Bogen, J., Fergus, T. & Walling,

D.E. (eds.) Erosion and Sediment Transport Measurement in Rivers:

Technological and Methodological Advances, 164�171. IAHS/AISH, Oslo.

Shields, A. 1936. Anwendung der aenlichkeitsmechanik und der turbulenz-

forschung auf die geschiebebewegung. Mitteilungen der PreussischenVer-

suchsanstalt fur Wasserbau und Schiffbau, Heft 26. Preussischen

Versuchsanstalt fur Wasserbau und Schiffbau, Berlin.

Warburton, J. 1992. Observation of bed load transport and channel bed

changes in a proglacial mountain stream. Arctic and Alpine Research 24,

195�203.

Wilcock, P.R. 1997. The components of fractional transport rate. Water

Resources Research 33:1, 247�258.

Wilcock, P.R. 2001. Toward a practical method for estimating sediment-

transport rates in gravel-bed rivers. Earth Surface Processes and Landforms

26:13, 1395�1408.

74 G. Vatne et al. NORSK GEOGRAFISK TIDSSKRIFT 62 (2008)