Variability of bed load measurement

Pitlick, John

doi:10.1029/wr024i001p00173

Cited by 49 publications

(30 citation statements)

References 8 publications

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“…Another striking feature is the very high variability of measured rates of bedload [13,14]. For given flow conditions measured rates can vary by an order of magnitude.…”

Section: The Urumqi He (River) Upstreammentioning

confidence: 97%

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Measuring bedload in gravel-bed mountain rivers: averaging methods and sampling strategies

et al. 2008

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A dataset of more than 1,000 individual bedload samples coupled with hydraulic flow variables (water depth and velocity) was collected on two high mountain rivers the torrent de Saint Pierre, a proglacial gravel-bed river in the French Alps, in July 2002 and the Urumqi River, in the Chinese Tianshan mountains during summer 2005 and 2006. Analysis of the dataset leads to question the usual section averaged sampling procedure of bedload using Helley-Smith type bedload sampler. It is shown that this procedure is inadequate to catch the full range of flow conditions. Comparison between moving averages on individual datasets and section averages furthermore show that this technique can lead to significantly different rating curves with predictions differing by more than an order of magnitude. Single point sampling is shown to be much more adequate than multiple point sampling and section averaging provided the dataset is sufficiently large.

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“…Another striking feature is the very high variability of measured rates of bedload [13,14]. For given flow conditions measured rates can vary by an order of magnitude.…”

Section: The Urumqi He (River) Upstreammentioning

confidence: 97%

“…Although clear trend can be seen on the datasets discussed here, individual bedload samples present a well known high variability [13,14]. It is then common to smooth the dataset in order to define clear trends and correlations between bedload and fluid flow variables.…”

Section: Data Scatter and Averaging Proceduresmentioning

confidence: 98%

Measuring bedload in gravel-bed mountain rivers: averaging methods and sampling strategies

et al. 2008

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“…Unfortunately, this is likely to increase errors associated with flow and transport variability (e.g. Pitlick, 1988;Gaweesh and Van Rijn, 1994;Kleinhans and Ten Brinke, 2001), but was considered to be less important than error incurred through changing discharge. Overall, between 45 and 50 samples were collected at each sample site, exceeding Gomez and Troutman's (1997) recommendation of 40 samples to reduce random and systematic error.…”

Section: Bed-load Sedimentmentioning

confidence: 99%

Hydrology, sediment transport dynamics and geomorphology of a variable flow river: The Mfolozi River, South Africa

Grenfell¹,

Ellery²

2012

WSA

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The co-efficient of variation for inter-annual streamflow of the Mfolozi River is extremely high at 79%. An analysis of flow frequency indicated that streamflow is skewed towards low-flow values, with a number of extremely large flood events occurring as outliers on the histogram. Streamflow variability in the Mfolozi River may be linked to multiple factors including a large catchment size, a seasonal climate of a dry winter and wet summer, evergreen vegetation in the catchment, variable precipitation and the occurrence of regionally pervasive climatic oscillations. This research aimed to address how streamflow variability impacted upon sediment transport and thus, geomorphology. It was found that sediment transport variability occurred at the intra-and inter-annual scale. Analysis of mean monthly sediment concentration and discharge showed a hysteresis effect, such that sediment concentration peaked prior to discharge in the early wet season. During the late wet season, peak discharges often had unexpectedly low sediment concentrations. Furthermore, data suggested the existence of long-term hysteresis that may be related to decadal-scale climatic oscillations that alter sediment availability and stream capacity, resulting in discharge peaking in 2000 and sediment concentration in 2005. However, more data are required to confirm this relationship. Variability in streamflow appears to share a causal relationship with sediment transport variability, as both are linked to variation in precipitation and the resultant impacts on vegetation growth and evapotranspiration rates. The variability of streamflow and sediment transport has implications for stream and floodplain geomorphology, and the hydrology of variable rivers should be considered when interpreting their geomorphology.

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“…Investigations showed that the sampling efficiency varied with collector type and deployment. For example, [27][28][29] observed that bag size, mesh width and sampling duration affected the sampling efficiency, [30] found that the orientation of the sampler and its size had an effect, and [31,32] showed that thickness of the sampler wall mattered. Several studies revealed that different types of Helley-Smith samplers yielded different sampling results [32][33][34][35][36][37][38][39][40][41].…”

Section: Introductionmentioning

confidence: 99%

A Comparison of Coarse Bedload Transport Measured with Bedload Traps and Helley-Smith Samplers

et al. 2008

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Gravel bedload transport rates were measured at eight study sites in coarse-bedded Rocky Mountain streams using 4-6 bedload traps deployed across the stream width and a 76 by 76 mm opening Helley Smith sampler. Transport rates obtained from bedload traps increased steeply with flow which resulted in steep and well-defined transport rating curves with exponents of 8 to 16. Gravel transport rates measured by the HelleySmith sampler started with much higher transport rates during low flows and increased less steeply, thus fitted bedload rating curves were less steep with exponents of 2 to 4. Transport rates measured with both samplers approached similar results near or above bankfull flow, but at 50 % of bankfull, transport rates from the bedload traps were 2-4 orders of magnitude lower than those obtained from the Helley-Smith sampler. The maximum bedload particle sizes also differed between the two samplers. They were smaller in the bedload traps than the Helley-Smith sampler at low flows, while at higher flows bedload traps collected larger particles than the Helley-Smith sampler. Differences in sampler opening size and sampling time contribute to the measured differences, but the biggest effect is likely attributable to the bedload traps being mounted on ground plates thus avoiding direct contact between the sampler and the bed and preventing involuntary particle pick up.

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Variability of bed load measurement

Cited by 49 publications

References 8 publications

Measuring bedload in gravel-bed mountain rivers: averaging methods and sampling strategies

Measuring bedload in gravel-bed mountain rivers: averaging methods and sampling strategies

Hydrology, sediment transport dynamics and geomorphology of a variable flow river: The Mfolozi River, South Africa

A Comparison of Coarse Bedload Transport Measured with Bedload Traps and Helley-Smith Samplers

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