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At‐a‐Point Bed Load Sampling in the Presence of Dunes
Author(s) -
Gomez Basil,
Hubbell D. W.,
Stevens H. H.
Publication year - 1990
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr026i011p02717
Subject(s) - sampling (signal processing) , bed load , statistics , range (aeronautics) , constant (computer programming) , point (geometry) , flow (mathematics) , environmental science , mathematics , hydrology (agriculture) , geology , computer science , geotechnical engineering , geometry , sediment transport , engineering , geomorphology , telecommunications , aerospace engineering , sediment , detector , programming language
Even during constant, or virtually constant, flow conditions, bed load transport rates are known to vary over a range of temporal scales. Previous studies have emphasized that, in order to provide an accurate estimate of the mean bed load transport rate at a given point, either many samples must be collected repeatedly or the sampling time must be long. We systematically evaluate errors associated with at‐a‐point bed load sampling during steady flow conditions in the presence of dunes and provide an indication of the way in which sampling should proceed in order to minimize sampling errors. The analysis is undertaken using laboratory data and a theoretical probability distribution function. It is assumed that bed load samplers have an efficiency of 100% and that the flow conditions and the configuration of the primary bed forms remain constant during the sampling period. In the presence of dunes, sampling should be accomplished using (1) the shortest practicable sampling time for each sample, (2) short, equally spaced time intervals between samples, and (3) as long a sampling period as is necessary to ensure that at least one primary bed form has passed the sampling point. Such procedures will provide information about high‐ and low‐frequency fluctuations in at‐a‐point bed load transport rates and a reasonably reliable estimate of the mean bed load transport rate. Only about 21 sequential samples are required to estimate the mean bed load transport rate at any given point. However, because the sampling time generally is short in comparison with the time that it takes a dune to pass the sampling point, between 50 and 100 samples are needed to define both high‐ and low‐frequency at‐a‐point rate variations. A knowledge of the prevailing bed configuration is necessary in order to ensure that sampling proceeds in accordance with these requirements.