Field data are used to study the size distribution of bedload in paved gravel-bed streams. Similarity analysis yields the results that all grain size ranges are of approximately equal transportability when the critical condition for breaking the pavement is exceeded. This result is only approximately correct due to deviations from similarity. However, it is adequate to justify development of a method for calculating total bedload, which requires only the subpavement median grain size rather than the size distribution. A method for calculating bedload size distribution that accounts for deviation from similarity is also developed.

Closure of "Bedload and Size Distribution in Paved Gravel-Bed Streams"

Real time measurements of sediment transport and bed morphology during channel altering flow and sediment transport events

Scrutiny of multifarious field and laboratory data amassed over nine decades reveals four distinct bedload transport regimes and demonstrates the search for a universal formula is a fallacious pursuit. In only one regime, in which the supply of transportable material is unconstrained, does the transport rate in some rivers approximate the expected proportional relationship with dimensionless specific stream power (ω∗). At the other extreme, transport occurs at or near the threshold of particle motion, and the availability of sediment is regulated by the characteristics of the bed surface. In each regime, there is an underlying variation of transport rates at a given discharge, that is neither obscured by long measurement times nor standardized methodologies, and to properly differentiate them, the bedload size must be known. We show a data-driven relationship based on measurements made over several years, across the entire flow range, that requires no a priori specification of the association between the transport rate and ω∗, can reveal nonlinear trends that may otherwise be masked by omni-present temporal and spatial variability. The demise of the search for a universal formula will be accelerated by the development of idiomatic relations that embrace the specificity of rivers in each transport regime.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsos.211932

Bedload transport: beyond intractability

The efficiency of the river machine

This study sought to characterise sediments in the unlined canal in Chokwe Irrigation Scheme (CIS), during dry (DS) and wet (WS) seasons. Laboratory analysis were performed on the sediment’s soluble extracts for pH, turbidity, total dissolved solids (TDS), sodium, calcium, magnesium, and potassium concentrations. Atterberg tests and particle size distribution (PSD) were also investigated for all sediment samples collected in the CIS main canal. Results suggest acceptable water pH and turbidity in both seasons. The concentration of TDS was found to be 250 and 300 ppm for the DS and WS, respectively. Sodium was the most predominant element in water and sediment samples, followed by potassium and calcium. The Liquid Limit, Plasticity Limit and Plasticity Index were 52%, 20% and 32%, respectively. A mean of 2.960 N/m2 was obtained for the critical shear stress of erosion. The main particle size in bedload sediments which were classified as saline were silt, fine sand, and clay. Overall, CIS is characterized by the occurrence of cohesive and varied degrees of uniformity in the sediments grain size. Considering the physicochemical properties of the canal bed sediments as an accurate representation of the surrounding farmer’s fields, sustainable agriculture practices may be at stake in the site. Therefore, some measures may be required to revert sediment accumulation to ensure long-term canal functionality and sustainability.

Cohesive and non-uniform sediment characteristics in the unlined canal of Chókwè Irrigation Scheme, Mozambique

Bedload Transport Sampling, Characterization and Modeling on a Southern Appalachian Ridge and Valley Stream

The purpose of this study was to establish an inverse algorithm to solve the analytic element groundwater modeling equations, developed by Anderson (2001 ), for state parameters based on head data from an appropriate field site. The analytical element model (AEM) equations developed by Anderson (2001) are a complex variable technique to describe flow regimes through a gap in a confining layer that otherwise separates two confined aquifers. Anderson's equations are based on the assumptions that hydraulic conductivity is constant in the respective confined aquifers. It also assumes a hydraulic conductivity of zero for the confining layers in the system. A Levenberg-Marquardt based inverse algorithm was developed and applied to synthetic data created by the forward application of Anderson's AEM equations based on state variables similar to those presented in the literature (Anderson 2001). The inverse algorithm was used to solve for the state parameters describing window length (L) and flux through the window (Q) given four head values observed in the forward solution. The inverse algorithm successfully predicted values for window length and flux through the window within 20% of the values used to create the synthetic head data. A study on the effect of an added observation point in the flow field was also performed. It was observed that an added observation point in the flow field resulted in better approximations of L and Q by the inverse algorithm. The algorithm was then applied to an actual field case, the Shelby Farms Site in Memphis, Tennessee, in an attempt to predict the window extent and flux through the window based on head observations from four wells installed within the window. Based on data from three separate occasions, the algorithm produced a value for window length ofL= 573.9 ft and flow through a unit slice of the window ofQ= -525.0 ft/day, which compares well with the value of 35,627 ft/day for the entire window profile from other recent studies at the Shelby Farms Site.

/pdf/the-inverse-application-of-conformal-mapping-techniques-to-csz82qtu13.pdf

The Inverse Application of Conformal Mapping Techniques to Describe Groundwater Flow-Regimes through a Window in the Upper Claiborne Confining Layer

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Bedload Transport Sampling, Characterization and Modeling on a Southern Appalachian Ridge and Valley Stream

The Inverse Application of Conformal Mapping Techniques to Describe Groundwater Flow-Regimes through a Window in the Upper Claiborne Confining Layer