Determining the dispersion characteristics of rivers from the frequency response of the system

Abstract

[1] A new method of determining the parameters of an aggregated dead zone model (ADZ) to predict longitudinal dispersion in rivers is presented. The method is based on the frequency response analysis (FRA) of observed field tests, which consist of tracer injections (input) and measurement of tracer in downstream sampling points (output) located downstream from the injection point. The ADZ is a combination of plug and completely mixed flow compartments. The ADZ parameters (number of compartments, mean residence time, and delay time) are evaluated by means of Bode plots that give the system order (number of compartments), gain, time constant (mean residence time of each compartment) and delay time. The FRA-ADZ method was checked with tracer data runs in two Spanish rivers, the Tagus and the Ebro rivers. The experimental tracer concentration versus time distributions were compared with the ADZ predicted curves, which were calculated using parameters obtained from the FRA method, and with curves predicted by several classical models. The residence time of several reaches within the two studied rivers was predicted by the FRA-ADZ method with a relative error lower than 10%. The method is generally applicable to ideal and nonideal inputs and is particularly well suited to arbitrary-shaped initial source concentration distributions.Citation: Lambertz, P., M. C. Palancar, J. M. Aragón, and R. Gil (2006), Determining the dispersion characteristics of rivers from the frequency response of the system, Water Resour. Res., 42, W09414,

Effect of nonlocal transverse mixing on river flows dispersion: A numerical study

“…In the outlined approach, the balance should be replaced by a suitable equivalent version referred to the 2‐D network of concentration cells. The proposed configuration would still be well fitted for a frequency response analysis of the system [ Lambertz et al , 2006]. However, the detailed elaboration of an extended version of the ADZ method is beyond the scope of the present work.…”

“… Manson et al [2001] elaborated a conservative semi‐Lagrangian numerical model for computing solute transport in fluvial systems with transient storage, focusing on stability and accuracy issues. Lambertz et al [2006] proposed a method for determining the parameters of an aggregated dead zone model to predict longitudinal dispersion in rivers, on the basis of the frequency response analysis of observed field tests. Marion et al [2008] presented a residence time model for stream transport of solutes accounting for the mass exchange between surface flow and subsurface retention zones.…”

Longitudinal Dispersion in Straight Open Channels: Anomalous Breakthrough Curves and First-Order Analytical Solution for the Depth-Averaged Concentration

“…Nevertheless, all the data available in the literature highlight a persistent skewness of the distribution and an increasing peripheral drift of the solute clouds that seem to be incompatible with a pre-asymptotic phase of the process [20][21][22][23][24], the reason for the failure of Taylor's asymptotic theory is likely related to the permanent cross-sectional non-uniformity of solute mass. Several attempts were made to relate the persistent concentration skewness to the presence of dead zones induced by morphological singularities as edges and corners or subsurface retention phenomena (e.g., [25][26][27]). Ahmad analysed the effect of variable transverse mixing on stream-wise dispersion in terms of longitudinal mixing length for different initial conditions [28] and a classic large-time Fickian behaviour.…”