What is it about?
The paper presents a 0-D model of an alluvial watercourse schematized in two connected reaches (mounatin and lowland parts), to simulate the morphological long-term evolution of a watershed.
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Why is it important?
The paper presents a 0-D model of an alluvial watercourse schematized in two connected reaches, evolving at the long time-scale and under the hypothesis of Local Uniform Flow. Each reach is defined by its geometry (constant length and width, time-changing slope) and grain-size composition of the bed, while the sediment transport is computed using a sediment rating curve. The slope evolution is provided by a 0-D mass balance and the evolution of the bed composition is computed by a 0-D Hirano equation. A system of differential equations, solved with a predictor-corrector scheme, is derived and applied to the schematic watercourse to simulate the morphological response to changing initial conditions, and the evolution towards long-term equilibrium conditions. Differently from a single-reach 0-D schematization with uniform grain-size, besides the simplifications adopted, the model proposed here simulates the behaviour of alluvial rivers in a physically-based way, showing a grain-size fining in the downstream direction accompanied by milder slopes, and a tendency to develop concave longitudinal profiles.
Perspectives
Aiming to replicate previous results obtained with more complex approaches, the 0-D model developed here is physically-based on typical hydro-morphological equations, even if described in a very simplified manner. Theoretically, the parameters used by physically-based models are measurable, but, in practice, this kind of codes needs to be calibrated and verified against observed data, because of the large number of parameters involved and the heterogeneity of their values. A typical dataset is formed by a continuous record of water flowing through a given cross section and some basin-scale averaged geometrical (river slope, width, length) and sedimentological (grain-size) information. In this regard, continuous records of sediment transport and water flow are necessary to calibrate and validate such models. The proposed mathematical system results implicit and non-linear and, therefore, it is not possible to find an analytical solution. For this reason, a numerical evaluation based on a predictor-corrector scheme is applied, showing the potential of the approach despite of the several simplifications involved. Solving 0-D models is much simpler and faster than solving a complete 1-D hydro-morphodynamic model, with a reduced loss of details at the large spatial and temporal scale.
Dr Michael Nones
Institute of Geophysics - Polish Academy of Sciences
Read the Original
This page is a summary of: Morphological reactions of schematic alluvial rivers: long simulations with a 0-D model, International Journal of Sediment Research, April 2017, Elsevier,
DOI: 10.1016/j.ijsrc.2017.04.002.
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