Traditionally, this fluvial ecosystems have been studied through observation performed either in the field or in laboratories, but this techniques have their limitations. Mainly, the time frame in which this evolution happens, over centuries or millennia, this fact makes some issues remain unresolved1 (Coulthard, 2012). As a response to this, in the last two decades different simulation models have emerged. This models try to abstract and simplify the processes that occur along the river systems that aim to depict the aspects that provoke the changes in river dynamics and morphology. Being a numerical model, the system is controlled and can be studied in an abstract way. The numerical models that arise to comprehend the river systems had different purposes that make them more or less suitable for the aim of the study. Landscape evolution models (LEMs) cover entire drainage basins with no so many detail; alluvial architecture models can give us the detail of the sedimentary facies, losing flow characteristics; and computational fluid dynamic models have the restriction of having a given channel form. (Coulthard, 2012).
1 Coulthard and Van de Wiel explain in further detail the scope of numerical models to simulate river systems.
For this project the numerical model that is going to be used is inside the LEMs, and in particular CAESAR-Lisflood software. The main reason for having chosen CAESAR is the ability that the software has to combine catchment simulations with detailed ones. CAESAR is a two dimensional flow and sediment transport model. It can simulate morphological changes in river catchments or reaches, on a flood by flood basis, over periods up to several thousands of years2. This software was developed by Tom Coulthard in 2000. The first aim of CAESAR was to understand the relation between climate and/or land cover changes and how fluvial systems had a geomorphic response to them. For this research a “catchment mode” was developed so as the behaviour of a whole basin could be understood3.
While working with the catchment mode, it appeared that the basic model could also predict erosion and deposition in river reaches, which led to the development of the “reach mode”. In this mode, water is input at a specific point over a given DEM. Water flows over the surface and the software simulates processes of erosion and deposition. This finding allows the model to predict the river dynamics with higher resolution. The software has continued evolving from 2005 onwards embodying other processes such as lateral erosion, slope processes and shear stress.
In order to understand how this processes really happen in a given example, and how different parameters such as amount of water flow, grainsize of the soil, vegetation and slope processes could influence the formation of this avulsion, a first experiment is carried. The first experiment done with the program was to test what will be the outputs of erosion/deposition in a simple meandering river. (Fig. 9)
2 Description in http://www.coulthard. org.uk/CAESAR.html. Additional information about purposes, requirements and findings can be also found in the website. 3 River Swale study, (Coult2hard and Macklin, 2001)
In this simple test the main behaviours of a meandric river is depicted, it can be observed the areas in which erosion and deposition takes place. The location of this phenomena will be useful to stablish the rules in which avulsion happens. The settings given to the programme where the ones by default. S. Ribot, Technical Essay.
Water Flow
Erosion / Deposition Process
Fig. 9 Water Flow and Erosion / Deposition Processes Studies using CAESAR
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