Abstract
The extreme versatility in different research fields of GRASS GIS is well known. A tool for the vertical sorting of sediments in river dynamics analysis is illustrated in this work. In particular, a GRASS GIS python module has been written which implements a forecasting sorting model by Blom&Parker (2006) to analyze river bed composition’s evolution in depth in terms of grainsize. The module takes a DEM and information relative to the bed load transport composition as input. It works in two different and consecutive phases: the first one uses the GRASS capabilities in analyzing geometrical features of the river bed along a chosen river reach, the second phase is the "numerical" one and implements the forecasting model itself, then executes statistical analyses and draws graphs, by the means of matplotlib library. Moreover, a specific procedure for the import of a laser scanner cloud of points is implemented, in case the raster DEM map is not available. At the moment, the module has been applied using flumes data from Saint Anthony Falls Laboratory (Minneapolis, MN) and some first results have been obtained, but the "testing" phase on other flume’s data is still in progress. Moreover the module has been written for GRASS 65 on a Ubuntu Linux machine, even if the debugging of a GRASS 64, Windowsversion, is also in progress. The final aim of this work is the application of the model on natural rivers, but there are still some drawbacks. First of all the need of a high resolution DEM in input, secondly the number and type of data in input (for example the bed load composition in volume fraction per each size considered) which is not easily obtainable, so the best solution is represented by testing the model on a well instrumented river reach to export in future the forecasting method to un-instrumented reaches.
Highlights
The vertical sorting of sediments in gravel and sandy-gravel bed rivers is one of the factors directly involved in the evolution processes of river morphology [1]
In order to obtain a better understanding and modeling of the main physical processes occurring in vertical sorting and due to the large amount of field work behind grainsize analyses on a real river, some prediction methods for the study of vertical sorting of sediments have been formulated in time [2]; [3]; [4]; [5]; [6]; [7]
The Equilibrium Sorting Model [8] has been implemented on the Open Source Geographical Informative System GRASS [9], and a specific tool, which can be integrated in the main GIS structure, has been created
Summary
The vertical sorting of sediments in gravel and sandy-gravel bed rivers is one of the factors directly involved in the evolution processes of river morphology [1]. The specific choice to implement the theoretical model in GIS has been realised in order to achieve the aim of computerizing the model prediction, simplifying the field work of sampling and sieving and classifying a terrain. In addition to this an other main scope is represented by obtaining the connection between the predictive capabilities of the model to the GIS capabilities in analyzing terrain morphology. The model application requires a priori an accurate knowledge and extraction of bedforms characteristics on the river bed surface, that GRASS GIS can automatically provide It is interesting testing the application of GIS at microscopical scale (i.e. grainsize specific scale)
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