Reproducing the DTM of a braided river throught ground survey: a quick and economical approach.

The main goal of several researches consists in monitoring the territory, with different survey techniques and analysis methods. Many survey methodologies may be applied to study 3Dimensional variation; generally the choice depends on the application for which the survey is asked, the size of the area, the accuracy and so on. Frequently a quick and economical approach should represents an useful strategy to gain land metric knowledge. In general, the knowledge of the territory depends on the application that needs it. A typical application is braided river analysis. The channels of a braided network are in continuous motion due to bed and bank scour during floods of even moderate intensity. Hence, braided rivers pose difficult problems of river regulation and management. To investigate the processes that control the morphodynamics of braided rivers, fluvial geomorphologists and engineers preliminary need a detailed survey. In the present work we investigate how to optimise the topographic survey of braided rivers, in the sense of reducing the number of topographic points that we have to survey, understanding which data distribution is needed to reproduce at best the complex bed surface. We performed tests based on two synthetic DTMs; exporting transversal cross-sections and/or break-lines from such synthetic surfaces, we simulated ground surveys, and then we tested in a didactic approach two interpolating algorithms developed in the open source and free software Geographical Information System (GIS) GRASS 5.4: the Inverse Distance Squared Weighted and the Regularized Spline with Tension. Finally, we applied the resulting indications to a field survey of a braided reach of Borbera River (north-western Italy).