DTM of a braided river: how to reproduce it?

A quick and economical survey is investigated to monitor the evolution of a braided river with ground topographic survey. Starting from synthetic DTM, different survey points and different interpolation methods are tested in a didactic approach to reproduce the braided river geometry. First of all, we tested a software used in the hydraulic engineering practice, HEC-RAS, interpolating from significant transversal cross-sections of the synthetic braided river DTM. And we found that HECRAS software is not able to interpolate in a reasonable way in presence of confluences or bifurcations, i.e. between cross-sections of a braided river. Hence, we started applying the simplest and most available interpolation method, Inverse Distance Weight method (IDW), to the synthetic braided river DTM through GRASS 5.3. But we ends up that such method needs a huge amount of data, on a regular grid if possible, also to reproduce a regular straight channel. Because this is not a realistic condition if you want to survey a reach of a braided river with ground techniques, we looked at Spline, Regularized Spline with Tension (RST) in particular. We applied RST to the same synthetic braided river DTM and observed that it works better than IDW interpolating from sites along cross-sections. We also investigated if RST works well when the channel bed is not flat in the transversal direction but assumes a more natural shape. In the near future we will investigate how optimize a topographic survey of a braided river with more natural cross-sections shape, trying to avoid the survey of the wet break-lines because they are not always well defined in field. Moreover, interpolations from cross-sections of variable spacing along the section, in function of the importance of the area, will be performed.