Morphohydraulic quantification of non spatialized datasets with the "Hydrosignature" sofware
A. Scharl, Y. Le Coarer · HAL (Le Centre pour la Communication Scientifique Directe) · 2005
A general problem with habitat modelling is finding a relationship between the physical habitat and the aquatic fauna. One way to describe the habitat is to quantify the hydraulic diversity by calculating the hydrosignature. The hydrosignature of a river unit at one discharge quantifies the hydraulic variety by calculating the surface (or volume) percentages in a depth and current velocity cross classification. The data sets used for quantification are the hydraulic measurements of verticals described by their depth and average velocity, which can be spatialized or not. The hydrosignature of a river unit that has been spatialized is more significant than a hydrosignature for which the location of measurement points is unknown. The results discussed in this article aim to improve hydrosignature calculations in terms of non-spatialized data sets. Three different methods designed to deal with such data can be distinguished: -NOXY: The field protocol consists in vertically measuring depths and mean velocities without recording location (no X and Y co-ordinates). NOXY directly takes into account the discrete information of verticals that have no spatial relationship between themselves. -NOXY2: The field protocol in this case is the same as NOXY. The difference between these two methods lies in the mode used to calculate the hydrosignatures assimilating the verticals to continuous information. -NOXY3: Concerning this protocol, the relative position of the verticals is recorded on-field, which then makes it possible to break down the described unit into cross sections that are perpendicular to the flow direction. This type of semi-spatialization also enables the assimilation to continuous hydraulic information. A total of 250 river units spatialized in a triangular irregular network (TIN) composed the test data set. This data set was degraded into a non-spatialized description to which NOXY, NOXY2 and NOXY3 were applied. Hydrosignatures calculated by the three different methods were compared with hydrosignatures resulting from the original TIN data set that was used as a reference. An index based on the same principle as that used for filters in spatial analysis applications was created for the purpose of comparing the two hydrosignatures. When it is not possible to apply geo-referencing methods, the NOXY3 semi-spatialized approach is recommended.