Using Hydraulic Model for Riparian Zone Boundary Delineation and Analyzing Its Changes Under Different Flood Senarios

Riparian zones are an essential and active part of the ecological environment of a river, but there is no commonly accepted and precise academic definition for it. In the methods of riparian zone boundary delineation covered in academic articles or among the official regulatory documents of various countries, the basis for its delineation is generally the highest floodplain boundary or a fixed buffer zone width. This paper focuses on modelling based on topography, surface and groundwater hydrology, vegetation, and soil data to delineate the boundary of the riparian area and to analyze its response during the course of different flood events. A computing program is developed to simulate the river-riparian system under different flood events and to generate riparian zone maps, taking as starting point the 2.5, 10, 50 and 100-year return period flood extent obtained by means of IBER, a two-dimensional hydrodynamic model. Results show that changes in topography and land use, as well as discharge direction between river and groundwater influence the extent of riparian zones. Additionally, during floods the riparian zone area increases much slowly than that of the flood, it continues to increase until the flood subsides, but this extent increase at last is limited at a certain level. The results of the modelling show that the setting of the calculation mesh size and groundwater horizontal propagation speed affect the time step value and determine the stability and accuracy of model. A small pixel achieves fine simulation results with high computational cost while a large pixel size can be used with a large time step, and thus it is more convenient for long simulation times. The method skips the traditional task of visually interpreting and identifying plant types to delineate riparian zones, thus reducing errors caused by subjective factors. The code, based on the riparian dynamics is presented as a proposal of a new riparian delineation approach, useful for research and management applications.