Author(s): Stefan Jocham; Markus Aufleger

Linked Author(s): Stefan Jocham, Markus Aufleger

Keywords: High-resolution bathymetric LIDAR data; Hydrodynamic numerical modelling; Instream habitat modelling; Water framework directive

Abstract: In the present study, the use of high-resolution bathymetric survey data from Airborne LIDAR Bathymetry (ALB) in hydrodynamic-numerical (HN) 2D modelling and instream habitat modelling was investigated. The aim was to assess the quality of modelled habitat suitability as a function of the spatial resolution of the basic geometry input. Two near-natural river reaches of different dimension in the grayling region were exemplary used therefore. With the help of ALB, survey data in the range of 20 - 40 survey points per square meter can be achieved. The accuracy of the surveyed points is in the range of 10 cm. Based on this high-resolution survey data base, HN 2D calculation meshes in varying spatial resolution were generated to calculate local hydraulic variables serving as input for instream habitat modelling for fish. By this means, the calculation of habitat suitability in dependency of the spatial resolution of the calculation mesh and the calculated local hydraulic variables could be assessed. The accuracy of calculated local hydraulic variables in dependency of the spatial resolution of the calculation mesh was also addressed herein. The results of the work show that a realistic representation of the river bed on the one hand and on the other hand the calibration of the HN 2D model play an important role for the calculation of plausible habitat suitabilities. The accurate representation of the local water depths and flow velocities, which are required for habitat modelling, is essential. Thereby, the necessary spatial resolution of the terrain model and calculation mesh depends on the size of the water body and the considered life stage of the fish species. The accurate representation of the shore line as transition between wetted and dry areas and thereby the representation of shallow water zones near the shore line is becoming more uncertain with lower resolved calculation meshes. This is important for modelling juvenile fish habitats, which are in need of areas that provide small water depths and low flow velocities. The calculation of habitat suitabilities for adult life stages of fish, which usually prefer areas with bigger water depths, is less dependent on the spatial resolution of the calculation mesh. In general, it can be stated that ALB data form a very good basis for the calculation of detailed local flow variables in high spatial resolution, which can be used subsequently for instream habitat modelling. The data offer the possibility to adapt the spatial resolution of the calculation mesh to the size of the river bed structures and the object of investigation.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022403

Year: 2022