Hydraulically related hydro‐morphological units: description based on a new conceptual mesohabitat evaluation model (MEM) using LiDAR data as geometric input

A new conceptual mesohabitat evaluation model was developed and applied to the Kamp River, Austria. The model uses a functional linkage of three parameters (velocity, depth and bottom shear stress) to distinguish six different mesohabitat types (riffle, fast run, run, pool, backwater and shallow water) based on two‐dimensional depth‐averaged hydrodynamic‐numerical modelling. The results clearly revealed the variety and change of mesohabitat‐units under various flow conditions (3.6–89 m 3 s −1 ). In particular for low‐energy habitats, a shift from shallow‐ to backwater habitats was recognized at increasing discharges. Fast runs featured a larger percentage of the total wetted area (9–33%) as discharges increased, whereas pool habitats showed low variability (means of around 15%). A velocity‐depth‐bottom shear stress relationship (VDSR) was most suitable to differentiate between mesohabitat patterns; this relationship was compared with Froude numbers and with velocity‐depth ratios using ANOVA statistical analysis. This study also documented that the accuracy of river geometry plays a decisive role in habitat descriptions. Different height tolerances for the computation mesh (0.2 m, 0.5 m, 1 m accuracy) based on LiDAR significantly reduced important mesohabitats.