How parameter weighting influences hydraulic unit mapping and fluvial mesohabitat assessment in Rivers

Mesoscale habitat approaches are increasingly popular and all rely on a definition and delineation of geomorphic (GU) and hydraulic (HU) units. Traditionally, experts perform GU–HU delineation in the field, but unsupervised algorithms are increasingly being developed. Such algorithms typically assume that the parameters selected for HU delineation (mostly water depth and flow velocity) are of equal importance. This study challenges that assumption by investigating the consequences of weighting parameters in the automatic delineation of HU. Using simulated hydraulic variables, we applied algorithmic HU delineation under various conditions and tested different parameter weightings. The resulting HU were compared to GU delineated using a field-based field approach. Additionally, a synthetic habitat suitability criterium was used to evaluate how parameter weights influence final habitat assessments. We found that weighting parameters influences the algorithmic HU delineation and the amount of predicted habitat; assuming equal importance for all parameters can lead to inaccurate conclusions in habitat assessments. We show that field- and algorithmic-based approaches used for mesohabitat delineation are not interchangeable, but rather are complimentary. This work contributes towards the integration of field- and algorithmic-based approaches.