C. Sabaton

MODELLING TEMPORAL VARIATIONS OF PHYSICAL HABITAT FOR BROWN TROUT (SALMO TRUTTA) IN HYDROPEAKING CONDITIONS

Hydropeaking generates significant fluctuations in flow in downstream river reaches, resulting in frequent and major changes in the physical conditions of the fish habitat. The microhabitat methodology, derived from the IFIM, focuses on minimum flow studies in by-pass sections, but has been adapted to two rivers subject to daily flow fluctuations (Ance du Nord and Oriege). Application of this methodology to hydropeaking conditions requires additional habitat descriptors to take into account the temporal aspects of peaking flows and their effects on trout habitat, i.e. flow and habitat chronologies analysed in duration and frequency. Hydropeaking and the natural upstream flow regime were compared. The results show that habitat variations are closely related to the flow regime and site morphology; hydropeaking effects on habitat parameters are different in wide and in deep profiles. It is suggested that, in both instances, hydraulic refugia are crucial for organisms to withstand the variations of physical variables. This approach helps in better understanding the physical limiting factors in situations of short-term flow fluctuations.