MODELING 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 dow studies in by-pass sections, bu t has been adapted to two rivers subject to daily flow fluctuations (A nce du Nord and Oriege). Application of this methodology to hydropeaki ng conditions requires additional habitat descriptors to take into acc ount the temporal aspects of peaking flows and their effects on trout habitat, i.e. flow and habitat chronologies analysed in duration and f requency. Hydropeaking and the natural upstream flow regime were compa red. The results show that habitat variations are closely related to t he how regime and site morphology; hydropeaking effects on habitat par ameters are different in wide and in deep profiles. It is suggested th at, 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 s hort-term flow fluctuations.