Developing a water discharge echohydrograph conditioned by specific ichthyofauna habitat conservation

Deriving from the concept of ecological flow that applies to aquatic ecosystems as a hole, in order to improve the monthly values determined for the Răstoliţa dam using the national legislation method, the specific local conditions required by ichthyofauna were considered in the development of a new discharge echohydrograph - QDFLT for Răstoliţa River, Romania. Hydrological statistics was used on a 30 years (1986-2015) dataset of daily averaged discharge values in order to determine and plot the corresponding hydrographs, the discharge ensurance/exceedance curve and the frequency curve that determined the discharge interval for the average ecological flow to be 1 - 1.5 m 3 /s. From the fish species present in the Răstoliţa River area the major ichthyofauna element, for which the habitat conservation conditions were to be met, was represented by Hucho hucho , a critically endangered species, that requires water depths of 0.50± 0.25 m. Hydraulic modelling processes that used in situ measured water depths, water level, water velocity and discharge data for profiles located on the Răstoliţa River determined a 1.3 ±0.1 m 3 /s average value for QDFLT. Using the ecological flow values determined according to the national legislation, there were applied considerations of climate change impact on the hydrodynamic conditions of the river and taxonomy principles in order to determine the QDFLT echohydrograph composed of 12 monthly specific minimal discharge values required by Hucho hucho .