Ecohydrological Modelling in the Ondas River, Brazil: Implications for Fisheries Management

This paper aimed to perform an ecohydrological analysis of the Ondas river basin, located in the Brazilian Cerrado, using the Physical Habitat Simulation (PHABSIM) model, in order to determine the monthly ecological flows for its lower course. For calibration and simulation in PHABSIM, field experiments were conducted during dry and rainy periods, in a 300-m stretch located in the lower course of the Ondas river. The estimate of monthly ecological flows was obtained by analysing the Weighted Usable Area of the ichthyofauna species of the river stretch, as a function of the streamflows with a probability of nonexceedance of 50% (Q₅₀), 60% (Q₆₀), 70% (Q₇₀), 80% (Q₈₀), 90% (Q₉₀) and 95% (Q₉₅). In the dry period, the ecological flow varied between 31.72 and 40.14 m³ s⁻¹, whereas in the rainy season, it presented values between 33.23 and 51.94 m³ s⁻¹. Considering the water use rights criterion of the State of Bahia, Brazil, where it is permissible to use up to 80% of the Q₉₀, it was verified that the adoption of ecological flows would considerably reduce the quantity of water that could be used for human purposes but would maintain the habitat of the bioindicator species studied. The ecological flow regime obtained provides subsidies for discussions and negotiations on the water resources management in the Ondas river basin, considering the ecohydrological aspects affecting the region, in addition to the water quantitative and qualitative factors.