APPLICABILITY OF THE APPROXIMATE DELTA METHOD FOR DETERMINATION OF THE REAERATION COEFFICIENT IN SUB-BASINS IN THE CENTRAL REGION OF RIO GRANDE DO SUL, BRAZIL

Resumen

The approximate delta method is a simplified experimental method easy to apply and low cost, it is based on the estimated surface reaeration, primary production, and respiration, basically using diurnal measurements of dissolved oxygen (DO). This study aimed to analyze the feasibility of applying this method to determine the reaeration coefficient (k_a) in sub-basins of the central region of Rio Grande do Sul. The study was carried out in four sub-basins of the Vacacaí Mirim River, and one sub-basin of the Vacacaí River. In the fluviometric stations studied, one determined the values of velocity, depth, and flow rate, as well as the DO profile during the photoperiod. In three of the sub-basins, it was not possible to determine the k_a due to the occurrence of minimum DO deficit before solar noon and/or to the formation of an inappropriate DO profile curve. In the other two sub-basins, it was possible to determine the coefficient, although with some limitations that need to be better investigated since this method is an important alternative to the traditional ones.