Relationship between stream flow and water quality in a river section

Abstract

The objective of this study was to evaluate the dynamics of water quality variables in relation to the stream flow rate in a cross section of the Catolé Grande River near the point of water uptake to supply the city of Itapetinga-BA. Water samples were collected by vertical integration in different months, corresponding to different flow rates. This work analyzed the hydrogenionic potential (pH), turbidity, total dissolved solids, salinity and total phosphorus of the water samples. The flow velocity was measured using a flow meter. The flow rate was calculated by the product of velocity by cross section area. The results showed that salinity, total dissolved solids and turbidity had similar behaviors in relation to the flow rate, with increased concentrations of these variables with increasing river flow rate, whereas the opposite was observed for pH. Phosphorus concentrations showed an exponential behavior as a function of flow rate, and the average values of this variable exceeded the limits stipulated by CONAMA Resolution 357 for the worst class of freshwater quality.